1.XX.01 EMBOS SOL - SEGGER

A product of SEGGER Microcontroller GmbH & Co. KG

embOS

Document: UM01001

Software version 4.06b

Revision: 0

Date: March 24, 2015

CPU-independent

User & Reference Guide

Real-Time

Operating System

www.segger.com

2 CHAPTER

Disclaimer

Specifications written in this document are believed to be accurate, but are not guar-

anteed to be entirely free of error. The information in this manual is subject to

change for functional or performance improvements without notice. Please make sure

your manual is the latest edition. While the information herein is assumed to be

accurate, SEGGER Microcontroller GmbH & Co. KG (SEGGER) assumes no responsibil-

ity for any errors or omissions. SEGGER makes and you receive no warranties or con-

ditions, express, implied, statutory or in any communication with you. SEGGER

specifically disclaims any implied warranty of merchantability or fitness for a particu-

lar purpose.

You may not extract portions of this manual or modify the PDF file in any way without

the prior written permission of SEGGER. The software described in this document is

furnished under a license and may only be used or copied in accordance with the

terms of such a license.

Trademarks

Names mentioned in this manual may be trademarks of their respective companies.

Brand and product names are trademarks or registered trademarks of their respec-

tive holders.

Contact address

SEGGER Microcontroller GmbH & Co. KG

In den Weiden 11

D-40721 Hilden

Germany

Tel.+49 2103-2878-0

Fax.+49 2103-2878-28

E-mail: support@segger.com

Internet: http://www.segger.com

Manual versions

This manual describes the current software version. If any error occurs, inform us

and we will try to assist you as soon as possible.

Print date: March 24, 2015

Software Revision Date By Description

4.06b 0 150324 MC Minor spelling and wording corrections.

4.06a 0 150318 MC Update to latest software version.

Minor spelling and wording corrections.

4.06 0 150312 TS Update to latest software version.

4.04a 0 141201 TS Update to latest software version.

4.04 0 141112 TS

Chapter "Tasks"

* Task priority description updated.

Chapter "Debugging"

* New error number

4.02a 0 140918 TS Update to latest software version.

Minor corrections.

4.02 0 140818 TS

New functions in chapter Time Measurement added:

OS_Config_SysTimer()

OS_GetTime_us()

OS_GetTime_us64()

4.00a 0 140723 TS

New function added in chapter SystemTick:

OS_StopTicklessMode()

New function added in chapter Profiling:

OS_STAT_Start()

OS_STAT_Stop()

OS_STAT_GetTaskExecTime()

4.00 0 140606 TS Tickless suppport added.

3.90a 0 140410 AW Software-Update, OS_TerminateTask() modified / corrected.

3.90 1 140312 SC Added cross-references to the API-lists.

3.90 0 140303 AW

New functions to globally enable / diasble Interrupts:

OS_INTERRUPT_MaskGlobal()

OS_INTERRUPT_UnmaskGlobal()

OS_INTERRUPT_PreserveGlobal()

OS_INTERRUPT_RestoreGlobal()

OS_INTERRUPT_PreserveAndMaskGlobal()

3.88h 0 131220 AW

New functions added, chapter "Sytem tick":

OS_GetNumIdleTicks();

OS_AdjustTime();

Chapter "System variable"

Description of internal variable OS_Global.TimeDex corrected

3.88g 1 131104 TS Corrections.

3.88g 0 131030 TS Update to latest software version.

Minor corrections.

3.88f 0 130922 TS Update to latest software version.

3.88e 0 130906 TS Update to latest software version.

3.88d 0 130904 AW Update to latest software version.

3.88c 0 130808 TS Update to latest software version.

3.88b 0 130528 TS Update to latest software version.

3.88a 0 130503 AW

Software update.

Event handling modified, the reset behaviour of events can be

controlled. New functions added, chapter "Events":

OS_EVENT_CreateEx();

OS_EVENT_SetResetMode();

OS_EVENT_GetResetMode();

Mailbox message size limits enlarged.

3.88 0 130219 TS Minor corrections.

3.86n 0 121210 AW

/TS Update to latest software version.

3.86l 0 121122 AW

Software update

OS_AddTickHook() function corrected.

Several functions modified to allow most of MISRA rule checks

3.86k 0 121004 TS Chapter "Queue"

* OS_Q_GetMessageSize() and OS_Q_PeekPtr() added.

4 CHAPTER 
UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
3.86i 0 120926 TS Update to latest software version.
3.86h 0 120906 AW Software update,
OS_EVENT handling with timeout corrected.
3.86g 0 120806 AW
Software update, OS_RetriggerTimer() corrected.
Task events explained more in detail. Additional software 
examples in the manual.
3.86f 0 120723 AW
Task events modified, default set to 32bit on 32bit CPUs.
Chapter 4: New API function OS_AddOnTerminateHook()
OS_ERR_TIMESLICE removed. A time slice value of zero is 
legal when creating tasks.
3.86e 0 120529 AW
Update to latest software version with corrected functions:
OS_GetSysStackBase()
OS_GetSysStackSize()
OS_GetSysStackSpace()
OS_GetSysStackUsed()
OS_GetIntStackBase()
OS_GetIntStackSize()
OS_GetIntStackSpace()
OS_GetIntStackUsed()
could not be used in release builds of embOS.
Manual corrections:
Several index entries corrected.
OS_EnterRegion() described more in detail.
3.86d 0 120510 TS Update to latest software version.
3.86c 0 120508 TS Update to latest software version.
3.86b 0 120502 TS
Chapter "Mailbox"
 * OS_PeekMail() added.
Chapter "Support" added.
Chapter "Debugging":
 * Application defined error codes added.
3.86 0 120323 AW
Timeout handling for waitable objects modified. A timeout will 
be returned from the waiting function, when the obeject was 
not avaialbale during the timeout time. Previous implementa-
tion of timeout functions might have returned a signaled state 
when the object was signaled after the timeout when the call-
ing task was blocked for a longer period by higher priorized 
tasks.
Modified functions:
OS_UseTimed(), Chapter 6.2.3
OS_WaitCSemaTimed(), Chapter 7.2.6
OS_GetMailTimed(), Chapter 8.5.8
OS_WaitMailTimed(), Chapter 8.5.10
OS_Q_GetPtrTimed(), Chapter 9.3.7
OS_EVENT_WaitTimed(), Chapter 11.2.4
OS_MEMF_AllocTimed(), Chapter 13.2.4
New Chapter 4.3. "Extending the task context" added. 
New functions added and described in the manual:
Chapter 4.4.14: OS_GetTaskName()
Chapter 4.4.14: OS_GetTimeSliceRem()
Handling of queues described mor in detail:
Chapter 9.3.5: OS_Q_GetPtr()
Chapter 9.3.6: OS_Q_GetPtrCond()
Chapter 9.3.7: OS_Q_GetPtrTimed()
Chapter 9.3.8: OS_Q_Purge()
Chapter 10, Task Events:
Type for task events OS_TASK_EVENT introduced. This type is 
used for all events and event masks. it defaults to unsigned 
char.
Chapter 2.4.3 "Priority inversion / inheritance" updated
Chapter 17.3.1 function names OS_Timing_Start() and 
OS_Timing_End() corrected in the API table.
Software Revision Date By Description

3.84c 1 120130 AW

/TS

Since version 3.82w of embOS, all pointer parameter pointing

to objects which were not modified by the function were

declared as const, but the manual was not updated accord-

ingly.

The prototype descriptions of the following API functions are

corrected now:

OS_GetTimerValue()

OS_GetTimerStatus()

OS_GetTimerPeriod()

OS_GetSemaValue()

OS_GetResourceOwner()

OS_Q_IsInUse()

OS_Q_GetMessageCnt()

OS_IsTask()

OS_GetEventsOccurred()

OS_GetCSemaValue()

OS_TICK_RemoveHook()

OS_MEMF_IsInPool()

OS_MEMF_GetMaxUsed()

OS_MEMF_GetNumBlocks()

OS_MEMF_GetBlockSize()

OS_GetSuspendCnt()

OS_GetPriority()

OS_EVENT_Get()

OS_Timing_Getus()

Chapter "Preface"

* Segger Logo replaced.

Chapter "Mailbox"

* OS_CREARTEMB() changed to OS_CreateMB().

Chapter "Queues"

* Typos corrected.

3.84c 0 120104 TS

Chapter "Events"

* Return value of OS_EVENT_WaitTimed() explained in more

detail

3.84b 0 111221 TS Chapter "Queues"

* OS_Q_PutBlocked() added.

3.84a 0 111207 TS General updates and corrections.

3.84 0 110927 TS

Chapter "Stacks"

* OS_GetSysStackBase() added.

* OS_GetSysStackSize() added.

* OS_GetSysStackUsed() added.

* OS_GetSysStackSpace() added.

* OS_GetIntStackBase() added.

* OS_GetIntStackSize() added.

* OS_GetIntStackUsed() added.

* OS_GetIntStackSpace() added.

3.82x 0 110829 TS Chapter "Debugging"

* New error code "OS_ERR_REGIONCNT" added.

3.82w 0 110812 TS New embOS generic sources.

Chapter 24 "Debugging" updated.

3.82v 0 110715 AW OS_Terminate() renamed to OS_TerminateTask().

3.82u 0 110630 TS New embOS generic sources.

Chapter 13: Fixed size memory pools modified.

3.82t 0 110503 TS New embOS generic sources. Trial time limitation increased.

3.82s 0 110318 AW

Chapter 5.2, "Timer" API functions table corrected.

All functions can be called from main(), task, ISR or Timer.

Chapter 6: OS_UseTimed() added.

Chapter 9: OS_Q_IsInUse() added.

3.82p 0 110112 AW

Chapter "Mailboxes"

* OS_PutMail()

* OS_PutMailCond()

* OS_PutMailFront()

* OS_PutMailFrontCond()

parameter declaration changed.

Chapter 4.3 API functions table corrected.

OS_Suspend() cannot be called from ISR or Timer.

3.82o 0 110104 AW Chapter "Mailboxes"

* OS_WaitMailTimed() added.

Software Revision Date By Description

6 CHAPTER

3.82n 0 101206 AW

Chapter "Taskroutines"

* OS_ResumeAllSuspendedTasks() added.

* OS_SetInitialSuspendCnt() added.

* OS_SuspendAllTasks() added.

Chapter "Time Measurement"

* Description of OS_GetTime32() corrected.

Chapter "List of error codes"

* New error codes added.

3.82k 0 100927 TS

Chapter "Taskroutines"

* OS_Delayus() added

* OS_Q_Delete() added

3.82i 0 100917 TS General updates and corrections.

3.82h 0 100621 AW

Chapter Event objects: Samples added.

Chapter: Configuration of target system: Detailed description

of OS_idle() added

3.82f 1 100505 TS Chapter Profiling added

Chapter SystemTick: OS_TickHandleNoHook() added.

3.82f 0 100419 AW Chapter Tasks: New function OS_IsRunning()added.

Chapter Tasks: Description of OS_Start() added.

3.82e 0 100309 TS

Chapter "Working with embOS - Recommendations" added

Chapter Basics

* Priority inversion image added

Chapter Interrupt

* subchapter "Using OS functions from high priority inter-

rupts"

added

Added text at chapter 22 "Performance and resource usage"

3.82 0 090922 TS

API function overview now contains information about allowed

context of function usage (main, task, ISR or timer)

TOC format corrected

3.80 0 090612 AW Scheduler optimized for higher task switching speed.

3.62.c 0 080903 SK

Chapter structure updated.

Chapter "Interrupts":

* OS_LeaveNestableInterruptNoSwitch() removed.

* OS_LeaveInterruptNoSwitch() removed.

Chapter "System tick":

* OS_TICK_Config() added.

3.60 2 080722 SK Contact address updated.

3.60 1 080617 SK

General updates.

Chapter "Mailboxes":

- OS_GetMailCond() / OS_GetMailCond1() corrected.

3.60 0 080117 OO General updates.

Chapter "System tick" added.

3.52 1 071026 AW Chapter "Task routines": Added OS_SetTaskName().

3.52 0 070824 OO

Chapter "Task routines": Added OS_ExtendTaskContext().

Chapter "Interrupts": Updated, added OS_CallISR() and

OS_CallNestableISR().

3.50c 0 070814 AW Chapter "List of libraries" updated, XR library type added.

3.40C 3 070716 OO Chapter “Performance and resource usage“ updated,

3.40C 2 070625 SK

Chapter “Debugging“, error codes updated:

- OS_ERR_ISR_INDEX added.

- OS_ERR_ISR_VECTOR added.

- OS_ERR_RESOURCE_OWNER added.

- OS_ERR_CSEMA_OVERFLOW added.

Chapter “Task routines“:

- OS_Yield() added.

Chapter “Counting semaphores“ updated.

- OS_SignalCSema(), additional information adjusted.

Chapter “Performance and resource usage“ updated:

- Minor changes in wording.

3.40A 1 070608 SK

Chapter “Counting semaphores“ updated.

- OS_SetCSemaValue() added.

- OS_CreateCSema(): Data type of parameter InitValue

changed from unsigned char to unsigned int.

- OS_SignalCSemaMax(): Data type of parameter MaxValue

changed from unsigned char to unsigned int.

- OS_SignalCSema(): Additional information updated.

Software Revision Date By Description

3.40 0 070516 SK

Chapter “Performance and resource usage“ added.

Chapter “Configuration of your target system (RTOSInit.c)“

renamed to “Configuration of your target system“.

Chapter “STOP\WAIT\IDLE modes“ moved into

chapter “Configuration of your target system“.

Chapter “time-related routines“ renamed to “Time measure-

ment“.

3.32o 9 070422 SK Chapter 4: OS_CREATETIMER_EX(), additional information

corrected.

3.32m 8 070402 AW

Chapter 4: Extended timer added.

Chapter 8: API overview corrected,

OS_Q_GetMessageCount()

3.32j 7 070216 AW Chapter 6: OS_CSemaRequest() function added.

3.32e 6 061220 SK About: Company description added.

Some minor formatting changes.

3.32e 5 061107 AW Chapter 7: OS_GetMessageCnt() return value corrected to

unsigned int.

3.32d 4 061106 AW Chapter 8: OS_Q_GetPtrTimed() function added.

3.32a 3 061012 AW

Chapter 3: OS_CreateTaskEx() function, description of

parameter pContext corrected.

Chapter 3: OS_CreateTaskEx() function, type of parameter

TimeSlice corrected.

Chapter 3: OS_CreateTask() function, type of parameter

TimeSlice corrected.

Chapter 9: OS_GetEventsOccured() renamed to

OS_GetEventsOccurred().

Chapter 10: OS_EVENT_WaitTimed() added.

3.32a 2 060804 AW Chapter 3: OS_CREATETASK_EX() function added.

Chapter 3: OS_CreateTaskEx() function added.

3.32 1 060717 OO Event objects introduced. Chapter 10 inserted which

describes event objects.

Previous chapter "Events" renamed to "Task events"

3.30 1 060519 OO New software version.

3.28 5 060223 OO All chapters: Added API tables.

Some minor changes.

3.28 4 051109 AW Chapter 7: OS_SignalCSemaMax() function added.

Chapter 14: Explanation of interrupt latencies and high / low

priorities added.

3.28 3 050926 AW Chapter 6: OS_DeleteRSema() function added.

3.28 2 050707 AW Chapter 4: OS_GetSuspendCnt() function added.

3.28 1 050425 AW Version number changed to 3.28 to fit to current ombOS ver-

sion.

Chapter 18.1.2: Type of return value of OS GetTime32() cor-

rected

3.26 050209 AW

Chapter 4: OS_Terminate() modified due to new features of

version 3.26.

Chapter 24: Source code version: additional compile time

switches and build process of libraries explained more in

detail.

3.24 041115 AW Chapter 6: Some prototype declarations showed in OS_SEMA

instead of OS_RSEMA. Corrected.

3.22 1 040816 AW Chapter 8: New Mailbox functions added

OS_PutMailFront()

OS_PutMailFront1()

OS_PutMailFrontCond()

OS_PutMailFrontCond1()

3.20 5 040621 RS

Software timers: Maximum timeout values and

OS_TIMER_MAX_TIME described.

Chapter 14: Description of rules for interrupt handlers

revised.

OS_LeaveNestableInterruptNoSwitch() added which was

not described before.

Software Revision Date By Description

8 CHAPTER

3.20 4 040329 AW OS_CreateCSema() prototype declaration corrected.

Return type is void.

OS_Q_GetMessageCnt() prototype declaration corrected.

OS_Q_Clear() function description added.

OS_MEMF_FreeBlock() prototype declaration corrected.

3.20 2 031128 AW OS_CREATEMB() Range for parameter MaxnofMsg cor-

rected. Upper limit is 65535, but was declared 65536 in

previous manuals.

3. 1 040831 AW Code samples modified: Task stacks defined as array of

int, because most CPUs require alignment of stack on inte-

ger aligned addresses.

3.20 1 031016 AW Chapter 4: Type of task priority parameter corrected to

unsigned char.

Chapter 4: OS_DelayUntil(): Sample program modified.

Chapter 4: OS_Suspend() added.

Chapter 4: OS_Resume() added.

Chapter 5: OS_GetTimerValue(): Range of return value

corrected.

Chapter 6: Sample program for usage of resource sema-

phores modified.

Chapter 6: OS_GetResourceOwner(): Type of return value

corrected.

Chapter 8: OS_CREATEMB(): Types and valid range of

parameter corrected.

Chapter 8: OS_WaitMail() added

Chapter 10: OS_WaitEventTimed(): Range of timeout

value specified.

3.12 1 021015 AW Chapter 8: OS_GetMailTimed() added

Chapter 11 (Heap type memory management) inserted

Chapter 12 (Fixed block size memory pools) inserted

3.10 3 020926

020924

020910

Index and glossary revised.

Section 16.3 (Example) added to Chapter 16 (Time-related

routines).

Revised for language/grammar.

Version control table added.

Screenshots added: superloop, cooperative/preemptive multi-

tasking, nested interrupts, low-res and hi-res measurement.

Section 1.3 (Typographic conventions) changed to table.

Section 3.2 added (Single-task system).

Section 3.8 merged with section 3.9 (How the OS gains con-

trol).

Chapter 4 (Configuration for your target system) moved to

after Chapter 15 (System variables).

Chapter 16 (Time-related routines) added.

Software Revision Date By Description

About this document

Assumptions

This document assumes that you already have a solid knowledge of the following:

• The software tools used for building your application (assembler, linker, C com-

piler)

• The C programming language

• The target processor

• DOS command line

If you feel that your knowledge of C is not sufficient, we recommend The C Program-

ming Language by Kernighan and Richie (ISBN 0-13-1103628), which describes the

standard in C-programming and, in newer editions, also covers the ANSI C standard.

How to use this manual

This manual explains all the functions and macros that the product offers. It assumes

you have a working knowledge of the C language. Knowledge of assembly program-

ming is not required.

Typographic conventions for syntax

This manual uses the following typographic conventions:

Style Used for

Body Body text.

Keyword Text that you enter at the command-prompt or that appears on

the display (that is system functions, file- or pathnames).

Parameter Parameters in API functions.

Sample Sample code in program examples.

Sample comment Comments in programm examples.

Reference Reference to chapters, sections, tables and figures or other docu-

ments.

GUIElement Buttons, dialog boxes, menu names, menu commands.

Emphasis Very important sections.

Table 1.1: Typographic conventions

EMBEDDED SOFTWARE

(Middleware)

emWin

Graphics software and GUI

emWin is designed to provide an effi-

cient, processor- and display control-

ler-independent graphical user

interface (GUI) for any application that

operates with a graphical display.

embOS

Real Time Operating System

embOS is an RTOS designed to offer

the benefits of a complete multitasking

system for hard real time applications

with minimal resources.

embOS/IP

TCP/IP stack

embOS/IP a high-performance TCP/IP

stack that has been optimized for

speed, versatility and a small memory

footprint.

emFile

File system

emFile is an embedded file system with

FAT12, FAT16 and FAT32 support. Var-

ious Device drivers, e.g. for NAND and

NOR flashes, SD/MMC and Compact-

Flash cards, are available.

USB-Stack

USB device/host stack

A USB stack designed to work on any

embedded system with a USB control-

ler. Bulk communication and most stan-

dard device classes are supported.

SEGGER TOOLS

Flasher

Flash programmer

Flash Programming tool primarily for micro con-

trollers.

J-Link

JTAG emulator for ARM cores

USB driven JTAG interface for ARM cores.

J-Trace

JTAG emulator with trace

USB driven JTAG interface for ARM cores with

Trace memory. supporting the ARM ETM (Embed-

ded Trace Macrocell).

J-Link / J-Trace Related Software

Add-on software to be used with SEGGER’s indus-

try standard JTAG emulator, this includes flash

programming software and flash breakpoints.

SEGGER Microcontroller GmbH & Co. KG develops

and distributes software development tools and ANSI C

software components (middleware) for embedded sys-

tems in several industries such as telecom, medical

technology, consumer electronics, automotive industry

and industrial automation.

SEGGER’s intention is to cut software development time

for embedded applications by offering compact flexible and easy to use middleware,

allowing developers to concentrate on their application.

Our most popular products are emWin, a universal graphic software package for embed-

ded applications, and embOS, a small yet efficient real-time kernel. emWin, written

entirely in ANSI C, can easily be used on any CPU and most any display. It is comple-

mented by the available PC tools: Bitmap Converter, Font Converter, Simulator and

Viewer. embOS supports most 8/16/32-bit CPUs. Its small memory footprint makes it

suitable for single-chip applications.

Apart from its main focus on software tools, SEGGER develops and produces programming

tools for flash micro controllers, as well as J-Link, a JTAG emulator to assist in develop-

ment, debugging and production, which has rapidly become the industry standard for

debug access to ARM cores.

Corporate Office:

http://www.segger.com

United States Office:

http://www.segger-us.com

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
11
 Introduction to embOS...................................................................................................19
1 What is embOS ....................................................................................... 20
2 Features.................................................................................................21
 Basic concepts...............................................................................................................23
1 Tasks.....................................................................................................24
1.1 Threads..................................................................................................24
1.2 Processes ............................................................................................... 24
2 Single-task systems (superloop)................................................................ 25
2.1 Advantages & disadvantages.....................................................................25
2.2 Using embOS in super-loop applications...................................................... 26
2.3 Migrating from superloop to multi-tasking ................................................... 26
3 Multitasking systems................................................................................27
3.1 Task switches..........................................................................................27
3.2 Cooperative task switch............................................................................27
3.3 Preemptive task switch............................................................................. 27
3.4 Preemptive multitasking ...........................................................................28
3.5 Cooperative multitasking ..........................................................................29
4 Scheduling.............................................................................................. 30
4.1 Round-robin scheduling algorithm..............................................................30
4.2 Priority-controlled scheduling algorithm ...................................................... 30
4.3 Priority inversion / priority inheritance........................................................31
5 Communication between tasks ..................................................................33
5.1 Periodic polling........................................................................................33
5.2 Event-driven communication mechanisms ...................................................33
5.3 Mailboxes and queues ..............................................................................33
5.4 Semaphores ...........................................................................................33
5.5 Events ...................................................................................................33
6 How task switching works ......................................................................... 34
6.1 Switching stacks...................................................................................... 35
7 Change of task status...............................................................................36
8 How the OS gains control ......................................................................... 37
9 Different builds of embOS.........................................................................38
9.1 Profiling .................................................................................................38
9.2 List of libraries ........................................................................................ 38
9.3 embOS functions context.......................................................................... 39
 Working with embOS.....................................................................................................41
1 General advice ........................................................................................ 42
1.1 Timers or task......................................................................................... 42
 Tasks .............................................................................................................................43
1 Introduction............................................................................................44
1.1 Example of a task routine as an endless loop............................................... 44
1.2 Example of a task routine that terminates itself ........................................... 44
2 Cooperative vs. preemptive task switches ................................................... 45
2.1 Disabling preemptive task switches for tasks of equal priority ........................45
2.2 Completely disabling preemptions for a task................................................45
3 Extending the task context ....................................................................... 46
3.1 Passing one parameter to a task during task creation ...................................46
Table of Contents

12
UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
3.2 Extending the task context individually at runtime ....................................... 46
3.3 Extending the task context by using own task structures .............................. 46
4 API functions .......................................................................................... 48
4.1 OS_AddOnTerminateHook()...................................................................... 50
4.2 OS_CREATETASK().................................................................................. 51
4.3 OS_CreateTask() .................................................................................... 53
4.4 OS_CREATETASK_EX() ............................................................................ 55
4.5 OS_CreateTaskEx() ................................................................................. 57
4.6 OS_Delay() ............................................................................................ 58
4.7 OS_DelayUntil()...................................................................................... 59
4.8 OS_Delayus() ......................................................................................... 60
4.9 OS_ExtendTaskContext() ......................................................................... 61
4.10 OS_GetpCurrentTask()............................................................................. 64
4.11 OS_GetPriority() ..................................................................................... 65
4.12 OS_GetSuspendCnt()............................................................................... 66
4.13 OS_GetTaskID() ..................................................................................... 67
4.14 OS_GetTaskName()................................................................................. 68
4.15 OS_GetTimeSliceRem()............................................................................ 69
4.16 OS_IsRunning() ...................................................................................... 70
4.17 OS_IsTask() ........................................................................................... 71
4.18 OS_Resume() ......................................................................................... 72
4.19 OS_ResumeAllSuspendedTasks()............................................................... 73
4.20 OS_SetInitialSuspendCnt() ....................................................................... 74
4.21 OS_SetPriority() ..................................................................................... 75
4.22 OS_SetTaskName() ................................................................................. 76
4.23 OS_SetTimeSlice() .................................................................................. 77
4.24 OS_Start() ............................................................................................. 78
4.25 OS_Suspend() ........................................................................................ 79
4.26 OS_SuspendAllTasks() ............................................................................. 80
4.27 OS_TerminateTask()................................................................................ 81
4.28 OS_WakeTask() ...................................................................................... 82
4.29 OS_Yield() ............................................................................................. 83
 Software timers..............................................................................................................85
1 Introduction ........................................................................................... 86
2 API functions .......................................................................................... 87
2.1 OS_CREATETIMER() ................................................................................ 88
2.2 OS_CreateTimer() ................................................................................... 89
2.3 OS_StartTimer() ..................................................................................... 90
2.4 OS_StopTimer()...................................................................................... 91
2.5 OS_RetriggerTimer() ............................................................................... 92
2.6 OS_SetTimerPeriod()............................................................................... 93
2.7 OS_DeleteTimer() ................................................................................... 94
2.8 OS_GetTimerPeriod()............................................................................... 95
2.9 OS_GetTimerValue()................................................................................ 96
2.10 OS_GetTimerStatus() .............................................................................. 97
2.11 OS_GetpCurrentTimer() ........................................................................... 98
2.12 OS_CREATETIMER_EX() ........................................................................... 99
2.13 OS_CreateTimerEx()...............................................................................100
2.14 OS_StartTimerEx().................................................................................101
2.15 OS_StopTimerEx() .................................................................................102
2.16 OS_RetriggerTimerEx() ...........................................................................103
2.17 OS_SetTimerPeriodEx() ..........................................................................104
2.18 OS_DeleteTimerEx()...............................................................................105
2.19 OS_GetTimerPeriodEx() ..........................................................................106
2.20 OS_GetTimerValueEx() ...........................................................................107
2.21 OS_GetTimerStatusEx() ..........................................................................108
2.22 OS_GetpCurrentTimerEx().......................................................................109
 Resource semaphores.................................................................................................111

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
13
1 Introduction.......................................................................................... 112
2 API functions ........................................................................................ 114
2.1 OS_CREATERSEMA().............................................................................. 115
2.2 OS_Use() ............................................................................................. 116
2.3 OS_UseTimed()..................................................................................... 118
2.4 OS_Unuse().......................................................................................... 119
2.5 OS_Request() ....................................................................................... 120
2.6 OS_GetSemaValue() .............................................................................. 121
2.7 OS_GetResourceOwner() ........................................................................ 122
2.8 OS_DeleteRSema()................................................................................ 123
 Counting Semaphores.................................................................................................125
1 Introduction.......................................................................................... 126
2 API functions ........................................................................................ 127
2.1 OS_CREATECSEMA().............................................................................. 128
2.2 OS_CreateCSema()................................................................................ 129
2.3 OS_SignalCSema() ................................................................................ 130
2.4 OS_SignalCSemaMax()........................................................................... 131
2.5 OS_WaitCSema() .................................................................................. 132
2.6 OS_WaitCSemaTimed() .......................................................................... 133
2.7 OS_CSemaRequest() ............................................................................. 134
2.8 OS_GetCSemaValue() ............................................................................ 135
2.9 OS_SetCSemaValue() ............................................................................ 136
2.10 OS_DeleteCSema()................................................................................ 137
 Mailboxes.....................................................................................................................139
1 Introduction.......................................................................................... 140
2 Basics .................................................................................................. 141
3 Typical applications................................................................................ 142
3.1 A keyboard buffer.................................................................................. 142
3.2 A buffer for serial I/O ............................................................................. 142
3.3 A buffer for commands sent to a task ....................................................... 142
4 Single-byte mailbox functions.................................................................. 143
5 API functions ........................................................................................ 144
5.1 OS_CreateMB() ..................................................................................... 145
5.2 OS_PutMail() / OS_PutMail1() ................................................................. 146
5.3 OS_PutMailCond() / OS_PutMailCond1() ................................................... 147
5.4 OS_PutMailFront() / OS_PutMailFront1()................................................... 148
5.5 OS_PutMailFrontCond() / OS_PutMailFrontCond1()..................................... 149
5.6 OS_GetMail() / OS_GetMail1()................................................................. 150
5.7 OS_GetMailCond() / OS_GetMailCond1() .................................................. 151
5.8 OS_GetMailTimed()................................................................................ 152
5.9 OS_WaitMail()....................................................................................... 153
5.10 OS_WaitMailTimed() .............................................................................. 154
5.11 OS_PeekMail() ...................................................................................... 155
5.12 OS_ClearMB() ....................................................................................... 156
5.13 OS_GetMessageCnt() ............................................................................. 157
5.14 OS_DeleteMB() ..................................................................................... 158
 Queues ........................................................................................................................159
1 Introduction.......................................................................................... 160
2 Basics .................................................................................................. 161
3 API functions ........................................................................................ 162
3.1 OS_Q_Create() ..................................................................................... 163
3.2 OS_Q_Put() .......................................................................................... 164
3.3 OS_Q_PutBlocked() ............................................................................... 165
3.4 OS_Q_PutTimed().................................................................................. 166
3.5 OS_Q_GetPtr()...................................................................................... 167
3.6 OS_Q_GetPtrCond()............................................................................... 168
3.7 OS_Q_GetPtrTimed() ............................................................................. 169

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3.8 OS_Q_Purge() .......................................................................................170
3.9 OS_Q_Clear() ........................................................................................171
3.10 OS_Q_GetMessageCnt()..........................................................................172
3.11 OS_Q_Delete() ......................................................................................173
3.12 OS_Q_IsInUse() ....................................................................................174
3.13 OS_Q_GetMessageSize().........................................................................175
3.14 OS_Q_PeekPtr().....................................................................................176
 Task events................................................................................................................177
1 Introduction ..........................................................................................178
2 API functions .........................................................................................179
2.1 OS_WaitEvent() .....................................................................................180
2.2 OS_WaitSingleEvent() ............................................................................181
2.3 OS_WaitEventTimed() ............................................................................182
2.4 OS_WaitSingleEventTimed() ....................................................................183
2.5 OS_SignalEvent()...................................................................................184
2.6 OS_GetEventsOccurred() ........................................................................186
2.7 OS_ClearEvents()...................................................................................187
 Event objects .............................................................................................................189
1 Introduction ..........................................................................................190
2 API functions .........................................................................................191
2.1 OS_EVENT_Create() ...............................................................................192
2.2 OS_EVENT_CreateEx()............................................................................193
2.3 OS_EVENT_Wait() ..................................................................................194
2.4 OS_EVENT_WaitTimed() .........................................................................195
2.5 OS_EVENT_Set()....................................................................................197
2.6 OS_EVENT_Reset() ................................................................................198
2.7 OS_EVENT_Pulse() .................................................................................199
2.8 OS_EVENT_Get() ...................................................................................200
2.9 OS_EVENT_Delete() ...............................................................................201
2.10 OS_EVENT_SetResetMode() ....................................................................202
2.11 OS_EVENT_GetResetMode() ....................................................................203
3 Examples of using event objects...............................................................204
3.1 Activate a task from interrupt by an event object .......................................204
3.2 Activating multiple tasks using a single event object ...................................205
 Heap type memory management...............................................................................207
1 Introduction ..........................................................................................208
2 API functions .........................................................................................209
2.1 OS_malloc() ..........................................................................................210
2.2 OS_free()..............................................................................................211
2.3 OS_realloc() ..........................................................................................212
 Fixed block size memory pools..................................................................................213
1 Introduction ..........................................................................................214
2 API functions .........................................................................................215
2.1 OS_MEMF_Create() ................................................................................216
2.2 OS_MEMF_Delete() ................................................................................217
2.3 OS_MEMF_Alloc()...................................................................................218
2.4 OS_MEMF_AllocTimed() ..........................................................................219
2.5 OS_MEMF_Request() ..............................................................................220
2.6 OS_MEMF_Release()...............................................................................221
2.7 OS_MEMF_FreeBlock() ............................................................................222
2.8 OS_MEMF_GetNumBlocks() .....................................................................223
2.9 OS_MEMF_GetBlockSize() .......................................................................224
2.10 OS_MEMF_GetNumFreeBlocks() ...............................................................225
2.11 OS_MEMF_GetMaxUsed() ........................................................................226
2.12 OS_MEMF_IsInPool() ..............................................................................227

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 Stacks........................................................................................................................229
1 Introduction.......................................................................................... 230
1.1 System stack ........................................................................................ 230
1.2 Task stack ............................................................................................ 230
1.3 Interrupt stack ...................................................................................... 230
1.4 Stack size calculation ............................................................................. 231
1.5 Stack-check .......................................................................................... 231
2 API functions ........................................................................................ 232
2.1 OS_GetStackBase() ............................................................................... 233
2.2 OS_GetStackSize() ................................................................................ 234
2.3 OS_GetStackSpace().............................................................................. 235
2.4 OS_GetStackUsed() ............................................................................... 236
2.5 OS_GetSysStackBase() .......................................................................... 237
2.6 OS_GetSysStackSize() ........................................................................... 238
2.7 OS_GetSysStackSpace()......................................................................... 239
2.8 OS_GetSysStackUsed() .......................................................................... 240
2.9 OS_GetIntStackBase() ........................................................................... 241
2.10 OS_GetIntStackSize() ............................................................................ 242
2.11 OS_GetIntStackSpace().......................................................................... 243
2.12 OS_GetIntStackUsed() ........................................................................... 244
 Interrupts....................................................................................................................245
1 What are interrupts? .............................................................................. 246
2 Interrupt latency ................................................................................... 247
2.1 Causes of interrupt latencies ................................................................... 247
2.2 Additional causes for interrupt latencies.................................................... 247
3 Zero interrupt latency ............................................................................ 249
4 High / low priority interrupts ................................................................... 250
4.1 Using OS functions from high priority interrupts......................................... 250
5 Rules for interrupt handlers..................................................................... 252
5.1 General rules ........................................................................................ 252
5.2 Additional rules for preemptive multitasking .............................................. 252
6 API functions ........................................................................................ 253
6.1 OS_CallISR() ........................................................................................ 254
6.2 OS_CallNestableISR() ............................................................................ 255
6.3 OS_EnterInterrupt() .............................................................................. 256
6.4 OS_LeaveInterrupt().............................................................................. 257
7 Enabling / disabling interrupts from C....................................................... 258
7.1 OS_IncDI() / OS_DecRI() ....................................................................... 259
7.2 OS_DI() / OS_EI() / OS_RestoreI().......................................................... 260
8 Definitions of interrupt control macros (in RTOS.h)..................................... 261
9 Nesting interrupt routines ....................................................................... 262
9.1 OS_EnterNestableInterrupt()................................................................... 263
9.2 OS_LeaveNestableInterrupt().................................................................. 264
9.3 OS_InInterrupt() ................................................................................... 265
10 Global interrupt enable / disable .............................................................. 266
10.1 OS_INTERRUPT_MaskGlobal() ................................................................. 267
10.2 OS_INTERRUPT_UnmaskGlobal() ............................................................. 267
10.3 OS_INTERRUPT_PreserveGlobal() ............................................................ 268
10.4 OS_INTERRUPT_PreserveAndMaskGlobal() ................................................ 269
10.5 OS_INTERRUPT_RestoreGlobal().............................................................. 269
11 Non-maskable interrupts (NMIs).............................................................. 270
 Critical Regions..........................................................................................................271
1 Introduction.......................................................................................... 272
2 API functions ........................................................................................ 273
2.1 OS_EnterRegion().................................................................................. 274
2.2 OS_LeaveRegion() ................................................................................. 275
 Time measurement....................................................................................................277

