2012 Microchip Technology Inc. DS51686E
MPLAB® XC32 C/C++ Compiler
User’s Guide
DS51686E-page 2 2012 Microchip Technology Inc.
Information contained in this publication regarding device
applications a nd the lik e is p ro vided on ly for yo ur con ve nien ce
and may be supers eded by up dates. I t is you r r es ponsibil it y to
ensure that your application meets with your specifications.
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OTHERWISE, RELATED TO THE INFORMATION,
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suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC,
KEELOQ, KEELOQ logo, MPLAB, PIC , PI Cmi cro, PIC START,
PIC32 logo, rfPIC and UNI/O are registered trademark s of
Microchip Technology Incorporated in the U.S.A. and other
countries.
FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor,
MXDEV, MXLAB, SEEVAL and The Embedded Control
Solutions Company are registered trademarks of Microchip
Technology Incorporated in the U.S.A.
Analog-for-the-Digital Age, Application Maestro, chipKIT,
chipKIT logo, CodeGuard, dsPICDEM, dsPICDEM.net,
dsPICworks, dsSPEAK, ECAN, ECONOMONITOR,
FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP,
Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB,
MPLINK, mTouch, Omniscient Code Generation, PICC,
PICC-18, PICDEM, PICDEM.net, PICkit, PICtail, REAL ICE,
rfLAB, Select Mode, Total Endurance, TSHARC,
UniWinDriver, WiperLock and ZENA are trademarks of
Microchip Technology Incorporated in the U.S.A. and other
countries.
SQTP is a service mark of Microchip T echnology Incorporated
in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2012, Microchip Technology Inc orporat ed, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
ISBN: 978-1-62076-455-8
Note the following details of the code protection feature on Microch ip devices:
• Microchip products meet the specification contained in their particular Microchip Data Sheet.
• Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
• There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
• Microchip is willing to work with the customer who is concerned about the integrity of their code.
• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digit al Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperiph erals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 3
Table of Contents
Preface ...........................................................................................................................7
Chapter 1. Compiler Overview
1.1 Introduction ...................................................................................................13
1.2 De vice De s cr i ption ........... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... ... 1 3
1.3 Co m p ile r Desc riptio n an d Do cu mentati o n ... .. ....... ...... ....... ........... ....... ......... 13
1.4 Compiler and Other Development Tools ...................................................... 15
Chapter 2. Common C Interface
2.1 Introduction ...................................................................................................17
2.2 Background – The Desire for Portable Code ...............................................17
2.3 Usi n g the C CI ........... ...... ....... ...... ....... ....... ...... ....... ....... ...... .. ....... ....... ...... ... 20
2.4 ANSI Standard Refinement ..........................................................................21
2.5 ANSI Standard Extensions ........................................................................... 29
2.6 Co m p ile r Fe a tures ........ .. ....... ...... ....... ....... ...... ....... ....... ...... ....... ...... ... ...... ... 4 3
Chapter 3 . Co mpiler Command Line Driver
3.1 Introduction ...................................................................................................45
3.2 Invoki n g the C o mp ile r . .. ....... ...... ....... .. ....... ...... ....... ....... ...... ....... ...... ....... ..... 45
3.3 The C Compilation Sequence ......................................................................49
3.4 The C++ Compilation Sequence ..................................................................51
3.5 Ru ntime F ile s .... .. ....... ...... ....... .. ....... ...... ....... ....... ...... ....... ....... ...... ....... ...... . 55
3.6 Sta rt -u p a nd In it ia li z a tio n ............. ....... ....... .. ...... ....... ....... ...... ....... .. ....... ...... . 58
3.7 Co m p ile r Output .. ....... ...... ....... ....... ...... ....... ...... ... ...... ....... ....... ...... ....... ...... . 58
3.8 Compiler Messages ......................................................................................60
3.9 Driver Option Descriptions ........................................................................... 60
Chapter 4. Device-Related Features
4.1 Introduction ...................................................................................................85
4.2 Device Support .............................................................................................85
4.3 Device Header Files .....................................................................................85
4.4 Sta c k ...... ...... ....... ....... ...... ... ...... ....... ...... ....... ....... ...... ....... ....... ...... ....... .. ..... 86
4.5 Using SFRs From C Code .... ................. .............. .. ................. .............. .. ......88
Chapter 5. ANSI C Standard Issues
5.1 Divergence from the ANSI C Standard ............... .. .......................................91
5.2 Extensions to the ANSI C Standard .............................................................91
5.3 Implementation-defined behavior .................................................................92
Chapter 6. Supported Data Types and Variables
6.1 Introduction ...................................................................................................93
6.2 Identifiers ......................................................................................................93
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 4 2012 Microchip Technology Inc.
6.3 Da ta Rep resen t a tio n ........ .. ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... ....... . 93
6.4 Integer Data Types ....................................................................................... 94
6.5 Fl o a tin g - P o in t D a ta T ype s ...... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... ... 9 6
6.6 Structur es and Unions ........... ............. ................................ .. ........................ 98
6.7 Poi n te r Type s . .. ....... ....... ...... ....... ...... ....... ....... ...... ....... .. ....... ...... ....... ....... . 100
6.8 Complex Data Types .................................................................................. 102
6.9 Constant Types and Format s .. ............ ............. .. .. ............. ............ .. ........... 102
6.10 Standard Type Qualifiers .............. ............... ........................... .. ................ 104
6.11 Com p ile r -S p e c if ic Qua lifier s .......... ....... ...... ....... ....... .. ....... ...... ....... ...... .... 1 05
6.12 V a riable A ttributes ..... ... ...... ....... ...... ....... ....... .. ...... ....... ....... ...... ....... ....... . 105
Chapter 7. Memory Allocation and Access
7.1 Introduction .................................................................................................109
7.2 Add r e s s S p a ce s . ....... ....... ...... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... . 109
7.3 Var ia b le s in Da t a Memory ......... ...... ....... ...... ....... ....... .. ....... ...... ....... ...... .... 1 1 0
7.4 Auto Variable Allocation and Access .......................................................... 112
7.5 Var ia b le s in Pr o g ra m M e m o r y ........... ....... ....... ...... ....... ....... ...... ....... .. ....... . 113
7.6 Var ia b le s in Re gi s t e rs .... ...... ....... ...... ....... ....... ...... .. ....... ....... ...... ....... ....... . 114
7.7 Dynamic Memory Allocation ....................................................................... 114
7.8 Memory Models .......................................................................................... 114
Chapter 8. Operators and Statements
8.1 Introduction .................................................................................................117
8.2 Inte g ral Pro m o ti o n . .. .. ....... ...... ....... ....... ...... ....... .. ....... ...... ....... ....... ...... ...... 1 1 7
8.3 Ty p e Re fe re n c e s ... .. .. ....... ...... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... . 118
8.4 Labels as Values ........................................................................................ 119
8.5 Conditional Operator Operands ................................................................. 120
8.6 Ca se R a n ges .... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... ....... ...... .... 1 20
Chapter 9. Regist er Usage
9.1 Introduction .................................................................................................121
9.2 Re giste r Us a g e . ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... ....... ...... .... 1 2 1
9.3 Re giste r C o n v en t io n s .. ... ...... ....... ...... ....... ....... ...... ....... ........... ....... ...... ...... 121
Chapter 10. Functions
10.1 Wri tin g F u nc t io n s ....... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... ...... 1 2 3
10.2 Function Attribut es and Specifiers .... ....................... ............. ............. ....... 123
10.3 Allocation of Function Code ..................................................................... 127
10.4 Changing the Default Function Allocation ................................................ 127
10.5 F u n c tion Size Limit s ..... ...... ....... ...... ....... ....... ...... ....... ....... ...... ....... ...... .... 1 2 8
10.6 F u n c tion Pa ra meters ...... ...... ....... ....... ...... ....... ...... ....... ....... .. ....... ...... ...... 128
10.7 Function Return Values ............................................................................ 130
10.8 Callin g F u nc tion s ... .. ....... ...... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... . 1 3 0
10.9 Inlin e Fu nctio n s ..... ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... ....... ...... .... 1 3 0
Chapter 11. Interrupts
11.1 Intr o d uction .......... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... .... 1 3 3
11.2 Interrupt O p e ra t io n ......... ...... ....... ....... ...... ....... .. ....... ...... ....... ....... ...... ...... 133
2012 Microchip Technology Inc. DS51686E-page 5
11.3 Writing an Interrupt Service Routine ........................................................134
11.4 Associating a Handle r Funct ion with an Exception Vector .......................139
11.5 Exception Handlers ..................................................................................141
11.6 Inte r ru p t S e rv ic e R o ut in e C ontext S w itc h in g . .. ... ...... ....... ....... ...... ....... ..... 141
11.7 L a tency ... .. ....... ....... .. ...... ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... .. ..... 142
11.8 Nest in g In te rrupts .............. ...... ....... ...... ....... ....... ...... ... ...... ....... ...... ....... ... 14 2
11.9 Enabling/Disabling Interrupts ...................................................................142
11.10 ISR Considerations ................................................................................142
Chapter 12. Main, Runtime Start-up and Reset
12.1 Intr o d uction .... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... ....... ... 14 3
12.2 T h e M a in Fun c tion .... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ..... 143
12.3 Runtime Start-up Code .............................................................................143
12.4 T h e O n Res e t R o u ti ne .. .. ....... ....... ...... .. ....... ....... ...... ....... ....... ...... ....... ..... 157
Chapter 13. Library Routines
13.1 Usin g L ib r ary Rou t in e s ........ ...... ....... ........... ....... ...... ....... ....... ...... ....... ..... 159
Chapter 14. Mixing C/C++ and Assembly Language
14.1 Intr o d uction .... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... ....... ... 16 1
14.2 Using Inline Assembly Language .............................................................161
14.3 Predefined Assembly Macros ...................................................................164
Chapter 15. Opti mizations
15.1 Intr o d uction .... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... ....... ... 16 7
Chapter 16. Preprocessing
16.1 Intr o d uction .... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... ....... ... 16 9
16.2 C/C++ Language Comments .................. .. .. ............... ............ ............... .... 169
16.3 P repro c e s so r Directives ...... .. ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... . 169
16.4 P ragm a D ire c ti ves ........ .. ....... ....... ...... ....... ...... ....... ....... ...... ....... ....... ...... . 171
16.5 Predefined Macros ...................................................................................172
Chapter 17. Linking Programs
17.1 Intr o d uction .... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... ....... ... 17 5
17.2 Repl a ci n g L ib r ary Sym b o ls .. .. ....... ...... ....... ...... ....... ....... ........... ...... ....... ... 17 5
17.3 Linker-Defined Symbols ...........................................................................175
17.4 Defa u lt L in k e r S c rip t ..... .. ... ...... ....... ...... ....... ....... ...... ....... .. ....... ...... ....... ...176
Appendix 18. Implementation-Defined Behavior
18.1 Intr o d uction .... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... ....... ... 19 1
18.2 High lig h ts ....... ...... ... ...... ....... ...... ....... ....... ...... ....... ....... ...... ....... ...... ... ...... . 191
18.3 Over v ie w ....... .. ....... ...... ....... ...... ....... ....... ...... ....... ....... .. ...... ....... ....... ...... . 191
18.4 Translation ....... ......... ......... ...... ......... ......... ......... ...... ......... ......... ....... ....... 192
18.5 E n v ironm e n t .... .. ....... ...... ....... ....... ...... .. ....... ....... ...... ....... ....... ...... ....... ..... 192
18.6 Identifiers ..................................................................................................193
18.7 Char a c te rs .. ... ...... ....... ....... ...... ....... ...... ....... .. ....... ....... ...... ....... ...... ....... ... 19 3
18.8 Integers ....................................................................................................194
18.9 F loa ting -Poin t .... ....... ...... ....... .. ....... ...... ....... ....... ...... ....... ....... ...... ....... ..... 194
18.10 Arrays and Pointers ................................................................................196
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 6 2012 Microchip Technology Inc.
18.11 Hints ....................................................................................................... 196
18.12 Structures, Unions, Enumerations, and Bit fiel ds ............. ........... ........... 197
18.13 Qualifiers ................................................................................................ 197
18.14 Declarators ............................................................................................. 198
18.15 Statements ............................................................................................. 198
18.16 Pre-Processing Directives ...................................................................... 198
18.17 Library Functions .................................................................................... 199
18.18 Architecture ............................................................................................ 202
Appendix 19. ASCII Character Set
Appendix 20. Deprecated Features
20.1 Intr o d uction .......... ...... ....... ....... ...... ....... ...... ....... ....... ...... ... ...... ....... ...... .... 2 0 5
20.2 Variables in Specified Registers ............................................................... 205
Glossary .....................................................................................................................207
Index ...........................................................................................................................225
Worldwide Sales and Service ...................................................................................238
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 7
Preface
MPLAB® XC32 C/C++ Compiler documentation and support information is discussed
in the sections below:
• Document Lay out
• Conventions Used
• Recommended Reading
• myMicrochip Personalized Notification Service
• The Microchip Web Site
• Microchip Forums
• Customer Support
NOTICE TO CUSTOMERS
All documentation becomes dated, and this manual is no exception. Microchip tools and documenta-
tion are constantly evolving to meet customer needs, so some actual dialogs and/or tool descriptions
may differ from those in this document.
For the most up-to-date information on development tools, see the MPLAB® IDE o r MPLAB X ID E
Help. Select the Help menu and then “Topics” or “Help Contents” to open a list of available Help files.
For the most current PDFs, please refer to our web site (http://www.microchip.com). Documents are
identified by “DSXXXXXA”, where “XXXXX” is the document number and “A” is the revision level of
the document. This number is located on the bottom of each page, in front of the page number.
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 8 2012 Microchip Technology Inc.
DOCUMENT LAYOUT
This document describes how to use GNU language tools to write code for 32-bit
applications. The document layout is as follows:
•Chapter 1. Compiler Overview – describes the compiler, development tools and
feature set.
•Chapter 2. Common C Interface – explains what you need to know about
making code portable.
•Chapter 3. Compiler Command Line Driver – describes how to use the
compiler from the command line.
•Chapter 4. Device- Relat ed Feat ures – describes the compiler header and
register definition files, as well as how to use with the SFRs.
•Chapter 5. ANSI C Standard Issues – describes the differences between the
C/C++ language supported by the compiler syntax and the standard ANSI-89 C.
•Chapter 6. Supported Data Types and Variables – describes the compiler
integer and pointer data types.
•Chapter 7. Memory Alloca tion an d Access – desc r ib es the co mpi le r run-t im e
model, including information on sections, initialization, memory models, the
software stack and much more.
•Chapter 8. Operators and Statements – discusses operators and statements.
•Chapter 9. Register Usag e – explains how to access and use SFRs.
•Chapter 10. Functions – details available functions.
•Chapter 11. Interrupts – describes how to use interrupts.
•Chapter 12. Main, Runtime Start-up and Reset – describes important elements
of C/C++ code.
•Chapter 13. Librar y Routin es – explains how to use libraries.
•Chapter 14. Mixing C/C++ and Assembly Language – provides guidelines for
using the compiler with 32-bit assembly language modules.
•Chapter 15. Optimizations – describes optimization options.
•Chapter 16. Pr epro ce ssing – details the preprocessing operation.
•Chapter 17. Linkin g Pro grams – explains how linking works.
•Appendix 18. Implementation-Defined Behavior – details compiler-specific
parameters described as implementation-defined in the ANSI standard.
•Appendix 19. ASCII Character Set” – contains the ASCII character set.
•Appendix 20. Deprecated Features – details features that are considered
obsolete.
Preface
2012 Microchip Technology Inc. DS51686E-page 9
CONVENTIONS USED
The following conventions may appear in this documentation:
DOCUMENTATION CONVENTIONS
Description Represents Examples
Arial font:
Italic characters Referenced books MPLAB® IDE User’s Guide
Emphasized text ...is the only compiler...
Initial caps A window the Output window
A dialog the Settings dialog
A menu selection select Enable Programmer
Quotes A field name in a window or dia-
log “Save project before build”
Underlined, italic text with
right angle bracket A menu path File>Save
Bold characters A dialog button Click OK
A tab Click the Power tab
Text in angle brackets < > A key on the keyboard Press <Enter>, <F1>
Courier fo nt:
Plain Courier Sample source code #define START
Filenames autoexec.bat
File paths c:\mcc18\h
Keywords _asm, _endasm, static
Comm and -li ne opti on s -Opa+, -Opa-
Bit values 0, 1
Constants 0xFF, ’A’
Italic Courier A variable argument file.o, where file can be
any valid filename
Square brackets [ ] Optional arguments mpasmwin [options]
file [options]
Curly brackets and pipe
character: { | } Choice of mutually exclusive
arguments; an OR selection errorlevel {0|1}
Ellipses... Replaces repeated text var_name [,
var_name...]
Repres en t s cod e sup pli ed by
user void main (void)
{ ...
}
Sidebar Text
Devic e Dependent.
This fea ture is not sup po r ted on
all devices. Devices supported
will be listed in the title or text.
xmemory attribute
DD
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 10 2012 Microchip Technology Inc.
RECOMMENDED READING
This documentation describes how to use the MPLAB XC32 C/C++ Compiler. Other
useful documents are listed below. The following Microchip documents are available
and recommended as supplemental reference resources.
Release Notes (Readme Files)
For the latest information on Microchip tools, read the associated Release Notes
(HTML files) included with the software.
MPLAB® Assembler , Linker and Utilities for PIC32 MCUs User’ s Guide (DS51833)
A guide to using the 32-bit assembler, object linker, object archiver/librarian and various
utilities.
32-Bit Language Tools Libraries (DS51685)
Lists all library functions provided with the MPLAB XC32 C/C++ Compiler with detailed
descriptions of their use.
Dinkum Compleat Libraries
The Dinkum Compleat Libraries are organized into a number of headers, files that you
include in your program to declare or define library facilities. A link to the Dinkum librar-
ies is available in the MPLAB X IDE application, on the My MPLAB X IDE tab, Refer-
ences & Featured Links section.
PIC32MX Configuration Settings
Lists the Configuration Bit settings for the Microchip PIC32MX devices supported by
the MPLAB XC32 C/C++ Compiler’s #pragma config.
Device-Specific Documentation
The Microchip website contains many documents that describe 32-bit device functions
and features. Among these are:
• Individual and family data sheets
• Family reference manuals
• Programmer’s reference manuals
C Standards Information
American National Standard for Information Systems – Programming Language – C.
American National Standards Institute (ANSI), 11 West 42nd. Street, New York,
New York, 10036.
This standard specifies the form and establishes the interpretation of programs
expressed in the programming language C. Its purpose is to promote portability,
reliabi lity, maintainabili ty and efficie nt exe cut ion of C language progr am s on a
variety of computing systems.
C++ Standards Information
Stroustrup, Bjarne, C++ Programming Language: Special Edition, 3rd Edition.
Addison-Wesley Professional; Indianapolis, Indiana, 46240.
ISO/IEC 14882 C++ Standard. The ISO C++ Standard is standardized by ISO (The
International Standards Organization) in collaboration with ANSI (The American
National Standards Institute), BSI (The British Standards Institute) and DIN (The
German national standards organization).
This standard specifies the form and establishes the interpretation of programs
expressed in the programming language C++. Its purpose is to promote portability ,
reliability, maintainability and efficient execution of C++ language programs on a
variety of computing systems.
Preface
2012 Microchip Technology Inc. DS51686E-page 11
C Reference Manuals
Harbison, Samuel P. and Steele, Guy L., C A Reference Manual, Fourth Edition,
Prentice-Hall, Englewood Cliffs, N.J. 07632.
Kernighan, Brian W. and Ritchie, Dennis M., The C Programming Language, Secon d
Edition. Prentice Hall, Englewood Cliffs, N.J. 07632.
Kochan, Steven G., Programming In ANSI C, Revised Edition. Hayden Books,
Indianapolis, Indiana 46268.
Plauger, P.J., The Standard C Library, Prentice-Hal l, Eng le wood Cliffs, N.J. 07632.
Van Sickle, Ted., Programming Microc ontrol lers in C, First Edition. LLH Technology
Publishing, Eagle Rock, Virginia 24085.
GCC Documents
http://gcc.gnu.org/onlinedocs/
http://sourceware.org/binutils/
myMICROCHIP PERSONALIZED NOTIFICATION SERVICE
Microchip's personal notification service helps keep customers current on their Micro-
chip products of interest. Subscribers will receive e-mail notification whenever there are
changes, updates, revisions or errata related to a specified product family or develop-
ment tool.
Please visit http://www .microchip.com/pcn to begin the registration process and select
your preferences to receive personalized notifications. A FAQ and registration details
are available on the page, which can be opened by selecting the link above.
When you are selecting your preferences, choosing “Development Systems” will pop-
ulate the list with available development tools. The main categories of tools are listed
below:
•Compilers – The latest information on Microchip C/C++ compilers, assemblers,
linkers and other language tools. These include all MPLAB C/C++ compilers; all
MPLAB assemblers (including MPASM™ assembler); all MPLAB linkers (includ-
ing MPLINK™ object linker); and all MPLAB librarians (including MPLIB™ object
librarian).
•Emulators – The latest information on Microchip in-circuit emulators.These
include the MPLAB REAL ICE™ and MPLAB ICE 2000 in-circuit emulators
•In-Circuit Debuggers – The latest information on Microchip in-circuit debuggers.
These include the MPLAB ICD 2 and 3 in-circuit debuggers and PICkit™ 2 and 3
debug exp ress .
•MPLAB IDE/MPLAB X IDE – The latest information on Microchip MPLAB IDE,
the Windows® Integrated Development Environment, or MPLAB X IDE, the open
source, cross-platform Integrated Development Environment. These lists focus on
the IDE, Project Manager, Editor and Simulator, as well as general editing and
debugging features.
•Programmers – The latest information on Microchip programmers. These include
the device (production) programmers MPLAB REAL ICE in-circuit emulator,
MPLAB ICD 3 in-circuit debugger , MPLAB PM3 and development (nonproduction)
programmers MPLAB ICD 2 in-circuit debugger, PICSTART® Plus and PICkit 2
and 3.
•Starter/Demo Boards – These include MPLAB Starter Kit boards, PICDEM™
demo boards, and various other evaluation boards.
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 12 2012 Microchip Technology Inc.
THE MI CR O C H IP WE B SIT E
Microchip provides online support via our web site at http://www.microchip.com. This
web site is used as a means to make files and information easily available to
customers. Accessible by using your favorite Internet browser, the web site contains
the following information:
•Product Support – Data sheets and errata, application notes and sample
programs, design resources, user’s guides and hardware support documents,
latest software releases and archived software
•General Technical Support – Frequently Asked Questions (FAQs), technical
support requests, online discussion groups, Microchip consultant program
member listing
•Business of Microchip – Product selector and ordering guides, latest Microchip
press releases, listing of seminars and events, listings of Microchi p sale s offices,
distributors and factory representatives
MICROCHIP FORUMS
Microchip provides additional online support via our web forums at
http://www.microchip.com/forums. Currently available forums are:
• Developm ent To ols
•8-bit PIC
® MCUs
• 16-bit PIC MCUs
• 32-bit PIC MCUs
CUSTOMER SUPPORT
Users of Microchip products can receive assistance through several channels:
• Distributor or Representative
• Local Sales Office
• Field Application Engineer (FAE)
• Technical Support
Customers should contact their distributor , representative or field application engineer
(FAE) for support. Local sales offices are also available to help customers. A listing of
sales offices and locations is included in the back of this document. See our web site
for a complete, up-to-date listing of sales offices.
Technical support is available through the web site at http://support.microchip.com.
Documentation errors or comments may be emailed to docerrors@microchip.com.
DOCUMENT REVISION HISTORY
Revision D (January 2012)
• Changed product name from MPLAB C32 C Compiler to MPLAB XC32 C/C++
Compiler. Completely reorganized document to align with other Microchip
compile r documentation .
Revision E (July 2012)
• Added information pertaining to C++ throughout the document.
• Added new section describing the Common Compiler Interface (CCI) Standard
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 13
Chapter 1. Compiler Overview
1.1 INTRODUCTION
The MPLAB XC32 C/C++ Compiler is defined and described in the following topics:
• Device Des crip t io n
• Compiler Description and Documentation
• Compiler and Other Development Tools
1.2 DEVICE DESCRIPTION
The MPLAB XC32 C/C++ Compiler fully supports all Microchip 32-bit devices.
1.3 COMPILER DESCRIPTION AND DOCUMENTATION
The MPLAB XC32 C/C++ Compiler is a full-featured, optimizing compiler that trans-
lates standard ANSI C programs into 32-bit device assembly language source. The
compiler also supports many command-line options and language extensions that
allow full access to the 32-bit device hardware capabilities, and affords fine control of
the compiler code generator.
The compiler is a port of the GCC compiler from the Free Software Foundation.
The compiler is available for several popular operating systems, including 32 and 64-bit
Windows®, Linux and Apple OS X.
The compiler can run in one of three operating modes: Free, Standard or PRO. The
S tandard and PRO operating modes are licensed modes and require an activation key
and Internet connectivity to enable them. Free mode is available for unlicensed cus-
tomers. The basic compiler operation, supported devices and available memory are
identical across all modes. The modes only differ in the level of optimization employed
by the compiler.
1.3.1 Conventions
Throughout this manual, the term “the compiler” is often used. It can refer to either all,
or some subset of, the collection of applications that form the MPLAB XC32 C/C++
Compiler. Often it is not important to know, for example, whether an action is performed
by the parser or code generator application, and it is sufficient to say it was performed
by “the compiler”.
It is also reasonable for “the compiler” to refer to the command-line driver (or just driver)
as this is the application that is always executed to invoke the compilation process. The
driver for the MPLAB XC32 C/C++ Compiler package is called xc32-gcc. The driver
for the C/ASM projects is also xc32-gcc. The driver for C/C++/ASM projects is
xc32-g++. The drivers and their options are discussed in Section 3.9 “Driver Option
Descriptions”. Following this view, “compiler options” should be considered com-
mand-line driver options, unless otherwise specified in this manual.
Similarly “compilation” refers to all, or some part of, the steps involved in generating
source code into an executable binary image.
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1.3.2 ANSI C Standards
The compiler is a fully validated compiler that conforms to the ANSI C standard as
defined by the ANSI specification (ANSI x3.159-1989) and described in Kernighan and
Ritchie’s The C Programming Language (second edition). The ANSI standard includes
extensions to the original C definition that are now standard features of the language.
These extensions enhance portability and offer increased capability. In addition, lan-
guage extensions for PIC32 MCU embedded-control applications are included.
1.3.3 Optimization
The compiler uses a set of sophisticated optimization passes that employ many
advanced techniques for generating efficient, compact code from C/C++ source. The
optimization passes include high-level optimizations that are applicable to any C/C++
code, as well as PIC32 MCU-specific optimizations that take advantage of the particu-
lar features of the device architecture.
For more on optimizations, see Chapter 15. “Optimizations”.
1.3.4 ANSI Standard Library Support
The compiler is distributed with a complete ANSI C standard library . All library functions
have been validated and conform to the ANSI C library standard. The library includes
functions for string manipulation, dynamic memory allocation, data conversion, time-
keeping and math functions (trigonometric, exponential and hyperbolic). The standard
I/O functions for file handling are also included, and, as distributed, they support full
access to the host file system using the command-line simulator. The fully functional
source code for the low-level file I/O functions is provided in the compiler distribution,
and may be used as a starting point for applications that require this capability.
1.3.5 ISO/IEC C++ Standard
The compiler is distributed with the 2003 Standard C++ Library.
1.3.6 Compiler Driver
The compiler includes a powerful command-line driver program. Using the driver
program, application programs can be compiled, assembled and linked in a single step.
1.3.7 Documentation
The C compiler is supported under both the MPLAB IDE v8.xx or higher, and the
MPLAB X IDE. For C++, MPLAB X IDE v1.40 or higher is required. For simplicity , both
IDEs are referred to throughout the book as simply MPLAB IDE.
Features that are unique to specific devices, and therefore specific compilers, are
noted with “DD” text the column (see the Preface) and text identifying the devices to
which the information applies.
Note: Do not specif y an MPLAB XC32 system incl ude directory (e. g.
/pic32mx/include/) in your project properties. The xc32-gcc and
xc32-g++ compilation drivers automatically select the XC libc or the Din-
kumware libc and their respective include-file directory for you. Manually
adding a system include file path may disrupt this mechanism and cause
the incorrect libc include files to be compiled into your project, causing a
conflict between the include files and the library . Note that adding a system
include path to your project properties has never been a recommended
practice.
Compiler Overview
2012 Microchip Technology Inc. DS51686E-page 15
1.4 COMPILER AND OTHER DEVELOPMENT TOOLS
The compiler works with many other Microchip tools including:
• MPLAB XC32 assembler and linker - see the “MPLAB® Assembler, Linker and
Utilities for PIC32 MCUs User’s Guide”.
• MPLAB IDE v8.xx and MPLAB X IDE (C++ required MPLAB X IDE v1.30 or
higher)
• The MPLAB Simulator
• All Microchip debug tools and programmers
• Demo boards and starter kits that support 32-bit devices
MPLAB® XC32 C/C++ Compiler User’s Guide
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NOTES:
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 17
Chapter 2. Common C Interface
2.1 INTRODUCTION
The Common C Interface (CCI) is available with all MPLAB XC C compilers and is
designed to enhance code portability between these compilers. For example,
CCI-conforming code would make it easier to port from a PIC18 MCU using the MPLAB
XC8 C compiler to a PIC32 MCU using the MPLAB XC32 C/C++ Compiler.
The CCI assumes that your source code already conforms to the ANSI Standard. If you
intend to use the CCI, it is your responsibility to write code that conforms. Legacy proj-
ects will need to be migrated to achieve conformance. A compiler option must also be
set to ensure that the operation of the compiler is consistent with the interface when the
project is built.
The following topics are examined in this chapter:
• Background — The Desire for Portable Code
• Using the CCI
• ANSI Standard Refinement
• ANSI Standard Extensions
• Compiler Features
2.2 BACKGROUND – THE DESIRE FOR PORT ABLE CODE
All programmers want to write portable source code.
Portability means that the same source code can be compiled and run in a different
execution environment than that for which it was written. Rarely can code be one hun-
dred percent portable, but the more tolerant it is to change, the less time and effort it
takes to have it running in a new environment.
Embedded engineers typically think of code portability as being across target devices,
but this is only part of the situation. The same code could be compiled for the same
target but with a dif ferent compiler . Differences between those compilers might lead to
the code failing at compile time or runtime, so this must be considered as well.
You may only write code for one target device and only use one brand of compiler , but
if there is no regulation of the compiler’s operation, simply updating your compiler ver-
sion may change your code’s behavior.
Code must be portable across targets, tools, and time to be truly flexible.
Clearly, this portability cannot be achieved by the programmer alone, since the com-
piler vendors can base their products on different technologies, implement different fea-
tures and code syntax, or improve the way their product works. Many a great compiler
optimization has broken many an unsuspecting project.
S tandards for the C language have been developed to ensure that change is managed
and code is more portable. The American National Standards Institute (ANSI) pub-
lishes standards for many disciplines, including programming languages. The ANSI C
Standard is a universally adopted standard for the C programming language.
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2.2.1 The ANSI Standard
The ANSI C S t andard has to reconcile two opposing goals: freedom for compilers ven-
dors to target new devices and improve code generation, with the known functional
operation of source code for programmers. If both goals can be met, source code can
be made portable.
The standard is implemented as a set of rules which detail not only the syntax that a
conforming C program must follow, but the semantic rules by which that program will
be interpreted. Thus, for a compiler to conform to the standard, it must ensure that a
conforming C program functions as described by the standard.
The standard describes implementation, the set of tools and the runtime environment
on which the code will run. If any of these change, e.g., you build for, and run on, a dif-
ferent target device, or if you update the version of the compiler you use to build, then
you are using a different implementation.
The standard uses the term behavior to mean the external appearance or action of the
program. It has nothing to do with how a program is encoded.
Since the standard is trying to achieve goals that could be construed as conflicting,
some specifications appear somewhat vague. For example, the standard states that an
int type must be able to hold at least a 16-bit value, but it does not go as far as saying
what the size of an int actually is; and the action of right-shifting a signed integer can
produce different results on different implementations; yet, these different results are
still ANSI C compliant.
If the standard is too strict, device architectures may not allow the compiler to conform1.
But, if it is too weak, programmers would see wildly differing results within different
compilers and architectures, and the standard would loose its effectiveness.
The standard organizes source code whose behavior is not fully defined into groups
that include the following behaviors:
Implementation-defined behavior
This is un spe ci fi ed beha vior wh er e e ach i mpl em enta tio n docume nts ho w th e c hoic e
is made.
Unspecified behavior
The standard provides two or more possibilities and imposes no further requirements
on which possi bi li ty is chosen in any part ic ula r instance.
Undefined behavior
This is behavior for which the standard imposes no requirements.
Code that strictly conforms to the standard does not produce output that is dependent
on any unspecified, undefined, or implementation-defined behavior. The size of an
int, which we used as an example earlier, falls into the category of behavior that is
defined by implementation. That is to say, the size of an int is defined by which com-
piler is being used, how that compiler is being used, and the device that is being tar-
geted.
All the MPLAB XC compilers conform to the ANS X3.159-1989 Standard for program-
ming languages (with the exception of the XC8 compiler’s inability to allow recursion,
as mentioned in the footnote). This is commonly called the C89 Standard. Some fea-
tures from the later standard, C99, are also supported.
1. Case in point: The mi d-ran ge PIC ® microcontrollers do not have a data stack. Because
a compi ler targ eting th is dev ice c annot i mplemen t recurs ion, i t (strict ly spe aking ) cann ot
conform to the ANSI C Standard. This example illustrate a situation in which the stan-
dard is too strict for mid-ran ge dev ic es and tools .
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 19
For freestanding implementations – or for what we typically call embedded applications
– the standard allows non-standard extensions to the language, but obviously does not
enforce how they are specified or how they work. When working so closely to the
device hardware, a programmer needs a means of specifying device setup and inter-
rupts, as well as utilizing the often complex world of small-device memory
architectures. This cannot be offered by the standard in a consistent way.
While the ANSI C Standard provides a mutual understanding for programmers and
compiler vendors, programmers need to consider the implementation-defined behavior
of their tools and the probability that they may need to use extensions to the C language
that are non-standard. Both of these circumstances can have an impact on code
portability.
2.2.2 The Common C Interface
The Common C Interface (CCI) supplements the ANSI C S tandard and makes it easier
for programmers to achieve consistent outcomes on all Microchip devices when using
any of the MPLAB XC C compilers.
It delivers the following improvements, all designed with portability in mind.
Refinement of the ANSI C Standard
The CCI documents specific behavior for some code in which actions are implemen-
tation-defined behavior under the ANSI C Standard. For example, the result of
right-shifting a signed integer is fully defined by the CCI. Note that many
implementation-defined items that closely couple with device characteristics, such as
the size of an int, are not defined by the CCI.
Consistent syntax for non-standard extensions
The CCI non-standard extensions are mostly implemented using keywords with a uni-
form synt ax. They re place keyw ords, mac ros and attrib ute s that are the nativ e com-
piler im plemen tation. The interp retation of the keyword ma y differ across each com-
piler, and any arguments to the keywords may be device specific.
Coding guidelines
The CCI may in dic at e adv ice on ho w cod e sho uld be writte n so tha t it ca n be por te d
to other devices o r comp ilers. Wh ile you may ch oose not to follow the advi ce, it wi ll
not conform to the CCI.
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2.3 USING THE CCI
The CCI allows enhanced portability by refining implementation-defined behavior and
standardizing the syntax for extensions to the language.
The CCI is something you choose to follow and put into effect, thus it is relevant for new
projects, although you may choose to modify existing projects so they conform.
For your project to conform to the CCI, you must do the following things.
Enable the CCI
Select the MPLAB IDE widget Use CCI Syntax in your project, or use the
command-line option that is equivalent.
Include <xc.h> in every module
Some CCI features are only enabled if this header is seen by the compiler.
Ensure ANSI compliance
Code that does not conform to the ANSI C Standard does not confirm to the CCI.
Observe refinements to ANSI by the CCI
Some ANSI implementation-defined behavior is defined explicitly by the CCI.
Use the CCI extensions to the language
Use the CCI extensions rather than the native language extensions
The next sections detail specific items associated with the CCI. These items are seg-
regated into those that refine the standard, those that deal with the ANSI C Standard
extensions, and other miscellaneous compiler options and usage. Guidelines are indi-
cated with these item s.
If any implementation-defined behavior or any non-standard extension is not discussed
in this document, then it is not part of the CCI. For example, GCC case ranges, label
addresses and 24-bit short long types are not part of the CCI. Programs which use
these features do not conform to the CCI. The compiler may issue a warning or error
to indicate when you use a non-CCI feature and the CCI is enabled.
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 21
2.4 ANSI STANDARD REFINEMENT
The following topics describe how the CCI refines the implementation-defined
behaviors outlined in the ANSI C Standard.
2.4.1 Source File Encoding
Under the CCI, a source file must be written using characters from the 7-bit ASCII set.
Lines may be terminated using a line feed (\n) or carria ge return (\r) that is immediately
followed by a line feed. Escaped characters may be used in character constants or
string literals to represent extended characters not in the basic character set.
2.4.1.1 EXAMPLE
The following shows a string constant being defined that uses escaped characters.
const char myName[] = "Bj\370rk\n";
2.4.1.2 DIFFERENCES
All compilers have used this character set.
2.4.1.3 MIGRATION TO THE CCI
No action required.
2.4.2 The Prototype for main
The prototype for the main() function is
int main(void);
2.4.2.1 EXAMPLE
The followi ng sh ows an examp le of ho w main() might be defined
int main(void)
{while(1)
process();
}
2.4.2.2 DIFFERENCES
The 8-bit compilers used a void return type for this function.
2.4.2.3 MIGRATION TO THE CCI
Each program has one definition for the main() function. Confirm the return type for
main() in all projects previously compiled for 8-bit targets.
2.4.3 Header File Specification
Header file specifications that use directory separators do not conform to the CCI.
2.4.3.1 EXAMPLE
The followi ng examp le sho ws two confor ming inc l ude direc ti ve s.
#include <usb_main.h>
#include "global.h"
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2.4.3.2 DIFFERENCES
Header file specifications that use directory separators have been allowed in previous
versions of all compilers. Compatibility problems arose when Windows-style separa-
tors "\" were used and the code compiled under other host operating systems. Under
the CCI, no directory specifiers should be used.
2.4.3.3 MIGRATION TO THE CCI
Any #include di rectives that use directory separators in the header file specifications
should be changed. Remove all but the header file name in the directive. Add the direc-
tory path to the compiler’s include search path or MPLAB IDE equivalent. This will force
the compiler to search the directories specified with this option.
For example, the following code:
#include <inc/lcd.h>
should be changed to:
#include <lcd.h>
and the path to the inc directory added to the compiler’s header search path in your
MPLAB IDE project properties, or on the command-line as follows:
-Ilcd
2.4.4 Include Search Paths
When you include a header file under the CCI, the file should be discoverable in the
paths searched by the compiler detailed below.
For any header files specified in angle bracket delimiters < >, the search paths should
be those specified by -I options (or the equivalent MPLAB IDE option), then the stan-
dard compiler include directories. The -I options are searched in the order in which
they are sp ecified.
For any file specified in quote characters " ", the search paths should first be the cur-
rent working directory . In the case of an MPLAB X project, the current working directory
is the directory in which the C source file is located. If unsuccessful, the search paths
should be the same directories searched when the header files is specified in angle
bracket delimiters.
Any other options to specify search paths for header files do not conform to the CCI.
2.4.4.1 EXAMPLE
If including a header file as in the following directive
#include "myGlobals.h"
The header file should be locatable in the current working directory, or the paths spec-
ifie d b y an y -I options, or the standard compiler directories. If it is located elsewhere,
this does not conform to the CCI.
2.4.4.2 DIFFERENCES
The compiler operation under the CCI is not changed. This is purely a coding guide line.
2.4.4.3 MIGRATION TO THE CCI
Remove any option that specifies header file search paths other than the -I option (or
the equivalent MPLAB IDE option), and use the -I option in place of this. Ensure the
header file can be found in the directories specified in this section.
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 23
2.4.5 The Number of Signifi cant Initial Characters in an Identifier
At least the first 255 characters in an identifier (internal and external) are significant.
This extends upon the requirement of the ANSI C Standard which states a lower num-
ber of significant characters are used to identify an object.
2.4.5.1 EXAMPLE
The following example shows two poorly named variables, but names which are
considered unique under the CCI.
int stateOfPortBWhenTheOperatorHasSelectedAutomaticModeAndMotorIsRunningFast;
int stateOfPortBWhenTheOperatorHasSelectedAutomaticModeAndMotorIsRunningSlow;
2.4.5.2 DIFFERENCES
Former 8-bit compilers used 31 significant characters by default, but an option allowed
this to be extended.
The 16- and 32-bit compilers did not impose a limit on the number of significant char-
acters.
2.4.5.3 MIGRATION TO THE CCI
No action required. You may take advantage of the less restrictive naming scheme.
2.4.6 Sizes of Types
The sizes of the basic C types, for example char, int and long, are not fully defined
by the CCI. These types, by design, reflect the size of registers and other architectural
features in the target device. They allow the device to efficiently access objects of this
type. The ANSI C Standard does, however, indicate minimum requirements for these
types, as specified in <limits.h>.
If you need fixed-size types in your project, use the types defined in <stdint.h>, e.g.,
uint8_t or int16_t. These types are consistently defined across all XC compilers,
even outside of the CCI.
Essentially , the C language offers a choice of two groups of types: those that offer sizes
and formats that are tailored to the device you are using; or those that have a fixed size,
regardless of the target.
2.4.6.1 EXAMPLE
The following example shows the definition of a variable, native, whose size will allow
efficient access on the target device; and a variable, fixed, w hos e si ze i s cle a rl y i n di -
cated and remains fixed, even though it may not allow efficient access on every device.
int native;
int16_t fixed;
2.4.6.2 DIFFERENCES
This is consistent with previous types implemented by the compiler.
2.4.6.3 MIGRATION TO THE CCI
If you require a C type that has a fixed size, regardless of the target device, use one of
the types defined by <stdint.h>.
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2.4.7 Plain char Types
The type of a plain char is unsigned char . It is generally recommended that all def-
initions for the char type explicitly state the signedness of the object.
2.4.7.1 EXAMPLE
The following example
char foobar;
defines an unsigned char object called foobar.
2.4.7.2 DIFFERENCES
The 8-bit compilers have always treated plain char as an unsigned type.
The 16- and 32-bit compilers used signed char as the default plain char type. The
-funsigned-char option on those compilers changed the default type to be
unsigned char.
2.4.7.3 MIGRATION TO THE CCI
Any definition of an object defined as a plain char and using the 16- or 32-bit compilers
needs review. Any plain char that was intended to be a signed quantity should be
replaced with an explicit definition, for example.
signed char foobar;
You may use the -funsigned-char option on XC16/32 to change the type of plain
char, but since this option is not supported on XC8, the code is not strictly conforming.
2.4.8 Signed Integer Representation
The value of a signed integer is determined by taking the two’s complement of the inte-
ger.
2.4.8.1 EXAMPLE
The following shows a variable, test, that is assigned the value -28 decimal.
signed char test = 0xE4;
2.4.8.2 DIFFERENCES
All compilers have represented signed integers in the way described in this section.
2.4.8.3 MIGRATION TO THE CCI
No action required.
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2.4.9 Integer conversion
When converting an integer type to a signed integer of insufficient size, the original
value is truncated from the most-significant bit to accommodate the target size.
2.4.9.1 EXAMPLE
The following shows an assignment of a value that will be truncated.
signed char destination;
unsigned int source = 0x12FE;
destination = source;
Under the CCI, the value of destination after the alignment will be -2 (i.e., the bit
pattern 0xFE).
2.4.9.2 DIFFERENCES
All compilers have performed integer conversion in an identical fashion to that
described in this section.
2.4.9.3 MIGRATION TO THE CCI
No action required.
2.4.10 Bit-wise Operations on Signed Values
Bitwise operations on signed values act on the two’s complement representation,
including the sign bit. See also Section 2.4.11 “Right-shifting Signed Values”.
2.4.10.1 EXAMPLE
The following shows an example of a negative quantity involved in a bitwise AND oper-
ation.
signed char output, input = -13;
output = input & 0x7E;
Under the CCI, the value of output after the assignment will be 0x72.
2.4.10.2 DIFFERENCES
All compilers have performed bitwise operations in an identical fashion to that
described in this section.
2.4.10.3 MIGRATION TO THE CCI
No action required.
2.4.11 Right-shifting Signed Values
Right-shifting a signed value will involve sign extension. This will preserve the sign of
the original value.
2.4.11.1 EXAMPLE
The following shows an example of a negative quantity involved in a bitwise AND oper-
ation.
signed char input, output = -13;
output = input >> 3;
Under the CCI, the value of output after the assignment will be -2 (i.e., the bit pattern
0xFE).
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2.4.11.2 DIFFERENCES
All compilers have performed right shifting as described in this section.
2.4.11.3 MIGRATION TO THE CCI
No action required.
2.4.12 Conversion of Union Member Accessed Using Member With
Different Type
If a union defines several members of different types and you use one member identi-
fier to try to access the contents of another (whether any conversion is applied to the
result) is implementation-defined behavior in the standard. In the CCI, no conversion is
applied and the bytes of the union object are interpreted as an object of the type of the
member being accessed, without regard for alignment or other possible invalid condi-
tions.
2.4.12.1 EXAMPLE
The following shows an example of a union defining several members.
union {
signed char code;
unsigned int data;
float offset;
} foobar;
Code that attempts to extract offset by reading data is not guaranteed to read the
correct value.
float result;
result = foobbar.data;
2.4.12.2 DIFFERENCES
All compilers have not converted union members accessed via other members.
2.4.12.3 MIGRATION TO THE CCI
No action required.
2.4.13 Default Bit-field int Type
The type of a bit-field specified as a plain int will be identical to that of one defined
using unsigned int . This is quite different to other objects where the types int,
signed and signed int are synonymous. It is recommended that the signedness of
the bit-field be explicitly stated in all bit-field definitions.
2.4.13.1 EXAMPLE
The following shows an example of a structure tag containing bit-fields which are
unsigned integers and with the size specified.
struct OUTPUTS {
int direction :1;
int parity :3;
int value :4;
};
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2.4.13.2 DIFFERENCES
The 8-bit compilers have previously issued a warning if type int was used for bit-fields,
but would implement the bit-field with an unsigned int type.
The 16- and 32-bit compilers have implemented bit-fields defined using int as having
a signed int type, unless the option -funsigned-bitfields was specified.
2.4.13.3 MIGRATION TO THE CCI
Any code that defines a bit-field with the plain int type should be reviewed. If the inten-
tion was for these to be signed quantities, then the type of these should be changed to
signed int, for example, in:
struct WAYPT {
int log :3;
int direction :4;
};
the bit-field type should be changed to signed int, as in:
struct WAYPT {
signed int log :3;
signed int direction :4;
};
2.4.14 Bit-fields S traddling a Stora g e Unit Boundary
Whether a bit-field can straddle a storage unit boundary is implementation-defined
behavior in the standard. In the CCI, bit-fields will not straddle a storage unit boundary;
a new storage unit will be allocated to the structure, and padding bits will fill the gap.
Note that the size of a storage unit differs with each compiler as this is based on the
size of the base data type (e.g., int) from which the bit-field type is derived. On 8-bit
compilers this unit is 8-bits in size; for 16-bit compilers, it is 16 bits; and for 32-bit com-
pilers, it is 32 bits in size.
2.4.14.1 EXAMPLE
The following shows a structure containing bit-fields being defined.
struct {
unsigned first : 6;
unsigned second :6;
} order;
Under the CCI and using XC8, the storage allocation unit is byte sized. The bit-field
second, will be allocated a new storage unit since there are only 2 bits remaining in
the first storage unit in which first is allocated. The size of this structure, order, will
be 2 bytes.
2.4.14.2 DIFFERENCES
This allocation is identical with that used by all previous compilers.
2.4.14.3 MIGRATION TO THE CCI
No action required.
2.4.15 The Allocation Order of Bits-field
The memory ordering of bit-fields into their storage unit is not specified by the ANSI C
Standard. In the CCI, the first bit defined will be the least significant bit of the storage
unit in which it will be allocated.
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2.4.15.1 EXAMPLE
The following shows a structure containing bit-fields being defined.
struct {
unsigned lo : 1;
unsigned mid :6;
unsigned hi : 1;
} foo;
The bit-field lo will be assigned the least significant bit of the storage unit assigned to
the structure foo. The bit-field mid will be assigned the next 6 least significant bits, and
hi, the most significant bit of that same storage unit byte.
2.4.15.2 DIFFERENCES
This is identical with the previous operation of all compilers.
2.4.15.3 MIGRATION TO THE CCI
No action required.
2.4.16 The NULL macro
The NULL macro is defined in <stddef.h>; however, its definition is implementa-
tion-defined behavior. Under the CCI, the definition of NULL is the expression (0).
2.4.16.1 EXAMPLE
The following shows a pointer being assigned a null pointer constant via the NULL
macro.
int * ip = NULL;
The value of NULL, (0), is implicitly cast to the destination type.
2.4.16.2 DIFFERENCES
The 32-bit compilers previously assigned NULL the expression ((void *)0).
2.4.16.3 MIGRATION TO THE CCI
No action required.
2.4.17 Floating-point sizes
Under the CCI, floating-point types must not be smaller than 32 bits in size.
2.4.17.1 EXAMPLE
The following shows the definition for outY, which will be at least 32-bit in size.
float outY;
2.4.17.2 DIFFERENCES
The 8-bit compilers have allowed the use of 24-bit float and double types.
2.4.17.3 MIGRATION TO THE CCI
When using 8-bit compilers, the float and double type will automatically be made
32 bits in size once the CCI mode is enabled. Review any source code that may have
assumed a float or double type and may have been 24 bits in size.
No migration is required for other compilers.
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 29
2.5 ANSI STANDARD EXTENSIONS
The following topics describe how the CCI provides device-specific extensions to the
standard.
2.5.1 Generic Header File
A single header file <xc.h> must be used to declare all compiler- and device-specific
types and SFRs. You must include this file into every module to conform with the CCI.
Some CCI definitions depend on this header being seen.
2.5.1.1 EXAMPLE
The following shows this header file being included, thus allowing conformance with the
CCI, as well as allowing access to SFRs.
#include <xc.h>
2.5.1.2 DIFFERENCES
Some 8-bit compilers used <htc.h> as the equivalent header. Previous versions of
the 16- and 32-bit compilers used a variety of headers to do the same job.
2.5.1.3 MIGRATION TO THE CCI
Change:
#include <htc.h>
used previously in 8-bit compiler code, or family-specific header files as in the following
examples:
#include <p32xxxx.h>
#include <p30fxxxx.h>
#include <p33Fxxxx.h>
#include <p24Fxxxx.h>
#include "p30f6014.h"
to:
#include <xc.h>
2.5.2 Absolute addressing
Variables and functions can be placed at an absolute address by using the __at()
construct.qualifier Note that XC16/32 may require the variable or function to be placed
in a special section for absolute addressing to work. Stack-based (auto and parame-
ter) variables cannot use the __at() specifier.
2.5.2.1 EXAMPLE
The following shows two variables and a function being made absolute.
int scanMode __at(0x200);
const char keys[] __at(123) = { ’r’, ’s’, ’u’, ’d’};
int modify(int x) __at(0x1000) {
return x * 2 + 3;
}
2.5.2.2 DIFFERENCES
The 8-bit compilers have used an @ symbol to specify an absolute address.
The 16- and 32-bit compilers have used the address attribute to specify an object’s
address.
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2.5.2.3 MIGRATION TO THE CCI
Avoid making objects and functions absolute if possible.
In XC8, change absolute object definitions such as the following example:
int scanMode @ 0x200;
to:
int scanMode __at(0x200);
In XC16/32, change code such as:
int scanMode __attribute__(address(0x200)));
to:
int scanMode __at(0x200);
2.5.2.4 CAVEATS
If the __at() and __section() specifiers are both applied to an object when using
XC8, the __section() specifier is currently ignored.
2.5.3 Far Objects and Functions
The __far qualifier may be used to indicate that variables or functions may be located
in ‘far memory’. Exactly what constitutes far memory is dependent on the target device,
but it is typically memory that requires more complex code to access. Expressions
involving far-qualified objects may generate slower and larger code.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this qualifier.
Some devices may not have such memory implemented, in which case, use of this
qualifier will be ignored. Stack-based (auto and parameter) variables cannot use the
__far specifier.
2.5.3.1 EXAMPLE
The following shows a variable and function qualified using __far.
__far int serialNo;
__far int ext_getCond(int selector);
2.5.3.2 DIFFERENCES
The 8-bit compilers have used the qualifier far to indicate this meaning. Functions
could not be qualified as far.
The 16-bit compilers have used the far attribute with both variables and functions.
The 32-bit compilers have used the far attribute with functions, only.
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2012 Microchip Technology Inc. DS51686E-page 31
2.5.3.3 MIGRATION TO THE CCI
For 8-bit compilers, change any occurrence of the far qual ifi er, as in the following
example:
far char template[20];
to __far, i.e., __far char template[20];
In the 16- and 32-bit compilers, change any occurrence of the far attribute, as in the
following
void bar(void) __attribute__ ((far));
int tblIdx __attribute__ ((far));
to
void __far bar(void);
int __far tblIdx;
2.5.3.4 CAVEATS
None.
2.5.4 Near Objects
The __near qualifier may be used to indicate that variables or functions may be
located in ‘near memory’. Exactly what constitutes near memory is dependent on the
target device, but it is typically memory that can be accessed with less complex code.
Expressions involving near-qualified objects may be faster and result in smaller code.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this qualifier.
Some devices may not have such memory implemented, in which case, use of this
qualifier will be ignored. Stack-based (auto and parameter) variables cannot use the
__near specifier.
2.5.4.1 EXAMPLE
The following shows a variable and function qualified using __near.
__near int serialNo;
__near int ext_getCond(int selector);
2.5.4.2 DIFFERENCES
The 8-bit compilers have used the qualifier near to indicate this meaning. Functions
could not be qualified as near.
The 16-bit compilers have used the near attribute with both variables and functions.
The 32-bit compilers have used the near attribute for functions, only.