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1 Introduction ..........................................................................................278
2 Low-resolution measurement...................................................................279
2.1 API functions .........................................................................................280
2.1.1 OS_GetTime() .......................................................................................281
2.1.2 OS_GetTime32()....................................................................................282
3 High-resolution measurement ..................................................................283
3.1 API functions .........................................................................................284
3.1.1 OS_Timing_Start() .................................................................................285
3.1.2 OS_Timing_End()...................................................................................286
3.1.3 OS_Timing_Getus() ................................................................................287
3.1.4 OS_Timing_GetCycles() ..........................................................................288
4 Example ...............................................................................................289
5 Micro second precise system time.............................................................291
5.1 API functions .........................................................................................291
5.2 OS_GetTime_us() ..................................................................................292
5.3 OS_GetTime_us64() ...............................................................................293
5.4 OS_Config_SysTimer()............................................................................294
5.4.1 pfGetTimerCycles() ................................................................................294
5.4.2 pfGetTimerIntPending() ..........................................................................294
5.4.3 Example ...............................................................................................295
 System variables........................................................................................................297
1 Introduction ..........................................................................................298
2 Time variables .......................................................................................299
2.1 OS_Global.............................................................................................299
2.2 OS_Global.Time .....................................................................................299
2.3 OS_Global.TimeDex................................................................................299
3 OS internal variables and data-structures ..................................................300
 System tick.................................................................................................................301
1 Introduction ..........................................................................................302
2 Tick handler ..........................................................................................303
2.1 API functions .........................................................................................303
2.1.1 OS_TICK_Handle() .................................................................................304
2.1.2 OS_TICK_HandleEx()..............................................................................305
2.1.3 OS_TICK_HandleNoHook() ......................................................................306
2.1.4 OS_TICK_Config()..................................................................................307
3 Hooking into the system tick....................................................................308
3.1 API functions .........................................................................................308
3.1.1 OS_TICK_AddHook() ..............................................................................309
3.1.2 OS_TICK_RemoveHook() ........................................................................310
4 Tickless support .....................................................................................311
4.1 OS_Idle()..............................................................................................311
4.2 Callback Function ...................................................................................312
4.3 API functions .........................................................................................313
4.3.1 OS_GetNumIdleTicks() ...........................................................................314
4.3.2 OS_AdjustTime() ...................................................................................315
4.3.3 OS_StartTicklessMode() ..........................................................................316
4.3.4 OS_StopTicklessMode()...........................................................................317
4.4 Frequently Asked Questions.....................................................................318
 Configuration of target system (BSP) ........................................................................319
1 Introduction ..........................................................................................320
2 Hardware-specific routines ......................................................................321
2.1 OS_Idle()..............................................................................................321
3 Configuration defines..............................................................................323
4 How to change settings...........................................................................324
4.1 Setting the system frequency OS_FSYS.....................................................324
4.2 Using a different timer to generate the tick-interrupts for embOS .................324
4.3 Using a different UART or baudrate for embOSView ....................................324

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4.4 Changing the tick frequency.................................................................... 324
5 STOP / HALT / IDLE modes ..................................................................... 326
 Profiling......................................................................................................................327
0.1 API functions ........................................................................................ 328
0.1.1 OS_STAT_Sample() ............................................................................... 329
0.1.2 OS_STAT_GetLoad() .............................................................................. 330
0.1.3 Sample application for OS_STAT_Sample() and OS_STAT_GetLoad()............ 331
0.1.4 OS_AddLoadMeasurement().................................................................... 332
0.1.5 OS_GetLoadMeasurement() .................................................................... 333
0.1.6 OS_CPU_Load ....................................................................................... 334
0.1.7 OS_STAT_Enable() ................................................................................ 335
0.1.8 OS_STAT_Disable() ............................................................................... 336
0.1.9 OS_STAT_GetTaskExecTime() ................................................................. 337
 embOSView: Profiling and analyzing.........................................................................339
1 Overview.............................................................................................. 340
2 Task list window .................................................................................... 341
3 System variables window........................................................................ 342
4 Sharing the SIO for terminal I/O.............................................................. 343
5 API functions ........................................................................................ 344
5.1 OS_SendString() ................................................................................... 345
5.2 OS_SetRxCallback()............................................................................... 346
6 Using the API trace ................................................................................ 347
7 Trace filter setup functions...................................................................... 349
8 API functions ........................................................................................ 350
8.1 OS_TraceEnable().................................................................................. 351
8.2 OS_TraceDisable()................................................................................. 352
8.3 OS_TraceEnableAll() .............................................................................. 353
8.4 OS_TraceDisableAll() ............................................................................. 354
8.5 OS_TraceEnableId()............................................................................... 355
8.6 OS_TraceDisableId() .............................................................................. 356
8.7 OS_TraceEnableFilterId()........................................................................ 357
8.8 OS_TraceDisableFilterId() ....................................................................... 358
9 Trace record functions............................................................................ 359
10 API functions ........................................................................................ 360
10.1 OS_TraceVoid()..................................................................................... 361
10.2 OS_TracePtr() ....................................................................................... 362
10.3 OS_TraceData() .................................................................................... 363
10.4 OS_TraceDataPtr() ................................................................................ 364
10.5 OS_TraceU32Ptr() ................................................................................. 365
11 Application-controlled trace example ........................................................ 366
12 User-defined functions ........................................................................... 367
 Performance and resource usage..............................................................................369
1 Introduction.......................................................................................... 370
2 Memory requirements ............................................................................ 371
3 Performance ......................................................................................... 372
4 Benchmarking ....................................................................................... 372
4.1 Measurement with port pins and oscilloscope............................................. 373
4.1.1 Oscilloscope analysis.............................................................................. 374
4.1.2 Example measurements AT91SAM7S, ARM code in RAM.............................. 375
4.1.3 Example measurements AT91SAM7S, Thumb code in FLASH ....................... 376
4.1.4 Measurement with high-resolution timer ................................................... 377
 Debugging..................................................................................................................379
1 Runtime errors ...................................................................................... 380
1.1 OS_DEBUG_LEVEL................................................................................. 380
2 List of error codes.................................................................................. 381

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3 Application defined error codes ................................................................385
 Supported development tools....................................................................................387
1 Overview ..............................................................................................388
 Limitations..................................................................................................................389
 Source code of kernel and library..............................................................................391
1 Introduction ..........................................................................................392
2 Building embOS libraries .........................................................................393
3 Major compile time switches ....................................................................394
3.1 OS_RR_SUPPORTED ...............................................................................394
 FAQ (frequently asked questions) .............................................................................395
 Support ......................................................................................................................397
1 Contacting support .................................................................................398
 Glossary.....................................................................................................................399

Chapter 1

Introduction to embOS

20 CHAPTER 1 Introduction to embOS

1.1 What is embOS

embOS is a priority-controlled multitasking system, designed to be used as an

embedded operating system for the development of real-time applications for a vari-

ety of microcontrollers.

embOS is a high-performance tool that has been optimized for minimal memory con-

sumption in both RAM and ROM, as well as high speed and versatility.

1.2 Features

Throughout the development process of embOS, the limited resources of microcon-

trollers have always been kept in mind. The internal structure of the real-time oper-

ating system (RTOS) has been optimized in a variety of applications with different

customers, to fit the needs of industry. Fully source-compatible implementations of

embOS are available for a variety of microcontrollers, making it well worth the time

and effort to learn how to structure real-time programs with real-time operating sys-

tems.

embOS is highly modular. This means that only those functions that are required are

linked into an application, keeping the ROM size very small. The minimum memory

consumption is little more than 1 Kbyte of ROM and about 30 bytes of RAM (plus

memory for stacks). A couple of files are supplied in source code to make sure that

you do not loose any flexibility by using embOS and that you can customize the sys-

tem to fully fit your needs.

The tasks you create can easily and safely communicate with each other using a

number of communication mechanisms such as semaphores, mailboxes, and events.

Some features of embOS include:

• Preemptive scheduling:

Guarantees that of all tasks in READY state the one with the highest priority exe-

cutes, except for situations where priority inheritance applies.

• Round-robin scheduling for tasks with identical priorities.

• Preemptions can be disabled for entire tasks or for sections of a program.

• Up to 4.294.967.296 priorities.

• Every task can have an individual priority, which means that the response of

tasks can be precisely defined according to the requirements of the application.

• Unlimited number of tasks

(limited only by the amount of available memory).

• Unlimited number of semaphores

(limited only by the amount of available memory).

• Two types of semaphores: resource and counting.

• Unlimited number of mailboxes

(limited only by the amount of available memory).

• Size and number of messages can be freely defined when initializing mailboxes.

• Unlimited number of software timers

(limited only by the amount of available memory).

• Up to 32-bit events for every task.

• Time resolution can be freely selected (default is 1ms).

• Easily accessible time variable.

• Power management.

• Calculation time in which embOS is idle can automatically be spent in low-power

mode.

power-consumption is minimized.

• Full interrupt support:

Interrupts can call any function except those that require waiting for data,

as well as create, delete or change the priority of a task.

Interrupts can wake up or suspend tasks and directly communicate with tasks

using all available communication methods (mailboxes, semaphores, events).

• Disabling interrupts for very short periods allows minimal interrupt latency.

• Nested interrupts are permitted.

• embOS has its own interrupt stack (usage optional).

• Application samples for an easy start.

• Debug build performs runtime checks that catch common programming errors

early on.

• Profiling and stack-check may be implemented by choosing specified libraries.

• Monitoring during runtime is available using embOSView via UART, Debug Com-

munications Channel (DCC) and memory read/write, or else via Ethernet.

• Very fast and efficient, yet small code.

• Minimal RAM usage.

22 CHAPTER 1 Introduction to embOS

• Core written in assembly language.

• API can be called from assembly, C or C++ code.

• Initialization of microcontroller hardware as sources (BSP).

Chapter 2

Basic concepts

This chapter explains some basic concepts behind embOS. It should be relativly easy

to read and is recommended before moving to other chapters.

24 CHAPTER 2 Basic concepts

2.1 Tasks

In this context, a task is a program running on the CPU core of a microcontroller.

Without a multitasking kernel (an RTOS), only one task can be executed by the CPU

at a time. This is called a single-task system. A real-time operating system allows the

execution of multiple tasks on a single CPU. All tasks execute as if they completely

“own” the entire CPU. The tasks are scheduled for execution, meaning that the RTOS

can activate and deactivate each task according to its priority, with the highest prior-

ity task being executed in general.

2.1.1 Threads

Threads are tasks which share the same memory layout. Two threads can access the

same memory locations. If virtual memory is used, the same virtual to physical

translation and access rights are used.

The embOS tasks are threads; they all have the same memory access rights and

translation (in systems with virtual memory).

2.1.2 Processes

Processs are tasks with their own memory layout. Two processes cannot normally

access the same memory locations. Different processes typically have different

access rights and (in case of MMUs) different translation tables.

Processes are not supported by the present version of embOS.

2.2 Single-task systems (superloop)

The classic way of designing embedded systems does not use the services of an

RTOS, which is also called "superloop design". Typically, no real time kernel is used,

so interrupt service routines (ISRs) are used for the real-time parts of the application

and for critical operations (at interrupt level). This type of system is typically used in

small, simple systems or if real-time behavior is not critical.

Typically, because no real-time kernel and only one stack is used, both program

(ROM) and RAM size for simple applications are smaller when compared to using an

RTOS. Of course, there are no inter-task synchronization problems with a superloop

application. However, superloops can become difficult to maintain if the program

becomes too large or uses complex interactions. As sequential processes cannot

interrupt themselves, reaction times depend on the execution time of the entire

sequence, resulting in a poor real-time behavior.

2.2.1 Advantages & disadvantages

Advantages

• Simple structure (for small applications)

• Low stack usage (only one stack required)

Disadvantages

• No "delay" capability

• Higher power consumption due to the lack of a sleep mode in most architectures

• Difficult to maintain as program grows

• Timing of all software components depends on all other software componts:

Small change in one place can have major side effects in other places

• Defeats modular programming

• Real time behavior only with interrupts

26 CHAPTER 2 Basic concepts

2.2.2 Using embOS in super-loop applications

In a true superloop application, no tasks are used, so the biggest advantage of using

an RTOS cannot be used unless the application is converted to use multitasking.

However, even with just a single task, using embOS has the following advantages:

• Software timers are available

• Power saving: Idle mode can be used

• Future extensions can be put in a separate task

2.2.3 Migrating from superloop to multi-tasking

A common situation is that an application exists for some time and has been

designed as single task, super loop application. At a certain point, the disadvantages

of this approach lead to a decision to use an RTOS. The typical question is then: How

do I do this?

The easiest way is to take the start application that comes with the embOS and put

your existing "superloop code" into one task. At this point you should also make sure

that the stack size of this task is sufficient. Later, additional functionality which is

added to the software can be put in one or more additional tasks; the functionality of

the super loop can also be distributed over multiple tasks.

2.3 Multitasking systems

In a multitasking system, there are different ways of distributing the CPU time

amongst different tasks. This process is called scheduling.

2.3.1 Task switches

There are two types of task switches, also called context switches: Cooperative and

preemptive task switches.

2.3.2 Cooperative task switch

A cooperative task switch is performed by the task itself. It requires the cooperation

of the task, hence the name. What happens is that the task blocks itself by calling a

blocking RTOS function such as OS_Delay() or OS_WaitEvent().

2.3.3 Preemptive task switch

A preemptive task switch is a task switch caused by an interrupt. Typically some

other high priority task becomes ready for execution and, as a result, the current

task is suspended.

Time

Low prio task High prio task ISR

Application level tasks

Interrupt

Interrupt service

Idle task

Priority

OS_Start()

OS_EVENT_Wait()

Interrupt (Tick)

Interrupt (Rx)

OS_EVENT_Set()

OS_Delay()

28 CHAPTER 2 Basic concepts

2.3.4 Preemptive multitasking

Real-time operating systems like embOS operate with preemptive multitasking. The

highest-priority task in the READY state always executes as long as the task is not

suspended by a call of any operating system function. A high-priority task waiting for

an event is signalled READY as soon as the event occurs. The event can be set by an

interrupt handler, which then activates the task immediately. Other tasks with lower

priority are suspended (preempted) as long as the high-priority task is executing.

A real-time operating system, such as embOS, normally comes with a regular timer

interrupt to interrupt tasks at regular intervals and to perform task switches if timed

task switches are necessary.

Time

ISR

Low priority task

High priority task

ISR puts high priority

task in READY state;

task switch occurs

Executing task is interrupted

Interrupted task

is completed

Higher priority task

Is executed

2.3.5 Cooperative multitasking

Cooperative multitasking requires all tasks to cooperate by using blocking functions.

A task switch can only take place if the running task blocks itself by calling a blocking

function such as OS_Delay() or OS_Wait...(). If tasks do not cooperate, the system

“hangs”, which means that other tasks have no chance of being executed by the CPU

while the first task is being carried out. This is illustrated in the diagram below. Even

if an ISR makes a higher-priority task ready to run, the interrupted task will be

resumed and complete before the task switch is made.

A pure cooperative multi-tasking system has the disadvantage of longer reaction

times when high priority tasks become ready for execution. This makes their usage in

embedded real-time systems uncommon.

Time

ISR

Low priority task

High priority task

ISR puts high priority

task in READY state

Executing task is interrupted

Interrupted task

is completed

Higher priority task

Is executed

30 CHAPTER 2 Basic concepts

2.4 Scheduling

There are different algorithms that determine which task to execute, called

schedulers. All schedulers have one thing in common: they distinguish between tasks

that are ready to be executed (in the READY state) and other tasks that are sus-

pended for some reason (delay, waiting for mailbox, waiting for semaphore, waiting

for event, and so on). The scheduler selects one of the tasks in the READY state and

activates it (executes the body of this task). The task which is currently executing is

referred to as the running task. The main difference between schedulers is the way

they distribute computation time between tasks in the READY state.

2.4.1 Round-robin scheduling algorithm

With round-robin scheduling, the scheduler has a list of tasks and, when deactivating

the running task, activates the next task that is in the READY state. Round-robin can

be used with either preemptive or cooperative multitasking. It works well if you do

not need to guarantee response time. Round-robin scheduling can be illustrated as

follows:

All tasks share the same priority; the possession of the CPU changes periodically

after a predefined execution time. This time is called a time slice, and may be defined

individually for every task.

2.4.2 Priority-controlled scheduling algorithm

In real-world applications, different tasks require different response times. For exam-

ple, in an application that controls a motor, a keyboard, and a display, the motor usu-

ally requires faster reaction time than the keyboard and display. While the display is

being updated, the motor needs to be controlled. This makes preemptive multitask-

ing essential. Round-robin might work, but because it cannot guarantee a specific

reaction time, an improved algorithm should be used.

In priority-controlled scheduling, every task is assigned a priority. Depending on

these priorities, one task gets chosen for execution according to one simple rule:

Note: The scheduler activates the task that has the highest priority of all

tasks in the READY state.

This means that every time a task with a priority higher than the running task

becomes ready, it immediately becomes the running task, thus the previous task gets

preempted. However, the scheduler can be switched off in sections of a program

where task switches are prohibited, known as critical regions.

embOS uses a priority-controlled scheduling algorithm with round-robin between

tasks of identical priority. One hint at this point: round-robin scheduling is a nice fea-

ture because you do not need to decide whether one task is more important than

another. Tasks with identical priority cannot block each other for longer than their

time slices. But round-robin scheduling also costs time if two or more tasks of identi-

cal priority are ready and no task of higher priority is ready, because execution con-

stantly switch between the identical-priority tasks. It is more efficient to assign a

different priority to each task, which will avoid unnecessary task switches.

2.4.3 Priority inversion / priority inheritance

The rule the scheduler obeys is:

Activate the task that has the highest priority of all tasks in the READY state.

But what happens if the highest-priority task is blocked because it is waiting for a

resource owned by a lower-priority task? According to the above rule, it would wait

until the low-priority task is resumed and releases the resource.

Up to this point, everything works as expected.

Problems arise when a task with medium priority becomes ready during the execu-

tion of the higher prioritized task.

When the higher priority task is suspended waiting for the resource, the task with the

medium priority will run until it finishes its work, because it has a higher priority than

the low-priority task.

In this scenario, a task with medium priority runs in place of the task with high prior-

ity. This is known as priority inversion.

The low priority task claims the semaphore with OS_Use(). An interrupt activates the

high priority task, which also calls OS_Use().

Meanwhile a task with medium priority becomes ready and runs when the high prior-

ity task is suspended.

The task with medium priority eventually calls OS_Delay() and is therefore sus-

pended. The task with lower priority now continues and calls OS_Unuse() to release

the resource semaphore. After the low priority task releases the semaphore, the high

priority task is activated and claims the semaphore.

To avoid this situation, embOS temporarily raises the low-priority task to high priority

until it releases the resource. This unblocks the task that originally had the highest

priority and can now be resumed. This is known as priority inheritance.

Time

Low priority task

OS_Use()

Interrupt activates high prio task

Medium priority task High priority task

With Priority Inversion

OS_Delay()

OS_Unuse()

32 CHAPTER 2 Basic concepts

With priority inheritance, the low priority task inherits the priority of the waiting high

priority task as long as it holds the resource semaphore. The lower priority task is

activated instead of the medium priority task when the high priority task tries to

claim the semaphore.

Time

OS_Use()

OS_Unuse()

Interrupt activates high prio task

OS_Unuse()

Priority inheritance

Low priority task Medium priority task High priority task

With Priority Inheritance

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
33
2.5 Communication between tasks
In a multitasking (multithreaded) program, multiple tasks and ISRs work completely
separately. Because they all work in the same application, it will sometimes be nec-
essary for them to exchange information with each other.
2.5.1 Periodic polling
The easiest way to communicate between different pieces of code is by using global
variables. In certain situations, it can make sense for tasks to communicate via glo-
bal variables, but most of the time this method has disadvantages.
For example, if you want to synchronize a task to start when the value of a global
variable changes, you must continually poll this variable, wasting precious computa-
tion time and energy, and the reaction time depends on how often you poll.
2.5.2 Event-driven communication mechanisms
When multiple tasks work with each other, they often have to:
• exchange data,
• synchronize with another task, or
• make sure that a resource is used by no more than one task at a time.
For these purposes embOS offers mailboxes, queues, semaphores and events.
2.5.3 Mailboxes and queues
A mailbox is a data buffer managed by the RTOS and is used for sending a message
to a task. It works without conflicts even if multiple tasks and interrupts try to access
the same mailbox simultaneously. embOS activates any task that is waiting for a
message in a mailbox the moment it receives new data and, if necessary, switches to
this task.
A queue works in a similar manner, but handles larger messages than mailboxes, and
each message may have an individual size.
For more information, refer to the chapters Mailboxes on page 139 and Queues on
page 159.
2.5.4 Semaphores
Two types of semaphores are used for synchronizing tasks and to manage resources
of any kind. The most common are resource semaphores, although counting sema-
phores are also used. For details and samples, refer to the chapters Resource sema-
phores on page 111 and Counting Semaphores on page 125.
2.5.5 Events
A task can wait for a particular event without consuming any calculation time. The
idea is as simple as it is convincing, there is no sense in polling if we can simply acti-
vate a task the moment the event it is waiting for occurs. This saves processor cycles
and energy and ensures that the task can respond to the event without delay. Typical
applications for events are those where a task waits for some data, a pressed key, a
received command or character, or the pulse of an external real-time clock.
For further details, refer to the chapters Task events on page 177 and Event objects
on page 189.

34 CHAPTER 2 Basic concepts

2.6 How task switching works

A real-time multitasking system lets multiple tasks run like multiple single-task pro-

grams, quasi-simultaneously, on a single CPU. A task consists of three parts in the

multitasking world:

• The program code, which typically resides in ROM

• A stack, residing in a RAM area that can be accessed by the stack pointer

• A task control block, residing in RAM.

The task’s stack has the same function as in a single-task system: storage of return

addresses of function calls, parameters and local variables, and temporary storage of

intermediate results and register values. Each task can have a different stack size.

More information can be found in chapter Stacks on page 229.

The task control block (TCB) is a data structure assigned to a task when it is created.

The TCB contains status information for the task, including the stack pointer, task

priority, current task status (ready, waiting, reason for suspension) and other man-

agement data. Knowledge of the stack pointer allows access to the other registers,

which are typically stored (pushed onto) the stack when the task is created and each

time it is suspended. This information allows an interrupted task to continue execu-

tion exactly where it left off. TCBs are only accessed by the RTOS.

2.6.1 Switching stacks

The following diagram demonstrates the process of switching from one stack to

another.

The scheduler deactivates the task to be suspended (Task 0) by saving the processor

registers on its stack. It then activates the higher-priority task (Task n) by loading

the stack pointer (SP) and the processor registers from the values stored on Task n's

stack.

Deactivating a task

The scheduler deactivates the task to be suspended (Task 0) as follows:

1. Save (push) the processor registers on the task's stack.

2. Save the stack pointer in the Task Control Block.

Activating a task

The scheduler activates the higher-priority task (Task n) by performing the sequence

in reverse order:

1. Load (pop) the stack pointer (SP) from the Task Control Block.

2. Load the processor registers from the values stored on Task n's stack.

Scheduler

CPU

Task 0

Stack

Task Control

block

CPU

registers

Free Stack

area

variables

temp. storage

ret. addresses

Task n

Stack

Task Control

block

CPU

registers

Free Stack

area

variables

temp. storage

ret. addresses

36 CHAPTER 2 Basic concepts

2.7 Change of task status

A task may be in one of several states at any given time. When a task is created, it is

placed into the READY state.

A task in the READY state is activated as soon as there is no other task in the READY

state with higher priority. Only one task may be running at a time. If a task with

higher priority becomes READY, this higher priority task is activated and the pre-

empted task remains in the READY state.

The running task may be delayed for or until a specified time; in this case it is placed

into the WAITING state and the next-highest-priority task in the READY state is acti-

vated.

The running task might need to wait for an event (or semaphore, mailbox or queue).

If the event has not yet occurred, the task is placed into the waiting state and the

next-highest-priority task in the READY state is activated.

A non-existent task is one that is not yet available to embOS; it either has been ter-

minated or was not created at all.

The following illustration shows all possible task states and transitions between

them.

Waiting

Ready Running

Scheduler

Not existing

OS_Terminate()

OS_CreateTask()

OS_CreateTaskEx()

API class such as

OS_Delay()

OS_Wait_...()

API class such as

OS_Signal...() or

delay expiration

2.8 How the OS gains control

When the CPU is reset, the special-function registers are set to their default values.

After reset, program execution begins. The PC register is set to the start address

defined by the start vector or start address (depending on the CPU). This start

address is usually in a startup module shipped with the C compiler, and is sometimes

part of the standard library.

The startup code performs the following:

• Loads the stack pointer(s) with the default values, which is for most CPUs

the end of the defined stack segment(s)

• Initializes all data segments to their respective values

• Calls the main() function.

The main() function is the part of your program which takes control immediately

after the C startup. Normally, embOS works with the standard C startup module with-

out any modification. If there are any changes required, they are documented in the

CPU & Compiler Specifics manual of the embOS documentation.

With embOS, the main() function is still part of your application program. Essentially,

main() creates one or more tasks and then starts multitasking by calling

OS_Start(). From this point, the scheduler controls which task is executed.

The main() function will not be interrupted by any of the created tasks because

those tasks execute only following the call to OS_Start(). It is therefore usually rec-

ommended to create all or most of your tasks here, as well as your control structures

such as mailboxes and semaphores. Good practice is to write software in the form of

modules which are (up to a point) reusable. These modules usually have an initializa-

tion routine, which creates any required task(s) and control structures.

A typical main() function looks similar to the following example:

Example

/**************************************************************************

* main

***************************************************************************

void main(void) {

OS_IncDI();

OS_InitKern(); /* Initialize OS (should be first !) */

OS_InitHW(); /* Initialize Hardware for OS (in RtosInit.c) */

/* Call Init routines of all program modules which in turn will create */

/* the tasks they need ... (Order of creation may be important) */

MODULE1_Init();

MODULE2_Init();

MODULE3_Init();

MODULE4_Init();

MODULE5_Init();

OS_Start(); /* Start multitasking */

}

With the call to OS_Start(), the scheduler starts the highest-priority task created in

main().

Note that OS_Start() is called only once during the startup process and does not

return.

Startup code

main()

OS_IncDI()

OS_InitKern()

OS_InitHW()

Additional initialization code;

creating at least one task.

OS_Start()

38 CHAPTER 2 Basic concepts

2.9 Different builds of embOS

embOS comes in different builds or versions of the libraries. The reason for different

builds is that requirements vary during development. While developing software, the

performance (and resource usage) is not as important as in the final version which

usually goes as release build into the product. But during development, even small

programming errors should be caught by use of assertions. These assertions are

compiled into the debug build of the embOS libraries and make the code a little

bigger (about 50%) and also slightly slower than the release or stack-check build

used for the final product.

This concept gives you the best of both worlds: a compact and very efficient build for

your final product (release or stack-check build of the libraries), and a safer (though

bigger and slower) build for development which will catch most common application

programming errors. Of course, you may also use the release build of embOS during

development, but it will not catch these errors.

2.9.1 Profiling

embOS supports profiling in profiling builds. Profiling makes precise information

available about the execution time of individual tasks. You may always use the profil-

ing libraries, but they require larger task control blocks, additional ROM (approxi-

mately 200 bytes) and additional runtime overhead. This overhead is usually

acceptable, but for best performance you may want to use non-profiling builds of

embOS if you do not use this feature.

2.9.2 List of libraries

In your application program, you need to let the compiler know which build of embOS

you are using. This is done by defining a single identifier prior to including RTOS.h.

Name Define

Debug code

Stack check

Profiling

Trace

Round Robin

Task names

Description

Extreme

Release OS_LIBMODE_XR Smallest fastest build.

Release OS_LIBMODE_R XX

Small, fast build, normally

used for release build of

application.

Stack check OS_LIBMODE_S XXX

Same as release, plus

stack checking.

Stack check

plus profil-

ing

OS_LIBMODE_SP XX XXSame as stack check, plus

profiling.

Debug OS_LIBMODE_D XX XXMaximum runtime check-

ing.

Debug plus

profiling OS_LIBMODE_DP XXX XXMaximum runtime check-

ing, plus profiling.

Debug

including

trace, pro-

filing

OS_LIBMODE_DT XXXXXX

Maximum runtime check-

ing, plus tracing API calls

and profiling.

Table 2.1: List of libraries

2.9.3 embOS functions context

Not all embOS functions can be called from every place in your application. We need

to distinguish between Main (before the call of OS_Start() ), Task, ISR and Software

timer.

Please consult the embOS API tables to be sure that an embOS function is allowed to

be called from your execution context, e.g. from an ISR. The embOS debug build

helps you to check that you do not violate these rules.

40 CHAPTER 2 Basic concepts

Chapter 3

Working with embOS

This chapter gives some recommendations on how to use embOS in your applica-

tions. These are simply recommendations that we feel are helpful when designing

and structuring an application.

42 CHAPTER 3 Working with embOS

3.1 General advice

- Avoid Round Robin if possible

- Avoid dynamically creating and terminating tasks

- Avoid nesting interrupts if possible

3.1.1 Timers or task

For periodic jobs you can use either a task or a software timer. An embOS software

timer has the advantage that it does not need its own task stack since it runs on the

system stack.

Chapter 4

Tasks

This chapter explains some basic concepts related to tasks and embOS task API func-

tions. It should be relatively easy to read and is recommended before moving to

other chapters.

44 CHAPTER 4 Tasks

4.1 Introduction

A task that should run under embOS needs a task control block (TCB), a stack, and a

task body written in C. The following rules apply to task routines:

• The task routine can either not take parameters (void parameter list), in which

case OS_CreateTask() is used to create it, or take a single void pointer as

parameter, in which case OS_CreateTaskEx() is used to create it.

• The task routine must not return.

• The task routine must be implemented as an endless loop or it must terminate

itself (see examples below).

4.1.1 Example of a task routine as an endless loop

/* Example of a task routine as an endless loop */

void Task1(void) {

while(1) {

DoSomething(); /* Do something */

OS_Delay(1); /* Give other tasks a chance */

}

4.1.2 Example of a task routine that terminates itself

/* Example of a task routine that terminates */

void Task2(void) {

char DoSomeMore;

do {

DoSomeMore = DoSomethingElse(); /* Do something */

OS_Delay(1); /* Give other tasks a chance */

} while (DoSomeMore);

OS_TerminateTask(0); /* Terminate yourself */

}

There are different ways to create a task; embOS offers a simple macro that makes

this easy and which is sufficient in most cases. However, if you are dynamically creat-

ing and deleting tasks, a function is available allowing “fine-tuning” of all parame-

ters. For most applications, at least initially, using the macro as in the sample start

project works fine.

4.2 Cooperative vs. preemptive task switches

In general, preemptive task switches are an important feature of an RTOS. Preemp-

tive task switches are required to guarantee responsiveness of high-priority, time-

critical tasks. However, it may be desireable to disable preemptive task switches for

certain tasks in some circumstances. The default behavior of embOS is to always

allow preemptive task switches.

4.2.1 Disabling preemptive task switches for tasks of equal

priority

In some situations, preemptive task switches between tasks running at identical pri-

orities are not desireable. To inhibit time slicing of equal-priority tasks, the time slice

of the tasks running at identical priorities must be set to zero as in the example

below:

#include "RTOS.h"

#define PRIO_COOP 10

#define TIME_SLICE_NULL 0

OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */

OS_TASK TCBHP, TCBLP; /* Task-control-blocks */

/********************************************************************/

static void TaskEx(void * pData) {

while (1) {

OS_Delay ((OS_TIME) pData);

}

/*********************************************************************

* main

*********************************************************************/

int main(void) {

OS_IncDI(); /* Initially disable interrupts */

OS_InitKern(); /* initialize OS */

OS_InitHW(); /* initialize Hardware for OS */

/* You need to create at least one task before calling OS_Start() */

OS_CreateTaskEx(&TCBHP, "HP Task", PRIO_COOP, TaskEx, StackHP,

sizeof(StackHP), TIME_SLICE_NULL, (void*) 50);

OS_CreateTaskEx(&TCBLP, "LP Task", PRIO_COOP, TaskEx, StackLP,

sizeof(StackLP), TIME_SLICE_NULL, (void*) 200);

OS_Start(); /* Start multitasking */

return 0;

}

4.2.2 Completely disabling preemptions for a task

This is simple: The first line of code should be OS_EnterRegion() as shown in the

following sample:

void MyTask(void *pContext) {

OS_EnterRegion(); /* Disable preemptive context switches */

while (1) {

// Do something. In the code, make sure that you call a blocking

// funtion periodically to give other tasks a chance to run.

}

Note: This will entirely disable preemptive context switches from that particular

task and will therefore affect the timing of higher-priority-tasks. Do not use this

carelessly.

46 CHAPTER 4 Tasks

4.3 Extending the task context

For some applications it might be useful or required to have individual data in tasks

that are unique to the task.

Local variables, declared in the task, are unique to the task and remain valid, even

when the task is suspended and resumed again.

When the same task function is used for multiple tasks, local variables in the task

may be used, but cannot be initialized individually for every task.

embOS offers different options to extend the task context.

4.3.1 Passing one parameter to a task during task creation

Very often it is sufficient to have just one individual parameter passed to a task.

Using the OS_CREATETASK_EX() or OS_CreateTaskEx() function to create a task

allows passing a void-pointer to the task. The pointer may point to individual data, or

may represent any data type that can be held within a pointer.

4.3.2 Extending the task context individually at runtime

Sometimes it may be required to have an extended task context for individual tasks

to store global data or special CPU registers such as floating-point registers in the

task context.

The standard libraries for file I/O, locale support and others may require task-local

storage for specific data like errno and other variables.

embOS enables extension of the task context for individual tasks during runtime by a

call of OS_ExtendTaskContext().

The sample application file ExtendTaskContext.c delivered in the application sam-

ples folder of embOS demonstrates how the individual task context extension can be

used.

4.3.3 Extending the task context by using own task structures

When complex data is needed for an individual task context, the

OS_CREATETASK_EX() or OS_CreateTaskEx() functions may be used, passing a

pointer to individual data structures to the task.

Alternatively you may define your own task structure which can be used.

Note, that the first item in the task structure must be an embOS task control struc-

ture OS_TASK. This can be followed by any amount and type of additional data of dif-

ferent types.

The following code shows the example application Start_Extended_OS_TASK.c which

is delivered in the sample application folder of embOS.

/*********************************************************************

* SEGGER MICROCONTROLLER GmbH & Co KG *

* Solutions for real time microcontroller applications *

**********************************************************************

----------------------------------------------------------------------

File : Start_Extended_OS_TASK.c

Purpose : Skeleton program for OS to demonstrate extended tasks

-------- END-OF-HEADER ---------------------------------------------

#include "RTOS.h"

#include <stdio.h>

/****** Define an own task structure with extended task context *****/

typedef struct {

OS_TASK Task; // OS_TASK must be the first element

OS_TIME Timeout; // Any other data may follow

char* pString;

} MY_APP_TASK;

/****** Variables ***************************************************/

OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */

MY_APP_TASK TCBHP, TCBLP; /* Task-control-blocks */

/*********************************************************************

* Task function

static void MyTask(void) {

char* pString;

OS_TIME Delay;

MY_APP_TASK* pThis;

pThis = (MY_APP_TASK*) OS_GetTaskID();

while (1) {

Delay = pThis->Timeout;

pString = pThis->pString;

printf(pString);

OS_Delay (Delay);

}

/***********************************************************************

* main

***********************************************************************/

int main(void) {

OS_IncDI(); /* Initially disable interrupts */

OS_InitKern(); /* Initialize OS */

OS_InitHW(); /* Initialize Hardware for OS */

* Create the extended tasks just as normal tasks.

* Note that the first paramater must be of type OS_TASK

OS_CREATETASK(&TCBHP.Task, "HP Task", MyTask, 100, StackHP);

OS_CREATETASK(&TCBLP.Task, "LP Task", MyTask, 50, StackLP);

* Give task contexts individual data

TCBHP.Timeout = 200;

TCBHP.pString = "HP task running\n";

TCBLP.Timeout = 500;

TCBLP.pString = "LP task running\n";

OS_Start(); /* Start multitasking */

return 0;

}

48 CHAPTER 4 Tasks
UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
4.4 API functions
Routine Description
main
Task
ISR
Timer
OS_AddOnTerminateHook()
Adds a hook (callback) function to the 
list of functions which are called when 
a task is terminated.
XX
OS_CREATETASK() Creates a task. X X
OS_CreateTask() Creates a task. X X
OS_CREATETASK_EX() Creates a task with parameter. X X
OS_CreateTaskEx() Creates a task with parameter. X X
OS_Delay() Suspends the calling task for a speci-
fied period of time. XX
OS_DelayUntil() Suspends the calling task until a spec-
ified time. XX
OS_Delayus() Waits for the given time in microsec-
onds XX
OS_ExtendTaskContext() Make global variables or processor 
registers task-specific. XX
OS_GetpCurrentTask()
Returns a pointer to the task control 
block structure of the currently run-
ning task.
XXXX
OS_GetPriority() Returns the priority of a specified task X X X X
OS_GetSuspendCnt() Returns the suspension count. X X X X
OS_GetTaskID() Returns the ID of the currently run-
ning task. XXXX
OS_GetTaskName() Returns the name of a task. X X X X
OS_GetTimeSliceRem() Returns the remaining time slice time 
of a task. XXXX
OS_IsRunning() Exxamine whether OS_Start() was 
called. XXXX
OS_IsTask() Determines whether a task control 
block actually belongs to a valid task. XXXX
OS_Resume()
Decrements the suspend count of 
specified task and resumes the task, if 
the suspend count reaches zero.
XX
OS_ResumeAllSuspendedTasks()
Decrements the suspend count of 
specified task and resumes the task, if 
the suspend count reaches zero.
XX
OS_SetInitialSuspendCnt() Sets an initial suspension count for 
newly created tasks. XXXX
OS_SetPriority() Assigns a specified priority to a speci-
fied task. XX
OS_SetTaskName() Allows modification of a task name at 
runtime. XXXX
OS_SetTimeSlice() Assigns a specified time slice value to 
a specified task. XXXX
OS_Start() Start the embOS kernel. X
OS_Suspend() Suspends the specified task and incre-
ments a counter. X
OS_SuspendAllTasks() Suspends all tasks except the running 
task. XXXX
Table 4.1: Task routine API list

OS_TerminateTask() Ends (terminates) a task. X X

OS_WakeTask() Ends delay of a task immediately. X X X

OS_Yield() Calls the scheduler to force a task

switch. X

Routine Description

main

Task

ISR

Timer

Table 4.1: Task routine API list

50 CHAPTER 4 Tasks

4.4.1 OS_AddOnTerminateHook()

Description

Adds a handler function to a list of functions that are called when a task is termi-

nated.

Prototype

void OS_AddOnTerminateHook (OS_ON_TERMINATE_HOOK * pHook,

OS_ON_TERMINATE_FUNC * pfUser);

Additional Information

For some applications, it may be useful to allocate memory or objects specific to

tasks. For other applications, it may be useful to have task-specific information on

the stack.

When a task is terminated, the task-specific objects may become invalid.

A callback function may be hooked into OS_TerminateTask() by calling

OS_AddOnTerminateHook() to allow the application to invalidate all task-specific

objects before the task is terminated.

The callback function of type OS_ON_TERMINATE_FUNC receives the ID of the termi-

nated task as its parameter.

OS_ON_TERMINATE_FUNC is defined as:

typedef void OS_ON_TERMINATE_FUNC(OS_CONST_PTR OS_TASK * pTask);

Important

The variable of type OS_ON_TERMINATE_HOOK must reside in memory as a global or

static variable. It may be located on a task stack, as local variable, but it must not

be located on any stack of any task that might be terminated.

Example

OS_ON_TERMINATE_HOOK _OnTerminateHook; /* Stack-space */

...

void OnTerminateHookFunc(OS_CONST_PTR OS_TASK * pTask) {

// This function is called when OS_TerminateTask() is called.

if (pTask == &MyTask) {

free(MytaskBuffer);

}

...

main(void) {

OS_AddOnTerminateHook(&_OnTerminateHook, OnTerminateHookFunc);

...

}

Parameter Description

pHook

Pointer to a variable of type OS_ON_TERMINATE_HOOK which will

be inserted into the linked list of functions to be called during

OS_TerminateTask().

pfUser Pointer to the function of type OS_TERMINATE_FUNC which shall

be called when a task is terminated.

Table 4.2: OS_AddOnTerminateHook() parameter list

4.4.2 OS_CREATETASK()

Description

Creates a task.

Prototype

void OS_CREATETASK ( OS_TASK * pTask,

char * pName,

void * pRoutine,

OS_PRIO Priority,

void * pStack);

Additional Information

OS_CREATETASK() is a macro which calls an OS library function. It creates a task and

makes it ready for execution by placing it into the READY state. The newly created

task will be activated by the scheduler as soon as there is no other task with higher

priority in the READY state. If there is another task with the same priority, the new

task will be placed immediately before it. This macro is normally used for creating a

task instead of the function call OS_CreateTask() because it has fewer parameters

and is therefore easier to use.

OS_CREATETASK() can be called either from main() during initialization or from any

other task. The recommended strategy is to create all tasks during initialization in

main() to keep the structure of your tasks easy to understand.

The absolute value of Priority is of no importance, only the value in comparison to

the priorities of other tasks matters.

OS_CREATETASK() determines the size of the stack automatically, using sizeof().

This is possible only if the memory area has been defined at compile time.

Important

The stack that you define must reside in an area that the CPU can address as stack.

Most CPUs cannot use the entire memory area as stack and require the stack to be

aligned to a multiple of the processor word size.

The task stack cannot be shared between multiple tasks and must be assigned to one

task only. The memory used as task stack cannot be used for other purposes unless

the task is terminated.

Parameter Description

pTask Pointer to a task control block structure.

pName Pointer to the name of the task. Can be NULL (or 0) if not used.

pRoutine Pointer to a function that should run as the task body.

Priority

Priority of the task. Must be within the following range:

1 <= Priority <= 28-1 = 0xFF for 8/16-bit CPUs

1 <= Priority <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Higher values indicate higher priorities.

The type OS_PRIO is defined as 32-bit value for 32-bit CPUs and

8-bit value for 8- or 16-bit CPUs by default.

pStack

Pointer to an area of memory in RAM that will serve as stack area

for the task. The size of this block of memory determines the size

of the stack area.

Table 4.3: OS_CREATETASK() parameter list

52 CHAPTER 4 Tasks

Example

OS_STACKPTR int UserStack[150]; /* Stack-space */

OS_TASK UserTCB; /* Task-control-blocks */

void UserTask(void) {

while (1) {

Delay (100);

}

void InitTask(void) {

OS_CREATETASK(&UserTCB, "UserTask", UserTask, 100, UserStack);

}

4.4.3 OS_CreateTask()

Description

Creates a task.

Prototype

void OS_CreateTask ( OS_TASK * pTask,

char * pName,

OS_PRIO Priority,

voidRoutine * pRoutine,

void * pStack,

unsigned StackSize,

unsigned char TimeSlice );

Additional Information

This function works the same way as OS_CREATETASK(), except that all parameters of

the task can be specified.

The task can be dynamically created because the stack size is not calculated auto-

matically as it is with the macro.

A time slice value of zero is allowed and disables round-robin task switches (see

sample in chapter Disabling preemptive task switches for tasks of equal priority on

page 45).

Important

The stack that you define must reside in an area that the CPU can address as stack.

Most CPUs cannot use the entire memory area as stack and require the stack to be

aligned to a multiple of the processor word size.

The task stack cannot be shared between multiple tasks and must be assigned to one

task only. The memory used as task stack cannot be used for other purposes unless

the task is terminated.

Parameter Description

pTask Pointer to a task control block structure.

pName Pointer to the name of the task. Can be NULL (or 0) if not used.

Priority

Priority of the task. Must be within the following range:

1 <= Priority <= 28-1 = 0xFF for 8/16-bit CPUs

1 <= Priority <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Higher values indicate higher priorities.

The type OS_PRIO is defined as a 32-bit value for 32-bit CPUs and

as an 8-bit value for 8- or 16-bit CPUs by default.

pRoutine Pointer to a function that should run as the task body.

pStack

Pointer to an area of memory in RAM that will serve as stack area

for the task. The size of this block of memory determines the size

of the stack area.

StackSize Size of the stack in bytes.

TimeSlice

Time slice value for round-robin scheduling. Has an effect only if

other tasks are running at the same priority. TimeSlice denotes

the time in embOS timer ticks that the task will run before it sus-

pends, thus enabling another task with the same priority.

The time slice value must be in the following range:

0 <= TimeSlice <= 255.

Table 4.4: OS_CreateTask() parameter list

54 CHAPTER 4 Tasks

Example

/* Demo-program to illustrate the use of OS_CreateTask */

OS_STACKPTR int StackMain[100], StackClock[50];

OS_TASK TaskMain,TaskClock;

OS_SEMA SemaLCD;

void Clock(void) {

while(1) {

/* Code to update the clock */

}

void Main(void) {

while (1) {

/* Your code */

}

void InitTask(void) {

OS_CreateTask(&TaskMain, NULL, 50, Main, StackMain, sizeof(StackMain), 2);

OS_CreateTask(&TaskClock, NULL, 100, Clock,StackClock,sizeof(StackClock),2);

}

4.4.4 OS_CREATETASK_EX()

Description

Creates a task and passes a parameter to the task.

Prototype

void OS_CREATETASK_EX ( OS_TASK * pTask,

char * pName,

void * pRoutine,

OS_PRIO Priority,

void * pStack,

void * pContext );

Additional Information

OS_CREATETASK_EX() is a macro calling an embOS library function. It works like

OS_CREATETASK() but allows passing a parameter to the task.

Using a void pointer as an additional parameter gives the flexibility to pass any kind

of data to the task function.

Example

The following example is delivered in the Samples folder of embOS.

Parameter Description

pTask Pointer to a task control block structure.

pName Pointer to the name of the task. Can be NULL (or 0) if not used.

pRoutine Pointer to a function that should run as the task body.

Priority

Priority of the task. Must be within the following range:

1 <= Priority <= 28-1 = 0xFF for 8/16-bit CPUs

1 <= Priority <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Higher values indicate higher priorities.

The type OS_PRIO is defined as a 32-bit value for 32-bit CPUs and

an 8-bit value for 8- or 16-bit CPUs per default.

pStack

Pointer to an area of memory in RAM that will serve as stack area

for the task. The size of this block of memory determines the size

of the stack area.

pContext Parameter passed to the created task function.

Table 4.5: OS_CREATETASK_EX() parameter list

56 CHAPTER 4 Tasks

/*------------------------------------------------------------------

File : Main_TaskEx.c

Purpose : Sample program for embOS using OC_CREATETASK_EX

--------- END-OF-HEADER --------------------------------------------*/

#include "RTOS.h"

OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */

OS_TASK TCBHP, TCBLP; /* Task-control-blocks */

/********************************************************************/

static void TaskEx(void* pVoid) {

while (1) {

OS_Delay ((OS_TIME) pVoid);

}

/*********************************************************************

* main

*********************************************************************/

int main(void) {

OS_IncDI(); /* Initially disable interrupts */

OS_InitKern(); /* initialize OS */

OS_InitHW(); /* initialize Hardware for OS */

/* You need to create at least one task before calling OS_Start() */

OS_CREATETASK_EX(&TCBHP, "HP Task", TaskEx, 100, StackHP, (void*) 50);

OS_CREATETASK_EX(&TCBLP, "LP Task", TaskEx, 50, StackLP, (void*) 200);

OS_SendString("Start project will start multitasking !\n");

OS_Start(); /* Start multitasking */

return 0;

}

4.4.5 OS_CreateTaskEx()

Description

Creates a task and passes a parameter to the task.

Prototype

void OS_CreateTaskEx ( OS_TASK * pTask,

char * pName,

OS_PRIO Priority,

voidRoutine * pRoutine,

void * pStack,

unsigned StackSize,

unsigned char TimeSlice,

void * pContext );

Additional Information

This function works the same way as OS_CreateTask() except that a parameter is

passed to the task function.

An example of parameter passing to tasks is shown under OS_CREATETASK_EX().

A time slice value of zero is allowed and disables round-robin task switches (see

sample in chapter Disabling preemptive task switches for tasks of equal priority on

page 45).

Important

The stack that you define must reside in an area that the CPU can address as stack.

Most CPUs cannot use the entire memory area as stack and require the stack to be

aligned to a multiple of the processor word size.

The task stack cannot be shared between multiple tasks and must be assigned to one

task only. The memory used as task stack cannot be used for other purposes unless

the task is terminated.

Parameter Description

pTask Pointer to a task control block structure.

pName Pointer to the name of the task. Can be NULL (or 0) if not used.

Priority

Priority of the task. Must be within the following range:

1 <= Priority <= 28-1 = 0xFF for 8/16-bit CPUs

1 <= Priority <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Higher values indicate higher priorities.

The type OS_PRIO is defined as a 32-bit value for 32-bit CPUs and

an 8-bit value for 8- or 16-bit CPUs per default.

pRoutine Pointer to a function that should run as the task body.

pStack

Pointer to an area of memory in RAM that will serve as stack area

for the task. The size of this block of memory determines the size

of the stack area.

StackSize Size of the stack in bytes.

TimeSlice

Time slice value for round-robin scheduling. Has an effect only if

other tasks are running at the same priority. TimeSlice denotes

the time in embOS timer ticks that the task will run until it sus-

pends; thus enabling another task with the same priority.

The time slice value must be in the following range:

0 <= TimeSlice <= 255.

pContext Parameter passed to the created task.

Table 4.6: OS_Create_TaskEx() parameter list

58 CHAPTER 4 Tasks

4.4.6 OS_Delay()

Description

Suspends the calling task for a specified period of time.

Prototype

void OS_Delay (OS_TIME ms);

Additional Information

The calling task is placed into the WAITING state for the period of time specified. The

task will stay in the delayed state until the specified time has expired. OS_Delay()

returns immediately if the parameter ms is less than or equal to zero. The parameter ms

specifies the precise interval during which the task is suspended given in basic time

intervals (usually 1/1000 seconds). The actual delay (in basic time intervals) will be

in the following range: ms - 1 <= delay <= ms, depending on when the interrupt for

the scheduler occurs.

After the expiration of the delay, the task is made ready and activated according to

the rules of the scheduler. A delay can be ended prematurely by another task or by

an interrupt handler calling OS_WakeTask().

Example

void Hello(void) {

printf("Hello");

printf("The next output will occur in 5 seconds");

OS_Delay (5000);

printf("Delay is over");

}

Parameter Description

Time interval to delay. Must be within the following range:

215 = 0x8000 <= ms <= 215-1 = 0x7FFF for 8/16-bit CPUs

231 = 0x80000000 <= ms <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Please note that these are signed values.

Table 4.7: OS_Delay() parameter list

4.4.7 OS_DelayUntil()

Description

Suspends the calling task until a specified time.

Prototype

void OS_DelayUntil (OS_TIME t);

Additional Information

The calling task will be put into the WAITING state until the time specified.

The OS_DelayUntil() function delays until the value of the time-variable OS_Time

reaches a certain value. It is very useful to avoid accumulating delays.

An embOS SysTick timer overflow is no problem as long as parameter t is within the

specified range.

Example

int sec,min;

void TaskShowTime(void) {

OS_TIME t0;

t0 = OS_GetTime();

while (1) {

ShowTime(); /* Routine to display time */

t0 += 1000;

OS_DelayUntil (t0);

if (sec < 59) {

sec++;

} else {

sec = 0;

min++;

}

In the example above, using OS_Delay() could lead to accumulating delays and

would cause the simple “clock” to be slow.

Parameter Description

Time to delay until. Must be within the following range:

0 <= t <= 216-1 = 0xFFFF = 65535 for 8/16-bit CPUs

0 <= t <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

and must meet the following additional condition

1 <= ( t - OS_Time) <= 215-1 = 0x7FFF = 32767 for 8/16-bit

CPUs

1 <= ( t- OS_Time) <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 4.8: OS_DelayUntil() parameter list

60 CHAPTER 4 Tasks

4.4.8 OS_Delayus()

Description

Waits for the given time in microseconds.

Prototype

void OS_Delayus (OS_U16 us);

Additional Information

This function can be used for short delays.

OS_Delayus() must only be called with interrupts enabled and after OS_InitKern()

and OS_InitHW() have been called. This only works when the embOS system timer is

running. The embOS debug build of OS_Delayus() checks that interrupts are

enabled, and if not then OS_Error() is called.

OS_Delayus() does not block task switches and does not block interrupts. Therefore,

the delay may not be accurate because the function may be interrupted for an unde-

fined time. The delay duration therefore is a minimum delay.

Example

void Hello(void) {

printf("Hello");

printf("The next output will occur in 500 microseconds");

OS_Delayus (500);

printf("Delay is over");

}

Parameter Description

Number of microseconds to delay. Must be within the following

range:

1 <= us <= 215-1 = 0x7FFF = 32767

Table 4.9: OS_Delay() parameter list

4.4.9 OS_ExtendTaskContext()

Description

The function may be used for a variety of purposes. Typical applications are:

• global variables such as “errno” in the C library, making the C-lib functions

thread-safe.

• additional, optional CPU / registers such as MAC / EMAC registers (multiply and

accumulate unit) if they are not saved in the task context per default.

• Coprocessor registers such as registers of a VFP (floating-point coprocessor).

• Data registers of an additional hardware unit such as a CRC calculation unit

This allows the user to extend the task context as required. A major advantage is

that the task extension is task-specific. This means that the additional information

(such as floating-point registers) needs to be saved only by tasks that actually use

these registers. The advantage is that the task switching time of other tasks is not

affected. The same is true for the required stack space: Additional stack space is

required only for the tasks which actually save the additional registers.

Prototype

void OS_ExtendTaskContext(const OS_EXTEND_TASK_CONTEXT * pExtendContext);

Additional Information

The OS_EXTEND_TASK_CONTEXT structure is defined as follows:

typedef struct OS_EXTEND_TASK_CONTEXT {

void (*pfSave) ( void * pStack);

void (*pfRestore)(const void * pStack);

} OS_EXTEND_TASK_CONTEXT;

The save and restore functions must be declared according the function type used in

the structure. The sample below shows how the task stack must be addressed to

save and restore the extended task context.

OS_ExtendTaskContext() is not available in the XR libraries.

Important

The task context can be extended only once per task. The function must not be called

multple times for one task.

Note that some ports of embOS use the mechanism of extending the task context for

individual tasks for CPU or compiler-specific purposes such as storing floating-point

registers or deliver a thread-local storage. In this case, the user cannot extend the

task context using OS_ExtendTaskContext(). Extended tasks created by

OS_CREATETASK_EX() or OS_CreateTaskEx() can still be used.

Parameter Description

pExtendContext

Pointer to the OS_EXTEND_TASK_CONTEXT structure which contains

the addresses of the specific save and restore functions that save

and restore the extended task context during task switches.

Table 4.10: OS_ExtendTaskContext() parameter list

62 CHAPTER 4 Tasks

Example

The following example is delivered in the Samples folder of embOS.

/*--------------------------------------------------------------------

File : ExtendTaskContext.c

Purpose : Sample program for embOS demonstrating how to dynamically

extend the task context.

This example adds a global variable to the task context of

certain tasks.

-------- END-OF-HEADER -----------------------------------------------

#include "RTOS.h"

OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */

OS_TASK TCBHP, TCBLP; /* Task-control-blocks */

int GlobalVar;

/*********************************************************************

* _Restore

* _Save

* Function description

* This function pair saves and restores an extended task context.

* In this case, the extended task context consists of just a single

* member, which is a global variable.

typedef struct {

int GlobalVar;

} CONTEXT_EXTENSION;

static void _Save(void * pStack) {

CONTEXT_EXTENSION * p;

p = ((CONTEXT_EXTENSION*)pStack) - (1 - OS_STACK_AT_BOTTOM); // Create pointer

// Save all members of the structure

p->GlobalVar = GlobalVar;

}

static void _Restore(const void * pStack) {

CONTEXT_EXTENSION * p;

p = ((CONTEXT_EXTENSION*)pStack) - (1 - OS_STACK_AT_BOTTOM); // Create pointer

// Restore all members of the structure

GlobalVar = p->GlobalVar;

}

/*********************************************************************

* Global variable which holds the function pointers

* to save and restore the task context.

const OS_EXTEND_TASK_CONTEXT _SaveRestore = {

_Save,

_Restore

};

/********************************************************************/

/*********************************************************************

* HPTask

* Function description

* During the execution of this function, the thread-specific

* global variable has always the same value of 1.

static void HPTask(void) {

OS_ExtendTaskContext(&_SaveRestore);

GlobalVar = 1;

while (1) {

OS_Delay(10);

}

/*********************************************************************

* LPTask

* Function description

* During the execution of this function, the thread-specific

* global variable has always the same value of 2.

static void LPTask(void) {

OS_ExtendTaskContext(&_SaveRestore);

GlobalVar = 2;

while (1) {

OS_Delay(50);

}

/*********************************************************************

* main

int main(void) {

OS_IncDI(); /* Initially disable interrupts */

OS_InitKern(); /* initialize OS */

OS_InitHW(); /* initialize Hardware for OS */

/* You need to create at least one task here ! */

OS_CREATETASK(&TCBHP, "HP Task", HPTask, 100, StackHP);

OS_CREATETASK(&TCBLP, "LP Task", LPTask, 50, StackLP);

OS_Start(); /* Start multitasking */

return 0;

}

64 CHAPTER 4 Tasks

4.4.10 OS_GetpCurrentTask()

Description

Returns a pointer to the task control block structure of the running task.

Prototype

OS_TASK* OS_GetpCurrentTask (void);

Return value

A pointer to the task control block structure.

Additional Information

This function may be used for determining which task is executing. This may be help-

ful if the reaction of any function depends on the currently running task.

4.4.11 OS_GetPriority()

Description

Returns the priority of a specified task.

Prototype

OS_PRIO OS_GetPriority (const OS_TASK* pTask);

Return value

Priority of the specified task (range 1 to 255).

Additional Information

If pTask is NULL, the function returns the priority of the currently running task. If

pTask does not specify a valid task, the debug build of embOS calls OS_Error(). The

release build of embOS cannot check the validity of pTask and may therefore return

invalid values if pTask does not specify a valid task.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.11: OS_GetPriority() parameter list

66 CHAPTER 4 Tasks

4.4.12 OS_GetSuspendCnt()

Description

The function returns the suspension count and thus suspension state of the specified

task. This function may be used to examine whether a task is suspended by previous

calls of OS_Suspend().

Prototype

unsigned char OS_GetSuspendCnt (const OS_TASK* pTask);

Return value

Suspension count of the specified task.

0: Task is not suspended.

>0: Task is suspended by at least one call of OS_Suspend().

Additional Information

If pTask does not specify a valid task, the debug build of embOS calls OS_Error().

The release build of embOS cannot check the validity of pTask and may therefore

return invalid values if pTask does not specify a valid task. When tasks are created

and terminated dynamically, OS_IsTask() may be called prior to calling

OS_GetSuspendCnt() to determine whether a task is valid. The returned value can be

used to resume a suspended task by calling OS_Resume() as often as indicated by the

returned value.

Example

/* Demo-function to illustrate the use of OS_GetSuspendCnt() */

void ResumeTask(OS_TASK* pTask) {

unsigned char SuspendCnt;

SuspendCnt = OS_GetSuspendCnt(pTask);

while (SuspendCnt > 0) {

OS_Resume(pTask); /* May cause a task switch */

SuspendCnt--;

}

Parameter Description

pTask Pointer to a task control block structure.

Table 4.12: OS_GetSuspendCnt() parameter list

4.4.13 OS_GetTaskID()

Description

Returns a pointer to the task control block structure of the currently running task.

This pointer is unique for the task and is used as a task Id.

Prototype

OS_TASK * OS_GetTaskID ( void );

Return value

A pointer to the task control block. A value of 0 (NULL) indicates that no task is exe-

cuting.

Additional Information

This function may be used for determining which task is executing. This may be help-

ful if the reaction of any function depends on the currently running task.

68 CHAPTER 4 Tasks

4.4.14 OS_GetTaskName()

Description

Returns a pointer to the name of a task.

Prototype

const char* OS_GetTaskName(const OS_TASK* pTask);

Return value

A pointer to the name of the task. A value of 0 (NULL) indicates that the task has no

name.

Additional Information

If pTask is NULL, the function returns the name of the running task. If not called from

a task with a NULL pointer as parameter, the return value is “OS_Idle()”. If pTask

does not specify a valid task, the debug build of embOS calls OS_Error(). The

release build of embOS cannot check the validity of pTask and may therefore return

invalid values if pTask does not specify a valid task.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.13: OS_GetTaskName() parameter list

4.4.15 OS_GetTimeSliceRem()

Description

Returns the remaining time slice value of a task.

Prototype

unsigned char OS_GetTimeSliceRem(const OS_TASK* pTask);

Return value

The remaining time slice value of the task.

Additional Information

If pTask is NULL, the function returns the remaining time slice of the running task. If

not called from a task with a NULL pointer as parameter, or if pTask does not specify

a valid task, the debug build of embOS calls OS_Error(). The release build of embOS

cannot check the validity of pTask and may therefore return invalid values if pTask

does not specify a valid task.

The function is unavailable when using an embOS build without round-robin support.

The embOS eXtreme release libraries do not support round robin. Furthermore, when

embOS is recompiled with OS_RR_SUPPORTED set to 0, the function will not be avail-

able.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.14: OS_GetTimeSliceRem() parameter list

70 CHAPTER 4 Tasks

4.4.16 OS_IsRunning()

Description

Determines whether the embOS scheduler was started by a call of OS_Start().

Prototype

unsigned char OS_IsRunning (void);

Return value

Character value:

0: Scheduler is not started.

!=0: Scheduler is running, OS_Start() has been called.

Additional Information

This function may be helpful for some functions which might be called from main() or

from running tasks.

As long as the scheduler is not started and a function is called from main(), blocking

task switches are not allowed.

A function which may be called from a task or main() may use OS_IsRunning() to

determine whether a blocking task switch is allowed.

4.4.17 OS_IsTask()

Description

Determines whether a task control block belongs to a valid task.

Prototype

char OS_IsTask (const OS_TASK* pTask);

Return value

Character value:

0: TCB is not used by any task

1: TCB is used by a task

Additional Information

This function checks if the specified task is present in the internal task list. When a

task is terminated it is removed from the internal task list.

In applications that create and terminate tasks dynamically, this function may be

useful to determine whether the task control block and stack for one task may be

reused for another task.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.15: OS_IsTask() parameter list

72 CHAPTER 4 Tasks

4.4.18 OS_Resume()

Description

Decrements the suspend count of the specified task and resumes it if the suspend

count reaches zero.

Prototype

void OS_Resume (OS_TASK* pTask);

Additional Information

The specified task's suspend count is decremented. When the resulting value is zero,

the execution of the specified task is resumed.

If the task is not blocked by other task blocking mechanisms, the task is placed in

the READY state and continues operation according to the rules of the scheduler.

In debug builds of embOS, OS_Resume() checks the suspend count of the specified

task. If the suspend count is zero when OS_Resume() is called, OS_Error() is called

with error OS_ERR_RESUME_BEFORE_SUSPEND.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.16: OS_Resume() parameter list

4.4.19 OS_ResumeAllSuspendedTasks()

Description

Decrements the suspend count of all tasks that have a nonzero suspend count and

resumes these tasks when their respective suspend count reaches zero.

Prototype

void OS_ResumeAllSuspendedTasks (void);

Additional Information

This function may be helpful to synchronize or start multiple tasks at the same time.

The function resumes all tasks, no specific task must be addressed.

The function may be used together with the functions OS_SuspendAllTasks() and

OS_SetInitialSuspendCnt().

The function may cause a task switch when a task with higher priority than the call-

ing task is resumed. The task switch will be executed after all suspended tasks are

resumed.

As this is a non-blocking function, the function may be called from all contexts, main,

ISR or timer.

The function may be called even if no task is suspended.

74 CHAPTER 4 Tasks

4.4.20 OS_SetInitialSuspendCnt()

Description

Sets the initial suspend count for newly created tasks to one. May be used to create

tasks which are initially suspended.

Prototype

void OS_SetInitialSuspendCnt (unsigned char SuspendCnt);

Additional Information

Can be called at any time from main(), any task, ISR or software timer.

After calling this function with nonzero SuspendCnt, all newly created tasks will be

automatically suspended with a suspend count of one.

This function may be used to inhibit further task switches, which may be useful dur-

ing system initailization.

Important

When this function is called from main() to initialize all tasks in suspended state, at

least one task must be resumed before the system is started by a call of OS_Start().

The initial suspend count should be reset to allow normal creation of tasks before the

system is started.

Example

/* Sample to demonstrate the use of OS_SetInitialSuspendCnt */

void InitTask(void) {

// High priority task started first after OS_Start().

OS_SuspendAllTasks(); // Ensure no other existing task can run.

OS_SetInitialSuspendCnt(1); // Ensure no newly created task will run.

// Perform application initialization.

... // New tasks may be created but cannot start.

... // Even when InitTask() blocks itself by a delay, no other task will run.

OS_SetInitialSuspendCnt(0); // Reset the initial suspend count for tasks.

// Resume all tasks that were blocked before or were created in suspended state.

OS_ResumeAllSuspendedTasks();

while (1) {

... // Do the normal work.

}

Parameter Description

SuspendCnt != 0: Tasks will be created in suspended state.

= 0: Tasks will be created normally without suspension.

Table 4.17: OS_SetInitialSuspendCnt() parameter list

4.4.21 OS_SetPriority()

Description

Assigns a priority to a specified task.

Prototype

void OS_SetPriority (OS_TASK* pTask,

OS_PRIO Priority);

Additional Information

Can be called at any time from any task or software timer. Calling this function might

lead to an immediate task switch.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pTask Pointer to a task control block structure.

Priority

Priority of the task. Must be within the following range:

1 <= Priority <= 28-1 = 0xFF for 8/16-bit CPUs

1 <= Priority <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Higher values indicate higher priorities.

The type OS_PRIO is defined as 32-bit value for 32-bit CPUs and

8-bit value for 8- or 16-bit CPUs per default.

Table 4.18: OS_SetPriority() parameter list

76 CHAPTER 4 Tasks

4.4.22 OS_SetTaskName()

Description

Allows modification of a task name at runtime.

Prototype

void OS_SetTaskName (OS_TASK* pTask,

const char* s);

Additional Information

Can be called at any time from any task or software timer.

When pTask is NULL, the name of the currently running task is modified.

Parameter Description

pTask Pointer to a task control block structure.

sPointer to a zero terminated string which is used as task name.

Table 4.19: OS_SetTaskName() parameter list

4.4.23 OS_SetTimeSlice()

Description

Assigns a time slice period to a specified task.

Prototype

unsigned char OS_SetTimeSlice (OS_TASK* pTask,

unsigned char TimeSlice);

Return value

Previous time slice period of the task.

Additional Information

Can be called at any time from any task or software timer. Setting the time slice

period only affects tasks running in round-robin mode. This means another task with

the same priority must exist.

The new time slice period is interpreted as a reload value. It is used after the next

activation of the task. It does not affect the remaining time slice of a running task.

A time slice value of zero is allowed, but disables round-robin task switches (see Dis-

abling preemptive task switches for tasks of equal priority on page 45).

Parameter Description

pTask Pointer to a task control block structure.

TimeSlice

New time slice period for the task. Must be within the following

range:

0 <= TimeSlice <= 255.

Table 4.20: OS_SetTimeSlice() parameter list

78 CHAPTER 4 Tasks

4.4.24 OS_Start()

Description

Starts the embOS scheduler.

Prototype

void OS_Start (void);

Additional Information

This function starts the embOS scheduler and should be the last function called from

main().

•OS_Start() marks embOS as running. The running state can be examined by a

call of the function OS_IsRunning().

•OS_Start() will activate and start the task with the highest priority.

•OS_Start() automatically enables interrupts.

•OS_Start() does not return.

•OS_Start() must not be called from a task, from an interrupt or an embOS

timer, and must be called from main() only once.

4.4.25 OS_Suspend()

Description

Suspends the specified task.

Prototype

void OS_Suspend (OS_TASK* pTask);

Additional Information

If pTask is NULL, the current task suspends.

If the function succeeds, execution of the specified task is suspended and the task's

suspend count is incremented. The specified task will be suspended immediately. It

can only be restarted by a call of OS_Resume().

Every task has a suspend count with a maximum value of OS_MAX_SUSPEND_CNT. If

the suspend count is greater than zero, the task is suspended.

In debug builds of embOS, upon calling OS_Suspend() more often than the maximum

value without calling OS_Resume() the task's internal suspend count is not incre-

mented and OS_Error() is called with error OS_ERR_SUSPEND_TOO_OFTEN.

Cannot be called from an interrupt handler or timer as this function may cause an

immediate task switch. The debug build of embOS will call the OS_Error() function

when OS_Suspend() is called from an interrupt handler.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.21: OS_Suspend() parameter list

80 CHAPTER 4 Tasks

4.4.26 OS_SuspendAllTasks()

Description

Suspends all tasks except the running task.

Prototype

void OS_SuspendAllTasks (void);

Additional Information

This function may be used to inhibit task switches. It may be useful during applica-

tion initialization or supervising.

The calling task will not be suspended.

After calling OS_SuspendAllTasks(), the calling task may block or suspend itself. No

other task will be activated unless one or more tasks are resumed again. The tasks

may be resumed individually by a call of OS_Resume() or all at once by a call of

OS_ResumeAllSuspendedTasks().

Example

/* Sample to demonstrate the use of OS_SuspendAllTasks */

void InitTask(void) {

// High priority task started first after OS_Start().

OS_SuspendAllTasks(); // Ensure no other existing task can run.

OS_SetInitialSuspendCnt(1); // Ensure no newly created task will run.

// Perform application initialization.

... // New tasks may be created but cannot start.

... // Even when InitTask() blocks itself by a delay, no other task will run.

OS_SetInitialSuspendCnt(0); // Reset the initial suspend count for tasks.

// Resume all tasks that were blocked before or were created in suspended state.

OS_ResumeAllSuspendedTasks();

while (1) {

... // Do the normal work.

}

4.4.27 OS_TerminateTask()

Description

Ends (terminates) a task.

Prototype

void OS_TerminateTask (OS_TASK* pTask);

Additional Information

If pTask is NULL, the current task terminates. The specified task will terminate imme-

diately. The memory used for stack and task control block can be reassigned.

Since version 3.26 of embOS, all resources which are held by a task are released

upon its termination. Any task may be terminated regardless of its state. This func-

tionality is default for any 16-bit or 32-bit CPU and may be changed by recompiling

embOS sources. On 8-bit CPUs, terminating tasks that hold any resources such as

semaphores, which may block other tasks, is prohibited.

Since embOS version 3.82u, OS_TerminateTask() replaces the deprecated function

OS_Terminate(), which may still be used.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.22: OS_Terminate() parameter list

82 CHAPTER 4 Tasks

4.4.28 OS_WakeTask()

Description

Ends delay of a specified task immediately.

Prototype

void OS_WakeTask (OS_TASK* pTask);

Additional Information

Places the specified task, which is already suspended for a certain amount of time by

a call of OS_Delay() or OS_DelayUntil(), back into the READY state.

The specified task will be activated immediately if it has a higher priority than the

task that had the highest priority before. If the specified task is not in the WAITING

state (because it has already been activated, or the delay has already expired, or for

some other reason), calling this function has no effect.

Parameter Description

pTask Pointer to a task control block structure.

Table 4.23: OS_WakeTask() parameter list

4.4.29 OS_Yield()

Description

Calls the scheduler to force a task switch.

Prototype

void OS_Yield (void);

Additional Information

If the task is running round-robin, it will be suspended if there is another task with

equal priority ready for execution.

84 CHAPTER 4 Tasks

Chapter 5

Software timers

86 CHAPTER 5 Software timers

5.1 Introduction

A software timer is an object that calls a user-specified routine after a specified

delay. An unlimited number of software timers can be defined with the macro

OS_CREATETIMER().

Timers can be stopped, started and retriggered much like hardware timers. When

defining a timer, you specify a routine to be called after the expiration of the delay.

Timer routines are similar to interrupt routines: they have a priority higher than the

priority of any task. For that reason they should be kept short just like interrupt rou-

tines.

Software timers are called by embOS with interrupts enabled, so they can be inter-

rupted by any hardware interrupt. Generally, timers run in single-shot mode, which

means they expire exctly once and call their callback routine exactly once. By calling

OS_RetriggerTimer() from within the callback routine, the timer is restarted with its

initial delay time and therefore functions as a periodic timer.

The state of timers can be checked by the functions OS_GetTimerStatus(),

OS_GetTimerValue() and OS_GetTimerPeriod().

Maximum timeout / period

The timeout value is stored as an integer, thus a 16-bit value on 8/16-bit CPUs, a 32-

bit value on 32-bit CPUs. The comparisons are done as signed comparisons because

expired time-outs are permitted. This means that only 15 bits can be used on 8/16

bit CPUs, 31-bits on 32-bit CPUs. Another factor to take into account is the maximum

time spent in critical regions. Timers may expire during critical regions, but because

the timer routine cannot be called from a critical region (timers are “put on hold”),

the maximum time that the system continuously spends in a critical region needs to

be deducted. In most systems, this is no more than a single tick. However, to be

safe, we have assumed that your system spends no more than a maximum of 255

consecutive ticks in a critical region and defined a macro which defines the maximum

timeout value. This macro, OS_TIMER_MAX_TIME, defaults to 0x7F00 on 8/16-bit sys-

tems and to 0x7FFFFF00 on 32-bit Systems as defined in RTOS.h. If your system

spends more than 255 consecutive ticks in a critical section, effectively disabling the

scheduler during this time (which is not recommended), you must make sure your

application uses shorter timeouts.