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2.5.4.3 MIGRATION TO THE CCI
For 8-bit compilers, change any occurrence of the near qualifier, as in the following
example:
near char template[20];
to __near, i.e., __near char template[20];
In 16- and 32-bit compilers, change any occurrence of the near attribute, as in the fol-
lowing
void bar(void) __attribute__ ((near));
int tblIdx __attribute__ ((near));
to
void __near bar(void);
int __near tblIdx;
2.5.4.4 CAVEATS
None.
2.5.5 Persistent Objects
The __persistent qualifier may be used to indicate that variables should not be
cleared by the runtime startup code.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this qualifier.
2.5.5.1 EXAMPLE
The following shows a variable qualified using __persistent.
__persistent int serialNo;
2.5.5.2 DIFFERENCES
The 8-bit compilers have used the qualifier, persistent, to indicate this meaning.
The 16- and 32-bit compilers have used the persistent attribute with variables to
indicate they were not to be cleared.
2.5.5.3 MIGRATION TO THE CCI
With 8-bit compilers, change any occurrence of the persistent qualifier , as in the fol-
lowing example:
persistent char template[20];
to __persistent, i.e., __persistent char template[20];
For the 16- and 32-bit compilers, change any occurrence of the persistent attribute,
as in the following
int tblIdx __attribute__ ((persistent));
to
int __persistent tblIdx;
2.5.5.4 CAVEATS
None.
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2012 Microchip Technology Inc. DS51686E-page 33
2.5.6 X and Y Data Objects
The __xdata and __ydata qualifiers may be used to indicate that variables may be
located in special memory regions. Exactly what constitutes X and Y memory is depen-
dent on the target device, but it is typically memory that can be accessed independently
on separate buses. Such memory is often required for some DSP instructions.
Use the native keywords discussed in the Differences section to look up information on
the semantics of these qualifiers.
Some devices may not have such memory implemented; in which case, use of these
qualifiers will be ignored.
2.5.6.1 EXAMPLE
The following shows a variable qualified using __xdata, as well as another variable
qualified with __ydata.
__xdata char data[16];
__ydata char coeffs[4];
2.5.6.2 DIFFERENCES
The 16-bit compilers have used the xmemory and ymemory space attribute with
variables.
Equivalent specifiers have never been defined for any other compiler.
2.5.6.3 MIGRATION TO THE CCI
For 16-bit compilers, change any occurrence of the space attributes xmemory or
ymemory, as in the following example:
char __attribute__((space(xmemory)))template[20];
to __xdata, or __ydata, i.e., __xdata char template[20];
2.5.6.4 CAVEATS
None.
2.5.7 Banked Data Objects
The __bank(num) qualifier may be used to indicate that variables may be located in
a particular data memory bank. The number, num, represents the bank number . Exactly
what constitutes banked memory is dependent on the target device, but it is typically a
subdivision of data memory to allow for assembly instructions with a limited address
width field.
Use the native keywords discussed in the Differences section to look up information on
the semantics of these qualifiers.
Some devices may not have banked data memory implemented, in which case, use of
this qualifier will be ignored. The number of data banks implemented will vary from one
device to another.
2.5.7.1 EXAMPLE
The following shows a variable qualified using __bank().
__bank(0) char start;
__bank(5) char stop;
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2.5.7.2 DIFFERENCES
The 8-bit compil ers ha ve used the fo ur qua lifie rs bank0, bank1, bank2 and bank3 to
indicate the same, albeit more limited, memory placement.
Equivalent specifiers have never been defined for any other compiler.
2.5.7.3 MIGRATION TO THE CCI
For 8-bit compilers, change any occurrence of the bankx qualifiers, as in the following
example:
bank2 int logEntry;
to __bank(, i.e., __bank(2) int logEntry;
2.5.7.4 CAVEATS
None.
2.5.8 Alignment of Objects
The __align(alignment) specifier may be used to indicate that variables must be
aligned on a memory address that is a multiple of the alignment specified. The align-
ment term must be a power of two. Positive values request that the object’s start
address be aligned; negative values imply the object’s end address be aligned.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this specifier.
2.5.8.1 EXAMPLE
The following shows variables qualified using __align() to ensure they end on an
address that is a multiple of 8, and start on an address that is a multiple of 2,
respectively.
__align(-8) int spacer;
__align(2) char coeffs[6];
2.5.8.2 DIFFERENCES
An alignment feature has never been implemented on 8-bit compilers.
The 16- and 32-bit compilers used the aligned attribute with variables.
2.5.8.3 MIGRATION TO THE CCI
For 16- and 32-bit compilers, change any occurrence of the aligned attribute, as in
the following example:
char __attribute__((aligned(4)))mode;
to __align, i.e., __align(4) char mode;
2.5.8.4 CAVEATS
This feature is not yet implemented on XC8.
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 35
2.5.9 EEPROM Objects
The __eeprom quali fier may be us ed to indi cate that va riables sh ould be po sitioned in
EEPROM.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this qualifier.
Some devices may not implement EEPROM. Use of this qualifier for such devices will
generate a warning. Stack-based (auto and parameter) variables cannot use the
__eeprom specifier.
2.5.9.1 EXAMPLE
The following shows a variable qualified using __eeprom.
__eeprom int serialNos[4];
2.5.9.2 DIFFERENCES
The 8-bit compilers have used the qualifier , eeprom, to indicate this meaning for some
devices.
The 16-bit compilers have used the space attribute to allocate variables to the memory
space used for EEPROM.
2.5.9.3 MIGRATION TO THE CCI
For 8-bit compilers, change any occurrence of the eeprom qualifier , as in the following
example:
eeprom char title[20];
to __eeprom, i.e., __eeprom char title[20];
For 16-bit compilers, change any occurrence of the eedata space attribute, as in the
following
int mainSw __attribute__ ((space(eedata)));
to
int __eeprom mainSw;
2.5.9.4 CAVEATS
XC8 does not implement the __eeprom qualifiers for any PIC18 devices; this qualifier
will work as expected for other 8-bit devices.
2.5.10 Interrupt Functions
The __interrupt(type) specifier may be used to indicate that a function is to act
as an interrupt service routine. The type is a comma-separated list of keywords that
indicate information about the interrupt function.
The current interrupt types are:
<empty>
Implement the default interrupt function
low_priority
The interr upt functio n corresponds to the low priori ty interrupt sou rce (XC8 – PIC18
only)
high_priority
The interrupt function corresponds to the high priority interrupt source (XC8)
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save(symbol-list)
Save on entry and restore on exit the listed symbols (XC16)
irq(irqid)
Specify the interrupt vector associated with this interrupt (XC16)
altirq(altirqid)
Specify the alternate interrupt vector associated with this interrupt (XC16)
preprologue(asm)
Specify assembly code to be executed before any compiler-generated interrupt code
(XC16)
shadow
Allow the ISR to utilise the shadow registers for context switching (XC16)
auto_psv
The ISR will set the PSVPAG register and restore it on exit (XC16)
no_auto_psv
The ISR will not set the PSVPAG register (XC16)
Use the native keywords discussed in the Differences section to look up information on
the semantics of this specifier.
Some devices may not implement interrupts. Use of this qualifier for such devices will
generate a warning. If the argument to the __interrupt specifier does not make
sense for the target device, a warning or error will be issued by the compiler.
2.5.10.1 EXAMPLE
The following shows a function qualified using __interrupt.
__interrupt(low_priority) void getData(void) {
if (TMR0IE && TMR0IF) {
TMR0IF=0;
++tick_count;
}
}
2.5.10.2 DIFFERENCES
The 8-bit compilers have used the interrupt and low_priority qualifiers to indi-
cate this meaning for some devices. Interrupt routines were by default high priority.
The 16- and 32-bit compilers have used the interrupt attribute to define interrupt
functions.
2.5.10.3 MIGRATION TO THE CCI
For 8-bit compilers, change any occurrence of the interrupt qualifier, as in the
following examples:
void interrupt myIsr(void)
void interrupt low_priority myLoIsr(void)
to the following, respectively
void __interrupt(high_priority) myIsr(void)
void __interrupt(low_priority) myLoIsr(void)
For 16-bit compilers, change any occurrence of the interrupt attribute, as in the fol-
lowing example:
void __attribute__((interrupt,auto_psv,(irq(52)))) myIsr(void);
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 37
to
void __interrupt(auto_psv,(irq(52)))) myIsr(void);
For 32-bit compilers, the __interrupt() keyword takes two parameters, the vector
number and the (optional) IPL value. Change code which uses the interrupt attri-
bute, similar to these examples:
void __attribute__((vector(0), interrupt(IPL7AUTO), nomips16))
myisr0_7A(void) {}
void __attribute__((vector(1), interrupt(IPL6SRS), nomips16))
myisr1_6SRS(void) {}
/* Determine IPL and context-saving mode at runtime */
void __attribute__((vector(2), interrupt(), nomips16))
myisr2_RUNTIME(void) {}
to
void __interrupt(0,IPL7AUTO) myisr0_7A(void) {}
void __interrupt(1,IPL6SRS) myisr1_6SRS(void) {}
/* Determine IPL and context-saving mode at runtime */
void __interrupt(2) myisr2_RUNTIME(void) {}
2.5.10.4 CAVEATS
None.
2.5.11 Packing Objects
The __pack specifier may be used to indicate that structures should not use memory
gaps to align structure members, or that individual structure members should not be
aligned.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this specifier.
Some compilers may not pad structures with alignment gaps for some devices and use
of this specifier for such devices will be ignored.
2.5.11.1 EXAMPLE
The following shows a structure qualified using __pack as well as a structure where
one member has been explicitly packed.
__pack struct DATAPOINT {
unsigned char type;
int value;
} x-point;
struct LINETYPE {
unsigned char type;
__pack int start;
long total;
} line;
2.5.11.2 DIFFERENCES
The __pack specifier is a new CCI specifier available with XC8. This specifier has no
apparent effect since the device memory is byte addressable for all data objects.
The 16- and 32-bit compilers have used the packed attr ib ute to indi cate that a str uc-
ture member was not aligned with a memory gap.
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2.5.11.3 MIGRATION TO THE CCI
No migration is required for XC8.
For 16- and 32-bit compilers, change any occurrence of the packed attribute, as in the
following example:
struct DOT
{char a;
int x[2] __attribute__ ((packed));
};
to:
struct DOT
{char a;
__pack int x[2];
};
Alternatively, you may pack the entire structure, if required.
2.5.11.4 CAVEATS
None.
2.5.12 Indicating Antiquated Objects
The __deprecate specifier may be used to indicate that an object has limited longev-
ity and should not be used in new designs. It is commonly used by the compiler vendor
to indicate that compiler extensions or features may become obsolete, or that better
features have been developed and which should be used in preference.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this specifier.
2.5.12.1 EXAMPLE
The following shows a function which uses the __deprecate keyword.
void __deprecate getValue(int mode)
{
//...
}
2.5.12.2 DIFFERENCES
No deprecate feature was implemented on 8-bit compilers.
The 16- and 32-bit compilers have used the deprecated attribute (note different spell-
ing) to indicate that objects should be avoided if possible.
2.5.12.3 MIGRATION TO THE CCI
For 16- and 32-bit compilers, change any occurrence of the deprecated attribute, as
in the following example:
int __attribute__(deprecated) intMask;
to:
int __deprecate intMask;
2.5.12.4 CAVEATS
None.
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 39
2.5.13 Assigning Objects to Sections
The __section() specifier may be used to indicate that an object should be located
in the named section (or psect, using the XC8 terminology). This is typically used when
the object has special and unique linking requirements which cannot be addressed by
existing compiler features.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this specifier.
2.5.13.1 EXAMPLE
The following shows a variable which uses the __section keyword.
int __section("comSec") commonFlag;
2.5.13.2 DIFFERENCES
The 8-bit compilers have used the #pragma psect directive to redirect objects to a
new section, or psect. The operation of the __section() specifier is different to this
pragma in several ways, described below.
Unlike with the pragma, the new psect created with __section() does not inherit the
flags of the psect in which the object would normally have been allocated. This means
that the new psect can be linked in any memory area, including any data bank. The
compiler will also make no assumptions about the location of the object in the new sec-
tion. Objects redirected to new psects using the pragma must always be linked in the
same memory area, albeit at any address in that area.
The __section() specifier allows objects that are initialized to be placed in a different
psect. Initialization of the object will still be performed even in the new psect. This will
require the automatic allocation of an additional psect (whose name will be the same
as the new psect prefixed with the letter i), which will contain the initial values. The
pragma cannot be used with objects that are initialized.
Objects allocated a different psect with __section() will be cleared by the runtime
startup code, unlike objects which use t he pragma.
Y ou must reserve memory , and locate via a linker option, for any new psect created with
a __section() specifier in the current XC8 compiler implementation.
The 16- and 32-bit compilers have used the section attribute to indicate a different
destination section name. The __section() specifier works in a similar way to the
attribute.
2.5.13.3 MIGRATION TO THE CCI
For XC8, change any occurrence of the #pragma psect directive, su ch as
#pragma psect text%%u=myText
int getMode(int target) {
//...
}
to the __section() specifier, as in
int __section ("myText") getMode(int target) {
//...
}
For 16- and 32-bit compilers, change any occurrence of the section attribute, as in
the following example:
int __attribute__((section("myVars"))) intMask;
to:
int __section("myVars") intMask;
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2.5.13.4 CAVEATS
With XC8, the __section() specifier cannot be used with any interrupt function.
2.5.14 Specifying Configuration Bits
The #pragma config directive may be used to program the configuration bits for a
device. The pragma has the form:
#pragma config setting = state|value
#pragma config register = value
where setting is a configuration setting descriptor (e.g., WDT), state is a descriptive
value (e.g., ON) and value is a numerical value. The register token may represent a
whole config ur ati on word reg ister, e.g., CONFIG1L.
Use the native keywords discussed in the Differences section to look up information on
the semantics of this directive.
2.5.14.1 EXAMPLE
The following shows configuration bits being specified using this pragma.
#pragma config WDT=ON, WDTPS = 0x1A
2.5.14.2 DIFFERENCES
The 8-bit compilers have used the __CONFIG() macro for some targets that did not
already have support for the #pragma config.
The 16-bit compilers have used a number of macros to specify the configuration set-
tings.
The 32-bit compilers supported the use of #pragma config.
2.5.14.3 MIGRATION TO THE CCI
For the 8-bit compilers, change any occurrence of the __CONFIG() macro, such as
__CONFIG(WDTEN & XT & DPROT)
to the #pragma config directive, as in
#pragma config WDTE=ON, FOSC=XT, CPD=ON
No migration is required if the #pragma config was already used.
For the 16-bit compilers, change any occurrence of the _FOSC() or _FBORPOR()
macros attribute, as in the following example:
_FOSC(CSW_FSCM_ON & EC_PLL16);
to:
#pragma config FCKSMEM = CSW_ON_FSCM_ON, FPR = ECIO_PLL16
No migration is required for 32-bit code.
2.5.14.4 CAVEATS
None.
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 41
2.5.15 Manifest Macros
The CCI defines the general form for macros that manifest the compiler and target
device characteristics. These macros can be used to conditionally compile alternate
source code based on the compiler or the target device.
The macros and macro families are details in Table 2-1.
2.5.15.1 EXAMPLE
The following shows code which is conditionally compiled dependent on the device
having EEPROM memory.
#ifdef __XC16__
void __interrupt(__auto_psv__) myIsr(void)
#else
void __interrupt(low_priority) myIsr(void)
#endif
2.5.15.2 DIFFERENCES
Some of these CCI macros are new (for example __CCI__), and others have different
names to previous symbols with identical meaning (for example __18F452 is now
__18F452__).
2.5.15.3 MIGRATION TO THE CCI
Any code which uses compiler-defined macros will need review. Old macros will con-
tinue to work as expected, but they are not compliant with the CCI.
2.5.15.4 CAVEATS
None.
TABLE 2-1: MANIFEST MACROS DEFINED BY THE CCI
Name Meaning if defined Example
__XC__ Compiled with an MPLAB XC compiler __XC__
__CCI__ Compiler is CCI compliant and CCI enforce-
ment is enabled __CCI__
__XC##__ The spe cific XC co mp iler u sed (## c an be 8,
16 or 32)__XC8__
__DEVICEFAMILY__ The family of the selected target device __dsPIC30F__
__DEVICENAME__ The selected target device name __18F452__
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2.5.16 In-line Assembly
The asm() statement may be used to insert assembly code in-line with C code. The
argument is a C string literal which represents a single assembly instruction. Obviously ,
the instructions contained in the argument are device specific.
Use the native keywords discussed in the Differences section to look up information on
the semant ics of this statement.
2.5.16.1 EXAMPLE
The following shows a MOVLW instruction being inserted in-line.
asm("MOVLW _foobar");
2.5.16.2 DIFFERENCES
The 8-bit compilers have used either the asm() or #asm ... #endasm constructs to
insert in-line assembly code.
This is the same syntax used by the 16- and 32-bit compilers.
2.5.16.3 MIGRATION TO THE CCI
For 8-bit compilers change any instance of #asm ... #endasm so that each instruction
in this #asm block is placed in its own asm() statement, for example:
#asm
MOVLW 20
MOVWF _i
CLRF Ii+1
#endasm
to
asm("MOVLW20");
asm("MOVWF _i");
asm("CLRFIi+1");
No migration is required for the 16- or 32-bit compilers.
2.5.16.4 CAVEATS
None.
Common C Interface
2012 Microchip Technology Inc. DS51686E-page 43
2.6 COMPILER FE ATURES
The following items detail compiler options and features that are not directly associated
with source code that
2.6.1 Enabling the CCI
It is assumed you are using the MPLAB X IDE to build projects that use the CCI. The
widget in the MPLAB X IDE Project Properties to enable CCI conformance is Use CCI
Syntax in the Compiler category. A widget with the same name is available in MPLAB
IDE v8 under the Compiler tab.
If you are not using this IDE, then the command-line options are --CCI for XC8 or
-mcci for XC16/32.
2.6.1.1 DIFFERENCES
This option has never been implemented previously.
2.6.1.2 MIGRATION TO THE CCI
Enable the option.
2.6.1.3 CAVEATS
None.
MPLAB® XC32 C/C++ Compiler User’s Guide
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NOTES:
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 45
Chapter 3. Compiler Command Line Driver
3.1 INTRODUCTION
The command line driver (xc32-gcc or xc32-g++) is the application that can be
invoked to perform all aspects of compilation, including C/C++ code generation,
assembly and link steps. Even if you use an IDE to assist with compilation, the IDE will
ultimately call xc32-gcc for C projects or xc32-g++ for C++ projects.
Although the internal compiler applications can be called explicitly from the command
line, using the xc32-gcc or xc32-g++ driver is the recommended way to use the
compiler as it hides the complexity of all the internal applications used and provides a
consistent interface for all compilation steps.
This chapter describes the steps the driver takes during compilation, files that the driver
can accept and produce, as well as the command line options that control the com-
piler’s operation. It also shows the relationship between these command line options
and the controls in the MPLAB IDE Build Options dialog.
Topics concerning the command line use of the driver are discussed below.
• Invoking the Compiler
• The C Compilation Sequence
• The C++ Compilation Sequence
• Runtime Files
• Start-up and Initialization
• Compiler Output
• Compiler Messages
• Driver Option Descriptions
3.2 INVOKING THE COMPILER
The compiler is invoked and runs on the command line as specified in the next section.
Additionally, environmental variables and input files used by the compiler are discussed
in the following sections.
3.2.1 Driver Command Line Format
The compilation driver program (xc32-gcc) compiles, assembles and links C and
assembly language modules and library archives. The xc32-g++ driver must be used
when the module source is written in C++. Most of the compiler command line options
are common to all implementations of the GCC toolset (MPLAB XC16 uses the GCC
toolset; XC8 does not). A few are specific to the compiler.
The basic form of the compiler command line is:
xc32-gcc [options] files
xc32-g++ [options] files
For example, to compile, assemble and link the C source file hello.c, creatin g the
absolute executable hello.elf,execute this command:
xc32-gcc -o hello.elf hello.c
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 46 2012 Microchip Technology Inc.
Or, to compile, assemble and link the C++ source file hello.cpp, creating the
absolute executable hello.elf, execute:
xc32-g++ -o hello.elf hello.cpp
The available options are described in Section 3.9 “Driver Option Descriptions”. It
is conventional to supply options (identifi ed by a leading dash “-” before the
filenames), although this is not mandatory.
The files may be any mixture of C/C++ and assembler source files, relocatable
object files (.o) or archive files. The order of the files is important. It may affect the
order in which code or data appears in memory or the search order for symbols. T ypi-
cally archive files are specified after source files. The file types are described in
Section 3.2.2 “Input File Types”.
Libraries is a list of user-defined object code library files that will be searched by the
linker , in addition to the standard C libraries. The order of these files will determine the
order in which they are searched. They are typically placed after the source filenames,
but this is not mandatory.
It is assumed in this manual that the compiler applications are either in the console’s
search path, the appropriate environment variables have been specified, or the full path
is specified when executing any application.
Environment Variables
The variables in this section are optional, but, if defined, they will be used by the
compiler. The compiler driver, or other subprogram, may choose to determine an
appropriate value for some of the following environment variables if they are not set.
The driver, or other subprogram, takes advantage of internal knowledge about the
installation of the compiler. As long as the installation structure remains intact, with all
subdirectories and executables remaining in the same relative position, the driver or
subprogram will be able to determine a usable value. The “XC32” variables should be
used for new projects; however , the “PIC32” variables may be used for legacy projects.
Note: Command line options and file name extensions are case sensitive.
TABLE 3-1: COMPILER-RELATED ENVIRONMENTAL VARIABLES
Option Definition
XC32_C_INCLUDE_PATH
PIC32_C_INCLUDE_PATH This varia bl e’s value is a semic ol on- separated li st of direc to ries ,
much like PATH. When the compiler searches for header files, it
tries the directories listed in the variable, after the directories
specified with -I but before the standard header file directories.
If the environment variable is undefined, the preprocessor
choos es an a ppropriate value based o n the st andard inst allation .
By default, the following directories are searched for include
files:
<install-path>\pic32mx\include
XC32_COMPILER_PATH
PIC32_COMPILER_PATH The v alue of PIC32_COMPILER_PATH is a semicolon-separated
list of directories, much like PATH. The compiler tries the directo-
ries thus specified when searchi ng for subprog rams, if it can’t
find the subprograms using PIC32_EXEC_PREFIX.
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2012 Microchip Technology Inc. DS51686E-page 47
XC32_EXEC_PREFIX
PIC32_EXEC_PREFIX If PIC32_EXEC_PREFIX is set, it specifies a prefix to use in the
names of subprograms executed by the compiler. No directory
delimi ter is added when this prefix i s c om bin ed w it h the nam e of
a subp rogram, but you can spe cify a p refix that ends w ith a sl ash
if you w is h. If th e co mp il er cannot find the subprogram us ing the
spec ified prefix, it tries looking in your PATH environment
variable.
If the PIC32_EXEC_PREFIX environment variable is unset or
set to an empty value, the compiler driver chooses an ap propri-
ate value based on the standard installation. If the installation
has not been modified, this will result in the driver being able to
locate the required sub programs.
Other prefixe s specified with the -B command line option take
precedence over the user- or driver-defined value of
PIC32_EXEC_PREFIX.
Under normal circumstances it is best to leave this value unde-
fined and let the driver locate subprograms itself.
XC32_LIBRARY_PATH
PIC32_LIBRARY_PATH This varia bl e’s value is a semic ol on- separated li st of direc to ries ,
much lik e PATH. This va riable s pecifies a list of direc tories to be
passed to the linker. The driver’s default evaluation of this vari-
able is:
<install-path>\lib; <install-path>\pic32mx\lib.
TMPDIR If TMPDIR is set, it specifies the directory to use for temporary
file s. The compi ler uses tempora ry files to hold the outp ut of one
stag e of compilati on that i s to be us ed as in put to the n ext st age:
for example, the output of the preprocessor, which is the input to
the compiler proper.
TABLE 3-1: COMPILER-RELATED ENVIRONMENTAL VARIABLES
Option Definition
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DS51686E-page 48 2012 Microchip Technology Inc.
3.2.2 Input File Types
The compilation driver recognizes the following file extensions, which are case
sensitive.
There are no compiler restrictions imposed on the names of source files, but be aware
of case, name-length and other restrictions imposed by your operating system. If you
are using an IDE, avoid assembly source files whose base name is the same as the
base name of any project in which the file is used. This may result in the source file
being overwritten by a temporary file during the build process.
The terms “source file” and “module” are often used when talking about computer
programs. They are often used interchangeably, but they refer to the source code at
different points in the compilation sequence.
A source file is a file that contains all or part of a program. They may contain C/C++
code, as well as preprocessor directives and commands. Source files are initially
passed to the preprocessor by the driver.
A module is the output of the preprocessor, for a given source file, after inclusion of any
header files (or other source files) which are specified by #include preprocessor
directives. All preprocessor directives and commands (with the possible exception of
some commands for debugging) have been removed from these files. These modules
are then passed to the remainder of the compiler applications. Thus, a module may be
the amalgamation of several source and header files. A module is also often referred
to as a translation unit. These terms can also be applied to assembly files, as they too
can include other header and source files.
TABLE 3-2: FILE NAMES
Extensions Definition
file.c A C so urce file that must be preprocessed.
file.cpp A C++ so urce file t hat mu st be preprocessed.
file.h A header file (not to be compiled or linked).
file.i A C source file that has already been pre-processed.
file.o An object file.
file.ii A C++ source file that has already been pre-processed.
file.s An assemb ly language sourc e file.
file.S An assemb ly language sourc e file that must be preprocessed .
other A file to be passed to the linker.
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2012 Microchip Technology Inc. DS51686E-page 49
3.3 THE C COMPILATION SEQUENCE
3.3.1 Single-step C Compilation
A single command-line instruction can be used to compile one file or multiple files.
3.3.1.1 COMPILING A SINGLE C FILE
This section demonstrates how to compile and link a single file. For the purpose of this
discussion, it is assumed the compiler's <install-dir>/bin directory has been
added to your PATH variable. The following are other directories of note:
•<install-dir>/pic32mx/include the directory for standard C header files.
•<install-dir>/pic32mx/include/proc the directory for PIC32MX
device-specific header files.
•<install-dir>/pic32mx/lib the directory structure for standard libraries
and start-up files.
•<install-dir>/pic32mx/include/peripheral the directory for PIC32MX
peripheral library include files.
•<install-dir>/pic32mx/lib/proc the directory for device-specific linker
script fragments, register definition files and configuration data may be found.
The following is a simple C program that adds two numbers. Create the following
program with any text editor and save it as ex1.c.
#include <xc.h>
#include <plib.h>
// Device-Specific Configuration-Bit settings
// SYSCLK = 80 MHz (8MHz Crystal/ FPLLIDIV * FPLLMUL / FPLLODIV)
// PBCLK = 40 MHz
// Primary Osc w/PLL (XT+,HS+,EC+PLL)
// WDT OFF
// Other options are don't care
//
#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1,
FWDTEN = OFF
#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_8
unsigned int x, y, z;
unsigned int
add(unsigned int a, unsigned int b)
{
return(a+b);
}
int
main(void)
{
/* Configure the target for maximum performance at 80 MHz. */
SYSTEMConfigPerformance(80000000UL);
x = 2;
y = 5;
z = add(x,y);
return 0;
}
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The first line of the program includes the header file xc.h, which provides definitions
for all Special Function Registers (SFRs) on that part.
Compile the program by typing the following at the prompt:
xc32-gcc –mprocessor=32MX795F512L -o ex1.out ex1.c
The command line option -o ex1.out names the output executable file (if the -o
option is not specified, then the output file is named a.out). The executable file may
be loaded into MPLAB IDE.
If a hex file is required, for example, to load into a device programmer, then use the
followin g command:
xc32-bin2hex ex1.out
This creates an Intel hex file named ex1.hex.
3.3.1.2 COMPILING MULTIPLE C FILES
This section demonstrates how to compile and link multiple files in a single step. Move
the Add() function into a file called add.c to demonstrate the use of multiple files in
an application. That is:
File 1
/* ex1.c */
#include <xc.h>
#include <plib.h>
// Device-Specific Configuration-Bit settings
// SYSCLK = 80 MHz (8MHz Crystal/ FPLLIDIV * FPLLMUL / FPLLODIV)
// PBCLK = 40 MHz
// Primary Osc w/PLL (XT+,HS+,EC+PLL)
// WDT OFF
// Other options are don't care
//
#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1,
FWDTEN = OFF
#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_8
int main(void);
unsigned int add(unsigned int a, unsigned int b);
unsigned int x, y, z;
int main(void)
{
/* Configure the target for maximum performance at 80 MHz. */
SYSTEMConfigPerformance(80000000UL);
x = 2;
y = 5;
z = Add(x,y);
return 0;
}
File 2
/* add.c */
#include <xc.h>
unsigned int
add(unsigned int a, unsigned int b)
{
return(a+b);
}
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2012 Microchip Technology Inc. DS51686E-page 51
Compile both files by typing the following at the prompt:
xc32-gcc -mprocessor=32MX795F512L -o ex1.out ex1.c add.c
This command compiles the modules ex1.c and add.c. The compiled modules are
linked with the compiler libraries and the executable file ex1.out is created.
3.3.2 Multi-step C Compilation
Make utilities and IDEs, such as MPLAB IDE, allow for an incremental build of projects
that contain multiple source files. When building a project, they take note of which
source files have changed since the last build and use this information to speed up
compilation.
For example, if compiling two source files, but only one has changed since the last
build, the intermediate file corresponding to the unchanged source file need not be
regenerated.
If the compiler is being invoked using a make utility, the make file will need to be con-
figured to use the int ermed iate files (.o files) and the options used to generate the
intermediate files (-c, see Section 3.9.2 “Options for Controlling the Kind of Out-
put”). Make utilities typically call the compiler multiple times: once for each source file
to generate an intermediate file, and once to perform the second stage compilation.
For example, the files ex1.c and add.c are to be compiled using a make utility. The
command lines that the make utility should use to compile these files might be
something like:
xc32-gcc -mprocessor=32MX795F512L -c ex1.c
xc32-gcc -mprocessor=32MX795F512L -c add.c
xc32-gcc -mprocessor=32MX795F512L -o ex1.out ex1.o add.o
3.4 THE C++ COMPILATION SEQUENCE
3.4.1 Single-step C++ Compilation
A single command-line instruction can be used to compile one file or multiple files.
3.4.1.1 COMPILING A SINGLE C++ FILE
This section demonstrates how to compile and link a single file. For the purpose of this
discussion, it is assumed the compiler's <install-dir>/bin directory has been
added to your PATH variable. The following are other directories of note:
•<install-dir>/pic32mx/include/cpp the directory for standard C++
header files.
•<install-dir>/pic32mx/include/proc the directory for
PIC32M Xd evi ce- sp ec ifi c head er files .
•<install-dir>/pic32mx/lib the directory structure for standard libraries
and start-up files.
•<install-dir>/pic32mx/include/peripheral the directory for PIC32
peripheral library include files.
•<install-dir>/pic32mx/lib/proc the directory for device-specific linker
script fragments, register definition files, and configuration data may be found.
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The following is a simple C++ program. Create the following program with any
plain-text editor and save it as ex2.cpp.
/* ex2.cpp */
#include <xc.h> // __XC_UART
#include <plib.h> // SYSTEMConfigPerformance()
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
using namespace std;
// Device-Specific Configuration-bit settings
#pragma config FPLLMUL=MUL_20, FPLLIDIV=DIV_2, FPLLODIV=DIV_1,
FWDTEN=OFF
#pragma config POSCMOD=HS, FNOSC=PRIPLL, FPBDIV=DIV_8
template <class T>
inline void print_elements (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << ' ';
}
std::cout << std::endl;
}
template <class T>
inline void insert_elements (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i)
{
coll.insert(coll.end(),i);
}
}
int main(void) {
// Configure the target for max performance at 80 MHz.
SYSTEMConfigPerformance (80000000UL);
// Direct stdout to UART 1 for use with the simulator
__XC_UART = 1;
deque<int> coll;
insert_elements(coll,1,9);
insert_elements(coll,1,9);
print_elements(coll, "on entry: ");
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2012 Microchip Technology Inc. DS51686E-page 53
//sort elements
sort (coll.begin(), coll.end());
print_elements(coll, "sorted: ");
//sorted reverse
sort (coll.begin(), coll.end(), greater<int>());
print_elements(coll, "sorted >: ");
while(1);
}
The first line of the program includes the header file xc.h, which provides definitions
for all Special Function Registers (SFRs) on the target device. The second file of the
program includes the header file plib.h, which provides the necessary prototypes for
the peripheral library.
Compile the program by typing the following at a command prompt.
xc32-g++ -mprocessor=32MX795F512L -Wl,--defsym=_min_heap_size=0xF000
-o ex2.elf ex2.cpp
The option -o ex2.elf names the output executable file. This elf file may be loaded
into MPLAB X IDE.
If a hex file is required, for example, to load into a device programmer, then use the
following command
xc32-bin2hex ex2.elf
This creates an Intel hex file named ex2.hex.
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3.4.2 Compiling Multiple C and C++ files
This section demonstrates how to compile and link multiple C and C++ files in a single
step.
File 1
/* main.cpp */
#include <xc.h> // __XC_UART
#include <plib.h> // SYSTEMConfigPerformance()
#include <iostream>
using namespace std;
// Device-Specific Configuration-bit settings
#pragma config FPLLMUL=MUL_20, FPLLIDIV=DIV_2, FPLLODIV=DIV_1,
FWDTEN=OFF
#pragma config POSCMOD=HS, FNOSC=PRIPLL, FPBDIV=DIV_8
// add() must have C linkage
extern "C" {
extern unsigned int add(unsigned int a, unsigned int b);
}
int main(void) {
int myvalue = 6;
// Configure the target for max performance at 80 MHz.
SYSTEMConfigPerformance (80000000UL);
// Direct stdout to UART 1 for use with the simulator
__XC_UART = 1;
std::cout << "original value: " << myvalue << endl;
myvalue = add (myvalue, 3);
std::cout << "new value: " << myvalue << endl;
while(1);
}
File 2
/* ex3.c */
unsigned int
add(unsigned int a, unsigned int b)
{
return(a+b);
}
Compile both files by typing the following at the prompt:
xc32-g++ -mprocessor=32MX795F512L -o ex3.elf main.cpp ex3.c
The command compiles the modules main.cpp and ex3.c. The compiled modules
are linked with the compiler libraries for C++ and the executable file ex3.elf is cre-
ated.
Note: Use the xc32-g++ driver (as opposed to the xc32-gcc driver) in order to link
the project with the C++ support libraries necessary for the C++ source file
in the project.
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3.5 RUNTIME FILES
In addition to the C/C++ and assembly source files specified on the command line,
there are also compiler-generated source files and pre-compiled library files which
might be compiled into the project by the driver. These files contain:
• C/C++ Standard library routines
• Implicitly called arithmetic routines
• User-defined library routines
• The runtime start-up code
3.5. 1 Library F ile s
The names of the C/C++ standard library files appropriate for the selected target
device, and other driver options, are determined by the driver.
The target libraries, called multilibs, are built multiple times with a permuted set of
options. When the compiler driver is called to compile and link an application, the driver
chooses the version of the target library that has been built with the same options.
By default, the 32-bit language tools use the directory
<install-directory>/lib/gcc/ to store the specific libraries and the directory
<install-directory>/<pic32mx>/lib to store the target-specific libraries. Both
of these directory structures contain subdirectories for each of the multilib combinations
specified above. These subdirectories, respectively, are as follows:
1. .
2. ./size
3. ./speed
4. ./mips32
5. ./no-float
6. ./mips32/no-float
7. ./size/mips32
8. ./size/no-float
9. ./size/mips32/no-float
10../speed/mips32
11../speed/no-float
12../speed/mips32/no-float
The target libraries that are distributed with the compiler are built for the following
options:
• Size versus speed (-Os vs. -O3)
• 16-bit versus 32-bit (-mips16 vs. -mno-mips16)
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By default the 32-bit language tools compile for -O0, -mno-mips16, and
-msoft-float. Therefore, the options that we are concerned with are -Os or -O3,
-mips16, and -mno-float. Libraries built with the following command line options
are made available:
1. Default command line options
2. -Os
3. -O3
4. -mips16
5. -mno-float
6. -mips16 -mno-float
7. -Os -mips16
8. -Os -mno-float
9. -Os -mips16 -mno-float
10.-O3 -mips16
11.-O3 -mno-float
12.-O3 -mips16 -mno-float
The following examples provide details on which of the multilibs subdirectories are
chosen.
1. xc32-gcc foo.c
xc32-g++ foo.cpp
For this example, no command line options have been specified (i.e., the default
command line options are being used). In this case, the .subdirectories are
used.
2. xc32-gcc -Os foo.c
xc32-g++ -Os foo.cpp
For this example, the command line option for optimizing for size has been
specifi ed (i.e., -Os is being used). In this case, the ./size subdirectories are
used.
3. xc32-gcc -O2 foo.c
xc32-g++ -O2 foo.cpp
For this example, the command line option for optimizing has been specified;
however, this command line option optimizes for neither size nor space (i.e., -O2
is being used). In this case, the .subdirectories are used.
4. xc32-gcc -Os -mips16 foo.c
xc32-g++ -Os -mips16 foo.cpp
For this example, the command line options for optimizing for size and for
MIPS16 code have been specified (i.e., -Os and -mips16 are being used). In
this ca se, the ./size/mips16 subdi re ctori es are used.
3.5.1.1 STANDARD LIBRARIES
The C/C++ standard libraries contain a standardized collection of functions, such as
string, math and input/output routines. The range of these functions are described in
Chapter 13. “Lib ra ry Routine s” .
These libraries also contain C/C++ routines that are implicitly called by the output code
of the code generator. These are routines that perform tasks such as floating-point
operations and that may not directly correspond to a C/C++ function call in the source
code.
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3.5.1.2 USER-DEFINED LIBRARIES
User-defined libraries may be created and linked in with programs as required. Library
files are more easy to manage and may result in faster compilation times, but must be
compatible with the target device and options for a particular project. Several versions
of a library may need to be created to allow it to be used for different projects.
User-created libraries that should be searched when building a project can be listed on
the command line along with the source files.
As with Standard C/C++ library functions, any functions contained in user-defined
libraries should have a declaration added to a header file. It is common practice to cre-
ate one or more header files that are packaged with the library file. These header files
can then be included into source code when required.
3.5.2 Periphera l Library Functions
Many of the peripherals of the PIC32MX devices are supported by the peripheral library
functions provided with the compiler tools. See the “32-Bit Language Tools Libraries”
(DS51685) for details on the functions provided.
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3.6 START-UP AND INITIALIZATION
For C:
There is only one start-up module, which initializes the C runtime environment.
The source code for this is found in
<install-directory>/pic32-libs/libpi32c/startup/crt0.S and it is
precompiled into the library <install-directory>/pic32mx/lib/crt0.o.
Multilib versions of these modules exist in order to support architectural differences
between device families.
For C++:
Code from five object files link sequentially to create a single initialization routine, which
initializes the C++ runtime environment.
The source code for this is found in
<install-directory>/pic32-libs/libpic32/startup.
The PIC32 precompiled startup objects are located in
<install-directory>/pic32mx/lib/ and the filenames are cpprt0.o,
crti.o, and crtn.o.
The GCC precompiled startup objects are located in
<install-directory>/lib/gcc/pic32mx/<gcc-version>/ and the file-
names are crtbegin.o and crtend.o. Multilib variations of these modules exist in
order to support architectural differences between device families and also optimization
settings.
For more information about what the code in these start-up modules actual does, see
Section 12.3 “Runtime Start-up Code”.
3.7 COMPILER OUTPUT
There are many files created by the compiler during the compilation. A large number of
these are intermediate files and some are deleted after compilation is complete, but
many remain and are used for programming the device, or for debugging purposes.
3.7.1 Output Files
The compilation driver can produce output files with the following extensions, which are
case-sensitive.
The names of many output files use the same base name as the source file from which
they were derived. For example the sourc e file input.c will create an object file called
input.o.
The main output file is an ELF file called a.out, unless you override that name using
the -o option.
TABLE 3-3: FILE NAMES
Extensions Definition
file.hex Executable file
file.elf ELF debug file
file.o Object file (intermediate file)
file.s Assembly code file (intermediate file)
file.i Prep rocessed C fil e (int erme diate file)
file.ii Preprocessed C++ file (intermediate file)
file.map Map file
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If you are using an IDE, such as MPLAB IDE, to specify options to the compiler, there
is typically a project file that is created for each application. The name of this project is
used as the base name for project-wide output files, unless otherwise specified by the
user. However check the manual for the IDE you are using for more details.
The compiler is able to directly produce a number of the output file formats which are
used by Microc hi p deve lop ment tools.
The default behavior of xc32-gcc and xc32-g++ is to produce an ELF output. To make
changes to the file’s output or the file names, see Section 3.9 “Driver Option
Descriptions”.
3.7.2 Diagnostic Files
T wo valuable files produced by the compiler are the assembly list file, produced by the
assembler, and the map file, produced by the linker.
The assembly list file contains the mapping between the original source code and the
generated assembly code. It is useful for information such as how C source was
encoded, or how assembly source may have been optimized. It is essential when con-
firming if compiler-produced code that accesses objects is atomic, and shows the
region in which all objects and code are placed.
The option to create a listing file in the assembler is -a (or -Wa,-a if passed to the
driver). There are many variants to this option, which may be found in the “MPLAB
Assembler , Linker and Utilities for PIC32 MCUs User’s Guide”(DS51833). To pass the
option from the compi ler, see Section 3.9.9 “Options for Assembling”.
There is one list file produced for each build. There is one assembler listing file for each
translation unit. This is a pre-link assembler listing so it will not show final addresses.
Thus, if you require a list file for each source file, these files must be compiled sepa-
rately, see Section 3.3.2 “Multi-step C Compilation”. This is the case if you build
using MPLAB IDE. Each list file will be assigned the module name and extension .lst.
The map fi le shows in formatio n relati ng to wh ere obje cts were pos itioned in memory. It
is useful for confirming that user-defined linker options were correctly processed, and
for determining the exact placement of objects and functions.
The option to create a map file in the linker is -Map file (or -Wl,-Map=file if
passed to the driver), which may be found in the “MPLAB Assembler, Linker and Utili-
ties for PIC32 Use r’s Guide”. To pass the option from the compiler, see
Section 3.9.10 “Options for Linking”.
There is one map file produced when you build a project, assuming the linker was
executed and ran to completion.
Note: Throughout this manual, the term project name will refer to the name of the
project created in the IDE.
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 60 2012 Microchip Technology Inc.
3.8 COMPILER MESSAGES
There are three types of messages. These are described below along with the
compiler’s behavior when encountering a message of each type.
Warning Messages indicate source code or some other situation that can be
compile d, but is un usual and ma y lead to a r untime failure of the c ode. The
code or situation that triggered the warning should be investigated; however,
compilation of the current module will continue, as will compilation of any
remaini ng mod ules.
Error Me ssages indicate source code that is illegal or that compilation of this code
cannot take place. Compilation will be attempted for the remaining source
code in the curr ent mod ule, but no addit ional m odu les will be comp iled an d
the compilation process will then conclude.
Fatal Er ror Message s indicate a si tuatio n that canno t a llow com pilati on to procee d
and which requires the compilation process to stop immediately.
For information on options that control compiler output of errors, warnings or
comments, see Section 3.9.4 “Options for Controlling the C++ Dialect”.
3.9 DRIVER OPTION DESCRIPTIONS
All single letter options are identified by a leading dash character, “-”, e.g. -c. Some
single letter options specify an additional data field which follows the option name
immediately and without any whitespace, e.g. -Idir. Options are case sensitive, so
-c is a different option to -C.
The compiler has many options for controlling compilation, all of which are case
sensitive.
• Options Specific to PIC32MX Devices
• Options for Controlling the Kind of Output
• Options for Controlling the C Dialect
• Options for Controlling the C++ Dialect
• Options for Debugging
• Options for Controlling Optimization
• Options for Controlling the Preprocessor
• Options for Assembling
• Options for Linking
• Options for Directory Search
• Options for Code Generation Conventions
Compiler Command Line Driver
2012 Microchip Technology Inc. DS51686E-page 61
3.9.1 Options S pecific to PIC32MX Devices
These options are specific to the device, not the compiler.
TABLE 3-4: PIC32MX DEVICE-SPECIFIC OPTIONS
Option Definition
-mprocessor Selects the device for which to compile.
(e.g., -mprocessor=32MX360F512L)
-mips16
-mno-mips16 Generate (do not generate) MIPS16 code.
-mno-float Do not use software floating-point libraries.
-G num Put global and static items less than or equal to num
bytes into the small data or bss section instead of the
normal data or bss section. This allows the data to be
accessed using a single instruction.
All mo dules s hould be compil ed with th e same -G num
value.
-membedded-data
-mno-embedded-data Allocate variables to the read-only data section first if
possi ble, the n ne xt in th e sma ll dat a se ction i f po ssibl e,
otherwise in data. This gives slightly slower cod e than
the default, but reduces the amount of RAM required
when executing, and thus may be preferred for some
embedded systems.
-muninit-const-in-rodata
-mno-uninit-const-in-rodata Put uninitialized const variables in the read-only data
section. This option is only meaningful in conjunction
with -membedded-data.
-mcheck-zero-division
-mno-check-zero-division Trap (do not trap) on integer division by zero. The
default is -mcheck-zero-division.
-mmemcpy
-mno-memcpy Forc e (do not force) the use of memcpy() for non-tri vial
bloc k mov es. The default is -mno-memcpy, which
allows GCC to inline most constant-sized copies.
-mlong-calls
-mno-long-calls Disable (do not disable) use of the jal instruction.
Calling functions using jal is more efficient but
requires the caller and callee to be in the same 256
megabyte segment.
This option has no effect on abicalls code. The default
is -mno-long-calls.
-mno-peripheral-libs -mno-peripheral-libs is now the default .
-mperipheral-libs is optional. By default, the
periphe ral libraries are linke d spec ifi ed via the
device-specific linker script. Do no t use the standard
periphe ral lib rari es when linki ng .
-msmart-io=[0|1|2] This option atte mpt s to st atic ally analy ze form at strin gs
passed to printf, scanf and the ‘f’ and ‘ v’ variations
of these functions. Uses of nonfloating-point format
arguments will be converted to use an integer-only
variati on of the libr ary fun cti on. For many application s,
this feature can reduce program-memory usage.
-msmart-io=0 disables this option, while
-msmart-io=2 causes the compiler to be optimistic
and convert function calls with variable or unknown
format arguments. -msmart-io=1 is the default and
will convert only when the compiler can prove that
floating-point support is not required.
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 62 2012 Microchip Technology Inc.
3.9.2 Options for Controlling the Kind of Output
The following options control the kind of output produced by the compiler.
-mappio-debug Enable the APPIN/APPOUT debugging library
functio ns for the MPLAB® ICD 3 d ebugge r and M PLAB
REAL I CE™ in-circ uit emul ator . T his feat ure allows you
to use the DBPRINTF and related functions and
macros as desc rib ed in the “32-b it Lan gua ge Tool
Libraries” document (DS51685). Enable this option
only when using a target PIC32 device that supports
the APPIN/APPOUT feature.
-mcci Enables the Microchip Common C Interface
compilation mode.
TABLE 3-5: KIND-OF-OUTPUT CONTROL OPTIONS
Option Definition
-c Compile or assemble the source files, but do not link. The default file
extension is .o.
-E Stop after the preprocessing stage (i.e., before running the compiler
proper). The default output file is stdout.
-fexceptions Enable exception handling. You may need to enable this option when
compiling C code that needs to interoperate properly with exception
handlers written in C++.
-o file Place the output in file.
-S Stop after compilation proper (i.e., before invoking the assembler). The
default output file extension is .s.
-v Print the commands executed during each stage of compilation.
-x You can specify the input language explicitly with the -x option:
-x language
S pecify exp licitly the la nguage for the fol lowing input fil es (rather than let ting
the compiler choose a default based on the file name suffix). This option
applies to all following input files until the next -x option. The following
values are supported by the compiler:
c
c++
c-header
cpp-output
assembler
assembler-with-cpp
-x none
Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes. This is the default behavior
but is needed if another -x option has been use d. For exa mp le:
xc32-gcc -x assembler foo.asm bar.asm -x none main.c
mabonga.s
Without the -x none, the compiler assumes all the input files are for the
assembler.
--help Print a description of the command line options.
TABLE 3-4: PIC32MX DEVICE-SPECIFIC OPTIONS (CONTINUED)
Option Definition
Compiler Command Line Driver
2012 Microchip Technology Inc. DS51686E-page 63
3.9.3 Options for Control ling the C Dialect
The following options define the kind of C dialect used by the compiler.
TABLE 3-6: C DIALECT CONTROL OPTIONS
Option Definition
-ansi Support all (and only) ANSI-standard C programs.
-aux-info filename Output to the given filename prototyped declarations for all
functions declared and/or defined in a translation unit,
including those i n he ader files. Th is option is si len tly ignored
in any language other than C. Besides declarations, the file
indicates, in comments, the origin of each declaration
(source file and line), whether the declaration was implicit,
prototyped or unprototyped (I, N fo r new or O for old,
respectively, in the first character after the line number and
the colon), and whether it came from a declaration or a
definition (C or F, respectively, in the following character). In
the case of func tion definitio ns, a K&R-style list of argume nts
followed by their declarations is also provided, inside
comments, after the declaration.
-fcheck-new /
-fno-check-new
(default)
Check that the pointer returned by operator new is non-null.
-fenforce-eh-specs
(default) /
-fno-enforce-eh-specs
Generate/Do not generate code to check for violation of
exception specifications at runtime. The
-fno-enforce-eh-specs option violates the C++
standard, but may be useful for reducing code size in
production builds, much like defining `NDEBUG'. This does
not give user code permission to throw exceptions in
violatio n of the ex cepti on spe cific ations; th e com piler w ill s till
optimize based on the specifications, so throwing an
unexpected exception will result in undefined behavior.
-ffreestanding Assert that compilation takes place in a freestanding
environment. This implies -fno-builtin. A freestanding
environment is one in which the standard library may not
exist, and program start-up may not necessarily be at main.
The most obvious example is an OS kernel. This is
equival ent to -fno-hosted.
-fno-asm Do not reco gnize asm, inline or typeof as a keywo rd, so
that cod e can use th ese words as identifiers. You can use
the keywords __asm__, __inline__ and __typeof__
instead.
-ansi implies -fno-asm.
-fno-builtin
-fno-builtin-function Don’t recognize built-in functions that do not begin with
__builtin_ as prefix.
-fno-exceptions Disable C++ exception handling. This option disables the
generation of extra code needed to propagate exceptions.
-fno-rtti Enable/Disable runtime type-identification features. The
-fno-rtti option disables generation of information about
every class with virtual functions for use by the C++ runtime
type identification features ('dynamic_cast' and 'typeid'). If
you don't use those parts of the language, you can save
some space by using this flag. Note that exception handling
uses the same information, but it will generate it as needed.
The 'dynamic_cast' operator can still be used for casts that
do not re quire run time typ e informa tion, i.e. cast s to void *
or to unambiguous base classes.
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 64 2012 Microchip Technology Inc.
3.9.4 Options for Controlling the C++ Dialect
The following options define the kind of C++ dialect used by the compiler.
-fsigned-char Let the type char be signed, like signed char.
(This is the default.)
-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
These options control whether a bit field is signed or
unsigned, when the declaration does not use either signed
or unsigned. By default, such a bit field is signed, unless
-traditional is used, in which case bit fields are always
unsigned.
-funsigned-char Let the type char be unsigned, like unsigned char.
-fwritable-strings Store strings in the writable data segment and do not make
them unique .
TABLE 3-7: C++ DIALECT CONTROL OPTIONS
Option Definition
-ansi Support all (and only) ANSI-standard C++ programs.
-aux-info filename Output to the given filename prototyped declarations for all
functions declared and/or defined in a translation unit,
includ ing those in h ead er files. Th is option is s ile ntl y i gno red
in any language other than C++. Besides declarations, the
file indicates, in comments, the origin of each declaration
(source file and line), whether the declaration was implicit,
prototyped or unprototyped (I, N for new or O for old,
respect ive ly, in the first character after the lin e num ber and
the colon), and whether it came from a declaration or a
definition (C or F, respectively, in the following character). In
the case of fun ction definitions , a K&R-style li st of argument s
follow ed by their decl ara tio ns is also prov id ed, ins id e
comments, after the declaration.
-ffreestanding Assert that compilation takes place in a freestanding
environment. This implies -fno-builtin. A freestanding
environment is one in which the standard library may not
exist, and program start-up may not necessarily be at main.
The most obvious example is an OS kernel. This is
equivalent to -fno-hosted.
-fno-asm Do no t reco gnize asm, inline or typeof as a k eyword, s o
that code can use these words as identifiers. You can use
the keywords __asm__, __inline__ and __typeof__
instead.
-ansi implies -fno-asm.
-fno-builtin
-fno-builtin-function Don’t recognize built-in functions that do not begin with
__builtin_ as prefix.
-fsigned-char Let the type char be signed, like signed char.
(This is the default.)
-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
These options control whether a bit field is signed or
unsigned, when the declaration does not use either signed
or unsigned. By default, such a bit field is signed, unless
-traditional is used, in which case bit fields are always
unsigned.
-funsigned-char Let the type char be unsigned, like unsigned char.
-fwritable-strings Store strings in the writable data segment and do not make
them unique.
TABLE 3-6: C DIALECT CONTROL OPTIONS (CONTINUED)
Option Definition
Compiler Command Line Driver
2012 Microchip Technology Inc. DS51686E-page 65
3.9.5 Options for Controlling Warnings and Errors
Warnings are diagnostic messages that report constructions that are not inherently
erroneous, but that are risky or suggest there may have been an error.
You can request many specific warnings with options beginning -W; for example,
-Wimplicit, to request warnings on implicit declarations. Each of these specific
warning options also has a negative form beginning -Wno- to turn off warnings; for
example, -Wno-implicit. This manual lists only one of the two forms, whichever is
not the default.
The following options control the amount and kinds of warnings produced by the
compiler.
TABLE 3-8: WARNING AND ERROR OPTIONS IMPLIED BY ALL WARNINGS
Option Definition
-fsyntax-only Check the code for syntax, but don’t do anything beyond that.
-pedantic Issue all the warnings demanded by strict ANSI C. Reject all
programs that use forbidden extensions.
-pedantic-errors Like -pedantic, except that errors are produced rather than
warnings.
-w Inhibit all warning messages.
-Wall This enables all the warnings about constructions that some
users consider questionable, and that are easy to avoid (or
modify to prevent the warning), even in conjunction with macros.
Note th at some wa rning flag s are not i mplied b y -Wall. Some of
them warn about constructions that users generally do not
consid er que stionable, but which occasionally yo u mig ht w is h to
check for; othe rs warn a bout c onstruc tions that ar e nece ssary or
hard to avoid in some cases, and there is no simple way to
modify the code to suppress the warning. Some of them are
enabled by -Wextra but many of them must be enabled
individually.
-Waddress Warn about suspicious uses of memory addresses. These
include using the address of a function in a conditional
expression, such as void func(void); if (func), and
comp arisons against the memo ry address of a string lit eral, such
as if (x == "abc"). Such uses typi cally ind icate a prog rammer
error: the ad dress o f a functi on alway s eval uates to true, so th eir
use in a c on ditional us ual ly in dic ates that the programmer forgot
the parentheses in a function call; and comparisons against
string literals result in unspecified behavior and are not portable
in C, so they usually indicate that the programmer intended to
use strcmp.
-Wchar-subscripts Warn if an array subscript has type char.
-Wcomment Warn whenever a comment-start sequence /* appears in a /*
comment, or whenever a Backslash-Newline appears in a //
comment.
-Wdiv-by-zero Warn about compile-time integer division by zero. To inhibit the
warning messages, use -Wno-div-by-zero. Floating-point
division by zero is not warned about, as it can be a legitimate
way of obtaining infinities and NaNs.
(This is the default.)
-Wformat Check calls to printf and scanf, etc., to make sure that the
arguments supplied have types appropriate to the format string
specified.
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 66 2012 Microchip Technology Inc.
-Wimplicit Equivalent to specifying both -Wimplicit-int and
-Wimplicit-function-declaration.
-Wimplicit-function-
declaration Give a warning whenever a function is used before being
declared.
-Wimplicit-int Warn when a declaration does not specify a type.
-Wmain Warn if the type of main is suspicious. main shou ld be a
function with external linkage, returning int, taking either zero,
two or three arguments of appropriat e types.
-Wmissing-braces Warn if an aggregate or union initializer is not fully bracketed. In
the following example, the initializer for a is not fully bracke ted ,
but that for b is fu lly br acketed.
int a[2][2] = { 0, 1, 2, 3 };
int b[2][2] = { { 0, 1 }, { 2, 3 } };
-Wno-multichar Warn if a mu lti- charac ter character constant is used. Usually ,
such constants are typographical errors. Since they have
implementation-defined values, they should not be used in
portable code. The following example illustrates the use of a
multi-character character constant:
char
xx(void)
{
return('xx');
}
-Wparentheses Warn if parentheses are omitted in certain contexts, such as
when there is an assignment in a context where a truth value is
expected, or when operators are nested whose precedence
people often find confusing.
-Wreturn-type Warn whenever a function is defined with a return-type that
defaults to int. Also warn about an y return s tatem ent with no
return-value in a function whose return-type is not void.
TABLE 3-8: WARNING AND ERROR OPTIONS IMPLIED BY A LL WARNINGS
Option Definition
Compiler Command Line Driver
2012 Microchip Technology Inc. DS51686E-page 67
-Wsequence-point Warn about code that may have undefined semantics because
of violations of sequence point rules in the C standard.
The C standard defines the order in which expressions in a C
program are evaluated in terms of sequence points, which
represen t a part ial orderin g between t he execu tion of p arts of the
program: those executed before the sequence point and those
execute d after it . These occur after the evaluation o f a full
expression (one which is not part of a larger expression), after
the evaluation of the first operand of a &&, ||, ? : or , (comma)
operator, before a function is call ed (but a fter the evaluati on of it s
argumen t s and th e expre ssio n deno ting th e cal led fun ction), an d
in certain other places. Other than as expressed by the
sequen ce poi nt r ule s, the orde r of evalu ati on of sube xp res si ons
of an expression is not specified. All these rules describe only a
partial order rather than a total order, since, for example, if two
functions are called within one expression with no sequence
point betw een them, the orde r in which the fun ctions are call ed is
not specified. However, the standards committee has ruled that
function calls do not overlap.
It is not specified when between sequence points modifications
to the values of objects take effect. Programs whose behavior
depends on this have undefined behavior. The C standard
specifies that “Between the previous and next sequence point,
an object shall have its stored value modified, at most once, by
the evaluation of an expression. Furthermore, the prior value
shall be read only to determine the value to be stored.” If a
program breaks these rules, the results on any particular
implem en t ation are entirely unpredict a ble .
Examples of code with undefined behavior are a = a++;,
a[n] = b[n++] and a[i++] = i;. Some more complic ate d
cases are not diagnosed by this option, and it may give an
occasional false positive result, but in general it has been found
fairly effective at detecting this sort of problem in programs.
-Wswitch Warn whenever a switch statement has an index of enumeral
type an d lacks a case f or one or more of the na med cod es of tha t
enumeration. (The presence of a default label prevents this
warning.) case labels outside the enumeration range also
provoke warnings when this option is used.
-Wsystem-headers Print warning messages for constructs found in system header
files. Warnings from system headers are normally suppressed
on the assumption that they usually do not indicate real
problems and would only make the compiler output harder to
read. Using this command line option tells the compiler to emit
warnings from system headers as if they occurred in user code.
However, note that using -Wall in conjunction with this option
does not warn about unknown pragmas in system headers. For
that, -Wunknown-pragmas must also be used.
-Wtrigraphs Warn if any trigraphs are encountered (assuming they are
enabled).
TABLE 3-8: WARNING AND ERROR OPTIONS IMPLIED BY A LL WARNINGS
Option Definition
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 68 2012 Microchip Technology Inc.
The following -W options are not implied by -Wall. Some of them warn about
constructions that users generally do not consider questionable, but which you might
occasionally wish to check for. Others warn about constructions that are necessary or
hard to avoid in some cases, and there is no simple way to modify the code to suppress
the warning.
-Wuninitialized Warn if an automatic variable is used without first being
initialized.
These w arni ngs are pos si bl e only wh en op tim iz ati on is enab led ,
becaus e they requi re data fl ow informati on that is co mputed on ly
when optimizing.
These warnings occur only for variables that are candidates for
register allocation. Therefore, they do not occur for a variable
that is d eclared volatile, or whose a ddress is take n, or whos e
size is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
structures, unions or arrays, even when they are in registers.
Note that there may be no warning about a variable that is used
only to compute a value that itself is never used, because such
computations may be deleted by data flow analysis before the
warnings are printed.
-Wunknown-pragmas Warn when a #pragma directive is encountered which is not
understood by the compiler. If this command line option is used,
warnings will even be issued for unknown pragmas in system
header files. This is not the case if the warnings were only
enabled by the -Wall co mm and line opti on.
-Wunused Warn whenever a variable is unused aside from its declaration,
whenever a function is declared static but never defined,
whenever a label is decl ared but not used, and wh enever a
statement computes a result that is explicitly not used.
In order to get a warning about an unused function parameter,
both -W and -Wunused must be specified.
Casting an expression to void suppresses this warning for an
expression. Similarly, the unused attribute suppresses this
warning for unused variables, parameters and labels.
-Wunused-function Warn whenever a static function is declared but not defined or a
non-inline static function is unused.
-Wunused-label Warn whenever a label is declared but not us ed. To suppress
this warning, use the unused attribute.
-Wunused-parameter Warn whenever a function parameter is unused aside from its
declaration. To suppr ess this war ning, us e the unused attribute.
-Wunused-variable W a rn whenever a local variab le or non-cons tant st atic variab le is
unused aside from its declaratio n. To suppres s this warn ing, use
the unused attribute.
-Wunused-value Warn whenever a statement computes a result that is explicitly
not used. To suppress this warning, cast the expression to void.
TABLE 3-8: WARNING AND ERROR OPTIONS IMPLIED BY A LL WARNINGS
Option Definition
Compiler Command Line Driver
2012 Microchip Technology Inc. DS51686E-page 69
TABLE 3-9: WARNING AND ERROR OPTIONS NOT IMPLIED BY ALL
WARNINGS
Option Definition
-W Print extra warning messages for these events:
• A nonvolatile automatic variable might be changed by a
call to longjmp. These warnings are po ssible only in
optimizing compilation. The compiler sees only the calls
to setjmp. It ca nnot know where longjmp will be calle d.
In fact, a signal handler could call it at any point in the
code. As a result, a warning may be generated even
when there is in fact no problem, because longjmp
cannot in fact be called at the place that would cause a
problem.
• A function could exit both via return value; and
return;. Completing the function body without passing
any return statement is treated as return;.
• An expression-statement or the left-hand side of a
comma expression contains no side effects. To suppress
the warning, cast the unused expression to void. For
examp le, an expression su ch as x[i,j] causes a
warnin g, but x[(void)i,j] doe s not.
• An unsigned value is compared against zero with < or <=.
• A comparis on like x<=y<=z appears, This is equivalent
to (x<=y ? 1 : 0) <= z, which is a different
interpre t ati on from that o f o rdin ary m athe ma tical notation.
• Storag e-cla ss specifi ers li ke static are not the first
things in a declaration. According to the C Standard, this
usage is obs ol es cent.
•If -Wall or -Wunused is also specified, warn about
unused arguments.
• A comparison between signed and unsigned values
could produce an incorrect result when the signed value
is converted to unsigned. (But don’t warn if
-Wno-sign-compare is also spe ci fie d.)
• An aggregate has a partly bracketed initializer. For
examp le, the foll owing code wo uld evoke su ch a warning ,
because braces are missing around the initializer for
x.h:
struct s { int f, g; };
struct t { struct s h; int i; };
struct t x = { 1, 2, 3 };
• An aggregate has an initializer that does not initialize all
members. For example, the following code would cause
such a warning, because x.h would be implicitly
initialized to zero:
struct s { int f, g, h; };
struct s x = { 3, 4 };
-Waggregate-return Warn if any functions that return structures or unions are
defined or called.
-Wbad-function-cast Warn w hen ev er a fu nc tio n c al l is cast to a non-m atc hin g typ e.
For example, warn if int foof() is cast to anything *.
-Wcast-align Warn whenever a pointer is cast, such that the required
alignment of the target is increased. For example, warn if a
char * is cast to an int *.
-Wcast-qual Warn whenever a pointer is cast, so as to remove a type
qualifier from the target type. For example, warn if a
const char * is cast to an ordinary char *.
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 70 2012 Microchip Technology Inc.
-Wconversion Warn if a prototype causes a type conversion that is different
from what would happen to the same argument in the
absence of a prototype. This includes conversions of fixed
point to fl oating and v ice versa, and convers ions changi ng the
width or signedness of a fixed point argument, except when
the same as the default promotion.
Also, warn if a negative integer constant expression is
implicitly converted to an unsigned type. For example, warn
about the assignment x = -1 if x is unsigned. But do not
warn about explicit casts like (unsigned) -1.
-Werror Make all warnings into errors.
-Winline Warn if a function can not be inlined, and either it was
declare d as in lin e, or else the -finline-functions option
was given.
-Wlarger-than-len Warn whenever an object of larger than len bytes is defined.
-Wlong-long
-Wno-long-long Warn if long long type is u sed. Thi s is defau lt. To inhib it the
warning messag es, use -Wno-long-long. Flags
-Wlong-long and -Wno-long-long are taken into account
only when -pedantic flag is used.
-Wmissing-declarations Warn if a global function is defined without a previous
declaration. Do so even if the definition itself provides a
prototype.
-Wmissing-
format-attribute If -Wformat is enabled, also warn about functions that might
be candidates for format attributes. Note these are only
possible candidates, not absolute ones. This option has no
effect unless -Wformat is enabled.
-Wmissing-noreturn Warn about functions that might be candidates for attribute
noreturn. These are only possible candidates, not absolute
ones. Care should be taken to manually verify functions. In
fact, do n ot ever return before addin g the noreturn attribute ,
otherwise subtle code generation bugs could be introduced.
-Wmissing-prototypes Warn if a global function is defined without a previous
prototype declaration. This warning is issued even if the
definit ion itse lf provide s a proto type. (Thi s option can be used
to detect global functions that are not declared in header
files.)
-Wnested-externs Warn if an extern declaration is encountered within a
function.
-Wno-deprecated-
declarations Do not warn about uses of functions, variables and types
marked as deprecated by using the deprecated attribut e.
-Wpadded Warn if padding is included in a structure, either to align an
elem ent of the stru ctur e or to align the whole structure.
-Wpointer-arith Warn about anything that depends on the size of a function
type or of void. The c ompil er assign s these t ypes a size o f 1,
for convenience in calculations with void * pointers and
pointers to functions.
-Wredundant-decls Warn if anything is declared more than once in the same
scope, even in cases where multiple declaration is valid and
changes nothing.
-Wshadow Warn whenever a local variable shadows another local
variable.
TABLE 3-9: WARNING AND ERROR OPTIONS NOT IMPLIED BY ALL
WARNINGS (CONTINUED)
Option Definition
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2012 Microchip Technology Inc. DS51686E-page 71
-Wsign-compare
-Wno-sign-compare Warn when a comparison between signed and unsigned
values could produce an incorrect result when the signed
value is converted to unsigned. This warning is also enabled
by -W. To get the other warnings of -W without this warning,
use -W -Wno-sign-compare.
-Wstrict-prototypes W a rn if a func tion is decla red or def ined withou t specify ing the
argument types. (An old-style function definition is permitted
witho ut a warning if prec eded by a decla ration whi ch specifies
the argument types.)
-Wtraditional Warn about certain constructs that behave differently in
traditional and ANSI C.
• Macro arguments occurring within string constants in the
macro body. These would substitute the argument in
traditional C, but are part of the constant in ANSI C.
• A function declared external in one block and then used
after the end of the block.
• A switch statement has an operand of type long.
• A no ns tatic functi on de cla r ati on fol lo ws a st atic one. This
construct is not accepted by some traditional C
compilers.
-Wundef Warn if an undefined identifier is evaluated in an #if
directive.
-Wunreachable-code Warn if the co mpile r detect s that cod e will never be execute d.
It is possible for this option to p r odu ce a wa rni ng eve n though
there are circumstances under which part of t he affected line
can be executed, so care should be taken when removing
app arently unreac hable code . For instan ce, when a function is
inlined, a warnin g may m ean that the line is unr eachable in
only one inlined copy of the function.
-Wwrite-strings Gi ve string cons tant s the type const char[length] so that
copying the address of one into a non-const char * pointer
gets a w arn ing . At co mpile time, th es e warnings help you find
code that you can try to write into a string constant, but only if
you h ave been very care ful abou t using const in declarati ons
and prototypes. Otherwise, it’s just a nuisance, which is why
-Wall does not request these warnings.
TABLE 3-9: WARNING AND ERROR OPTIONS NOT IMPLIED BY ALL
WARNINGS (CONTINUED)
Option Definition
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 72 2012 Microchip Technology Inc.
3.9.6 Options for Debugging
The following options are used for debugging.
3.9.7 Options for Control ling Optimization
The following options control compiler optimizations.
TABLE 3-10: DEBUGGING OPTIONS
Option Definition
-g Produce deb ugg ing inform ati on.
The compi ler su ppo rts the use of -g with -O making it p ossible to
debug optimized code. The shortcuts taken by optimized code may
occasionally produce surprising results:
• Some declared variables may not exist at all
• Flow of control may briefly move unexpectedly
• Some statements may not be executed because they compute
constant results or their values were already at hand
• Some statements may execute in different places because they
were moved out of loops
Nevertheless it proves possible to debug optimized output. This makes
it reasonable to use the optimizer for programs that might have bugs.
-Q Makes the compiler print out each function name as it is compiled, and
print some statistics about each pass when it finishes.
-save-temps
-save-temps=cwd Do n’t del ete interm edi ate files . Place them in the cur rent dire ct ory and
name them based on the source file. Thus, compiling foo.c with -c
-save-temps would produce the following files:
foo.i (preprocessed file)
foo.s (asse mbl y lan gua ge fil e)
foo.o (object file)
-save-temps=obj Simi lar to -save-temps=cwd, but if the -o option is specified, the
tem porar y files are based on the object file. If t he -o option is not
specified, the -save-temps=obj switch behaves like –save-temps.
For example:
xc32-gcc -save-temps=obj -c foo.c
xc32-gcc -save-temps=obj -c bar.c -o dir/xbar.o
xc32-gcc -save-temps=obj foobar.c -o dir2/yfoobar
would cr eate foo.i, foo.s, dir/xbar.i, dir/xbar.s,
dir2/yfoobar.i, dir2/yfoobar.s, and dir2/yfoobar.o.
TABLE 3-11: GENERAL OPTIMIZATION OPTIONS
Option Definition
-O0 Do not optim ize . (This is the default.)
Without -O, the compiler’s goal is to reduce the cost of compilation and to make
debuggi ng produce the expe cted result s. S tatement s are indepen dent: if you stop
the program with a breakpoint between statements, you can then assign a new
value to any variable or change the program counter to any other statement in
the function and get exactly the results you would expect from the source code.
The compiler only allocates variables declared register in registers.
-O
-O1 Optimization level 1. Optimizing compilation takes somewhat longer, and a lot
more host memory for a large function.
With -O, the compiler tries to reduce code size and execution time.
When -O is specified, the compiler turns on -fthread-jumps and
-fdefer-pop. The compiler turns on -fomit-frame-pointer.
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2012 Microchip Technology Inc. DS51686E-page 73
The following options control specific optimizations. The -O2 option turns on all of
these optimizations except -funroll-loops, -funroll-all-loops and
-fstrict-aliasing.
You can use the following flags in the rare cases when “fine-tuning” of optimizations to
be perform ed is desired .
-O2 Optimization level 2. The compiler performs nearly all su pport ed optimi zations
that do not involve a space-speed trade-off. -O2 turns on all optional
optimizations except for loop unrolling (-funroll-loops), function inlining
(-finline-functions), and strict aliasing optimizations
(-fstrict-aliasing). It also turns on force copy of memory operands
(-fforce-mem) and Fr ame Pointer el imin ation ( -fomit-frame-pointer). As
compared to -O, this op tion inc reases b oth compil ation tim e and th e perfor mance
of the generated code.
-O3 Optimization level 3. -O3 turns on all optimizations specified by -O2 an d also
turns on the inline-functions option.
-Os Optimi ze for size. -Os ena bles all -O2 optimi zations that do not typi cally in crease
code size. It also performs further optimizations designed to reduce code size.
TABLE 3-12: SPECIFIC OPTIMIZATION OPTIONS
Option Definition
-falign-functions
-falign-functions=
n
Align the start of functions to the next power-of-two greater than n,
skipping up to n bytes. For instance, -falign-functions=32
aligns functions to the next 32-byte boundary, but
-falign-functions=24 would align to the next 32-byte
boundary only if this can be done by skipping 23 bytes or less.
-fno-align-functions and -falign-functions=1 are
equivalent and mean that functions are not aligned.
The asse mbler only su ppo rts this fla g w he n n is a po wer of tw o , so
n is rounded up. If n is not specified, use a machine-dependent
default.
-falign-labels
-falign-labels=n Align all branch targets to a power-of-two boundary, skipping up to
n bytes like -falign-functions. This option can easily make
code slowe r , because it mus t insert dum my operations for when the
branch target is reached in the usual flow of the code.
If -falign-loops or -falign-jumps are applicable and are
greater than this value, then their values are used instead.
If n is not spec ified , u se a m achin e-de penden t defa ult w hich is ver y
likely to be 1, mea ning no alignm ent.
-falign-loops
-falign-loops=n Align loops to a power-of-two boundary, skipping up to n bytes like
-falign-functions. The hope is that the loop is executed many
times, w hich mak es up for any execu tion of the dummy operati ons.
If n is not specified, use a machine-dependent default.
-fcaller-saves Enable values t o be allocated in registers that are clobbered by
function calls, by em itti ng extra ins truc ti ons to sa ve and resto r e t he
registers around such calls. Such allocation is done only when it
seems to result in better code than would otherwise be produced.
-fcse-follow-jumps In common subexpression elimination, scan through jump
instruct ions when the target of the jump is not reached by any oth er
path. For ex ample , when CSE encounte rs an if statement with an
else clause, CSE follows the jump when the condition tested is
false.
TABLE 3-11: GENERAL OPTIMIZATION OPTIONS (CONTINUED)
Option Definition
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 74 2012 Microchip Technology Inc.
-fcse-skip-blocks This is simi lar to -fcse-follow-jumps, but causes CSE to
follow jumps which conditionally skip over blocks. When CSE
enco unte rs a sim ple if statement with no else clause,
-fcse-skip-blocks causes CSE to follow the jump around the
body of the if.
-fexpensive-
optimizations Perform a number of minor optimizations that are relatively
expensive.
-ffunction-section
s
-fdata-sections
Place each function or data item into its own section in the output
file. The name of the function or the name of the data item
determines the section's name in the output file.
Only use t hese opti ons when there are s ignifica nt benefit s for doi ng
so. When you specify these options, the assembler and linker may
create larger object and executable files and is also slower.
-fgcse Perform a global common subexpression elimination pass. This
pass also performs global constant and copy propagation.
-fgcse-lm When -fgcse-lm is enabled, global common subexpression
elimination attempts to move loads which are only killed by stores
into themselves. This allows a loop containing a load/store
sequence to change to a load outside the loop, and a copy/store
within the loop.
-fgcse-sm When -fgcse-sm is enabl ed, a store motion pass is r un after
global common subexpression elimination. This pass attempts to
move stores out of loops. When used in conjunction with
-fgcse-lm, loops contain ing a load/s tore sequenc e can change to
a load before the loop and a store after the loop.
-fmove-all-movable
sForces all invariant computations in loops to be moved outside the
loop.
-fno-defer-pop Always pop the arguments to each function call as soon as that
function returns. The co mp iler normall y let s argume nt s accum ulate
on the stack for several function calls and pops them all at once.
-fno-peephole
-fno-peephole2 Disable machine specific peephole optimizations. Peephole
optimizations occur at various points during the compilation.
-fno-peephole disables peephole optimization on machine
instru ct ion s, w hi le -fno-peephole2 disable s hi gh l eve l peephole
optimizations. To disable peephole entirely, use both options.
-foptimize-
register-move
-fregmove
Attempt to reassign register numbers in move instructions and as
operands of other simple instructions in order to maximize the
amount of register tying.
-fregmove and -foptimize-register-moves are the same
optimization.
-freduce-all-givs Forces all general-induction variables in loops to be strength
reduced.
These options may generate better or worse code. Results are
highly dependent on the structure of loops within the source code.
-frename-registers Attempt to avoid false dependencies in scheduled code by making
use of registers left over after register allocation. This optimization
most benefits processors with lots of registers. It can, however,
make debugging impossible, since variables no longer stay in a
“home register”.
-frerun-cse-after-
loop Rerun common subexpression elimination after loop optimizations
has been performed.
-frerun-loop-opt Run the loo p optimizer t wice.
TABLE 3-12: SPECIFIC OPTIMIZATION OPTIONS (CONTINUED)
Option Definition
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2012 Microchip Technology Inc. DS51686E-page 75
-fschedule-insns Attempt to reorder instructions to eliminate instruction stalls due to
required data being unavailable.
-fschedule-insns2 Simil ar to -fschedule-insns, but reque sts an addit ional p a ss of
instruction scheduling after register allocation has been done.
-fstrength-reduce Perform the optimizations of loop strength reduction and
elimination of iteration variables.
-fstrict-aliasing Allow s the com piler to assume the stric test ali asing rules applic able
to the language being compiled. For C, this activates optimizations
based on the type of expressions. In particular, an object of one
type is assum ed neve r to reside at the same add res s as an object
of a different type, unless the types are almost the same. For
exampl e, an unsigned int c an ali as an int, but not a void* or
a double. A character type may alias any other type.
Pay special attention to code like this:
union a_union {
int i;
double d;
};
int f() {
union a_union t;
t.d = 3.0;
return t.i;
}
The practic e of reading from a dif fe rent union mem ber than the one
most recently written to (called “type-punning”) is common. Even
with -fstrict-aliasing, type-punning is allowed, provided the
memory is accessed through the union type. So, the code above
works as expec ted. However, this code might not:
int f() {
a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
return *ip;
}
-fthread-jumps Perform optimizations where a check is made to see if a jump
branches to a lo cation w here ano ther co mpari son sub sumed by t he
first is found. If so, the first branch is redirected to either the
destinat ion of the second branc h or a point imm ediately following it ,
depending on whether the condition is known to be true or false.
-funroll-loops Perform the optimization of loop unrolling. This is only done for
loops whose number of iterations can be determined at compile
time or run time. -funroll-loops implies both
-fstrength-reduce and -frerun-cse-after-loop.
-funroll-all-loops Perf orm the optimiza tio n o f lo op u nrol li ng. This is do ne for a ll l oops
and usually makes programs run more slowly.
-funroll-all-loops implies -fstrength-reduce, as well as
-frerun-cse-after-loop.
TABLE 3-12: SPECIFIC OPTIMIZATION OPTIONS (CONTINUED)
Option Definition
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 76 2012 Microchip Technology Inc.
Options of the form -fflag specify machine-independent flags. Most flags have both
positive and negative forms. The negative form of -ffoo would be -fno-foo. In the
table below, only one of the forms is listed (the one that is not the default.)
TABLE 3-13: MACHINE-INDEPENDENT OPTIMIZATION OPTIONS
Option Definition
-fforce-mem Force memory operands to be copied into registers
before doing arithmetic on them. This produces better
code by making all memory re ferences pot ential comm on
subexpressions. When they are not common
subexpressions, in struction combination should eliminate
the separate register load. The -O2 option turns on this
option.
-finline-functions Integrate all simple functions into their callers. The
compil er h euristicall y de ci des w hi ch fun cti ons are simple
enough to be worth integra tin g in thi s way. If all calls to a
given fu nction are i ntegrated, a nd the function is declared
static, then the function is normally not output as
assembler code in its own right.
-finline-limit=n By default, the compiler limits the size of functions that
can be inlin ed. This flag allows the contr ol of this lim it for
function s that ar e ex plicit ly marked as inli ne (i.e. , mar ked
with the inline keyword). n is the size of functi ons that
can be inlined in number of pseudo instructions (not
counting parameter handling). The default value of n is
10000. Increasing this value can result in more inlined
code at the cost of compilation time and memory
consumption.
Decreasing usually makes the compilation faster and
less code is inlined (which presumably means slower
progra ms). Th is option is p a rtic ula rly us eful for pro gra ms
that use inlining.
Note: Pseudo instruction represents, in this particular
context, an abstract measurement of function's size. In
no way d oes it represent a count of a ssembly instruc tions
and as such, its exact meaning might change from one
release of the compiler to an another.
-fkeep-inline-functions Ev en if all cal ls to a give n function are integr ated, and the
function is declared static, output a separate run time
callable version of the function. This switch does not
affect extern inline functions.
-fkeep-static-consts Emit variables are declared static const when
optimization isn't turned on, even if the variables are not
referenced.
The compiler enables this option by default. If you want
to force the compiler to check if the variable was
referenced, regardless of whether or not optimization is
turned on, use the -fno-keep-static-consts
option.
-fno-function-cse Do not put function addresses in registers. Make each
instruction that calls a constant function contain the
function's address explicitly.
This option results in less efficient code, but some
strange hacks that alter the assembler output may be
confused by the optimizations performed when this
option is not used .
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2012 Microchip Technology Inc. DS51686E-page 77
-fno-inline Do not pay attention to the inline keyword. Normally
this option is used to keep the compiler from expanding
any functions inline. If optimization is not enabled, no
functions can be expanded inline.
-fomit-frame-pointer Do not keep the Frame Pointer in a register for functions
that don't need one. This avoids the instructions to save,
set up and restore Frame Pointers. It also makes an
extra register av ailable in man y functions.
-foptimize-sibling-calls Optimize sibling and tail recursive calls.
TABLE 3-13: MACHINE-INDEPENDENT OPTIMIZATION OPTIONS
Option Definition
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 78 2012 Microchip Technology Inc.
3.9.8 Options for Control ling the Preprocessor
The following options control the compiler preprocessor.
TABLE 3-14: PREPROCESSOR OPTIONS
Option Definition
-C Tell the preprocessor not to discard comments. Used with the -E
option.
-dD Tell the preprocessor to not remove macro definitions into the output,
in their proper sequence.
-Dmacro Define macro macro with string 1 as its definition.
-Dmacro=defn Define macro macro as defn. All instances of -D on the command
line are processed before any -U options.
-dM Tell the preprocessor to output only a list of the macro definitions that
are in effect at the end of preprocessing. Used with the -E option.
-dN Like -dD except that the macro arguments and contents are omitted.
Only #define name is included in the output.
-fno-show-column Do not print column numbers in diagnostics. This may be necessary if
diagnos tics a re being s canne d by a prog ram that do es not un derst and
the column numbers, such as DejaGnu.
-H Print the name of each header file used, in addition to other normal
activities.
-I- Any dir ect ories yo u sp ecify with -I opt ions before th e -I- opti ons are
searched only for the case of #include “file”. They are not
searched for #include <file>.
If additional directories are specified with -I options after the -I-,
these d irec tories are s ea r ch ed for all #include di rectives . (Ordinarily
all -I directories are used this way.)
In addition, the -I- option inhibits the use of the current directory
(where the curren t input file c ame from) as the fi rst searc h dire ctory fo r
#include “file”. There is no way to override this effect of -I-.
With -I. you can specify searching the directory that was current
when the compiler was invoked. That is not exactly the same as what
the preprocessor does by default, but it is often satisfactory.
-I- does not inhibit the use of the standard system directories for
header files. Thus, -I- and -nostdinc are indepe ndent.
-Idir Add the directory dir to the head of the list of directories to be
searched for header files. This can be used to override a system
header file, substituting your own version, since these directories are
searched before the system header file directories. If you use more
than one -I option, the directories are scanned in left-to-right order.
The standard system directories come after.
-idirafter dir Add the directory dir to the second include path. The directories on
the second include path are searched when a header file is not found
in any of the directories in the main include path (the one that -I adds
to).
-imacros file Process file as input, discarding the resulting output, before
processing the regular input file. Because the output generated from
the f ile is d is car ded , th e o nly effect of -imacros file is to make the
macros defined in file available for use in the main input.
Any -D and -U options on the command line are always processed
before -imacros file, regardless of the order in which they are
written. All the -include and -imacros opt ions ar e proces sed in th e
order in which they are written.
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2012 Microchip Technology Inc. DS51686E-page 79
-include file Process file as input before processing the regular input file. In effect,
the contents of file are compiled first. Any -D and -U options on the
command line are always processed before -include file,
regardless of the order in which they are written. All the -include
and -imacros options are processed in the order in which they are
written.
-M Tell the preprocessor to output a rule suitable for make describing the
dependencies of each object file. For each source file, the
preprocessor outputs one make-rule whose target is the object file
name for that source file and whose dependencies are all the
#include header files it uses. This rule may be a single line or may
be continued with \-newline if it is long. The list of rules is printed
on standard output instead of the preprocessed C program.
-M implies -E (see Section 3.9.2 “Options for Controlling the Kind
of Output”).
-MD Like -M but the dependency information is written to a file and
compil ati on con t in ues . T he fil e c ontaining the depende nc y i nformation
is given the same name as the source file with a .d extension.
-MF file When used wi th -M or -MM, specifies a file in which to write the
dependencies. If no -MF switch is given, the preprocessor sends the
rules to the same place it would have sent preprocessed output.
When used with the driver options, -MD or -MMD, -MF, overri des the
default dep endency output file .
-MG Treat missing header files as generated files and assume they live in
the same directory as th e source file . If -MG is sp ecifi ed, th en eithe r -M
or -MM m ust also be s pec ified. -MG is not suppo r ted wit h -MD or -MMD.
-MM Like -M but the output mentions only the user header files included
with #include “file” . System he ader files inc luded with #include
<file> are omitted.
-MMD Like -MD except mention only user header files, not system header
files.
-MP This option instructs CPP to add a phony target for each dependency
other than the main file, causing each to depend on nothing. These
dummy rules work around errors make gives if you remove header
files without updating the make-file to match.
This is typical output:
test.o: test.c test.h
test.h:
-MQ Same as -MT, but it quotes any characters which are special to make.
-MQ '$(objpfx)foo.o' gives $$(objpfx)foo.o: foo.c
The default target is automatically quoted, as if it were given with -MQ.
-MT target Change the target of the rule emitted by dependency generation. By
default, CPP takes the name of the mai n inp ut fil e, inc lu din g any p ath,
deletes any file suffix such as .c, and appends the platform’s usual
object suffix. The result is the target.
An -MT optio n sets the ta rget to be exactly the str ing you s pecify. If you
want multiple targets, you can specify them as a single argument to
-MT, or use multiple -MT opti ons.
For example:
-MT '$(objpfx)foo.o' might give $(objpfx)foo.o: foo.c
TABLE 3-14: PREPROCESSOR OPTIONS (CONTINUED)
Option Definition
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 80 2012 Microchip Technology Inc.
-nostdinc Do not search the standard system directories for header files. Only
the directories you have specified with -I options (and the current
directory, if appropriate) are searched. (See Section 3.9.11 “Options
for Directory Search”) for information on -I.
By using both -nostdinc and -I-, the include-file search path can
be limited to only those directories explicitly specified.
-P Tell the preprocessor not to generate #line directives. Used with the
-E option (see Section 3.9.2 “Options for Controlling the Kind of
Output”).
-trigraphs Support ANSI C trigraphs. The -ansi option also has this effect.
-Umacro Und efi ne ma cro macro. -U options are evaluated after all -D options,
but before any -include and -imacros options.
-undef Do not pred efi ne any nons t an dard macros (includin g arch itec tu re
flags).
TABLE 3-14: PREPROCESSOR OPTIONS (CONTINUED)
Option Definition
Compiler Command Line Driver
2012 Microchip Technology Inc. DS51686E-page 81
3.9.9 Options for Assembling
The following options control assembler operations.
3.9.10 Options for Linking
If any of the options -c, -S or -E are used, the linker is not run and object file names
should not be used as arguments.
TABLE 3-15: ASSEMBLY OPTIONS
Option Definition
-Wa,option Pass option as an option to the assem bl er. If option contains
commas, it is split into multiple options at the commas.
TABLE 3-16: LINKING OPTIONS
Option Definition
-fill=<options A memory-fill option to be passed on to the linker.
-Ldir Add director y dir to the list of directories to be searched for libraries
specified by the command line option -l.
-llibrary Search the lib rary name d library when linking.
The link er s earc he s a s t an dard li st of directories fo r th e l ibra r y, whic h
is actua lly a file named liblibrary.a. The lin ker then uses thi s file
as if it had been specified precisely by name.
It makes a difference where in the command you write this option.
The linker processes libraries and object files in the order they are
specified. Thus, foo.o -lz bar.o searches library z after file
foo.o but before bar.o. If bar.o refers to functions in libz.a,
those functions may not be loaded.
The direct orie s sea rch ed inc lude several st an dard system
directories, plus any that you specify with -L.
Normally the files found this way are library files (archive files whose
members are object files). The linker handles an archive file by
scanning through it for members which define symbols that have
been referenced but not defined yet. But if the file found is an
ordinary object file, it is linked in the usual fashion. The only
difference between using an -l option (e.g., -lmylib) and
specifying a file name (e.g., libmylib.a) is that -l searches
several direct ories, as specified.
By default the linker is directed to search:
<install-path>\lib
for libraries specified with the -l option. For a compiler installed into
the default location, this would be:
Program Files\Microchip\mplab32\<version>\lib
This behavior can be overridden using the environment variables.
See also the INPUT and OPTIONAL linker script directives.
-nodefaultlibs Do not use the standard system libraries when linking. Only the
libraries you specify are passed to the linker. The compiler may
generate calls to memcmp, memset and memcpy. These entries are
usually resolved by entries in the standard compiler libraries. These
entry points should be supplied through some other mechanism
when this option is specified.
-nostdlib Do not use the standard sys tem start-up fi les or libraries when
linking. No st a rt-up files and o nly th e l ibraries you s pec ify are pas sed
to the linker. The compiler may generate calls to memcmp, memset
and memcpy. These entries are usually resolved by entries in
standard compiler libraries. These entry points should be supplied
through some other mechanism when this option is specified.
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3.9.11 Options for Directory Search
The following options specify to the compiler where to find directories and files to
search.
-s Remove all symbol table and relocation information from the
executable.
-u symbol Pretend symbol is undefined to force linking of library modules to
define the symbol. It is legitimate to use -u multiple times with
different symbols to force loading of additional library modules.
-Wl,option Pass option as a n optio n to th e link er. If option contains commas,
it is split into multiple options at the commas.
-Xlinker option Pass option as an option to the linker. You can use this to supply
system- speci fic link er options that the co mpiler do es not kno w how t o
recognize.
TABLE 3-17: DIRECTORY SEARCH OPTIONS
Option Definition
-Bprefix This option specifies where to find the executables, libraries,
include files and data files of the compiler itself.
The compiler driver program runs one or more of the
sub-programs xc32-cpp, xc32-as and xc32-ld. It tries
prefix as a prefix for each program it tries to run.
For each sub-program to be run, the compiler driver first tries the
-B prefix, if any. Lastly, the driver searches the current PATH
environment variable for the subprogram.
-B prefixes that effectively specify directory names also apply to
libraries in the linker, because the compiler translates these
options into -L options for the linker. They also apply to include
files in the preprocessor, because the compiler translates these
options into -isystem options for the preprocessor. In this case,
the compiler appends include to the prefix.
-specs=file Proces s fi le after the comp iler reads in the s t andard specs file, in
order to override the defaults that the xc32-gcc driver program
uses when determining what switches to pass to xc32-as,
xc32-ld, etc. More than one -specs=file can be specified on
the command line, and they are processed in order, from left to
right.
TABLE 3-16: LINKING OPTIONS (CONTINUED)
Option Definition
Compiler Command Line Driver
2012 Microchip Technology Inc. DS51686E-page 83
3.9.12 Options for Code Generati on Conventions
Options of the form -fflag specify machine-independent flags. Most flags have both
positive and negative forms. The negative form of -ffoo would be -fno-foo. In the
table below, only one of the forms is listed (the one that is not the default).
TABLE 3-18: CODE GENERATION CONVENTION OPTIONS
Option Definition
-fargument-alias
-fargument-noalias
-fargument-
noalias-global
S pe cify the pos sible relati onship s among p arameters and betwee n
parameters and global data.
-fargument-alias speci fies that arguments (parameters) may
alias each other and may alias global storage.
-fargument-noalias specifies that arguments do not alias
each other, but may alias global storage.
-fargument-noalias-global sp ecifies that arguments do not
alias each other and do not alias global storage.
Each language automatically uses whatever option is required by
the language standard. You should not need to use these options
yourself.
-fcall-saved-reg Treat the register named reg as an allocatable register saved by
functions. It may be allocated even for temporaries or variables
that live across a call. Functions compiled this way saves and
restores the register reg if they use it.
It is an error to use this flag with the Frame Pointer or Stack
Pointer. Use of this flag for other registers that have fixed
pervasive ro les in the machine’s execution m odel produces
disastrous results.
A different sort of disaster results from the use of this flag for a
register in which function values are returned.
This flag should be used consistently through all modules.
-fcall-used-reg Treat the register named reg as an allocatable reg ister tha t is
clobbered by function calls. It may be allocated for temporaries or
variabl es that do not liv e across a call. Fun ctions com piled this way
do not save and restore the register reg.
It is an error to use this flag with the Frame Pointer or Stack
Pointer. Use of this flag for other registers that have fixed
pervasive ro les in the machine’s execution m odel produces
disastrous results.
This flag should be used consistently through all modules.
-ffixed-reg Treat the register named reg as a fixed registe r. Genera ted code
should never refer to it (except perhaps as a Stack Pointer, Frame
Pointer or in some othe r fixe d role).
reg must be the name of a register (e.g., -ffixed-$0).
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-finstrument-
functions Generate instrumentation calls for entry and exit to functions. Just
after function entry and just before function exit, the following
profiling functions are called with the address of the current
function and its call site.
void __cyg_profile_func_enter
(void *this_fn, void *call_site);
void __cyg_profile_func_exit
(void *this_fn, void *call_site);
The first argument is the address of the start of the current
function, which may be looked up exactly in the symbol table.
The profiling functions should be provided by the user.
Function instrumentation requires the use of a Frame Pointer.
Some optimization levels disable the use of the Frame Pointer.
Using -fno-omit-frame-pointer prevents this.
This instrumentation is also done for functions expanded inline in
other functions. The profiling calls indicates where, conceptually,
the inline function is entered and exited. This means that
addressable versions of such functions must be available. If all
your uses of a function are expanded inline, this may mean an
additional expansion of code size. If you use extern inline in
your C code, an addressable version of such functions must be
provided.
A function may be given the attribute
no_instrument_function, in which case this instrumentation
is not done.
-fno-ident Ignore the #ident directi ve .
-fpack-struct Pack all structure members together without holes. Usually you
would not want to use this option, since it makes the code
sub-opti mal, and t he of fset s of str ucture membe rs won’t agree wit h
system libraries.
-fpcc-struct-
return Return short struct and union v alues in me mory like l onger
ones, rather than in registers. This convention is less efficient, but
it h as the a dvant age of a llowing cap ability between 32-bit c ompiled
files and files compiled with other compilers.
Short structures and unions are those whose size and alignment
match that of an integer type.
-fno-short-double By de faul t, th e c om pil er u ses a double type equiva len t to float.
This option makes double equivalent to long double. Mixing
this option across modules can have unexpected results if
modules share double data either directly through argument
passage or indirectly through shared buffer space. Libraries
provided with the product function with either switch setting.
-fshort-enums Allocate to an enum type only as many bytes as it needs for the
declared range of possible values. Specifically, the enum type is
equivalent to the smallest integer type that has enough room.
-fverbose-asm
-fno-verbose-asm Put ex tra comment ary info rmation in the genera ted assem bly code
to make it more readable.
-fno-verbose-asm, the default, causes the extra information to
be omitted and is useful when comparing two assembler files.
-fvolatile Consider all memory references through pointers to be volatile.
-fvolatile-global Consider all memory references to external and global data items
to be volatile. The use of this switch has no effect on static data.
-fvolatile-static Consider all memory references to static data to be volatile.
TABLE 3-18: CODE GENE RATION CONVENTION OPTIONS (CONTINUED)
Option Definition
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Chapter 4. Device-Related Features
4.1 INTRODUCTION
The MPLAB XC32 C/C++ Compiler supports a number of special features and exten-
sions to the C/C++ language which are designed to ease the task of producing
ROM-based applications. This chapter documents the special language features which
are specific to these devices.
• Device Sup por t
• Device Head er Files
•Stack
• Using SFRs From C Code
4.2 DEVICE SUPPORT
MPLAB XC32 C/C++ Compiler aims to support all PIC32 devices. However, new
devices in these families are frequently released. Check the readme document for a full
list of all available devices.
4.3 DEVICE HE ADER FILES
There is one header file that is recommended be included into each source file you
write. The file is <xc.h> and is a generic file that will include other device-specific
header files when you build your project.
Inclusion of this file will allow access to SFRs via special variables, as well as
#defines which allow the use of conventional register names from within assembly
langu age files .
4.3.1 CP0 Register Definitions Header File
The CP0 register definitions header file (cp0defs.h) is a file that contains definitions
for the CP0 registers and their fields. In addition, it contains macros for accessing the
CP0 registers.
The CP0 register definitions header file is located in the pic32mx/include directory
of your compiler installation directory. The CP0 register definitions header file is
automatically included when you include the generic device header file, xc.h.
The CP0 register definitions header file was designed to work with either Assembly or
C/C++ files. The CP0 register definitions header file is dependent on macros defined
within the processor generic header file).
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4.4 STACK
The PIC32 devices use what is referred to in this user’s guide as a “software stack”.
This is the typical stack arrangement employed by most computers and is ordinary data
memory accessed by a push-and-pop type instruction and a stack pointer register . The
term “hardware stack” is used to describe the stack employed by Microchip 8-bit
devices, which is only used for storing function return addresses.
The PIC32 devices use a dedicated stack pointer register sp (register 29) for use as a
software Stack Pointer. All processor stack operations, including function calls, inter-
rupts and exceptions, use the software stack. It points to the next free location on the
stack. The stack grows downward, towards lower memory addresses.
By default, the size of the stack is 1024 bytes. The size of the stack may be changed
by specifying the size on the linker command line using the
--defsym_min_stack_size linker command line option. An example of allocating
a stack of 2048 bytes using the command line is:
xc32-gcc foo.c -Wl,--defsym,_min_stack_size=2048
The run-time stack grows downward from higher addresses to lower addresses. Two
working registers are used to manage the stack:
• Register 29 (sp) – This is the Stack Pointer. It points to the next free location on
the stack.
• Register 30 (fp) – This is the Frame Pointer. It points to the current function’s
frame.
No stack overflow detection is supplied.
The C/C++ run-time start-up module initializes the stack pointer during the start-up
and initialization sequence, see Section 12.3.2 “Initialize Stack Pointer and Heap”.
4.4.1 Configuration Bit Access
The PIC32 devices have several locations which contain the Configuration bits or
fuses. These bits specify fundamental device operation, such as the oscillator mode,
watchdog timer , programming mode and code protection. Failure to correctly set these
bits may result in code failure, or a non-running device.
The #pragma config directive specifies the processor-specific configuration
settings (i.e., Configuration bits) to be used by the application. Refer to the “PIC32MX
Configuration Settings” online help (found under MPLAB
IDE>Help>Topics>Language Tools) for more information. (If using the compiler from
the command line, this help file is located at the default location at:
Program Files/Microchip/<install-dir>/doc/hlpPIC32MXConfigSet.chm.)
Configuration settings may be specified with multiple #pragma config directives.
The compiler verifies that the configuration settings specified are valid for the processor
for which it is compiling. If a given setting in the Configuration word has not been
specifi ed in any #pragma config directive, the bits associated with that setting
default to the unprogrammed value. Configuration settings should be specified in only
a single translation unit (a C/C++ file with all of its include files after preprocessing).
For each Configuration word for which a setting is specified with the #pragma config
directive, the compiler generates a read-only data section named .config_address,
where address is the hexadecimal representation of the address of the Configuration
word. For example, if a configuration setting was specified for the Configuration word
located at address 0xBFC02FFC, a read-only data section named
.config_BFC02FFC would be created.
•Syntax
•Example
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2012 Microchip Technology Inc. DS51686E-page 87
4.4.1.1 SYNTAX
The following shows the meta syntax notation for the different forms the pragma may
take.
pragma-config-directive:
# pragma config setting-list
setting-list:
setting
| setting-list, setting
setting:
setting-name = value-name
The setting-name and value-name are device specific and can be determined by
utilizing the PIC32MX Configuration Settings document.
All #pragma config directives should be placed outside of a function definition as
they do not define executable code.
4.4.1.2 EXAMPLE
The following ex amp le sho ws how the #pragma config directive might be utilized.
The example does the following:
• Enables the Watchdog Timer
• Sets the Watchdog Postscaler to 1:128
• Selects th e HS Oscillator for the Primary Oscillator
#pragma config FWDTEN = ON, WDTPS = PS128
#pragma config POSCMOD = HS
...
int main (void)
{
...
}
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4.5 USING SFRS FR OM C CODE
The Special Function Registers (SFRs) are registers which control aspects of the MCU
operation or that of peripheral modules on the device. These registers are memory
mapped, which means that they appear at specific addresses in the device memory
map. With some registers, the bits within the register control independent features.
Memory-mapped SFRs are accessed by special C variables that are placed at the
addresses of the registers and use special attributes. These variables can be accessed
like any ordinary C variable so that no special syntax is required to access SFRs.
The SFR variables are predefined in header files and will be accessible once the
<xc.h> header file (see Section 4.3 “Device Header Files”) has been included into
your source code. Structures are also defined by these header files to allow access to
bits within the SFR.
The names given to the C variables, which map over the registers and bit variables, or
bit fields, within the registers are based on the names specified in the device data
sheet. The names of the structures that hold the bit fields will typically be those of the
corresponding register followed by bits. For example, the following shows code that
includes the generic header file, clears PORTB as a whole and sets bit 2 of PORTB
using the structure/bit field definitions.
#include <xc.h>
int main(void)
{PORTB = 0x00;
PORTBbits.RB2 = 1;
}
For use with assembly, the PORTB register is declared as: .extern PORTB.
To confirm the names that are relevant for the device you are using, check the device
specific header file that <xc.h> will include for the definitions of each variable. These
file s wi ll be l ocat ed in th e pic32mx/include/proc directory of the compiler and will
have a name that represents the device. There is a one-to-one correlation between
device and header file name that will be included by <xc.h>, e.g. when compiling for
a PIC32MX360F512L device, the <xc.h> header file will include
<p32mx360f512l.h>. Remember that you do not need to include this chip-specific
file into your source code; it is automatically included by <xc.h>.
Some of the PIC32 SFRs have associated registers that allow the bits within the SFR
to be set, cleared or toggled atomically. For example, the PORTB SFR has the write-only
registers PORTBSET, PORTBCLR and PORTBINV associated with it. Writing a ‘1’ to a bit
location in these registers sets, clears or toggles, respectively , the corresponding bit in
the PORTB SFR. So to set bit 1 in PORTB, you can use the following code:
PORTBSET = 0x2;
or alternatively, using macros provided in the device header files:
PORTBSET = _PORTB_RB1_MASK;
The same operation can also be achieved using the peripheral library functions, for
example
mPORTBSetBits(BIT_1);
Always ensure that you confirm the operation of peripheral modules from the device
data sheet.
Note: The symbols PORTB and PORTBbits refer to the same register and resolve
to the same address. Writing to one register will change the values held by
both.
Device-Related Features
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4.5.1 CP0 Register Definitions
When the CP0 register definitions header file is included from an Assembly file, the
CP0 registers are defined as:
#define _CP0_register_name $register_number, select_number
For example, the IntCtl register is defined as:
#define _CP0_INTCTL $12, 1
When the CP0 register definitions header file is included from a C file, the CP0 registers
and selects are defined as:
#define _CP0_register_name register_number
#define _CP0_register_name_SELECT select_number
For example, the IntCtl register is defined as:
#define _CP0_INTCTL 12
#define _CP0_INTCTL_SELECT 1
4.5.2 CP0 Register Fie ld Definitions
When the CP0 register definitions header file is included from either an Assembly or a
C/C++ file, three #defines exist for each of the CP0 register fields.
_CP0_register_name_field_name_POSITION – the starting bit location
_CP0_register_name_field_name_MASK – the bits that are part of this field are
set
_CP0_register_name_field_name_LENGTH – the number of bits that this field
occupies
For example, the vector spacing field of the IntCtl register has the following defines:
#define _CP0_INTCTL_VS_POSITION 0x00000005
#define _CP0_INTCTL_VS_MASK 0x000003E0
#define _CP0_INTCTL_VS_LENGTH 0x00000005
4.5.3 CP0 Access Macros
When the CP0 register definitions header file is included from a C file, CP0 access
macros are defined. Each CP0 register may have up to six different access macros
defined:
_CP0_GET_register_name () Returns the value for register, register_name.
_CP0_SET_register_name (val) Sets the register, register_name, to val, and
returns void. Only defined for registers that contain a
writable field.
_CP0_XCH_register_name (val) Sets the register, register_name, to val, and
returns the previous register value. Only defined for
registers that contain a writable field.
_CP0_BIS_register_name (set) Sets the register, register_name, to (reg |= set),
and returns the previous register value. Only defined
for registers that contain writable bit fields.
_CP0_BIC_register_name (clr) Sets th e register , register_name, to (reg &= ~clr),
and returns the previous register value. Only defined
for registers that contain writable bit fields.
_CP0_BCS_register_name (clr,
set) Sets the register, register_name, to
(reg = (reg & ~clr) | set), and returns the previous
register value. Only defined for registers that contain
writable bit fiel ds.
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4.5.4 Address Translation Macros
System code may need to translate between virtual and physical addresses, as well as
between kernel segment addresses. Macros are provided to make these translations
easier and to determine the segment an address is in.
KVA_TO_PA(v) Translate a kernel virtual address to a physical address.
PA_TO_KVA0(pa) Translate a physical address to a KSEG0 virtual address.
PA_TO_KVA1(pa) Translate a physical address to a KSEG1 virtual address.
KVA0_TO_KVA1(v) Translate a KSEG0 virtual address to a KSEG1 virtual address.
KVA1_TO_KVA0(v) Translate a KSEG1 virtual address to a KSEG0 virtual address.
IS_KVA(v) Evaluates to 1 if the address is a kernel segment virtual address, zero
otherwise.
IS_KVA0(v) Evalu ate to 1 if the ad dress is a KSEG0 virtua l addres s, zero otherwis e.
IS_KVA1(v) Evalu ate to 1 if the ad dress is a KSEG1 virtua l addres s, zero otherwis e.
IS_KVA01(v) Evaluate to 1 if the address is either a KSEG0 or a KSEG1 virtual
address, zero otherwise.
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Chapter 5. ANSI C Standard Issues
This compiler conforms to the ANS X3.159-1989 Standard for programming languages.
This is commonly called the C89 Standard. It is referred to as the ANSI C Standard in
this manual. Some features from the later standard C99 are also supported.
• Divergence from the ANSI C Standard
• Extensions to the ANSI C Standard
• Implementation-defined behavior
5.1 DIVERGENCE FROM THE ANSI C STANDARD
There are no divergences from the ANSI C standard.
5.2 EXTENSIONS TO THE ANSI C STANDARD
C/C++ code for the MPLAB XC32 C/C++ Compiler differs from the ANSI C standard in
these areas: keywords, statements and expressions.
5.2.1 Keyword Differences
The new keywords are part of the base GCC implementation and the discussions in the
referenced sections are based on the standard GCC documentation, tailored for the
specific syntax and semantics of the 32-bit compiler port of GCC.
• Specifying Attributes of Variables – Section 6.12 “Variable Attributes”
• Specifying Attributes of Functions – Section 10.2 “Function Attributes and
Specifiers”
• Inline Functions – Section 10.9 “Inline Functions”
• Variables in Specified Registers – Section 6.12 “Variable Attributes”
• Comple x Numb ers – Section 6.8 “Complex Data Types”
• Referring to a Type with typeof – Section 6.10 “Standard Type Qualifiers”
5.2.2 Statement Differences
The statement differences are part of the base GCC implementation, and the discus-
sions in the referenced sections are based on the standard GCC documentation,
tailored for the specific syntax and semantics of the 32-bit compiler port of GCC.