Extended software timers

Sometimes it may be useful to pass a parameter to the timer callback function. This

allows the callback function to be shared between different software timers.

Since version 3.32m of embOS, the extended timer structure and related extended

timer functions were implemented to allow parameter passing to the callback func-

tion.

Except for the different callback function with parameter passing, extended timers

behave exactly the same as regular embOS software timers and may be used in par-

allel with these.

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
87
5.2 API functions
Routine Description
main
Task
ISR
Timer
OS_CREATETIMER() Macro that creates and starts a software-
timer. XXXX
OS_CreateTimer() Creates a software timer without starting it. X X X X
OS_StartTimer() Starts a software timer. X X X X
OS_StopTimer() Stops a software timer. X X X X
OS_RetriggerTimer() Restarts a software timer with its initial 
time value. XXXX
OS_SetTimerPeriod() Sets a new timer reload value for a software 
timer. XXXX
OS_DeleteTimer() Stops and deletes a software timer. X X X X
OS_GetTimerPeriod() Returns the current reload value of a soft-
ware timer. XXXX
OS_GetTimerValue() Returns the remaining timer value of a soft-
ware timer. XXXX
OS_GetTimerStatus() Returns the current timer status of a soft-
ware timer. XXXX
OS_GetpCurrentTimer() Returns a pointer to the data structure of 
the timer that just expired. XXXX
OS_CREATETIMER_EX() Macro that creates and starts an extended 
software-timer. XXXX
OS_CreateTimerEx() Creates an extended software timer without 
starting it. XXXX
OS_StartTimerEx() Starts an extended timer. X X X X
OS_StopTimerEx() Stops an extended timer. X X X X
OS_RetriggerTimerEx() Restarts an extended timer with its initial 
time value. XXXX
OS_SetTimerPeriodEx() Sets a new timer reload value for an 
extended timer. XXXX
OS_DeleteTimerEx() Stops and deletes an extended timer. X X X X
OS_GetTimerPeriodEx() Returns the current reload value of an 
extended timer. XXXX
OS_GetTimerValueEx() Returns the remaining timer value of an 
extended timer. XXXX
OS_GetTimerStatusEx() Returns the current timer status of an 
extended timer. XXXX
OS_GetpCurrentTimerEx() Returns a pointer to the data structure of 
the extended timer that just expired. XXXX
Table 5.1: Software timers API

88 CHAPTER 5 Software timers

5.2.1 OS_CREATETIMER()

Description

Macro that creates and starts a software timer.

Prototype

void OS_CREATETIMER (OS_TIMER* pTimer,

OS_TIMERROUTINE* Callback,

OS_TIME Timeout);

Additional Information

embOS keeps track of the timers by using a linked list. Once the timeout is expired,

the callback routine will be called immediately (unless the current task is in a critical

region or has interrupts disabled).

This deprecated macro uses the functions OS_CreateTimer() and OS_StartTimer().

It is supplied for backward compatibility; in newer applications these routines should

instead be called directly.

OS_TIMERROUTINE is defined in RTOS.h as follows:

typedef void OS_TIMERROUTINE(void);

Source of the macro (in RTOS.h):

#define OS_CREATETIMER(pTimer, c, d) \

OS_CreateTimer(pTimer, c, d); \

OS_StartTimer(pTimer);

Example

OS_TIMER TIMER100;

void Timer100(void) {

LED = LED ? 0 : 1; /* Toggle LED */

OS_RetriggerTimer(&TIMER100); /* Make timer periodic */

}

void InitTask(void) {

/* Create and start Timer100 */

OS_CREATETIMER(&TIMER100, Timer100, 100);

}

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Callback

Pointer to the callback routine to be called by the RTOS after

expiration of the delay. The callback function must be a void

function which does not take any parameter and does not return

any value.

Timeout

Initial timeout in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 5.2: OS_CREATETIMER() parameter list

5.2.2 OS_CreateTimer()

Description

Creates a software timer (but does not start it).

Prototype

void OS_CreateTimer (OS_TIMER* pTimer,

OS_TIMERROUTINE* Callback,

OS_TIME Timeout);

Additional Information

embOS keeps track of the timers by using a linked list. Once the timeout is expired,

the callback routine will be called immediately (unless the current task is in a critical

region or has interrupts disabled). The timer is not automatically started. This must

be done explicitly by a call of OS_StartTimer() or OS_RetriggerTimer().

OS_TIMERROUTINE is defined in RTOS.h as follows:

typedef void OS_TIMERROUTINE(void);

Example

OS_TIMER TIMER100;

void Timer100(void) {

LED = LED ? 0 : 1; /* Toggle LED */

OS_RetriggerTimer(&TIMER100); /* Make timer periodic */

}

void InitTask(void) {

/* Create Timer100, start it elsewhere */

OS_CreateTimer(&TIMER100, Timer100, 100);

OS_StartTimer(&TIMER100);

}

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Callback Pointer to the callback routine to be called by the RTOS after

expiration of the delay.

Timeout

Initial timeout in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 5.3: OS_CreateTimer() parameter list

90 CHAPTER 5 Software timers

5.2.3 OS_StartTimer()

Description

Starts a software timer.

Prototype

void OS_StartTimer (OS_TIMER* pTimer);

Additional Information

OS_StartTimer() is used for the following reasons:

• Start a timer which was created by OS_CreateTimer(). The timer will start with

its initial timer value.

• Restart a timer which was stopped by calling OS_StopTimer(). In this case, the

timer will continue with the remaining time value which was preserved by stop-

ping the timer.

Important

This function has no effect on running timers. It also has no effect on timers that are

not running, but have expired: use OS_RetriggerTimer() to restart those timers.

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Table 5.4: OS_StartTimer() parameter list

5.2.4 OS_StopTimer()

Description

Stops a software timer.

Prototype

void OS_StopTimer (OS_TIMER* pTimer);

Additional Information

The actual value of the timer (the time until expiration) is maintained until

OS_StartTimer() lets the timer continue. The function has no effect on timers that

are not running, but have expired.

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Table 5.5: OS_StopTimer() parameter list

92 CHAPTER 5 Software timers

5.2.5 OS_RetriggerTimer()

Description

Restarts a software timer with its initial time value.

Prototype

void OS_RetriggerTimer (OS_TIMER* pTimer);

Additional Information

OS_RetriggerTimer() restarts the timer using the initial time value programmed at

creation of the timer or with the function OS_SetTimerPeriod().

OS_RetriggerTimer() can be called regardless the state of the timer. A running

timer will continue using the full initial time. A timer that was stopped before or had

expired will be restarted.

Example

OS_TIMER TIMERCursor;

BOOL CursorOn;

void TimerCursor(void) {

if (CursorOn) ToggleCursor(); /* Invert character at cursor-position */

OS_RetriggerTimer(&TIMERCursor); /* Make timer periodic */

}

void InitTask(void) {

/* Create and start TimerCursor */

OS_CREATETIMER(&TIMERCursor, TimerCursor, 500);

}

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Table 5.6: OS_RetriggerTimer() parameter list

5.2.6 OS_SetTimerPeriod()

Description

Sets a new timer reload value for a software timer.

Prototype

void OS_SetTimerPeriod (OS_TIMER* pTimer,

OS_TIME Period);

Additional Information

OS_SetTimerPeriod() sets the initial time value of the specified timer. Period is the

reload value of the timer to be used as initial value when the timer is retriggered by

OS_RetriggerTimer().

Example

OS_TIMER TIMERPulse;

void TimerPulse(void) {

TogglePulseOutput(); /* Toggle output */

OS_RetriggerTimer(&TIMERPulse); /* Make timer periodic */

}

void InitTask(void) {

/* Create and start Pulse Timer with first pulse = 500ms */

OS_CREATETIMER(&TIMERPulse, TimerPulse, 500);

/* Set timer period to 200 ms for further pulses */

OS_SetTimerPeriod(&TIMERPulse, 200);

}

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Period

Timer period in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 5.7: OS_SetTimerPeriod() parameter list

94 CHAPTER 5 Software timers

5.2.7 OS_DeleteTimer()

Description

Stops and deletes a software timer.

Prototype

void OS_DeleteTimer (OS_TIMER* pTimer);

Additional Information

The timer is stopped and therefore removed from the linked list of running timers. In

debug builds of embOS, the timer is also marked as invalid.

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Table 5.8: OS_DeleteTimer() parameter list

5.2.8 OS_GetTimerPeriod()

Description

Returns the current reload value of a software timer.

Prototype

OS_TIME OS_GetTimerPeriod (const OS_TIMER* pTimer);

Return value

Typ e OS_TIME, which is defined as an integer between

1 and 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between

1 and <= 231-1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer

values.

Additional Information

The period returned is the reload value of the timer which was set as initial value

when the timer was created or which was modified by a call of

OS_SetTimerPeriod(). This reload value will be used as time period when the timer

is retriggered by OS_RetriggerTimer().

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Table 5.9: OS_GetTimerPeriod() parameter list

96 CHAPTER 5 Software timers

5.2.9 OS_GetTimerValue()

Description

Returns the remaining timer value of a software timer.

Prototype

OS_TIME OS_GetTimerValue (const OS_TIMER* pTimer);

Return value

Type OS_TIME, which is defined as an integer between

1 and 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between

1 and <= 231-1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer

values.

The returned timer value is the remaining timer time in embOS tick units until expi-

ration of the timer.

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Table 5.10: OS_GetTimerValue() parameter list

5.2.10 OS_GetTimerStatus()

Description

Returns the current timer status of a software timer.

Prototype

unsigned char OS_GetTimerStatus (const OS_TIMER* pTimer);

Return value

Denotes whether the specified timer is running or not:

0: timer has stopped

! = 0: timer is running.

Parameter Description

pTimer Pointer to the OS_TIMER data structure which contains the data of

the timer.

Table 5.11: OS_GetTimerStatus parameter list

98 CHAPTER 5 Software timers

5.2.11 OS_GetpCurrentTimer()

Description

Returns a pointer to the data structure of the timer that just expired.

Prototype

OS_TIMER* OS_GetpCurrentTimer (void);

Return value

A pointer to the control structure of a timer.

Additional Information

The return value of OS_GetpCurrentTimer() is valid during execution of a timer call-

back function; otherwise it is undefined. If only one callback function should be used

for multiple timers, this function can be used for examining the timer that expired.

The example below shows one usage of OS_GetpCurrentTimer(). Since version

3.32m of embOS, the extended timer structure and functions may be used to gener-

ate and use a software timer with an individual parameter for the callback function.

Please be aware that OS_TIMER must be the first member of the structure.

Example

#include "RTOS.H"

/**********************************************************

* Types

typedef struct { /* Timer object with its own user data */

OS_TIMER Timer; /* OS_TIMER must be the first element */

void* pUser;

} TIMER_EX;

/**********************************************************

* Variables

TIMER_EX Timer_User;

int a;

/**********************************************************

* Local Functions

static void _CreateTimer(TIMER_EX* timer, OS_TIMERROUTINE* Callback,

OS_UINT Timeout, void* pUser) {

timer->pUser = pUser;

OS_CreateTimer(&timer->Timer, Callback, Timeout);

}

/* Timer callback function for multiple timers */

static void _cb(void) {

TIMER_EX* p = (TIMER_EX*)OS_GetpCurrentTimer();

void* pUser = p->pUser; /* Examine user data */

OS_RetriggerTimer(&p->Timer); /* Retrigger timer */

}

/**********************************************************

* main

int main(void) {

OS_InitKern(); /* Initialize OS */

OS_InitHW(); /* Initialize Hardware for OS */

_CreateTimer(&Timer_User, _cb, 100, &a);

OS_Start(); /* Start multitasking */

return 0;

}

5.2.12 OS_CREATETIMER_EX()

Description

Macro that creates and starts an extended software timer.

Prototype

void OS_CREATETIMER_EX (OS_TIMER_EX* pTimerEx,

OS_TIMER_EX_ROUTINE* Callback,

OS_TIME Timeout

void* pData)

Additional Information

embOS keeps track of the timers by using a linked list. Once the timeout is expired,

the callback routine will be called immediately (unless the current task is in a critical

region or has interrupts disabled).

This macro uses the functions OS_CreateTimerEx() and OS_StartTimerEx().

OS_TIMER_EX_ROUTINE is defined in RTOS.h as follows:

typedef void OS_TIMER_EX_ROUTINE(void* pVoid);

Source of the macro (in RTOS.h):

#define OS_CREATETIMER_EX(pTimerEx, cb, Timeout, pData) \

OS_CreateTimerEx(pTimerEx, cb, Timeout, pData); \

OS_StartTimerEx(pTimerEx)

Example

OS_TIMER_EX TIMER100;

OS_TASK TCB_HP;

void Timer100(void* pTask) {

LED = LED ? 0 : 1; /* Toggle LED */

if (pTask != NULL) {

OS_SignalEvent(0x01, (OS_TASK*)pVoid);

}

OS_RetriggerTimerEx(&TIMER100); /* Make timer periodic */

}

void InitTask(void) {

/* Create and start Timer100 */

OS_CREATETIMER_EX(&TIMER100, Timer100, 100, (void*) &TCB_HP);

}

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended software timer.

Callback

Pointer to the callback routine to be called by the RTOS after

expiration of the delay. The callback function must be of type

OS_TIMER_EX_ROUTINE which takes a void pointer as parameter

and does not return any value.

Timeout

Initial timeout in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

pData A void pointer which is used as parameter for the extended timer

callback function.

Table 5.12: OS_CREATETIMER_EX() parameter list

100 CHAPTER 5 Software timers

5.2.13 OS_CreateTimerEx()

Description

Creates an extended software timer (but does not start it).

Prototype

void OS_CreateTimerEx (OS_TIMER_EX* pTimerEx,

OS_TIMER_EX_ROUTINE* Callback,

OS_TIME Timeout,

void* pData)

Additional Information

embOS keeps track of timers by using a linked list. Once the timeout has expired, the

callback routine will be called immediately (unless the current task is in a critical

region or has interrupts disabled).

The extended software timer is not automatically started. This must be done explic-

itly by a call of OS_StartTimerEx() or OS_RetriggerTimerEx().

OS_TIMER_EX_ROUTINE is defined in RTOS.h as follows:

typedef void OS_TIMER_EX_ROUTINE(void* pVoid);

Example

OS_TIMER_EX TIMER100;

OS_TASK TCB_HP;

void Timer100(void* pTask) {

LED = LED ? 0 : 1; /* Toggle LED */

if (pTask != NULL) {

OS_SignalEvent(0x01, (OS_TASK*) pVoid);

}

OS_RetriggerTimerEx(&TIMER100); /* Make timer periodic */

}

void InitTask(void) {

/* Create Timer100, start it elsewhere later on*/

OS_CreateTimerEx(&TIMER100, Timer100, 100, (void*) & TCB_HP);

}

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended software timer.

Callback Pointer to the callback routine of type OS_TIMER_EX_ROUTINE to

be called by the RTOS after expiration of the timer.

Timeout

Initial timeout in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

pData A void pointer which is used as parameter for the extended timer

callback function.

Table 5.13: OS_CreateTimerEx() parameter list

101

5.2.14 OS_StartTimerEx()

Description

Starts an extended software timer.

Prototype

void OS_StartTimerEx (OS_TIMER_EX* pTimerEx);

Additional Information

OS_StartTimerEx() is used for the following reasons:

• Start an extended software timer which was created by OS_CreateTimerEx().

The timer will start with its initial timer value.

• Restart a timer which was stopped by calling OS_StopTimerEx(). In this case,

the timer will continue with the remaining time value which was preserved by

stopping the timer.

Important

This function has no effect on running timers. It also has no effect on timers that are

not running, but have expired. Use OS_RetriggerTimerEx() to restart those timers.

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended software timer.

Table 5.14: OS_StartTimereEx() parameter list

102 CHAPTER 5 Software timers

5.2.15 OS_StopTimerEx()

Description

Stops an extended software timer.

Prototype

void OS_StopTimerEx (OS_TIMER_EX* pTimerEx);

Additional Information

The actual time value of the extended software timer (the time until expiration) is

maintained until OS_StartTimerEx() lets the timer continue. The function has no

effect on timers that are not running, but have expired.

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended software timer.

Table 5.15: OS_StopTimerEx() parameter list

103

5.2.16 OS_RetriggerTimerEx()

Description

Restarts an extended software timer with its initial time value.

Prototype

void OS_RetriggerTimerEx (OS_TIMER_EX* pTimerEx);

Additional Information

OS_RetriggerTimerEx() restarts the extended software timer using the initial time

value which was programmed at creation of the timer or which was set using the

function OS_SetTimerPeriodEx().

OS_RetriggerTimerEx() can be called regardless of the state of the timer. A running

timer will continue using the full initial time. A timer that was stopped before or had

expired will be restarted.

Example

OS_TIMER_EX TIMERCursor;

OS_TASK TCB_HP;

BOOL CursorOn;

void TimerCursor(void* pTask) {

if (CursorOn != 0) ToggleCursor(); /* Invert character at cursor-position */

OS_SignalEvent(0x01, (OS_TASK*) pTask);

OS_RetriggerTimerEx(&TIMERCursor); /* Make timer periodic */

}

void InitTask(void) {

/* Create and start TimerCursor */

OS_CREATETIMER_EX(&TIMERCursor, TimerCursor, 500, (void*)&TCB_HP);

}

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended software timer.

Table 5.16: OS_RetriggerTimerEx() parameter list

104 CHAPTER 5 Software timers

5.2.17 OS_SetTimerPeriodEx()

Description

Sets a new timer reload value for an extended software timer.

Prototype

void OS_SetTimerPeriodEx (OS_TIMER_EX* pTimerEx,

OS_TIME Period);

Additional Information

OS_SetTimerPeriodEx() sets the initial time value of the specified extended soft-

ware timer. Period is the reload value of the timer to be used as initial value when

the timer is retriggered the next time by OS_RetriggerTimerEx().

A call of OS_SetTimerPeriodEx() does not affect the remaining time period of an

extended software timer.

Example

OS_TIMER_EX TIMERPulse;

OS_TASK TCB_HP;

void TimerPulse(void* pTask) {

OS_SignalEvent(0x01, (OS_TASK*) pTask);

OS_RetriggerTimerEx(&TIMERPulse); /* Make timer periodic */

}

void InitTask(void) {

/* Create and start Pulse Timer with first pulse == 500ms */

OS_CREATETIMER_EX(&TIMERPulse, TimerPulse, 500, (void*)&TCB_HP);

/* Set timer period to 200 ms for further pulses */

OS_SetTimerPeriodEx(&TIMERPulse, 200);

}

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended software timer.

Period

Timer period in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 5.17: OS_SetTimerPeriodEx() parameter list

105

5.2.18 OS_DeleteTimerEx()

Description

Stops and deletes an extended software timer.

Prototype

void OS_DeleteTimerEx(OS_TIMER_EX* pTimerEx);

Additional Information

The extended software timer is stopped and removed from the linked list of running

timers. In debug builds of embOS, the timer is also marked as invalid.

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the timer.

Table 5.18: OS_DeleteTimerEx() parameter list

106 CHAPTER 5 Software timers

5.2.19 OS_GetTimerPeriodEx()

Description

Returns the current reload value of an extended software timer.

Prototype

OS_TIME OS_GetTimerPeriodEx (OS_TIMER_EX* pTimerEx);

Return value

Type OS_TIME, which is defined as an integer between

1 and 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between

1 and <= 231-1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer

values.

Additional Information

The period returned is the reload value of the timer which was set as initial value

when the timer was created or which was modified by a call of

OS_SetTimerPeriodEx(). This reload value will be used as time period when the

timer is retriggered by OS_RetriggerTimerEx().

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended timer.

Table 5.19: OS_GetTimerPeriodEx() parameter list

107

5.2.20 OS_GetTimerValueEx()

Description

Returns the remaining timer value of an extended software timer.

Prototype

OS_TIME OS_GetTimerValueEx(OS_TIMER_EX* pTimerEx);

Return value

Typ e OS_TIME, which is defined as an integer between

1 and 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between

1 and <= 231-1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer

values.

The returned time value is the remaining timer value in embOS tick units until expi-

ration of the extended software timer.

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the timer.

Table 5.20: OS_GetTimerValueEx() parameter list

108 CHAPTER 5 Software timers

5.2.21 OS_GetTimerStatusEx()

Description

Returns the current timer status of an extended software timer.

Prototype

unsigned char OS_GetTimerStatusEx (OS_TIMER_EX* pTimerEx);

Return value

Denotes whether the specified timer is running or not:

0: timer has stopped

! = 0: timer is running.

Parameter Description

pTimerEx Pointer to the OS_TIMER_EX data structure which contains the

data of the extended timer.

Table 5.21: OS_GetTimerStatusEx parameter list

109

5.2.22 OS_GetpCurrentTimerEx()

Description

Returns a pointer to the data structure of the extended timer that just expired.

Prototype

OS_TIMER_EX* OS_GetpCurrentTimerEx (void);

Return value

A pointer to the control structure of an extended software timer.

Additional Information

The return value of OS_GetpCurrentTimerEx() is valid during execution of a timer

callback function; otherwise it is undefined. If one callback function should be used

for multiple extended timers, this function can be used for examining the timer that

expired.

Example

#include "RTOS.H"

OS_TIMER_EX MyTimerEx;

/********************************************************

* Local Functions

void cbTimerEx(void* pData) { /* Timer callback function for multiple timers */

OS_TIMER_EX* pTimerEx;

pTimerEx = OS_GetpCurrentTimerEx();

OS_SignalEvent(0x01, (OS_TASK*) pData);

OS_RetriggerTimer(pTimerEx); /* Retrigger timer */

}

110 CHAPTER 5 Software timers

111

Chapter 6

Resource semaphores

112 CHAPTER 6 Resource semaphores

6.1 Introduction

Resource semaphores are used for managing resources by avoiding conflicts caused

by simultaneous use of a resource. The resource managed can be of any kind: a part

of the program that is not reentrant, a piece of hardware like the display, a flash

prom that can only be written to by a single task at a time, a motor in a CNC control

that can only be controlled by one task at a time, and a lot more.

The basic procedure is as follows:

Any task that uses a resource first claims it calling the OS_Use() or OS_Request()

routines of embOS. If the resource is available, the program execution of the task

continues, but the resource is blocked for other tasks. If a second task now tries to

use the same resource while it is in use by the first task, this second task is sus-

pended until the first task releases the resource. However, if the first task that uses

the resource calls OS_Use() again for that resource, it is not suspended because the

resource is blocked only for other tasks.

The following diagram illustrates the process of using a resource:

A resource semaphore contains a counter that keeps track of how many times the

resource has been claimed by calling OS_Request() or OS_Use() by a particular task.

It is released when that counter reaches zero, which means the OS_Unuse() routine

must be called exactly the same number of times as OS_Use() or OS_Request(). If it

is not, the resource remains blocked for other tasks.

On the other hand, a task cannot release a resource that it does not own by calling

OS_Unuse(). In debug builds of embOS, a call of OS_Unuse() for a semaphore that is

not owned by this task will result in a call to the error handler OS_Error().

Example of using resource semaphores

Here, two tasks access an LC display completely independently from each other. The

LCD is a resource that needs to be protected with a resource semaphore. One task

may not interrupt another task which is writing to the LCD, because otherwise the

following might occur:

• Task A positions the cursor

• Task B interrupts Task A and repositions the cursor

• Task A writes to the wrong place in the LCD's memory.

To avoid this type of situation, every time the LCD must be accessed by a task, it is

first claimed by a call to OS_Use() (and is automatically waited for if the resource is

blocked). After the LCD has been written to, it is released by a call to OS_Unuse().

OS_Use()

Access resource

OS_Unuse()

113

* Demo program to illustrate the use of resource semaphores

OS_STACKPTR int StackMain[100], StackClock[50];

OS_TASK TaskMain,TaskClock;

OS_RSEMA SemaLCD;

void TaskClock(void) {

char t = -1;

char s[] = "00:00";

while(1) {

while (TimeSec == t) {

Delay(10);

}

t = TimeSec;

s[4] = TimeSec % 10 + '0';

s[3] = TimeSec / 10 + '0';

s[1] = TimeMin % 10 + '0';

s[0] = TimeMin / 10 + '0';

OS_Use(&SemaLCD); /* Make sure noone else uses LCD */

LCD_Write(10, 0, s);

OS_Unuse(&SemaLCD); /* Release LCD */

}

void TaskMain(void) {

signed char pos ;

LCD_Write(0, 0, "Software tools by Segger!”);

OS_Delay(2000);

while (1) {

for ( pos=14 ; pos >=0 ; pos-- ) {

OS_Use(&SemaLCD); /* Make sure noone else uses LCD */

LCD_Write(pos, 1, "train"); /* Draw train */

OS_Unuse(&SemaLCD); /* Release LCD */

OS_Delay(500);

}

OS_Use(&SemaLCD); /* Make sure noone else uses LCD */

LCD_Write(0, 1, " ");

OS_Unuse(&SemaLCD); /* Release LCD */

}

void InitTask(void) {

OS_CREATERSEMA(&SemaLCD); /* Creates resource semaphore */

OS_CREATETASK(&TaskMain, 0, Main, 50, StackMain);

OS_CREATETASK(&TaskClock, 0, Clock, 100, StackClock);

}

In most applications the routines that access a resource should automatically call

OS_Use() and OS_Unuse() so that when using the resource you do not need to worry

about it and can use it just as you would in a single-task system. The following is an

example of how to implement a resource into the routines that actually access the

display:

* Simple example when accessing single line dot matrix LCD

OS_RSEMA RDisp; /* Define resource semaphore */

void UseDisp() { /* Simple routine to be called before using display */

OS_Use(&RDisp);

}

void UnuseDisp() { /* Simple routine to be called after using display */

OS_Unuse(&RDisp);

}

void DispCharAt(char c, char x, char y) {

UseDisp();

LCDGoto(x, y);

LCDWrite1(ASCII2LCD(c));

UnuseDisp();

}

void DISPInit(void) {

OS_CREATERSEMA(&RDisp);

}

114 CHAPTER 6 Resource semaphores

6.2 API functions

Routine Description

main

Task

ISR

Timer

OS_CREATERSEMA() Macro that creates a resource semaphore. X X

OS_Use() Claims a resource and blocks it for other tasks. X X

OS_UseTimed() Tries to claim a resource within a given time. X X

OS_Unuse() Releases a semaphore currently in use by a

task. XX

OS_Request()

Requests a specified semaphore, blocks it for

other tasks if it is available. Continues execu-

tion in any case.

OS_GetSemaValue() Returns the value of the usage counter of a

specified resource semaphore. XX

OS_GetResourceOwner() Returns a pointer to the task that is currently

using (blocking) a resource. XX

OS_DeleteRSema() Deletes a specified resource semaphore. X X

Table 6.1: Resource semaphore API functions

115

6.2.1 OS_CREATERSEMA()

Description

Macro that creates a resource semaphore.

Prototype

void OS_CREATERSEMA (OS_RSEMA* pRSema);

Additional Information

After creation, the resource is not blocked; the value of the counter is zero.

Parameter Description

pRSema Pointer to the data structure for a resource semaphore.

Table 6.2: OS_CREATESEMA() parameter list

116 CHAPTER 6 Resource semaphores

6.2.2 OS_Use()

Description

Claims a resource and blocks it for other tasks.

Prototype

int OS_Use (OS_RSEMA* pRSema);

Return value

The counter value of the semaphore.

A value greater than one denotes the resource was already locked by the calling task.

Additional Information

The following situations are possible:

• Case A: The resource is not in use.

If the resource is not used by a task, which means the counter of the semaphore

is zero, the resource will be blocked for other tasks by incrementing the counter

and writing a unique code for the task that uses it into the semaphore.

• Case B: The resource is used by this task.

The counter of the semaphore is incremented. The program continues without a

break.

• Case C: The resource is being used by another task.

The execution of this task is suspended until the resource semaphore is released.

In the meantime if the task blocked by the resource semaphore has a higher pri-

ority than the task blocking the semaphore, the blocking task is assigned the pri-

ority of the task requesting the resource semaphore. This is called priority

inheritance. Priority inheritance can only temporarily increase the priority of a

task, never reduce it.

An unlimited number of tasks can wait for a resource semaphore. According to the

rules of the scheduler, of all the tasks waiting for the resource the task with the high-

est priority will acquire the resource and continue program execution.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pRSema Pointer to the data structure for a resource semaphore.

Table 6.3: OS_Use() parameter list

117

The following diagram illustrates how OS_Use() works:

Resource

in use?

Wait for resource

to be released

Mark current task

as owner

Usage counter = 1

return

Increase Usage

counter

Yes, by

other task

Yes, by this task

OS_Use(...)

return

118 CHAPTER 6 Resource semaphores

6.2.3 OS_UseTimed()

Description

Tries to claim a resource and blocks it for other tasks if it is available within a speci-

fied time.

Prototype

int OS_UseTimed(OS_RSEMA* pRSema, OS_TIME TimeOut)

Return value

0: Failed, semaphore not available before timeout.

>0: Success, resource semaphore was available. The counter value of the sema-

phore.

A value greater than one denotes the resource was already locked by the calling task.

Additional Information

The following situations are possible:

• Case A: The resource is not in use.

If the resource is not used by a task, which means the counter of the semaphore

is zero, the resource will be blocked for other tasks by incrementing the counter

and writing a unique code for the task that uses it into the semaphore.

• Case B: The resource is used by this task.

The counter of the semaphore is incremented. The program continues without a

break.

• Case C: The resource is being used by another task.

The execution of this task is suspended until the resource semaphore is released

or the timeout time expired. In the meantime if the task blocked by the resource

semaphore has a higher priority than the task blocking the semaphore, the

blocking task is assigned the priority of the task requesting the resource sema-

phore. This is called priority inheritance. Priority inheritance can only temporarily

increase the priority of a task, never reduce it.

If the resource semaphore becomes available during the timeout, the calling task

claims the resource and the function returns a value greater than zero, other-

wise, if the resource does not become available, the function returns zero.

When the calling task is blocked by higher priority tasks for a period longer than the

timeout value, it may happen that the resource semaphore becomes available before

the calling task is resumed. Anyhow, the function will not claim the resource because

it was not availbale within the requested time.

An unlimited number of tasks can wait for a resource semaphore. According to the

rules of the scheduler, of all the tasks waiting for the resource the task with the high-

est priority will acquire the resource and continue program execution.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pRSema Pointer to the data structure of a resource semaphore.

TimeOut

Maximum time until the resource semaphore should be available.

Timer period in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs.

Table 6.4: OS_UseTimed() parameter list

119

6.2.4 OS_Unuse()

Description

Releases a semaphore currently in use by a task.

Prototype

void OS_Unuse (OS_RSEMA* pRSema)

Additional Information

OS_Unuse() may be used on a resource semaphore only after that semaphore has

been used by calling OS_Use() or OS_Request(). OS_Unuse() decrements the usage

counter of the semaphore which must never become negative. If this counter

becomes negative, a debug build will call the embOS error handler OS_Error() with

error code OS_ERR_UNUSE_BEFORE_USE. In a debug build OS_Error() will also be

called if OS_Unuse() is called from a task which does not own the resource. The

error code is OS_ERR_RESOURCE_OWNER in this case.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pRSema Pointer to the data structure for a resource semaphore.

Table 6.5: OS_Unuse() parameter list

120 CHAPTER 6 Resource semaphores

6.2.5 OS_Request()

Description

Requests a specified semaphore and blocks it for other tasks if it is available. Contin-

ues execution in any case.

Prototype

char OS_Request (OS_RSEMA* pRSema);

Return value

1: Resource was available, now in use by the calling task.

0: Resource was not available.

Additional Information

The following diagram illustrates how OS_Request() works:

Example

if (OS_Request(&RSEMA_LCD) ) {

DispTime(); /* Access the resource LCD */

OS_Unuse(&RSEMA_LCD); /* Resource LCD is no longer needed */

} else {

... // Do something else

}

Parameter Description

pRSema Pointer to the data structure for a resource semaphore.

Table 6.6: OS-Request() parameter list

OS_Request (RSEMA*ps)

return 0

Resource in use by other task ?

In use by this task ?

Inc Usage counter

Mark current task

as owner

Usage counter = 1

return 1return 1

Yes

121

6.2.6 OS_GetSemaValue()

Description

Returns the value of the usage counter of a specified resource semaphore.

Prototype

int OS_GetSemaValue (const OS_SEMA* pSema);

Return value

The counter of the semaphore.

A value of zero means the resource is available.

Parameter Description

pRSema Pointer to the data structure for a resource semaphore.

Table 6.7: OS_GetSemaValue() parameter list

122 CHAPTER 6 Resource semaphores

6.2.7 OS_GetResourceOwner()

Description

Returns a pointer to the task that is currently using (blocking) a resource.

Prototype

OS_TASK* OS_GetResourceOwner (const OS_RSEMA* pSema);

Return value

Pointer to the task that holds the resource.

A value of NULL means the resource is available.

Parameter Description

pRSema Pointer to the data structure for a resource semaphore.

Table 6.8: OS_GetResourceOwner() parameter list

123

6.2.8 OS_DeleteRSema()

Description

Deletes a specified resource semaphore. The memory of that semaphore may be

reused for other purposes or may be used for creating another resources semaphore

using the same memory.

Prototype

void OS_DeleteRSema (OS_RSEMA* pRSema);

Additional Information

Before deleting a resource semaphore, make sure that no task is claiming the

resource semaphore. A debug build of embOS will call OS_Error() with the error

code OS_DEL_RSEMA_DELETE if a resource semaphore is deleted when it is already in

use. In systems with dynamic creation of resource semaphores, you must delete a

resource semaphore before recreating it. Failure to so may cause semaphore han-

dling to work incorrectly.

Parameter Description

pRSema Pointer to a data structure of type OS_RSEMA.

Table 6.9: OS_DeleteRSema parameter list

124 CHAPTER 6 Resource semaphores

125

Chapter 7

Counting Semaphores

126 CHAPTER 7 Counting Semaphores

7.1 Introduction

Counting semaphores are counters that are managed by embOS. They are not as

widely used as resource semaphores, events or mailboxes, but they can be very

useful sometimes. They are used in situations where a task needs to wait for

something that can be signaled one or more times. The semaphores can be accessed

from any point, any task, or any interrupt by any means.

Example of using counting semaphores

OS_STACKPTR int Stack0[96], Stack1[64]; /* Task stacks */

OS_TASK TCB0, TCB1; /* Data-area for tasks (task-control-blocks) */

OS_CSEMA SEMALCD;

void Task0(void) {

while(1) {

Disp("Task0 will wait for task 1 to signal");

OS_WaitCSema(&SEMALCD);

Disp("Task1 has signaled !!");

OS_Delay(100);

}

void Task1(void) {

while(1) {

OS_Delay(5000);

OS_SignalCSema(&SEMALCD);

}

void InitTask(void) {

OS_CREATECSEMA(&SEMALCD); /* Create Semaphore */

OS_CREATETASK(&TCB0, NULL, Task0, 100, Stack0); /* Create Task0 */

OS_CREATETASK(&TCB1, NULL, Task1, 50, Stack1); /* Create Task1 */

}

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
127
7.2 API functions
Routine Description
main
Task
ISR
Timer
OS_CREATECSEMA() Macro that creates a counting semaphore with 
an initial count value of zero. XX
OS_CreateCSema() Creates a counting semaphore with a specified 
initial count value. XX
OS_SignalCSema() Increments the counter of a semaphore. X X X
OS_SignalCSemaMax() Increments the counter of a semaphore up to 
a specified maximum value. XXX
OS_WaitCSema() Decrements the counter of a semaphore. X X
OS_CSemaRequest() Decrements the counter of a semaphore, if 
available. XXX
OS_WaitCSemaTimed() Decrements a semaphore counter if the sema-
phore is available within a specified time. XX
OS_GetCSemaValue() Returns the counter value of a specified sema-
phore. XXX
OS_SetCSemaValue() Sets the counter value of a specified sema-
phore.  XX
OS_DeleteCSema() Deletes a specified semaphore. X X
Table 7.1: Counting semaphores API functions

128 CHAPTER 7 Counting Semaphores

7.2.1 OS_CREATECSEMA()

Description

Macro that creates a counting semaphore with an initial count value of zero.

Prototype

void OS_CREATECSEMA (OS_CSEMA* pCSema);

Additional Information

To create a counting semaphore a data structure of the type OS_CSEMA must be

defined in memory and initialized using OS_CREATECSEMA(). The value of a sema-

phore created by using this macro is zero. If for any reason you need create a sema-

phore with an initial counting value greater than zero, use the function

OS_CreateCSema().

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

Table 7.2: OS_CREATECSEMA() parameter list

129

7.2.2 OS_CreateCSema()

Description

Creates a counting semaphore with a specified initial count value.

Prototype

void OS_CreateCSema (OS_CSEMA* pCSema,

OS_UINT InitValue);

Additional Information

To create a counting semaphore a data structure of the type OS_CSEMA must be

defined in memory and initialized using OS_CreateCSema().