• Labels as Values – Section 8.4 “Labels as Values”
• Conditionals with Omitted Operands – Section 8.5 “Conditional Operator Op er-
ands”
• Case Ranges – Section 8.6 “Case Ranges”
5.2.3 Expression Differences
Expression differences are:
• Binary constants – Section 6.9 “Constant Types and Formats”.
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5.3 IMPLEMENTATION-DEFINED BEHAVIOR
Certain features of the ANSI C standard have implementation-defined behavior. This
means that the exact behavior of some C code can vary from compiler to compiler . The
exact behavior of the MPLAB XC32 C/C++ Compiler is detailed throughout this docu-
mentation, and is fully summarized in Appendix 18. “Implementation-Defined
Behavior”.
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Chapter 6. Supp orte d Da ta Types and Variab le s
6.1 INTRODUCTION
The MPLAB XC32 C/C++ Compiler supports a variety of data types and attributes.
These data types and variables are discussed here. For information on where variables
are stored in memory, see Chapter 7. “Memory Allocation and Access”.
• Data Representation
• Integer Data Types
• Floating-Point Data Types
• Structures and Uni ons
• Pointer Types
• Comple x Data Types
• Constant Types and For mats
• Standard Type Qualifiers
• Compiler-Specific Qualifiers
• Variable Attributes
6.2 IDENTIFIERS
A C/C++ variable identifier (the following is also true for function identifiers) is a
sequence of letters and digits, where the underscore character “_” counts as a letter.
Identifiers cannot start with a digit. Although they may start with an underscore, such
identifiers are reserved for the compiler’s use and should not be defined by your pro-
grams. Such is not the case for assembly domain identifiers, which often begin with an
underscore
Identifier s are case se ns iti ve, so main is different than Main.
All characters are significant in an identifier , although identifiers longer than 31 charac-
ters in length are less portable.
6.3 DATA REPR ES EN TATI ON
The compiler stores multibyte values in little-endian format. That is, the Least
Significant Byte is stored at the lowest address.
For example, the 32-bit value 0x12345678 would be stored at address 0x100 as:
Address 0x100 0x101 0x102 0x103
Data 0x78 0x56 0x34 0x12
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6.4 INTEGER DATA TYPES
Integer values in the compiler are represented in 2’s complement and vary in size from
8 to 64 bits. These values are available in compiled code via limits.h.
6.4.1 Signed and Unsigned Character Types
By default, values of type plain char are signed values. This behavior is
implementation-defined by the C standard, and some environments1 define a plain
C/C++ char value to be unsigned. The command line option -funsigned-char can
be used to set the default type to unsigned for a given translation unit.
6.4.2 limits.h
The limits.h header file defines the ranges of values which can be represented by
the integer types.
Type Bits Min Max
char, signed char 8 -128 127
unsigned char 80255
short, signed short 16 -32768 32767
unsigned short 16 0 65535
int, signed int, long, signed long 32 -231 231-1
unsigned int, unsigned long 32 0 232-1
long long, signed long long 64 -263 263-1
unsigned long long 64 0 264-1
1. Notably, PowerPC and ARM.
Macro name Value Description
CHAR_BIT 8 The size, in bits, of the smallest non-bit field
object.
SCHAR_MIN -128 The minimum value possible for an object of
type signed char.
SCHAR_MAX 127 The maximu m value pos s ible for an object of
type signed char.
UCHAR_MAX 255 The maximu m value pos s ible for an object of
type unsigned char.
CHAR_MIN -128 (or 0, see
Section 6.4.1 “Signed
and Unsigned
Character Types”)
The minimum value possible for an object of
type char.
CHAR_MAX 127 (or 255, see
Section 6.4.1 “Signed
and Unsigned
Character Types”)
The maximum value possible for an object of
type char.
MB_LEN_MAX 16 The maximum length of multibyte character in
any locale.
SHRT_MIN -32768 The minimum value possible for an object of
type short int.
SHRT_MAX 32767 The maximum value possible for an object of
type short int.
USHRT_MAX 65535 The maximum value possible for an object of
type unsigned short int.
Supported Data Types and Variables
2012 Microchip Technology Inc. DS51686E-page 95
INT_MIN -231 The minimum value possible for an object of
type int.
INT_MAX 231-1 The maximum value possible for an object of
type int.
UINT_MAX 232-1 The maximum value possible for an object of
type unsigned int.
LONG_MIN -231 The minimum value possible for an object of
type long.
LONG_MAX 231-1 The maximum value possible for an object of
type long.
ULONG_MAX 232-1 The maximum value possible for an object of
type unsigned long.
LLONG_MIN -263 The minimum value possible for an object of
type long long.
LLONG_MAX 263-1 The maximum value possible for an object of
type long long.
ULLONG_MAX 264-1 The maximum value possible for an object of
type unsigned long long.
Macro name Value Description
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6.5 FLOATING-POINT DATA TYPES
The compiler uses the IEEE-754 floating-point format. Detail regarding the
implementation limits is available to a translation unit in float.h.
Variables may be declared using the float, double and long double keywords,
respectively , to hold values of these types. Floating-point types are always signed and
the unsigned keyword is illegal when specifying a floating-point type. All floating-point
values are represented in little endian format with the Least Significant Byte at the
lower address.
This format is described in Table 6-1, where:
• Sign is the sign bit which indicates if the number is positive or negative
• For 32-bit floating point values, the exponent is 8 bits which is stored as excess
127 (i.e. an exponent of 0 is stored as 127).
• For 64-bit floating point values, the exponent is 11 bits which is stored as excess
1023 (i.e. an exponent of 0 is stored as 1023).
• Mantissa is the mantissa, which is to the right of the radix point. There is an
implied bit to the left of the radix point which is always 1 except for a zero value,
where the implied bit is zero. A zero value is indicated by a zero exponent.
The value of this number for 32-bit floating point values is:
(-1)sign x 2(exponent-127) x 1. mantissa
and for 64-bit values
(-1)sign x 2(exponent-1023) x 1. mantissa.
Here is an example of the IEEE 754 32-bit format shown in Table 6-1. Note that the
Most Significant bit of the mantissa column (i.e. the bit to the left of the radix point) is
the implied bit, which is assumed to be 1 unless the exponent is zero (in which case
the float is zero).
The example in Table 6-1 can be calculated manually as follows.
The sign bit is zero; the biased exponent is 251, so the exponent is 251-127=124. Take
the binary number to the right of the decimal point in the mantissa. Convert this to dec-
imal and divide it by 223 where 23 is the number of bits taken up by the mantissa, to
give 0.302447676659. Add 1 to this fraction. The floating-point number is then given
by:
-1021241.302447676659
which becomes:
12.126764793256e+371.302447676659
which is approximately equal to:
2.77000e+37
Type Bits
float 32
double 32
long double 64
TABLE 6-1: FLOATING-POINT FORMAT EXAMPLE IEEE 7 54
Format Number Biased exponen t 1.mantissa Decimal
32-bit 7DA6B69Bh
11111011b 1.0100110101101101
0011011b 2.77000e+37
(251) (1.302447676659) —
Supported Data Types and Variables
2012 Microchip Technology Inc. DS51686E-page 97
Binary floating-point values are sometimes misunderstood. It is important to remember
that not every floating-point value can be represented by a finite sized floating-point
number. The size of the exponent in the number dictates the range of values that the
number can hold, and the size of the mantissa relates to the spacing of each value that
can be represented exactly. Thus the 64-bit floating-point format allows for values with
a larger range of values and that can be more accurately represented.
So, for example, if you are using a 32-bit wide floating-point type, it can exactly store
the value 95000.0. However, the next highest number it can represent is (approxi-
mately) 95000.00781 and it is impossible to represent any value in between these two
in such a type as it will be rounded. This implies that C/C++ code which compares float-
ing-point type may not behave as expected. For example:
volatile float myFloat;
myFloat = 95000.006;
if(myFloat == 95000.007) // value will be rounded
LATA++; // this line will be executed!
in which the result of the if() expression will be true, even though it appears the two
values being compared are different.
The characteristics of the floating-point formats are summarized in Table 6-2. The sym-
bols in this table are preprocessor macros which are available after including
<float.h> in your source code. Two sets of macros are available for float and
double types, where XXX represents FLT and DBL, respectively. So, for example,
FLT_MAX represents the maximum floating-point value of the float type. DBL_MAX
represents the same values for the double type. As the size and format of float-
ing-point data types are not fully specified by the ANSI Standard, these macros allow
for more portable code which can check the limits of the range of values held by the
type on this implementation.
TABLE 6-2: RANGES OF FLOATING-POINT TYPE VALUES
Symbol Meaning 32-bit Value 64-bit Value
XXX_RADIX Radix of exponent representation 2 2
XXX_ROUNDS Rounding mode for addition 1
XXX_MIN_EXP Min. n such that FL T_RADIXn-1 is
a normalized float value -125 -1021
XXX_MIN_10_E
XP Min. n such that 10n is a
normalized float value -37 -307
XXX_MAX_EXP Max. n such that FLT_RADIXn-1
is a normalized float value 128 1024
XXX_MAX_10_E
XP Max. n such that 10n is a
normalized float value 38 308
XXX_MANT_DIG Number of FLT_RADIX ma ntis s a
digits 24 53
XXX_EPSILON The smallest number whi ch
added to 1.0 does not yield 1.0 1.1920929e-07 2.22044604925
03131e-16
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6.6 STRUCTURES AND UNIONS
MPLAB XC32 C/C++ Compiler supports struct and union types. Structures and
unions only differ in the memory offset applied to each member.
These types will be at least 1 byte wide. Bit fields are fully supported.
No padding of structure members is added.
S tructures and unions may be passed freely as function arguments and function return
values. Pointers to structures and unions are fully supported.
6.6.1 Structure and Union Qualifiers
The MPLAB XC32 C/C++ Compiler supports the use of type qualifiers on structures.
When a qualifier is applied to a structure, all of its members will inherit this qualification.
In the following example the structure is qualified const.
const struct {
int number;
int *ptr;
} record = { 0x55, &i };
In this case, the entire structure will be placed into the program memory and each
member will be read-only. Remember that all members are usually initialized if a struc-
ture is const as they cannot be initialized at runtime.
If the members of the structure were individually qualified const, but the structure was
not, then the structure would be positioned into RAM, but each member would be
read-only. Compare the following structure with the above.
struct {
const int number;
int * const ptr;
} record = { 0x55, &i};
6.6.2 Bit Fields in Structures
MPLAB XC32 C/C++ Compiler fully supports bit fields in structures.
Bit fields are always allocated within 8-bit storage units, even though it is usual to use
the ty pe unsigned int in the definition. Storage units are aligned on a 32-bit bound-
ary, although this can be changed using the packed attribute.
The first bit defined will be the Least Significant bit of the word in which it will be stored.
When a bit field is declared, it is allocated within the current 8-bit unit if it will fit; other-
wise, a new byte is allocated within the structure. Bit fields can never cross the bound-
ary between 8-bit allocation units. For example, the declaration:
struct {
unsigned lo : 1;
unsigned dummy : 6;
unsigned hi : 1;
} foo;
will produce a structure occupying 1 byte. If foo was ultimately linked at address 10H,
the field lo will be bit 0 of address 10H; hi will be bit 7 of address 10H. The Least Sig-
nifi cant bit of dummy will be bit 1 of address 10H and the Most Significant bit of dummy
will be bit 6 of address 10h.
Supported Data Types and Variables
2012 Microchip Technology Inc. DS51686E-page 99
Unnamed bit fields may be declared to pad out unused space between active bits in
control registers. For example, if dummy is never referenced, the structure above could
have been decl ar ed as:
struct {
unsigned lo : 1;
unsigned : 6;
unsigned hi : 1;
} foo;
A structure with bit fields may be initialized by supplying a comma-se p arated li st of i ni -
tial values for each field. For example:
struct {
unsigned lo : 1;
unsigned mid : 6;
unsigned hi : 1;
} foo = {1, 8, 0};
S tructures with unnamed bit fields may be initialized. No initial value should be supplied
for the unnamed members, for example:
struct {
unsigned lo : 1;
unsigned : 6;
unsigned hi : 1;
} foo = {1, 0};
will initia lize the members lo and hi correctly.
The MPLAB XC compiler supports anonymous unions. These are unions with no iden-
tifier and whose members can be accessed without referencing the enclosing union.
These unions can be used when placing inside structures. For example:
struct {
union {
int x;
double y;
};
} aaa;
int main(void)
{aaa.x = 99;
// ...}
Here, the union is not named and its members accessed as if they are part of the struc-
ture. Anonymous unions are not part of any C Standard and so their use limits the por-
tability of any code.
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6.7 POINTER TYPES
There are two basic pointer types supported by the MPLAB XC32 C/C++ Compiler:
data pointers and function pointers. Data pointers hold the addresses of variables
which can be indirectly read, and possible indirectly written, by the program. Function
pointers hold the address of an executable function which can be called indirectly via
the pointer.
6.7.1 Combining Type Qualifiers and Pointers
It is helpful to first review the ANSI C/C++ standard conventions for definitions of
pointer typ es.
Pointers can be qualified like any other C/C++ object, but care must be taken when
doing so as there are two quantities associated with pointers. The first is the actual
pointer itself, which is treated like any ordinary C/C++ variable and has memory
reserved for it. The second is the target, or targets, that the pointer references, or to
which the pointer points. The general form of a pointer definition looks like the following:
target_type_&_qualifiers * pointer’s_qualifiers pointer’s_name;
Any qualifiers to the right of the * (i.e. next to the pointer’s name) relate to the pointer
variable itself. The type and any qualifiers to the left of the * relate to the pointer’s tar-
gets. This makes sense since it is also the * operator that dereferences a pointer , which
allows you to get from the pointer variable to its current target.
Here are three examples of pointer definitions using the volatile qualifier . The fields
in the definitions have been highlighted with spacing:
volatile int * vip ;
int * volatile ivp ;
volatile int * volatile vivp ;
The first example is a pointer called vip. It contains the address of int objects that
are qualified volatile. The pointer itself — the variable that holds the address — is
not volatile; however, the objects that are accessed when the pointer is derefer-
enced are treated as being volatile. In other words, the target objects accessible via
the pointer may be externally modified.
The second example is a pointer called ivp which also contains the address of int
objects. In this example, the pointer itself is volatile, that is, the address the pointer
contains may be externally modified; however , the objects that can be accessed when
dereferencing the pointer are not volatile.
The last example is of a pointer called vivp which is itself qualified volatile, and
which also holds the address of volatile objects.
Bear in mind that one pointer can be assigned the addresses of many objects; for
example, a pointer that is a parameter to a function is assigned a new object address
every time the function is called. The definition of the pointer must be valid for every
target address assigned.
6.7.2 Data Pointers
Pointers in the compiler are all 32 bits in size. These can hold an address which can
reach all memory locations.
Note: Care must be taken when describing pointers. Is a “const pointer” a pointer
that points to const objec ts, or a po int er t hat is const itself? You can talk
about “pointers to const” and “const pointers” to help clarify the definition,
but such terms may not be universally understood.
Supported Data Types and Variables
2012 Microchip Technology Inc. DS51686E-page 101
6.7.3 Function Pointers
The MPLAB XC compiler fully supports pointers to functions, which allows functions to
be called indirectly. These are often used to call one of several function addresses
stored in a user-defined C/C++ array, which acts like a lookup table.
Function pointers are always 32 bits in size and hold the address of the function to be
called.
Any attempt to call a function with a function pointer containing NULL will result in an
ifetch Bus Error.
6.7.3.1 S PECIAL POINTER TARGETS
Pointers and integers are not interchangeable. Assigning an integer constant to a
pointer will generate a warning to this effect. For example:
const char * cp = 0x123; // the compiler will flag this as bad code
There is no information in the integer constant, 0x123, relating to the type or size of the
destination. This code is also not portable and there is a very good chance of code fail-
ure if pointers are assigned integer addresses and dereferenced, particularly for PIC®
devices that have more than one memory space.
Always take the address of a C/C++ object when assigning an address to a pointer. If
there is no C/C++ object defined at the destination address, then define or declare an
object at this address which can be used for this purpose. Make sure the size of the
object matches the range of the memory locations that can be accessed.
For example, a checksum for 1000 memory locations starting at address 0xA0001000
is to be generated. A pointer is used to read this data. You may be tempted to write
code such as :
int * cp;
cp = 0xA0001000; // what resides at 0xA0001000???
and increment the pointer over the data. A much better solution is this:
int * cp;
int __attribute__((address(0xA0001000))) inputData [1000];
cp = &inputData;
// cp is incremented over inputData and used to read values there
In th is ca se, th e c om piler can de te rm in e t h e si ze of t h e t a r get a nd the me m ory space.
The array size and type indicates the size of the pointer target.
Take care when comparing (subtracting) pointers. For example:
if(cp1 == cp2)
; take appropriate action
The ANSI C standard only allows pointer comparisons when the two pointer targets are
the same object. The address may extend to one element past the end of an array.
Comparisons of pointers to integer constants are even more risky, for example:
if(cp1 == 0xA0000100)
; take appropriate action
A NULL pointer is the one instance where a constant value can be assigned to a pointer
and this is handled correctly by the compiler. A NULL pointer is numerically equal to 0
(zero), but this is a special case imposed by the ANSI C standard. Comparisons with
the macro NULL are also allowed.
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6.8 COMPLEX DATA TY PES
Complex data types are currently not implemented in MPLAB XC32 C/C++ Compiler.
6.9 CONSTANT TYPES AND FORMATS
A constant is used to represent a numerical value in the source code, for example 123
is a constant. Like any value, a constant must have a C/C++ type. In addition to a con-
stant’s type, the actual value can be specified in one of several formats. The format of
integral constants specifies their radix. MPLAB XC32 C supports the ANSI standard
radix specifiers as well as ones which enables binary constants to be specified in C
code.
The formats used to specify the radices are given in Table 6-3. The letters used to spec-
ify binary or hexadecimal radices are case insensitive, as are the letters used to specify
the hexadecimal digits.
Any integral constant will have a type of int, long int or long long int, so that
the type can hold the value without overflow. Constants specified in octal or hexadeci-
mal may also be assigned a type of unsigned int, unsigned long int or
unsigned long long int if the signed counterparts are too small to hold the value.
The default types of constants may be changed by the addition of a suffix after the dig-
its, e.g. 23U, where U is the suffix. Table 6-4 shows the possible combination of suffixes
and the types that are considered when assigning a type. So, for example, if the suffix
l is specified and the value is a decimal constant, the compiler will assign the type
long int, if that type will hold the constant; otherwise, it will assigned long long
int. If the constant was specified as an octal or hexadecimal constant, then unsigned
types are also considered.
Here is an example of code that may fail because the default type assigned to a con-
stant is not appropriate:
unsigned long int result;
TABLE 6-3: RADIX FORMATS
Radix Format Example
binary 0b number or 0B number 0b10011010
octal 0 number 0763
decimal number 129
hexadecimal 0x number or 0X number 0x2F
TABLE 6-4: SUFFIXES AND ASSIGNED TYPES
Suffix Decimal Octal or Hexadecimal
u or Uunsigned int
unsigned long int
unsigned long long int
unsigned int
unsigned long int
unsigned long long int
l or Llong int
long long int long int
unsigned long int
long long int
unsigned long long int
u or U, and l or Lunsigned long int
unsigned long long int unsigned long int
unsigned long long int
ll or LL long long int long long int
unsigned long long int
u or U, and ll or LL unsigned long long int unsigned long long int
Supported Data Types and Variables
2012 Microchip Technology Inc. DS51686E-page 103
unsigned char shifter;
int main(void)
{shifter = 40;
result = 1 << shifter;
// code that uses result
}
The constant 1 will be assigned an int type hence the result of the shift operation will
be an int and the upper bits of the long variabl e, result, can never be set, regard-
less of how much the constant is shifted. In this case, the value 1 shifted left 40 bits will
yield the result 0, not 0x10000000000.
The following uses a suffix to change the type of the constant, hence ensure the shift
result has an unsigned long type.
result = 1UL << shifter;
Floatin g-poi nt con stants have double type unless suffixed by f or F, in which case it
is a float co ns tant. The suffixes l or L specify a long double type.
Character constants are enclosed by single quote characters, ’, for example ’a’. A
character constant has int type, although this may be optimized to a char type later
in the compilation.
Multi-byte character constants are accepted by the compiler but are not supported by
the standard libraries.
S tring constants, or string literals, are enclosed by double quote characters “, for exam-
ple “hello world”. The type of string constants is const char * and the character
that make up the string are stored in the program memory, as are all objects qualified
const.
To comply with the ANSI C standard, the compiler does not support the extended char-
acter set in characters or character arrays. Instead, they need to be escaped using the
backslash character, as in the following example:
const char name[] = "Bj\370rk";
printf(“%s's Resum\351”, name); \\ prints “Bjørk's Resumé”
Assigning a string literal to a pointer to a non-const char will generate a warning from
the compiler. This code is legal, but the behavior if the pointer attempts to write to the
string will fail. For example:
char * cp= “one”; // “one” in ROM, produces warning
const char * ccp= “two”; // “two” in ROM, correct
Defining and initializing a non-const array (i.e. not a pointer definition) with a string,
for example:
char ca[]= “two”; // “two” different to the above
is a special case and produces an array in data space which is initialized at start-up
with the string “two” (copied from program space), whereas a string constant used in
other contexts represents an unnamed const -qualified array , accessed directly in pro-
gram space.
The MPLAB XC32 C/C++ Compiler will use the same storage location and label for
strings that have identical character sequences. For example, in the code snippet
if(strncmp(scp, “hello world”, 6) == 0)
fred = 0;
if(strcmp(scp, “hello world”) == 0)
fred++;
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the two identical character string greetings will share the same memory locations. The
link-time optimization must be enabled to allow this optimization when the strings may
be located in different modules.
Two adjacent string constants (i.e. two strings separated only by white space) are con-
cat enated by the compiler. Thus:
const char * cp = “hello” “ world”;
will assign the pointer with the address of the string “hello world “.
6.10 STANDARD TYPE QUALIFIERS
Type qualifiers provide additional information regarding how an object may be used.
The MPLAB XC32 C/C++ Compiler supports both ANSI C qualifiers and additional spe-
cial qualifiers which are useful for embedded applications and which take advantage of
the PIC MCU architecture.
6.10.1 Const Type Qualifier
The MPLAB XC32 C/C++ Compiler supports the use of the ANSI type qualifiers const
and volatile.
The const type qualifier is used to tell the compiler that an object is read only and will
not be modified. If any attempt is made to modify an object declared const, the com-
piler will issue a warning or error.
Usually a const object must be initialized when it is declared, as it cannot be assigned
a value at any point at runtime. For example:
const int version = 3;
will define version as being an int variable that will be placed in the program mem-
ory, will always contain the value 3, and which can never be modified by the program.
Objects qualified const are placed into the program memory unless the
-mno-embedded-data option is used.
6.10.2 Volatile Type Qualifier
The volatile type qualifier is used to tell the compiler that an object cannot be guar-
anteed to retain its value between successive accesses. This prevents the optimizer
from eliminating apparently redundant references to objects declared volatile
because it may alter the behavior of the program to do so.
Any SFR which can be modified by hardware or which drives hardware is qualified as
volatile, and any variables which may be modified by interrupt routines should use
this qualifier as well. For example:
extern volatile unsigned int WDTCON __attribute__((section("sfrs")));
The volatile qualifier does not guarantee that any access will be atomic, but the
compiler will try to implement this.
The code produced by the compiler to access volatile objects may be different than
that to access ordinary variables, and typically the code will be longer and slower for
volatile objects, so only use this qualifier if it is necessary. However failure to use
this qualifier when it is required may lead to code failure.
Another use of the volatile keyword is to prevent variables from being removed if
they are not used in the C/C++ source. If a non-volatile variable is never used, or
used in a way that has no ef fect on the program’s function, then it may be removed
before code is generated by the compiler.
Supported Data Types and Variables
2012 Microchip Technology Inc. DS51686E-page 105
A C/C++ statement that consists only of a volatile variable’s name will produce code
that reads the variable’s memory location and discards the result. For example the
entire statement:
PORTB;
will produce assembly code the reads PORTB, but does nothing with this value. This is
useful for some peripheral registers that require reading to reset the state of interrupt
flags. Normally such a statement is not encoded as it has no effect.
6.11 COMPILER-SPECIFIC QUALIFIERS
There are no non-standard qualifiers implemented in MPLAB XC32 C/C++ Compiler.
Attributes are used to control variables and functions.
6.12 VARIABLE ATTRIBUTES
The compiler keyword attribute allows you to specify special attributes of variables
or structure fields. This keyword is followed by an attribute specification inside double
parentheses.
To specify multiple attributes, separate them by commas within the double
parentheses, for example:
attribute ((aligned (16), packed)).
address (addr)
Specify an absolute virtual address for the variable. This attribute can be used in
conjunction with a section attribute. For data variables, the address is typically in the
range [0xA0000000,0xA00FFFFC], as defined in the linker script as the
‘kseg1_data_mem’ region. This attribute can be used to start a group of variables at a
specific address:
int foo __attribute__((section(“mysection”),address(0xA0001000)));
int bar __attribute__((section(“mysection”)));
int baz __attribute__((section(“mysection”)));
Keep in mind that the compiler performs no error checking on the specified address.
The section will be located at the specified address regardless of the memory-region
ranges listed in the linker script or the actual ranges on the target device. This
application code is responsible for ensuring that the address is valid for the target
device and application.
Also, be aware that variables attributed with an absolute address are not accessed via
GP-relative addressing. This means that they may be more expensive to access than
non-address attributed variables.
In addition, to make effective use of absolute sections and the new best-fit allocator,
standard program-memory and data-memory sections should not be mapped in the
linker script. The built-in linker script does not map most standard sections such as the
.text, .data, .bss, or .ramfunc section. By not mapping these sections in the
linker script, we allow these sections to be allocated using the best-fit allocator rather
than the sequential allocator. Sections that are unmapped in the linker script can flow
around absolute sections whereas sections that are linker-script mapped are grouped
together and allocated sequentially , potentially causing conflicts with absolute sections.
Note: It is important to use variable attributes consistently throughout a project.
For example, if a variable is defined in file A with the aligned attribute, and
declared extern in file B without aligned, then a link error may res ul t.
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Finally , note that “small” data and bss (.sdata, .sbss, etc.) sections are still mapped
in the built-in default linker script. This is because “small” data variables must be
grouped together so that they are within range of the more ef ficient GP-relative
addressing mode. To avoid conflict with these linker-script mapped sections, choose
high addresses for your absolute-address variables.
aligned (n)
The attributed variable will be aligned on the next n byte boundary.
The aligned attribute can also be used on a structure member. Such a member will
be aligned to the indicated boundary within the structure.
If the alignment value n is omitted, the alignment of the variable is set 8 (the largest
alignment value for a basic data type).
Note that the aligned attribute is used to increase the alignment of a variable, not
reduce it. To decrease the alignment value of a variable, use the packed attribute.
cleanup (function)
Indicate a function to call when the attributed automatic function scope variable goes
out of scope.
The indicated function should take a single parameter, a pointer to a type compatible
with the attributed variable, and have void return type.
deprecated
deprecated (msg)
When a variable specified as deprecated is used, a warning is generated. The
optional msg argument, which must be a string, will be printed in the warning, if present.
packed
The attributed variable or structure member will have the smallest possible alignment.
That is, no alignment padding storage will be allocated for the declaration. Used in
combination with the aligned attribute, packed can be used to set an arbitrary
alignment restriction greater or lesser than the default alignment for the type of the
variable or structure member.
section (“section-name”)
Place the variable into the named section.
For example,
unsigned int dan __attribute__ ((section (“.quixote”)))
Variable dan will be placed in section .quixote.
The -fdata-sections command line option has no effect on variables defined with
a section attr ibute unl ess unique_section is also specified.
Note: In almost all cases, you will want to combine the address attribute with the
space attribute to indicate code or data.
Supported Data Types and Variables
2012 Microchip Technology Inc. DS51686E-page 107
space (space)
The space attribute can be used to direct the compiler to allocate a variable in
specific memory spaces.
unique_section
Place the variable in a uniquely named section, just as if -fdata-sections had been
specified. If the variable also has a section attribute, use that section name as the
prefix for generating the unique section name.
For example,
int tin __attribute__ ((section (“.ofcatfood”), unique_section)
Variable tin will be placed in section .ofcatfood.
unused
Indicate to the compiler that the variable may not be used. The compiler will not issue
a warning for this variable if it is not used.
weak
The weak attribute causes the declaration to be emitted as a weak symbol. A weak
symbol indicates that if a global version of the same symbol is available, that version
should be used instead.
When weak is applied to a reference to an external symbol, the symbol is not required
for linking. For examp le:
extern int __attribute__((__weak__)) s;
int foo() {
if (&s) return s;
return 0; /* possibly some other value */
}
In the above program, if s is not defined by some other module, the program will still
link but s will not be given an address. The conditional verifies that s has been defined
(and returns its value if it has). Otherwise ‘0’ is returned. There are many uses for this
feature, mostly to provide generic code that can link with an optional library.
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NOTES:
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 109
Chapter 7. Memory Allocation and Access
7.1 INTRODUCTION
There are two broad groups of RAM-based variables: auto/parameter variables, which
are allocated to some form of stack, and global/static variables, which are positioned
freely throughout the data memory space. The memory allocation of these two groups
is discussed separately in the following sections.
• Address Spaces
• Variables in Data Memory
• Auto Variable Allocation and Access
• Variables in Program Memory
• Variables in Registers
• Dynamic Memory Allocation
• Memory Models
7.2 ADDRESS SPACES
Unlike the 8- and 16-bit PIC devices, the PIC32 has a unified programming model.
PIC32 devices provide a single 32-bit wide address space for all code, data, peripher-
als and Configuration bits.
Memory regions within this single address space are designated for different purposes;
for example, as memory for instruction code or memory for data. Internally the device
uses separate buses1 to access the instructions and data in these regions, thus allow-
ing for parallel access. The terms program memory and data memory, which are used
on the 8- and 16-bit PIC devices, are still relevant on PIC32 devices, but the smaller
parts implement these in different address spaces.
All addresses used by the CPU within the device are virtual addresses. These are
mapped to physical addresses by the system control processor (CP0).
1.The device can be considered a Harvard architecture in terms of its internal bus arrangement.
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7.3 VARIABLES IN DATA MEMORY
Most variables are ultimately positioned into the data memory. The exceptions are
non-auto variables which are qualified as const, which are placed in the program
memory space, see Section 6.10.1 “Const Type Qualifier”.
Due to the fundamentally different way in which auto variables and non-auto vari-
ables are allocated memory, they are discussed separately. To use the C/C++ language
terminology, these two groups of variables are those with automatic storage duration
and those with permanent storage duration, respectively.
7.3.1 Non-auto Variable Allocation
Non-auto variables (those with permanent storage duration) are located by the com-
piler into any of the available data banks. This is done in a two-stage process: placing
each variable into an appropriate section and later linking that section into data mem-
ory.
The compiler considers three categories of non-auto variable, which all relate to the
value the variable should contain by the time the program begins. The following sec-
tions are used for the categories described.
.pbss These sections are used to store variables which use the persistent attri-
bute, whose values should not be altered by the runtime start-up code. They
are not cleared or otherwise modified at start-up.
.bss These sections (also .sbss) contain any uninitialized variables, which are not
assigned a value when they are defined, or variables which should be
cleared by the runtime start-up code.
.data These sec tions (also .sdata) contai n the RAM ima ge of any ini tialized v ari-
ables, which are assigned a non-zero initial value when they are defined and
which must have a value copied to them by the runtime start-up code.
Note that the data section used to hold initialized variables is the section that holds the
RAM variables themselves. There is a corresponding section (called .dinit) that is
placed into program memory (so it is non-volatile) and which is used to hold the initial
values that are copied to the RAM variables by the runtime start-up code.
7.3.2 Sta tic Variables
All static variables have permanent storage duration, even those defined inside a
function which are “local static” variables. Local static variables only have scope in
the function or block in which they are defined, but unlike auto variables, their memory
is reserved for the entire duration of the program. Thus, they are allocated memory like
other non-auto variables. Static variables may be accessed by other functions via
pointers since they have permanent duration.
Note: The terms “local” and “global” are commonly used to describe variables, but
are not ones defined by the language standard. The term “local variable” is
often taken to mean a variable which has scope inside a function, and
“global variable” is one which has scope throughout the entire program.
However, the C/C++ language has three common scopes: block, file (i.e.
internal linkage) and program (i.e. external linkage), so using only two
terms to describe these can be confusing. For example, a static variable
defined outside a function has scope only in that file, so it is not globally
accessible, but it can be accessed by more than one function inside that
file, so it is not local to any one function either. In terms of memory alloca-
tion, variables are allocated space based on whether it is an auto or not,
hence the grouping in the following sections.
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Variables which are static are guaranteed to retain their value between calls to a
function, unless explicitly modified via a pointer.
Variables which are static and which are initialized only have their initial value
assigned once during the program’s execution. Thus, they may be preferable over ini-
tialized auto objects which are assigned a value every time the block they are defined
in begins execution. Any initialized static variables are initialized in the same way as
other non-auto initialized objects by the runtime start-up code, see
Section 3.5.2 “Peripheral Library Functions”. Static variables are located in the
same sections as their non-static counterparts.
7.3.3 Non-auto Variable Size Limits
Arrays of any type (including arrays of aggregate types) are fully supported by the com-
piler. So too are the structure and union aggregate types, see Section 6.6 “Structures
and Unions”. There are no theoretical limits as to how large these objects can be
made.
7.3.4 Changing the Default Non-auto Vari able Allocation
There are several ways in which non-auto variables can be located in locations other
than the default.
Variables can be placed in other device memory spaces by the use of qualifiers. For
example if you wish to place variables in the program memory space, then the const
specifier should be used (see Section 6.10.1 “Const Type Qualifier”).
If you wish to prevent all variables from using one or more data memory locations so
that these locations can be used for some other purpose, you are best defining a vari-
able (or array) using the address attribute so that it consumes the memory space, see
Section 6.12 “Variable Attributes”.
If only a few non-auto variables are to be located at specific addresses in data space
memory , then the variables can be located using the address attribute. This attribute is
described in Section 6.12 “Variable Attributes”.
7.3.5 Data Memory Allocation Macros
Macros are provided for many commonly used attributes in order to enhance user code
readability.
__section__(s) Apply the section attrib ute with sec ti on nam e s.
__unique_section__ Apply the unique_section attribute.
__ramfunc__ Locate the attributed function in the RAM function code
section.
__longramfunc__ Locate the attributed function in the RAM function code
section and apply the longcall attribute.
__longcall__ Apply the longcall attribute.
__ISR(v,ipl) Apply the interrupt attrib ute with prio rity leve l ipl
and the vector attribute with vector number v.
__ISR_AT_VECTOR(v,ipl) Apply the interrupt attrib ute with prio rity leve l ipl
and the at_vector attribute with vector number v.
__ISR_SINGLE__ Specifies a function as an Interrupt Service Routine in
single-vector mode. This places a jump at the
single-vector location to the interrupt handler.
__ISR_SINGLE_AT_VECTOR_
_ Places the entire single-vector interrupt handler at the
vector 0 loca tion. When used, ensure that the vect or
spacing is set to accommodate the size of the handler.
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7.4 AUTO VARIABLE ALLOCATION AND ACCESS
This section discusses allocation of auto variables (those with automatic storage dura-
tion). This also includes function parameter variables, which behave like auto vari-
ables, as well as temporary variables defined by the compiler.
The auto (short for automatic) variables are the default type of local variable. Unless
explicitly declared to be static, a local variable will be made auto. The auto
keyword may be used if desired.
The auto variables, as their name suggests, automatically come into existence when
a function is executed, then disappear once the function returns. Since they are not in
existence for the entire duration of the program, there is the possibility to reclaim mem-
ory they use when the variables are not in existence and allocate it to other variables
in the program.
The PIC32’ s sof tware stac k is used to st ore all auto variables. Functions are reentrant
and each instance of the function has its own area of memory on the stack for its auto
and parameter variables, as described below. See Section 4.4 “Stack” and
Section 12.3.2 “Initialize Stack Pointer and Heap” for more information on the st ack.
The compiler dedicates General Purpose Register 29 as the software S tack Pointer . All
processor stack operations, including function call, interrupts and exceptions use the
software stack. The stack grows downward from high addresses to low addresses.
By default, the size of the stack is 1024 bytes. The size of the stack may be changed
by specifying the size on the linker command line using the
--defsym_min_stack_size linker command line option. An example of allocating
a stack of 2048 bytes using the command line is:
xc32-gcc foo.c -Wl,--defsym,_min_stack_size=2048
The run-time stack grows downward from higher addresses to lower addresses (see
Figure 7-1). The compiler uses two working registers to manage the stack:
• Register 29 (sp) – This is the Stack Pointer. It points to the next free location on
the stack.
• Register 30 (fp) – This is the Frame Pointer. It points to the current function’s
frame. Each function, if required, creates a new frame from which automatic and
temporary variables are allocated. Compiler optimization may eliminate Stack
Pointer references via the Frame Pointer to equivalent references via the Stack
Pointer. This optimization allows the Frame Pointer to be used as a General
Purpose Register.
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FIGURE 7-1: STACK FRAME
The the standard qualifiers const and volatile may both be used with auto vari-
ables and these do not affect how they are positioned in memory. This implies that a
local const-qual ified object is still an auto object and, as such, will be allocated mem-
ory on the stack in the data memory, not in the program memory like with non-auto
const objects.
7.4.1 Local Variable Size Limits
There is no theoretical maximum size for auto variables.
7.5 VARIABLES IN PROGRAM MEMORY
The only variables that are placed into program memory are those that are not auto
and which have been qualified const. If the -mno-embedded-data option is used,
then even const objects are placed in RAM rather than the program memory. Any
auto variables qualified const are placed on the stack along with other auto vari-
ables.
Any const-qualified (auto or non-auto) variable will always be read-only and any
attempt to write to these in your source code will result in an error being issued by the
compiler.
A const object is usually defined with initial values, as the program cannot write to
these objects at runtime. However this is not a requirement. An uninitialized const
object is allocated space in the bss section, along with other uninitialized RAM vari-
ables, but is still read-only.
const char IOtype = ’A’; // initialized const object
const char buffer[10]; // I just reserve memory in RAM
Stack grows
toward
lower
addresses
FP
Caller
Space for more
arguments if
necessary
S pace for argument 4
S pace for argument 3
S pace for argument 2
S pace for argument 1
Local variables and
temporary values
Register save area
Space for arguments
used in function calls
Callee
SP
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7.5.1 Size Limitati ons of const Variables
There is no theoretical maximum size for const variables .
7.5.2 Changing the Default Allocation
If you only intend to prevent all variables from using one or more program memory loca-
tions so that you can use those locations for some other purpose, you are best reserv-
ing the memory using the memory adjust options.
If only a few non-auto const variables are to be located at specific addresses in
program space memory, then the variables should use the address attribute to locate
them at the desired location. This attribute is described in Section 6.12 “Variable
Attributes”.
7.6 VARIABLES IN REGISTERS
Allocating variables to registers, rather than to a memory location, can make code more
efficient. With MPLAB XC32 C/C++ Compiler, variables may be allocated to registers
as part of code optimizations. For optimization levels 1 and higher, the values assigned
to variables may cached in a register . During this time, the memory location associated
with the variable may not hold a valid value.
The register keyword may be used to indicate your preference for the variable to be
allocated a register, but this is just a recommendation and may not be honored. The
specific register may be indicated as well, but this is not recommended as your register
choice may conflict with the needs of the compiler. For example:
register unsigned int foo __asm__("at");
will attempt to allocate foo to the at register. As indicated in Section 10.6 “Function
Parameters”, parameters may be passed to a function via a register.
7.7 DYNAMIC MEMORY ALLOCATION
The run-time heap is an uninitialized area of data memory that is used for dynamic
memory allocation using the standard C library dynamic memory management
functions, calloc, malloc and realloc along with the C++ new operator. Most C++
applications will require a heap.
If you do not use any of these functions, then you do not need to allocate a heap. By
default, a heap is not created.
If you do want to use dynamic memory allocation, either directly, by calling one of the
memory allocation functions, or indirectly, by using a standard C library function that
uses one of these functions, then a heap must be created. A heap is created by
specifying its size on the linker command line using the --defsym_min_heap_size
linker command line option. An example of allocating a heap of 512 bytes using the
comm and line is:
xc32-gcc foo.c -Wl,--defsym,_min_heap_size=512
An example of allocating a heap of 0xF000 bytes using the xc32-g++ driver is:
xc32-g++ vector.cpp -Wl,--defsym,_min_heap_size=0xF000
The linker allocates the heap immediately before the stack.
7.8 MEMOR Y MO DE LS
MPLAB XC32 C/C++ Compiler does not use fixed memory models to alter allocation of
variables to memory.
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The -G opti on (see Section 3.9.1 “Options Specific to PIC32MX Devices” ), which
controls the gp-relative addressing threshold, is similar to the
small-data/large-data/scalar-data memory models offered by the Microchip MPLAB
XC16 compiler. The value specified with this option indicates the maximum size of
objects that will be allocated to the small data sections, e.g. sbss, sdata, etc.
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Chapter 8. Operators and Statements
8.1 INTRODUCTION
The MPLAB XC32 C/C++ Compiler supports all ANSI operators. The exact results of
some of these are implementation defined. Implementation-defined behavior is fully
documented in Appendix 18. “Implementation-Defined Behavior”. The following
sections illustrate code operations that are often misunderstood, as well as additional
operations that the compiler is capable of performing.
• Integral Promotion
• Type References
• Labels as Values
• Condit ion al Op er ato r Oper ands
• Case Ranges
8.2 INTEGRAL PROMOTION
When there is more than one operand to an operator , they typically must be of exactly
the same type. The compiler will automatically convert the operands, if necessary, so
they do have the same type. The conversion is to a “larger” type so there is no loss of
information; however, the change in type can cause different code behavior to what is
sometimes expected. These form the standard type conversions.
Prior to these type conversions, some operands are unconditionally converted to a
larger type, even if both operands to an operator have the same type. This conversion
is called integral promotion and is part of Standard C behavior. The MPLAB XC32
C/C++ Compiler performs these integral promotions where required, and there are no
options that can control or disable this operation. If you are not aware that the type has
changed, the results of some expressions are not what would normally be expected.
Integral promotion is the implicit conversion of enumerated types, signed or
unsigned varieties of char, short int or bit field types to either signed int or
unsigned int. If the result of the conversion can be represented by an signed int,
then that is the destination type, otherwise the conversion is to unsigned int.
Consider the following example:
unsigned char count, a=0, b=50;
if(a - b < 10)
count++;
The unsigned char result of a - b is 206 (which is not less than 10), but both a and
b are converted to signed int via integral promotion before the subtraction takes
place. The result of the subtraction with these data types is -50 (which is less than 10)
and hence the body of the if() statement is executed.
If the result of the subtraction is to be an unsigned quantity, then apply a cast. For
example:
if((unsigned int)(a - b) < 10)
count++;
The comparison is then done using unsigned int, in this case, and the body of the
if() would not be executed.
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Another problem that frequently occurs is with the bitwise compliment operator , ~. This
operator toggles each bit within a value. Consider the following code:
unsigned char count, c;
c = 0x55;
if( ~c == 0xAA)
count++;
If c contains the value 0x55, it often assumed that ~c will produce 0xAA, however the
result is 0xFFFFFFAA and so the comparison in the above example would fail. The
compiler may be able to issue a mismatched comparison error to this effect in some
circumstances. Again, a cast could be used to change this behavior.
The consequence of integral promotion as illustrated above is that operations are not
performed with char -type operands, but with int -type operands. However there are
circumstances when the result of an operation is identical regardless of whether the
operands are of type char or int. In these cases, the MPLAB XC32 C/C++ Compiler
will not perform the integral promotion so as to increase the code efficiency. Consider
the following example:
unsigned char a, b, c;
a = b + c;
S trictly speaking, this statement requires that the values of b and c should be promoted
to unsigned int, the addition performed, the result of the addition cast to the type of
a, and then the assignment can take place. Even if the result of the unsigned int
addition of the promoted values of b and c was different to the result of the unsigned
char addi ti on of th es e val ues with out pr omot ion, af te r the unsigned int result was
converted back to unsigned char, the final result would be the same. If an 8-bit addi-
tion is more efficient than a 32-bit addition, the compiler will encode the former.
If, in the above example, the type of a was unsigned int, then integral promotion
would have to be performed to comply with the ANSI C standard.
8.3 TYPE REFERE NCES
Another way to refer to the type of an expression is with the typeof keyword. This is
a non-standard extension to the language. Using this feature reduces your code
portability.
The syntax f or using this keyword looks like sizeof, but the construct acts
semantically like a type name defined with typedef.
There are two ways of writing the argument to typeof: with an expression or with a
type. Here is an example with an expression:
typeof (x[0](1))
This assumes th at x is an array of functions; the type described is that of the values of
the functions.
Here is an example with a typename as the argument:
typeof (int *)
Here the type described is a pointer to int.
If you are writing a header file that must work when included in ANSI C programs, write
__typeof__ ins tea d of typeof.
A typeof con st ruct ca n be used anywhere a typedef name co uld be used. For
example, you can use it in a declaration, in a cast, or inside of sizeof or typeof.
• This declares y with the type of what x points to:
typeof (*x) y;
• This declares y as an array of such values:
typeof (*x) y[4];
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• This declares y as an array of pointers to characters:
typeof (typeof (char *)[4]) y;
It is equivalent to the following traditional C declaration:
char *y[4];
To see the meaning of the declaration using typeof, and why it might be a useful way
to write, let’s rewrite it with these macros:
#define pointer(T) typeof(T *)
#define array(T, N) typeof(T [N])
Now the declaration can be rewritten this wa y:
array (pointer (char), 4) y;
Thus, array (pointer (char), 4) is the type of arrays of four pointers to char.
8.4 LABELS AS VALUES
You can get the address of a label defined in the current function (or a containing
function) with the unary operator ‘&&’. This is a non-standard extension to the language.
Using this feature reduces your code portability.
The value return ed has type void *. This value is a constant and can be used
wherever a constant of that type is valid. For example:
void *ptr;
...
ptr = &&foo;
To use these values, you need to be able to jump to one. This is done with the
computed goto statement, goto *exp;. For example:
goto *ptr;
Any expression of type void * is allowe d.
One way of using these constants is in initializing a static array that will serve as a jump
table:
static void *array[] = { &&foo, &&bar, &&hack };
Then you can select a label with indexing, like this:
goto *array[i];
Such an array of label values serves a purpose much like that of the switch
statement. The switch statement is cleaner and therefore preferable to an array.
Another use of label values is in an interpreter for threaded code. The labels within the
interpreter function can be stored in the threaded code for fast dispatching.
This mechanism can be misused to jump to code in a different function. The compiler
cannot prevent this from happening, so care must be taken to ensure that target
addresses are valid for the current function.
Note: This does not check whether the subscript is in bounds. (Array indexing in
C never does.)
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8.5 CONDITIONAL OPERATOR OPERANDS
The middle operand in a conditional expression may be omitted. Then if the first
operand is nonzero, its value is the value of the conditional expression. This is a
non-standard extension to the language. Using this feature reduces your code
portability.
Therefore, the expression:
x ? : y
has the value of x if that is nonzero; otherwise, the value of y.
This example is perfectly equivalent to:
x ? x : y
In this simple case, the ability to omit the middle operand is not especially useful. When
it becomes useful is when the first operand does, or may (if it is a macro argument),
contain a side effect. Then repeating the operand in the middle would perform the side
effect twice. Omitting the middle operand uses the value already computed without the
undesirable effects of recomputing it.
8.6 CAS E RANGES
You can specify a range of consecutive values in a single case label, like this:
case low ... high:
This has the same effect as the proper number of individual case labels, one for each
integer value from low to high, inclusive. This is a non-standard extension to the lan-
guage. Using this feature reduces your code portability.
This feature is especially useful for ranges of ASCII character codes:
case 'A' ... 'Z':
Be careful: Write spaces around the ..., otherwise it may be parsed incorrectly when
you use it with integer values. For example, write this:
case 1 ... 5:
rather than this:
case 1...5:
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Chapter 9. Register Usage
9.1 INTRODUCTION
This chapter examines registers used by the compiler to generate assembly from
C/C++ source code.
• Register Usage
• Register Conventions
9.2 REGISTE R USAGE
The assembly generated from C/C++ source code by the compiler will use certain reg-
isters that are present on the PIC MCU device. The compiler assumes that nothing
other than code it generates can alter the contents of these registers, but an extended
assembly language format can be used to indicate to the compiler registers used in
assembly code so that code can be adjusted accordingly.
9.3 REGISTER CONVENTIONS
The 32 general purpose registers contained in the PIC32 are shown in T able 9-1. Some
of these registers are assigned a dedicated task by the compiler. The name used in
assembly code and the usage is indicated.
TABLE 9-1: REGISTER CONVENTIONS
Register
Number Software
Name Use
$0 zero Always 0 when read.
$1 at Asse mb ler tem po rar y variable.
$2-$3 v0-v1 Return value from functions.
$4-$7 a0-a3 Used for passing arguments to functions.
$8-$15 t0-t7 Temporary regi st ers us ed by com pi le r for expres si on eva lu ation.
Values not saved across function calls.
$16-$23 s0-s7 Temporary registers whose values are saved across function
calls.
$24-$25 t8-t9 Tem por ary registers used by com pi le r for expr es si on eva lu atio n.
Values not saved across function calls.
$26-$27 k0-k1 Reserved for interrupt/trap handler.
$28 gp Global Pointer.
$29 sp Stack Pointe r.
$30 fp or s8 Frame Pointer if needed. Additional temporary saved register if
not.
$31 ra Return address for functions.
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Chapter 10. Functions
The following sections describe how function definitions are written, and specifically
how they can be customized to suit your application. The conventions used for param-
eters and return values, as well as the assembly call sequences are also discussed.
• Writing Functions
• Function Attributes and Specifiers
• Allocation of Function Code
• Changing the Default Function Allocation
• Function Size Limits
• Function Parameters
• Function Return Values
• Calling Fu nc tio ns
• Inline Functions
10.1 WRITING FUNCTIONS
Functions may be written in the usual way in accordance with the C/C++ language.
The only specifier that has any effect on function is static. Interrupt functions are
defined with the use of the interrupt attribute, see Section 10.2 “Function Attr ibutes
and Specifiers”.
A function defined using the static specifier only affects the scope of the function, i.e.
limits the places in the source code where the function may be called. Functions that
are static may only be directly called from code in the file in which the function is
defined. The equivalent symbol used in assembly code to represent the function may
change if the function is static, see Section 7.3.2 “St atic V ariables”. This specifier
does not change the way the function is encoded.
10.2 FUNCTION ATTRIBUTES AND SPECIFIERS
10.2.1 Function Attributes
address(addr)
The address attribute specifies an absolute virtual address for the function. Be sure to
specify the address attribute using an appropriate virtual address for the target device.
The address is typically in the range [0x9D000000,0x9D0FFFFC], as defined in the
linker script as the ‘kseg0_program_mem’ memory region. For example,
__attribute__((address(0x9D008000))) void bar (void);
The compiler performs no error checking on the address. The section containing the
function will be located at the specified address regardless of the memory-regions
specified in the linker script or the actual memory ranges on the target device. The
application code must ensure that the address is valid for the target device.
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To make effective use of absolute sections and the new best-fit allocator, standard
program-memory and data-memory sections should not be mapped in the linker script.
The built-in linker script does not map most standard sections such as the .text,
.data, .bss, or .ramfunc sections. By not mapping these sections in the linker
script, we allow these sections to be allocated using the best-fit allocator rather than
the sequential allocator. Sections that are unmapped in the linker script can flow around
absolute sections, whereas sections that are linker-script mapped are grouped
together and allocated sequentially , potentially causing conflicts with absolute sections.
alias (“symbol”)
Indicates that the function is an alias for another symbol. For example:
void foo (void) { /* stuff */ }
__attribute__ ((alias(“foo”))) void bar (void);
Symbol bar is considered to be an alias for the symbol foo.
always_inline
If the function is declared inline, always inline the function, even if no optimization
level was specified.
at_vector
Place the body of the function at the indicated exception vector address.
See Chapter 11. “Interrupts” and Section 11.5 “Exception Handlers”.
const
If a pure function determines its return value exclusively from its parameters (i.e., does
not examine any global variables), it may be declared const, allowing for even more
aggressive optimization. Note that a function which de-references a pointer argument
is not const since the pointer de-reference uses a value which is not a parameter,
even though the pointer itself is a parameter.
deprecated
deprecated (msg)
When a function specified as deprecated is used, a warning is generated. The
optional msg argument, which must be a string, will be printed in the warning if present.
The deprecated attribute may also be used for variables and types.
far
Always invoke the function by first loading its address into a register and then using the
contents of that register. This allows calling a function located beyond the 28-bit
addressing range of the direct CALL instruction.
format (type, format_index, first_to_check)
The format attribute indicates that the function takes a printf, scanf, strftime,
or strfmon style format string and arguments and that the compiler should type check
those arguments against the format string, just as it does for the standard library
functions.
The type parameter is one of printf, scanf, strftime or strfmon (optionally with
surrounding double underscores, e.g., __printf__) and determines how the format
string will be interpreted.
The format_index parameter specifies which function parameter is the format string.
Function parameters are numbered from the left-most parameter, starting from 1.
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The first_to_check parameter specifies which parameter is the first to check
against the format string. If first_to_check is zero, type checking is not performed,
and the compiler only checks the format string for consistency (e.g., vfprintf).
format_arg (index)
The format_arg attribute specifies that a function manipulates a printf style format
string and that the compiler should check the format string for consistency . The function
attribute which is a format string is identified by index.
interrupt (priority)
Generate prologue and epilogue code for the function as an interrupt handler function.
See Chapter 11. “Interrupts”. The argument specifies the interrupt priority using the
symbols ip1 to ip7 to represent the 7 levels of priority.
longcall
Functionally equivalent to far.
malloc
Any non-Null Pointer return value from the indicated function will not alias any other
pointer which is live at the point when the function returns. This allows the compiler to
improve optimization.
mips16
Generate code for the function in the MIPS16 instruction set.
naked
Generate no prologue or epilogue code for the function.
near
Always invo ke the func tion w ith an absolute CALL instruction, even when the
-mlong-calls command line option is specified.
noinline
The function will never be considered for inlining.
nomips16
Always generate code for the function in the MIPS32® instruction set, even when
compiling the translation unit with the -mips16 command line option.
nonnull (index, ...)
Indicate to the compiler that one or more pointer arguments to the function must be
non-null. If the compiler determines that a Null Pointer is passed as a value to a
non-null argument, and the -Wnonnull command line option was specified, a warning
diagnostic is issued.
If no arguments are given to the nonnull attribute, all pointer arguments of the
function are marked as non-null.
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noreturn
Indicate to the compiler that the function will never return. In some situations, this can
allow the compiler to generate more efficient code in the calling function since
optimizations can be performed without regard to behavior if the function ever did
return. Functions declared as noreturn should always have a r eturn type of void.
pure
If a function has no side effects other than its return value, and the return value is
dependent only on parameters and/or (nonvolatile) global variables, the compiler can
perform more aggressive optimizations around invocations of that function. Such
functions can be indicated with the pure attribute.
ramfunc
Treat the function as if it was in data memory. Allocate the function at the highest
appropriately aligned address for executable code. Note that due to ramfunc
alignment and placement requirements, the address attribute should not be used with
the ramfunc attribute. The presence of the ramfunc secti on causes t he linker to em it
the symbols necessary for the crt0.S start-up code to initialize the bus matrix
appropriately for executing code out of data memory. Use this attribute along with the
far/longcall attribute and the section attribute. For example:
__attribute__((ramfunc,section(“.ramfunc”),far,unique_section))
unsigned int myramfunct (void_
{ /* code */ }
A macro in the sys/attribs.h header file makes the ramfunc attribute simple to use:
#include <sys/attribs.h>
__longramfunc__ unsigned int myramfunct (void)
{ /* code */ }
section(“name”)
Place the function into the named section.
For example:
void __attribute__ ((section (“.wilma”))) baz () {return;}
Function baz will be placed in section .wilma.
The -ffunction-sections command line option has no effect on functions defined
with a section attribute.
unique_section
Place the function in a uniquely named section, as if -ffunction-sections had
been specified. If the function also has a section attribute, use that section name as
the prefix for generating the unique section name.
For example:
void __attribute__ ((section (“.fred”), unique_section) foo (void)
{return;}
Function foo will be placed in section .fred.foo.
unused
Indicate to the compiler that the function may not be used. The compiler will not issue
a warning for this function if it is not used.
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2012 Microchip Technology Inc. DS51686E-page 127
used
Indicate to the compiler that the function is always used and code must be generated
for the function even if the compiler cannot see a reference to the function. For
example, if inline assembly is the only reference to a static function.
vector
Generate a branch instruction at the indicated exception vector which targets the
function. See Chapter 11. “Interrupts” and Section 11.5 “Exception Handlers”.
warn_unused_result
A warning will be issued if the return value of the indicated function is unused by a
caller.
weak
A weak symbol indicates that if another version of the same symbol is available, that
version should be used instead. For example, this is useful when a library function is
implemented such that it can be overridden by a user written function.
10.3 ALLOCATION OF FUNCTION CODE
Code associated with C/C++ functions is normally always placed in the program Flash
memory of the target device.
Functions may be located in and executed from RAM rather than Flash by using the
__ramfunc__ and __longramfunc__ macr os.
Functions specified as a RAM function will be copied to RAM by the start-up code and
all calls to those functions will reference the RAM location. Functions located in RAM
will be in a different 512MB memory segment than functions located in program
memory , so the longcall attribute should be applied to any RAM function, which will
be called from a function not in RAM. The __longramfunc__ macro will apply the
longcall attribute as well as place the function in RAM1.
#include <sys/attribs.h>
/* function ‘foo’ will be placed in RAM */
void __ramfunc__ foo (void)
{
}
/* function ‘bar’ will be placed in RAM and will be invoked
using the full 32 bit address */
void __longramfunc__ bar (void)
{
}
10.4 CHANGING THE DEFAULT FUNCTION ALLOCATION
The assembly code associated with a C/C++ function can be placed at an absolute
address. This can be accomplished by using the address attribute and specifying the
virtual address of the function, see Section 6.12 “Variable Attributes”.
Functions can also be placed at specific positions by placing them in a user-defined
section and then linking this section at an appropriate address, see
Section 6.12 “Variable Attributes”.
1. Specifying __longramfunc__ is functionally equivalent to specifying both __ramfunc__ and
__longcall__.
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10.5 FUNCTION SIZE LIMITS
There are no theoretical limits as to how large functions can be made.
10.6 FUNCTION PARAMETERS
MPLAB XC uses a fixed convention to pass arguments to a function. The method used
to pass the arguments depends on the size and number of arguments involved.
The Stack Pointer is always aligned on an 8-byte boundary.
• All integer types smaller than a 32-bit integer are first converted to a 32-bit value.
The first four 32 bits of arguments are passed via registers a0-a3 (see Table 10-1
for how many registers are required for each data type).
• Although some arguments may be passed in registers, space is still allocated on
the stack for all arguments to be passed to a function (see Figure 10-1). Applica-
tion code should not assume that the current argument value is on the stack, even
when space is allocated.
• When calling a function:
-Registers a0-a3 are used for passing arguments to functions. Values in these
registers are not preserved across function calls.
-Registers t0-t7 and t8-t9 are caller saved registers. The callin g function
must push these values onto the stack for the registers’ values to be saved.
-Registers s0-s7 are called saved registers. The function being called must
save any of these registers it modifies.
-Register s8 is a saved register if the optimizer eliminates its use as the Frame
Pointer. s8 is a reserved register otherwise.
-Register ra contains the return address of a function call.
Note: The names “argument” and “parameter” are often used interchangeably,
but typically an argument is the actual value that is passed to the function
and a parameter is the variable defined by the function to store the argu-
ment.
TABLE 10-1: REGISTERS REQUIRED
Data Ty pe Number of Registers Required
char 1
short 1
int 1
long 1
long long 2
float 1
double 1
long double 2
structure Up to 4, depending on the size of the struct.
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2012 Microchip Technology Inc. DS51686E-page 129
FIGURE 10-1: PASSING ARGUMENTS
Example 1:
int add (int, int)
a= add (5, 10);
SP + 4
SP
a0
a1
undefined
undefined
5
10
Example 2:
void foo (long double, long double)
call= foo (10.5, 20.1);
SP + 12
SP
undefined
SP + 8
SP + 4 undefined
a0
a3
10.5
a1
a2 20.1
void calculate (long double, long double, int)
calculate (50.3, 100.0, .10);
SP + 12
SP
undefined
SP + 8
SP + 4 undefined
a0
a3 100.0
a1
a2
.10
50.3
SP + 16
Example 3:
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10.7 FUNCTION RETURN VALUES
Function return values are returned in registers.
If a function needs to return an actual structure or union — not a pointer to such an
object — the called function copies this object to an area of memory that is reserved by
the caller. The caller passes the address of this memory area in register $4 when the
function is called. The function also returns a pointer to the returned object in register
v0. Having the caller supply the return object’s space allows re-entrance.
10.8 CALLING FUNCTIONS
By default, functions are called using the direct form of the call (jal) instruction. This
allows calls to destinations within a 256 MB segment. This operation can be changed
through the use of attributes applied to functions or command-line options so that a lon-
ger, but unrestricted, call is made.
The -mlong-calls option, see Section 3.9.1 “Options Specific to PIC32MX
Devices”, forces a register form of the call to be employed by default. Generated code
is longer, but calls are not limited in terms of the destination address.
The attributes longcall or far can be used with a function definition to always
enforce the longer call sequence for that function. The near attribute can be used with
a function so that calls to it use the shorter direct call, even if the -mlong-calls option
is in force.
10.9 INLINE FUNCTIONS
By declaring a function inline, you can direct the compiler to integrate that function’s
code into the code for its callers. This usually makes execution faster by eliminating the
function-call overhead. In addition, if any of the actual argument values are constant,
their known values may permit simplifications at compile time, so that not all of the
inline function’s code needs to be included. The effect on code size is less predictable.
Machine code may be larger or smaller with inline functions, depending on the
particular case.
To declare a function inline, use the inline keyword in its declaration, like this:
inline int
inc (int *a)
{
(*a)++;
}
(If you are using the -traditional option or the -ansi option, write __inline__
instead of inline.) You can also make all “simple enough” functions inline with the
command-line option -finline-functions. The compiler heuristically decides
which functions are simple enough to be worth integrating in this way, based on an
estimate of the function’s size.
Note: Function inlining will only take place when the function’s definition is visible
(not just the prototype). In order to have a function inlined into more than
one source file, the function definition may be placed into a header file that
is included by each of the source files.
Note: The inline keyword will only be recognized with -finline or
optimizations enabled.
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2012 Microchip Technology Inc. DS51686E-page 131
Certain usages in a function definition can make it unsuitable for inline substitution.
Among these usages are: use of varargs, use of alloca, use o f variab le-siz ed dat a,
use of computed goto and use of nonlocal goto. Using the command-line option
-Winline will warn when a function marked inline could not be substituted, and will
give the reason for the failure.
In co mpiler syntax, the inline keyword does not affect the linkage of the function.
When a function is both inline and static, if all calls to the function are integrated
into the caller and the function’s address is never used, then the function’s own
assembler code is never referenced. In this case, the compiler does not actually output
assembler code for the function, unless you specify the command-line option
-fkeep-inline-functions. Some calls cannot be integrated for various reasons
(in particular, calls that precede the function’s definition cannot be integrated and
neither can recursive calls within the definition). If there is a nonintegrated call, then the
function is compiled to assembler code as usual. The function must also be compiled
as usual if the program refers to its address, because that can’t be inlined. The compiler
will only eliminate inline functions if they are declared to be static and if the func-
tion definition precedes all uses of the function.
When an inline function is not static, then the compiler must assume that there
may be calls from other source files. Since a global symbol can be defined only once
in any program, the function must not be defined in the other source files, so the calls
therein ca nnot be integr ate d. Ther efore, a non- static inline function is always
compiled on its own in the usual fashion.
If you specify both inline and extern in the function definition, then the definition is
used only for inlining. In no case is the function compiled on its own, not even if you
refer to its address explicitly . Such an address becomes an external reference, as if you
had only declared the function and had not defined it.
This combination of inline and extern has a similar effect to a macro. Put a function
definition in a header file with these keywords and put another copy of the definition
(lacking inline and extern) in a library file. The definition in the header file will cause
most calls to the function to be inlined. If any uses of the function remain, they will refer
to the single copy in the library.
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NOTES:
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 133
Chapter 11. Interrupts
11.1 INTRODUCTION
Interrupt processing is an important aspect of most microcontroller applications.
Interrupts may be used to synchronize software operations with events that occur in
real time. When interrupts occur, the normal flow of software execution is suspended,
and special functions are invoked to process the event. At the completion of interrupt
processing, previous context information is restored and normal execution resumes.
PIC32MX devices support multiple interrupts, from both internal and external sources.
The devices allow high-priority interrupts to override any lower priority interrupts that
may be in progress.
The compiler provides full support for interrupt processing in C/C++ or inline assembly
code. This chapter presents an overview of interrupt processing.
• Interrupt Operation
• Writing an Interrupt Service Routine
• Associating a Handler Function with an Exception Vector
• Exception Handlers
• Interrupt Service Routine Context Switching
• Latency
• Nesting Interrupts
• Enabling/Disabling Interrupts
• ISR Considerations
11.2 INTERRUPT OPERATION
The compiler incorporates features allowing interrupts to be fully handled from C/C++
code. Interrupt functions are often called interrupt handlers or Interrupt Service Rou-
tines (ISRs).
Each interrupt source typically has a control bit in an SFR which can disable that inter-
rupt source. Check your device data sheet for full information how your device handles
interrupts.
Interrupt code is the name given to any code that executes as a result of an interrupt
occurring. Interrupt code completes at the point where the corresponding return from
interrupt instruction is executed. This contrasts with main-line code, which, for a free-
standing application, is usually the main part of the program that executes after reset.
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11.3 WRITING AN INTERRUPT SERVICE ROUTINE
An interrupt handler function is different to an ordinary function in that it handles the
context save and restore to ensure that upon return from interrupt, the program context
is maintained.A different code sequence is used to return from these functions as well.
Several attributes can be used to ensure that the compiler generates the correct code
for an ISR. Macros are provided so that this is easier to accomplish, see the following
sections.
There are several actions that the compiler needs to take to generate an interrupt ser-
vice routine. The compiler has to be told to use an alternate form of return code. The
function also needs to be linked to the interrupt vector. Only the mip32 instruction set
can be used in ISRs, so the compiler must be told to generate code using this instruc-
tion set, even if the option to generate mip16 instructions has been used.
An interrupt function must be declared as type void and may not have parameters.
This is the only function prototype that makes sense for an interrupt function since they
are never directly called in the source code.
Interrupt functions must not be called directly from C/C++ code (due to the different
return instruction that is used), but they themselves may call other functions, both
user-defined and library functions, but be aware that this may use additional registers
which will need to be saved and restored by the context switch code.
A function is marked as an interrupt handler function (also known as an Interrupt
Service Routine or ISR) via either the interrupt attribute or the interrupt pragma1. While
each method is functionally equivalent to the other, the interrupt attribute is more
commonly used and therefore the recommended method. The interrupt is specified as
handling interrupts of a specific priority level or for operating in single vector mode.
11.3.1 Int e rr u pt Att ri b u te
__attribute__((interrupt([IPLn[SRS|SOFT|AUTO]])))
Where n is in the range of 0..7, inclusive.
Use the interrupt attribute to indicate that the specified function is an interrupt handler.
The compiler generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present. The generated code preserves context
by either using a shadow register set (SRS) or using generated software instructions
(SOFT) to push context onto the stack. See Example 11-1 for an interrupt attribute.
EXAMPLE 11-1: INTERRUPT ATTRIBUTE
void __attribute__((interrupt(IPL7SRS))) bambam (void);
Many PIC32 devices allow us to specify, via configuration-bit settings, which interrupt
priority level will use the shadow register set (e.g., #pragma config
FSRSSEL=PRIORITY_7). Refer to the device data sheet to determine if your PIC32
target device supports this feature. This means we must specify which context-saving
mechanism to use for each interrupt handler. The compiler will generate interrupt
function prologue and epilogue code utilizing shadow register context saving for the
IPLnSRS Interrupt Priority Level (IPL) specifier. It will use software context saving for
the IPLnSOFT IPL specifier.
1. Note that pre-processor macros are not expanded in pragma directives.
Note: Application code is responsible for applying the correct value to the
matching handler routine.
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2012 Microchip Technology Inc. DS51686E-page 135
The compiler also supports an IPLnAUTO IPL specifier that uses the run-time value in
SRSCTL to de termine whether it sh ould use sof tware or SRS cont ext-sa ving code. The
compiler defaults to using IPLnAUTO when the IPL specifier is omitted from the
interrupt() attribute.
For devices that do not support a shadow register set for interrupt context saving, use
IPLnSOFT for all interrupt handlers.
11.3.2 Int e rr u pt Prag ma
# pragma interrupt function-name IPLn[AUTO|SOFT|SRS] [vector
[@]vector-number [, vector-number-list]]
# pragma interrupt function-name single [vector [@] 0
Where n is in the range of 0..7, inclusive.
The IPLn [AUTO|SOFT|SRS] IPL specifier may be all uppercase or all lowercase.
The function definition for a handler function indicated by an interrupt pragma must
follow in the same translation unit as the pragma itself.
The interrupt attribute will also indicate that a function definition is an interrupt
handler. It is functionally equivalent to the interrupt pragma.
For example, the definitions of foo below both indicate that it is an interrupt handler
function for an interrupt of priority 4 that uses software context saving.
#pragma interrupt foo IPL4SOFT
void foo (void)
is functionally equivalent to
void __attribute__ ((interrupt(IPL4SOFT))) foo (void)
11.3.3 __ISR Macros
The <sys/attribs.h> header file provides macros intended to simplify the
application of attributes to interrupt functions. There are also vector macros defined in
the processor header files. (See the appropriate header file in the compiler’s
/pic32mx/include/proc directory.)
• __ISR(V, IPL)
• __ISR_AT_VECTOR(v, IPL)
• Interrupt-Vector Macros
11.3.3.1 __ISR(V, IPL)
Use the __ISR(v, IPL) macro to assign the vector-number location and associate it
with the specified IPL. This will place a jump to the interrupt handler at the associated
vector location. This macro also applies the nomips16 attribute since PIC32MX
devices require that interrupt handlers must use the MIPS32 instruction set.
Note: SRS has the shortest latency and SOFT has a longer latency due to
registers saved on the stack. AUTO adds a few cycles to test if SRS or SOFT
should be used.
Note: The interrupt pragma is provided only for compatibility when porting code
from other compilers. The interrupt function attribute is the preferred and
more common way to write an interrupt service routine.
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EXAMPLE 11-2: CORE TIMER VECTOR, IPL2SOFT
#include <xc.h>
#include <sys/attribs.h>
void __ISR(_CORE_TIMER_VECTOR, IPL2SOFT) CoreTimerHandler(void);
Example 1 1-2 creates an interrupt handler function for the core timer interrupt that has
an interrupt priority level of two. The compiler places a dispatch function at the
associated vector location. To reach this function, the core timer interrupt flag and
enable bits must be set, and the interrupt priority should be set to a level of two. The
compiler generates software context-saving code for this handler function.
EXAMPLE 11-3: CORE SOFTWARE 0 VECTOR, IPL3SRS
#include <xc.h>
#include <sys/attribs.h>
void __ISR(_CORE_SOFTWARE_0_VECTOR,IPL3SRS)
CoreSoftwareInt0Handler(void);
Example 1 1-3 creates an interrupt handler function for the core software interrupt 0 that
has an interrupt priority level of three. The compiler places a dispatch function at the
associated vector location. To reach this function, the core software interrupt flag and
enable bits must be set, and the interrupt priority should be set to a level of three. The
device configuration fuses must assign Shadow Register Set 1 to interrupt priority level
three. The compiler generates code that assumes that register context will be saved in
SRS1.
EXAMPLE 11-4: CORE SOFTWARE 1 VECTOR, IPL0AUTO
#include <xc.h>
#include <sys/attribs.h>
void __ISR(_CORE_SOFTWARE_1_VECTOR, IPL0AUTO)
CoreSoftwareInt1Handler(void);
Example 1 1-4 creates an interrupt handler function for the core software interrupt 1 that
has an interrupt priority level of zero. The compiler places a dispatch function at the
associated vector location. T o reach this function, the core software interrupt 1 flag and
enable bits must be set, and the interrupt priority should be set to a level of zero. The
compiler generates code that determines at run time whether software context saving
is required.
EXAMPLE 11-5: CORE SOFTWARE 1 VECTOR, DEFAULT
#include <xc.h>
#include <sys/attribs.h>
void __ISR(_CORE_SOFTWARE_1_VECTOR) _CoreSoftwareInt1Handler(void);
Example 11-5 is functionally equivalent to Example 3. Because the IPL specifier is
omitted, the compiler assumes IPL0AUTO.
11.3.3.2 __ISR_AT_VECTOR(v, IPL)
Use the __ISR_AT_VECTOR(v, IPL) to place the entire interrupt handler at the
vector location and associate it with the software-assigned interrupt priority . Application
code is responsible for making sure that the vector spacing is set to accommodate the
size of the handler . This macro also applies the nomips16 attribute since ISR functions
are required to be MIPS32.
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EXAMPLE 11-6: CORE TIMER VECTOR, IPL2SOFT
#include <xc.h>
#include <sys/attribs.h>
void __ISR_AT_VECTOR(_CORE_TIMER_VECTOR, IPL2SOFT)
CoreTimerHandler(void);
Example 1 1-6 creates an interrupt handler function for the core timer interrupt that has
an in ter rup t pr iori ty leve l of t wo. The c omp iler pl aces the ent ire i nte rru pt ha ndl er at th e
vector location. It does not use a dispatch function. T o reach this function, the core timer
interrupt flag and enable bits must be set, and the interrupt priority should be set to a
level of two. The compiler generates software context-saving code for this handler
function.
11.3.3.3 INTERRUPT-VECTOR MACROS
Each processor-support header file provides a macro for each interrupt-vector number
(for example, /pic32mx/include/proc/p32mx360f512l.h. See the appropriate
header file in the compiler install directory). When used in conjunction with the
__ISR() macro provided by the sys\attribs.h header file, these macros help
make an Interrupt Service Routine easier to write and maintain.
EXAMPLE 11-7: INTERRUPT-VECTOR WITH HANDLER
#include <xc.h>
#include <sys/attribs.h>
void __ISR (_TIMER_1_VECTOR, IPL7SRS) Timer1Handler (void);
Example 1 1-7 creates an interrupt handler function for the T imer 1 interrupt that has an
interrupt priority level of seven. The compiler places a dispatch function at the vector
location associated with macro _TIMER_1_VECTOR as defined in the device-specific
header file. To reach this function, the Timer 1 interrupt flag and enable bits must be
set, and the interrupt priority should be set to a level of seven. For devices that allow
assignment of shadow registers to specific IPL values, the device Configuration bit
settings must assign Shadow Register Set 1 to interrupt priority level seven. The
compiler generates code that assumes that register context will be saved in SRS1.
Example 11-8 uses the peripheral library provided with the compiler to set up Timer 1
for an interrupt using priority level 7. The code is written to toggle pin RD0.
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EXAMPLE 11-8: FULL TIMER 1 EXAMPLE WITH PERIPHERAL LIBRARY
/* Blink an LED on the PIC32MX Ethernet Starter Kit using the
* PIC32MX795F512L target device.
*/
#include <xc.h>
#include <plib.h>
#include <sys/attribs.h>
// Configuration Bit settings using the config pragma
// SYSCLK = 80 MHz (8MHz Crystal/ FPLLIDIV * FPLLMUL / FPLLODIV)
// PBCLK = 10 MHz
// Primary Osc w/PLL (XT+,HS+,EC+PLL)
// WDT OFF
// Other options are “do not care”
//
#pragma config FPLLMUL=MUL_20, FPLLIDIV=DIV_2, FPLLODIV=DIV_1, FWDTEN=OFF
#pragma config POSCMOD=HS, FNOSC=PRIPLL, FPBDIV=DIV_8
// Calculate the PR1 (period) at compile time
#define SYS_FREQ (80000000L)
#define PB_DIV 8
#define PRESCALE 256
#define TOGGLES_PER_SEC 1
#define T1_TICK (SYS_FREQ/PB_DIV/PRESCALE/TOGGLES_PER_SEC)
int main(void)
{
// STEP 1
// Configure the device for maximum performance but do not change the PBDIV
// Given the options, this function will change the flash wait states, RAM
// wait state and enable prefetch cache but will not change the PBDIV.
// The PBDIV value is already set via the config pragma FPBDIV option above.
SYSTEMConfig(SYS_FREQ, SYS_CFG_WAIT_STATES | SYS_CFG_PCACHE);
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// STEP 2. configure Timer 1 using internal clock, 1:256 prescale
OpenTimer1(T1_ON | T1_SOURCE_INT | T1_PS_1_256, T1_TICK);
// set up the timer interrupt with a priority of 7
ConfigIntTimer1(T1_INT_ON | T1_INT_PRIOR_7);
// enable multi-vector interrupts
INTEnableSystemMultiVectoredInt();
// configure PORTDbits.RD0 = output
mPORTDSetPinsDigitalOut(BIT_0);
while(1);
}
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// STEP 3. configure the Timer 1 interrupt handler
// Determine shadow-register or software-stack context saving at
// runtime by using the IPL7AUTO priority specifier.
// Note that the n value in IPLnAUTO _must_ match the priority
// of the timer1 interrupt source configured above.
#ifdef __cplusplus
// For C linkage when compiling for C++
extern "C" {
#endif /* __cplusplus */
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2012 Microchip Technology Inc. DS51686E-page 139
void __ISR(_TIMER_1_VECTOR, IPL7AUTO) Timer1Handler(void)
{
// clear the interrupt flag
mT1ClearIntFlag();
// .. things to do
// .. in this case, toggle the LED
mPORTDToggleBits(BIT_0);
}
#ifdef __cplusplus
}
#endif
11.4 ASSOCIATING A HANDLER FUNCTION WITH AN EXCEPTION VECTOR
For PIC32MX devices, there are 64 exception vectors, numbered 0..63 inclusive. Each
interrupt source is mapped to an exception vector as specified in the device data sheet.
By default, four words of space are reserved at each vector address for a dispatch to
the handler function for that exception source.
An interrupt handler function can be associated with an interrupt vector either as the
target of a dispatch function located at the exception vector address, or as being
located directly at the exception vector address. A single handler function can be the
target of multiple dispatch functions.
The association of a handler function to one or more exception vector addresses is
specified via a vector attribute on the function declaration. For compatibility purposes,
you may also associate a handler function to a vector address using a clause of the
interrupt pragma, a separate vector pragma, or a vector attribute on the function
declaration.
11.4.1 Vector Attribute
A handler function can be associated with one or more exception vector addresses via
an attribute. The at_vector attribute indicates that the handler function should itself
be placed at the exception vector address. The vector attribute indicates that a dis-
patch function should be created at the exception vector address(es) which will transfer
control to the handler function.
For example, the following declaration specifies that function foo will be create d as an
interrupt handler function of priority four. foo will be located at the address of exception
vector 54.
void __attribute__ ((interrupt(IPL4SOFT))) __attribute__
((at_vector(54))) foo (void)
The following declaration specifies that function foo will be created as an interrupt
handler function of priority four. Define dispatch functions targeting foo at exception
vector addresses 52 and 53.
void __attribute__ ((interrupt(IPL4SOFT))) __attribute__
((vector(53, 52))) foo (void)
Handler functions that are linked directly to the vector will be executed faster . Although
the vector spacing can be adjusted, there is limited space between vectors and linking
a substantial handler function directly at a vector may cause it to overlap the higher vec-
tor locations, preventing their use. In such situations, using a dispatch function is a
safer option.
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11.4.2 Int e rr u pt Prag ma Clau s e
The interrupt pragma has an optional vector clause following the priority specifier.
# pragma interrupt function-name IPL-specifier [vector
[@]vector-number [, vector-number-list]]
A dispatch functi on targeting the spe ci fi ed hand ler func tio n will be created at the
exception vector address for the specified vector numbers. If the first vector number is
specified with a preceding “@” symbol, the handler function itself will be located there
directly.
For example, the following pragma specifies that function foo will be created as an
interrupt handler function of priority four . foo will be located at the address of exception
vector 54. A dispatch function targeting foo will be created at exception vector address
34.
#pragma interrupt foo IPL4AUTO vector @54, 34
The following pragma specifies that function bar will be created as an interrupt handler
function of priority five. bar will be located in general purpose program memory (.text
section). A dispatch function targeting bar will be created at exception vector address
23.
#pragma interrupt bar IPL5SOFT vector 23
11.4.3 Vector Pragma
The vector pragma creates one or more dispatch functions targeting the indicated
function. For target functions specified with the interrupt pragma, this functions as
if the vector clause had been used. The target function of a vector pragma can be
any function, including external functions implemented in assembly or by other means.
# pragma vector function-name vector vector-number [,
vector-number-list]
The following pragma defines a dispatch function targeting foo at exception vector
address 54.
#pragma vector foo 54
Note: The interrupt pragma and its vector clause are provided only for compatibil-
ity when porting code from other compilers. The vector function attribute is
the preferred way to associate a handler function to an exception vector
address.
Note: The vector pragma is provided only for compatibility when porting code
from other compilers. The vector function attribute is the preferred way to
associate a handler function to an exception vector address.
Interrupts
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11.5 EXCEPTION HANDLERS
The PIC32MX devices also have two exception vectors for non-interrupt exceptions.
These exceptions are grouped into bootstrap exceptions and general exceptions.
11.5.1 Boot strap Exception
A reset exception is any exception which occurs while bootstrap code is running
(StatusBEV=1). All reset exceptions are vectored to 0xBFC00380.
At this location, the 32-bit toolchain places a branch instruction targeting a function
named _bootstrap_exception_handler(). In the standard library, a default
weak version of this function is provided which merely goes into an infinite loop. If the
user application provides an implementation of
_bootstrap_exception_handler(), that implementation will be used instead.
11.5.2 General Exception
A general exception is any non-interrupt exception which occurs during program
execution outside of bootstrap code (StatusBEV=0). General exceptions are vectored
to offset 0x180 from EBase.
At this location, the 32-bit toolchain places a branch instruction targeting a function
named _general_exception_context(). The provided implementation of this
function saves context, calls an application handler function, restores context and
performs a return from the exception instruction. The context saved is the hi and lo
registers and all General Purpose Registers except s0-s8, which are defined to be
preserved by all called functions and so are not necessary to actively save here again.
The values of the Cause and Status registers are passed to the application handler
function (_general_exception_handler()). If the user application provides an
imple men tation of _general_exception_context(), that implementation will be
used instea d.
void _general_exception_handler (unsigned cause, unsigned status);
A weak default implementation of _general_exception_handler() is provided in
the standard library which merely goes into an infinite loop. If the user application
provides an implementation of _general_exception_handler(), that
implementation will be used instead.
11.6 INTERRUPT SERVICE ROUTINE CONTEXT SWITCHING
The standard calling convention for C/C++ functions will already preserve zero,
s0-s7, gp, sp, and fp. k0 and k1 are used by the compiler to access and preserve
non-GPR context, but are always accessed atomically (i.e., in sequences with global
interrupts disabled), so they need not be preserved actively. A handler function will
actively preserve the a0-a3, t0-t9, v0, v1 and ra registers in addition to the
standard registers.
An interrupt handler function will also actively save and restore processor status
registers that are utilized by the handler function. Specifically, the EPC, SR, hi and lo
registers are preserved as context.
Handler functions may use a shadow register set to preserve the General Purpose
Registers, enabling lower latency entry into the application code of the handler
function. On some devices, the shadow register set is assigned to an interrupt priority
level (IPL) using the device Configuration bit settings (e.g., #pragma config
FSRSSEL=PRIORITY_6). While on other devices, the shadow register set may be hard
wired to IPL7. Consult the target device’s data sheet for more information on the
shadow register set.
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11.6.1 Context Restoration
Any objects saved by software are automatically restored by software before the inter-
rupt function returns. The order of restoration is the reverse to that used when context
is saved.
11.7 LATENCY
There are two elements that affect the number of cycles between the time the interrupt
source occurs and the execution of the first instruction of your ISR code. These are:
•Processor Servicing of Interrupt – The amount of time it takes the processor to
recognize the interrupt and branch to the first address of the interrupt vector. To
determine this value, refer to the processor data sheet for the specific processor
and interrupt source being used.
•ISR Code – The compiler saves the registers that were used by the ISR. This
includes the TODO registers. Moreover, if the ISR calls an ordinary function, then
the compiler will save all the working registers, even if they are not all used explic-
itly in the ISR itself. This must be done, because the compiler cannot know, in
general, which resources are used by the called function.
11.8 NESTING INTERRUPTS
Interrupts may be nested. The interrupt priority scheme implemented in the PIC32
architecture allows you to specify which interrupt sources may be interruptible by
others. See your device data sheet for explicit details on interrupt operation.
11.9 ENABLING/DISABLING INTERRUPTS
Macros are available in the PIC32 peripheral library to control aspects of interrupt
operation. See the Microchip PIC32MX Peripheral Library documentation for more
information.
11.10 ISR CONSIDERATIONS
There are few issues arising with interrupt functions.
As with all compilers, limiting the number of registers used by the interrupt function, or
any functions called by the interrupt function, may result in less context switch code
being generated and executed by the compiler , see Section 11.7 “Latency”. Keeping
interrupt functions small and simple will help you achieve this.
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USER’S GUIDE
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Chapter 12. Main, Runtime Start-up and Rese t
12.1 INTRODUCTION
When creating C/C++ code, there are elements that are required to ensure proper pro-
gram operation: a main function must be present; start-up code will be needed to ini-
tialize and clear variables and setup registers and the processor; and reset conditions
will need to be handled .
• The Main Function
• Runtime Start-up Code
• The On Reset Routine
12.2 THE MAIN FUNCTION
The identifier main is special. It must be used as the name of a function that will be the
first function to execute in a program. You must always have one and only one function
called main in your programs. Code associated with main, however, is not the first
code to execute after reset. Additional code provided by the compiler and known as the
runtime start-up code is executed first and is responsible for transferring control to the
main() function.
12.3 RUNTIME START-UP CODE
A C/C++ program requires certain objects to be initialized and the processor to be in a
particular state before it can begin execution of its function main(). It is the job of
the runtime start-up code to perform these tasks. The runtime start-up code is exe-
cuted before main(), but if you require any special initialization to be performed imme-
diately after reset, you should use on reset feature described in Section 12.4 “The On
Reset Routine”
The PIC32MX start-up code must perform the following:
1. Jump to NMI Handler if an NMI Occurred
2. Initialize Stack Pointer and Heap
3. Initialize Global Pointer
4. Initialize or Clear Variables and RAM Functions Using the Data-Initialization
Template
5. Initialize Bus Matrix Registers
6. Call “On Bootstrap” Procedure
7. Change Locati on of Excep tio n Vectors
8. For C++, call the C++ initialization code to invoke all constructors for file-scope
static storage objects
9. Call Ma in
The followi ng prov is io ns are made re gardi ng the run- tim e model :
• Kernel mode only
• KSEG1 only
• RAM functions are attributed with __ramfunc__ or __longramfunc__,
(defined in sys/attribs.h) meaning that all RAM functions end up in
the .ramfunc section and the function is ramfunc attributed.
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12.3.1 Jump to NMI Handler if an NMI Occurred
If an NMI caused entry to the Reset vector, a jump to an NMI handler procedure
(_nmi_handler) occurs. A weak version of the NMI handler procedure is provided
that performs an ERET. The _nmi_handler function must be attributed with
nomips16 [e.g., __attribute__((nomips16))] since the start-up code jumps to
this function.
12.3.2 Initial ize Stack Pointer and Heap
The Stack Pointer (sp) register must be initialized in the start-up code. To enable the
start-up code to initialize the sp register , the linker script must initialize a variable which
points to the end of KSEG1 data memory1. This variable is named _stack. The user
can change the minimum amount of stack space allocated by providing the command
line option --defsym _min_stack_size=N to the linker. _min_stack_size is
provided by the linker script with a default value of 1024.
On a similar note, the user may wish to utilize a heap with their application. While the
start-up code does not need to initialize the heap, the standard C libraries (sbrk) must
be made aware of the heap location and its size. The linker script creates a variable to
identify the beginning of the heap. The location of the heap is the end of the utilized
KSEG1 data memory. This variable is named _heap. The user can change the
minimum amount of heap space allocated by providing the command line option
--defsym _min_heap_size=M to the linker . _min_heap_size is provided by the
linker script with a default value of 0. If the heap is used when the heap size is set to
zero, the behavior is the same as when the heap usage exceeds the minimum heap
size. Namely, it overflows int o the space allocated for the stack.
The heap and the stack use the unallocated KSEG1 data memory, with the heap
starting from a low address in KSEG1 data memory , and growing upwards towards the
stack while the stack starts at a higher address in KSEG1 data memory and grows
downwards towards the heap. The linker attempt to allocate the heap and stack
together in the largest gap of memory available in the KSEG1 data memory region. If
enough space is not available based on the minimum amount of heap size and stack
size requested, the linker issues an error.
1. The end of data memory is different based on whether RAM functi o n s exi st. If RAM functions exist, then
part of the DRM must be configured for the ker nel program to contain the RA M f unctions, and the Stack
Pointer is located one word prior to the beginning of the DRM kernel program boundary address. If RAM
functions do not exist, then the Stack Pointer is located at the true end of DRM.
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FIGURE 12-1: STACK AND HEAP LAYOUT
FIGURE 12-2: STACK AND HEAP LAYOUT WITH RAM FUNCTIONS
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12.3.3 Initialize Global Pointer
The compiler toolchain supports Global Pointer (gp) relative addressing. Loads and
stores to data residing within 32KB of either side of the address stored in the gp register
can be performed in a single instruction using the gp register as the base register.
Without the Global Pointer, loading data from a static memory area takes two
instructions – one to load the Most Significant bits of the 32-bit constant address
computed by the compiler/linker and one to do the data load.
To utilize gp-relative addressing, the compiler and assembler must group all of the
“small” variables and constants into one of the following sections:
The linker must then group all of the above input sections together. This grouping is
handled by the default linker script. The run-time start-up code must initialize the gp
register to point to the “middle” of this output section. To enable the start-up code to
initialize the gp register, the linker script must initialize a variable which is 32 KB from
the start of the output section containing the “small” variables and constants. This
variab le is named _gp (to match core linker scripts). Besides being initialized in the
standard GPR set, the Global Pointer must also be initialized in the register shadow set.
FIGURE 12-3: GLOBAL POINTER LOCATION
• .lit4. • lit8
• .sdata. • sbss
• .sdata.* • sbss.*
• .gnu.linkonce.s.* • .gnu.linkonce.sb.*
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12.3.4 Initialize or Clear Variables and RAM Functions Using the
Data-Initialization Template
Those non-auto objects which are not initialized must be cleared before execution of
the program begins. This task is also performed by the runtime start-up code.
Uninitialized variables are those which are not auto objects and which are not
assigned a value in their definition, for example output in the following example:
int output;
int main(void) { ...
Such uninitialized objects will only require space to be reserved in RAM where they will
reside and be accessed during program execution (runtime).
There are two uninitialized data sections—.sbss and .bss. The .sbss section is a
data segment containing uninitialized variables less than or equal to n bytes where n
is determined by the -Gn command line option. The .bss section is a data segment
containing uninitialized variables not included in .sbss.
Another task of the runtime start-up code is to ensure that any initialized variables con-
tain their initial value before the program begins execution. Initialized variables are
those which are not auto objects and which are assigned an initial value in their defi-
nition, for example input in the following example:
int input = 88;
int main(void) { ...
Such initialized objects have two components: their initial value (0x0088 in the above
example) stored in program memory (i.e. placed in the HEX file), and space for the
variable reserved in RAM, which will reside and be accessed during program execution
(runtime).
The runtime start-up code will copy all the blocks of initial values from program memory
to RAM so the variables will contain the correct values before main is ex ecuted.
Since auto objects are dynamically created, they require code to be positioned in the
function in which they are defined to perform their initialization. It is possible that the
initial value of an auto object may change on each instance of the function and so the
initial values cannot be stored in program memory and copied. As a result, initialized
auto objects are not considered by the runtime start-up code, but are instead initialized
by assembly code in each function output.
Variables whose contents should be preserved over a reset, or even power off, should
be qualified with the persistent attribute, see Section 6.10 “Standard Type Qual-
ifiers”. Such variables are linked at a different area of memory and are not altered by
the runtime start-up code in any way.
Four initialized data sections exist:.sdata, .data, .lit4, and .lit8. The .sdata
section is a data segment containing initialized variables less than or equal to n bytes
where n is determined by the -Gn command line option. The .data secti on is a data
segment containing initialized variables not included in .sdata. The .lit4 and
.lit8 sections contain constants, which the assembler stores in memory rather than
in the instruction stre am.
Note: Initialized auto variables can impact code perform ance, particularly if the
objects are large in size. Consider using global or static objects instead.
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In order to clear or initialize these sections, the linker c reates a data-initialization
template, which is loaded into an output section named .dinit. The linker creates
this special .dinit section, allocated in program memory, to hold the template for
the run-time initialization of data. The C/C++ start-up module, crt0.o, interprets this
template and copies initial data values into initialized data sections. This includes
sec tions cont ainin g ramfunc attributed functions. Other data sections (such as .bss)
are cleared before the main() function is called. The persistent data section (.pbss)
is not affected. When the application’s main program takes control, all variables and
RAM functions in data memory have been initialized.
The data initialization template contains one record for each output section in data
memory. The template is terminated by a null instruction word. The format of a data
initialization record is:
/* data init record */
struct data_record {
char *dst; /* destination address */
unsigned int len; /* length in bytes */
unsigned int format; /* format code */
char dat[0]; /* variable-length data */
};
The first element of the record is a pointer to the section in data memory. The second
and third elements are the section length and format code, respectively. The last
element is an optional array of data bytes. For bss-type sections, no data bytes are
required.
Currently supported format codes are:
• 0 – Fill the output section with zeros
• 1 – Copy each byte of data from the data array
12.3.5 Initial ize Bus Matrix Registers
The bus matrix registers (BMXDKPBA, BMXDUDBA, BMXDUPBA) should be initialized by
the start-up code if any RAM functions exist; otherwise, these registers should not be
modified. To determine whether any RAM functions exist in the application, the linker
provides a variable that contains the length of the .ramfunc section 1. This va riabl e is
named _ramfunc_length. In addition, the linker provides a 2K-aligned variable
required for the boundary register (BMXDKPBA). The variable is named
_bmxdkpba_address. The default linker script also provides two variables that
contain the address of the bus matrix registers. These variables are named
_bmxdkpba_address, _bmxdudba_address, and _bmxdupba_address. The
following calculations are used to calculate these addresses:
_bmxdudba_address = LENGTH(${DATA_MEMORY_LOCATION}) ;
_bmxdupba_address = LENGTH(${DATA_MEMORY_LOCATION}) ;
The linker ensures that RAM functions are aligned to a 2K alignment boundary as is
required by the BMXDKPBA register.
1. All functions attributed with __ramfunc__ or __longramfunc__ are placed in the
.ramfunc section.
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FIGURE 12-4: BUS MATRIX INITIALIZATION
12.3.5.1 INITIALIZE CP0 REGISTERS
The CP0 registers are initialized in the following order:
1. Count register
2. Compare register
3. EBase register
4. IntCtl register
5. Cause register
6. Status register
12.3.5. 2 HA RDWA RE EN ABLE REG IS T ER (HWREna – CP0 REGISTER 7,
SELECT 0)
This register contains a bit mask that determines which hardware registers are
accessible via the RDHWR instruction. Privileged software may determine which of the
hardware registers are accessible by the RDHWR instruction. In doing so, a register may
be virtualized at the cost of handling a Reserved Instruction Exception, interpreting the
instruction, and returning the virtualized value. For example, if it is not desirable to
provide direct access to the Count register, access to the register may be individually
disabled, and the return value can be virtualized by the operating system.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.3 BAD VIRTUAL ADDRESS REGISTER (BadVAddr – CP0 REGISTER 8,
SELECT 0)
This register is a read-only register that captures the most recent virtual address that
caused an Address Error exception (AdEL or AdES).
No initialization is performed on this register in the PIC32MX start-up code.
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12.3.5.4 COUNT REGISTER (Count – CP0 REGISTER 9, SELECT 0)
This register acts as a timer, incrementing at a constant rate, whether or not an
instruction is executed, retired, or any forward progress is made through the pipeline.
The counter increments every other clock if the DC bit in the Cause register is ‘0’. The
Count register can be written for functional or diagnostic purposes, including at Reset
or to synchronize processors. By writing the CountDM bit in the Debug register, it is
possible to control whether the Count register continues incrementing while the
processor is in Debug mode.
This register is cleared in the PIC32MX start-up code.
12.3.5.5 COMPARE REGISTER (Compare – CP0 REGISTER 11, SELECT 0)
This register acts in conjunction with the Count register to implement a timer and timer
interrupt function. The timer interrupt is an output of the core. The Compare register
maintains a stable value and does not change on its own. When the value of the Count
register equals the value of the Compare register, the SI_TimerInt pin is asserted.
This pin remains asserted until the Compare register is written. The SI_TimerInt pin
can be fed back into the core on one of the interrupt pins to generate an interrupt. For
diagnostic purposes, the Compare register is a read/write register. In normal use,
however, the Compare register is write-only. Writing a value to the Compare register,
as a side effect, clears the timer interrupt.
This register is set to 0xFFFFFFFF in the PIC32MX start-up code.
12.3.5.6 STATUS REGISTER (Status – CP0 REGIST ER 12, SE LE CT 0)
This register is a read/write register that contains the operating mode, Interrupt
Enabling, and the diagnostic states of the processor . Fields of this register combine to
create operating modes for the processor.
The following settings are initialized by the PIC32MX start-up code
(0b000000000x0xx0?00000000000000000):
• Access to Coprocessor 0 not allowed in User mode (CU0 = 0)
• User mode uses configured endianess (RE = 0)
• No change to exception vectors location (BEV = no change)
• No change to flag bits that indicate reason for entry to the Reset exception vector
(SR, NMI = no change)
• Interrupt masks are cleared to disable any pending interrupt requests (IM7..IM2
= 0, IM1..IM0 = 0)
• Interrupt priority level is 0 (IPL = 0)
• Base mode is Kernel mode (UM = 0)
• Error level is n ormal (ERL = 0)
• Exception level is normal (EXL = 0)
• Interrupts are disabled (IE = 0)
12.3.5.7 INTERRUPT CONTROL REGISTER (IntCtl – CP0 REGISTER 12,
SELECT 1)
This register controls the expanded interrupt capability added in Release 2 of the
Architecture, including vectored interrupts and support for an external interrupt
controller.
This register contains the vector spacing for interrupt handling. The vector spacing
portion of this register (bits 9..5) is initialized with the value of the _vector_spacing
symbol by the PIC32MX start-up code. All other bits are set to ‘1’.
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12.3.5.8 SHADOW REGISTER CONTROL REGISTER (SRSCtl – CP0 REGISTER
12, SELECT 2)
This register controls the operation of the GPR shadow sets in the processor.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.9 SHADOW REGISTER MAP REGISTER (SRSMap – CP0 REGISTER 12,
SELECT 3)
This register contains eight 4-bit fields that provide the mapping from a vector number
to the shadow set number to use when servicing such an interrupt. The values from this
register are not used for a non-interrupt exception, or a non-vectored interrupt
(CauseIV = 0 or IntCtlVS = 0). I n such cases, the shadow se t number comes from
SRSCtlESS. If SRSCtlHSS is zero, the results of a software read or write of this
register are UNPREDICTABLE. The operation of the processor is UNDEFINED if a
value is written to any field in this register that is greater than the value of SRSCtlHSS.
The SRSMap register contains the shadow register set numbers for vector numbers
7..0. The same shadow set number can be established for multiple interrupt vectors,
creating a many-to-one mapping from a vector to a single shadow register set number .
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.10 CAUSE REGISTER (Cause – CP0 REGISTER 13, SELECT 0)
This register primarily describes the cause of the most recent exception. In addition,
fields also control software interrupt requests and the vector through which interrupts
are dispatched. With the exception of the DC, IV, and IP1..IP0 fields, all fields in the
Cause register are read-only. Release 2 of the Architecture added optional support for
an External Interrupt Controller (EIC) interrupt mode, in which IP7..IP2 are
interpreted as the Requested Interrupt Priority Level (RIPL).
The following settings are initialized by the PIC32MX start-up code:
• Enable counting of Count register (DC = no change)
• Use the special exception vector (16#200) (IV = 1)
• Disable software interrupt requests (IP1..IP0 = 0)
12.3.5.11 EXCEPTION PROGRAM COUNTER (EPC – CP0 REGISTER 14, SELECT
0)
This register is a read/write register that contains the address at which processing
resumes after an exception has been serviced. All bits of the EPC register are
significant and must be writable. For synchronous (precise) exceptions, the EPC
contains one of the following:
• The virtual address of the instruction that was the direct cause of the exception
• The virtual address of the immediately preceding branch or jump instruction, when
the exception causing instruction is a branch delay slot and the Branch Delay
bit in the Cause register is set.
On new exceptions, the processor does not write to the EPC register when the EXL bit
in the Status register is set; however, the register can still be writt en via the MTC0
instruction.
No initialization is performed on this register in the PIC32MX start-up code.
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12.3.5.12 PROCESSOR IDENTIFICATION REGISTER (PRId – CP0 REGISTER 15,
SELECT 0)
This register is a 32-bit read-only register that contains information identifying the
manufacturer, manufacturer options, processor identification, and revision level of the
processor.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.13 EXCEPTION BASE REGISTER (EBase – CP0 REGISTER 15, SELECT 1)
This register is a read/write register containing the base address of the exception
vectors used when StatusBEV equals 0, and a read-only CPU number value that may
be used by software to distinguish different processors in a multi-processor system.
The EBase register provides the ability for software to identify the specific processor
within a multi-processor system, and allows the exception vectors for each processor
to be different, especially in systems composed of heterogeneous processors. Bits
31..12 of the EBase register are concatenated with zeros to form the base of the
exception vectors when StatusBEV is 0. The exception vector base address comes
from fixed defaults when StatusBEV is 1, or for any EJT AG Debug exception. The reset
state of bits 31..12 of the EBase register initialize the exception base register to
16#80000000, providing backward compatibility with Release 1 implementations. Bits
31..30 of the EBase register are fixed with the value 2#10 to force the exception base
address to be in KSEG0 or KSEG 1 unm app ed virtu al add re ss segm ents.
If the value of the exception base register is to be changed, this must be done with
StatusBEV equal 1. The operation of the processor is UNDEFINED if the Exception
Base field is written with a different value when StatusBEV is 0.
Combining bits 31..30 with the Exception Base field allows the base address of the
exception vectors to be placed at any 4K byte page boundary . If vectored interrupts are
used, a vector offset greater than 4K byte can be generated. In this case, bit 12 of the
Exception Base field must be zero. The operation of the processor is UNDEFINED if
software writes bit 12 of the Exception Base field with a 1 and enables the use of a
vectored interrupt whose offset is greater than 4K bytes from the exception base
address.
This register is initialized with the value of the _ebase_address symbol by the
PIC32MX start-up code. _ebase_address is provided by the linker script with a
default value of the start of KSEG1 program memory. The user can change this value
by providing the command line option -–defsym _ebase_address=A to the linker.
12.3.5.13.1 Config Register (Config – CP0 Register 16, Select 0)
This register specifies various configuration and capabilities information. Most of the
fields in the Config register are initialized by hardware during the Reset exception
process, or are constant.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.13.2 Config1 Register (Config1 – CP0 Register 16, Select 1)
This register is an adjunct to the Config register and encodes additional information
about the capabilities present on the core. All fields in the Config1 register are
read-only.
No initialization is performed on this register in the PIC32MX start-up code.
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12.3.5.13.3 Config2 Register (Config2 – CP0 Register 16, Select 2)
This register is an adjunct to the Config register and is reserved to encode additional
capabilities information. Config2 is allocated for showing the configuration of level 2/3
caches. These fields are reset to 0 because L2/L3 caches are not supported on the
core. All fields in the Config2 register are read-only.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.13.4 Config3 Register (Config3 – CP0 Register 16, Select 3)
This register encodes additional capabilities. All fields in the Config3 register are
read-only.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.14 DEBUG REGISTER (Debug – CP0 REGISTER 23, SELECT 0)
This register is used to control the debug exception and provide information about the
cause of the debug exception, and when re-entering at the debug exception vector due
to a normal exception in Debug mode. The read-only information bits are updated
every time the debug exception is taken, or when a normal exception is taken when
already in Debug mode. Only the DM bit and the EJTAGver field are valid when read
from non-Debug mode. The values of all other bits and fields are UNPREDICTABLE.
Operation of the processor is UNDEFINED if the Debug register is written from
non-Debug mode.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.15 TRACE CONTROL REGISTER (TraceControl – CP0 REGISTER 23,
SELECT 1)
This register provides control and status information. The TraceControl register is
only implemented if the EJTAG Trace capability is present.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.16 T RACE CONTROL 2 REGISTER (TraceControl2 – CP0 REGISTER 23,
SELECT 2)
This register provides additional control and status information. The TraceControl2
register is only implemented if the EJTAG Trace capability is present.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.17 USER T RACE DATA REGISTER (UserTraceData – CP0 REGISTER 23,
SELECT 3)
When this register is written to, a trace record is written indicating a type 1 or type 2
user format. This type is based on the UT bit in the TraceControl register. This
register cannot be written in consecutive cycles. The trace output data is
UNPREDICTABLE if this register is written in consecutive cycles. The
UserTraceData register is only implemented if the EJT AG Trace capability is present.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.18 TRACEBPC REGISTER (TraceBPC – CP0 REGIST ER 23, SE LE CT 4)
This register is used to control start and stop of tracing using an EJTAG hardware
breakpoint. The hardware breakpoint would then be set as a triggered source and
optionally also as a Debug exception breakpoint. The TraceBPC register is only
implemented if both the hardware breakpoints and the EJTAG Trace cap are present.
No initialization is performed on this register in the PIC32MX start-up code.
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12.3.5.19 DEBUG2 REGISTER (Debug2 – CP0 REGISTER 23, SELECT 5)
This register holds additional information about complex breakpoint exceptions. The
Debug2 register is only implemented if complex hardware breakpoints are present.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.20 DEBUG EXCEPTION PROGRAM COUNTER (DEPC – CP0 REGISTER
24, SELECT 0)
This register is a read/write register that contains the address at which processing
resumes after a debug exception or Debug mode exception has been serviced. For
synchronous (precise) debug and Debug mode exceptions, the DEPC contains either:
• The virtual address of the instruction that was the direct cause of the debug
excepti on, or
• The virtual address of the immediately preceding branch or jump instruction, when
the debug exception causing instruction is in a branch delay slot, and the Debug
Branch Delay (DBD) bit in the Debug register is set.
For asynchronous debug exceptions (debug interrupt, complex break), the DEPC
contains the virtual address of the instruction where execution should resume after the
debug handler code is executed.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.21 ERROR EXCEPTION PROGRAM COUNTER (ErrorEPC – CP0
REGISTER 30, SELECT 0)
This register is a read/write register , similar to the EPC register , except that it is used on
error exceptions. All bits of the ErrorEPC are significant and must be writable. It is also
used to store the program counter on Reset, Soft Reset, and Non-Maskable Interrupt
(NMI) exceptions. The ErrorEPC register contains the virtual address at which
instruction processing can resume after servicing an error. This address can be:
• The virtual address of the instruction that caused the exception, or
• The virtual address of the immediately preceding branch or jump instruction when
the error causing instruction is a branch delay slot.