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

InitValue

Initial count value of the semaphore:

0 <= InitValue <= 216-1 = 0xFFFF for 8/16-bit CPUs

0 <= InitValue <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Table 7.3: OS_CreateCSema() parameter list

130 CHAPTER 7 Counting Semaphores

7.2.3 OS_SignalCSema()

Description

Increments the counter of a semaphore.

Prototype

void OS_SignalCSema (OS_CSEMA* pCSema);

Additional Information

OS_SignalCSema() signals an event to a semaphore by incrementing its counter. If

one or more tasks are waiting for an event to be signaled to this semaphore, the task

with the highest priority becomes the running task. The counter can have a maxi-

mum value of 0xFFFF for 8/16-bit CPUs or 0xFFFFFFFF for 32-bit CPUs. It is the

responsibility of the application to make sure that this limit is not exceeded. A debug

build of embOS detects a counter overflow and calls OS_Error() with error code

OS_ERR_CSEMA_OVERFLOW if an overflow occurs.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

Table 7.4: OS_SignalCSema() parameter list

131

7.2.4 OS_SignalCSemaMax()

Description

Increments the counter of a semaphore up to a specified maximum value.

Prototype

void OS_SignalCSemaMax (OS_CSEMA* pCSema,

OS_UINT MaxValue);

Additional Information

As long as current value of the semaphore counter is below the specified maximum

value, OS_SignalCSemaMax() signals an event to a semaphore by incrementing its

counter. If one or more tasks are waiting for an event to be signaled to this sema-

phore, the tasks are placed into the READY state and the task with the highest prior-

ity becomes the running task.

Calling OS_SignalCSemaMax() with a MaxValue of 1 makes a counting semaphore

behave like a binary semaphore. Consider using a binary resource instead.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

MaxValue

Limit of semaphore count value.

1 <= MaxValue <= 216-1 = 0xFFFF for 8/16-bit CPUs

1 <= MaxValue <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Table 7.5: OS_SignalCSemaMax() parameter list

132 CHAPTER 7 Counting Semaphores

7.2.5 OS_WaitCSema()

Description

Decrements the counter of a semaphore.

Prototype

void OS_WaitCSema (OS_CSEMA* pCSema);

Additional Information

If the counter of the semaphore is not zero, the counter is decremented and program

execution continues.

If the counter is zero, WaitCSema() waits until the counter is incremented by another

task, a timer or an interrupt handler by a call to OS_SignalCSema(). The counter is

then decremented and program execution continues.

An unlimited number of tasks can wait for a semaphore. According to the rules of the

scheduler, of all the tasks waiting for the semaphore, the task with the highest prior-

ity will continue program execution.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

Table 7.6: OS_WaitCSema() parameter list

133

7.2.6 OS_WaitCSemaTimed()

Description

Decrements a semaphore counter if the semaphore is available within a specified

time.

Prototype

int OS_WaitCSemaTimed (OS_CSEMA* pCSema,

OS_TIME TimeOut);

Return value

0: Failed, semaphore not available before timeout.

1: OK, semaphore was available and counter decremented.

Additional Information

If the counter of the semaphore is not zero, the counter is decremented and program

execution continues.

If the counter is zero, WaitCSemaTimed() waits until the semaphore is signaled by

another task, a timer, or an interrupt handler by a call to OS_SignalCSema(). The

counter is then decremented and program execution continues. If the semaphore was

not signaled within the specified time the program execution continues, but returns a

value of zero. An unlimited number of tasks can wait for a semaphore. According to

the rules of the scheduler, of all the tasks waiting for the semaphore, the task with

the highest priority will continue program execution.

When the calling task is blocked by higher priority tasks for a longer period than the

timeout value, it may happen, that the semaphore becomes signaled after the time-

out time before the calling task continues. In this case, the function returns with tim-

eout, because the semaphore was not availbale within the requested time. In this

case, the state of the semaphore is not modified by OS_WaitCSemaTimed().

Important

This function must not be called from within an interrupt handler.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

TimeOut

Maximum time until semaphore should be available

Timer period in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs.

Table 7.7: OS_WaitCSemaTimed parameter list

134 CHAPTER 7 Counting Semaphores

7.2.7 OS_CSemaRequest()

Description

Decrements the counter of a semaphore, if it is signaled.

Prototype

char OS_CSemaRequest (OS_CSEMA* pCSema);

Return value

0: Failed, semaphore was not signaled.

1: OK, semaphore was available and counter was decremented once.

Additional Information

If the counter of the semaphore is not zero, the counter is decremented and program

execution continues.

If the counter is zero, OS_CSemaRequest() does not wait and does not modify the

semaphore counter. The function returns with error state.

Because this function never blocks a calling task, this function may be called from an

interrupt handler.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

Table 7.8: OS_CSemaRequest() parameter list

135

7.2.8 OS_GetCSemaValue()

Description

Returns the counter value of a specified semaphore.

Prototype

int OS_GetCSemaValue (const OS_SEMA* pCSema);

Return value

The counter value of the semaphore.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

Table 7.9: OS_GetCSemaValue() parameter list

136 CHAPTER 7 Counting Semaphores

7.2.9 OS_SetCSemaValue()

Description

Sets the counter value of a specified semaphore.

Prototype

OS_U8 OS_SetCSemaValue (OS_SEMA* pCSema,

OS_UINT Value);

Return value

0: In any case.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

Value

Count value of the semaphore:

0 <= InitValue <= 216-1 = 0xFFFF for 8/16-bit CPUs

0 <= InitValue <= 232-1 = 0xFFFFFFFF for 32-bit CPUs

Table 7.10: OS_SetCSemaValue() parameter list

137

7.2.10 OS_DeleteCSema()

Description

Deletes a specified semaphore.

Prototype

void OS_DeleteCSema (OS_CSEMA* pCSema);

Additional Information

Before deleting a semaphore, make sure that no task is waiting for it and that no

task will signal that semaphore at a later point.

A debug build of embOS will reflect an error if a deleted semaphore is signaled.

Parameter Description

pCSema Pointer to a data structure of type OS_CSEMA.

Table 7.11: OS_DeleteCSema() parameter list

138 CHAPTER 7 Counting Semaphores

139

Chapter 8

Mailboxes

140 CHAPTER 8 Mailboxes

8.1 Introduction

In the preceding chapters task synchronization by the use of semaphores was

described. Unfortunately, semaphores cannot transfer data from one task to another.

If we need to transfer data between tasks for example via a buffer, we could use a

resource semaphore every time we accessed the buffer. But doing so would make the

program less efficient. Another major disadvantage would be that we could not

access the buffer from an interrupt handler, because the interrupt handler is not

allowed to wait for the resource semaphore.

One solution would be the usage of global variables. In this case we would need to

disable interrupts each time and in each place that we accessed these variables. This

is possible, but it is a path full of pitfalls. It is also not easy for a task to wait for a

character to be placed in a buffer without polling the global variable that contains the

number of characters in the buffer. Again, there is solution — the task could be noti-

fied by an event signaled to the task each time a character is placed in the buffer.

This is why there is an easier way to do this with a real-time OS:

The use of mailboxes.

141

8.2 Basics

A mailbox is a buffer that is managed by the real-time operating system. The buffer

behaves like a normal buffer; you can deposit something (called a message) and

retrieve it later. Mailboxes usually work as FIFO: first in, first out. So a message that

is deposited first will usually be retrieved first. “Message” might sound abstract, but

very simply it means “item of data”. It will become clearer in the typical applications

explained in the following section.

A mailbox can be used by more than one producer but should be used by one con-

sumer only. This means that more than one task or interrupt handler is allowed to

deposit new data into the mailbox, but it does not make sense to retrieve messages

by multiple tasks.

Limitations:

The number of mailboxes and buffers is limited only by the amount of available mem-

ory.

The message size, number of messages and buffer size per mailbox are limited by

software design.

Message size: 1 <= x <= 32767 bytes.

Number of messages: 1 <= x <= 32767 on 8 or 16bit CPUs.

Number of messages: 1 <= x <= 231-1 on 32bit CPUs.

Maximum buffer size for one mailbox: 65536 bytes (64KB) on 16bit CPUs

Maximum buffer size for one mailbox: 232 bytes on 32bit CPUs

These limitations have been placed on mailboxes to guarantee efficient coding and

also to ensure efficient management. These limitations are normally not a problem.

142 CHAPTER 8 Mailboxes

8.3 Typical applications

8.3.1 A keyboard buffer

In most programs, you use either a task, a software timer or an interrupt handler to

check the keyboard. When a key has been pressed, that key is deposited into a mail-

box that is used as a keyboard buffer. The message is then retrieved by the task that

handles keyboard input. The message in this case is typically a single byte that holds

the key code; the message size is therefore one byte.

The advantage of a keyboard buffer is that management is very efficient; you do not

need to worry about it, because it is reliable, proven code and you have a type-ahead

buffer at no extra cost. In addition, a task can easily wait for a key to be pressed

without having to poll the buffer. It simply calls the OS_GetMail() routine for that

particular mailbox. The number of keys that can be deposited in the type-ahead

buffer depends only on the size of the mailbox buffer, which you define when creating

the mailbox.

8.3.2 A buffer for serial I/O

In most cases, serial I/O is done with the help of interrupt handlers. The communica-

tion to these interrupt handlers is very easy with mailboxes. Both your task programs

and your interrupt handlers deposit or retrieve data into/from the same mailbox. As

with a keyboard buffer, the message size is one character.

For interrupt-driven sending, the task deposits the character(s) in the mailbox using

OS_PutMail() or OS_PutMailCond(); the interrupt handler that is activated when a

new character can be sent retrieves the character(s) with OS_GetMailCond().

For interrupt-driven receiving, the interrupt handler that is activated when a new

character is received deposits it in the mailbox using OS_PutMailCond(); the task

receives it using OS_GetMail() or OS_GetMailCond().

8.3.3 A buffer for commands sent to a task

Assume you have one task controlling a motor, as you might have in applications that

control a machine. A simple way to give commands to this task would be to define a

structure for commands. The message size would then be the size of this structure.

143

8.4 Single-byte mailbox functions

In many (if not the most) situations, mailboxes are used simply to hold and transfer

single-byte messages. This is the case, for example, with a mailbox that takes the

character received or sent via serial interface, or normally with a mailbox used as a

keyboard buffer. In some of these cases, time is very critical, especially if a lot of

data is transferred in short periods of time.

To minimize the overhead caused by the mailbox management of embOS, variations

on some mailbox functions are available for single-byte mailboxes. The general func-

tions OS_PutMail(), OS_PutMailCond(), OS_GetMail(), and OS_GetMailCond() can

transfer messages of sizes between 1 and 32767 bytes each.

Their single-byte equivalents OS_PutMail1(), OS_PutMailCond1(), OS_GetMail1(),

and OS_GetMailCond1() work the same way with the exception that they execute

much faster because management is simpler. It is recommended to use the single-

byte versions if you transfer a lot of single-byte data via mailboxes.

The routines OS_PutMail1(), OS_PutMailCond1(), OS_GetMail1(), and

OS_GetMailCond1() work exactly the same way as their universal equivalents and

are therefore not described separately. The only difference is that they can only be

used for single-byte mailboxes.

144 CHAPTER 8 Mailboxes
UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
8.5 API functions
Routine Explanation
main
Task
ISR
Timer
OS_CreateMB() Creates a new mailbox. X X
OS_PutMail() / 
OS_PutMail1()
Stores a new message of a predefined size in 
a mailbox.  XX
OS_PutMailCond() / 
OS_PutMailCond1()
Stores a new message of a predefined size in 
a mailbox, if the mailbox is able to accept 
one more message.
XXXX
OS_PutMailFront() / 
OS_PutMailFront1()
Stores a new message of a predefined size 
into a mailbox in front of all other messages. 
This new message will be retrieved first.
XX
OS_PutMailFrontCond() / 
OS_PutMailFrontCond1()
Stores a new message of a predefined size 
into a mailbox in front of all other messages, 
if the mailbox is able to accept one more 
message.
XXXX
OS_GetMail() / 
OS_GetMail1()
Retrieves a message of a predefined size 
from a mailbox. X
OS_GetMailCond() / 
OS_GetMailCond1()
Retrieves a message of a predefined size 
from a mailbox, if a message is available. XXXX
OS_GetMailTimed()
Retrieves a new message of a predefined size 
from a mailbox, if a message is available 
within a given time.
XX
OS_WaitMail() Waits until a mail is available, but does not 
retrieve the message from the mailbox. XX
OS_WaitMailTimed()
Suspends the calling task until a mail is 
available or until the timeout expires, but 
does not retrieve the message from the mail-
box.
XX
OS_PeekMail() Reads a mail from a mailbox without remov-
ing it  XXXX
OS_ClearMB() Clears all messages in a specified mailbox. X X X X
OS_GetMessageCnt() Returns number of messages currently in a 
specified mailbox. XXXX
OS_DeleteMB() Deletes a specified mailbox. X X
Table 8.1: Mailboxes API functions

145

8.5.1 OS_CreateMB()

Description

Creates a new mailbox.

Prototype

void OS_CreateMB (OS_MAILBOX* pMB,

unsigned short sizeofMsg,

unsigned int maxnofMsg,

void* pMsg);

Example

Mailbox used as keyboard buffer:

OS_MAILBOX MBKey;

char MBKeyBuffer[6];

void InitKeyMan(void) {

/* Create mailbox, functioning as type ahead buffer */

OS_CreateMB(&MBKey, 1, sizeof(MBKeyBuffer), &MBKeyBuffer);

}

Mailbox used for transferring complex commands from one task to another:

* Example of mailbox used for transferring commands to a task

* that controls a motor

typedef struct {

char Cmd;

int Speed[2];

int Position[2];

} MOTORCMD ;

OS_MAILBOX MBMotor;

#define NUM_MOTORCMDS 4

char BufferMotor[sizeof(MOTORCMD) * NUM_MOTORCMDS];

void MOTOR_Init(void) {

/* Create mailbox that holds commands messages */

OS_CreateMB(&MBMotor, sizeof(MOTORCMD), NUM_MOTORCMDS, &BufferMotor);

}

Parameter Description

pMB Pointer to a data structure of type OS_MAILBOX reserved for man-

aging the mailbox.

sizeofMsg Size of a message in bytes. (1 <= sizeofMsg <= 32767)

maxnoMsg Maximum number of messages. (1 <= MaxnofMsg <= 32767)

pMsg

Pointer to a memory area used as buffer. The buffer must be big

enough to hold the given number of messages of the specified

size: sizeofMsg * maxnoMsg bytes.

Table 8.2: OS_CreateMB() parameter list

146 CHAPTER 8 Mailboxes

8.5.2 OS_PutMail() / OS_PutMail1()

Description

Stores a new message of a predefined size in a mailbox.

Prototype

void OS_PutMail (OS_MAILBOX* pMB,

const void* pMail);

void OS_PutMail1 (OS_MAILBOX* pMB,

const char* pMail);

Additional Information

If the mailbox is full, the calling task is suspended.

Because this routine might require a suspension, it must not be called from an inter-

rupt routine. Use OS_PutMailCond()/OS_PutMailCond1() instead if you need to

store data in a mailbox from within an ISR.

When using a debug build of embOS, calling from an interrupt routine will call the error

handler OS_Error() with error code OS_ERR_IN_ISR.

Important

This function must not be called from within an interrupt handler.

Example

Single-byte mailbox as keyboard buffer:

OS_MAILBOX MBKey;

char MBKeyBuffer[6];

void KEYMAN_StoreKey(char k) {

OS_PutMail1(&MBKey, &k); /* Store key, wait if no space in buffer */

}

void KEYMAN_Init(void) {

/* Create mailbox functioning as type ahead buffer */

OS_CreateMB(&MBKey, 1, sizeof(MBKeyBuffer), &MBKeyBuffer);

}

Parameter Description

pMB Pointer to the mailbox.

pMail Pointer to the message to store.

Table 8.3: OS_PutMail() / OS_PutMail1() parameter list

147

8.5.3 OS_PutMailCond() / OS_PutMailCond1()

Description

Stores a new message of a predefined size in a mailbox, if the mailbox is able to

accept one more message.

Prototype

char OS_PutMailCond (OS_MAILBOX* pMB,

const void* pMail);

char OS_PutMailCond1 (OS_MAILBOX* pMB,

const char* pMail);

Return value

0: Success; message stored.

1: Message could not be stored (mailbox is full).

Additional Information

If the mailbox is full, the message is not stored.

This function never suspends the calling task. It may therefore be called from an

interrupt routine.

Example

OS_MAILBOX MBKey;

char MBKeyBuffer[6];

char KEYMAN_StoreCond(char k) {

return OS_PutMailCond1(&MBKey, &k); /* Store key if space in buffer */

}

This example can be used with the sample program shown earlier to handle a mail-

box as keyboard buffer.

Parameter Description

pMB Pointer to the mailbox.

pMail Pointer to the message to store.

Table 8.4: OS_PutMailCond() / OS_PutMailCond1() overview

148 CHAPTER 8 Mailboxes

8.5.4 OS_PutMailFront() / OS_PutMailFront1()

Description

Stores a new message of a predefined size at the beginning of a mailbox in front of

all other messages. This new message will be retrieved first.

Prototype

void OS_PutMailFront (OS_MAILBOX* pMB,

const void* pMail);

void OS_PutMailFront1 (OS_MAILBOX* pMB,

const char* pMail);

Additional Information

If the mailbox is full, the calling task is suspended. Because this routine might

require a suspension, it must not be called from an interrupt routine. Use

OS_PutMailFrontCond()/OS_PutMailFrontCond1() instead if you need to store data

in a mailbox from within an ISR.

This function is useful to store “emergency” messages into a mailbox which must be

handled quickly.

It may also be used in general instead of OS_PutMail() to change the FIFO structure

of a mailbox into a LIFO structure.

Important

This function must not be called from within an interrupt handler.

Example

Single-byte mailbox as keyboard buffer which will follow the LIFO pattern:

OS_MAILBOX MBCmd;

char MBCmdBuffer[6];

void KEYMAN_StoreCommand(char k) {

OS_PutMailFront1(&MBCmd, &k); /* Store command, wait if no space in buffer*/

}

void KEYMAN_Init(void) {

/* Create mailbox for command buffer */

OS_CreateMB(&MBCmd, 1, sizeof(MBCmdBuffer), &MBCmdBuffer);

}

Parameter Description

pMB Pointer to the mailbox.

pMail Pointer to the message to store.

Table 8.5: OS_PutMailFront() / OS_PutMailFront1() parameter list

149

8.5.5 OS_PutMailFrontCond() / OS_PutMailFrontCond1()

Description

Stores a new message of a predefined size into a mailbox in front of all other mes-

sages, if the mailbox is able to accept one more message. The new message will be

retrieved first.

Prototype

char OS_PutMailFrontCond (OS_MAILBOX* pMB,

const void* pMail);

char OS_PutMailFrontCond1 (OS_MAILBOX* pMB,

const char* pMail);

Return value

0: Success; message stored.

1: Message could not be stored (mailbox is full).

Additional Information

If the mailbox is full, the message is not stored. This function never suspends the

calling task. It may therefore be called from an interrupt routine. This function is

useful to store “emergency” messages into a mailbox which must be handled quickly.

It may also be used in general instead of OS_PutMailCond() to change the FIFO

structure of a mailbox into a LIFO structure.

Parameter Description

pMB Pointer to the mailbox.

pMail Pointer to the message to store.

Table 8.6: OS_PutMailFrontCond() / OS_PutMailFrontCond1() parameter list

150 CHAPTER 8 Mailboxes

8.5.6 OS_GetMail() / OS_GetMail1()

Description

Retrieves a new message of a predefined size from a mailbox.

Prototype

void OS_GetMail (OS_MAILBOX* pMB,

void* pDest);

void OS_GetMail1 (OS_MAILBOX* pMB,

char* pDest);

Additional Information

If the mailbox is empty, the task is suspended until the mailbox receives a new mes-

sage. Because this routine might require a suspension, it must not be called from an

interrupt routine. Use OS_GetMailCond/OS_GetMailCond1 instead if you need to

retrieve data from a mailbox from within an ISR.

Important

This function must not be called from within an interrupt handler.

Example

OS_MAILBOX MBKey;

char WaitKey(void) {

char c;

OS_GetMail1(&MBKey, &c);

return c;

}

Parameter Description

pMB Pointer to the mailbox.

pDest

Pointer to the memory area that the message should be stored

at. Make sure that it points to a valid memory area and that there

is sufficient space for an entire message. The message size (in

bytes) was defined when the mailbox was created.

Table 8.7: OS_GetMail() / OS_GetMail1() parameter list

151

8.5.7 OS_GetMailCond() / OS_GetMailCond1()

Description

Retrieves a new message of a predefined size from a mailbox, if a message is

available.

Prototype

char OS_GetMailCond (OS_MAILBOX* pMB,

void* pDest);

char OS_GetMailCond1 (OS_MAILBOX* pMB,

char* pDest);

Return value

0: Success; message retrieved.

1: Message could not be retrieved (mailbox is empty); destination remains

unchanged.

Additional Information

If the mailbox is empty, no message is retrieved and pDest remains unchanged, but

the program execution continues. This function never suspends the calling task. It

may therefore also be called from an interrupt routine.

Example

OS_MAILBOX MBKey;

* If a key has been pressed, it is taken out of the mailbox and returned to caller.

* Otherwise 0 is returned.

char GetKey(void) {

char c = 0;

OS_GetMailCond1(&MBKey, &c);

return c;

}

Parameter Description

pMB Pointer to the mailbox.

pDest

Pointer to the memory area that the message should be stored

at. Make sure that it points to a valid memory area and that there

is sufficient space for an entire message. The message size (in

bytes) was defined when the mailbox was created.

Table 8.8: OS_GetMailCond() / OS_GetMailCond1() parameter list

152 CHAPTER 8 Mailboxes

8.5.8 OS_GetMailTimed()

Description

Retrieves a new message of a predefined size from a mailbox, if a message is avail-

able within a given time.

Prototype

char OS_GetMailTimed (OS_MAILBOX* pMB,

void* pDest,

OS_TIME Timeout);

Return value

0: Success; message retrieved.

1: Message could not be retrieved (mailbox is empty); destination remains

unchanged.

Additional Information

If the mailbox is empty, no message is retrieved, pDest remains unchanged and the

task is suspended for the given timeout. The task continues execution according to

the rules of the scheduler as soon as a mail is available within the given timeout, or

after the timeout value has expired.

When the calling task is blocked by higher priority tasks for a period longer than the

timeout value, it may happen that mail becomes available before the calling task is

resumed. Anyhow, the function returns with timeout because the mail was not avail-

bale within the requested time. In this case, no mail is retrieved from the mailbox.

Important

This function must not be called from within an interrupt handler.

Example

OS_MAILBOX MBKey;

* If a key has been pressed, it is taken out of the mailbox and returned to caller.

* Otherwise, 0 is returned.

char GetKey(void) {

char c = 0;

OS_GetMailTimed(&MBKey, &c, 10); /* Wait for 10 timer ticks */

return c;

}

Parameter Description

pMB Pointer to the mailbox.

pDest

Pointer to the memory area that the message should be stored

at. Make sure that it points to a valid memory area and that there

is sufficient space for an entire message. The message size (in

bytes) has been defined upon creation of the mailbox.

Timeout

Maximum time in timer ticks until the requested mail must be

available. The data type OS_TIME is defined as an integer, there-

fore valid values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 8.9: OS_GetMailTimed() parameter list

153

8.5.9 OS_WaitMail()

Description

Waits until a mail is available, but does not retrieve the message from the mailbox.

Prototype

void OS_WaitMail (OS_MAILBOX* pMB);

Additional Information

If the mailbox is empty, the task is suspended until a mail is available, otherwise the

task continues. The task continues execution according to the rules of the scheduler

as soon as a mail is available, but the mail is not retrieved from the mailbox.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pMB Pointer to the mailbox.

Table 8.10: OS_WaitMail() parameter list

154 CHAPTER 8 Mailboxes

8.5.10 OS_WaitMailTimed()

Description

Waits until a mail is available or the timeout has expired, but does not retrieve the

message from the mailbox.

Prototype

char OS_WaitMailTimed (OS_MAILBOX* pMB,

OS_TIME Timeout);

Return value

0: Success; message available.

1: Timeout; no message available within the given timeout time.

Additional Information

If the mailbox is empty, the task is suspended for the given timeout. The task contin-

ues execution according to the rules of the scheduler as soon as a mail is available

within the given timeout, or after the timeout value has expired.

When the calling task is blocked by higher priority tasks for a period longer than the

timeout value, it may happen that mail becomes available before the calling task is

resumed. In this case the function returns with timeout, because the mail was not

available within the requested time.

Important

This function must not be called from within an interrupt handler.

Parameter Description

pMB Pointer to the mailbox.

Timeout

Maximum time in timer ticks until the requested mail must be

available. The data type OS_TIME is defined as an integer, there-

fore valid values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 8.11: OS_WaitMail() parameter list

155

8.5.11 OS_PeekMail()

Description

Peeks a mail from a mailbox without removing the mail.

Prototype

char OS_PeekMail (OS_MAILBOX* pMB,

void* pDest);

Return value

0: Success; message available.

1: Message could not be retrieved (mailbox is empty).

Additional Information

This function is non-blocking and never suspends the calling task. It may therefore

be called from an interrupt routine.

Parameter Description

pMB Pointer to the mailbox.

pDest Pointer to a buffer that should receive the mail

Table 8.12: OS_PeekMail() parameter list

156 CHAPTER 8 Mailboxes

8.5.12 OS_ClearMB()

Description

Clears all messages in a specified mailbox.

Prototype

void OS_ClearMB (OS_MAILBOX* pMB);

Additional Information

OS_ClearMB() may cause a task switch.

Example

OS_MAILBOX MBKey;

* Clear keyboard type ahead buffer

void ClearKeyBuffer(void) {

OS_ClearMB(&MBKey);

}

Parameter Description

pMB Pointer to the mailbox.

Table 8.13: OS_ClearMB() parameter list

157

8.5.13 OS_GetMessageCnt()

Description

Returns the number of messages currently available in a specified mailbox.

Prototype

unsigned int OS_GetMessageCnt (OS_MAILBOX* pMB);

Return value

The number of messages in the mailbox.

Parameter Description

pMB Pointer to the mailbox.

Table 8.14: OS_GetMessageCnt() parameter list

158 CHAPTER 8 Mailboxes

8.5.14 OS_DeleteMB()

Description

Deletes a specified mailbox.

Prototype

void OS_DeleteMB (OS_MAILBOX* pMB);

Additional Information

To keep the system fully dynamic, it is essential that mailboxes can be created

dynamically. This also means there must be a way to delete a mailbox when it is no

longer needed. The memory that has been used by the mailbox for the control struc-

ture and the buffer can then be reused or reallocated.

It is the programmer's responsibility to:

• make sure that the program no longer uses the mailbox to be deleted

• make sure that the mailbox to be deleted actually exists (i.e. has been created

first).

In a debug build OS_Error() will also be called, if OS_DeleteMB() is called while

tasks are waiting for new data from the mailbox. The error code in this case is

OS_ERR_MAILBOX_DELETE.

Example

OS_MAILBOX MBSerIn;

void Cleanup(void) {

OS_DeleteMB(&MBSerIn);

}

Parameter Description

pMB Pointer to the mailbox.

Table 8.15: OS_DeleteMB() parameter list

159

Chapter 9

Queues

160 CHAPTER 9 Queues

9.1 Introduction

In the preceding chapter, intertask communication using mailboxes was described.

Mailboxes can handle small messages with fixed data size only.

Queues enable intertask communication with larger messages or with messages of

differing lengths.

161

9.2 Basics

A queue consists of a data buffer and a control structure that is managed by the real-

time operating system. The queue behaves like a normal buffer; you can deposit

something (called a message) in the queue and retrieve it later. Queues work as

FIFO: first in, first out. So a message that is deposited first will be retrieved first.

There are three major differences between queues and mailboxes:

1. Queues accept messages of differing lengths. When depositing a message into a

queue, the message size is passed as a parameter.

2. Retrieving a message from the queue does not copy the message, but returns a

pointer to the message and its size. This enhances performance because the data

is copied only when the message is written into the queue.

3. The retrieving function must delete every message after processing it.

4. A new message can only be retrieved from the queue when the previous message

was deleted from the queue.

Both the number and size of queues is limited only by the amount of available

memory. Any data structure can be written into a queue, the message size is not

fixed.

Similar to mailboxes, queues can be used by more than one producer but should be

used by one consumer only. This means that more than one task or interrupt handler

is allowed to deposit new data into the queue, but it does not make sense to retrieve

messages by multiple tasks.

The queue data buffer contains the messages and some additional management

information. Each message has a message header containing the message size. The

define OS_Q_SIZEOF_HEADER defines the size of the message header.

Additionally, the queue buffer will be aligned for those CPUs which need data align-

ment. Therefore the queue data buffer size must be bigger than the sum of all mes-

sages.

162 CHAPTER 9 Queues
UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
9.3 API functions
Routine Description
main
Task
ISR
Timer
OS_Q_Create() Creates and initializes a message queue. X X X X
OS_Q_Put() Stores a new message of given size in a 
queue. XXXX
OS_Q_PutBlocked()
Stores a new message of given size in a 
queue. Blocks the calling task when queue is 
full.
X
OS_Q_PutTimed()
Stores a new message of given size in a queue 
within a given timeout time. Suspends the 
calling task when the queue is full.
XX
OS_Q_GetPtr() Retrieves a message from a queue. X X
OS_Q_GetPtrCond()
Retrieves a message from a queue, if one 
message is available or returns without sus-
pension.
XXXX
OS_Q_GetPtrTimed() Retrieves a message from a queue within a 
specified time, if one message is available. XX
OS_Q_Purge() Deletes the last retrieved message in a queue. X X X X
OS_Q_Clear() Deletes all message in a queue. X X X X
OS_Q_GetMessageCnt() Returns the number of messages currently in a 
queue. XXXX
OS_Q_Delete() Deletes a specified queue. X X X X
OS_Q_IsInUse() Delivers information about the usage state of 
the queue. XXXX
OS_Q_GetMessageSize() Returns the size of the first message in the 
queue. XXXX
OS_Q_PeekPtr() Retrieves a message from a queue without 
removing it. XXXX
Table 9.1: Queues API

163

9.3.1 OS_Q_Create()

Description

Creates and initializes a message queue.

Prototype

void OS_Q_Create (OS_Q* pQ,

void* pData,

OS_UINT Size);

Example

#define MESSAGE_CNT 100

#define MESSAGE_SIZE 100

#define MEMORY_QSIZE MESSAGE_CNT * (MESSAGE_SIZE + OS_Q_SIZEOF_HEADER)

static OS_Q _MemoryQ;

static char _acMemQBuffer[MEMORY_QSIZE];

void MEMORY_Init(void) {

OS_Q_Create(&_MemoryQ, &_acMemQBuffer, sizeof(_acMemQBuffer));

}

Additional Information

The define OS_Q_SIZEOF_HEADER can be used to calculate the additional management

information bytes needed for each message in the queue data buffer. But it does not

account for the additional space needed for data alignment. Thus the number of mes-

sages that can actually be stored in the queue buffer depends on the message sizes.

Parameter Description

pQ Pointer to a data structure of type OS_Q reserved for the manage-

ment of the message queue.

pData Pointer to a memory area used as data buffer for the queue.

Size Size in bytes of the data buffer.

Table 9.2: OS_Q_Create() parameter list

164 CHAPTER 9 Queues

9.3.2 OS_Q_Put()

Description

Deposits a new message of given size in a queue.

Prototype

int OS_Q_Put (OS_Q* pQ,

const void* pSrc,

OS_UINT Size);

Return value

0: Success, message stored.

1: Message could not be stored (queue is full).

Additional Information

This routine never suspends the calling task and may therefore be called from an

interrupt routine.

When the message is deposited into the queue, the entire message is copied into the

queue buffer, not only the pointer to the data. Therefore the message content is pro-

tected and remains valid until it is retrieved and accessed by a task reading the mes-

sage.

Example

int MEMORY_Write(const char* pData, OS_UINT Len) {

return OS_Q_Put(&_MemoryQ, pData, Len);

}

Parameter Description

pQ Pointer to a data structure of type OS_Q reserved for the manage-

ment of the message queue.

pSrc Pointer to the message to store.

Size Size of the message to store.

Table 9.3: OS_Q_Put() parameter list

165

9.3.3 OS_Q_PutBlocked()

Description

Deposits a new message of given size in a queue.

Prototype

void OS_Q_PutBlocked (OS_Q* pQ,

const void* pSrc,

OS_UINT Size);

Additional Information

If the queue is full, the calling task is suspended. Because this routine might require

a suspension, it must not be called from an interrupt routine. Use OS_Q_Put()

instead if you need to deposit messages in a queue from within an ISR.

Important

This function must not be called from within an interrupt handler.

When using a debug build of embOS, calling from an interrupt handler will call the

error handler OS_Error() with error code OS_ERR_IN_ISR .

Example

void StoreMessage(const char* pData, OS_UINT Len)

OS_Q_PutBlocked(&_MemoryQ, pData, Len);

}

Parameter Description

pQ Pointer to a data structure of type OS_Q reserved for the manage-

ment of the message queue.

pSrc Pointer to the message to store.

Size Size of the message to store.

Table 9.4: OS_Q_Put() parameter list

166 CHAPTER 9 Queues

9.3.4 OS_Q_PutTimed()

Description

Deposits a new message of given size in a queue if space is available within a given

time.

Prototype

int OS_Q_PutTimed (OS_Q* pQ,

const void* pSrc,

OS_UINT Size,

OS_TIME Timeout);

Return value

0: Success, message stored.

1: Message could not be stored within the specified time (insufficient space).

Additional Information

If the queue holds insufficient space, the calling task is suspended until space for the

message is available, or the specified timeout time has expired.

If the message could be deposited into the queue within the sepcified time, the func-

tion returns zero.

As the calling function may be suspended, the function must not be called from an

interrupt routine or timer. A debug build of embOS will call the embOS error function

OS_Error() if this function is called from an interrupt handler or timer.

Example

int MEMORY_WriteTimed(const char* pData, OS_UINT Len, OS_TIME Timeout) {

return OS_Q_PutTimed(&_MemoryQ, pData, Len, Timeout);

}

Parameter Description

pQ Pointer to a data structure of type OS_Q reserved for the manage-

ment of the message queue.

pSrc Pointer to the message to store.

Size Size of the message to store.

Timeout

Maximum time in timer ticks until the requested message must

be stored into the queue.

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 9.5: OS_Q_Put() parameter list

167

9.3.5 OS_Q_GetPtr()

Description

Retrieves a message from a queue.

Prototype

int OS_Q_GetPtr (OS_Q* pQ,

void** ppData);

Return value

The size of the retrieved message.

Sets the pointer ppData to the message that should be retrieved.

Additional Information

If the queue is empty, the calling task is suspended until the queue receives a new

message. Because this routine might require a suspension, it must not be called from

an interrupt routine or timer. Use OS_GetPtrCond() instead. The retrieved message

is not removed from the queue, this must be done by a call of OS_Q_Purge() after

the message was processed. Only one message can be processed at a time.

As long as the message is not removed from the queue, the queue is marked “in

use”.

A following call of OS_Q_GetPtr() or OS_Q_GetPtrCond() is not allowed before

OS_Q_Purge() is called as long as the queue is in use.

Consecutive calls of OS_Q_GetPtr() without calling OS_Q_Purge() will call the embOS

error handler OS_Error() in debug builds of embOS.

Example

static void MemoryTask(void) {

int Len;

char* pData;

while (1) {

Len = OS_Q_GetPtr(&_MemoryQ, &pData); /* Get message */

Memory_WritePacket(*(U32*)pData, Len); /* Process message */

OS_Q_Purge(&_MemoryQ); /* Delete message */

}

Parameter Description

pQ Pointer to the queue.

ppData Address of pointer to the message to be retrieved from queue.

Table 9.6: OS_Q_GetPtr() parameter list

168 CHAPTER 9 Queues

9.3.6 OS_Q_GetPtrCond()

Description

Retrieves a message from a queue if a message is available.

Prototype

int OS_Q_GetPtrCond (OS_Q* pQ,

void** ppData);

Return value

0: No message available in queue.

>0: Size of the message that was retrieved from the queue.

Sets the pointer ppData to the message that should be retrieved.

Additional Information

If the queue is empty, the function returns zero and the value of ppData is undefined.

This function never suspends the calling task. It may therefore be called from an

interrupt routine or timer. If a message could be retrieved it is not removed from the

queue, this must be done by a call of OS_Q_Purge() after the message was pro-

cessed.

As long as the message is not removed from the queue, the queue is marked “in

use”.

A following call of OS_Q_GetPtrCond() or OS_Q_GetPtr() is not allowed before

OS_Q_Purge() is called as long as the queue is in use.

Consecutive calls of OS_Q_GetPtrCond() without calling OS_Q_Purge() will call the

embOS error handler OS_Error() in debug builds of embOS.