Unlike the EPC register, there is no corresponding branch delay slot indication for the
ErrorEPC register.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.5.22 DEBUG EXCEPTION SAVE REGISTER (DeSave – CP0 REGISTER 31,
SELECT 0)
This register is a read/write register that functions as a simple memory location. This
register is used by the debug exception handler to save one of the GPRs that is then
used to save the rest of the context to a pre-determined memory area (such as in the
EJTAG Probe). This register allows the safe debugging of exception handlers and other
types of code where the existence of a valid stack for context saving cannot be
assumed.
No initialization is performed on this register in the PIC32MX start-up code.
12.3.6 Call “On Bootstrap” Procedure
A procedure is called after initializing the CP0 registers. This procedure allows users to
perform actions during bootstrap (i.e., while StatusBEV is set) and before entering into
the main routine. An empty weak version of this procedure (_on_bootstrap) is
provided with the start-up code. This procedure may be used for performing hardware
initialization and/or for initializing the environment required by an RTOS.
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12.3.7 Change Location of Exception Vectors
Immediately before executing any application code, the StatusBEV is cleared to
change the location of the exception vectors from the bootstrap location to the normal
location.
12.3.8 Call the C++ initialization code
Invoke all constructors for C++ file-scope static-storage objects. The startup code must
call the constructors last because the low-level initialization must be done before exe-
cuting application code.
12.3.9 Call Main
The last thing that the start-up code performs is a call to the main routine. If the user
returns from main, the start-up code goes into an infinite loop.
12.3.10 Symbols Required by Start-up Code and C/C++ Library
This section details the symbols that are required by the start-up code and C/C++
library. Currently the default linker script defines these symbols. If an application
provides a custom linker script, the user must ensure that all of the following symbols
are provided in order for the start-up code and C library to function:
Symbol Name Description
_bmxdkpba_address The address t o place into the BMXDKPBA register if
_ramfunc_length is greater than 0.
_bmxdudba_address The address t o place into the BMXDUDBA register if
_ramfunc_length is greater than 0.
_bmxdupba_address The address t o place into the BMXDUPBA register if
_ramfunc_length is greater than 0.
_ebase_address The location of EBASE.
_end The end of data allocation.
_gp Points to the “middle” of the small variables region.
By convention this is 0x8000 bytes from the first
location used for small variables.
_heap The starting location of the heap in DRM.
_ramfunc_begin The starting location of the RAM functions. This
should be located at a 2K boundary as it is used to
initialize the BMXDKPBA register.
_ramfunc_length The length of the .ramfunc section.
_stack The starting location of the stack in DRM.
Remember that the stack grows from the bottom of
data memory so this symbol should point to the
bottom of the section allocated for the stack.
_vector_spacing T he initiali zation val ue for the vect or spacing field in
the IntCtl register.
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12.3.11 Exceptions
In addition, two weak general exception handlers are provided that can be overridden
by the application — one to handle exceptions when StatusBEV is 1
(_bootstrap_exception_handler), and one to handle exceptions when
StatusBEV is 0 (_general_exception_handler). Both the weak Reset exception
handler and the weak general exception handler provided with the start-up code enters
an infinite loop. The start-up code arranges for a jump to the reset exception handler to
be located at 0xBFC00380, and a jump to the general exception handler to be located
at EBASE + 0x180.
Both handlers must be attributed with the nomips16 [e.g., __attribute__
((nomips16))], since the start-up code jumps to these functions.
FIGURE 12-5: EXCEPTIONS
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12.4 THE ON RESET ROUTINE
Some hardware configurations require special initialization, often within the first few
instruction cycles after reset. To achieve this, there is a hook provided via the on reset
routine.
This routine is called after initializing a minimum ‘C’ context. An empty weak version of
this procedure (_on_reset) is provided with the start-up code. A stub for this routine
can be found in pic32-libs/libc/stubs in the installation directory of your
compiler.
Special consideration needs to be taken by the user if this procedure is written in ‘C’.
Most importantly, statically allocated variables are not initialized (with either the speci-
fied initializer or a zero as required for uninitialized variables).The stack pointer has
been initialized when this routine is called.
12.4.1 Clearing Objects
The runtime start-up code will clear all memory locations occupied by uninitialized
variables so they will contain zero before main() is execute d.
Variables whose contents should be preserved over a reset should use the
persistent attribute, see Sec tion 6.10 “Standard Type Qualifiers” for more infor-
mation. Such variables are linked in a different area of memory and are not altered by
the runtime start-up code in any way.
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Chapter 13. Library Routines
13.1 USING LIBRARY ROUTINES
Library functions or routines (and any associated variables) will be automatically linked
into a program once they have been referenced in your source code. The use of a func-
tion from one library file will not include any other functions from that library. Only used
library functions will be linked into the program output and consume memory.
Your program will require declarations for any functions or symbols used from libraries.
These are contained in the standard C header (.h) files. Header files are not library
files and the two files types should not be confused. Library files contain precompiled
code, typically functions and variable definitions; the header files provide declarations
(as opposed to definitions) for functions, variables and types in the library files, as well
as other preprocessor macros.
#include <math.h> // declare function prototype for sqrt
int main(void)
{
double i;
// sqrt referenced; sqrt will be linked in from library file
i = sqrt(23.5);
}
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Chapter 14. Mixing C/C++ and Assembly Language
14.1 INTRODUCTION
Assembly language code can be mixed with C/C++ code using two different tech-
niques: writing assembly code and placing it into a separate assembler module, or
including it as in-line assembly in a C/C++ module.This section describes how to use
assembly language and C/C++ modules together. It gives examples of using C/C++
variables and functions in assembly code, and examples of using assembly language
variables and functions in C/C++.
The more assembly code a project contains, the more difficult and time consuming its
maintenance will be. As the project is developed, the compiler may work in different
ways as some optimizations look at the entire program. The assembly code is more
likely to fail if the compiler is updated due to differences in the way the updated compiler
may work. These factors do not affect code written in C/C++
• Using Inline Assembly Language
• Predefined Assembly Macros
14.2 USING INLINE ASSEMBLY LANGUAGE
Within a C/C++ function, the asm statement may be used to insert a line of assembly
language code into the assembly language that the compiler generates. Inline
assembly has two forms: simple and extended.
In the simple form, the assembler instruction is written using the syntax:
asm ("instruction");
where instruction is a valid assembly-language construct. If you are writing inline
assembly in ANSI C programs, write __asm__ instead of asm.
In an extended assembler instruction using asm, the operands of the instruction are
specified using C/C++ expressions. The extended syntax is:
asm("template" [ : [ "constraint"(output-operand) [ , ... ] ]
[ : [ "constraint"(input-operand) [ , ... ] ]
[ "clobber" [ , ... ] ]
]
]);
You must specify an assembler instruction template, plus an operand constraint
string for each operand. The template specifies the instruction mnemonic, and
optionally placeholders for the operands. The constraint strings specify operand
constraints, for example, that an operand must be in a register (the usual case), or that
an operand must be an immediate value.
Note: If assembly must be added, it is preferable to write this as self-contained
routine in a separate assembly module rather than in-lining it in C code.
Note: Only a single string can be passed to the simple form of inline
assembly.
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Constraint letters and modifiers supported by the compiler are listed in Table 14-1
through Table 14-4.
TABLE 14-1: REGISTER CONSTRAINT LETTERS SUPPORTED BY THE
COMPILER
TABLE 14-2: INTEGER CONSTRAINT LETTERS SUPPORTED BY THE
COMPILER
TABLE 14-3: GENERAL CONSTRAINT LETTERS SUPPORTED BY THE
COMPILER
TABLE 14-4: CONSTRAINT MODIFIERS SUPPORTED BY THE COMPILER
Examples:
• Insert Bit Field
• Multiple Assembler Instructions
Letter Constraint
cA register suitable for use in an indirect jump
dAn address register . This is equiv alent to @code{r} unles s generating MI PS16
code
ka Registers that can be used as the target of multiply-accumulate instructions
lThe @code{lo} register. Use this register to store values that are no bigger
than a word
xThe concatenated @code{hi} and @code{lo} registers. Use thi s register to
store double-word values
Letter Constraint
IA signed 32-bit constant (for arithmetic instructions)
JInteger zero
KAn unsigned 32-bit constant (for logic instructions)
LA signed 32-b it const ant in which the lower 32 bi ts are ze ro. Such con st ants can
be loaded using @code{lui}
MA constant that cannot be loaded using @code{lui}, @code{addiu}or
@code{ori}
NA constant in the range -65535 to -1 (inclusive)
OA signed 15-bit constant
PA constant in the range 1 to 65535 (inclusive)
Letter Constraint
RAn address that can be used in a non-macro load or store.
Letter Constraint
=Means that this operand is write-only for this instruction: the previous value is
discarded and replaced by output data
+Means that this operand is both read and written by the instruction
&Means that this operand is an earlyclobber operand, which is modified
before the instruction is finished using the input operands. Therefore, this
operand may not lie in a register that is used as an input operand or as part of
any memory address
dSecond register for operand number n, i.e., %dn..
qFourth register for operand number n, i.e., %qn..
tThird register for operand number n, i.e., %tn..
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Insert Bit Field
This example demonstrates how to use the INS instruction to insert a bit field into a
32-bit wide variable. This function-like macro uses inline assembly to emit the INS
instruction, which is not commonly generated from C/C++ code.
/* MIPS32r2 insert bits */
#define _ins(tgt,val,pos,sz) __extension__({ \
unsigned int __t = (tgt), __v = (val); \
__asm__ ("ins %0,%z1,%2,%3" /* template */ \
: "+d" (__t) /* output */ \
: "dJ" (__v), "I" (pos), "I" (sz)); /* input */ \
__t; \
})
Here __v, pos, and sz are input operands. The __v operand is constrained to be of
type 'd' (an address register) or 'J' (integer zero). The pos and sz operands are con-
strained to be of type 'I' (a signed 32-bit constant).
The __t output operand is constrained to be of type 'd' (an address register). The '+'
modifier means that this operand is both read and written by the instruction and so the
operand is both an input and an output.
The following example shows this macro in use.
unsigned int result;
void example (void)
{
unsigned int insertval = 0x12;
result = 0xAAAAAAAAu;
result = _ins(result, insertval, 4, 8);
/* result is now 0xAAAAA12A */
}
For this example, the compiler may generate assembly code similar to the following.
li $2,-1431699456 # 0xaaaa0000
ori $2,$2,0xaaaa # 0xaaaa0000 | 0xaaaa
li $3,18 # 0x12
ins $2,$3,4,8 # inline assembly
lui $3,%hi(result) # assign the result back
j $31 # return
sw $2,%lo(result)($3)
Multiple Assembler Instructions
This example demonstrates how to use the WSBH and ROTR instructions together for a
byte swap. The WSBH instruction is a 32-bit byte swap within each of the two halfwords.
The ROTR instruction is a rotate right by immediate. This function-like macro uses inline
assembly to create a “byte-swap word” using instructions that are not commonly gen-
erated from C/C++ code.
The following shows the definition of the function-like macro, _bswapw.
/* MIPS32r2 byte-swap word */
#define _bswapw(x) __extension__({ \
unsigned int __x = (x), __v; \
__asm__ ("wsbh %0,%1;\n\t" \
"rotr %0,16" /* template */ \
: "=d" (__v) /* output */ \
: "d" (__x)) /* input*/ ; \
__v; \
})
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Here __x is the C expression for the input operand. The operand is constrained to be
of type 'd', which denotes an address register.
The C expr ession __v is the output operand. This operand is also constrained to be of
type 'd'. The '=' means that this operand is write-only for this instruction: the previous
value is discarded and replaced by output data.
The function-like macro is shown in the following example assigning to result the
content of value, swapped.
unsigned int result;
int example (void)
{
unsigned int value = 0x12345678u;
result = _bswapw(value);
/* result == 0x78563412 */
}
The compiler may generate assembly code similar to the following for this example:
li$2,305397760 # 0x12340000
addiu$2,$2,22136 # 0x12340000 + 0x5678
wsbh $2,$2; # From inline asm
rotr $2,16 # From inline asm
lui$2,%hi(result) # assign back to result
j $31 # return
sw$3,%lo(result)($2)
14.2.1 Equivalent Assembly Symbo ls
C/C++ symbols can be accessed directly with no modification in extended assembly
code.
14.3 PREDEFI N ED ASSE MBLY MACR OS
Several predefined macros are available once you include <xc.h>. The exact operation
of these macros is dependent on the instruction set employed. Table 14-5 shows
general purpose predefined macros and their operation.
TABLE 14-5: PREDEFINED MACROS
Macro Description
_nop() Insert a No Operation instruction
_ehb() Insert Execution Hazard Barrier instruction
_sync() Insert Synchronize Shared Memory instruction
_wait() Insert instruction to enter Standby mode
_mfc0(rn, sel) See <xc.h> file
_mtc0(rn, sel, v) See <xc.h> file
_mxc0(rn, sel, v) See <xc.h> file
_bcc0(rn, sel, clr) For the CP0 register specified by rn and sel, clear bits
corresponding to those bits in clr which are non-zero
_bsc0(rn, sel, set) For the CP0 register specified by rn and sel, clear bits
corresponding to those bits in clr which are non-zero
_bcsc0(rn, sel, clr,
set) For the CP0 register specified by rn and sel, clear bits
corresponding to those bits in clr which are non-zero, and
set bits corresponding to those bits in set which are non-zero
for the C P0 regi ster specifi ed by rn and sel, clear bit s corre-
spondi ng to those bit s in clr which are non-ze ro, and set bit s
corresponding to those bits in set which are non-zero
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_clz(x) Count leading zeroes in x
_ctz(x) Count trailing ze roes in x
_clo(x) Count leading ones in x
_dclz(x) Simulate 64-bit count leading zeroes in x
_dclo(x) Simulate 64-bit count leading ones in x
_dctz(x Simulate 64-bit count trailing zeroes in x
_wsbh(x) See <xc.h> file
_bswapw(x) See <xc.h> file
_ins(tgt,val,pos,sz) See <xc.h> file
_ext(x,pos,sz) See <xc.h> file
_jr_hb() See <xc.h> file
_wrpgpr(regno, val) See <xc.h> file
_rdpgpr(regno) See <xc.h> file
_get_byte(addr,
errp) Return the lea st si gni fic ant byte of addr
_get_half(addr,
errp) Return the lea st si gni fic ant 16-bit word of addr
_get_word(addr,
errp) Return the lea st si gni fic ant 32-bit word of addr
_get_dword(addr,
errp) Return the lea st si gni fic ant 64-bit of addr
_put_byte(addr, v) Write the least significant byte of addr with v
_put_half(addr, v) Write the least significant 16-bit word of addr with v
_put_word(addr, v) Write the least significant 32-bit word of addr with v
_put_dword(addr, v) Write the least significant 64-bit word of addr with v
TABLE 14-5: PREDEFINED MACROS
Macro Description
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Chapter 15. Optimizations
15.1 INTRODUCTION
Different MPLAB XC32 C/C++ Compiler editions support different levels of optimiza-
tion. Some editions are free to download and others must be purchased. Visit
http://www.microchip.com/MPLABXCcompilers for more information on C and C++
licenses.
The compiler editions are:
Setting Optimization Levels
Different optimizations may be set ranging from no optimization to full optimization,
depending on your compiler edition. When debugging code, you may wish to not
optimize your code to ensure expected program flow.
For details on compiler options used to set optimizations, see Section 3.9.7 “Options
for Controlling Optimization”.
Edition Cost Description
Professional (PRO) Yes Implemented with the highest optimizations and
performanc e lev el s.
Standard (STD) Yes Implemented with ample optimizations levels and high
performanc e lev el s.
Free No Implemented with the most code optimizations
restrictions.
Evaluati on (EVAL) No PRO edition enabled for 60 days and then reverts to
Free edi tion.
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Chapter 16. Preprocessing
16.1 INTRODUCTION
All C/C++ source files are preprocessed before compilation. Assembly source files that
use the .S extension (upper case) are also preprocessed. A large number of options
control the operation of the preprocessor and preprocessed code, see
Section 3.9.8 “Options for Controlling the Preprocessor”.
• C/C++ Language Comments
• Preprocessor Directives
• Pragma Directives
• Predefined Macros
16.2 C/C++ LANGUAGE COMMENTS
A C/C++ comment is ignored by the compiler and can be used to provide information
to someone reading the source code. They should be used freely.
Comments may be added by enclosing the desired characters within /* and */. The
comment can run over multiple lines, but comments cannot be nested. Comments can
be placed anywhere in C/C++ code, even in the middle of expressions, but cannot be
placed in character constants or string literals.
Since comments cannot be nested, it may be desirable to use the #if preprocessor
directive to comment out code that already contains comments, for example:
#if 0
result = read(); /* TODO: Jim, check this function is right */
#endif
Single-line, C++ style comments may also be specified. Any characters following // to
the end of the line are taken to be a comment and will be ignored by the compiler, as
shown below:
result = read(); // TODO: Jim, check this function is right
16.3 PREPROCESSOR DIRECTIVES
MPLAB XC32 C/C++ Compiler accepts all the standard preprocessor directives, which
are listed in Table 16-1.
TABLE 16-1: PREPROCESSOR DIRECTIVES
Directive Meaning Example
#Pre proce ssor null directive, do nothing #
#assert Generate error if condition false #assert SIZE > 10
#define Define prep roc esso r macro #define SIZE 5
#define FLAG
#define add(a,b) ((a)+(b))
#elif Short for #else #if see #ifdef
#else Conditionally include source lines see #if
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Macro expansion using arguments can use the # character to convert an argument to
a string, and the ## sequence to concatenate arguments. If two expressions are being
concatenated, consider using two macros in case either expression requires
substitution itself, so for example,
#define paste1(a,b) a##b
#define paste(a,b) paste1(a,b)
lets you use the paste macro to concatenate two expressions that themselves may
require further expansion. The replacement token is rescanned for more macro identi-
fiers, but remember that once a particular macro identifier has been expanded, it will
not be expanded again if it appears after concatenation.
The type and conversion of numeric values in the preprocessor domain is the same as
in the C domain. Preprocessor values do not have a type, but acquire one as soon as
they are converted by the preprocessor . Expressions may overflow their allocated type
in the same way that C expressions may overflow.
Overflow may be avoided by using a constant suffix. For example, an L after the num-
ber indicates it should be interpreted as a long once converted.
So for example:
#define MAX 100000*100000
and
#define MAX 100000*100000L
(note the L suffix) will define the values 0x540be400 and 0x2540be400, respectively.
#endif Terminate conditional source inclusio n see #if
#error Generate an error message #error Size too big
#if Include source lines if constant
expression true #if SIZE < 10
c = process(10)
#else
skip();
#endif
#ifdef Include source lines if preprocessor
symbol defined #ifdef FLAG
do_loop();
#elif SIZE == 5
skip_loop();
#endif
#ifndef Include source lines if preprocessor
symbol not defined #ifndef FLAG
jump();
#endif
#include Include tex t file into source #include <stdio.h>
#include "project.h"
#line Specify line number and filename for
listing #line 3 final
#nn (Where nn is a number) short for
#line nn #20
#pragma Compiler specific options Refer to Section 16.4 “Pragma
Directives”
#undef Unde fines preprocessor symbol #undef FLAG
#warning Generate a warning message #warning Length not set
TABLE 16-1: PREPROCESSOR DIRECTIVES (CONTINUED)
Directive Meaning Example
Preprocessing
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16.4 PRAGMA DIRECTIVE S
There are certain compile-time directives that can be used to modify the behavior of the
compiler. These are implemented through the use of the ANSI standard #pragma
facility. Any pragma which is not understood by the compiler will be ignored.
The format of a pragma is:
#pragma keyword options
where keyword is one of a set of keywords, some of which are followed by certain
options. A description of the keywords is given below.
#pragma interrupt
Mark a function as an interrupt handler. The prologue and epilogue code for the
function will perform more extensive context preservation. Note that the interrupt
attribute (rather than this pragma) is the recommended mechanism for marking a
func tion as an int err upt han dler. The i nterr upt pr agma i s prov ided fo r comp atib ility with
other compilers. See Chapter 11. “Interru pts” and Section 11.5 “Exception
Handlers”.
#pragma vector
Generate a branch instruction at the indicated exception vector which targets the
function. Note that the vector attribute (rather than this pragma) is the recommended
mechanism for generating an exception/interrupt vector. See Chapter 11. “Interrupts”
and Section 11.5 “Exception Handlers”.
#pragma config
The #pragma config directive specifies the processor-specific configuration settings
(i.e., Configuration bits) to be used by the application. See Section 11.3.2 “Interrupt
Pragma”.
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16.5 PREDEFINED MACROS
These predefined macros are available for use with the compiler:
• 32-Bit C/C++ Compiler Macros
• SDE Compatibility Macros
16.5.1 32-Bit C/C++ Compiler Macros
The compiler defines a number of macros, most with the prefix “_MCHP_,” which
characterize the various target specific options, the target processor and other aspects
of the host environment.C/C++
_MCHP_SZINT 32 o r 64, dep endin g on comm and li ne opti ons
to set the size of an integer (-mint32
-mint64)
_MCHP_SZLONG 32 o r 64, dep endin g on comm and li ne opti ons
to set the size of an integer (-mlong32
-mlong64)
_MCHP_SZPTR 32 always since all poi nters are 32 bits
__mchp_no_float De fin ed if -mno-float specified
__NO_FLOAT Defin ed if -mno-float specified
__PIC__
__pic__ The translation unit is being compiled for
positi on ind epe nde nt cod e
__PIC32MX
__PIC32MX__ Always defined
__PIC32_FEATURE_SET__ The compiler predefines a macro based on
the features available for the selected device.
These macros are intended to be used when
writing code to take advantage of features
available on newer devices while maintaining
compatibility with older devices.
Examples: PIC32MX795F512L would use
__PIC32_FEATURE_SET__ == 795,
and PIC32MX340F128H would use
__PIC32_FEATURE_SET__ == 340
PIC32MX Defin ed if -ansi is not spec ifie d
__LANGUAGE_ASSEMBLY
__LANGUAGE_ASSEMBLY__
_LANGUAGE_ASSEMBLY
Defined if compiling a pre-processed
assembly file (.S files)
LANGUAGE_ASSEMBLY Defined if compiling a pre-processed
assembly file (.S files) and -ansi is not
specified
__LANGUAGE_C
__LANGUAGE_C__
_LANGUAGE_C
Defined if compiling a C file
LANGUAGE_C Defin ed if c ompil ing a C file and -ansi is not
specified
__LANGUAGE_C_PLUS_PLUS
__cplusplus
_LANGUAGE_C_PLUS_PLUS__
Defined if compiling a C++ file
__EXCEPTIONS Defined if X++ exceptions are enabled
__GXX_RTTI Defined if runtime type information is enabled
Preprocessing
2012 Microchip Technology Inc. DS51686E-page 173
__processor__ Wher e “processor” i s the capit alized argum ent
to the -mprocessor option. e.g.,
-mprocessor=32mx12f3456 will define
__32MX12F3456__
__XC Always defined to indicate this is a Microchip
XC compiler
__XC32 Always defined to indicate this the XC32
compiler
__VERSION__ The __VERSION__ macro expands to a
string c onst ant descri bing t he compi ler in u se.
Do not rely on its contents having any
particular form, but it should contain at least
the rele ase number. Use the
__XC32_VERSION macro for a numeric
version number
__XC32_VERSION or
__C32_VERSION__ T he C comp iler defines the co nstant
__XC32_VERSION, giving a numeric value
to the version identifier. This macro can be
used to construct applications that take
advantage of new compiler features while still
rema in ing back w ard com p a tible with older
versions. The value is based upon the major
and m inor version numbe rs of the current
release. For example, release version 1.03
will hav e a __XC32_VERSION defini tion of
1030. Thi s ma cro c an be us ed , in con jun cti on
with standar d pre processor compar ison
statements, to conditionally include/exclude
various code constructs
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16.5.2 SDE Compatibility Macros
The MIPS® SDE (Software Development Environment) defines a number of macros,
most with the prefix “_MIPS_,” which characterize various target specific options, some
determined by command line options (e.g., -mint64). Where applicable, these
macros will be defined by the compiler in order to ease porting applications and
middleware from the SDE to the compiler.
_MIPS_SZINT 32 o r 64, dep endin g on comm and li ne opti ons
to set the size of an integer (-mint32
-mint64)
_MIPS_SZLONG 32 o r 64, dep endin g on comm and li ne opti ons
to set the size of an integer (-mlong32
-mlong64)
_MIPS_SZPTR 32 always since all poi nters are 32 bits
__mips_no_float De fin ed if -mno-float specified
__mips__
_mips
_MIPS_ARCH_PIC32MX
_MIPS_TUNE_PIC32MX
_R3000
__R3000
__R3000__
__mips_soft_float
__MIPSEL
__MIPSEL__
_MIPSEL
Always defined
R3000
MIPSEL Defin ed if -ansi is not spec ifie d
_mips_fpr Defin ed as 32
__mips16 Defin ed if -mips16 speci fied
__mips Defin ed as 32
__mips_isa_rev De fin ed as 2
_MIPS_ISA Defin ed as _MIPS_ISA_MIPS32
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USER’S GUIDE
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Chapter 17. Linking Programs
17.1 INTRODUCTION
The compiler will automatically invoke the linker unless the compiler has been
requested to stop after producing an intermediate file.
Linker scripts are used to specify the available memory regions and where sections
should be positioned in those regions.
The linker creates a map file which details the memory assigned to sections. The map
file is the best place to look for memory information.
• Replacing Library Symbols
• Linker-De fin ed Sy mbo ls
• Default Linker Script
17.2 REPLACING LIBRA RY SYMBOLS
Unlike with the Microchip MPLAB XC8 compiler, not all library functions can be
replaced with user-defined routines using MPLAB XC32 C/C++ Compiler. Only weak
library functions (see Section 6.12 “Variable Attributes”) can be replaced in this way .
For those that are weak, any function you write in your code will replace an identically
named function in the library files.
17.3 LINKER-DEFINED SY MBOLS
The 32-bit linker defines several symbols that may be used in your C code develop-
ment. Please see the “MPLAB® Assembler , Linker and Utilities for PIC32 MCUs User’s
Guide”(DS51833) for more information.
The linker defines the symbols _ramfunc_begin and _bmxdkpba_address, which
represent the starting address in RAM where ram functions will be accessed, and the
corresponding address in the program memory from which the functions will be copied.
They are used by the default runtime start-up code to initialize the bus matrix if ram
functions exist in the project, see Section 10.3 “Allocation of Function Code”.
The linker also defines the symbol _stack, which is used by the runtime start-up code
to initialize the stack pointer. This symbol represents the starting address for the
softwar e stac k .
All the above symbols are rarely required for more programs, but may assist you if you
are writing your own runtime start-up code.
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17.4 DEFAULT LINKER SCRIPT
The default linker script is located in the
<install-directory>/pic32mx/lib/ldscripts/elf32pic32mx.x file.
When compiling with the xc32-gcc or xc32-g++ compilation driver, the linker uses this
file as the default linker script. The driver passes the path to the default linker script
using the -T linker option.
The default linker script contains the following categories of information:
• Output Format and Entry Points
• Default Values for Minimum Stack and Heap Sizes
• Processor Definiti ons Include File
- Inc lu si on of Pr oce ss or -Specific Object File (s)
- OPTIONAL Inclusion of Processor-Specific Peripheral Libraries
- Base Exception Vector Address and Vector Spacing Symbols
- Memory Address Equates
- Memory Regions
- Configuration Words Input/Output Section Map
• Input/Output Section Map
17.4.1 Output Format and Entr y Points
The first several lines of the default linker script define the output format and the entry
point for the application. Copies of the default linker scripts are provided in
program files/.../<install-dir>/pic32mx/lib/ldscripts.
OUTPUT_FORMAT("elf32-tradlittlemips")
OUTPUT_ARCH(pic32mx)
ENTRY(_reset)
The OUTPUT_FORMAT line selects the object file format for the output file. The output
object file format generated by the 32-bit language tools is a traditional, little-endian,
MIPS, ELF32 format.
The OUTPUT_ARCH line selects the specific machine architecture for the output file.
The output files generated by the 32-bit language tools contain information that
identifies the file was generated for the PIC32MX architecture.
The ENTRY line selects the entry point of the application. This is the symbol identifying
the location of the first instruction to execute. The 32-bit language tools begins
execution at the instruction identified by the _reset label.
Note: All addresses specified in the linker scripts should be specified as virtual
addresses, not physical addresses.
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17.4.2 Default Values for Minimum Stack and Heap Sizes
The next section of the default linker script provides default values for the minimum
stack and heap sizes.
/*
* Provide for a minimum stack and heap size
* - _min_stack_size - represents the minimum space that must
* be made available for the stack. Can
* be overridden from the command line
* using the linker's --defsym option.
* - _min_heap_size - represents the minimum space that must
* be made available for the heap. Can
* be overridden from the command line
* using the linker's --defsym option.
*/
EXTERN (_min_stack_size _min_heap_size)
PROVIDE(_min_stack_size = 0x400) ;
PROVIDE(_min_heap_size = 0) ;
The EXTERN line ensures that the rest of the linker script has access to the default
values of _min_stack_size and _min_heap_size assuming that the user does not
override these values using the linker’s --defsym command line option.
The two PROVIDE lines ensure that a default value is provided for both
_min_stack_size and _min_heap_size. The default value for the minimum stack
size is 1024 bytes (0x400). The default value for the minimum heap size is 0 by tes .
17.4.3 Processor Definitions Include File
The next line in the default linker script pulls in information specific to the processor.
INCLUDE procdefs.ld
The file procdefs.ld is included in the linker script at this point. The file is searched
for in the current directory and in any directory specified with the -L command line
option. The compiler shell ensures that the correct directory is passed to the linker with
the -L command line option based on the processor selected with the -mprocessor
comm and line opti on.
The processor definitions linker script contains the following pieces of information:
• Inclu si on of Processor -Specific Object File (s)
• Base Exception Vector Address and Vector Spacing Symbols
• Memory Address Equates
• Memory Regions
• Configuration Words Input/Output Section Map
17.4.3.1 INCLUSION OF PROCESSOR-SPECIFIC OBJECT FILE(S)
This section of the processor definitions linker script ensures that the
processor-specific object file(s) get included in the link.
/**************************************************************
* Processor-specific object file. Contains SFR definitions.
**************************************************************/
INPUT(“processor.o”)
The INPUT line specifies that processor.o should be included in the link as if this file
were named on the command line. The linker attempts to find this file in the current
directory . If it is not found, the linker searches through the library search paths (i.e., the
paths specifi ed with the -L command line option).
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17.4.3.2 OPTIONAL INCLUSION OF PROCESSOR-SPECIFIC PERIPHERAL
LIBRARIES
This section of the processor definitions linker script ensures that the
processor-specific peripheral libraries get included, but only if the files exist.
/*********************************************************************
* Processor-specific peripheral libraries are optional
*********************************************************************/
OPTIONAL("libmchp_peripheral.a")
OPTIONAL("libmchp_peripheral_32MX795F512L.a")
The OPTIONAL lines specify that libmchp_peripheral.a and
libmchp_peripheral_32MX795F512L.a should be included in the link as if the
files were named on the command line. The linker attempts to find these files in the cur-
rent directory. If they are not found in the current directory, the linker searches through
the library search paths. If they are not found in the library search paths, the link pro-
cess continues without error. The linker will error only when a symbol from the periph-
eral library is required but not found elsewhere.
17.4.3.3 BASE EXCEPTION VECTOR ADDRESS AND VECTOR SPACING
SYMBOLS
This section of the processor definitions linker script defines values for the base
exception vector address and vector spacing.
/**************************************************************
* For interrupt vector handling
**************************************************************/
_vector_spacing= 0x00000001;
_ebase_address= 0x9FC01000;
The first line defines a value of 1 for _vector_spacing. The available memory for
exceptions only supports a vector spacing of 1. The second line defines the location of
the base exception vector address (EBASE).
On some devices, the base exception vector address is located in the KSEG0 boot
segment. On other devices, the size of the KSEG0 boot segment is not sufficient for
the vector table, so the base exception vector address is located in the KSEG0 program
segment. In general, devices with at least 12 KB in the KSEG0 boot segment use the
boot flash for the exception vector table. Devices with less than 12 KB in the KSEG0
boot segment use the KSEG0 program segment for the exception vector table. Be sure
to check the procdefs.ld include file for the default address for your target device.
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17.4.3.4 MEMORY ADDRESS EQUATES
This section of the processor definitions linker script provides information about certain
memory addresses required by the default linker script.
/**************************************************************
* Memory Address Equates
**************************************************************/
_RESET_ADDR = 0xBFC00000;
_BEV_EXCPT_ADDR = 0xBFC00380;
_DBG_EXCPT_ADDR = 0xBFC00480;
_DBG_CODE_ADDR = 0xBFC02000;
_GEN_EXCPT_ADDR = _ebase_address + 0x180;
The _RESET_ADDR defines the processor’s Reset address. This is the virtual begin
address of the IFM boot section in Kernel mode.
The _BEV_EXCPT_ADDR defines the address that the processor jumps to when an
exception is encountered and StatusBEV = 1.
The _DBG_EXCPT_ADDR defines the address that the processor jumps to when a
debug exception is encountered.
The _DBG_CODE_ADDR defines the address that is the start address of the debug
executive. Note that this address may vary depending on the size of the KSEG0 boot
segment on your target device.
The _GEN_EXCPT_ADDR defines the address that the processor jumps to when an
exception is encountered and StatusBEV = 0.
17.4.3.5 MEMORY REGIONS
This section of the processor definitions linker script provides information about the
memory regions that are available on the device.
/**************************************************************
* Memory Regions
*
* Memory regions without attributes cannot be used for
* orphaned sections. Only sections specifically assigned to
* these regions can be allocated into these regions.
**************************************************************/
MEMORY
{
kseg0_program_mem (rx) : ORIGIN = 0x9D000000, LENGTH = 0x8000
kseg0_boot_mem : ORIGIN = 0x9FC00490, LENGTH = 0x970
exception_mem : ORIGIN = 0x9FC01000, LENGTH = 0x1000
kseg1_boot_mem : ORIGIN = 0xBFC00000, LENGTH = 0x490
debug_exec_mem : ORIGIN = 0xBFC02000, LENGTH = 0xFF0
config3 : ORIGIN = 0xBFC02FF0, LENGTH = 0x4
config2 : ORIGIN = 0xBFC02FF4, LENGTH = 0x4
config1 : ORIGIN = 0xBFC02FF8, LENGTH = 0x4
config0 : ORIGIN = 0xBFC02FFC, LENGTH = 0x4
kseg1_data_mem (w!x) : ORIGIN = 0xA0000000, LENGTH = 0x2000
sfrs : ORIGIN = 0xBF800000, LENGTH = 0x10000
}
Eleven memory regions are defined with an associated start address and length:
1. Program memory region (kseg0_program_mem) for application code
2. Boot memory regions (kseg0_boot_mem and kseg1_boot_mem)
3. Exception memory region (exception_mem)
4. Debug executive memory region (debug_exec_mem)
5. Configuration memory regions (config3, config2, config1, and config0)
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6. Data memory region (kseg1_data_mem)
7. SFR memory region (sfrs)
The default linker script uses these names to locate sections into the correct regions.
Sections which are non-standard become orphaned sections. The attributes of the
memory regions are used to locate these orphaned sections. The attributes (rx)
specify that read-only sections or executable sections can be located into the program
memory regions. Similarly, the attributes (w!x) specify that sections that are not
read-only and not executable can be located in the data memory region. Since no
attributes are specified for the boot memory region, the configuration memory regions,
or the SFR memory region, only specified sections may be located in these regions
(i.e., orphaned sections may not be located in the boot memory regions, the exception
memory region, the configuration memory regions, the debug executive memory
region, or the SFR memory region).
17.4.3.6 CONFIGURATION WORDS INPUT/OUTPUT SECTION MAP
The last section in the processor definitions linker script is the input/output section map
for Configuration Words. This section map is additive to the Input/Output Section Map
found in the default linker script (see Section 17.4.4 “Input/Output Section Map”). It
defines how input sections for Configuration Words are mapped to output sections for
Configuration Words. Note that input sections are portions of an application that are
defined in source code, while output sections are created by the linker. Generally,
several input sections may be combined into a single output section. All output sections
are specified within a SECTIONS command in the linker script.
For each Configuration Word that exists on the specific processor, a distinct output
section named .config_address exists where address is the location of the
Configuration Word in memory . Each of these sections contains the data created by the
#pragma config directive (see Section 16.4 “Prag ma Dire ctives ” ) for that
Configuration Word. Each section is assigned to their respective memory region
(confign).
SECTIONS
{
.config_BFC02FF0 : {
*(.config_BFC02FF0)
} > config3
.config_BFC02FF4 : {
*(.config_BFC02FF4)
} > config2
.config_BFC02FF8 : {
*(.config_BFC02FF8)
} > config1
.config_BFC02FFC : {
*(.config_BFC02FFC)
} > config0
}
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17.4.4 Input/Output Section Map
The last section in the default linker script is the input/output section map. The section
map is the heart of the linker script. It defines how input sections are mapped to output
sections. Note that input sections are portions of an application that are defined in
source code, while output sections are created by the linker. Generally, several input
sections may be combined into a single output section. All output sections are specified
within a SECTIONS command in the linker script.
The following output sections may be created by the linker:
• .reset Section
• .bev_excpt Section
• .dbg_excpt Section
• .dbg_code Section
• .app_excpt Section
• .vector_0 .. .vector_63 Sections
• .start-up Section
• .text Section
• .rodata Sectionn
• .sdata2 Section
• .sbss2 S ection
• .dbg_data Section
•.data Section
•.got Section
• .sdata Section
•.lit8 Section
•.lit4 Section
• .sbss Section
• .bss Section
• .heap Section
• .stack Section
• .ramfunc Section
• Stack Location
• Debug Sections
17.4.4.1 .RESET SECTION
This section contains the code that is executed when the processor performs a Reset.
This section is located at the Reset address (_RESET_ADDR), as specified in the
processor definitions linker script and is assigned to the boot memory region
(kseg1_boot_mem). The .reset output section also con tains the C start-up code
from the .reset.startup input section.
.reset _RESET_ADDR :
{
KEEP(*(.reset))
KEEP(*(.reset.startup))
} > kseg1_boot_mem
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17.4.4.2 .BEV_EXCPT SECTION
This section contains the handler for exceptions that occur when StatusBEV = 1. This
section is located at the BEV exception address (_BEV_EXCPT_ADDR) as specified in
the processor definitions linker script and is assigned to the boot memory region
(kseg1_boot_mem).
.bev_excpt _BEV_EXCPT_ADDR :
{
(*(.bev_handler))
} > kseg1_boot_mem
17.4.4. 3 .DB G_ EX CP T SECTIO N
This section reserves space for the debug exception vector. This section is only
allocated if the symbol _DEBUGGER has been defined. (This symbol is defined if the
-mdebugger command line option is specified to the shell.) This section is located at
the debug exception address (_DBG_EXCPT_ADDR) as specified in the processor
definitions linker script and is assigned to the boot memory region
(kseg1_boot_mem). The section is marked as NOLOAD as it is only intended to ensure
that application code cannot be placed at locations reserved for the debug executive.
.dbg_excpt _DBG_EXCPT_ADDR (NOLOAD) :
{
. += (DEFINED (_DEBUGGER) ? 0x8 : 0x0);
} > kseg1_boot_mem
17.4.4.4 .DBG_CODE SECTION
This section reserves space for the debug exception handler. This section is only
allocated if the symbol _DEBUGGER has been defined. (This symbol is defined if the
-mdebugger command line option is specified to the shell.) This section is located at
the debug code address (_DBG_CODE_ADDR) as specified in the processor definitions
linker script and is assigned to the debug executive memory region
(debug_exec_mem). The section is marked as NOLOAD because it is only intended to
ensure that application code cannot be placed at locations reserved for the debug
executive.
.dbg_code _DBG_CODE_ADDR (NOLOAD) :
{
. += (DEFINED (_DEBUGGER) ? 0xFF0 : 0x0);
} > debug_exec_mem
17.4.4.5 .APP_EXCPT SECTION
This section contains the handler for exceptions that occur when StatusBEV = 0. This
section is located at the general exception address (_GEN_EXCPT_ADDR) as sp ecifi ed
in the processor definitions linker script and is assigned to the exception memory
region (exception_mem).
.app_excpt _GEN_EXCPT_ADDR :
{
KEEP(*(.gen_handler))
} > exception_mem
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17.4.4.6 .VECTOR_0 .. .VECTOR_63 SECTIONS
These sections contain the handler for each of the interrupt vectors. These sections are
located at the correct vectored addresses using the formula:
_ebase_address + 0x200 + (_vector_spacing << 5) * n
where n is the respective vector number.
Each of the sections is followed by an assert that ensures the code located at the vector
does not exceed the vector spacing specified.
.vector_n _ebase_address + 0x200 + (_vector_spacing << 5) * n :
{
KEEP(*(.vector_n))
} > exception_mem
ASSERT (SIZEOF(.vector_n) < (_vector_spacing << 5), "function at
exception vector n too large")
17.4.4.7 .START-UP SECTION
In XC32, the C and C++ startup code is located in the .reset section. We maintain
the .startup output section in the default linker script for backwards compatibility
purpose s onl y.
.startup ORIGIN(kseg0_boot_mem) :
{
*(.startup)
} > kseg0_boot_mem
17.4.4.8 .TEXT SECTION
The standard executable code sections are no longer mapped to the .text output
section. However, a few special executable sections are still mapped here as shown
below. This section is assigned to the program memory region
(kseg0_program_mem) and has a fill value of NOP (0).
The built-in linker script no longer maps standard .text executable code input
sections. By not mapping these sections in the linker script, we allow these sections to
be allocated using the best-fit allocator rather than the sequential allocator. Sections
that are unmapped in the linker script, can flow around absolute sections specified in
code whereas sections that are linker-script mapped are grouped together and
allocated sequentially, potentially causing conflicts with absolute sections (using the
address function attribute).
.text ORIGIN(kseg0_program_mem) :
{
*(.stub .gnu.linkonce.t.*)
KEEP (*(.text.*personality*))
*(.gnu.warning)
*(.mips16.fn.*)
*(.mips16.call.*)
} > kseg0_program_mem =0
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17.4.4.9 C++ INITIALIZATION SECTIONS
The sections .init, .preinit_array, .init_array, .fini_array, .ctors, and
.dtors are all used for the construction and destruction of file-scope static-storage
C++ objects.
/* Global-namespace object initialization */
.init :
{
KEEP (*crti.o(.init))
KEEP (*crtbegin.o(.init))
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o *crtn.o ).init))
KEEP (*crtend.o(.init))
KEEP (*crtn.o(.init))
. = ALIGN(4) ;
} >kseg0_program_mem
.fini :
{
KEEP (*(.fini))
. = ALIGN(4) ;
} >kseg0_program_mem
.preinit_array :
{
PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP (*(.preinit_array))
PROVIDE_HIDDEN (__preinit_array_end = .);
. = ALIGN(4) ;
} >kseg0_program_mem
.init_array :
{
PROVIDE_HIDDEN (__init_array_start = .);
KEEP (*(SORT(.init_array.*)))
KEEP (*(.init_array))
PROVIDE_HIDDEN (__init_array_end = .);
. = ALIGN(4) ;
} >kseg0_program_mem
.fini_array :
{
PROVIDE_HIDDEN (__fini_array_start = .);
KEEP (*(SORT(.fini_array.*)))
KEEP (*(.fini_array))
PROVIDE_HIDDEN (__fini_array_end = .);
. = ALIGN(4) ;
} >kseg0_program_mem
.ctors :
{
/* XC32 uses crtbegin.o to find the start of
the constructors, so we make sure it is
first. Because this is a wildcard, it
doesn't matter if the user does not
actually link against crtbegin.o; the
linker won't look for a file to match a
wildcard. The wildcard also means that it
doesn't matter which directory crtbegin.o
is in. */
KEEP (*crtbegin.o(.ctors))
KEEP (*crtbegin?.o(.ctors))
/* We don't want to include the .ctor section from
the crtend.o file until after the sorted ctors.
The .ctor section from the crtend file contains the
end of ctors marker and it must be last */
Linking Programs
2012 Microchip Technology Inc. DS51686E-page 185
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .ctors))
KEEP (*(SORT(.ctors.*)))
KEEP (*(.ctors))
. = ALIGN(4) ;
} >kseg0_program_mem
.dtors :
{
KEEP (*crtbegin.o(.dtors))
KEEP (*crtbegin?.o(.dtors))
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
KEEP (*(SORT(.dtors.*)))
KEEP (*(.dtors))
. = ALIGN(4) ;
} >kseg0_program_mem
17.4.4.10 .RODATA SECTION
S tandard read-only sections are not mapped in the linker script. A few special read-only
sections are still mapped in the linker script, but most sections are unmapped, allowing
them to be handled by the best fit allocator. This section is assigned to the program
memory region (kseg0_program_mem).
.rodata :
{
*(.gnu.linkonce.r.*)
*(.rodata1)
} > kseg0_program_mem
17.4.4.11 .SDATA2 SECTION
This section collects the small initialized constant global and static data from all of the
application’s input files. Because of the constant nature of the data, this section is also
a read-only section. This section is assigned to the program memory region
(kseg0_program_mem).
/*
* Small initialized constant global and static data can be
* placed in the .sdata2 section. This is different from
* .sdata, which contains small initialized non-constant
* global and static data.
*/
.sdata2 :
{
*(.sdata2 .sdata2.* .gnu.linkonce.s2.*)
} > kseg0_program_mem
Note: The order of the input sections within each output section is significant.
MPLAB® XC32 C/C++ Compiler User’s Guide
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17.4.4.12 .SBSS2 SECTION
This section collects the small uninitialized constant global and static data from all of
the application’s input files. Because of the constant nature of the data, this section is
also a read-only section. This section is assigned to the program memory region
(kseg0_program_mem).
/*
* Uninitialized constant global and static data (i.e.,
* variables which will always be zero). Again, this is
* different from .sbss, which contains small non-initialized,
* non-constant global and static data.
*/
.sbss2 :
{
*(.sbss2 .sbss2.* .gnu.linkonce.sb2.*)
} > kseg0_program_mem
17.4.4.13 .DBG_DATA SECTION
This section reserves space for the data required by the debug exception handler . This
section is only allocated if the symbol _DEBUGGER has been defined. (This symbol is
defined if the -mdebugger command line option is specified to the shell.) This section
is assigned to the data memory region (kseg1_data_mem). The se ction is mark ed as
NOLOAD as it is only intended to ensure that application data cannot be placed at
locations reserved for the debug executive.
.dbg_data (NOLOAD) :
{
. += (DEFINED (_DEBUGGER) ? 0x200 : 0x0);
} > kseg1_data_mem
17.4.4.14 .DATA SECTION
The linker generates a data-initialization template that the C start-up code uses to
initialize variables.
17.4.4. 15 .GOT SECTIO N
This section collects the global offset table from all of the application’s input files. This
section is assigned to the data memory region (kseg1_data_mem) with a load address
located in the program memory region (kseg0_program_mem). A symbol is defined
to represent the location of the Global Pointer (_gp).
_gp = ALIGN(16) + 0x7FF0 ;
.got :
{
*(.got.plt) *(.got)
} > kseg1_data_mem AT> kseg0_program_mem
Linking Programs
2012 Microchip Technology Inc. DS51686E-page 187
17.4.4.16 .SDATA SECTION
This section collects the small initialized data from all of the application’s input files.
This section is assigned to the data memory region (kseg1_data_mem) with a load
address located in the program memory region (kseg0_program_mem). Symbols are
defined to represent the virtual begin (_sdata_begin) and end (_sdata_end)
addresses of this section.
/*
* We want the small data sections together, so
* single-instruction offsets can access them all, and
* initialized data all before uninitialized, so
* we can shorten the on-disk segment size.
*/
.sdata :
{
_sdata_begin = . ;
*(.sdata .sdata.* .gnu.linkonce.s.*)
_sdata_end = . ;
} > kseg1_data_mem AT> kseg0_program_mem
17.4.4.17 .LIT8 SECTION
This section collects the 8-byte constants which the assembler decides to store in
memory rather than in the instruction stream from all of the application’s input files. This
section is assigned to the data memory region (kseg1_data_mem) with a load address
located in the program memory region (kseg0_program_mem).
.lit8 :
{
*(.lit8)
} > kseg1_data_mem AT> kseg0_program_mem
17.4.4.18 .LIT4 SECTION
This section collects the 4-byte constants which the assembler decides to store in
memory rather than in the instruction stream from all of the application’s input files. This
section is assigned to the data memory region (kseg1_data_mem) with a load address
located in the program memory region (kseg0_program_mem). A symbol is defined
to represent the virtual end address of the initialized data (_data_end).
.lit4 :
{
*(.lit4)
} > kseg1_data_mem AT> kseg0_program_mem
_data_end = . ;
MPLAB® XC32 C/C++ Compiler User’s Guide
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17.4.4.19 .SBSS SECTION
This section collects the small uninitialized data from all of the application’s input files.
This section is assigned to the data memory region (kseg1_data_mem). A symbol is
defined to represent the virtual begin address of uninitialized data (_bss_begin).
Symbols are also defined to represent the virtual begin (_sbss_begin) and end
(_sbss_end) addresses of this section.
_bss_begin = . ;
.sbss :
{
_sbss_begin = . ;
*(.dynsbss)
*(.sbss .sbss.* .gnu.linkonce.sb.*)
*(.scommon)
_sbss_end = . ;
} > kseg1_data_mem
17.4.4.20 .BSS SECTION
This section collects the uninitialized data from all of the application’s input files. This
section is assigned to the data memory region (kseg1_data_mem). A symbol is
defined to represent the virtual end address of uninitialized data (_bss_end). A symbol
is also to represent the virtual end address of data memory (_end).
.bss :
{
*(.dynbss)
*(.bss .bss.* .gnu.linkonce.b.*)
*(COMMON)
/*
* Align here to ensure that the .bss section occupies
* space up to _end. Align after .bss to ensure correct
* alignment even if the .bss section disappears because
* there are no input sections.
*/
. = ALIGN(32 / 8) ;
} > kseg1_data_mem
. = ALIGN(32 / 8) ;
_end = . ;
_bss_end = . ;
17.4.4.21 .HEAP SECTION
The linker now dynamically reserves an area of memory for the heap. The .heap
section is no longer mapped in the linker script. The linker finds the largest unused gap
of memory after all other sections are allocated and uses that gap for both the heap and
the stack. The minimum amount of space reserved for the heap is determined by the
symbol _min_heap_size.
17.4.4. 22 .STACK SECTION
The linker now dynamically reserves an area of memory for the stack. The .stack
section is no longer mapped in the linker script. The linker finds the largest unused gap
of memory after all other sections are allocated and uses that gap for both the heap and
the stack. The minimum amount of space reserved for the stack is determined by the
symbol _min_stack_size.
Linking Programs
2012 Microchip Technology Inc. DS51686E-page 189
17.4.4.23 .RAMFUNC SECTION
The linker now dynamically collects the ‘ramfunc’ attributed and “.ramfunc” named
sections and allocates them sequentially in an appropriate range of memory. The first
ramfunc attributed function is placed at the highest appropriately aligned address.
The presence of a ramfunc section causes the linker to emit the symbols necessary for
the crt0.S start-up code to initialize the PIC32 bus matrix appropriately.
/*
* RAM functions go at the end of our stack and heap allocation.
* Alignment of 2K required by the boundary register (BMXDKPBA).
*
* RAM functions are now allocated by the linker. The linker generates
* _ramfunc_begin and _bmxdkpba_address symbols depending on the
* location of RAM functions.
*/
_bmxdudba_address = LENGTH(kseg1_data_mem) ;
_bmxdupba_address = LENGTH(kseg1_data_mem) ;
17.4.4. 24 STACK LOCATION
A symbol is defined to represent the location of the Stack Pointer (_stack). As
described previously, the heap and the stack are now allocated to the largest available
gap of memory after other sections have been allocated.
For PIC32 devices with more than 64K of data memory, GP relative addressing mode
should not be used. To avoid conflict of using GP-relative addressing to the linker gen-
erated symbols, allocate the symbols in section “_linkergenerated”: extern
unsigned int __attribute__((section(“_linkergenerated”)))
_splim;
MPLAB® XC32 C/C++ Compiler User’s Guide
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17.4.4.25 DEBUG SECTIONS
The debug sections contain DWARF2 debugging information. They are not loaded into
program Flash.
/* Stabs debugging sections. */
.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
/* DWARF debug sections.
Symbols in the DWARF debugging sections are relative to the
beginning
of the section so we begin them at 0. */
/* DWARF 1 */
.debug 0 : { *(.debug) }
.line 0 : { *(.line) }
/* GNU DWARF 1 extensions */
.debug_srcinfo 0 : { *(.debug_srcinfo) }
.debug_sfnames 0 : { *(.debug_sfnames) }
/* DWARF 1.1 and DWARF 2 */
.debug_aranges 0 : { *(.debug_aranges) }
.debug_pubnames 0 : { *(.debug_pubnames) }
/* DWARF 2 */
.debug_info 0 : { *(.debug_info .gnu.linkonce.wi.*) }
.debug_abbrev 0 : { *(.debug_abbrev) }
.debug_line 0 : { *(.debug_line) }
.debug_frame 0 : { *(.debug_frame) }
.debug_str 0 : { *(.debug_str) }
.debug_loc 0 : { *(.debug_loc) }
.debug_macinfo 0 : { *(.debug_macinfo) }
/* SGI/MIPS DWARF 2 extensions */
.debug_weaknames 0 : { *(.debug_weaknames) }
.debug_funcnames 0 : { *(.debug_funcnames) }
.debug_typenames 0 : { *(.debug_typenames) }
.debug_varnames 0 : { *(.debug_varnames) }
.debug_pubtypes 0 : { *(.debug_pubtypes) }
.debug_ranges 0 : { *(.debug_ranges) }
/DISCARD/ : { *(.rel.dyn) }
.gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
/DISCARD/ : { *(.note.GNU-stack) }
/DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*)
*(.discard) }
MPLAB® XC32 C/C++ COMPILER
USER’S GUIDE
2012 Microchip Technology Inc. DS51686E-page 191
Appendix 18. Implementation-Defined Behavior
18.1 INTRODUCTION
This chapter discusses the choices for implementation defined behavior in compiler.
18.2 HIGHLIGHTS
Items discussed in this chapter are:
•Overview
• Translation
• Environment
• Identifiers
•Characters
• Integers
• Floating-Point
• Arrays and Pointers
•Hints
• Structures, Unions, Enumerations, and Bit fields
• Qualifiers
•Declarators
• Statements
• Pre-Processing Directives
• Library Functions
• Architecture
18.3 OVERVIEW
ISO C requires a conforming implementation to document the choices for behaviors
defined in the standard as “implementation-defined.” The following sections list all such
areas, the choices made for the compiler , and the corresponding section number from
the ISO/IEC 9899:1999 standard.
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18.4 TRANSLATION
18.5 ENVIRONMENT
ISO Standard: “How a diagnostic is identified (3.10, 5.1.1.3).”
Implementation: All output to stderr is a diagnostic.
ISO Standard: “Whether each nonempty sequence of white-space characters other
than new-line is retained or replaced by one space character in transla-
tion phase 3 (5.1.1.2).”
Implementation: Each sequence of whitespace is replaced by a single character.
ISO Standard: “The name and type of the function called at program start-up in a free-
standing environment (5.1.2.1).”
Implementation: int main (void);
ISO Standard: “The effect of program termination in a freestanding environment
(5.1.2.1).”
Implementation: An infinite loop (branch to self) instruction will be executed.
ISO Standard: “An alternative manner in which the main function may be defined
(5.1.2.2.1).”
Implementation: int main (void);
ISO Standard: “The values given to the strings pointed to by the argv argument to
main (5.1.2.2.1).”
Implementation: No arguments are passed to main. Reference to argc or argv is
undefined.
ISO Standard: “What con st itut es an int eractiv e dev ic e (5.1.2 .3).”
Implementation: Application defined.
ISO Standard: “Signals for which the equivalent of signal(sig, SIG_IGN); is
executed at program start-up (7.14.1.1).”
Implementation: Signals are application defined.
ISO Standard: “The form of the status returned to the host environment to indicate
unsuccessful termination when the SIGABRT signal is raised and not
caught (7.20 .4. 1).”
Implementation: The host environment is application defined.
ISO Standard: “The form s o f the statu s re turn ed to the host env iro nm ent by the exit
function to report successful and unsuccessful termination (7.20.4.3).”
Implementation: The host environment is application defined.
ISO Standard: “The status returned to the host environment by the exit function if
the value of its argument is other than zero, EXIT_SUCCESS, or
EXIT_FAILURE (7.20.4.3).”
Implementation: The host environment is application defined.
ISO Standard: “The set of environment names and the method for altering the environ-
ment list used by the getenv function (7.2 0.4. 4).”
Implementation: The host environment is application defined.
ISO Standard: “The mann er of execution of the string by the syste m function
(7.20.4.5).”
Implementation: The host environment is application defined.
Implementation-Defined Behavior
2012 Microchip Technology Inc. DS51686E-page 193
18.6 IDENTIFIERS
18.7 CHARACTERS
ISO Standard: “Which additional multibyte characters may appear in identifiers and
their correspondence to universal character names (6.4.2).”
Implementation: No.
ISO Standard: “The number of sig nif ica nt ini tia l chara cte rs in an ide ntif ier (5.2 .4.1 ,
6.4.2).”
Implementation: All characters are significant.
ISO Standard: “The number of bits in a byte (C90 3.4, C99 3.6).”
Implementation: 8.
ISO Standard: “The values of the members of the execution character set (C90 and
C99 5.2.1).”
ISO Standard: “The unique value of the member of the execution character set pro-
duced fo r each of the st and ard alp habeti c esc ape s equences (C90 and
C99 5.2.2).”
Implementation: The execution c haracter set is ASCII.
ISO Standard: “The value of a char object into which has been stored any character
other than a member of the basic execution character set (C90 6.1.2.5,
C99 6.2.5).”
Implementation: The value of the char object is the 8-bit binary representation of the
character in the source character set. That is, no translation is done.
ISO Standard: “Which of signed char or unsigned char has the same range, represen-
tation, and behavior as “plain” char (C90 6.1.2.5, C90 6.2.1.1, C99
6.2.5, C99 6.3.1.1). ”
Implementation: By default, signed char is functionally equivalent to plain char. The
options -funsigned-char and -fsigned-char ca n be used to
change the defaul t.
ISO Standard: “The mapping of members of the source character set (in character
const ant s and string literal s) to m embers of the execu tion c haracte r set
(C90 6.1.3.4, C99 6.4.4.4, C90 and C99 5.1.1.2).”
Implementation: The binary representation of the source character set is preserved to
the execution character set.
ISO Standard: “The value of an integer character constant co ntaining mo re than one
character or containing a character or escape sequence that does not
map to a single-byte execution character (C90 6.1.3.4, C99 6.4.4.4).”
Implementation: The compiler determines the value for a multi-character character con-
stan t one ch aracte r at a time . The previo us v alue is sh ift ed lef t by eight,
and the bit p attern of the ne xt char acter is masked in. The final res ult is
of type int. If the result is large r than ca n be repres ented by an int, a
warning diagnostic is issued and the value truncated to int size.
ISO Standard: “The value of a wide character constant containing more than one mul-
tibyte character, or containing a multibyte character or escape
sequence not represented in the extended execution character set
(C90 6.1.3.4, C99 6.4.4.4).”
Implementation: See previous.
ISO Standard: “The current locale used to convert a wide character constant consist-
ing of a single multibyte character that maps to a member of the
extended execution character set into a corresponding wide character
code (C90 6.1.3.4, C99 6.4.4.4).”
Implementation: LC_ALL
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18.8 INTEGERS
18.9 FLOATING-POINT
ISO Standard: “The curre nt l oc ale us ed t o c onv ert a w id e string literal i nto co rres pon d-
ing wide character codes (C90 6.1.4, C99 6.4.5).”
Implementation: LC_ALL
ISO Standard: “The value of a string literal containing a multibyte character or escape
sequence not represented in the execution character set (C90 6.1.4,
C99 6.4.5).”
Implementation: The binary representation of the characters is preserved from the
source cha rac ter set .
ISO Standard: “Any extended integer types that exist in the implementation (C99
6.2.5).”
Implementation: There are no extend ed int ege r types .
ISO Standard: “Whether signed integer types are represented using sign and magni-
tude, two’s complement, or one’s complement, and whether the
extraordinary value is a trap representation or an ordinary value (C99
6.2.6.2).”
Implementation: All integer types are represented as tw o’s complement, and all bit pat-
terns are ordinary values.
ISO Standard: “The rank of any extended integer type relative to another extended
integer type with the same precision (C99 6.3.1.1).”
Implementation: No extended integer types are supported.
ISO Standard: “The resul t of, or the signal rais ed b y, converting an inte ger to a signed
integer type when the value cannot be represented in an object of that
type (C90 6.2.1.2, C99 6.3.1.3).”
Implementation: When converting value X to a type of width N, the value of the result is
the Least Significant N bits of the 2’s complement representation of X.
That is, X is truncated to N bits. No signal is raised.
ISO Standard: “The results of some bitwise operations on signed integers (C90 6.3,
C99 6.5).”
Implementation: Bitwise operations on signed values act on the 2’s complement repre-
sentation, including the sign bit. The result of a signed right shift
expression is sign extended.
C99 allows some aspects of signed ‘<<’ to be undefined. The compiler
does not do so.
ISO Standard: “The accuracy of the floating-point operations and of the library func-
tions in <math.h> and <complex.h> that return floating-point results
(C90 and C99 5.2.4.2.2).”
Implementation: The accuracy is unknown.
ISO Standard: “The accuracy of the conversions between floating-point internal repre-
sent ations a nd string represent ations performe d by the library f unctions
in <stdio.h>, <stdlib.h>, and <wchar.h> (C90 and C99 5.2.4.2.2).”
Implementation: The accuracy is unknown.
ISO Standard: “The rounding behaviors characterized by non-standard values of
FLT_ROUNDS (C90 and C99 5.2.4.2.2).”
Implementation: No such values are used.
ISO Standard: “The evaluation methods characterized by non-standard negative val-
ues of FLT_EVAL_METHOD (C90 and C99 5.2.4.2.2).”
Implementation: No such values are used.
Implementation-Defined Behavior
2012 Microchip Technology Inc. DS51686E-page 195
ISO Standard: “The directio n of r ounding when an integer is convert ed to a float-
ing-point number that cannot exactly represent the original value (C90
6.2.1.3, C99 6.3.1.4).”
Implementation: C9 9 Annex F is followed.
ISO Standard: “The direc tion of ro und ing when a floati ng-poin t numb er is co nver ted to
a narrower floating-point number (C90 6.2.1.4, 6.3.1.5).”
Implementation: C9 9 Annex F is followed.
ISO Standard: “How the nearest representable value or the larger or smaller repre-
sent able value im mediately a djacent to the ne arest represen table valu e
is chosen for certain floating constants (C90 6.1.3.1, C99 6.4.4.2).”
Implementation: C9 9 Annex F is followed.
ISO Standard: “Whether and how floating expressions are contracted when not disal-
lowed by the FP_CONTRACT pragma (C99 6.5).”
Implementation: The pragma is not imple me nte d.
ISO Standard: “The default state for the FENV_ACCESS pragma (C99 7.6.1).”
Implementation: This pragma is not implemented.
ISO Standard: “Additional floating-point exceptions, rounding modes, environments,
and classifications, and their macro names (C99 7.6, 7.12).”
Implementation: None supported.
ISO Standard: “The default state for the FP_CONTRACT pragma (C99 7.12.2).”
Implementation: This pragma is not implemented.
ISO Standard: “Whether the “inexact” floating-point exception can be raised when the
rounded res ult actually does equ al the mathe ma tic al res ult in an IE C
60559 conformant implementation (C99 F.9).”
Implementation: Unknown.
ISO Standard: “Whether the “underflow” (and “inexact”) floating-point exception can
be raised when a result is tiny but not inexact in an IEC 60559 confor-
mant implementation (C99 F.9).”
Implementation: Unknown.
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18.10 ARRAYS AND POINTERS
18.11 HINTS
ISO Standard: “The result of converting a pointer to an integer or vice versa (C90
6.3.4, C99 6.3.2.3). ”
Implementation: A cast from a n in teg er to a p ointer or vice versa result s us es th e bi nary
representation of the source type, reinterpreted as appropriate for the
des tination type.
If the source type is larger than the destination type, the Most Signifi-
cant bit s are dis carded. Wh en casting fro m a pointer t o an integer, if the
source typ e is small er than the des tin ati on type, the result is sign
extended. When casting from an integer to a pointer, if the source type
is smaller than the destination type, the result is extended based on the
signedness of the source type.
ISO Standard: “The size of the result of subtracting two pointers to elements of the
same array (C90 6.3.6, C99 6.5.6).”
Implementation: 32-bit signed integer.
ISO Standard: “The extent to which suggestions made by using the register stor-
age-class specifier are effective (C90 6.5.1, C99 6.7.1).”
Implementation: The register storage class specifier generally has no effect.
ISO Standard: “The extent to which suggestions made by using the inline function
specifier are effective (C99 6.7.4).”
Implementation: If -fno-inline or -O0 are specified, no functions will be inlined,
even if specified with the inline specifier. Otherwise, the function
may or may not be inlined dependent on the optimization heuristics of
the compiler.
Implementation-Defined Behavior
2012 Microchip Technology Inc. DS51686E-page 197
18.12 STRUCTURES, UNIONS, ENUMERATIONS, AND BIT FIELDS
18.13 QUALIFIERS
ISO Standard: “A member of a union object is accessed using a member of a different
type (C90 6.3.2.3).”
Implementation: The corresponding bytes of the union object are interpreted as an
object of the type of the member being accessed without regard for
alignment or other possible invalid conditions.
ISO Standard: “Whether a “plain” int bit field is treated as a signed int bit field or
as an unsigned int bit f iel d (C9 0 6.5. 2, C9 0 6.5. 2.1 , C99 6. 7.2 , C99
6.7.2.1).”
Implementation: By default, a plain int bit field is treated as a signed integer. This
behavior can be altered by use of the -funsigned-bitfields
comma nd lin e optio n.
ISO Standard: “Allowable bit field types other than _Bool, signed int, and
unsigned int (C99 6.7.2.1).”
Implementation: No other types are supported.
ISO Standard: “Whether a bit field can straddle a storage unit boundary (C90 6.5.2.1,
C99 6.7.2.1).”
Implementation: No.
ISO Standard: “The order of allocation of bit fields within a unit (C90 6.5.2.1, C99
6.7.2.1).”
Implementation: Bit fields are allocated left to right.
ISO Standard: “The alignment of non-bit field members of structures (C90 6.5.2.1, C99
6.7.2.1).”
Implementation: Each membe r is loc ated to th e low est avail abl e of fset al lowabl e acco rd-
ing to the alignment restrictions of the member type.
ISO Standard: “The integer type compatible with each enumerated type (C90 6.5.2.2,
C99 6.7.2.2).”
Implementation: If the enu meratio n val ues are all non-ne gat ive, th e type i s unsigned
int, else it is int. The -fshort-enums command line option can
change thi s.
ISO Standard: “What const itutes an ac cess to an objec t that has v olatil e-quali fied t ype
(C90 6.5.3, C99 6.7.3).”
Implementation: Any expression which uses the value of or stores a value to a volatile
object is considered an access to that object. There is no guarantee
that such an access is atomic.
If an expression contains a reference to a volatile object but neither
uses the v alue nor stores to the object, the expressi on is consi dered an
acces s to t he vol atile object o r not depending on th e ty pe of the object.
If the object is of scalar type, an aggregate type with a single member
of scalar type, or a union with members of (only) scalar type, the
expression is cons ider ed an acces s to th e volatil e object. Other wise ,
the expression is evaluated for its side effects but is not considered an
access to the volatile object.
For example:
volatile int a;
a; /* access to ‘a’ since ‘a’ is scalar */
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18.14 DECLARATORS
18.15 STATEMENTS
18.16 PRE-PROCESSING DIRECTIVES
ISO Standard: “The maximum number of declarators that may modify an arithmetic,
structure or union type (C90 6.5.4).”
Implementation: No limit.
ISO Standard: “The maximum number of case values in a switch statement (C90
6.6.4.2).”
Implementation: No limit.
ISO Standard: “How sequences in both forms of header names are mapped to head-
ers or external source file names (C90 6.1.7, C99 6.4.7).”
Implementation: The character sequence between the delimiters is considered to be a
string which is a file name for the host environment.
ISO Standard: “Whether the value of a character constant in a constant expression
that controls conditional inclusion matches the value of the same char-
acter constant in the execution character set (C90 6.8.1, C99 6.10.1).”
Implementation: Yes.
ISO Standard: “Whether the value of a single-character character constant in a
const ant ex press ion that c ontrols condit ional i nclus ion may have a ne g-
ative value (C90 6.8.1, C99 6.10.1). ”
Implementation: Yes.
ISO Standard: “The places that are searched for an included < > delimited header,
and how t he places are spe ci fie d o r th e header is ide nti fie d (C 9 0 6 .8.2 ,
C99 6.10.2).”
Implementation: <install
directory>/lib/gcc/pic32mx/3.4.4/include
<install directory>/pic32mx/include
ISO Standard: “How the named sourc e fil e is se arc hed for in an incl ude d “” delimited
header (C90 6.8.2, C99 6.10.2).”
Implementation: The comp iler first search es for the named file in the directory co ntaining
the including file, the directories specified by the -iquote command
line option (if any), then the directories which are searched for a < >
delimited header.
ISO Standard: “The method by which preprocessing tokens are combined into a
header name (C90 6.8.2, C99 6.10.2).”
Implementation: All tokens, including whitespace, are considered part of the header file
nam e. Macro expansion is no t per formed on tokens inside the de limit-
ers.
ISO Standard: “The nesting limit for #include processing (C90 6.8.2, C99 6.10.2).”
Implementation: No limit.
ISO Standard: “The beh avior on each reco gnized non -STDC #pragma directive (C90
6.8.6, C99 6.10.6).”
Implementation: See Section 6.12 “Variable Attribute s”.
ISO Standard: “The definitio n s for __DATE_ _ and __TIME_ _ when respectively,
the date and time of translation are not available (C90 6.8.8, C99
6.10.8).”
Implementation: The date and time of translation are always available.
Implementation-Defined Behavior
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18.17 LIBRARY FUNCTIONS
ISO Standard: “The Null Pointer constant to whic h the macro N ULL ex pands (C90
7.1.6, C99 7.17).”
Implementation: (void *)0
ISO Standard: “Any lib rary facil ities avail able to a freest anding p rogram, oth er than the
minimal set required by clause 4 (5.1.2.1).”
Implementation: See the “32-Bit Language Tools Libraries” (DS51685).
ISO Standard: “The format of the diagnostic printed by the assert m acro (7.2.1.1).”
Implementation: “F ailed assertion ‘message’ at line line of ‘filename’.\n”
ISO Standard: “The default state for the FENV_ACCESS pragma (7.6.1).”
Implementation: Unimplemented.
ISO Standard: “The represen tation of floatin g-po int exception flag s sto red by the
fegetexceptflag function (7.6.2.2).”
Implementation: Unimplemented.
ISO Standard: “Whether th e feraiseexcept function raises the inexact exceptio n
in addition to the overflow or underflow exception (7.6.2.3).”
Implementation: Unimplemented.
ISO Standard: “Floating environment macros other than FE_DFL_ENV th at can be
used as th e a rgum en t to the fesetenv or feupdateenv function
(7.6.4.3, 7.6. 4.4).”
Implementation: Unimplemented.
ISO Standard: “Strings other than “C” and “” that may be passed as the second
argument to the setlocale function (7.11.1.1).”
Implementation: None.
ISO Standard: “The types defined for float_t and double_t when the value of
the FLT_EVAL_METHOD macro is less than 0 or greater than 2 (7.12).”
Implementation: Unimplemented.
ISO Standard: “The infinity to which the INFINITY macro expands, if any (7.12).”
Implementation: Unimplemented.
ISO Standard: “The quiet NaN to which the NAN macro expands, when it is defined
(7.12).”
Implementation: Unimplemented.
ISO Standard: “Domain errors for the mathematics functions, other than those
required by this International Standard (7.12.1).”
Implementation: None.
ISO Standard: “The values returned by the mathematics functions, and whether
errno is set to the value of the macro EDOM, on domain errors
(7.12.1).”
Implementation: errno is set to EDOM on domain errors.
ISO Standard: “Whether the mathematics functions set errno to the value of the
macro ERANGE on overflow and/or underflow range errors (7.12.1).”
Implementation: Yes.
ISO Standard: “The default state for the FP_CONTRACT pragma (7.12.2)
Implementation: Unimplemented.
ISO Standard: “Whether a domain error occurs or zero is returned when the fmod
function has a second argument of zero (7.12.10.1).”
Implementation: NaN is returned.
ISO Standard: “The base-2 logarithm of the modulus use d by the remquo function in
reducing the quotient (7.12.10.3).”
Implementation: Unimplemented.
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ISO Standard: “The set of signals, their semantics, and their default handling (7.14).”
Implementation: The default handling of signals is to always return failure. Actual signal
handling is application defined.
ISO Standard: “If the equ ivalent of signal(sig, SIG_DFL); is not executed prior
to the call of a signal handler, the blocking of the signal that is per-
formed (7.14.1.1).”
Implementation: Application defined.
ISO Standard: “Whether the equivalent of signal(sig, SIG_DFL); is executed
prior to the call of a signal handler for the signal SIGILL (7.14.1.1).”
Implementation: Application defined.
ISO Standard: “Signal values other than SIGFPE, SIGILL, and SIGSEGV that corre-
spond to a computational exception (7.14.1.1).”
Implementation: Application defined.
ISO Standard: “Whether the last line of a text stream requires a terminating new-line
character (7.19.2).”
Implementation: Yes.
ISO Standard: “Whether space characters that are written out to a text stream immedi-
ately before a new-line character appear when read in (7.19.2).”
Implementation: Yes.
ISO Standard: “The number o f n ull cha ract ers th at ma y be appen ded to dat a writ ten to
a binary stream (7.19.2).”
Implementation: No null characters are appended to a binary stream.
ISO Standard: “Whether the file position indicator of an append-mode stream is ini-
tially positioned at the beginning or end of the file (7.19.3).”
Implementation: Application defined. The system level function open is called with the
O_APPEND flag.
ISO Standard: “Whether a write on a text stream causes the associated file to be trun-
cated beyond that point (7.19.3).”
Implementation: Application defined.
ISO Standard: “The characteristics of file buffering (7.19.3).”
ISO Standard: “Whether a zero-length file actually exists (7.19.3).”
Implementation: Application defined.
ISO Standard: “The rules for composing valid file names (7.19.3).”
Implementation: Application defined.
ISO Standard: “Whether the same file can be open multiple times (7.19.3).”
Implementation: Application defined.
ISO Standard: “The nature and choice of encoding s used for multibyte characters in
files (7.19.3).”
Implementation: Encodin gs are the sa me for each file .
ISO Standard: “The effect of the remove funct ion on an open file (7.1 9.4. 1).”
Implementation: Application defined. The system function unlink is called.
ISO Standard: “The effect if a file with the new name exists prior to a call to the
rename function (7.19.4.2).”
Implementation: Application defined. The system function link is called to create the
new filename, then unlink is called to remove the old filename. Typi-
cally, link will fail if the new filename already exists.
ISO Standard: “Whether an open temporary file is removed upon abnormal program
termination (7.19.4.3).”
Implementation: No.
ISO Standard: “What hap pen s when the tmpnam function is called more than
TMP_MAX times (7.19.4.4).”
Implementation-Defined Behavior
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Implementation: Temporary names will wrap around and be reused.
ISO Standard: “Which changes of m ode ar e permitted (if any ), and u nde r w h at circ um -
stances (7.19.5.4).”
Implementation: The file is closed via the system level close function and re-opened
with the open function with the new mode. No additional restriction
beyond those of the applicati on defi ne d open and close functions
are imposed.
ISO Standard: “The style used to print an infinity or NaN, and the meaning of the
n-char-sequence if that style is printed for a NaN (7.19.6.1, 7.24.2.1).”
Implementation: No char sequenc e is prin ted .
NaN is printed as “NaN”.
Infinity is printed as “[-/+]Inf”.
ISO Standard: “The output for %p conversi on in t he fprintf or fwprintf func-
tion (7.19.6. 1, 7.24 .2.1).”
Implementation: Functionally equivalent to %x.
ISO Standard: “The interpretation of a - character that is neither the first nor the last
character, nor the second where a ^ character is the first, in the scan-
list for %[ conversio n in the fscanf or fwscanf function (7.19.6.2,
7.24.2.1).”
Implementation: Unknown
ISO Standard: “The set o f se que nc es m at che d b y th e %p conv ers ion in th e fscanf
or fwscanf function (7.19.6.2, 7.24.2.2).”
Implementation: The same set of sequences matched by %x.
ISO Standard: “The interpretation of the input item corresponding to a %p conversion
in the fscanf or fwscanf function (7.19.6.2, 7.24.2.2).”
Implementation: If the result is not a valid pointer, the behavior is undefined.
ISO Standard: “The value to which the macro errno is set by the fgetpos,
fsetpos, or ftell functions on failure (7.19.9.1, 7.19.9.3,
7.19.9.4).”
Implementation: If the result exceeds LONG_MAX, errno is set to ERANGE.
Other errors are application defined according to the application defini-
tion of the lseek function.
ISO Standard: “The meaning of the n-char-sequence in a string converted by the
strtod, strtof, strtold, wcstod, wcstof, or wcstold
function (7.20.1.3, 7.24.4.1.1).”
Implementation: No meaning is attached to the seq uence.
ISO Standard: “Whether or not the strtod, strtof, strtold, wcstod,
wcstof, or wcstold function set s errno to ERANGE when und er-
flow occurs (7.20.1.3, 7.24.4.1.1).”
Implementation: Yes.
ISO Standard: “Whether the calloc, malloc, and realloc functions return a
Null Pointer or a pointer to an allocated object when the size requested
is zero (7.20.3).”
Implementation: A pointer to a statically allocated object is returned.
ISO Standard: “Whether open output streams are flushed, open streams are closed,
or temporary files are removed when the abort function is called
(7.20.4.1).”
Implementation: No.
ISO Standard: “The termination status returned to the host environment by the abort
function (7.20.4.1).”
Implementation: By default, there is no host environment.
ISO Standard: “The val ue returned b y the system funct ion when it s argum ent is not a
Null Pointer (7.20.4.5).”
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18.18 ARCHITECTURE
Implementation: Application defined.
ISO Standard: “The local time zone and Daylight Saving Time (7.23.1).”
Implementation: Application defined.
ISO Standard: “The era for the clock function (7.23.2.1).”
Implementation: Application defined.
ISO Standard: “The positive value fo r tm_isdst in a normalized tmx structure
(7.23.2.6).”
Implementation: 1.
ISO Standard: “The replacement string for the %Z specifier to the strftime,
strfxtime, wcsftime, and wcsfxtime functions in the “C”
locale (7.23.3.5, 7.23.3.6, 7.24.5.1, 7.24.5.2).”
Implementation: Unimplemented.
ISO Standard: “Whether or when the trigonometric, hyperbolic, base-e exponential,
base-e logarithmic, error, and log gamma functions raise the inexact
exception in an IEC 60559 conformant implementation (F.9).”
Implementation: No.
ISO Standard: “Wheth er the in exact exception ma y be raised when the round ed resu lt
actually does equal the mathematical result in an IEC 60559 confor-
mant implementation (F.9).”
Implementation: No.
ISO Standard: “Whether the underflow (and inexact) exception may be raised when a
result is tiny but not inexact in an IEC 60559 conformant implementa-
tion (F.9).”
Implementation: No.
ISO Standard: “Whether the functions honor the Rounding Direction mode (F.9).”
Implementation: The Rounding mode is not forced.
ISO Standard: “The values or expressions assigned to the macros specified in the
headers <float.h>, <limits.h>, and <stdint.h> (C90 and
C99 5.2.4.2, C99 7.18.2, 7.18.3).”
Implementation: See Section 6.4.2 “limits.h”.
ISO Standard: “The number, order, and encoding of bytes in any object (when not
exp licitly specified in the stan dard) (C99 6.2. 6.1).”
Implementation: Little endian, populated from Least Significant Byte first. See
Section 6.3 “Data Representation”.
ISO Standard: “The value of the result of the size of operator (C90 6.3.3.4, C99
6.5.3.4).”
Implementation: See Section 6.3 “Data Representation”.
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Appendix 19. ASCII Character Set
TABLE 19-1: ASCII CHARACTER SET
Mo st Significant Character
Least
Significant
Character
Hex01 2 34567
0NUL DLE Space 0 @ P ‘ p
1SOH DC1 ! 1 A Q a q
2STX DC2 " 2 B R b r
3ETX DC3 # 3 C S c s
4EOT DC4 $ 4 D T d t
5ENQ NAK % 5 E U e u
6ACK SYN & 6 F V f v
7Bell ETB ’ 7 G W g w
8BS CAN ( 8 H X h x
9HT EM ) 9 I Y i y
ALF SUB * : J Z j z
BVT ESC + ; K [ k {
CFF FS , < L \ l |
DCR GS - = M ] m }
ESO RS . > N ^ n ~
FSI US / ? O _ o DEL
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NOTES:
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USER’S GUIDE
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Appendix 20. Depr ecated Features
20.1 INTRODUCTION
The features described below are considered to be obsolete and have been replaced
with more advanced functionality. Projects which depend on deprecated features will
work properly with versions of the language tools cited. The use of a deprecated
feature will result in a warning; programmers are encouraged to revise their projects in
order to eliminate any dependency on deprecated features. Support for these features
may be removed entirely in future versions of the language tools.
Deprecated features covered are:
Variables in Specified Registers
20.2 VARIABLES IN SPECIFIED REGISTERS
The compiler allows you to put a few global variables into specified hardware registers.
You can also specify the register in which an ordinary register variable should be
allocated.
• Global register variables reserve registers throughout the program. This may be
useful in programs such as programming language interpreters which have a
couple of global variables that are accessed very often.
• Local register variables in specific registers do not reserve the registers. The
compiler’s data flow analysis is capable of determining where the specified
registers contain live values, and where they are available for other uses. Stores
into local register variables may be deleted when they appear to be unused.
References to local register variables may be deleted, moved or simplified.
These local variables are sometimes convenient for use with the extended inline
assembly (see Chapter 14. “Mixing C/C++ and Assembly Language”), if you want
to write one output of the assembler instruction directly into a particular register. (This
will work provided the register you specify fits the constraints specified for that operand
in the inline assembly statement).
20.2.1 Defining Global Register Variables
You can define a global register variable like this:
register int *foo asm ("w8");
Here w8 is the name of the register which should be used. Choose a register that is
normally saved and restored by function calls (W8-W13), so that library routines will not
clobber it.
Note: Using too many registers, in particular register W0, may impair the ability of
the 32-bit compiler to compile. It is not recommended that registers be
placed into fixed registers.
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Defining a global register variable in a certain register reserves that register entirely for
this use, at least within the current compilation. The register will not be allocated for any
other purpose in the functions in the current compilation. The register will not be saved
and restored by these functions. S tores into this register are never deleted even if they
would appear to be dead, but references may be deleted, moved or simplified.
It is not safe to access the global register variables from signal handlers, or from more
than one thread of control, because the system library routines may temporarily use the
register for other things (unless you recompile them especially for the task at hand).
It is not safe for one function that uses a global register variable to call another such
function foo by way of a third function lose that was compiled without knowledge of
this variable (i.e., in a source file in which the variable wasn’t declared). This is because
lose might save the register and put some other value there. For example, you can’t
expect a global register variable to be available in the comparison-function that you
pass to qsort, since qsort might have put something else in that register. This
problem can be avoided by recompiling qsort with the same global register variable
definition.
If you want to recompile qsort or other source files that do not actually use your global
register variable, so that they will not use that register for any other purpose, then it
suffices to specify the compiler command-line option -ffixed-reg. You need not
actually add a global register declaration to their source code.
A function that can alter the value of a global register variable cannot safely be called
from a function compiled without this variable, because it could clobber the value the
caller expects to find there on return. Therefore, the function that is the entry point into
the part of the program that uses the global register variable must explicitly save and
restore the value that belongs to its caller.
The library function longjmp will restore to each global register variable the value it
had at the time of the setjmp.
All global register variable declarations must precede all function definitions. If such a
declaration appears after function definitions, the register may be used for other
purposes in the preceding functions.
Global register variables may not have initial values because an executable file has no
means to supply initial contents for a register.
20.2.2 Specifying Registers for Local Variables
You can define a local register variable with a specified register like this:
register int *foo asm ("w8");
Here w8 is the name of the register that should be used. Note that this is the same
syntax used for defining global register variables, but for a local variable it would appear
within a function.
Defining such a register variable does not reserve the register; it remains available for
other uses in places where flow control determines the variable’s value is not live.
Using this feature may leave the compiler too few available registers to compile certain
functions.
This option does not ensure that the compiler will generate code that has this variable
in the register you specify at all times. You may not code an explicit reference to this
registe r in an asm statement and assume it will always refer to this variable.
Assignments to local register variables may be deleted when they appear to be
unused. References to local register variables may be deleted, moved or simplified.
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Glossary
A
Absolute Section
A section with a fixed (absolute) address that cannot be changed by the linker.
Access Memory
PIC18 Only – Special registers on PIC18 devices that allow access regardless of the
setting of the Bank Select Register (BSR).
Access Entry Points
Access entry points provide a way to transfer control across segments to a function
which may not be defined at link time. They support the separate linking of boot and
secure application segments.
Address
Value that identifies a location in memory.
Alphabetic Character
Alphabetic characters are those characters that are letters of the arabic alphabet
(a,b,…,z,A,B, …,Z).
Alphanumeric
Alphanumeric characters are comprised of alphabetic characters and decimal digits
(0,1, …, 9).
ANDed Breakpoints
Set up an ANDed condition for breaking, i.e., breakpoint 1 AND breakpoint 2 must
occur at the same time before a program halt. This can only be accomplished if a data
breakpoint and a program memory breakpoint occur at the same time.
Anonymous Structure
32-bit C/C++ Compiler – An unnamed structure.
PIC18 C Compiler – An unnamed structure that is a member of a C union. The mem-
bers of an anonymous structure may be accessed as if they were members of the
enclosing union. For example, in the following code, hi and lo are members of an
anonymous structure inside the union caster.
union castaway
int intval;
struct {
char lo; //accessible as caster.lo
char hi; //accessible as caster.hi
};
} caster;
ANSI
American National Standards Institute is an organization responsible for formulating
and approving standards in the United States.
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Application
A set of software and hardware that may be controlled by a PIC® microcontroller.
Archive/Archiver
An archive/library is a collection of relocatable object modules. It is created by assem-
bling multiple source files to object files, and then using the archiver/librarian to com-
bine the object files into one archive/library file. An archive/library can be linked with
object modules and other archives/libraries to create executable code.
ASCII
American S tandard Code for Information Interchange is a character set encoding that
uses 7 binary digits to represent each character. It includes upper and lower case
letters, digits, symbols and control characters.
Assembly/Assembler
Assembly is a programming language that describes binary machine code in a sym-
bolic form. An assembler is a language tool that translates assembly language source
code into machine code.
Assigned Section
A section which has been assigned to a target memory block in the linker command file.
Asynchronously
Multiple events that do not occur at the same time. This is generally used to refer to
interrupts that may occur at any time during processor execution.
Attribute
Characteristics of variables or functions in a C program which are used to describe
machine-specific properties.
Attribute, Section
Characteristics of sections, such as “executable”, “readonly”, or “data” that can be
specified as flags in the assembler .section directive.
B
Binary
The base two numbering system that uses the digits 0-1. The rightmost digit counts
ones, the next counts multiples of 2, then 22 = 4, etc.
Breakpoint
Hardware Breakpoint: An event whose execution will cause a halt.
Software Breakpoint: An address where execution of the firmware will halt. Usually
achieved by a special break instruction.
Build
Compile and link all the source files for an application.
C
C\C++
C is a general-purpose programming language which features economy of expression,
modern control flow and data structures, and a rich set of operators. C++ is the
object-oriented version of C.
Calibration Memory
A special function register or registers used to hold values for calibration of a PIC
microcontroller on-board RC oscillator or other device peripherals.
Glossary
2012 Microchip Technology Inc. DS51686E-page 209
Central Processing Unit
The part of a device that is responsible for fetching the correct instruction for execution,
decoding that instruction, and then executing that instruction. When necessary , it works
in conjunction with the arithmetic logic unit (ALU) to complete the execution of the
instruction. It controls the program memory address bus, the data memory address
bus, and acce sses to the stack.
Clean
Clean removes all intermediary project files, such as object, hex and debug files, for
the active project. These files are recreated from other files when a project is built.
COFF
Common Object File Format. An object file of this format contains machine code,
debugging and other information.
Command Line Interface
A means of communication between a program and its user based solely on textual
input and output.
Compiler
A program that translates a source file written in a high-level language into machine
code.
Conditional Assembly
Assembly language code that is included or omitted based on the assembly-time value
of a specified expression.
Conditional Compilation
The act of compiling a program fragment only if a certain constant expression, specified
by a preprocessor directive, is true.
Configuration Bits
Special-purpose bits programmed to set PIC microcontroller modes of operation. A
Configuration bit may or may not be preprogrammed.
Control Directives
Directives in assembly language code that cause code to be included or omitted based
on the assembly-time value of a specified expression.
CPU
See Central Processing Unit.
Cross Reference File
A file that references a table of symbols and a list of files that references the symbol. If
the symbol is defined, the first file listed is the location of the definition. The remaining
files contain references to the symbol.
D
Data Directives
Data directives are those that control the assembler’s allocation of program or data
memory and provide a way to refer to data items symbolically; that is, by meaningful
names.
Data Memory
On Microchip MCU and DSC devices, data memory (RAM) is comprised of General
Purpose Registers (GPRs) and S pecial Function Registers (SFRs). Some devices also
have EEPROM data memory.
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Debug/Debugger
See ICE/ICD.
Debugging Information
Compiler and assembler options that, when selected, provide varying degrees of infor-
mation used to debug application code. See compiler or assembler documentation for
details on selecting debug options.
Deprecate d Feat ures
Features that are still supported for legacy reasons, but will eventually be phased out
and no longer used.
Device Programmer
A tool used to program electrically programmable semiconductor devices such as
microcontrollers.
Digital Signal Controller
A digital signal controller (DSC) is a microcontroller device with digital signal processing
capability, i.e., Microchip dsPIC® DSC devices.
Digital Signal Processing/Digital Signal Processor
Digital Signal Processing (DSP) is the computer manipulation of digital signals, com-
monly analog signals (sound or image) which have been converted to digital form (sam-
pled). A digital signal processor is a microprocessor that is designed for use in digital
signal pr oc essi ng.
Directives
Statements in source code that provide control of the language tool’s operation.
Download
Download is the process of sending data from a host to another device, such as an
emulator, programmer or target board.
DWARF
Debug With Arbitrary Record Format. DWARF is a debug information format for ELF
files.
E
EEPROM
Electrically Erasable Programmable Read Only Memory. A special type of PROM that
can be erased electrically. Data is written or erased one byte at a time. EEPROM
retains its contents even when power is turned off.
ELF
Executable and Linking Format. An object file of this format contains machine code.
Debugging and other information is specified in with DWARF. ELF/DWARF provide
better debugging of optimized code than COFF.
Emulation/Emulator
See ICE/ICD.
Endianness
The ordering of bytes in a multi-byte object.
Environment
MPLAB PM3 – A folder containing files on how to program a device. This folder can be
transferred to a SD/MMC card.
Glossary
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Epilogue
A portion of compiler-generated code that is responsible for deallocating stack space,
restoring registers and performing any other machine-specific requirement specified in
the runtime model. This code executes after any user code for a given function,
immediately prior to the function return.
EPROM
Erasable Programmable Read Only Memory. A programmable read-only memory that
can be erased usually by exposure to ultraviolet radiation.
Error/Error File
An error reports a problem that makes it impossible to continue processing your
program. When possible, an error identifies the source file name and line number
where the problem is apparent. An error file contains error messages and diagnostics
generated by a language tool.
Event
A description of a bus cycle which may include address, data, pass count, external
input, cycle type (fetch, R/W), and time stamp. Events are used to describe triggers,
breakpoints and interrupts.
Executable Code
Software that is ready to be loaded for execution.
Export
Send data out of the MPLAB IDE in a standardized format.
Expressions
Combinations of constants and/or symbols separated by arithmetic or logical
operators.
Extended Microcontroller Mod e
In extended microcontroller mode, on-chip program memory as well as external mem-
ory is available. Execution automatically switches to external if the program memory
address is greater than the internal memory space of the PIC18 device.
Extended Mode (PIC18 MCUs)
In Extended mode, the compiler will utilize the extended instructions (i.e., ADDFSR,
ADDULNK, CALLW, MOVSF, MOVSS, PUSHL, SUBFSR and SUBULNK) and the indexed
with literal offset addressing.
External Label
A label that has extern al lin ka ge.
Extern al Lin kag e
A function or variable has external linkage if it can be referenced from outside the
module in wh ich it is defined.
Exte rnal Symbol
A symbol for an identifier which has external linkage. This may be a reference or a
definition.
External Symbol Resolu tio n
A process performed by the linker in which external symbol definitions from all input
modules are collected in an attempt to resolve all external symbol references. Any
external symbol references which do not have a corresponding definition cause a linker
error to be reported.
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External Input Line
An external input signal logic probe line (TRIGIN) for setting an event based upon
external signals.
External RAM
Off-chip Read/Write memory.
F
Fatal Error
An error that will halt compilation immediately. No further messages will be produced.
File Registers
On-chip data memory, including General Purpose Registers (GPRs) and Special
Function Registers (SFRs).
Filter
Determine by selection what data is included/excluded in a trace display or data file.
Flash
A type of EEPROM where data is written or erased in blocks instead of bytes.
FNOP
Forced No Operation. A forced NOP cycle is the second cycle of a two-cycle instruc-
tion. Since the PIC microcontroller architecture is pipelined, it prefetches the next
instruction in the physical address space while it is executing the current instruction.
However, if the current instruction changes the program counter, this prefetched
instruction is explicitly ignored, causing a forced NOP cycle.
Frame Pointer
A pointer that references the location on the stack that separates the stack-based
arguments from the stack-based local variables. Provides a convenient base from
which to access local variables and other values for the current function.
Free-Standing
An implementation that accepts any strictly conforming program that does not use
complex types and in which the use of the features specified in the library clause (ANSI
‘89 standard clause 7) is confined to the contents of the standard headers <float.h>,
<iso646.h>, <limits.h>, <stdarg.h>, <stdbool.h>, <stddef.h> and
<stdint.h>.
G
GPR
General Purpose Register. The portion of device data memory (RAM) available for
general use.
H
Halt
A stop of program execution. Executing Halt is the same as stopping at a breakpoint.
Heap
An area of memory used for dynamic memory allocation where blocks of memory are
allocated and freed in an arbitrary order determined at runtime.
Hex Code/Hex File
Hex code is executable instructions stored in a hexadecimal format code. Hex code is
contained in a hex file.
Glossary
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Hexadecimal
The base 16 numbering system that uses the digits 0-9 plus the letters A-F (or a-f). The
digits A-F represent hexadecimal digits with values of (decimal) 10 to 15. The rightmost
digit counts ones, the next counts multiples of 16, then 162 = 256, etc.
High Level Language
A language for writing programs that is further removed from the processor than
assembly.
I
ICE/ICD
In-Circuit Emulator/In-Circuit Debugger: A hardware tool that debugs and programs a
target device. An emulator has more features than an debugger, such as trace.
In-Circuit Emulation/In-Circuit Debug: The act of emulating or debugging with an
in-circuit emulator or debugger.
-ICE/-ICD: A device (MCU or DSC) with on-board in-circuit emulation or debug circuitry .
This device is always mounted on a header board and used to debug with an in-circuit
emulator or debugger.
ICSP™ Programming Capability
In-Circuit Serial Programming™ programming capability. A method of programming
Microchip embedded devices using serial communication and a minimum number of
device pins.
IDE
Integrated Development Environment, as in MPLAB IDE.
Identifier
A function or va riabl e name .
IEEE
Institute of Electrical and Electronics Engineers.
Import
Bring data into the MPLAB IDE from an outside source, such as from a hex file.
Initialized Data
Data which is defined with an initial value. In C,
int myVar=5;
defines a va riable which will reside in an initialized data section.
Instruction Set
The collection of machine language instructions that a particular processor
understands.
Instructions
A sequence of bits that tells a central processing unit to perform a particular operation
and can contain data to be used in the operation.
Internal Linkage
A function or variable has internal linkage if it can not be accessed from outside the
module in wh ich it is defined.
International Organization for Standardization
An organization that sets standards in many businesses and technologies, including
computing and communications. Also known as ISO.
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Interrupt
A signal to the CPU that suspends the execution of a running application and transfers
control to an Interrupt Service Routine (ISR) so that the event may be processed. Upon
completion of the ISR, normal execution of the application resumes.
Interrupt Handler
A routine that processes special code when an interrupt occurs.
Interrupt Service Request (IRQ)
An event which causes the processor to temporarily suspend normal instruction exe-
cution and to start executing an interrupt handler routine. Some processors have
several interrupt request events allowing different priority interrupts.
Interrupt Service Routine (ISR)
Language tools – A function that handles an interrupt.
MPLAB IDE – User-generated code that is entered when an interrupt occurs. The loca-
tion of the code in program memory will usually depend on the type of interrupt that has
occurred.
Interrupt Vector
Address of an interrupt service routine or interrupt handler.
L
L-value
An expression that refers to an object that can be examined and/or modified. An l-value
expression is used on the left-hand side of an assignment.
Latency
The time between an event and its response.
Library/Librarian
See Archive/Archiver.
Linker
A language tool that combines object files and libraries to create executable code,
resolving references from one module to another.
Linker Script Files
Linker script files are the command files of a linker. They define linker options and
describe available memory on the target platform.
Listing Directives
Listing directives are those directives that control the assembler listing file format. They
allow the spec ifi ca tio n of titles , paginati on and othe r listi ng co ntr ol .
Listing File
A listing file is an ASCII text file that shows the machine code generated for each C/C++
source statement, assembly instruction, assembler directive, or macro encountered in
a source file.
Little Endian
A data ordering scheme for multibyte data whereby the least significant byte is stored
at the lower addresses.
Glossary
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Local Label
A local label is one that is defined inside a macro with the LOCAL directive. These
labels are particular to a given instance of a macro’s instantiation. In other words, the
symbols and labels that are declared as local are no longer accessible after the ENDM
macro is encountered.
Logic Probes
Up to 14 logic probes can be connected to some Microchip emulators. The logic probes
provide external trace inputs, trigger output signal, +5V, and a common ground.
Loop-Back Test Board
Used to test the functionality of the MPLAB REAL ICE™ in-circuit emulator.
LVDS
Low Voltage Differential Signaling. A low noise, low-power, low amplitude method for
high-speed (gigabits per second) data transmission over copper wire.
With standard I/0 signaling, data storage is contingent upon the actual voltage level.
Voltage level can be affected by wire length (longer wires increase resistance, which
lowers voltage). But with L VDS, data storage is distinguished only by positive and neg-
ative voltage values, not the voltage level. Therefore, data can travel over greater
lengths of wire while maintaining a clear and consistent data stream.
Source: http://www.webopedia.com/TERM/L/LVDS.html.
M
Machine Code
The representation of a computer program that is actually read and interpreted by the
processor. A program in binary machine code consists of a sequence of machine
instructions (possibly interspersed with data). The collection of all possible instructions
for a particular processor is known as its “instruction set”.
Machine Language
A set of instructions for a specific central processing unit, designed to be usable by a
processo r with out bei ng trans lat ed.
Macro
Macro instruction. An instruction that represents a sequence of instructions in
abbreviated form.
Macro Directives
Directives that control the execution and data allocation within macro body definitions.
Makefile
Export to a file the instructions to Make the project. Use this file to Make your project
outside of MPLAB IDE, i.e., with a make.
Make Project
A command that rebuilds an application, recompiling only those source files that have
changed since the last complete compilation.
MCU
Microcontroller Unit. An abbreviation for microcontroller. Also µC.
Memory Model
For C compilers, a representation of the memory available to the application. For the
PIC18 C compiler , a description that specifies the size of pointers that point to program
memory.
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Message
Text displayed to alert you to potential problems in language tool operation. A message
will not stop operation.
Microcontroller
A highly integrated chip that contains a CPU, RAM, program memory, I/O ports and
timers.
Microcontroller Mode
One of the possible program memory configurations of PIC18 microcontrollers. In
microcontroller mode, only internal execution is allowed. Thus, only the on-chip pro-
gram memory is available in microcontroller mode.
Microprocessor Mode
One of the possible program memory configurations of PIC18 microcontrollers. In
microprocessor mode, the on-chip program memory is not used. The entire program
memory is mapped externally.
Mnemonics
Text instructions that can be translated directly into machine code. Also referred to as
opcodes.
MPASM™ Assembler
Microchip Technology’s relocatable macro assembler for PIC microcontroller devices,
KeeLoq® devices and Microchip memory devices.
MPLAB Language Tool for Device
Microchip’s C compilers, assemblers and linkers for specified devices. Select the type
of language tool based on the device you will be using for your application, e.g., if you
will be creating C code on a PIC18 MCU, select the MPLAB C Compiler for PIC18
MCUs.
MPLAB ICD
Microchip’s in-circuit debuggers that works with MPLAB IDE. See ICE/ICD.
MPLAB IDE
Microchip’s Integrated Development Environment. MPLAB IDE comes with an editor,
project manager and simulator.
MPLAB PM3
A device programmer from Microchip. Programs PIC18 microcontrollers and dsPIC
digital signal controllers. Can be used with MPLAB IDE or stand-alone. Replaces
PRO MATE II.
MPLAB REAL ICE In-Circuit Emulator
Microchip’s next-generation in-circuit emulators that works with MPLAB IDE. See
ICE/ICD.
MPLAB SIM
Microchip’s simulator that works with MPLAB IDE in support of PIC MCU and dsPIC
DSC devices.
MPLIB™ Object Librarian
Microchip’s librarian that can work with MPLAB IDE. MPLIB librarian is an object librar-
ian for use with COFF object modules created using either MP ASM assembler (mpasm
or mpasmwin v2.0) or MPLAB C18 C compiler.
Glossary
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MPLINK™ Object Linker
MPLINK linker is an object linker for the Microchip MPASM assembler and the
Microchip C18 C compiler . MPLINK linker also may be used with the Microchip MPLIB
librarian. MPLINK linker is designed to be used with MPLAB IDE, though it does not
have to be.
MRU
Most Recently Used. Refers to files and windows available to be selected from MPLAB
IDE main pull down menus.
N
Native Data Size
For Native trace, the size of the variable used in a Watch window must be of the same
size as the selected device’s data memory: bytes for PIC18 devices and words for
16-bit devices.
Nesting Depth
The maximum level to which macros can include other macros.
Node
MPLAB IDE project component.
Non-Extended Mode (PIC18 MCUs)
In Non-Extended mode, the compiler will not utilize the extended instructions nor the
indexed with literal offset addressing.
Non Real Time
Refers to the processor at a breakpoint or executing single-step instructions or MPLAB
IDE being run in simulator mode.
Non-Volatile Storage
A storage device whose contents are preserved when its power is off.
NOP
No Operation. An instruction that has no effect when executed except to advance the
program counter.
O
Object Code/Object File
Object code is the machine code generated by an assembler or compiler . An object file
is a file containing machine code and possibly debug information. It may be immedi-
ately executable or it may be relocatable, requiring linking with other object files, e.g.,
libraries, to produce a complete executable program.
Object File Directives
Directives that are used only when creating an object file.
Octal
The base 8 number system that only uses the digits 0-7. The rightmost digit counts
ones, the next digit counts multiples of 8, then 82 = 64, etc.
Off-Chip Memory
Off-chip memory refers to the memory selection option for the PIC18 device where
memory may reside on the target board, or where all program memory may be supplied
by the emulator. The Memory tab accessed from Options>Development Mode pro-
vides the Off-Chip Memory selection dialog box.
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Opcodes
Operational Codes. See Mnemonics.
Operators
Symbols, like the plus sign ‘+’ and the minus sign ‘-’, that are used when forming
well-defined expressions. Each operator has an assigned precedence that is used to
determine order of evaluation.
OTP
One Time Programmable. EPROM devices that are not in windowed packages. Since
EPROM needs ultraviolet light to erase its memory, only windowed devices are
erasable.
P
Pass Counter
A counter that decrements each time an event (such as the execution of an instruction
at a particular address) occurs. When the pass count value reaches zero, the event is
satisfied. You can assign the Pass Counter to break and trace logic, and to any
sequential event in the complex trigger dialog.
PC
Person al Comp ute r or Progra m Counte r.
PC Host
Any PC running a supported Windows operating system.
Persistent Data
Data that is never cleared or initialized. Its intended use is so that an application can
preserve data across a device reset.
Phantom Byte
An unimplemented byte in the dsPIC DSC architecture that is used when treating the
24-bit instruction word as if it were a 32-bit instruction word. Phantom bytes appear in
dsPIC DSC hex files.
PIC MCUs
PIC microcontrollers (MCUs) refers to all Microchip microcontroller families.
PICkit™ 2 and 3 Programmer/Debugger
Microchip’s developmental device programmers with debug capability through Debug
Express. See the Readme files for each tool to see which devices are supported.
Plug-ins
The MPLAB IDE has both built-in components and plug-in modules to configure the
system for a variety of software and hardware tools. Several plug-in tools may be found
under the Tools menu.
Pod
The enclosure for an in-circuit emulator or debugger. Other names are “Puck”, if the
enclosure is round, and “Probe”, not be confused with logic probes.
Power-on-Reset Emulation
A software randomization process that writes random values in data RAM areas to
simulate uninitialized values in RAM upon initial power application.
Pragma
A directive that has meaning to a specific compiler. Often a pragma is used to convey
implementation-defined information to the compiler. MPLAB C30 uses attributes to
convey this information.
Glossary
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Precedence
Rules that define the order of evaluation in expressions.
Prod ucti o n Pr og r am m er
A production programmer is a programming tool that has resources designed in to pro-
gram devices rapidly . It has the capability to program at various voltage levels and com-
pletely adheres to the programming specification. Programming a device as fast as
possible is of prime importance in a production environment where time is of the
essence as the application circuit moves through the assembly line.
Profile
For MPLAB SIM simulator, a summary listing of executed stimulus by register.
Program Counter
The location that contains the address of the instruction that is currently executing.
Program Counter Unit
32-bit assembler – A conceptual representation of the layout of program memory. The
program counter increments by 2 for each instruction word. In an executable section,
2 program counter units are equivalent to 3 bytes. In a read-only section, 2 program
counter units are equivalent to 2 bytes.
Program Memory
MPLAB IDE – The memory area in a device where instructions are stored. Also, the
memory in the emulator or simulator containing the downloaded target application
firmware.
32-bit assembler/compiler – The memory area in a device where instructions are
stored.
Project
A project contains the files needed to build an application (source code, linker script
files, etc.) along with their associations to various build tools and build options.
Prologue
A portion of compiler-generated code that is responsible for allocating stack space, pre-
serving registers and performing any other machine-specific requirement specified in
the runtime model. This code executes before any user code for a given function.
Prototype System
A term referring to a user's target application, or target board.
PWM Signals
Pulse Width Modulation Signals. Certain PIC MCU devices have a PWM peripheral.
Q
Qualifier
An address or an address range used by the Pass Counter or as an event before
another operation in a complex trigger.
R
Radix
The number base, hex, or decimal, used in specifying an address.
RAM
Random Access Memory (Data Memory). Memory in which information can be
accessed in any order.
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Raw Dat a
The binary representation of code or data associated with a section.
Read Only Memory
Memory hardware that allows fast access to permanently stored data but prevents
addition to or modification of the data.
Real Time
When an in-circuit emulator or debugger is released from the halt state, the processor
runs in Real Time mode and behaves exactly as the normal chip would behave. In Real
Time mode, the real time trace buffer of an emulator is enabled and constantly captures
all selected cycles, and all break logic is enabled. In an in-circuit emulator or debugger ,
the processor executes in real time until a valid breakpoint causes a halt, or until the
user halts the execution.
In the simulator, real time simply means execution of the microcontroller instructions as
fast as they can be simulated by the host CPU.
Real-Time Watch
A W atch window where the variables change in real-time as the application is run. See
individual tool documentation to determine how to set up a real-time watch. Not all tools
support real-time watches.