Example

static void MemoryTask(void) {

int Len;

char* pData;

while (1) {

Len = OS_Q_GetPtrCond(&_MemoryQ, &pData); /* Check message */

if (Len > 0) {

Memory_WritePacket(*(U32*)pData, Len); /* Process message */

OS_Q_Purge(&_MemoryQ); /* Delete message */

} else {

DoSomethingElse();

}

Parameter Description

pQ Pointer to the queue.

ppData Address of pointer to the message to be retrieved from queue.

Table 9.7: OS_Q_GetPtrCond() parameter list

169

9.3.7 OS_Q_GetPtrTimed()

Description

Retrieves a message from a queue within a specified time if a message is available.

Prototype

int OS_Q_GetPtrTimed (OS_Q* pQ,

void** ppData,

OS_TIME Timeout);

Return value

0: No message available in queue.

>0: Size of the message that was retrieved from the queue.

Sets the pointer ppData to the message that should be retrieved.

Additional Information

If the queue is empty no message is retrieved, the task is suspended for the given

timeout and the value of ppData is undefined. The task continues execution accord-

ing to the rules of the scheduler as soon as a message is available within the given

timeout, or after the timeout value has expired.

When the calling task is blocked by higher priority tasks for a period longer than the

timeout value, it may happen that a message becomes available before the calling

task is resumed. Anyhow, the function returns with timeout because the message

was not availbale within the requested time. In this case the state of the queue is not

modified by OS_Q_GetPtrTimed() and a pointer to the message is not delivered.

As long as a message was retrieved and the message is not removed from the queue,

the queue is marked “in use”.

A following call of OS_Q_GetPtrTimed() is not allowed before OS_Q_Purge() is called

as long as the queue is in use.

Consecutive calls of OS_Q_GetPtrTimed() without calling OS_Q_Purge() after retriev-

ing a message call the embOS error handler OS_Error() in debug builds of embOS.

Example

static void MemoryTask(void) {

int Len;

char* pData;

while (1) {

Len = OS_Q_GetPtrTimed(&_MemoryQ, &pData, 10); /* Check message */

if (Len > 0) {

Memory_WritePacket(*(U32*)pData, Len); /* Process message */

OS_Q_Purge(&_MemoryQ); /* Delete message */

} else { /* Timeout */

DoSomethingElse();

}

Parameter Description

pQ Pointer to the queue.

ppData Address of pointer to the message to be retrieved from queue.

Timeout

Maximum time in timer ticks until the requested message must

be available. The data type OS_TIME is defined as an integer,

therefore valid values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 9.8: OS_Q_GetPtrTimed() parameter list

170 CHAPTER 9 Queues

9.3.8 OS_Q_Purge()

Description

Deletes the last retrieved message in a queue.

Prototype

void OS_Q_Purge (OS_Q* pQ);

Additional Information

This routine should be called by the task that retrieved the last message from the

queue, after the message is processed.

Once a message was retrieved by a call of OS_Q_GetPtr(), OS_Q_GetPtrCond() or

OS_Q_GetPtrTimed(), the message must be removed from the queue by a call of

OS_Q_Purge() before a following message can be retrieved from the queue. Consec-

utive calls of OS_Q_GetPtr(), OS_Q_GetPtrCond() or OS_Q_GetPtrTimed() will call

the embOS error handler OS_Error() in embOS debug builds.

Consecutive calls of OS_Q_Purge() or calling OS_Q_Purge() without having retrieved

a message from the queue will also call the embOS error handler OS_Error() in

embOS debug builds.

Example

static void MemoryTask(void) {

int Len;

char* pData;

while (1) {

Len = OS_Q_GetPtr(&_MemoryQ, &pData); /* Get message */

Memory_WritePacket(*(U32*)pData, Len); /* Process message */

OS_Q_Purge(&_MemoryQ); /* Delete message */

}

Parameter Description

pQ Pointer to the queue.

Table 9.9: OS_Q_Purge() parameter list

171

9.3.9 OS_Q_Clear()

Description

Deletes all message in a queue.

Prototype

void OS_Q_Clear (OS_Q* pQ);

Additional Information

When the queue is in use, a debug build of embOS will call OS_Error() with error

code OS_ERR_QUEUE_INUSE.

Parameter Description

pQ Pointer to the queue.

Table 9.10: OS_Q_Clear() parameter list

172 CHAPTER 9 Queues

9.3.10 OS_Q_GetMessageCnt()

Description

Returns the number of messages that are currently stored in a queue.

Prototype

int OS_Q_GetMessageCnt (const OS_Q* pQ);

Return value

The number of messages in the queue.

Parameter Description

pQ Pointer to the queue.

Table 9.11: OS_Q_GetMessageCnt() parameter list

173

9.3.11 OS_Q_Delete()

Description

Deletes a specific queue.

Prototype

void OS_Q_Delete (OS_Q* pQ);

Additional Information

To keep the system fully dynamic, it is essential that queues can be created dynami-

cally. This also means there must be a way to delete a queue when it is no longer

needed. The memory that has been used by the queue for the control structure and

the buffer can then be reused or reallocated.

It is the programmer's responsibility to:

• make sure that the program no longer uses the queue to be deleted

• make sure that the queue to be deleted actually exists (i.e. has been created

first).

When the queue is in use, a debug build of embOS will call OS_Error() with error

code OS_ERR_QUEUE_INUSE.

When tasks are waiting, a debug build of embOS will call OS_Error() with error code

OS_ERR_QUEUE_DELETE is called.

Example

OS_Q QSerIn;

void Cleanup(void) {

OS_Q_Delete(&QSerIn);

}

Parameter Description

pQ Pointer to the queue.

Table 9.12: OS_Q_Delete() parameter list

174 CHAPTER 9 Queues

9.3.12 OS_Q_IsInUse()

Description

Delivers information whether the queue is actually in use.

Prototype

OS_BOOL OS_Q_IsInUse(const OS_Q* pQ)

Return value

0: Queue is not in use

!=0: Queue is in use and may not be deleted or cleared.

Additional Information

A queue must not be cleared or deleted when it is in use.

In use means a task or function actually accesses the queue and holds a pointer to a

message in the queue.

OS_Q_IsInUse() can be used to examine the state of the queue before it can be

cleared or deleted, as these functions must not be performed as long as the queue is

used.

Example

void DeleteQ(OS_Q* pQ) {

OS_IncDI(); // Avoid state change of the queue by task or interrupt

// Wait until queue is not used

while (OS_Q_IsInUse(pQ) != 0) {

OS_Delay(1);

}

OS_Q_Delete(pQ);

OS_DecRI();

}

Parameter Description

pQ Pointer to the queue.

Table 9.13: OS_Q_IsInUse() parameter list

175

9.3.13 OS_Q_GetMessageSize()

Description

Returns the size of the first message.

Prototype

int OS_Q_GetMessageSize (OS_Q* pQ)

Return value

The size of the first message or zero when no message is available.

Additional Information

If the queue is empty OS_Q_GetMessageSize returns zero. If a message is available

OS_Q_GetMessageSize returns the size of that message. The message is not

retrieved from the queue.

Example

static void MemoryTask(void) {

int Len;

Len = OS_Q_GetMessageSize(&_MemoryQ); /* Get message length */

if (Len > 0) {

printf(“Message with size %d retrieved\n”, Len);

}

Parameter Description

pQ Pointer to the queue.

Table 9.14: OS_Q_GetMessageSize() parameter list

176 CHAPTER 9 Queues

9.3.14 OS_Q_PeekPtr()

Description

Retrieves a message from a queue.

Prototype

int OS_Q_PeekPtr (OS_Q* pQ,

void** ppData);

Return value

The size of the retrieved message or zero when no new message is available.

Sets the pointer ppData to the message that should be retrieved.

Additional Information

If the queue is empty zero is returned.

The retrieved message is not removed from the queue. Use OS_GetPtr()/

OS_Q_Purge() to retrieve and remove a message from the queue.

Example

static void MemoryTask(void) {

int Len;

char* pData;

while (1) {

OS_IncDI(); // Avoid state changes of the queue by task or interrupt

Len = OS_Q_PeekPtr(&_MemoryQ, &pData); /* Get message */

if (Len > 0) {

Memory_WritePacket(*(U32*)pData, Len); /* Process message */

}

OS_RESTORE_I();

}

Warning

Ensure the queues state is not altered as long as a message is processed. That is the

reason for calling OS_IncDI() in the sample. Ensure no cooperative task switch is

performed, as this may also alter the queue state and buffer. OS_EnterRegion()

does not inhibit cooperative task switches!

Parameter Description

pQ Pointer to the queue.

ppData Address of pointer to the message to be retrieved from queue.

Table 9.15: OS_Q_PeekPtr() parameter list

177

Chapter 10

Task events

178 CHAPTER 10 Task events

10.1 Introduction

Task events are another way of communication between tasks. In contrast to sema-

phores and mailboxes, task events are messages to a single, specified recipient. In

other words, a task event is sent to a specified task.

The purpose of a task event is to enable a task to wait for a particular event (or for

one of several events) to occur. This task can be kept inactive until the event is sig-

naled by another task, a S/W timer or an interrupt handler. The event can consist of

anything that the software has been made aware of in any way. For example, the

change of an input signal, the expiration of a timer, a key press, the reception of a

character, or a complete command.

Every task has an individual bit-mask, which per default is 32bit wide on 32bit CPUs,

and 8bits wide on 16- and 8-bit CPUs. This means that 32 or 8 different events can

be signaled to and distinguished by every task. By calling OS_WaitEvent(), a task

waits for one of the events specified as a bitmask. As soon as one of the events

occurs, this task must be signaled by calling OS_SignalEvent(). The waiting task will

then be put in the READY state immediately. It will be activated according to the

rules of the scheduler as soon as it becomes the task with the highest priority of all

the tasks in the READY state.

By changing the definition of OS_TASK_EVENT which is defined as unsigned long on

32bit CPUs and unsigned char on 16- or 8-bit CPUs per default, the task events can

be expanded to 16 or 32 bits thus allowing more different events, or reduced to

smaller data types on 32bit CPUs.

Changing the definition of OS_TASK_EVENT can only be done when using the embOS

sources in a project, or when the libraries are rebuilt from sources with the modified

definition

179

10.2 API functions

Routine Description

main

Task

ISR

Timer

OS_WaitEvent()

Waits for one of the events specified in

the bitmask and clears the event memory

after an event occurs.

OS_WaitSingleEvent()

Waits for one of the events specified as

bitmask and clears only that event after

it occurs.

OS_WaitEventTimed()

Waits for the specified events for a given

time, and clears the event memory after

an event occurs.

OS_WaitSingleEventTimed()

Waits for the specified events for a given

time; after an event occurs, only that

event is cleared.

OS_SignalEvent() Signals event(s) to a specified task. X X X X

OS_GetEventsOccurred() Returns a list of events that have

occurred for a specified task. XX

OS_ClearEvents() Returns the actual state of events and

then clears the events of a specified task. XXXX

Table 10.1: Events API functions

180 CHAPTER 10 Task events

10.2.1 OS_WaitEvent()

Description

Waits for one of the events specified in the bitmask and clears the event memory

after an event occurs.

Prototype

OS_TASK_EVENT OS_WaitEvent (OS_TASK_EVENT EventMask);

Return value

All events that have actually occurred.

Additional Information

If none of the specified events are signaled, the task is suspended. The first of the

specified events will wake the task. These events are signaled by another task, a S/W

timer or an interrupt handler. Any bit in the event mask may enable the correspond-

ing event.

When a task shall wait on multiple events, all of the specified events shall be

requested by a single call of OS_WaitEvent() and all events must be be handled

when the function returns.

Note that all events of the task are cleared when the function returns, even those

events that were not given as parameter in the eventmask. Consecutive calls of

OS_WaitEvent() with different event masks will not work, as all events are cleared

when the function returns. Events may got lost. OS_WaitSingleEvent() may be used

for this case.

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and unsigned char for

8- or 16-bit CPUs per default. It may be modified to any other type when embOS

sources are used in a project, or when the libraries are rebuilt with a modified defini-

tion.

Example

void Task(void) {

OS_TASK_EVENT MyEvents;

while(1) {

MyEvents = OS_WaitEvent(3); /* Wait for event 1 or 2 to be signaled */

/* Handle ALL events */

if (MyEvents & (1 << 0)) {

_HandleEvent1();

}

if (MyEvents & (1 << 1)) {

_HandleEvent2();

}

For a further example, see OS_SignalEvent().

Parameter Description

EventMask

The events that the task will be waiting for. The type

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and

unsigned char for 8- or 16-bit CPUs per default.

Table 10.2: OS_WaitEvent() parameter list

181

10.2.2 OS_WaitSingleEvent()

Description

Waits for one or more of the events specified by the Eventmask and clears only those

events that were specified in the eventmask.

Prototype

OS_TASK_EVENT OS_WaitSingleEvent (OS_TASK_EVENT EventMask);

Return value

All requested events that have actually occurred.

Additional Information

If none of the specified events are signaled, the task is suspended. The first of the

requested events will wake the task. These events are signaled by another task, a S/

W timer, or an interrupt handler. Any bit in the event mask may enable the corre-

sponding event. When the function returns, it delivers all of the requested events.

The requested events are cleared in the event state of the task. All other events

remain unchanged and will not be returned.

OS_WaitSingleEvent() may be used in consecutive calls with individual requests.

Only requested events will be handled, no other events can get lost.

When the function waits on multiple events, the returned value must be evaluated

because the function returns when at least one of the requested events was signaled.

When the function requests a single event, the returned value does not need to be

evaluated.

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and unsigned char for

8- or 16-bit CPUs per default. It may be modified to any other type when embOS

sources ar used in a project, or when the libraries are rebuilt with a modified defini-

tion.

Example

void Task(void) {

OS_TASK_EVENT MyEvents;

while(1) {

MyEvents = OS_WaitSingleEvent(3); /* Wait for event 1 or 2 to be signaled */

/* Handle ALL events */

if (MyEvents & (1 << 0)) {

_HandleEvent1();

}

if (MyEvents & (1 << 1)) {

_HandleEvent2();

}

OS_WaitSingleEvent((1 << 2)); /* Wait for event 3 to be signaled */

_HandleEvent3();

OS_WaitSingleEvent((1 << 3)); /* Wait for event 4 to be signaled */

_HandleEvent4();

}

Parameter Description

EventMask The events that the task will be waiting for.

Table 10.3: OS_WaitSingleEvent() parameter list

182 CHAPTER 10 Task events

10.2.3 OS_WaitEventTimed()

Description

Waits for the specified events for a given time, and clears the event memory after

one of the requsted events occurs, or after the timeout expired.

Prototype

OS_TASK_EVENT OS_WaitEventTimed (OS_TASK_EVENT EventMask,

OS_TIME TimeOut);

Return value

The events that have actually occurred within the specified time.

0 if no events were signaled in time.

Additional Information

If none of the specified events are available, the task is suspended for the given

time. The first of the requested events will wake the task if the event is signaled by

another task, a S/W timer, or an interrupt handler within the specified TimeOut time.

If none of the requested events is signaled, the task is activated after the specified

timeout and all actual events are returned and then cleared.

Note that the function returns all events that were signaled within the given timeout

time, even those which were not requested.

The calling function must evaluate the returned value.

Consecutive calls of OS_WaitEventTimed() with different event masks will not work,

as all events are cleared when the function returns. Events may got lost.

OS_WaitSingleEventTimed() may be used for this case.

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and unsigned char for

8- or 16-bit CPUs per default.

It may be modified to any other type when embOS sources ar used in a project, or

when the libraries are rebuilt with a modified definition.

Example

void Task(void) {

OS_TASK_EVENT MyEvents;

while(1) {

MyEvents = OS_WaitEvent_Timed(3, 10); /* Wait for events 1+2 for 10 ms */

if ((MyEvents & 0x3) == 0) {

_HandleTimeout();

} else {

if (MyEvents & (1 << 0)) {

_HandleEvent1();

}

if (MyEvents & (1 << 1)) {

_HandleEvent2();

}

Parameter Description

EventMask The events that the task will be waiting for.

Timeout

Maximum time in timer ticks until the events must be signaled.

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 10.4: OS_WaitEventTimed() parameter list

183

10.2.4 OS_WaitSingleEventTimed()

Description

Waits for the specified events for a given time; after an event occurs, only the

requested events are cleared.

Prototype

OS_TASK_EVENT OS_WaitSingleEventTimed (OS_TASK_EVENT EventMask,

OS_TIME TimeOut);

Return value

The masked events that have actually occurred within the specified time.

0 if no masked events were signaled in time.

Additional Information

If none of the specified events are available, the task is suspended for the given

time. The first of the specified events will wake the task if the event is signaled by

another task, a S/W timer or an interrupt handler within the specified TimeOut time.

If no event is signaled, the task is activated after the specified timeout and the

function returns zero. Any bit in the event mask may enable the corresponding event.

All unmasked events remain unchanged.

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and unsigned char for

8- or 16-bit CPUs per default. It may be modified to any other type when embOS

sources ar used in a project, or when the libraries are rebuilt with a modified defini-

tion.

Example

void Task(void) {

OS_TASK_EVENT MyEvents;

while(1) {

MyEvents = OS_WaitSingleEventTimed(3, 10); /* Wait for event 1 or 2 to be

signaled within 10ms */

/* Handle requested events */

if (MyEvents == 0) {

_HandleTimeout;

} else {

if (MyEvents & (1 << 0)) {

_HandleEvent1();

}

if (MyEvents & (1 << 1)) {

_HandleEvent2();

}

if (OS_WaitSingleEvent((1 << 2), 10) == 0) {

_HandleTimeout();

} else {

_HandleEvent3();

}

Parameter Description

EventMask The events that the task will be waiting for.

Timeout

Maximum time in timer ticks until the events must be signaled.

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 10.5: OS_WaitSingleEventTimed() parameter list

184 CHAPTER 10 Task events

10.2.5 OS_SignalEvent()

Description

Signals event(s) to a specified task.

Prototype

void OS_SignalEvent (OS_TASK_EVENT Event,

OS_TASK* pTask);

Additional Information

If the specified task is waiting for one of these events, it will be put in the READY

state and activated according to the rules of the scheduler.

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and unsigned char for

8- or 16-bit CPUs per default. It may be modified to any other type when embOS

sources ar used in a project, or when the libraries are rebuilt with a modified defini-

tion.

Example

The task that handles the serial input and the keyboard waits for a character to be

received either via the keyboard (EVENT_KEYPRESSED) or serial interface

(EVENT_SERIN):

* Just a small demo for events

#define EVENT_KEYPRESSED (1)

#define EVENT_SERIN (2)

OS_STACKPTR int Stack0[96]; // Task stacks

OS_TASK TCB0; // Data area for tasks (task control blocks)

void Task0(void) {

OS_TASK_EVENT MyEvent;

while(1)

MyEvent = OS_WaitEvent(EVENT_KEYPRESSED | EVENT_SERIN)

if (MyEvent & EVENT_KEYPRESSED) {

/* handle key press */

}

if (MyEvent & EVENT_SERIN) {

/* Handle serial reception */

}

void TimerKey(void) {

/* More code to find out if key has been pressed */

OS_SignalEvent(EVENT_SERIN, &TCB0); /* Notify Task that key was pressed */

}

void InitTask(void) {

OS_CREATETASK(&TCB0, 0, Task0, 100, Stack0); /* Create Task0 */

}

Parameter Description

Event

The event(s) to signal:

1 means event 1

2 means event 2

4 means event 3

...

128 means event 8.

Multiple events can be signaled as the sum of the single events

(for example, 6 will signal events 2 & 3).

pTask Task that the events are sent to.

Table 10.6: OS_SignalEvent() parameter list

185

If the task was only waiting for a key to be pressed, OS_GetMail() could simply be

called. The task would then be deactivated until a key is pressed. If the task has to

handle multiple mailboxes, as in this case, events are a good option.

186 CHAPTER 10 Task events

10.2.6 OS_GetEventsOccurred()

Description

Returns a list of events that have occurred for a specified task.

Prototype

OS_TASK_EVENT OS_GetEventsOccurred (const OS_TASK* pTask);

Return value

The event mask of the events that have actually occurred.

Additional Information

By calling this function, the actual events remain signaled. The event memory is not

cleared. This is one way for a task to find out which events have been signaled. The

task is not suspended if no events are signaled.

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and unsigned char for

8- or 16-bit CPUs per default. It may be modified to any other type when embOS

sources ar used in a project, or when the libraries are rebuilt with a modified defini-

tion.

Parameter Description

pTask The task who's event mask is to be returned,

NULL means current task.

Table 10.7: OS_GetEventsOccurred() parameter list

187

10.2.7 OS_ClearEvents()

Description

Returns the actual state of events and then clears the events of a specified task.

Prototype

OS_TASK_EVENT OS_ClearEvents (OS_TASK* pTask);

Return value

The events that were actually signaled before clearing.

OS_TASK_EVENT is defined as unsigned long for 32bit CPUs and unsigned char for

8- or 16-bit CPUs per default. It may be modified to any other type when embOS

sources ar used in a project, or when the libraries are rebuilt with a modified defini-

tion.

Parameter Description

pTask The task who's event mask is to be returned,

NULL means current task.

Table 10.8: OS_ClearEvents() parameter list

188 CHAPTER 10 Task events

189

Chapter 11

Event objects

190 CHAPTER 11 Event objects

11.1 Introduction

Event objects are another type of communication and synchronization objects. In

contrast to task-events, event objects are standalone objects which are not owned by

any task.

The purpose of an event object is to enable one or multiple tasks to wait for a partic-

ular event to occur. The tasks can be kept suspended until the event is set by another

task, a S/W timer, or an interrupt handler. The event can be anything that the soft-

ware is made aware of in any way. Examples include the change of an input signal,

the expiration of a timer, a key press, the reception of a character, or a complete

command.

Compared to a task event, the signaling function does not need to know which task is

waiting for the event to occur.

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
191
11.2 API functions
Routine Description
main
Task
ISR
Timer
OS_EVENT_Create() Creates an event object. Must be called 
before the event object can be used. XXXX
OS_EVENT_CreateEx() Creates an event object and allows selection 
of the reset behavior of the event. XXXX
OS_EVENT_Wait() Waits for an event. X
OS_EVENT_WaitTimed()
Waits for an event with timeout and option-
ally resets the event according the reset 
mode.
XX
OS_EVENT_Set() Sets the events, or resumes waiting tasks. X X X X
OS_EVENT_Reset() Resets the event to none-signaled state. X X X X
OS_EVENT_Pulse() Sets the event, resumes waiting tasks, if any, 
and then resets the event. XXXX
OS_EVENT_Get() Returns the state of an event object. X X
OS_EVENT_Delete() Deletes the specified event object. X X
OS_EVENT_SetResetMode() Sets the reset behaviour of events to auto-
matic, manual or semiauto. XXXX
OS_EVENT_GetResetMode() Retrieves the current the reset behaviour 
mode of an event object. XXXX
Table 11.1: Event object API functions

192 CHAPTER 11 Event objects

11.2.1 OS_EVENT_Create()

Description

Creates an event object and resets the event.

Prototype

void OS_EVENT_Create (OS_EVENT* pEvent)

Additional Information

Before the event object can be used, it must be created by a call of

OS_EVENT_Create(). On creation, the event is set in non-signaled state, and the list

of waiting tasks is deleted. Therefore, OS_EVENT_Create() must not be called for an

event object which was already created before.

A debug build of embOS cannot check whether the specified event object was already

created.

The event is created with the default reset behavior which is semiauto.

Since version 3.88a of embOS, the reset behavior of the event can be modified by a

call of the function OS_EVENT_SetResetMode().

Example

OS_EVENT _HW_Event;

OS_EVENT_Create(&HW_Event); /* Create and initialize event object */

Parameter Description

pEvent Pointer to an event object data structure.

Table 11.2: OS_EVENT_Create() parameter list

193

11.2.2 OS_EVENT_CreateEx()

Description

Creates an event object with specified rest behavior and resets the event.

Prototype

void OS_EVENT_Create (OS_EVENT* pEvent, OS_EVENT_RESET_MODE ResetMode)

Additional Information

Before the event object can be used, it must be created by a call of

OS_EVENT_Create() or OS_EVENT_CreateEx(). On creation, the event is set in non-

signaled state, and the list of waiting tasks is deleted.

Therefore, OS_EVENT_CreateEx() must not be called for an event object which was

already created before.

A debug build of embOS cannot check whether the specified event object was already

created.

Since version 3.88a of embOS, the reset behavior of the event can be controlled by

different reset modes which may be passed as parameter to the new function

OS_EVENT_CreateEx() or may be modified by a call of OS_EVENT_SetResetMode().

• OS_EVENT_RESET_MODE_SEMIAUTO:

This reset mode is the default mode used with all previous versions of embOS.

The reset behavior unfortunately is not consistent and depends on the function

called to set or wait for an event. This reset mode is defined for compatibility

with older embOS versions (prior version 3.88a). Calling OS_EVENT_Create()

sets the reset mode to OS_EVENT_RESET_MODE_SEMIAUTO to be compatible with

older embOS versions.

• OS_EVENT_RESET_MODE_AUTO:

This mode sets the reset behavior of an event object to automatic clear. When an

event is set, all waiting tasks are resumed and the event is cleared automatically,

except waiting tasks called OS_EVENT_WaitTimed() and the timeout of the task

expired before the event was set.

• OS_EVENT_RESET_MODE_MANUAL:

This mode sets the event to manual reset mode. When an event is set, all waiting

tasks are resumed and the event object remains signaled. The event must be

reset by one task which was waiting for the event.

Example

OS_EVENT _HW_Event;

/* Create and initialize an event object with automatic reset */

OS_EVENT_CreateEx(&HW_Event, OS_EVENT_RESET_MODE_AUTO);

Parameter Description

pEvent Pointer to an event object data structure.

ResetMode

Specifies the reset behavior of the event object. One of the pre-

defined reset modes can be used:

OS_EVENT_RESET_MODE_SEMIAUTO

OS_EVENT_RESET_MODE_AUTO

OS_EVENT_RESET_MODE_MANUAL

which are dscribed under Additional information

Table 11.3: OS_EVENT_CreateEx() parameter list

194 CHAPTER 11 Event objects

11.2.3 OS_EVENT_Wait()

Description

Waits for an event and suspends the calling task as long as the event is not signaled.

Prototype

void OS_EVENT_Wait (OS_EVENT* pEvent)

Additional Information

pEvent must address an existing event object, which must be created before the call

of OS_EVENT_Wait(). A debug build of embOS will check whether pEvent addresses a

valid event object and will call OS_Error() with error code OS_ERR_EVENT_INVALID in

case of an error.

The state of the event object after calling OS_EVENT_Wait() depends on the reset

mode of the event object wich was set by creating the event object by a call of

OS_EVENT_CreateEx() or OS_EVENT_SetResetMode().

•With reset mode OS_EVENT_RESET_MODE_SEMIAUTO:

This is the default mode when the event object was created with

OS_EVENT_Create(). This was the only mode available in embOS versions prior

version 3.88a.

If the specified event object is already set, the calling task resets the event and

continues operation.

If the specified event object is not set, the calling task is suspended until the

event object becomes signaled. The event is not reset when the task resumes.

•With reset mode OS_EVENT_RESET_MODE_AUTO:

If the specified event object is already set, the calling task resets the event and

continues operation.

If the specified event object is not set, the calling task is suspended until the

event object becomes signaled and then the event object is reset when the wait-

ing task resumes.

•With reset mode OS_EVENT_RESET_MODE_MANUAL:

If the specified event object is already set, the calling task continues operation.

The event object remains signaled.

If the specified event object is not set, the calling task is suspended until the

event object becomes signaled. Then the waiting task is resumed and the event

object remains signaled. The event object must be reset by the calling task.

Important

This function must not be called from within an interrupt handler or software timer.

A debug build of embOS will call OS_Error() when OS_EVENT_Wait() is called from

an ISR or timer.

Example

OS_EVENT_Wait(&_HW_Event); // Wait for event object

OS_EVENT_Reset(&_HW_Event); // Reset the event

Parameter Description

pEvent Pointer to the event object that the task will be waiting for.

Table 11.4: OS_EVENT_Wait() parameter list

195

11.2.4 OS_EVENT_WaitTimed()

Description

Waits for an event and suspends the calling task for a specified time as long as the

event is not signaled.

Prototype

char OS_EVENT_WaitTimed (OS_EVENT* pEvent,

OS_TIME Timeout)

Return value

0 success, the event was signaled within the specified time.

1 if the event was not signaled within the specified timeout time.

Additional Information

pEvent must address an existing event object, which must be created before the call

of OS_EVENT_WaitTimed(). A debug build of embOS will check whether pEvent

addresses a valid event object and will call OS_Error() with error code

OS_ERR_EVENT_INVALID in case of an error.

If the specified event object is not set, the calling task is suspended until the event

object becomes signaled or the timeout time has expired.

When the timeout expired and the event was not signaled during the specified time-

out time, OS_EVENT_WaitTimed() returns 1.

If the specified event object is already set, or becomes signaled within the specified

timeout time, the state of the event depends on the reset mode of the event.

•With reset mode OS_EVENT_RESET_MODE_SEMIAUTO:

This is the default mode when the event object was created with

OS_EVENT_Create(). This was the only mode available in embOS versions prior

version 3.88a.

If the specified event object is already set, the calling task resets the event and

continues operation.

If the event object becomes signaled within the specified timeout time, the event

is reset and the function returns without timeout result.

•With reset mode OS_EVENT_RESET_MODE_AUTO:

If the specified event object is already set, the calling task resets the event and

continues operation.

If the event object becomes signaled within the specified timeout time, the event

is reset and the function returns without timeout result.

•With reset mode OS_EVENT_RESET_MODE_MANUAL:

If the specified event object is already set, the calling task continues operation.

The event object remains signaled.

If the specified event object is not set, the calling task is suspended until the

event object becomes signaled. When the event object is signaled within the

specified timeout time, the waiting task is resumed and the event object remains

signaled. The event object must be reset by the calling task.

The function returns without timeout result.

Parameter Description

pEvent Pointer to the event object that the task will be waiting for.

Timeout

Maximum time in timer ticks until the event must be signaled.

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Table 11.5: OS_EVENT_WaitTimed() parameter list

196 CHAPTER 11 Event objects

When the calling task is blocked by higher priority tasks for a longer period than the

timeout value, it may happen, that the event becomes signaled after the timeout

time before the calling task continues. In this case, the function returns with time-

out, because the event was not available within the requested time. In this case, the

state of the event is not modified by OS_EVENT_WaitTimed() regardless the reset

mode.

Important

This function must not be called from within an interrupt handler or software timer.

A debug build of embOS will call OS_Error() when OS_EVENT_Wait() is called from

an ISR or timer.

Example

if (OS_EVENT_WaitTimed(&_HW_Event, 10) == 0) {

/* event was signaled within timeout time, handle event */

...

} else {

/* event was not signaled within timeout time, handle timeout */

...

}

197

11.2.5 OS_EVENT_Set()

Description

Sets an event object to signaled state, or resumes tasks which are waiting at the

event object.

Prototype

void OS_EVENT_Set (OS_EVENT* pEvent)

Additional Information

pEvent must address an existing event object, which must be created before by a call

of OS_EVENT_Create(). A debug build of embOS will check whether pEvent addresses

a valid event object and will call OS_Error() with error code OS_ERR_EVENT_INVALID in

case of an error.

If no tasks are waiting at the event object, the event object is set to signaled state.

If at least one task is already waiting at the event object, all waiting tasks are

resumed. The state of the event object after calling OS_EVENT_Set() then depends

on the reset mode of the event object.

•With reset mode OS_EVENT_RESET_MODE_SEMIAUTO:

This is the default mode when the event object was created with

OS_EVENT_Create(). This was the only mode available in embOS versions prior

version 3.88a.

If tasks were waiting, the event is reset when the waiting tasks are resumed.

•With reset mode OS_EVENT_RESET_MODE_AUTO:

The event object is automatically reset when waiting tasks are resumed and con-

tinue operation.

•With reset mode OS_EVENT_RESET_MODE_MANUAL:

The event object remains signaled when waiting tasks are resumed and continue

operation. The event object must be reset by the calling task.

Example

Examples on how to use the OS_EVENT_Set() function are shown in the section

“Examples”.

Parameter Description

pEvent Pointer to the event object which should be set to signaled state.

Table 11.6: OS_EVENT_Set() parameter list

198 CHAPTER 11 Event objects

11.2.6 OS_EVENT_Reset()

Description

Resets the specified event object to non-signaled state.

Prototype

void OS_EVENT_Reset (OS_EVENT* pEvent)

Additional Information

pEvent must address an existing event object, which has been created before by a

call of OS_EVENT_Create(). A debug build of embOS will check whether pEvent

addresses a valid event object and will call OS_Error() with the error code

OS_ERR_EVENT_INVALID in case of an error.

Example

OS_EVENT_Reset(&_HW_Event); /* Reset event object to non-signaled state */

Parameter Description

pEvent Pointer to the event object which should be reset to non-signaled

state.

Table 11.7: OS_EVENT_Reset() parameter list

199

11.2.7 OS_EVENT_Pulse()

Description

Signals an event object and resumes waiting tasks, then resets the event object to

non-signaled state.

Prototype

void OS_EVENT_Pulse (OS_EVENT* pEvent);

Additional Information

If any tasks are waiting at the event object, the tasks are resumed. The event object

remains in non-signaled state, regardless the reset mode.

A debug build of embOS will check whether pEvent addresses a valid event object

and will call OS_Error() with the error code OS_ERR_EVENT_INVALID in case of an

error.

Parameter Description

pEvent Pointer to the event object which should be pulsed.

Table 11.8: OS_EVENT_Pulse() parameter list

200 CHAPTER 11 Event objects

11.2.8 OS_EVENT_Get()

Description

Returns the state of an event object.

Prototype

unsigned char OS_EVENT_Get (const OS_EVENT* pEvent);

Return value

0: Event object is not set to signaled state

1: Event object is set to signaled state.

Additional Information

By calling this function, the actual state of the event object remains unchanged.

pEvent must address an existing event object, which has been created before by a

call of OS_EVENT_Create().

A debug build of embOS will check whether pEvent addresses a valid event object

and will call OS_Error() with error code OS_ERR_EVENT_INVALID in case of an error.

Parameter Description

pEvent Pointer to an event object who’s state should be examined.

Table 11.9: OS_EVENT_Get() parameter list

201

11.2.9 OS_EVENT_Delete()

Description

Deletes an event object.

Prototype

void OS_EVENT_Delete (OS_EVENT* pEvent);

Additional Information

To keep the system fully dynamic, it is essential that event objects can be created

dynamically. This also means there must be a way to delete an event object when it

is no longer needed. The memory that has been used by the event object’s control

structure can then be reused or reallocated.

It is your responsibility to make sure that:

• the program no longer uses the event object to be deleted

• the event object to be deleted actually exists (has been created first)

• no tasks are waiting at the event object when it is deleted.

pEvent must address an existing event object, which has been created before by a

call of OS_EVENT_Create()or OS_EVENT_CreateEx().

A debug build of embOS will check whether pEvent addresses a valid event object

and will call OS_Error() with error code OS_ERR_EVENT_INVALID in case of an error.

If any task is waiting at the event object which is deleted, a debug build of embOS

calls OS_Error() with error code OS_ERR_EVENT_DELETE.

To avoid any problems, an event object should not be deleted in a normal application.

Parameter Description

pEvent Pointer to an event object which should be deleted.

Table 11.10: OS_EVENT_Delete() parameter list

202 CHAPTER 11 Event objects

11.2.10 OS_EVENT_SetResetMode()

Description

Used to set the reset behavior mode of an event object.

Prototype

void OS_EVENT_SetResetMode (OS_EVENT* pEvent, OS_EVENT_RESET_MODE ResetMode)

Additional Information

pEvent must address an existing event object, which has been created before by a

call of OS_EVENT_Create()or OS_EVENT_CreateEx().

A debug build of embOS will check whether pEvent addresses a valid event object

and will call OS_Error() with error code OS_ERR_EVENT_INVALID in case of an error.

Implementation of event objects in embOS versions before 3.88a unfortunately was

not consistent with respect to the state of the event after calling OS_EVENT_Set() or

OS_EVENT_Wait() wait functions.

The state of the event was different when tasks were waiting or not.

Since embOS version 3.88a, the state of the event (reset behavior) can be controlled

after creation by the new function OS_EVENT_SetResetMode(), or during creation by

the new OS_EVENT_CreateEx() function.

The following reset modes are defined an can be used as parameter:

•OS_EVENT_RESET_MODE_SEMIAUTO:

This reset mode is the default mode used with all previous versions of embOS.

The reset behavior unfortunately is not consistent and depends on the function

called to set or wait for an event. This reset mode is defined for compatibility

with older embOS versions (prior version 3.88a). Calling OS_EVENT_Create()

sets the reset mode to OS_EVENT_RESET_MODE_SEMIAUTO to be compatible with

older embOS versions.

•OS_EVENT_RESET_MODE_AUTO:

This mode sets the reset behavior of an event object to automatic clear. When an

event is set, all waiting tasks are resumed and the event is cleared automatically,

except waiting tasks called OS_EVENT_WaitTimed() and the timeout of the task

expiered before the event was set.

•OS_EVENT_RESET_MODE_MANUAL:

This mode sets the event to manual reset mode. When an event is set, all waiting

tasks are resumed and the event object remains signaled. The event must be

reset by one task which was waiting for the event.

Parameter Description

pEvent Pointer to an event object which should be deleted.

ResetMode

Specifies the reset behavior of the event object. One of the pre-

defined reset modes can be used:

OS_EVENT_RESET_MODE_SEMIAUTO

OS_EVENT_RESET_MODE_AUTO

OS_EVENT_RESET_MODE_MANUAL

which are dscribed under Additional information

Table 11.11: OS_EVENT_Delete() parameter list

203

11.2.11 OS_EVENT_GetResetMode()

Description

Retrieves the current reset mode of an event object.

Prototype

OS_EVENT_RESET_MODE OS_EVENT_GetResetMode (OS_EVENT* pEvent);

Additional Information

pEvent must address an existing event object, which has been created before by a

call of OS_EVENT_Create()or OS_EVENT_CreateEx().

A debug build of embOS will check whether pEvent addresses a valid event object

and will call OS_Error() with error code OS_ERR_EVENT_INVALID in case of an error.

Since version 3.88a of embOS, the reset mode of an event object can be controlled

by the new OS_EVENT_CreateEx() function or set after creation using the new func-

tion OS_EVENT_SetResetMode(). If needed, the current setting of the reset mode can

be retrieved with OS_EVENT_GetResetMode().

Example

OS_EVENT_Wait(&_HW_Event); // Wait for event object

if (OS_EVENT_GetResetMode(&_HW_Event) == OS_EVENT_RESET_MODE_MANUAL) {

OS_EVENT_Reset(&_HW_Event); // Reset the event

}

Parameter Description

pEvent Pointer to an event object which should be deleted.

Table 11.12: OS_EVENT_Delete() parameter list

204 CHAPTER 11 Event objects

11.3 Examples of using event objects

This chapter shows some examples on how to use event objects in an application.

11.3.1 Activate a task from interrupt by an event object

The following code example shows usage of an event object which is signaled from an

ISR handler to activate a task.

The waiting task should reset the event after waiting for it.

static OS_EVENT _HW_Event;

/************************************************************

* _ISRhandler

static void _ISRhandler(void) {

// Perform some simple & fast processing in ISR //

...

// Wake up task to do the rest of the work

OS_EVENT_Set(&_Event);

}

/************************************************************

* _Task

static void _Task(void) {

while (1) {

OS_EVENT_Wait(&_Event);

OS_EVENT_Reset(&_Event);

// Do the rest of the work (which has not been done in the ISR)

}

205

11.3.2 Activating multiple tasks using a single event object

The following sample program shows how to synchronize multiple tasks with one

event object. The sample program is delivered with embOS in the “Application” or

“Samples” folder.

/********************************************************************

* SEGGER MICROCONTROLLER SYSTEME GmbH

* Solutions for real time microcontroller applications

*********************************************************************

File : Main_EVENT.c

Purpose : Sample program for embOS using EVENT object

--------- END-OF-HEADER --------------------------------------------*/

#include "RTOS.h"

OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */

OS_TASK TCBHP, TCBLP; /* Task-control-blocks */

/********************************************************************/

/****** Interface to HW module **************************************/

void HW_Wait(void);

void HW_Free(void);

void HW_Init(void);

/********************************************************************/

/****** HW module ***************************************************/

OS_STACKPTR int _StackHW[128]; /* Task stack */

OS_TASK _TCBHW; /* Task-control-block */

/****** local data **************************************************/

static OS_EVENT _HW_Event;

/****** local functions *********************************************/

static void _HWTask(void) {

/* Initialize HW functionality */

OS_Delay(100);

/* Init done, send broadcast to waiting tasks */

HW_Free();

while (1) {

OS_Delay (40);

}

/****** global functions ********************************************/

void HW_Wait(void) {

OS_EVENT_Wait(&_HW_Event);

}

void HW_Free(void) {

OS_EVENT_Set(&_HW_Event);

}

void HW_Init(void) {

OS_CREATETASK(&_TCBHW, "HWTask", _HWTask, 25, _StackHW);

OS_EVENT_Create(&_HW_Event);

}

206 CHAPTER 11 Event objects

/********************************************************************/

/****** Main application ********************************************/

static void HPTask(void) {

HW_Wait(); /* Wait until HW module is set up */

while (1) {

OS_Delay (50);

}

static void LPTask(void) {

HW_Wait(); /* Wait until HW module is set up */

while (1) {

OS_Delay (200);

}

/*********************************************************************

* main

**********************************************************************/

int main(void) {

OS_IncDI(); /* Initially disable interrupts */

OS_InitKern(); /* Initialize OS */

OS_InitHW(); /* Initialize Hardware for OS */

HW_Init(); /* Initialize HW module */

/* You need to create at least one task before calling OS_Start() */

OS_CREATETASK(&TCBHP, "HP Task", HPTask, 100, StackHP);

OS_CREATETASK(&TCBLP, "LP Task", LPTask, 50, StackLP);

OS_SendString("Start project will start multitasking !\n");

OS_Start(); /* Start multitasking */

return 0;

}

207

Chapter 12

Heap type memory management

208 CHAPTER 12 Heap type memory management

12.1 Introduction

ANSI C offers some basic dynamic memory management functions. These are mal-

loc, free, and realloc.

Unfortunately, these routines are not thread-safe, unless a special thread-safe imple-

mentation exists in the compiler specific runtime libraries; they can only be used

from one task or by multiple tasks if they are called sequentially. Therefore, embOS

offer task-safe variants of these routines. These variants have the same names as

their ANSI counterparts, but are prefixed OS_; they are called OS_malloc(),

OS_free(), OS_realloc(). The thread-safe variants that embOS offers use the stan-

dard ANSI routines, but they guarantee that the calls are serialized using a resource

semaphore.

If heap memory management is not supported by the standard C-libraries for a spe-

cific CPU, embOS heap memory management is not implemented.

Heap type memory management is part of the embOS libraries. It does not use any

resources if it is not referenced by the application (that is, if the application does not

use any memory management API function).

Note that another aspect of these routines may still be a problem: the memory used

for the functions (known as heap) may fragment. This can lead to a situation where

the total amount of memory is sufficient, but there is not enough memory available

in a single block to satisfy an allocation request.

209

12.2 API functions

API routine Description

main

Task

ISR

Timer

OS_malloc() Allocates a block of memory on the heap. X X

OS_free() Frees a block of memory previously allocated. X X

OS_realloc() Changes allocation size. X X

Table 12.1: Heap type memory manager API functions

210 CHAPTER 12 Heap type memory management

12.2.1 OS_malloc()

Description

OS_malloc() is a thread safe malloc function.

Prototype

void* OS_malloc(unsigned int Size);

Return value

Upon successful completion with size not equal 0, OS_malloc() returns a pointer to

the allocated space. Otherwise, it returns a null pointer.

Parameter Description

Size Size of memory block to be allocated in bytes.

Table 12.2: OS_malloc() parameter list

211

12.2.2 OS_free()

Description

OS_free() is a thread safe free function.

Prototype

void OS_free(void* pMemBlock);

Parameter Description

pMemBlock Pointer to a memory block previously allocated with malloc.

Table 12.3: OS_free() parameter list

212 CHAPTER 12 Heap type memory management

12.2.3 OS_realloc()

Description

OS_realloc() is a thread safe ralloc function.

Prototype

void* OS_realloc(void* pMemBlock, unsigned int NewSize);

Return value

OS_realloc() returns a pointer to the reallocated memory block.

Parameter Description

pMemBlock Pointer to a memory block previously allocated with malloc.

NewSize New size for the memory block in bytes.

Table 12.4: OS_realloc() paramter list

213

Chapter 13

Fixed block size memory pools

214 CHAPTER 13 Fixed block size memory pools

13.1 Introduction

Fixed block size memory pools contain a specific number of fixed-size blocks of mem-

ory. The location in memory of the pool, the size of each block, and the number of

blocks are set at runtime by the application via a call to the OS_MEMF_CREATE() func-

tion. The advantage of fixed memory pools is that a block of memory can be allo-

cated from within any task in a very short, determined period of time.

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
215
13.2 API functions
All API functions for fixed block size memory pools are prefixed OS_MEMF_.
API routine Description
main
Task
ISR
Timer
Create / Delete
OS_MEMF_Create() Creates fixed block memory pool. X X
OS_MEMF_Delete() Deletes fixed block memory pool. X X
Allocation
OS_MEMF_Alloc()
Allocates memory block from a given 
memory pool. Wait indefinitely if no block 
is available.
XX
OS_MEMF_AllocTimed()
Allocates memory block from a given 
memory pool. Wait no longer than given 
time limit if no block is available.
XX
OS_MEMF_Request() Allocates block from a given memory pool, 
if available. Non-blocking. XXXX
Release
OS_MEMF_Release() Releases memory block from a given 
memory pool. XXXX
OS_MEMF_FreeBlock() Releases memory block from any pool. X X X X
Info
OS_MEMF_GetNumFreeBlocks() Returns the number of available blocks in 
a pool. XXXX
OS_MEMF_IsInPool() Returns !=0 if block is in memory pool. X X X X
OS_MEMF_GetMaxUsed() Returns the maximum number of blocks in 
a pool which have been used at a time. XXXX
OS_MEMF_GetNumBlocks() Returns the number of blocks in a pool. X X X X
OS_MEMF_GetBlockSize() Returns the size of one block of a given 
pool. XXXX
Table 13.1: Memory pools API functions

216 CHAPTER 13 Fixed block size memory pools

13.2.1 OS_MEMF_Create()

Description

Creates and initializes a fixed block size memory pool.

Prototype

void OS_MEMF_Create (OS_MEMF* pMEMF,

void* pPool,

OS_UINT NumBlocks,

OS_UINT BlockSize);

Additional Information

OS_MEMF_SIZEOF_BLOCKCONTROL gives the number of bytes used for control and

debug purposes. It is guaranteed to be 0 in release or stack-check builds. Before

using any memory pool, it must be created. A debug build of libraries keeps track of

created and deleted memory pools. The release and stack-check builds do not.

The maximum number of blocks and the maximum block size is for 16Bit CPUs 32768

and for 32Bit CPUs 2147483648.

Example

#define NUM_BLOCKS (16)

#define BLOCK_SIZE (16)

#define POOL_SIZE (NUM_BLOCKS * (BLOCK_SIZE + OS_MEMF_SIZEOF_BLOCKCONTROL))

OS_U8 aPool[POOL_SIZE];

OS_MEMF MyMEMF;

void Init(void) {

/* Create 16 Blocks with size of 16 Bytes */

OS_MEMF_Create(&MyMEMF, aPool, NUM_BLOCKS, BLOCK_SIZE);

}

Note

OS_MEMF_SIZEOF_BLOCKCONTROL is always zero because additional debug code is not

implemented. It is only designed for future use.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

pPool Pointer to memory to be used for the memory pool. Required size

is: NumBlocks * (BlockSize + OS_MEMF_SIZEOF_BLOCKCONTROL).

NumBlocks Number of blocks in the pool.

BlockSize Size in bytes of one block.

Table 13.2: OS_MEMF_Create() parameter list

217

13.2.2 OS_MEMF_Delete()

Description

Deletes a fixed block size memory pool. After deletion, the memory pool and memory

blocks inside this pool can no longer be used.

Prototype

void OS_MEMF_Delete (OS_MEMF* pMEMF);

Additional Information

This routine is provided for completeness. It is not used in the majority of

applications because there is no need to dynamically create/delete memory pools.

For most applications it is preferred to have a static memory pool design; memory

pools are created at startup (before calling OS_Start()) and will never be deleted.

A debug build of libraries mark the memory pool as deleted.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Table 13.3: OS_MEMF_Delete() parameter list

218 CHAPTER 13 Fixed block size memory pools

13.2.3 OS_MEMF_Alloc()

Description

Requests allocation of a memory block. Waits until a block of memory is available.

Prototype

void* OS_MEMF_Alloc (OS_MEMF* pMEMF,

int Purpose);

Return value

Pointer to the allocated block.

Additional Information

If there is no free memory block in the pool, the calling task is suspended until a

memory block becomes available. The retrieved pointer must be delivered to

OS_MEMF_Release() as a parameter to free the memory block. The pointer must not

be modified.

Note

The parameter Purpose is never used because additional debug code is not imple-

mented. It is only designed for future use.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Purpose

This is a parameter which is used for debugging purpose only. Its

value has no effect on program execution, but may be remem-

bered in debug builds to allow runtime analysis of memory allo-

cation problems.

Table 13.4: OS_MEMF_Alloc() parameter list

219

13.2.4 OS_MEMF_AllocTimed()

Description

Requests allocation of a memory block. Waits until a block of memory is available or

the timeout has expired.

Prototype

void* OS_MEMF_AllocTimed (OS_MEMF* pMEMF,

OS_TIME Timeout,

int Purpose);

Return value

!=NULL pointer to the allocated block

NULL if no block could be allocated within the specified time.

Additional Information

If there is no free memory block in the pool, the calling task is suspended until a

memory block becomes available or the timeout has expired. The retrieved pointer

must be delivered to OS_MEMF_Release() as parameter to free the memory block.

The pointer must not be modified.

When the calling task is blocked by higher priority tasks for a longer period than the

timeout value, it may happen, that the memory block becomes available after the

timeout time before the calling task continues. In this case, the function returns with

timeout, because the memory block was not availbale within the requested time.

Note

The parameter Purpose is never used because additional debug code is not imple-

mented. It is only designed for future use.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Timeout

Time limit before timeout, given in ticks. 0 or negative values are

permitted.

Timeout in basic embOS time units (nominal ms):

The data type OS_TIME is defined as an integer, therefore valid

values are

1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs

1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs

Purpose

This is a parameter which is used for debugging purpose only. Its

value has no effect on program execution, but may be remem-

bered in debug builds to allow runtime analysis of memory allo-

cation problems.

Table 13.5: OS_MEMF_AllocTimed()

220 CHAPTER 13 Fixed block size memory pools

13.2.5 OS_MEMF_Request()

Description

Requests allocation of a memory block. Continues execution in any case.

Prototype

void* OS_MEMF_Request (OS_MEMF* pMEMF,

int Purpose);

Return value

!=NULL pointer to the allocated block

NULL if no block has been allocated.

Additional Information

The calling task is never suspended by calling OS_MEMF_Request(). The retrieved

pointer must be delivered to OS_MEMF_Release() as parameter to free the memory

block. The pointer must not be modified.

Note

The parameter Purpose is never used because additional debug code is not imple-

mented. It is only designed for future use.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Purpose

This is a parameter which is used for debugging purpose only. Its

value has no effect on program execution, but may be remem-

bered in debug builds to allow runtime analysis of memory allo-

cation problems.

Table 13.6: OS_MEMF_Request() parameter list

221

13.2.6 OS_MEMF_Release()

Description

Releases a memory block that was previously allocated.

Prototype

void OS_MEMF_Release (OS_MEMF* pMEMF,

void* pMemBlock);

Additional Information

The pMemBlock pointer must be the one that was delivered from any retrieval func-

tion described above. The pointer must not be modified between allocation and

release. The memory block becomes available for other tasks waiting for a memory

block from the pool. If any task is waiting for a fixed memory block, it is activated

according to the rules of the scheduler.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

pMemBlock Pointer to the memory block to free.

Table 13.7: OS_MEMF_Release() parameter list

222 CHAPTER 13 Fixed block size memory pools

13.2.7 OS_MEMF_FreeBlock()

Description

Releases a memory block that was previously allocated. The memory pool does not

need to be denoted.

Prototype

void OS_MEMF_FreeBlock (void* pMemBlock);

Additional Information

The pMemBlock pointer must be the one that was delivered form any retrieval func-

tion described above. The pointer must not be modified between allocation and

release. This function may be used instead of OS_MEMF_Release(). It has the advan-

tage that only one parameter is needed. embOS itself will find the associated mem-

ory pool. The memory block becomes available for other tasks waiting for a memory

block from the pool. If any task is waiting for a fixed memory block, it is activated

according to the rules of the scheduler.

Parameter Description

pMemBlock Pointer to the memory block to free.

Table 13.8: OS_MEMF_FreeBlock() parameter list

223

13.2.8 OS_MEMF_GetNumBlocks()

Description

Information routine to examine the total number of available memory blocks in the

pool.

Prototype

int OS_MEMF_GetNumBlocks (const OS_MEMF* pMEMF);

Return value

Returns the number of blocks in the specified memory pool. This is the value that

was given as parameter during creation of the memory pool.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Table 13.9: OS_MEMF_GetNumBlocks() parameter list

224 CHAPTER 13 Fixed block size memory pools

13.2.9 OS_MEMF_GetBlockSize()

Description

Information routine to examine the size of one memory block in the pool.

Prototype

int OS_MEMF_GetBlockSize (const OS_MEMF* pMEMF);

Return value

Size in bytes of one memory block in the specified memory pool. This is the value of

the parameter when the memory pool was created.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Table 13.10: OS_MEMF_GetBlockSize() parameter list

225

13.2.10 OS_MEMF_GetNumFreeBlocks()

Description

Information routine to examine the number of free memory blocks in the pool.

Prototype

int OS_MEMF_GetNumFreeBlocks (OS_MEMF* pMEMF);

Return value

The number of free blocks actually available in the specified memory pool.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Table 13.11: OS_MEMF_GetNumFreeBlocks() parameter list

226 CHAPTER 13 Fixed block size memory pools

13.2.11 OS_MEMF_GetMaxUsed()

Description

Information routine to examine the amount of memory blocks in the pool that were

used concurrently since creation of the pool.

Prototype

int OS_MEMF_GetMaxUsed (const OS_MEMF* pMEMF);

Return value

Maximum number of blocks in the specified memory pool that were used concurrently

since the pool was created.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

Table 13.12: OS_MEMF_GetMaxUsed() parameter list

227

13.2.12 OS_MEMF_IsInPool()

Description

Information routine to examine whether a memory block reference pointer belongs to

the specified memory pool.

Prototype

char OS_MEMF_IsInPool (const OS_MEMF* pMEMF,

const void* pMemBlock);

Return value

0: Pointer does not belong to memory pool.

1: Pointer belongs to the pool.

Parameter Description

pMEMF Pointer to the control data structure of memory pool.

pMemBlock Pointer to a memory block that should be checked

Table 13.13: OS_MEMF_IsInPool() parameter list

228 CHAPTER 13 Fixed block size memory pools

229

Chapter 14

Stacks

230 CHAPTER 14 Stacks

14.1 Introduction

The stack is the memory area used for storing the return address of function calls,

parameters, and local variables, as well as for temporary storage. Interrupt routines

also use the stack to save the return address and flag registers, except in cases

where the CPU has a separate stack for interrupt functions. Refer to the CPU &

Compiler Specifics manual of embOS documentation for details on your processor's

stack. A “normal” single-task program needs exactly one stack. In a multitasking

system, every task must have its own stack.

The stack needs to have a minimum size which is determined by the sum of the stack

usage of the routines in the worst-case nesting. If the stack is too small, a section of

the memory that is not reserved for the stack will be overwritten, and a serious pro-

gram failure is most likely to occur. embOS monitors the stack size (and, if available,

also interrupt stack size in a debug build), and calls the failure routine OS_Error() if

it detects a stack overflow. However, embOS cannot reliably detect a stack overflow.

A stack that has been defined larger than necessary does not hurt; it is only a waste

of memory. To detect a stack overflow, the debug and stack-check builds of embOS

fill the stack with control characters when it is created and check these characters

every time the task is deactivated. If an overflow is detected, OS_Error() is called.

14.1.1 System stack

Before embOS takes over control (before the call to OS_Start()), a program uses

the so-called system stack. This is the same stack that a non-embOS program for

this CPU would use. After transferring control to the embOS scheduler by calling

OS_Start(), the system stack is used when no task is executed for the following:

•embOS scheduler

• embOS software timers (and the callback).

For details regarding required size of your system stack, refer to the CPU & Compiler

Specifics manual of embOS documentation.

14.1.2 Task stack

Each embOS task has a separate stack. The location and size of this stack is defined

when creating the task. The minimum size of a task stack pretty much depends on

the CPU and the compiler. For details, see the CPU & Compiler Specifics manual of

embOS documentation.

14.1.3 Interrupt stack

To reduce stack size in a multitasking environment, some processors use a specific

stack area for interrupt service routines (called a hardware interrupt stack). If there

is no interrupt stack, you will need to add stack requirements of your interrupt ser-

vice routines to each task stack.

Even if the CPU does not support a hardware interrupt stack, embOS may support a

separate stack for interrupts by calling the function OS_EnterIntStack() at begin-

ning of an interrupt service routine and OS_LeaveIntStack() at its very end. In case

the CPU already supports hardware interrupt stacks or if a separate interrupt stack is

not supported at all, these function calls are implemented as empty macros.

We recommend using OS_EnterIntStack() and OS_LeaveIntStack() even if there is

currently no additional benefit for your specific CPU, because code that uses them

might reduce stack size on another CPU or a new version of embOS with support for

an interrupt stack for your CPU. For details about interrupt stacks, see the CPU &

Compiler Specifics manual of embOS documentation.

231

14.1.4 Stack size calculation

embOS includes stack size calculation routines. embOS fills the task stacks as also

the system stack and the interrupt stack with a pattern byte.

embOS checks at runtime how many bytes at the end of the stack still include the

pattern byte. With it the amount of used and unused stack can be calculated.

14.1.5 Stack-check

embOS includes stack-check routines. embOS fills the task stacks as also the system

stack and the interrupt stack with a pattern byte.

embOS checks periodically if the last pattern byte at the end of the stack is overwrit-

ten. embOS calls OS_Error() when this bytes is overwritten.

232 CHAPTER 14 Stacks
UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
14.2 API functions
Routine Description
main
Task
ISR
Timer
OS_GetStackBase() Returns the base address of a task stack. X X X X
OS_GetStackSize() Returns the size of a task stack. X X X X
OS_GetStackSpace() Returns the unused portion of a task stack. X X X X
OS_GetStackUsed() Returns the used portion of a task stack. X X X X
OS_GetSysStackBase() Returns the base address of the system stack. X X X X
OS_GetSysStackSize() Returns the size of the system stack. X X X X
OS_GetSysStackSpace() Returns the unused portion of the system 
stack. XXXX
OS_GetSysStackUsed() Returns the used portion of the system stack. X X X X
OS_GetIntStackBase() Returns the base address of the interrupt 
stack. XXXX
OS_GetIntStackSize() Returns the size of the interrupt stack. X X X X
OS_GetIntStackSpace() Returns the unused portion of the interrupt 
stack. XXXX
OS_GetIntStackUsed() Returns the used portion of the interrupt 
stack. XXXX
Table 14.1: Stacks API functions

233

14.2.1 OS_GetStackBase()

Description

Returns a pointer to the base of a task stack.

Prototype

void* OS_GetStackBase (OS_TASK* pTask);

Return value

The pointer to the base address of the task stack.

Additional Information

This function is only available in the debug and stack-check builds of embOS,

because only these builds initialize the stack space used for the tasks.

Example

void CheckStackBase(void) {

printf("Addr Stack[0] %x", OS_GetStackBase(&TCB[0]);

OS_Delay(1000);

printf("Addr Stack[1] %x", OS_GetStackBase(&TCB[1]);

OS_Delay(1000);

}

Parameter Description

pTask The task who's stack base should be returned.

NULL denotes the current task.

Table 14.2: OS_GetStackBase() parameter list

234 CHAPTER 14 Stacks

14.2.2 OS_GetStackSize()

Description

Returns the size of a task stack.

Prototype

unsigned int OS_GetStackSize (OS_TASK* pTask);

Return value

The size of the task stack in bytes.

Additional Information

This function is only available in the debug and stack-check builds of embOS,

because only these builds initialize the stack space used for the tasks.

Example

void CheckStackSize(void) {

printf("Size Stack[0] %d", OS_GetStackSize(&TCB[0]);

OS_Delay(1000);

printf("Size Stack[1] %d", OS_GetStackSize(&TCB[1]);

OS_Delay(1000);

}

Parameter Description

pTask The task who's stack size should be checked.

NULL means current task.

Table 14.3: OS_GetStackSize() parameter list

235

14.2.3 OS_GetStackSpace()

Description

Returns the unused portion of a task stack.

Prototype

unsigned int OS_GetStackSpace (OS_TASK* pTask);

Return value

The unused portion of the task stack in bytes.

Additional Information

In most cases, the stack size required by a task cannot be easily calculated, because

it takes quite some time to calculate the worst-case nesting and the calculation itself

is difficult.

However, the required stack size can be calculated using the function

OS_GetStackSpace(), which returns the number of unused bytes on the stack. If

there is a lot of space left, you can reduce the size of this stack and vice versa.

This function is only available in the debug and stack-check builds of embOS,

because only these builds initialize the stack space used for the tasks.

Important

This routine does not reliably detect the amount of stack space left, because it can

only detect modified bytes on the stack. Unfortunately, space used for register stor-

age or local variables is not always modified. In most cases, this routine will detect

the correct amount of stack bytes, but in case of doubt, be generous with your stack

space or use other means to verify that the allocated stack space is sufficient.

Example

void CheckStackSpace(void) {

printf("Unused Stack[0] %d", OS_GetStackSpace(&TCB[0]);

OS_Delay(1000);

printf("Unused Stack[1] %d", OS_GetStackSpace(&TCB[1]);

OS_Delay(1000);

}

Parameter Description

pTask The task who's stack space should be checked.

NULL denotes the current task.

Table 14.4: OS_GetStackSpace() parameter list

236 CHAPTER 14 Stacks

14.2.4 OS_GetStackUsed()

Description

Returns the used portion of a task stack.

Prototype

unsigned int OS_GetStackUsed (OS_TASK* pTask);

Return value

The used portion of the task stack in bytes.

Additional Information

In most cases, the stack size required by a task cannot be easily calculated, because

it takes quite some time to calculate the worst-case nesting and the calculation itself

is difficult.

However, the required stack size can be calculated using the function

OS_GetStackUsed(), which returns the number of used bytes on the stack. If there is

a lot of space left, you can reduce the size of this stack and vice versa.

This function is only available in the debug and stack-check builds of embOS,

because only these builds initialize the stack space used for the tasks.

Important

This routine does not reliably detect the amount of stack space used, because it can

only detect modified bytes on the stack. Unfortunately, space used for register stor-

age or local variables is not always modified. In most cases, this routine will detect

the correct amount of stack bytes, but in case of doubt, be generous with your stack

space or use other means to verify that the allocated stack space is sufficient.

Example

void CheckStackUsed(void) {

printf("Used Stack[0] %d", OS_GetStackUsed(&TCB[0]);

OS_Delay(1000);

printf("Used Stack[1] %d", OS_GetStackUsed(&TCB[1]);

OS_Delay(1000);

}

Parameter Description

pTask The task who's stack usage should be checked.

NULL denotes the current task.

Table 14.5: OS_GetStackUsed() parameter list

237

14.2.5 OS_GetSysStackBase()

Description

Returns a pointer to the base of the system stack.

Prototype

void* OS_GetSysStackBase (void);

Return value

The pointer to the base address of the system stack.

Example

void CheckSysStackBase(void) {

printf("Addr System Stack %x", OS_GetSysStackBase());

}

238 CHAPTER 14 Stacks

14.2.6 OS_GetSysStackSize()

Description

Returns the size of the system stack.

Prototype

unsigned int OS_GetSysStackSize (void);

Return value

The size of the system stack in bytes.

Example

void CheckSysStackSize(void) {

printf("Size System Stack %d", OS_GetSysStackSize());

}

239

14.2.7 OS_GetSysStackSpace()

Description

Returns the unused portion of the system stack.

Prototype

unsigned int OS_GetSysStackSpace (void);

Return value

The unused portion of the system stack in bytes.

Additional Information

This function is only available in the debug and stack-check builds of embOS.

Important

This routine does not reliably detect the amount of stack space left, because it can

only detect modified bytes on the stack. Unfortunately, space used for register stor-

age or local variables is not always modified. In most cases, this routine will detect

the correct amount of stack bytes, but in case of doubt, be generous with your stack

space or use other means to verify that the allocated stack space is sufficient.

Example

void CheckSysStackSpace(void) {

printf("Unused System Stack %d", OS_GetSysStackSpace());

240 CHAPTER 14 Stacks

14.2.8 OS_GetSysStackUsed()

Description

Returns the used portion of the system stack.

Prototype

unsigned int OS_GetSysStackUsed (void);

Return value

The used portion of the system stack in bytes.

Additional Information

This function is only available in the debug and stack-check builds of embOS.

Important

This routine does not reliably detect the amount of stack space used, because it can

only detect modified bytes on the stack. Unfortunately, space used for register stor-

age or local variables is not always modified. In most cases, this routine will detect

the correct amount of stack bytes, but in case of doubt, be generous with your stack

space or use other means to verify that the allocated stack space is sufficient.

Example

void CheckSysStackUsed(void) {

printf("Used System Stack %d", OS_GetSysStackUsed());

241

14.2.9 OS_GetIntStackBase()

Description

Returns a pointer to the base of the interrupt stack.

Prototype

void* OS_GetIntStackBase (void);

Return value

The pointer to the base address of the interrupt stack.

Additional Information

This function is only available when an interrupt stack exists.

Example

void CheckIntStackBase(void) {

printf("Addr Interrupt Stack %x", OS_GetIntStackBase());

}

242 CHAPTER 14 Stacks

14.2.10 OS_GetIntStackSize()

Description

Returns the size of the interrupt stack.

Prototype

unsigned int OS_GetIntStackSize (void);

Return value

The size of the interrupt stack in bytes.

Additional Information

This function is only available when an interrupt stack exists.

Example

void CheckIntStackSize(void) {

printf("Size Interrupt Stack %d", OS_GetIntStackSize());

}

243

14.2.11 OS_GetIntStackSpace()

Description

Returns the unused portion of the interrupt stack.

Prototype

unsigned int OS_GetIntStackSpace (void);

Return value

The unused portion of the interrupt stack in bytes.

Additional Information

This function is only available in the debug and stack-check builds and when an inter-

rupt stack exists.

Important

This routine does not reliably detect the amount of stack space left, because it can

only detect modified bytes on the stack. Unfortunately, space used for register stor-

age or local variables is not always modified. In most cases, this routine will detect

the correct amount of stack bytes, but in case of doubt, be generous with your stack

space or use other means to verify that the allocated stack space is sufficient.

Example

void CheckIntStackSpace(void) {

printf("Unused Interrupt Stack %d", OS_GetIntStackSpace());

}

244 CHAPTER 14 Stacks

14.2.12 OS_GetIntStackUsed()

Description

Returns the used portion of the interrupt stack.

Prototype

unsigned int OS_GetIntStackUsed (void);

Return value

The used portion of the interrupt stack in bytes.

Additional Information

This function is only available in the debug and stack-check builds and when an inter-

rupt stack exists.

Important

This routine does not reliably detect the amount of stack space used, because it can

only detect modified bytes on the stack. Unfortunately, space used for register stor-

age or local variables is not always modified. In most cases, this routine will detect

the correct amount of stack bytes, but in case of doubt, be generous with your stack

space or use other means to verify that the allocated stack space is sufficient.

Example

void CheckIntStackUsed(void) {

printf("Used Interrupt Stack %d", OS_GetIntStackUsed());

}

245

Chapter 15

Interrupts

This chapter explains how to use interrupt service routines (ISRs) in cooperation with

embOS. Specific details for your CPU and compiler can be found in the CPU & Com-

piler Specifics manual of the embOS documentation.

246 CHAPTER 15 Interrupts

15.1 What are interrupts?

Interrupts are interruptions of a program caused by hardware. When an interrupt

occurs, the CPU saves its registers and executes a subroutine called an interrupt ser-

vice routine, or ISR. After the ISR is completed, the program returns to the high-

est-priority task in the READY state. Normal interrupts are maskable; they can occur

at any time unless they are disabled with the CPU's “disable interrupt” instruction.

ISRs are also nestable - they can be recognized and executed within other ISRs.

There are several good reasons for using interrupt routines. They can respond very

quickly to external events such as the status change on an input, the expiration of a

hardware timer, reception or completion of transmission of a character via serial

interface, or other types of events. Interrupts effectively allow events to be pro-

cessed as they occur.

247

15.2 Interrupt latency

Interrupt latency is the time between an interrupt request and the execution of the

first instruction of the interrupt service routine.

Every computer system has an interrupt latency. The latency depends on various fac-

tors and differs even on the same computer system. The value that one is typically

interested in is the worst case interrupt latency.

The interrupt latency is the sum of a lot of different smaller delays explained below.

15.2.1 Causes of interrupt latencies

• The first delay is typically in the hardware: The interrupt request signal needs to

be synchronized to the CPU clock. Depending on the synchronization logic, typi-

cally up to 3 CPU cycles can be lost before the interrupt request has reached the

CPU core.

• The CPU will typically complete the current instruction. This instruction can take

a lot of cycles; on most systems, divide, push-multiple, or memory-copy instruc-

tions are the instructions which require most clock cycles. On top of the cycles

required by the CPU, there are in most cases additional cycles required for mem-

ory access. In an ARM7 system, the instruction STMDB SP!,{R0-R11,LR}; (Push

parameters and perm. register) is typically the worst case instruction. It stores

13 32-bit registers on the stack. The CPU requires 15 clock cycles.

• The memory system may require additional cycles for wait states.

• After the current instruction is completed, the CPU performs a mode switch or

pushes registers (typically, PC and flag registers) on the stack. In general, mod-

ern CPUs (such as ARM) perform a mode switch, which requires less CPU cycles

than saving registers.

• Pipeline fill

Most modern CPUs are pipelined. Execution of an instruction happens in various

stages of the pipeline. An instruction is executed when it has reached its final

stage of the pipeline. Because the mode switch has flushed the pipeline, a few

extra cycles are required to refill the pipeline.

15.2.2 Additional causes for interrupt latencies

There can be additional causes for interrupt latencies.

These depend on the type of system used, but we list a few of them.

• Latencies caused by cache line fill.

If the memory system has one or multiple caches, these may not contain the

required data. In this case, not only the required data is loaded from memory,

but in a lot of cases a complete line fill needs to be performed, reading multiple

words from memory.

• Latencies caused by cache write back.

A cache miss may cause a line to be replaced. If this line is marked as dirty, it

needs to be written back to main memory, causing an additional delay.

• Latencies caused by MMU translation table walks.

Translation table walks can take a considerable amount of time, especially as

they involve potentially slow main memory accesses. In real-time interrupt han-

dlers, translation table walks caused by the TLB not containing translations for

the handler and/or the data it accesses can increase interrupt latency signifi-

cantly.

• Application program.

Of course, the application program can cause additional latencies by disabling

interrupts. This can make sense in some situations, but of course causes add.

latencies.

• Interrupt routines.

On most systems, one interrupt disables further interrupts. Even if the interrupts

are re-enabled in the ISR, this takes a few instructions, causing add. latency.

• RTOS (Real-time Operating system).

An RTOS also needs to temporarily disable the interrupts which can call API-func-

tions of the RTOS. Some RTOSes disable all interrupts, effectively increasing

248 CHAPTER 15 Interrupts

interrupt latencies for all interrupts, some (like embOS) disable only low-priority

interrupts and do thereby not affect the latency of high priority interrupts.

249

15.3 Zero interrupt latency

Zero interrupt latency in the strict sense is not possible as explained above. What we

mean when we say “Zero interrupt latency” is that the latency of high-priority inter-

rupts is not affected by the RTOS; a system using embOS will have the same worst-

case interrupt latency for high priority interrupts as a system running without

embOS.

Why is Zero latency important?

In some systems, a maximum interrupt response time or latency can be clearly

defined. This max. latency can arise from requirements such as maximum reaction

time for a protocol or a software UART implementation that requires very precise tim-

ing.

One customer implemented a UART receiving at up to 800KHz in software using FIQ

(fast interrupt) on a 48 MHz ARM7. This would be impossible to do if fast interrupts

were disabled even for short periods of time.

In a lot of embedded systems, the quality of the product depends on the reaction

time and therefor latency. Typical examples would be systems which periodically read

a value from an A/D converter at high speed, where the accuracy depends on accu-

rate timing. Less jitter means a better product.

Why can a high priority ISR not use the OS API ?

embOS disables low priority interrupts when embOS data structures are modified.

During this time high priority ISR are enabled. If they would call an embOS function,

which also modifies embOS data, the embOS data structures would be corrupted.

How can a high priority ISR communicate with a task ?

The most common way is to use global variables, e.g. a periodically read from an

ADC and the result is stored in a global variable

Another way is to set an interrupt request for a low priority interrupt in your

high priority ISR, which can then communicate or wake up one or more tasks. This

might be helpful if you want to receive several data in your high priority ISR. The low

priority ISR may then store the data bytes in a message queue or mailbox for exam-

ple.