Recursive Calls
A function that calls itself, either directly or indirectly.
Recursion
The concept that a function or macro, having been defined, can call itself. Great care
should be taken when writing recursive macros; it is easy to get caught in an infinite
loop where there will be no exit from the recursion.
Reentrant
A function that may have multiple, simultaneously active instances. This may happen
due to either direct or indirect recursion or through execution during interrupt
processing.
Relaxation
The process of converting an instruction to an identical, but smaller instruction. This is
usef ul for savi ng on co de size. MP LAB ASM3 0 currentl y knows how to RELAX a CALL
instruction into an RCALL instruction. This is done when the symbol that is being called
is within +/- 32k instruction words from the current instruction.
Relocatable
An object whose address has not been assigned to a fixed location in memory.
Relocatable Section
32-bit assembler – A section whose address is not fixed (absolute). The linker assigns
addresses to relocatable sections through a process called relocation.
Relocation
A process performed by the linker in which absolute addresses are assigned to relo-
catable sections and all symbols in the relocatable sections are updated to their new
addresses.
ROM
Read Only Memory (Program Memory). Memory that cannot be modified.
Run
The command that releases the emulator from halt, allowing it to run the application
code and change or respond to I/O in real time.
Glossary
2012 Microchip Technology Inc. DS51686E-page 221
Run-time Model
Describes the use of target architecture resources.
S
Scenario
For MPLAB SIM simulator, a particular setup for stimulus control.
Section
A portion of an application located at a specific address of memory.
Section Attribute
A characteristic ascribed to a section (e.g., an access section).
Sequenced Breakpoints
Breakpoints that occur in a sequence. Sequence execution of breakpoints is
bottom-up; the last breakpoint in the sequence occurs first.
Serialized Quick Turn Programming
Serialization allows you to program a serial number into each microcontroller device
that the Device Programmer programs. This number can be used as an entry code,
password or ID number .
Shell
The MPASM assembler shell is a prompted input interface to the macro assembler.
There are two MPASM assembler shells: one for the DOS version and one for the
Windows version.
Simulator
A software progr am that mod els th e operati on of devi c es.
Single Step
This command steps though code, one instruction at a time. After each instruction,
MPLAB IDE updates register windows, watch variables, and status displays so you can
analyze and debug instruction execution. You can also single step C compiler source
code, but instead of executing single instructions, MPLAB IDE will execute all assembly
level instructions generated by the line of the high level C statement.
Skew
The information associated with the execution of an instruction appears on the proces-
sor bus at different times. For example, the executed opcodes appears on the bus as
a fetch during the execution of the previous instruction, the source data address and
value and the destination data address appear when the opcodes is actually executed,
and the destination data value appears when the next instruction is executed. The trace
buffer captures the information that is on the bus at one instance. Therefore, one trace
buffer entry will contain execution information for three instructions. The number of cap-
tured cycles from one piece of information to another for a single instruction execution
is referred to as the skew.
Skid
When a hardware breakpoint is used to halt the processor, one or more additional
instructions may be executed before the processor halts. The number of extra
instructions executed after the intended breakpoint is referred to as the skid.
Source Code
The form in which a computer program is written by the programmer. Source code is
written in a formal programming language which can be translated into machine code
or executed by an interpreter.
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Source File
An ASCII text file containing source code.
Special Function Registers (SFRs)
The portion of data memory (RAM) dedicated to registers that control I/O processor
functions, I/O status, timers or other modes or peripherals.
SQTPsm
See Serialized Quick Turn Programming.
Stack, Hardwar e
Locations in PIC microcontroller where the return address is stored when a function call
is made.
Stack, Software
Memory used by an application for storing return addresses, function parameters, and
local variables. This memory is typically managed by the compiler when developing
code in a high-level language.
MPLAB Starter Kit for Device
Microchip’s starter kits contains everything needed to begin exploring the specified
device. View a working application and then debug and program you own changes.
Static RAM or SRAM
Static Random Access Memory. Program memory you can read/write on the target
board that does not need refreshing frequently.
Status Bar
The S t atus Bar is located on the bottom of the MPLAB IDE window and indicates such
current information as cursor position, development mode and device, and active tool
bar.
Step Into
This command is the same as Single S tep. S tep Into (as opposed to S tep Over) follows
a CALL instruction into a subroutine.
Step Over
S tep Over allows you to debug code without stepping into subroutines. When stepping
over a CALL instruction, the next breakpoint will be set at the instruction after the CALL.
If for some reason the subroutine gets into an endless loop or does not return properly ,
the next breakpoint will never be reached. The Step Over command is the same as
Single Step except for its handling of CALL instructions.
Step Out
Step Out allows you to step out of a subroutine which you are currently stepping
through. This command executes the rest of the code in the subroutine and then stops
execution at the return address to the subroutine.
Stimulus
Input to the simulator, i.e., data generated to exercise the response of simulation to
external signals. Often the data is put into the form of a list of actions in a text file.
Stimulus may be asynchronous, synchronous (pin), clocked and register.
Stopwatch
A counter for measuring execution cycles.
Storage Class
Determines the lifetime of the memory assoc iat ed with the ide ntifie d objec t.
Glossary
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Storage Qualifier
Indicates special properties of the objects being declared (e.g., const).
Symbol
A symbol is a general purpose mechanism for describing the various pieces which
comprise a program. These pieces include function names, variable names, section
names, file names, struct/enum/union tag names, etc. Symbols in MPLAB IDE refer
mainly to variable names, function names and assembly labels. The value of a symbol
after linking is its value in me mory.
Symbol, Absolute
Represents an immediate value such as a definition through the assembly .equ
directive.
System Window Control
The system window control is located in the upper left corner of windows and some dia-
logs. Clicking on this control usually pops up a menu that has the items “Minimize,”
“Maximize,” and “Close.”
T
Target
Refers to user hardware.
Target Application
Software residing on the target board.
Target Board
The circuitry and programmable device that makes up the target application.
Target Processor
The microcontroller device on the target application board.
Template
Lines of text that you build for inserting into your files at a later time. The MPLAB Editor
stores templates in template files.
Tool Bar
A row or column of icons that you can click on to execute MPLAB IDE functions.
Trace
An emulator or simulator function that logs program execution. The emulator logs pro-
gram execution into its trace buffer which is uploaded to MPLAB IDE’s trace window.
Trace Memory
Trace memory contained within the emulator. Trace memory is sometimes called the
trace buf fer.
Trace Macro
A macro that will provide trace information from emulator data. Since this is a software
trace, the macro must be added to code, the code must be recompiled or reassembled,
and the target device must be programmed with this code before trace will work.
Trigger Output
Trigger output refers to an emulator output signal that can be generated at any address
or address range, and is independent of the trace and breakpoint settings. Any number
of trigger output points can be set.
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Trigraphs
Three-character sequences, all starting with ??, that are defined by ISO C as
replacements for single characters.
U
Unassigned Section
A section which has not been assigned to a specific target memory block in the linker
command file. The linker must find a target memory block in which to allocate an
unassigned section.
Uninitialized Data
Data which is defined without an initial value. In C,
int myVar;
defines a variable which will reside in an uninitialized data section.
Upload
The Upload function transfers data from a tool, such as an emulator or programmer , to
the host PC or from the target board to the emulator.
USB
Universal Serial Bus. An external peripheral interface standard for communication
between a computer and external peripherals over a cable using bi-serial transmission.
USB 1.0/1.1 supports data transfer rates of 12 Mbps. Also referred to as high-speed
USB, USB 2.0 supports data rates up to 480 Mbps.
V
Vector
The memory locations that an application will jump to when either a reset or interrupt
occurs.
W
Warning
MPLAB IDE – An alert that is provided to warn you of a situation that would cause phys-
ical damage to a device, software file, or equipment.
32-bit assembler/compiler – Warnings report conditions that may indicate a problem,
but do not halt processing. In MPLAB C30, warning messages report the source file
name and line number, but include the text ‘warning:’ to distinguish them from error
messages.
Watch Variable
A variable that you may monitor during a debugging session in a Watch window.
Watch Window
Watch windows contain a list of watch variables that are updated at each breakpoint.
Watchdog Timer (WDT)
A timer on a PIC microcontroller that resets the processor after a selectable length of
time. The WDT is enabled or disabled and set up using Configuration bits.
Workbook
For MPLAB SIM stimulator, a setup for generation of SCL stimulus.
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Index
Symbols
.app_excpt Section ......................................... 182
.bev_excpt Section ......................................... 182
.bss ..................................................................... 147
.bss Section ........................................................ 188
.config_address .......................................... 180
.data .................................................................. 147
.data Section ..................................................... 186
.dbg_data Section ..................................... 186
.dbg_excpt Section ......................................... 182
.got Section ......................................................... 186
.h files, see header files
.heap .................................................................. 188
.lit4 .................................................................. 147
.lit4 Section ..................................................... 187
.lit8 .................................................................. 147
.lit8 Section ..................................................... 187
.ramfunc ........................................................... 148
.ramfunc Section .............................................. 189
.reset Section ................................................... 181
.rodata Section ................................................ 185
.sbss .................................................................. 147
.sbss Section ..................................................... 188
.sbss2 Section ................................................... 186
.sdata ................................................................ 147
.sdata Section ................................................... 187
.sdata2 Section ................................................ 185
.stack Section ................................................... 188
.startup Section .............................................. 183
.text Section ..................................................... 183
.vector_n Sections .......................................... 183
“On Bootstrap” Proce dure ..................................... 154
# preprocessor operator ........................................ 170
## preprocessor operator ...................................... 170
#define ............................................................... 78
#ident .................................................................. 84
#if ......................................................................... 71
#include ........................................................78, 79
#line .................................................................... 80
#pragma ............................................................... 68
#pragma config ............................................. 171
#pragma interrupt ..................................... 171
#pragma vector ............................................. 171
Numerics
-msmart-io= ...................................................... 61
PIC32MX Device-Specific Options
-msmart-io= ............................................... 61
0b binary radix specifier ........................................ 102
32-Bit C Compiler Macros ..................................... 172
A
a0-a3 ..................................................................141
absolute functions ...................................................29
absolute variables ...................................................29
addressr Attribute .............................................123
alias (symbol) .............................................124
__align qualifier .......................................................34
aligned (n) .............................................105, 106
always_inline ...............................................124
anonymous unions ..................................................99
-ansi ................................................. 63, 64, 80, 130
ANSI C Standard
conformance ....................................................91
implementation-defined behavior .....................92
ANSI C standard .....................................................18
ANSI C, Strict ..........................................................65
ANSI Standard Library Support ...............................14
arrays ....................................................................111
as dummy pointer targets ...............................101
initialization .....................................................103
ASCII Character Set ..............................................203
ASCII characters
extended ........................................................103
asm .......................................................................161
asm C statement .....................................................42
assembly code
mixing with C ..................................................161
assembly list files .................................................... 59
Assembly Options ...................................................81
-Wa ..................................................................81
attribute .........................................................105
Attribute, Function
address ......................................................123
alias (symbol) ......................................124
always_inline ........................................124
at_vector ..................................................124
const ...........................................................124
deprecated ...............................................124
far ................................................................124
format (type, format_index,
first_to_check) .....................124
format_arg (index) ............................125
interrupt ..................................................125
longcall ....................................................125
malloc .........................................................125
mips16 .........................................................125
naked ...........................................................125
near ..............................................................125
noinline ....................................................125
no_instrument_function ....................84
nomips16 ....................................................125
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 226 2012 Microchip Technology Inc.
nonnull (index, ...) .......................125
noreturn ...............................................70, 126
pure ..............................................................126
ramfunc) ....................................................126
section (name) ......................................126
unique_section ......................................126
unused .........................................................126
used ..............................................................127
vector .........................................................127
warn_unused_result ............................127
weak ..............................................................127
Attribu te, Varia bl e
aligned (n) ......................................105, 106
cleanup (function) ............................106
deprecated ...............................................106
packed .........................................................106
section (“name”) .................................106
space ...........................................................107
unique_section ......................................107
unused .........................................................107
weak ..............................................................107
at_vector Attribute .................................124
auto variab les ..............................................110, 112
initilization .......................................................147
memory allocation ...................................112–113
Automatic Variable .............................................68, 69
-aux-info ......................................................63, 64
B
-B .......................................................................47, 82
Bad Virtual Address Register ................................149
BadVAddr. See Bad Virtual Address Register
__bank qualifier .......................................................33
_BEV_EXCPT_ADDR ...................................179, 182
biased exponent ......................................................96
binary constants
C code ............................................................102
Bit Fields ..................................................................64
bit-fields .................................................. 26, 27, 98–99
bitwis e compl em ent operator .................................118
BMXDKPBA ...........................................................148
_bmxdkpba_address ...............................148, 155
BMXDUDBA ...........................................................148
_bmxdudba_address ...............................148, 155
BMXDUPBA ...........................................................148
_bmxdupba_address ...............................148, 155
Boot Memory Region
kseg0_boot_mem ......................................179
kseg1_boot_mem ......................................179
Bootstrap Exception ..............................................141
_bootstrap_exception_handler ...........156
_bootstrap_exception_handler() ......141
Branch Delay ..................................................151
_bss_begin ......................................................188
_bss_end ...........................................................188
Bus Matrix Register ...............................................148
BMXDKPBA ....................................................148
BMXDUDBA ....................................................148
BMXDUPBA ....................................................148
C
-C ............................................................................78
-c ...................................................................... 62, 81
C Dialect Control Options .................................. 63, 64
-ansi ....................................................... 63, 64
-aux-info .............................................. 63, 64
-ffreestanding ........................................63
-fno-asm ................................................ 63, 64
-fno-builtin ....................................... 63, 64
-fno-signed-bitfields .......................64
-fno-unsigned-bitfields ..................64
-fsigned-bitfields ..............................64
-fsigned-char ..........................................64
-funsigned-bitfields .........................64
-funsigned-char .....................................64
-fwritable-strings ..............................64
-traditional ...........................................130
-ffreestanding ........................................64
C Stack Usage .......................................................112
C standard libraries .................................................56
__C32_VERSION__ ...........................................173
Call Main ................................................................155
calloc ................................................................114
Case Rang es .........................................................120
Cast ..............................................................68, 69, 70
casting ...................................................................117
Cause ...................................................................151
Cause Register ......................................................151
Cause Register ....................................................150
CCI ..........................................................................19
char ....................................................64, 65, 94, 128
char data type s ........................................................24
character constants
in C .................................................................103
CHAR_BIT .............................................................94
CHAR_MAX .............................................................94
CHAR_MIN .............................................................94
cleanup (function) ...................................106
clearing vari ables ...................................................147
Code Generatio n Conventions Options ...................83
-fargument-alias ...................................83
-fargument-noalias ..............................83
-fargument-noalias-global .............83
-fcall-saved .............................................83
-fcall-used ...............................................83
-ffixed .........................................................83
-finstrument-functions .....................84
-fno-ident .................................................84
-fno-short-double .................................84
-fno-verbose-asm ...................................84
-fpack-struct ..........................................84
-fpcc-struct-return ............................84
-fshort-enums ..........................................84
-fverbose-asm ..........................................84
-fvolatile .................................................84
-fvolatile-global .................................84
-fvolatile-static .................................84
Code Size, Reduce ............................................ 72, 73
Command Line Option, Compiler
-fdate-sections ...................................106
Index
2012 Microchip Technology Inc. DS51686E-page 227
-ffunction-sections ......................... 126
-fshort-enums ........................................ 197
-funsigned-bitfields ....................... 197
-funsigned-char ..................................... 94
-iquote ...................................................... 198
-l .................................................................... 81
-mdebugger ........................................182, 186
-mips16 .................................................56, 125
-mips16 -mno-float .............................. 56
-mlong-calls .......................................... 125
-mno-float ................................................. 56
-mprocessor ............................................. 177
-o ex1.out ................................................. 50
-O3 .................................................................. 56
-O3 -mips16 ............................................... 56
-O3 -mips16 -mno-float .................... 56
-O3 -mno-float ....................................... 56
-Os .................................................................. 56
-Os -mips16 ............................................... 56
-Os -mips16 -mno-float .................... 56
-Os -mno-float ....................................... 56
-Wall ............................................................. 68
-Wnonnull ................................................. 125
Command Line Option, Linker
--defsym .................................................... 177
--defsym_min_stack_size ................ 112
-L .................................................................. 177
Command-Line Simulator ........................................ 14
Comments ..........................................................65, 78
common comp iler interface ..................................... 19
Comm on Sube xp res si on Elim in atio n ...........73, 74, 75
Comm on Sube xp res si ons ....................................... 76
Compare ............................................................. 150
Compare Register ................................................. 150
Compare Registe r ............................................... 150
Compiler
Driver ..........................................................45, 82
compiler operating mode ......................................... 13
Conditional Expression ......................................... 120
Conditionals with Omitted Operands ..................... 120
Config ................................................................ 152
Config Register ..................................................... 152
Config1 ............................................................. 152
Config1 Register ................................................... 152
Config2 ............................................................. 153
Config2 Register ................................................... 153
Config3 ............................................................. 153
Config3 Register ................................................... 153
confign ............................................................. 180
Configuration Memory Region
config3, config2, config1,
config0 ........................................ 179
Configuration Pragma ........................................86, 87
Configuration Words ..........................................86, 87
const .................................................................. 124
const objects
initialization .................................................... 104
const objects
storage loc ati on .............................................. 113
const qualifier ........................................................ 104
constants
C specifiers ....................................................102
character ........................................................103
string, see string literals .................................103
conversion between types .....................................117
Count ...........................................................149, 150
Count Register ......................................................150
Count Register .................................................... 150
CountDM ...............................................................150
CP0 .......................................................................149
CP0 Access Macros ................................................89
CP0 Regi ste rs ....................................................... 149
Customer Support ...................................................12
D
-D .......................................................................78, 80
data me mor y .........................................................110
Data Memory Region
kseg1_data_mem ......................................180
Data Memory Space ..............................................114
data types
floating point .....................................................97
size of ..........................................................23, 97
_data_end .........................................................187
DBD. See Debug Branch Delay
_DBG_CODE_ADDR ......................................179, 182
_DBG_EXCPT_ADDR ...................................179, 182
-dD .........................................................................78
Debug ..................................................................153
Debug Branc h Dela y .............................................154
Debug Exception Program Counter ......................154
Debug Exception Save Register ...........................154
Debug Executi v e Memory Re gion
debug_exec_mem ......................................179
Debug Regi ster .....................................................153
Debug Register .................................................... 150
Debug Sec tio ns .....................................................190
Debug2 ................................................................154
Debug2 Register ...................................................154
debug_exec_mem .............................................182
_DEBUGGER ..................................................182, 186
Debugging Information ............................................72
Debugging Options ..................................................72
-g ....................................................................72
-Q ....................................................................72
-save-temps ...............................................72
Defini ng Gl oba l Re gis ter Varia bl es .......................205
--defsym ...........................................................177
--defsym _ebase_address=A ..................152
--defsym _min_heap_size=M ..................144
--defsym _min_stack_size=N ................144
--defsym, _min_heap_size .....................114
--defsym_min_stack_size .......................112
DEPC. See Debug Exception Program Counter
__deprecate qualifier ............................................... 38
deprecated Attribute ..........................................70
deprecated Attribute .......................106, 124
DeSave ................................................................154
device support .........................................................85
diagnostic files ......................................................... 59
Directories ..........................................................78, 80
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 228 2012 Microchip Technology Inc.
Directory Search Options ........................................82
-B ...............................................................47, 82
-specs= ........................................................82
-dM .........................................................................78
-dN .........................................................................78
Documentation
Conventions .......................................................9
Layout ................................................................8
double .....................................................84, 96, 128
driver
input files ..........................................................46
driver option
CCI ...................................................................43
driver options ................................................46, 60–83
E
-E ......................................................62, 78, 79, 80, 81
EBase ..................................................................152
EBase Register ....................................................152
_ebase_address ......................................152, 155
__eeprom qualifier ...................................................35
EJTAGver .............................................................153
_end ..............................................................155, 188
endianism ................................................................96
ENTRY ..................................................................176
Environment Variables
PIC32_C_INCLUDE_PATH .............................46
PIC32_C_INCLUDE_PATH .........................46
PIC32_COMPILER_PATH ............................46
PIC32_EXEC_PREFIX ................................47
PIC32_LIBRARY_ PATH ............................47
TMPDIR ...........................................................47
XC32_C_INCLUDE_PATH ............................46
XC32_COMPILER_PATH ..............................46
XC32_EXEC_PREFIX ...................................47
XC32_LIBRARY_ PATH ..............................47
EPC .......................................................................151
EPC Register ..........................................141, 151, 154
ERET .....................................................................144
Error Control Options
-pedantic-errors ...................................65
-Werror ........................................................70
Error Exception Program Counter .........................154
ErrorEPC. See Error Exception Program Counter
Excepti on Base Reg is ter .......................................152
Excepti on Mem ory Region
exception_mem ........................................179
Excepti on Progra m Coun ter ..................................151
Excepti on Vector ...................................................139
exception_mem ...............................................182
EXL Bit ..................................................................151
exponent ..................................................................96
extended character set ..........................................103
Extensions ...............................................................79
EXTERN ................................................................177
extern ............................................... 70, 76, 84, 131
External Interrupt Controller ..................................151
F
F constant suffix ....................................................103
-falign-functions ........................................73
-falign-labels ...............................................73
-falign-loops .................................................73
far .......................................................................124
__far qualifier ...........................................................30
-fargument-alias ..........................................83
-fargument-noalias .....................................83
-fargument-noalias-global .....................83
fatal error messages ................................................60
-fcaller-saves ...............................................73
-fcall-saved ....................................................83
-fcall-used ......................................................83
-fcse-follow-jumps .....................................73
-fcse-skip-blocks ........................................74
-fdata-sections ..................................... 74, 106
-fdefer-pop. See -fno-defer
-fexpensive-optimizations .....................74
-ffixed ........................................................ 83, 206
-fforce-mem ................................................ 73, 76
-ffreestanding ......................................... 63, 64
-ffunction-sections ........................... 74, 126
-fgcse ..................................................................74
-fgcse-lm ...........................................................74
-fgcse-sm ...........................................................74
File Extens ion s ........................................................48
file.c ...........................................................48
file.h ...........................................................48
file.i ...........................................................48
file.ii .........................................................48
file.o ...........................................................48
file.S ...........................................................48
file.s ...........................................................48
file types
input ..................................................................46
file.c ..................................................................48
file.h ..................................................................48
file.i ..................................................................48
file.o ..................................................................48
file.S ..................................................................48
file.s ..................................................................48
-finline-functions ..................70, 73, 76, 130
-finline-limit=n ..........................................76
-finstrument-functions ............................84
-fkeep-inline-functions ................. 76, 131
-fkeep-static-consts .................................76
Flags, Positive and Negative ............................. 76, 83
float ........................................................84, 96, 128
float.h ................................................................96
float ing -poi nt con st ant suffixes ..............................103
Floating-Point Format
double ...........................................................96
float .............................................................96
long double ...............................................96
floating-point types ..................................................97
biased ex pon ent ...............................................96
exponent ...........................................................96
rounding ...........................................................97
-fmove-all-movables ...................................74
-fno ................................................................. 76, 83
-fno-asm ....................................................... 63, 64
-fno-builtin .............................................. 63, 64
Index
2012 Microchip Technology Inc. DS51686E-page 229
-fno-defer-pop ............................................... 74
-fno-function-cse ....................................... 76
-fno-ident ........................................................ 84
-fno-inline ...................................................... 77
-fno-keep-static-consts ......................... 76
-fno-peephole ................................................. 74
-fno-peephole2 ............................................... 74
-fno-short-double ....................................... 84
-fno-show-column .......................................... 78
-fno-signed-bitfields .............................. 64
-fno-unsigned-bitfields ......................... 64
-fno-verbose-asm .......................................... 84
-fomit-frame-pointer .....................72, 73, 77
-foptimize-register-move ....................... 74
-foptimize-sibling-calls ....................... 77
format (type, format_index,
first_to_check) ....................................... 124
format_arg (index) ................................... 125
fp ......................................................................... 141
-fpack-struct ................................................. 84
-fpcc-struct-return ................................... 84
Frame Pointer (W14) ..........................................77, 83
-freduce-all-givs ....................................... 74
-fregmove ........................................................... 74
-frename-registers ..................................... 74
-frerun-cse-after-loop ......................74, 75
-frerun-loop-opt .......................................... 74
-fschedule-insns .......................................... 75
-fschedule-insns2 ....................................... 75
-fshort-enums ..........................................84, 197
-fsigned-bitfields ..................................... 64
-fsigned-char ................................................. 64
-fstrength-reduce ....................................... 75
-fstrict-aliasing ..................................73, 75
-fsyntax-only ................................................. 65
-fthread-jumps ..........................................72, 75
function
parameters ..............................................112, 128
pointers .......................................................... 101
specifiers ........................................................ 123
functions
absolute ........................................................... 29
static ......................................................... 123
written in assembler ....................................... 161
-funroll-all-loops ................................73, 75
-funroll-loops ..........................................73, 75
-funsigned-bitfields .........................64, 197
-funsigned-char .......................................64, 94
-fverbose-asm ................................................. 84
-fvolatile ........................................................ 84
-fvolatile-global ....................................... 84
-fvolatile-static ....................................... 84
-fwritable-strings ..................................... 64
G
-g ........................................................................... 72
-G num .................................................................. 61
General Except ion ................................................. 141
_general_exception_context() ........... 141
_general_exception_handler ................ 156
_GEN_EXCPT_ADDR ...................................179, 182
Global Register Variables ......................................205
-Gn .......................................................................147
_gp ........................................................146, 155, 186
gp ...................................................................141, 146
H
-H ............................................................................78
Hardware Enable Register ....................................149
header file
search path ......................................................22
Header Files ......................................46, 48, 78, 79, 80
header files .......................................................21, 159
device ..........................................................85, 88
Heap ...................................................................... 144
_heap ...........................................................144, 155
--help ..................................................................62
Hex File ...................................................................50
hexadecimal constants
C code ............................................................102
hi ..........................................................................141
High-Priority Interrupts ..........................................133
HWREna ................................................................149
I
-I .......................................................................78, 80
-I- ....................................................................78, 80
identifiers
unique length of ................................................23
-idirafter ........................................................78
-imacros ........................................................78, 80
implementation-defined behavior ............................92
-include ........................................................79, 80
Include Files ............................................................82
inc remental builds ...................................................51
Inhibit Warnings .......................................................65
initialized variables ................................................ 147
Inline .............................................................70, 73, 76
inline .....................................................77, 84, 130
INPUT ..................................................................177
input files .................................................................46
int ..................................................................94, 128
IntCtl ................................................................150
integer constants ...................................................102
integer suffixes ......................................................102
Integer Values
char ................................................................94
int ..................................................................94
long ................................................................94
long long ....................................................94
short .............................................................94
signed char ...............................................94
signed int .................................................94
signed long ...............................................94
signed long long ...................................94
signed short ............................................94
unsigned char ..........................................94
unsigned int ............................................94
unsigned long ..........................................94
unsigned long long ..............................94
unsigned short ........................................94
integral promotion ..................................................117
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 230 2012 Microchip Technology Inc.
Internet Address, Microchip .....................................12
Interrupt
High Priority ....................................................133
Lower Priority .................................................133
interrupt .........................................................125
Interrupt Attribute ...................................................134
interrupt Attribute ..........................................125
Interrupt Control Register ......................................150
interrupt functions
context switching ............................................142
interrupt handler function .......................................134
Interrupt Pragma ...................................................135
Interrupt Pragma Clause .......................................139
__interrupt qualifier ..................................................35
INT_MAX ................................................................95
INT_MIN ................................................................95
-iquote ..............................................................198
__ISR(v, ipl) ...............................................135
__ISR_AT_VECTOR(v, ipl) .......................136
-isystem .............................................................82
K
k0 ..........................................................................141
k1 ..........................................................................141
kseg0_program_mem ............... 183, 185, 186, 187
KSEG1 Data Memory ............................................144
kseg1_boot_mem ......................................181, 182
kseg1_data_mem ..............................186, 187, 188
L
-L ...............................................................81, 82, 177
-l ............................................................................81
L constant suffix ....................................................102
__LANGUAGE_ASSEMBLY .................................172
__LANGUAGE_ASSEMBLY__ ............................172
_LANGUAGE_ASSEMBLY ...................................172
LANGUAGE_ASSEMBLY ......................................172
__LANGUAGE_C ..................................................172
__LANGUAGE_C__ .............................................172
_LANGUAGE_C ....................................................172
LANGUAGE_C ......................................................172
libraries ....................................................................55
search order .....................................................46
user-defined .....................................................57
Library .....................................................................81
ANSI Standard .................................................14
limits.h .............................................................94
CHAR_BIT ......................................................94
CHAR_MAX ......................................................94
CHAR_MIN ......................................................94
INT_MAX ........................................................95
INT_MIN ........................................................95
LLONG_MAX ....................................................95
LLONG_MIN ....................................................95
LONG_MAX ......................................................95
LONG_MIN ......................................................95
MB_LEN_MAX .................................................94
SCHAR_MAX ....................................................94
SCHAR_MIN ....................................................94
SHRT_MAX ......................................................94
SHRT_MIN ......................................................94
UCHAR_MAX ....................................................94
UINT_MAX ......................................................95
ULLONG_MAX .................................................95
ULONG_MAX ....................................................95
USHRT_MAX ....................................................94
link .....................................................................200
Linker .......................................................................81
linker scripts ...........................................................175
Linking Options ........................................................81
-L ............................................................... 81, 82
-l .....................................................................81
-nodefaultlibs ........................................81
-nostdlib ....................................................81
-s .....................................................................82
-u .....................................................................82
-Wl ..................................................................82
-Xlinker ......................................................82
little endian format ...................................................96
little-endian ..............................................................93
LLONG_MAX ...........................................................95
LLONG_MIN ...........................................................95
lo ..........................................................................141
Local Register Variables ................................ 205, 206
long ............................................................... 94, 128
Long double ....................................................128
long double ................................................ 84, 96
long long ..............................................70, 94, 128
longcall ...........................................................125
longcall Attribute .............................................127
LONG_MAX .............................................................95
LONG_MIN .............................................................95
__longramfunc__ ...........................................127
Loop Optimizer ........................................................74
Loop Unrolling .........................................................75
Lower-Priority Interrupts ........................................133
M
-M ............................................................................79
macro ..........................................................78, 80, 131
Macros
__C32_VERSION_ ......................................173
__LANGUAGE_ASSEMBLY ..........................172
__LANGUAGE_ASSEMBLY__ .....................172
_LANGUAGE_ASSEMBLY ............................172
LANGUAGE_ASSEMBLY ...............................172
__LANGUAGE_C ...........................................172
__LANGUAGE_C__ ......................................172
_LANGUAGE_C .............................................172
LANGUAGE_C ...............................................172
_mchp_no_float ......................................172
_MCHP_SZINT .............................................172
_MCHP_SZLONG ...........................................172
_MCHP_SZPTR .............................................172
__NO_FLOAT ...............................................172
__PIC__ .......................................................172
__pic__ .......................................................172
__PIC32_FEATURE_SET__ .....................172
__PIC32MX ..................................................172
__PIC32MX__ .............................................172
PIC32MX .......................................................172
__processor__ ........................................173
Index
2012 Microchip Technology Inc. DS51686E-page 231
__VERSION__ ............................................. 173
main ..................................................................... 143
main function ....................................................21, 143
main-li ne code ....................................................... 133
malloc .........................................................114, 125
mantissa .................................................................. 96
map files .................................................................. 59
-mappio-debug ................................................. 62
MB_LEN_MAX ........................................................ 94
-mcheck-zero-division .............................. 61
_MCHP_ ................................................................ 172
_mchp_no_float ............................................. 172
_MCHP_SZINT .................................................... 172
_MCHP_SZLONG ................................................. 172
_MCHP_SZPTR .................................................... 172
-MD ......................................................................... 79
-mdebugger ...............................................182, 186
-membedded-data ............................................ 61
memory allocation ................................................. 109
data me mo r y .................................................. 110
function code .................................................. 127
non-auto va riab les ....................................... 110
program memory ............................................ 113
static variables ............................................... 110
memory models ..................................................... 114
messages
error, see error messages
fatal error .......................................................... 60
types of ............................................................ 60
-MF ......................................................................... 79
-MG ......................................................................... 79
_min_heap_size ......................................144, 177
_min_stack_size ...................................144, 177
_MIPS_ ................................................................ 174
__mips ................................................................ 174
__mips__ ........................................................... 174
_mips .................................................................. 174
__mips16 ........................................................... 174
-mips16 ..................................................56, 61, 125
mips16 ................................................................ 125
-mips16 -mno-float ..................................... 56
_MIPS_ARCH_PIC32MX ................................... 174
__MIPSEL ........................................................... 174
__MIPSEL__ ...................................................... 174
_MIPSEL ............................................................. 174
MIPSEL ................................................................ 174
_mips_fpr ......................................................... 174
_MIPS_ISA ......................................................... 174
__mips_isa_rev ............................................. 174
_mips_no_float ............................................. 174
__mips_soft_float ..................................... 174
_MIPS_SZINT .................................................... 174
_MIPS_SZLONG ................................................. 174
_MIPS_SZPTR .................................................... 174
_MIPS_TUNE_PIC32MX ................................... 174
-mlong-calls ............................................61, 125
-MM ......................................................................... 79
-MMD ....................................................................... 79
-mmemcpy ............................................................. 61
-mno-check-zero-division ....................... 61
-mno-embedded-data .....................................61
-mno-float ...................................................56, 61
-mno-long-calls ............................................61
-mno-memcpy ......................................................61
-mno-mips16 .................................................56, 61
-mno-peripheral-libs ................................61
-mno-uninit-const-in-rodata ................61
-MP .........................................................................79
-mprocessor ...............................................61, 177
-MQ .........................................................................79
-msoft-float ....................................................56
-MT .........................................................................79
MTC0 Instruction ...................................................151
-muninit-const-in-rodata .......................61
myMicrochip Personalized Notification Service .......11
N
naked ..................................................................125
near .....................................................................125
__near qualifier ........................................................31
_nmi_handler ..................................................144
-nodefaultlibs ...............................................81
__NO_FLOAT ......................................................172
noinline ...........................................................125
no_instrument_function Attribute ....84
NOLOAD .........................................................182, 186
nomips16 ............................................125, 144, 156
nonnull (index, ...) ..............................125
non-volatile RAM ...................................................104
NOP .......................................................................183
noreturn ...........................................................126
noreturn Attribute ...............................................70
-nostdinc ......................................................78, 80
-nostdlib ...........................................................81
NULL macro ............................................................28
NULL pointers .......................................................101
O
-O ............................................................................72
-o .......................................................................50, 62
-o ex1.out ........................................................50
-O0 ....................................................................56, 72
-O1 .........................................................................72
-O2 ....................................................................73, 76
-O3 ....................................................................56, 73
-O3 -mips16 ......................................................56
-O3 -mips16 -mno-float ............................56
-O3 -mno-float ...............................................56
Object File ....................................................74, 79, 81
Omitted Operands .................................................120
_on_reset .........................................................157
Optimization Control Options ..................................72
-falign-functions ................................73
-falign-labels ........................................73
-falign-loops ..........................................73
-fcaller-saves ........................................73
-fcse-follow-jumps ..............................73
-fcse-skip-blocks ................................74
-fdata-sections .....................................74
-fexpensive-optimizations .............74
-fforce-mem ...............................................76
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 232 2012 Microchip Technology Inc.
-ffunction-sections ............................74
-fgcse ...........................................................74
-fgcse-lm ....................................................74
-fgcse-sm ....................................................74
-finline-functions ..............................76
-finline-limit=n ...................................76
-fkeep-inline-functions ..................76
-fkeep-static-consts .........................76
-fmove-all-movables ............................74
-fno-defer-pop ........................................74
-fno-function-cse ................................76
-fno-inline ...............................................77
-fno-peephole ..........................................74
-fno-peephole2 ........................................74
-fomit-frame-pointer .........................77
-foptimize-register-move ................74
-foptimize-sibling-calls ................77
-freduce-all-givs ................................74
-fregmove ....................................................74
-frename-registers ..............................74
-frerun-cse-after-loop ....................74
-frerun-loop-opt ...................................74
-fschedule-insns ...................................75
-fschedule-insns2 ................................75
-fstrength-reduce ................................75
-fstrict-aliasing ................................75
-fthread-jumps ........................................75
-funroll-all-loops ..............................75
-funroll-loops ........................................75
-O ....................................................................72
-O0 ..................................................................72
-O1 ..................................................................72
-O2 ..................................................................73
-O3 ..................................................................73
-Os ..................................................................73
Optimization, Loop ..................................................74
Optimization, Peephole ...........................................74
Options
Assembling .......................................................81
C Dialect Control .........................................63, 64
Code Generation Convent ions .........................83
Debugging ........................................................72
Directory Search ..............................................82
Linking ..............................................................81
Optimization Control .........................................72
Output Contro l ..................................................62
Prep roce ssor Control .......................................78
Warnings and Errors Control ............................65
-Os ....................................................................56, 73
-Os -mips16 ......................................................56
-Os -mips16 -mno-float ............................56
-Os -mno-float ...............................................56
Output Contro l Opt ion s ............................................62
-c ....................................................................62
-E ....................................................................62
--help ...........................................................62
-o ....................................................................62
-S ....................................................................62
-v ....................................................................62
-x ....................................................................62
output files
name s of ...........................................................58
OUTPUT_ARCH ....................................................176
OUTPUT_FORMAT ...............................................176
P
-P ............................................................................80
__pack qualifier .......................................................37
packed ................................................................106
parameters, see function, parameters
-pedantic ..................................................... 65, 70
-pedantic-errors ..........................................65
Peephole Optimization ............................................74
__persisten qualifier ................................................32
persistent qualifier ..........................................147
persistent qualif ier .........................................157
__PIC__ ..............................................................172
__pic__ ..............................................................172
PIC32_C_INCLUDE_PATH .....................................46
PIC32_C_INCLUDE_PATH .................................46
PIC32_COMPILER_PATH ...................................46
PIC32_EXEC_PREFIX ........................................47
__PIC32_FEATURE_SET__ ............................172
PIC32_LIBRARY_ PATH ...................................47
__PIC32MX .........................................................172
__PIC32MX__ ....................................................172
PIC32MX ..............................................................172
PIC32MX Device-Specific Options
-G num ...........................................................61
-mappio-debug ..........................................62
-mcheck-zero-division .......................61
-membedded-data .....................................61
-mips16 .........................................................61
-mlong-calls .............................................61
-mmemcpy ......................................................61
-mno-check-zero-division ................61
-mno-embedded-data ..............................61
-mno-float .................................................61
-mno-long-calls .....................................61
-mno-memcpy ...............................................61
-mno-mips16 ...............................................61
-mno-peripheral-libs .........................61
-mno-uninit-const-in-rodata .........61
-mprocessor ...............................................61
-muninit-const-in-rodata ................61
PIC32MX Start-up Code ........................................144
pointer
comparisons ...................................................101
definitions .......................................................100
qualifiers .........................................................100
types ...............................................................100
Pointers ...................................................................70
Frame ......................................................... 77, 83
Stack ................................................................83
pointers .......................................................... 100–101
assigning dummy targets ...............................101
assigning integers ..........................................101
function ...........................................................101
powerup routine .....................................................157
pragma directives ..................................................171
Pragmas
Index
2012 Microchip Technology Inc. DS51686E-page 233
#pragma config ..........................86, 87, 171
#pragma interrupt .............................. 171
#pragma vector ..................................... 171
Predefined Macros ................................................ 172
prefix ....................................................................... 82
preprocessing ........................................................ 169
preprocessor
type conversions ............................................ 170
Prep rocessor Control Opt ions ................................. 78
-C .................................................................... 78
-D .................................................................... 78
-dD .................................................................. 78
-dM .................................................................. 78
-dN .................................................................. 78
-fno-show-column ................................... 78
-H .................................................................... 78
-I .................................................................... 78
-I- .................................................................. 78
-idirafter ................................................. 78
-imacros ...................................................... 78
-include ...................................................... 79
-M .................................................................... 79
-MD .................................................................. 79
-MF .................................................................. 79
-MG .................................................................. 79
-MM .................................................................. 79
-MMD ............................................................... 79
-MQ .................................................................. 79
-MT .................................................................. 79
-nostdinc ................................................... 80
-P .................................................................... 80
-trigraphs ................................................. 80
-U .................................................................... 80
-undef ........................................................... 80
preproc essor directives ..................................169–170
preprocessor macros
predefined ........................................................ 41
PRId ..................................................................... 152
__processor__ ............................................... 173
Processor Identification Register ........................... 152
processor.o .................................................... 177
program memory ................................................... 113
Program Memory Regi on
kseg0_program_mem .............................. 179
proje ct name ........................................................... 59
PROVIDE ............................................................. 177
Provisions ................................................................ 58
pure ..................................................................... 126
Q
-Q ........................................................................... 72
qualifier
__align ............................................................. 34
auto ............................................................. 112
__bank ............................................................. 33
const .............................................................. 104
__deprecate ..................................................... 38
__eeprom ......................................................... 35
__far ................................................................. 30
__interrupt ........................................................ 35
__near .............................................................. 31
__pack ..............................................................37
__persistent ......................................................32
persistent ........................................147, 157
__section ..........................................................39
volatile ............................................................104
__xdata ............................................................33
__ydata ............................................................33
qualifiers .........................................................104–105
and auto va riab les .......................................112
and structures ..................................................98
R
__R3000 ..............................................................174
__R3000__ .........................................................174
_R3000 ................................................................174
R3000 ..................................................................174
ra ..........................................................................141
radix specifiers
C code ............................................................102
__ramfunc__ ....................................................127
ramfunc ..............................................................126
_ramfunc_begin .............................................155
_ramfunc_length ...................................148, 155
RAW Depe nde nc y ...................................................75
RDHWR ..................................................................149
Readi ng, Re co mm en ded .........................................10
read-only variables ................................................104
realloc ..............................................................114
Reduce Code Size .............................................72, 73
register ....................................................205, 206
Register Conventions ............................................121
registers
allocation to ....................................................114
Requested Interrupt Priority Level ......................... 151
_reset ................................................................176
reset
code executed after ........................................157
_RESET_ADDR .............................................179, 181
Return Type .............................................................66
runtime sta r tup code
variable initialization ....................................... 147
rx ..........................................................................180
S
-S .......................................................................62, 81
-s ............................................................................82
s0-s7 ..................................................................141
-save-temps ......................................................72
sbrk .....................................................................144
_sbss_begin ....................................................188
_sbss_end .........................................................188
SCHAR_MAX ...........................................................94
SCHAR_MIN ...........................................................94
Scheduling ...............................................................75
_sdata_begin ..................................................187
_sdata_end ......................................................187
SDE Compatibility Macros .....................................174
__mips .........................................................174
__mips__ ....................................................174
_mips ...........................................................174
__mips16 ....................................................174
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 234 2012 Microchip Technology Inc.
_MIPS_ARCH_PIC32MX ............................174
__MIPSEL ....................................................174
__MIPSEL__ ...............................................174
_MIPSEL ......................................................174
MIPSEL .........................................................174
_mips_fpr ..................................................174
_MIPS_ISA ..................................................174
__mips_isa_rev ......................................174
_mips_no_float ......................................174
__mips_soft_float ..............................174
_MIPS_SZINT .............................................174
_MIPS_SZLONG ..........................................174
_MIPS_SZPTR .............................................174
_MIPS_TUNE_PIC32MX ............................174
__R3000 ......................................................174
__R3000__ ..................................................174
_R3000 .........................................................174
R3000 ...........................................................174
Section
Configuration Words ........................................86
section .....................................................................74
section (“name”) ........................................106
section (name) .............................................126
__section qualifier ...................................................39
SECTIONS Command ...................................180, 181
SFR Memory Re gio n
sfrs ..............................................................180
SFRs .......................................................................88
Shadow Register Control Register ........................151
Shadow Register Map Register .............................151
short .............................................................94, 128
SHRT_MAX .............................................................94
SHRT_MIN .............................................................94
sign bit .....................................................................96
signed char ......................................................94
signed int ........................................................94
signed long ......................................................94
signed long long ..........................................94
signed short ....................................................94
Simulator, Command-Line .......................................14
SI_TimerInt ....................................................150
size of types ............................................................97
sp ...................................................................141, 144
space Attribute ....................................................107
Special Function Registers ......................................50
special function registers, see SFRs
Specifying Registers for Local Variables ...............206
-specs= ................................................................82
SR ..........................................................................141
SRSCtl ................................................................151
SRSMap ................................................................151
Stack
C Usage .........................................................112
Pointer (W15) ..............................................83, 86
_stack .................................................144, 155, 189
Stack Location .......................................................189
Stack Pointer .........................................................144
Standard I/O Function s ...........................................14
standard library files
Start-up and Initialization .........................................58
For C ................................................................58
For C++ ............................................................58
static ........................................................................84
static functions .................................................123
static vari ab les .......................................................110
static variables .................................................147
Status ................................................................150
Stat us Register ......................................................150
StatusBEV .................................................. 152, 156
storage dura tio n .....................................................110
string literals ..........................................................103
concatenation .................................................104
storage loc ati on ..............................................103
type of .............................................................103
Strings .....................................................................64
struct types, see structures
Structure .........................................................128
structure bit-fields ....................................................98
structure qualifiers ...................................................98
structures .................................................................98
bit-fields in ........................................................98
switch .......................................................................67
symbol .....................................................................82
Syntax Check ..........................................................65
System Function
link ..............................................................200
unlink .........................................................200
System Head er File s ......................................... 67, 79
T
t0-t9 ...................................................................141
temporary variables ...............................................112
TMPDIR ..................................................................47
Trace Co ntro l Regist er ..........................................153
TraceBPC ...........................................................153
TraceBPC Register ................................................153
TraceControl ..................................................153
TraceControl2 ...............................................153
-traditional ............................................ 64, 130
Traditi onal C ............................................................71
Trigraphs ........................................................... 67, 80
-trigraphs .........................................................80
Type Conversion .....................................................70
type conversions ....................................................117
U
-U ...................................................................... 78, 80
-u ............................................................................82
U constant suffix ....................................................102
UCHAR_MAX ...........................................................94
UINT_MAX .............................................................95
ULLONG_MAX .........................................................95
ULONG_MAX ...........................................................95
-undef ..................................................................80
uninitilized variables ..............................................147
unions
anonymous .......................................................99
qualifiers ...........................................................98
unique_section ..................................... 107, 126
unlink ................................................................200
unnamed bit-fields ...................................................99
Index
2012 Microchip Technology Inc. DS51686E-page 235
unnamed structure members .................................. 99
Unroll Loop .............................................................. 75
unsigned char ................................................. 94
unsigned int ................................................... 94
unsigned long ................................................. 94
unsigned long long ..................................... 94
unsigned short ............................................... 94
unused Attribute ....................................68, 107, 126
Unused Function Parameter ................................... 68
Unused Variable ...................................................... 68
unused variables
removing ........................................................ 104
USB ....................................................................... 224
used Attribute ...................................................... 127
User Trace Data Register ...................................... 153
UserTraceData ............................................... 153
USHRT_MAX ........................................................... 94
V
-v ........................................................................... 62
v0 ......................................................................... 141
v1 ......................................................................... 141
variables
absolute ........................................................... 29
auto ............................................................. 112
in program memory .................................113–114
in registers ..................................................... 114
initialization .................................................... 147
sizes ................................................................. 97
static ......................................................... 110
storage dura tio n ............................................. 110
Variables in Specified Registers ............................ 205
vector ................................................................ 127
Vector Pragma ...................................................... 140
_vector_spacing ...........................150, 155, 178
__VERSION__ .................................................... 173
volatile ..................................................................... 84
volatile qualifier ..................................................... 104
W
-W ...........................................................65, 68, 69, 71
-w ........................................................................... 65
w!x ....................................................................... 180
-Wa ......................................................................... 81
-Waggregate-return ..................................... 69
-Wall ....................................................65, 68, 69, 71
warning messages .................................................. 60
Warnings and Errors Control Options ..................... 65
-fsyntax-only .......................................... 65
-pedantic ................................................... 65
-pedantic-errors ................................... 65
-W .................................................................... 69
-w .................................................................... 65
-Waggregate-return .............................. 69
-Wall ............................................................. 65
-Wbad-function-cast ........................... 69
-Wcast-align ............................................ 69
-Wcast-qual ............................................... 69
-Wchar-subscripts ................................ 65
-Wcomment ................................................... 65
-Wconversion ............................................ 70
-Wdiv-by-zero ..........................................65
-Werror .............................................................70
-Wformat ......................................................65
-Wimplicit .................................................66
-Wimplicit-function-declaration 66
-Wimplicit-int ........................................66
-Winline ......................................................70
-Wlarger-than- ........................................70
-Wlong-long ...............................................70
-Wmain ...........................................................66
-Wmissing-braces ...................................66
-Wmissing-declarations ....................70
-Wmissing-format-attribute ...........70
-Wmissing-noreturn ..............................70
-Wmissing-prototypes .........................70
-Wmultichar ...............................................66
-Wnested-externs ...................................70
-Wno-long-long ........................................70
-Wno-sign-compare ................................71
-Wpadded ......................................................70
-Wparentheses ..........................................66
-Wpointer-arith .....................................70
-Wredundant-decls ................................70
-Wreturn-type ..........................................66
-Wsequence-point ...................................67
-Wshadow ......................................................70
-Wsign-compare ........................................71
-Wstrict-prototypes ............................71
-Wswitch ......................................................67
-Wsystem-headers ...................................67
-Wtraditional ..........................................71
-Wtrigraphs ...............................................67
-Wundef ........................................................71
-Wuninitialized .....................................68
-Wunknown-pragmas ................................68
-Wunreachable-code ..............................71
-Wunused ......................................................68
-Wunused-function ................................68
-Wunused-label ........................................68
-Wunused-parameter ..............................68
-Wunused-value ........................................68
-Wunused-variable ................................68
-Wwrite-strings .....................................71
-Wno-multichar .................................................66
Warnings, Inhibit ......................................................65
warn_unused_result ...................................127
Watchdog Timer ....................................................224
-Wbad-function-cast ...................................69
-Wcast-align ....................................................69
-Wcast-qual ......................................................69
-Wchar-subscripts ........................................65
-Wcomment ...........................................................65
-Wconversion ....................................................70
-Wdiv-by-zero .................................................65
weak ..............................................................107, 127
Web Site, Microchip ................................................12
-Werror ................................................................70
-Wformat ........................................................65, 70
-Wimplicit ........................................................66
-Wimplicit-function-declaration ......66
MPLAB® XC32 C/C++ Compiler User’s Guide
DS51686E-page 236 2012 Microchip Technology Inc.
-Wimplicit-int ...............................................66
-Winline ......................................................70, 131
-Wl .........................................................................82
-Wlarger-than- ...............................................70
-Wlong-long ......................................................70
-Wmain ..................................................................66
-Wmissing-braces ..........................................66
-Wmissing-declarations ............................70
-Wmissing-format-attribute ..................70
-Wmissing-noreturn .....................................70
-Wmissing-prototypes ................................70
-Wmultichar ......................................................66
-Wnested-externs ..........................................70
-Wno- ....................................................................65
-Wno-deprecated-declarations .............70
-Wno-div-by-zero ..........................................65
-Wno-long-long ...............................................70
-Wno-multichar ...............................................66
-Wnonnull .........................................................125
-Wno-sign-compare ...................................69, 71
-Wpadded .............................................................70
-Wparentheses .................................................66
-Wpointer-arith ............................................70
-Wredundant-decls ........................................70
-Wreturn-type .................................................66
-Wsequence-point ..........................................67
-Wshadow .............................................................70
-Wsign-compare ...............................................71
-Wstrict-prototypes ...................................71
-Wswitch .............................................................67
-Wsystem-headers ..........................................67
-Wtraditional .................................................71
-Wtrigraphs ......................................................67
-Wundef ................................................................71
-Wuninitialized ............................................68
-Wunknown-pragmas ...................................67, 68
-Wunreachable-code .....................................71
-Wunused ........................................................68, 69
-Wunused-function ........................................68
-Wunused-label ...............................................68
-Wunused-parameter .....................................68
-Wunused-value ...............................................68
-Wunused-variable ........................................68
-Wwrite-strings ............................................71
X
-x ............................................................................62
xc.h header file .....................................................85
XC32_C_INCLUDE_PATH ...................................46
XC32_COMPILER_PATH .....................................46
XC32_EXEC_PREFIX ..........................................47
xc32-gcc .............................................................45
XC32_LIBRARY_ PATH .....................................47
__xdata qualifier ......................................................33
-Xlinker .............................................................82
Y
__ydata qualifier ......................................................33
Index
2012 Microchip Technology Inc. DS51686E-page 237
NOTES:
DS51686E-page 238 2012 Microchip Technology Inc.
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Fax: 60-3-6201-9859
Malaysia - Penang
Tel: 60-4-227-8870
Fax: 60-4-227-4068
Philippines - Manila
Tel: 63-2-634-9065
Fax: 63-2-634-9069
Singapore
Tel: 65-6334-8870
Fax: 65-6334-8850
Taiwan - Hsin Chu
Tel: 886-3-5778-366
Fax: 886-3-5770-955
Taiwan - Kaohsiung
Tel: 886-7-536-4818
Fax: 886-7-330-9305
Taiwan - Taipei
Tel: 886-2-2500-6610
Fax: 886-2-2508-0102
Thailand - Bangkok
Tel: 66-2-694-1351
Fax: 66-2-694-1350
EUROPE
Austria - Wels
Tel: 43-7242-2244-39
Fax: 43-7242-2244-393
Denmark - Cop e nha gen
Tel: 45-4450-2828
Fax: 45-4485-2829
France - Paris
Tel: 33-1-69-53-63-20
Fax: 33-1-69-30-90-79
Germany - Munich
Tel: 49-89-627-144-0
Fax: 49-89-627-14 4-44
Italy - Milan
Tel: 39-0331-742611
Fax: 39-0331-466781
Netherlands - Drunen
Tel: 31-416-690399
Fax: 31-416-690340
Spai n - Madrid
Tel: 34-91-708-08-90
Fax: 34-91-708-08 -91
UK - Wokingham
Tel: 44-118-921- 5869
Fax: 44-118-921-5820
Worldwide Sales and Service
08/02/11