250 CHAPTER 15 Interrupts

15.4 High / low priority interrupts

Most CPUs support interrupts with different priorities. Different priorities have two

effects:

• If different interrupts occur simultaneously, the interrupt with higher priority

takes precedence and its ISR is executed first.

• Interrupts can never be interrupted by other interrupts of the same or lower level

of priority.

How many different levels of interrupts there are depend on the CPU and the inter-

rupt controller. Details are explained in the CPU/MCU/SOC manuals and the CPU &

Compiler Specifics manual of embOS. embOS distinguishes two different levels of

interrupts: High / Low priority interrupts. The embOS port specific documentation

explains where “the line is drawn”, which interrupts are considered high and which

interrupts are considered low priority. In general, the differences are:

Low priority interrupts

• May call embOS API functions

• Latencies caused by embOS

High priority interrupts

• May not call embOS API functions

• No Latencies caused by embOS (Zero latency)

Example of different interrupt priority levels

Let's assume we have a CPU which support 8 interrupt priority levels. With embOS, the 3

highest priority levels are treated as “High priority interrupts”. ARM CPUs support

normal interrupts (IRQ) and fast interrupt (FIQ). Using embOS, the FIQ is treated as

“High priority interrupt”. With most implementations, the high-priority threshold is

adjustable. For details, refer to the processor specific embOS manual.

15.4.1 Using OS functions from high priority interrupts

High priority interrupts may not use embOS functions at all. This is a limitation which

results from zero-latency: embOS does never disable high priority interrupts. This

means that high priority interrupts can interrupt the operating system at any time,

even in critical situations such as the modification of linked lists and double linked

list. This is a design decision that has been taken because zero interrupt latencies

for high priority interrupts are usually more important than the ability to call OS

functions.

There is a way to still use OS functions from high priority interrupts indirectly:

High priority interrupt triggers a low priority interrupt usually by setting an interrupt

requestflag. That low priority interrupt may now call OS functions.

251

The task 1 is interrupted by a high priority interrupt. This high priority interrupt is

not allowed to call an embOS API function directly. Therefore the high priority inter-

rupt triggers a low priority interrupt, which is allowed to call embOS API functions.

The low priority interrupt calls an embOS API function to resume task 2.

Time

Task1 High priority

interrupt Low priority

interrupt

Task2

Task1 is in terrupted

by a high priority interrupt

High priority interrupt

triggers low priority interrupt

Low priority interrupt calls embOS

API function to resume Task2

252 CHAPTER 15 Interrupts

15.5 Rules for interrupt handlers

15.5.1 General rules

There are some general rules for interrupt service routines (ISRs). These rules apply

to both single-task programming as well as to multitask programming using embOS.

• ISR preserve all registers.

Interrupt handlers must restore the environment of a task completely. This

environment normally consists of the registers only, so the ISR must make sure

that all registers modified during interrupt execution are saved at the beginning

and restored at the end of the interrupt routine

• Interrupt handlers must be finished quickly.

Intensive calculations should be kept out of interrupt handlers. An interrupt han-

dler should only be used for storing a received value or to trigger an operation in

the regular program (task). It should not wait in any form or perform a polling

operation.

15.5.2 Additional rules for preemptive multitasking

A preemptive multitasking system like embOS needs to know if the program that is

executing is part of the current task or an interrupt handler. This is because embOS

cannot perform a task switch during the execution of an ISR; it can only do so at the

end of an ISR.

If a task switch were to occur during the execution of an ISR, the ISR would continue

as soon as the interrupted task became the current task again. This is not a problem

for interrupt handlers that do not allow further interruptions (which do not enable

interrupts) and that do not call any embOS functions.

This leads us to the following rule:

• ISR that re-enable interrupts or use any embOS function need to call

OS_EnterInterrupt() at the beginning, before executing any other command,

and before they return, call OS_LeaveInterrupt() as last command.

If a higher priority task is made ready by the ISR, the task switch then occurs in the

routine OS_LeaveInterrupt(). The end of the ISR is executed at a later point, when

the interrupted task is made ready again. If you debug an interrupt routine, do not

be confused. This has proven to be the most efficient way of initiating a task switch

from within an interrupt service routine.

UM01001 User & Reference Guide for embOS © 1995 - 2015 SEGGER Microcontroller GmbH & Co. KG
253
15.6 API functions
The following table lists all interrupt related API functions of embOS.
Routine Description
main
Task
ISR
Timer
OS_DI()
Disables interrupts. Does not 
change the interrupt disable 
counter.
XX X
OS_EI() Unconditionally enables Inter-
rupt. XX X
OS_IncDI()
Increments the interrupt dis-
able counter (OS_DICnt) and 
disables interrupts.
XXXX
OS_RestoreI()
Restores the state of the inter-
rupt flag, based on the inter-
rupt disable counter.
XXXX
OS_DecRI()
Decrements the counter and 
enables interrupts if the 
counter reaches 0.
XXXX
OS_EnterInterrupt() Informs embOS that interrupt 
code is executing. X
OS_LeaveInterrupt()
Informs embOS that the end 
of the interrupt routine has 
been reached; executes task 
switching within ISR.
X
OS_EnterNestableInterrupt()
Informs embOS that interrupt 
code is executing and reen-
ables interrupts.
X
OS_LeaveNestableInterrupt()
Informs embOS that the end 
of the interrupt routine has 
been reached; executes task 
switching within ISR.
X
OS_CallISR() Interrupt entry function. X
OS_CallNestableISR() Interrupt entry function sup-
porting nestable interrupts. X
OS_INTERRUPT_MaskGlobal()
Disable all interrupts (high 
and low priority) uncondition-
ally.
XXXX
OS_INTERRUPT_UnmaskGlobal() Enable all interrupts (high and 
low priority) unconditionally. XXXX
OS_INTERRUPT_PreserveGlobal() Preserves the current interrupt 
enable state XXXX
OS_INTERRUPT_PreserveAndMaskGlobal()
Preserves the current interrupt 
enable state and then disables 
all interrupts.
XXXX
OS_INTERRUPT_RestoreGlobal()
Restores the interrupt enable 
state which was preserved 
before.
XXXX
Table 15.1: Interrupt API functions

254 CHAPTER 15 Interrupts

15.6.1 OS_CallISR()

Description

Entry function for use in an embOS interrupt handler. Nestable interrupts disabled.

Prototype

void OS_CallISR (void (*pRoutine)(void));

Additional Information

OS_CallISR() can be used as entry function in an embOS interrupt handler, when

the corresponding interrupt should not be interrupted by another embOS interrupt.

OS_CallISR() sets the interrupt priority of the CPU to the user definable ’fast’ inter-

rupt priority level, thus locking any other embOS interrupt.

Fast interrupts are not disabled.

Note: For some specific CPUs OS_CallISR() must be used to call an interrupt

handler because OS_EnterInterrupt() / OS_LeaveInterrupt() may not be avail-

able.

Refer to the CPU specific manual.

Example

#pragma interrupt void OS_ISR_Tick(void) {

OS_CallISR(_IsrTickHandler);

}

Parameter Description

pRoutine Pointer to a routine that should run on interrupt.

Table 15.2: OS_CallISR() parameter list

255

15.6.2 OS_CallNestableISR()

Description

Entry function for use in an embOS interrupt handler. Nestable interrupts enabled.

Prototype

void OS_CallNestableISR (void (*pRoutine)(void));

Additional Information

OS_CallNestableISR() can be used as entry function in an embOS interrupt handler,

when interruption by higher prioritized embOS interrupts should be allowed.

OS_CallNestableISR() does not alter the interrupt priority of the CPU, thus keeping

all interrupts with higher priority enabled.

Note: For some specific CPUs OS_CallNestableISR() must be used to call an

interrupt handler because OS_EnterNestableInterrupt() /

OS_LeaveNestableInterrupt() may not be available.

Refer to the CPU specific manual.

Example

#pragma interrupt void OS_ISR_Tick(void) {

OS_CallNestableISR(_IsrTickHandler);

}

Parameter Description

pRoutine Pointer to a routine that should run on interrupt.

Table 15.3: OS_CallNestableISR() parameter list

256 CHAPTER 15 Interrupts

15.6.3 OS_EnterInterrupt()

Note: This function may not be available in all ports.

Description

Informs embOS that interrupt code is executing.

Prototype

void OS_EnterInterrupt (void);

Additional Information

If OS_EnterInterrupt() is used, it should be the first function to be called in the

interrupt handler. It must be used with OS_LeaveInterrupt() as the last function

called. The use of this function has the following effects, it:

• disables task switches

• keeps interrupts in internal routines disabled.

An example is shown in the the description of OS_LeaveInterrupt().

257

15.6.4 OS_LeaveInterrupt()

Note: This function may not be available in all ports.

Description

Informs embOS that the end of the interrupt routine has been reached; executes

task switching within ISR.

Prototype

void OS_LeaveInterrupt (void);

Additional Information

If OS_LeaveInterrupt() is used, it should be the last function to be called in the

interrupt handler. If the interrupt has caused a task switch, it will be executed

(unless the program which was interrupted was in a critical region).

Example using OS_EnterInterrupt()/OS_LeaveInterrupt()

_interrupt void ISR_Timer(void) {

OS_EnterInterrupt();

OS_SignalEvent(1,&Task);/* Any functionality could be here */

OS_LeaveInterrupt();

}

258 CHAPTER 15 Interrupts

15.7 Enabling / disabling interrupts from C

During the execution of a task, maskable interrupts are normally enabled. In certain

sections of the program, however, it can be necessary to disable interrupts for short

periods of time to make a section of the program an atomic operation that cannot be

interrupted. An example would be the access to a global volatile variable of type long

on an 8/16-bit CPU. To make sure that the value does not change between the two or

more accesses that are needed, interrupts must be temporarily disabled:

Bad example:

volatile long lvar;

void routine (void) {

lvar ++;

}

The problem with disabling and re-enabling interrupts is that functions that disable/

enable the interrupt cannot be nested.

Your C compiler offers two intrinsic functions for enabling and disabling interrupts.

These functions can still be used, but it is recommended to use the functions that

embOS offers (to be precise, they only look like functions, but are macros in reality).

If you do not use these recommended embOS functions, you may run into a problem

if routines which require a portion of the code to run with disabled interrupts are

nested or call an OS routine.

We recommend disabling interrupts only for short periods of time, if possible. Also,

you should not call routines when interrupts are disabled, because this could lead to

long interrupt latency times (the longer interrupts are disabled, the higher the inter-

rupt latency). As long as you only call embOS functions with interrupts enabled, you

may also safely use the compiler-provided intrinsics to disable interrupts.

259

15.7.1 OS_IncDI() / OS_DecRI()

The following functions are actually macros defined in RTOS.h, so they execute very

quickly and are very efficient. It is important that they are used as a pair: first

OS_IncDI(), then OS_DecRI().

OS_IncDI()

Short for Increment and Disable Interrupts. Increments the interrupt disable

counter (OS_DICnt) and disables interrupts.

OS_DecRI()

Short for Decrement and Restore Interrupts. Decrements the counter and

enables interrupts if the counter reaches 0.

Example

volatile long lvar;

void routine (void) {

OS_IncDI();

lvar ++;

OS_DecRI();

}

OS_IncDI() increments the interrupt disable counter which is used for the entire OS

and is therefore consistent with the rest of the program in that any routine can be

called and the interrupts will not be switched on before the matching OS_DecRI() has

been executed.

If you need to disable interrupts for a short moment only where no routine is called,

as in the example above, you could also use the pair OS_DI() and OS_RestoreI().

These are a bit more efficient because the interrupt disable counter OS_DICnt is not

modified twice, but only checked once. They have the disadvantage that they do not

work with routines because the status of OS_DICnt is not actually changed, and they

should therefore be used with great care. In case of doubt, use OS_IncDI() and

OS_DecRI().

260 CHAPTER 15 Interrupts

15.7.2 OS_DI() / OS_EI() / OS_RestoreI()

OS_DI()

Short for Disable Interrupts. Disables interrupts. Does not change the interrupt

disable counter.

OS_EI()

Short for Enable Interrupts. Refrain from using this function directly unless you are

sure that the interrupt enable count has the value zero, because it does not take the

interrupt disable counter into account.

OS_RestoreI()

Short for Restore Interrupts. Restores the status of the interrupt flag, based on the

interrupt disable counter.

Example

volatile long lvar;

void routine (void) {

OS_DI();

lvar++;

OS_RestoreI();

}

261

15.8 Definitions of interrupt control macros (in RTOS.h)

#define OS_IncDI() { OS_ASSERT_DICnt(); OS_DI(); OS_DICnt++; }

#define OS_DecRI() { OS_ASSERT_DICnt(); if (--OS_DICnt==0) OS_EI(); }

#define OS_RestoreI() { OS_ASSERT_DICnt(); if (OS_DICnt==0) OS_EI(); }

262 CHAPTER 15 Interrupts

15.9 Nesting interrupt routines

By default, interrupts are disabled in an ISR because the CPU disables interrupts with

the execution of the interrupt handler. Re-enabling interrupts in an interrupt handler

allows the execution of further interrupts with equal or higher priority than that of

the current interrupt. These are known as nested interrupts, illustrated in the dia-

gram below:

For applications requiring short interrupt latency, you may re-enable interrupts inside

an ISR by using OS_EnterNestableInterrupt() and OS_LeaveNestableInterrupt()

within the interrupt handler.

Nested interrupts can lead to problems that are difficult to track; therefore it is not

really recommended to enable interrupts within an interrupt handler. As it is impor-

tant that embOS keeps track of the status of the interrupt enable/disable flag, the

enabling and disabling of interrupts from within an ISR must be done using the func-

tions that embOS offers for this purpose.

The routine OS_EnterNestableInterrupt() enables interrupts within an ISR and

prevents further task switches; OS_LeaveNestableInterrupt() disables interrupts

right before ending the interrupt routine again, thus restores the default condition.

Re-enabling interrupts will make it possible for an embOS scheduler interrupt to

shortly interrupt this ISR. In this case, embOS needs to know that another ISR is still

running and that it may not perform a task switch.

Time

Task ISR 1 ISR 3ISR 2

Interrupt 1

Interrupt 2

Interrupt 3

263

15.9.1 OS_EnterNestableInterrupt()

Note: This function may not be available in all ports.

Description

Re-enables interrupts and increments the embOS internal critical region counter,

thus disabling further task switches.

Prototype

void OS_EnterNestableInterrupt (void);

Additional Information

This function should be the first call inside an interrupt handler when nested inter-

rupts are required. The function OS_EnterNestableInterrupt() is implemented as a

macro and offers the same functionality as OS_EnterInterrupt() in combination

with OS_DecRI(), but is more efficient, resulting in smaller and faster code.

Example

Refer to the example for OS_LeaveNestableInterrupt().

264 CHAPTER 15 Interrupts

15.9.2 OS_LeaveNestableInterrupt()

Note: This function may not be available in all ports.

Description

Disables further interrupts, then decrements the embOS internal critical region

count, thus re-enabling task switches if the counter has reached zero again.

Prototype

void OS_LeaveNestableInterrupt (void);

Additional Information

This function is the counterpart of OS_EnterNestableInterrupt(), and must be the

last function call inside an interrupt handler when nested interrupts have been

enabled by OS_EnterNestableInterrupt().

The function OS_LeaveNestableInterrupt() is implemented as a macro and offers

the same functionality as OS_LeaveInterrupt() in combination with OS_IncDI(),

but is more efficient, resulting in smaller and faster code.

Example using OS_EnterNestableInterrupt()/OS_LeaveNestableInterrupt()

_interrupt void ISR_Timer(void) {

OS_EnterNestableInterrupt();

OS_SignalEvent(1,&Task);/* Any functionality could be here */

OS_LeaveNestableInterrupt();

}

265

15.9.3 OS_InInterrupt()

Description

This function can be called to examine if the calling function is running in an interrupt

context.

Prototype

unsigned char OS_InInterrupt (void);

Return value

0: Code is not executed in interrupt handler.

!=0: Code is executed in an interrupt handler.

Additional Information

The function delivers the value of the embOS variable OS_InInt which is incremented

in OS_EnterInterrupt() and OS_EnterNestableInterrupt(). The variable OS_InInt is

decremented in OS_LeaveInterrupt() and OS_LeaveNestableInterrupt(). Previous

versions of embOS implemented this functionallity in debug libraries only. Since ver-

sion 3.88c, the internal variable is included in all libraries and can be examined by a

call of OS_InInterrupt().

For application code, it may be useful to know if it is called from interrupt or task,

because some functions must not be called from an interrupt-handler.

266 CHAPTER 15 Interrupts

15.10 Global interrupt enable / disable

The embOS interrupt enable and disable functions enable and disable embOS inter-

rupts only. If a system is setup to support high and low priority interrupts and

embOS is configured to suppport “zero latency” interrupts as described before, the

embOS functions to enable and disable interrupts affect the low priority interrupts

only.

High priority interrupts, called “zero latency interrupts” are never enabled or disabled

by the previous described embOS functions.

In an application it may be required to disable and enable all interrupts.

Since version 3.90, embOS comes with API functions which allows enabling and dis-

abling all interrupts. These functions have the prefix OS_INTERRUPT_ and allow a

“global” handling of the interrupt enable / disable state of the CPU.

These functions affect the state of the CPU unconditionally.

They should be used carefully.

267

15.10.1 OS_INTERRUPT_MaskGlobal()

Description

This function disables high and low priority interrupts unconditionally.

Prototype

void OS_INTERRUPT_MaskGlobal (void);

Additional Information

OS_INTERRUPT_MaskGlobal() disables all interrupts in a fast and efficient way.

Note that the system does not track the interrupt state when calling the function.

Therefore the function should not be called when the state is unknown.

Interrupts can be re-enabled by calling OS_INTERRUPT_UnmaskGlobal().

After calling OS_INTERRUPT_MaskGlobal(), no embOS function except the interrupt

enable function OS_INTERRUPT_UnmaskGlobal() should be called, because the inter-

rupt state is not saved by the function and not noticed by embOS. An embOS API

function may re-enable interrupts. The excat behaviour depends on the CPU.

15.10.2 OS_INTERRUPT_UnmaskGlobal()

Description

This function enables high and low priority interrupts unconditionally.

Prototype

void OS_INTERRUPT_UnmaskGlobal (void);

Additional Information

OS_INTERRUPT_UnmaskGlobal() must be called to re-enable interrupts which were

disabled before by a call of OS_INTERRUPT_MaskGlobal().

The function re-enables high and low priority interrupts unconditionally.

OS_INTERRUPT_MaskGlobal() and OS_INTERRUPT_UnmaskGlobal() should be used

as a pair. The call cannot be nested, because the state is not saved.

This kind of global interrupt disable/enable should only be used when the interrupt

enable state is well known and interrupts are enabled.

Between OS_INTERRUPT_MaskGlobal() and OS_INTERRUPT_UnmaskGlobal(), no

function should be called when it is not known if the function alters the interrupt

enable state.

If the interrupt state is not known, the functions OS_INTERRUPT_PreserveGlobal()

or OS_INTERRUPT_PreserveAndMaskGlobal() and OS_INTERRUPT_RestoreGlobal()

shall be used as decribed later on.

Example

void Sample(void) {

OS_INTERRUPT_MaskGlobal(); // Disable interrupts

// Execute any code that should be executed with interrupts disabled

// No embOS function should be called

...

OS_INTERRUPT_UnmaskGlobal(); // Re-enable interrupts unconditionally

}

268 CHAPTER 15 Interrupts

15.10.3 OS_INTERRUPT_PreserveGlobal()

Description

This function can be called to preserve the current interrupt enable state of the CPU.

Prototype

void OS_INTERRUPT_PreserveGlobal (OS_U32 *pState);

Additional Information

If the interrupt enable state is not known and interrupts should be disabled by a call

of OS_INTERRUPT_MaskGlobal(), the current interrupt enbale state can be preserved

and restored later by a call of OS_INTERRUPT_RestoreGlobal().

Note that the interrupt state is not kept by embOS. After disabling the interrupts by

a call of OS_INTERRUPT_MaskGlobal(), no embOS API function should be called,

because embOS functions might re-enable interrupts.

Example

void Sample(void) {

OS_U32 IntState;

OS_INTERRUPT_PreserveGlobal(&IntState); // Remember the interrupt enable state.

OS_INTERRUPT_MaskGlobal(); // Disable interrupts

// Execute any code that should be executed with interrupts disabled

// No embOS function should be called

...

OS_INTERRUPT_RestoreGlobal(&IntState); // Restore the interrupt enable state

}

Parameter Description

pState Pointer to an OS_U32 variable that receives the interrupt state.

Table 15.4: OS_CallNestableISR() parameter list

269

15.10.4 OS_INTERRUPT_PreserveAndMaskGlobal()

Description

This function preserves the current interrupt enable state of the CPU and then dis-

ables high and low priority interrupts.

Prototype

void OS_INTERRUPT_PreserveAndMaskGlobal (OS_U32 *pState);

Additional Information

The function store the current interrupt enable state into the variable pointed to by

pState and then disables high and low priority interrupts.

The interrupt state can be restored later by a corresponding call of

OS_INTERRUPT_RestoreGlobal().

The pair of function calls OS_INTERRUPT_PreserveAndMaskGlobal() and

OS_INTERRUPT_RestoreGlobal() can be nested, as long as the interrupt enable state

is stored into an individual variable on each call of

OS_INTERRUPT_PreserveAndMaskGlobal().

This function pair should be used when the interrupt enable state is not known when

interrupts shall be enabled.

15.10.5 OS_INTERRUPT_RestoreGlobal()

Description

This function must be called to restore the interrupt enable state of the CPU which

was preserved before.

Prototype

void OS_INTERRUPT_RestoreGlobal (OS_U32 *pState);

Additional Information

Restores the interrupt enable state which was saved before by a call of

OS_INTERRUPT_PreserveGlobal() or OS_INTERRUPT_PreserveAndMaskGlobal().

If interrupts were enabled before they were disabled globally, the function reenables

them.

Example

void Sample(void) {

OS_U32 IntState;

OS_INTERRUPT_PreserveGlobal(&IntState); // Remember the interrupt enable state.

OS_INTERRUPT_MaskGlobal(); // Disable interrupts

// Execute any code that should be executed with interrupts disabled

// No embOS function should be called

...

OS_INTERRUPT_RestoreGlobal(&IntState); // Restore the interrupt enable state

}

Parameter Description

pState Pointer to an OS_32 variable that receives the interrupt state.

Table 15.5: OS_CallNestableISR() parameter list

Parameter Description

pState Pointer to an OS_U32 that holds the interrupt enable state.

Table 15.6: OS_CallNestableISR() parameter list

270 CHAPTER 15 Interrupts

15.11 Non-maskable interrupts (NMIs)

embOS performs atomic operations by disabling interrupts. However, a non-maskable

interrupt (NMI) cannot be disabled, meaning it can interrupt these atomic operations.

Therefore, NMIs should be used with great care and may under no circumstances call

any embOS routines.

271

Chapter 16

Critical Regions

272 CHAPTER 16 Critical Regi ons

16.1 Introduction

Critical regions are program sections during which the scheduler is switched off,

meaning that no task switch and no execution of software timers are allowed except

in situations where the running task must wait. Effectively, preemptions are switched

off.

A typical example for a critical region would be the execution of a program section

that handles a time-critical hardware access (for example writing multiple bytes into

an EEPROM where the bytes must be written in a certain amount of time), or a sec-

tion that writes data into global variables used by a different task and therefore

needs to make sure the data is consistent.

A critical region can be defined anywhere during the execution of a task. Critical

regions can be nested; the scheduler will be switched on again after the outermost

loop is left. Interrupts are still legal in a critical region. Software timers and inter-

rupts are executed as critical regions anyhow, so it does not hurt but does not do any

good either to declare them as such. If a task switch becomes due during the execu-

tion of a critical region, it will be performed right after the region is left.

273

16.2 API functions

Routine Description

main

Task

ISR

Timer

OS_EnterRegion() Indicates to the OS the beginning of a critical

region. XXXX

OS_LeaveRegion() Indicates to the OS the end of a critical region. X X X X

Table 16.1: Critical regions API functions

274 CHAPTER 16 Critical Regi ons

16.2.1 OS_EnterRegion()

Description

Indicates to the OS the beginning of a critical region.

Prototype

void OS_EnterRegion (void);

Additional Information

OS_EnterRegion() is not actually a function but a macro. However, it behaves very

much like a function but is much more efficient. Using the macro indicates to embOS

the beginning of a critical region.

A critical region counter (OS_Global.Counters.Cnt.Region), which is 0 by default, is

incremented so that the routine can be nested. The counter will be decremented by a

call to the routine OS_LeaveRegion(). If this counter reaches 0 again, the critical

region ends.

Interrupts are not disabled using OS_EnterRegion(); however, preemptive task

switches are disabled in a critical region.

If any interrupt triggers a task switch, the task switch is delayed and kept pending

until the final call of OS_LeaveRegion(). When the OS_RegionCnt reaches 0 again, a

pending task switch is executed.

Cooperative task switches are not affected and will be executed in critical regions.

When the task is running in a critical region and then calls any blocking embOS func-

tion, the task will be suspended.

When the task is resumed again, the task-specific OS_RegionCnt is restored, the

task continues to run in a critical region until OS_LeaveRegion() is called.

Example

void SubRoutine(void) {

OS_EnterRegion();

/* The following code will not be interrupted by the OS */

/* Preemptive task switches are blocked until the call of OS_leaveRegion() */

OS_LeaveRegion();

}

275

16.2.2 OS_LeaveRegion()

Description

Indicates to the OS the end of a critical region.

Prototype

void OS_LeaveRegion (void);

Additional Information

OS_LeaveRegion() is not actually a function but a macro. However, it behaves very

much like a function but is much more efficient. Usage of the macro indicates to

embOS the end of a critical region.

A critical region counter (OS_Global.Counters.Cnt.Region), which is 0 by default, is

decremented. If this counter reaches 0 again, the critical region ends.

A task switch which became pending during a critical region will be executed in

OS_Enterregion() when the OS_RegionCnt reaches 0 again.

Example

Refer to the example for OS_EnterRegion().

276 CHAPTER 16 Critical Regi ons

277

Chapter 17

Time measurement

embOS supports 2 types of time measurement:

• Low resolution (using a time variable)

• High resolution (using a hardware timer)

Both are explained in this chapter.

278 CHAPTER 17 Time measurement

17.1 Introduction

embOS supports two basic types of run-time measurement which may be used for

calculating the execution time of any section of user code. Low-resolution measure-

ments use a time base of ticks, while high-resolution measurements are based on a

time unit called a cycle. The length of a cycle depends on the timer clock frequency.

279

17.2 Low-resolution measurement

The system time variable OS_Global.Time is measured in ticks, or ms. The low-reso-

lution functions OS_GetTime() and OS_GetTime32() are used for returning the cur-

rent contents of this variable. The basic idea behind low-resolution measurement is

quite simple: The system time is returned once before the section of code to be

timed and once after, and the first value is subtracted from the second to obtain the

time it took for the code to execute.

The term low-resolution is used because the time values returned are measured in

completed ticks. Consider the following: with a normal tick of one ms, the variable

OS_Time is incremented with every tick-interrupt, or once every ms. This means that

the actual system time can potentially be more than what a low-resolution function

will return (for example, if an interrupt actually occurs at 1.4 ticks, the system will

still have measured only one tick as having elapsed). The problem becomes even

greater with runtime measurement, because the system time must be measured

twice. Each measurement can potentially be up to one tick less than the actual time,

so the difference between two measurements could theoretically be inaccurate by up

to one tick.

The following diagram illustrates how low-resolution measurement works. We can see

that the section of code actually begins at 0.5 ms and ends at 5.2 ms, which means

that its actual execution time is (5.2 - 0.5) = 4.7 ms. However with a tick of one ms,

the first call to OS_GetTime() returns 0, and the second call returns 5. The measured

execution time of the code would therefore result in (5 - 0) = 5 ms.

For many applications, low-resolution measurement may be fully sufficient for your

needs. In some cases, it may be more desirable than high-resolution measurement

due to its ease of use and faster computation time.

OS_Time

6 ms0 ms 5 ms4 ms3 ms2 ms1 ms

Code to be timed

OS_GetTime() => 0 OS_GetTime() => 5

0.5 ms 5.2 ms

280 CHAPTER 17 Time measurement

17.2.1 API functions

Routine Description

main

Task

ISR

Timer

OS_GetTime() Returns the current system time in ticks. X X X X

OS_GetTime32() Returns the current system time in ticks as a

32-bit value. XXXX

Table 17.1: Low-resolution measurement API functions

281

17.2.1.1 OS_GetTime()

Description

Returns the current system time in ticks.

Prototype

int OS_GetTime (void);

Return value

The system variable OS_Global.Time as a 16- or 32-bit integer value.

Additional Information

This function returns the system time as a 16-bit value on 8/16-bit CPUs, and as a

32-bit value on 32-bit CPUs. The OS_Global.Time variable is a 32-bit value. There-

fore, if the return value is 32-bit, it is simply the entire contents of the OS_Time vari-

able. If the return value is 16-bit, it is the lower 16 bits of the OS_Global.OS_Time

variable.

282 CHAPTER 17 Time measurement

17.2.1.2 OS_GetTime32()

Description

Returns the current system time in ticks as a 32-bit value.

Prototype

int OS_GetTime32 (void);

Return value

The system variable OS_Global.Time as a 32-bit integer value.

Additional Information

This function always returns the system time as a 32-bit value. Because the

OS_Global.Time variable is also a 32-bit value, the return value is simply the entire

contents of the OS_Global.Time variable.

283

17.3 High-resolution measurement

High-resolution measurement uses the same routines as those used in profiling

builds of embOS, allowing for fine-tuning of time measurement. While system resolu-

tion depends on the CPU used, it is typically about one µs, making high-resolution

measurement about 1000 times more accurate than low-resolution calculations.

Instead of measuring the number of completed ticks at a given time, an internal

count is kept of the number of cycles that have been completed. Look at the illustra-

tion below, which measures the execution time of the same code used in the low-res-

olution calculation. For this example, we assume that the CPU has a timer running at

10 MHz and is counting up. The number of cycles per tick is therefore (10 MHz / 1

kHz) = 10,000. This means that with each tick-interrupt, the timer restarts at 0 and

counts up to 10,000.

The call to OS_Timing_Start() calculates the starting value at 5,000 cycles, while

the call to OS_Timing_End() calculates the ending value at 52,000 cycles (both val-

ues are kept track of internally). The measured execution time of the code in this

example would therefore be (52,000 - 5,000) = 47,000 cycles, which corresponds to

4.7 ms.

Although the function OS_Timing_GetCycles() may be used for returning the execu-

tion time in cycles as above, it is typically more common to use the function

OS_Timing_Getus(), which returns the value in microseconds (µs). In the above

example, the return value would be 4,700 µs.

Data structure

All high-resolution routines take as parameter a pointer to a data structure of type

OS_TIMING, defined as follows:

#define OS_TIMING OS_U32

OS_Time

6 ms0 ms 5 ms4 ms3 ms2 ms1 ms

Code to be timed

OS_GetTime() => 0 OS_GetTime() => 5

0.5 ms 5.2 ms

284 CHAPTER 17 Time measurement

17.3.1 API functions

Routine Description

main

Task

ISR

Timer

OS_Timing_Start() Marks the beginning of a code section to be

timed. XXXX

OS_Timing_End() Marks the end of a code section to be timed. X X X X

OS_Timing_Getus()

Returns the execution time of the code

between OS_Timing_Start() and

OS_Timing_End() in microseconds.

XXXX

OS_Timing_GetCycles()

Returns the execution time of the code

between OS_Timing_Start() and

OS_Timing_End() in cycles.

XXXX

Table 17.2: High-resolution measurement API functions

285

17.3.1.1 OS_Timing_Start()

Description

Marks the beginning of a section of code to be timed.

Prototype

void OS_Timing_Start (OS_TIMING* pCycle);

Additional Information

This function must be used with OS_Timing_End().

Parameter Description

pCycle Pointer to a data structure of type OS_TIMING.

Table 17.3: OS_TimingStart() parameter list

286 CHAPTER 17 Time measurement

17.3.1.2 OS_Timing_End()

Description

Marks the end of a section of code to be timed.

Prototype

void OS_Timing_End (OS_TIMING* pCycle);

Additional Information

This function must be used with OS_Timing_Start().

Parameter Description

pCycle Pointer to a data structure of type OS_TIMING.

Table 17.4: OS_TimingEnd() parameter list

287

17.3.1.3 OS_Timing_Getus()

Description

Returns the execution time of the code between OS_Timing_Start() and

OS_Timing_End() in microseconds.

Prototype

OS_U32 OS_Timing_Getus (const OS_TIMING* pCycle);

Additional Information

The execution time in microseconds (µs) as a 32-bit integer value.

Parameter Description

pCycle Pointer to a data structure of type OS_TIMING.

Table 17.5: OS_Timing_Getus() parameter list

288 CHAPTER 17 Time measurement

17.3.1.4 OS_Timing_GetCycles()

Description

Returns the execution time of the code between OS_Timing_Start() and

OS_Timing_End() in cycles.

Prototype

OS_U32 OS_Timing_GetCycles (OS_TIMING* pCycle);

Return value

The execution time in cycles as a 32-bit integer.

Additional Information

Cycle length depends on the timer clock frequency.

Parameter Description

pCycle Pointer to a data structure of type OS_TIMING.

Table 17.6: OS_Timing_GetCycles() parameter list

289

17.4 Example

The following sample demonstrates the use of low-resolution and high-resolution

measurement to return the execution time of a section of code:

/**********************************************************

* SEGGER MICROCONTROLLER SYSTEME GmbH

* Solutions for real time microcontroller applications

***********************************************************

File : SampleHiRes.c

Purpose : Demonstration of embOS Hires Timer

--------------END-OF-HEADER------------------------------*/

#include "RTOS.H"

#include <stdio.h>

OS_STACKPTR int Stack[1000]; /* Task stacks */

OS_TASK TCB; /* Task-control-blocks */

volatile int Dummy;

void UserCode(void) {

for (Dummy=0; Dummy < 11000; Dummy++); /* Burn some time */

}

* Measure the execution time with low resolution and return it in ms (ticks)

int BenchmarkLoRes(void) {

OS_TIME t;

t = OS_GetTime();

UserCode(); /* Execute the user code to be benchmarked */

t = OS_GetTime() - t;

return (int)t;

}

* Measure the execution time with hi resolution and return it in us

OS_U32 BenchmarkHiRes(void) {

OS_TIMING t;

OS_Timing_Start(&t);

UserCode(); /* Execute the user code to be benchmarked */

OS_Timing_End(&t);

return OS_Timing_Getus(&t);

}

void Task(void) {

int tLo;

OS_U32 tHi;

char ac[80];

while (1) {

tLo = BenchmarkLoRes();

tHi = BenchmarkHiRes();

sprintf(ac, "LoRes: %d ms\n", tLo);

OS_SendString(ac);

sprintf(ac, "HiRes: %d us\n", tHi);

OS_SendString(ac);

}

/**********************************************************

* main

**********************************************************/

void main(void) {

OS_InitKern(); /* Initialize OS */

OS_InitHW(); /* Initialize Hardware for OS */

/* You need to create at least one task here ! */

OS_CREATETASK(&TCB, "HP Task", Task, 100, Stack);

OS_Start(); /* Start multitasking */

}

290 CHAPTER 17 Time measurement

The output of the sample is as follows:

LoRes: 7 ms

HiRes: 6641 us

LoRes: 7 ms

HiRes: 6641 us

LoRes: 6 ms

291

17.5 Micro second precise system time

The following functions return the current system time in micro second resolution.

The function OS_Config_SysTimer() setups the necessary parameters.

The following functions are not available when the compiler does not support a 64bit

data type (long long).

17.5.1 API functions

Routine Description

main

Task

ISR

Timer

OS_GetTime_us() Returns the current system time in usec as a

32 bit value. XXXX

OS_GetTime_us64()

Returns the current system time in usec as a

64 bit value. This function is not available with

all embOS ports.

XXXX

OS_Config_SysTimer() Configures system time parameters. In gen-

eral called from RTOSInit.c. XXXX

Table 17.7: Micro second accurate system time API functions

292 CHAPTER 17 Time measurement

17.5.2 OS_GetTime_us()

Description

Returns the current system time in micro seconds as a 32 bit value.

Prototype

OS_U32 OS_GetTime_us();

Return value

The execution time in micro seconds as a 32-bit unsigned integer value.

Additional Information

OS_GetTime_us() returns only correct values if the function OS_Config_SysTimer()

was called at initialization time.

293

17.5.3 OS_GetTime_us64()

Description

Returns the current system time in micro seconds as a 64 bit value.

Prototype

OS_U64 OS_GetTime_us();

Return value

The execution time in micro seconds as a 64-bit unsigned integer value.

Additional Information

OS_GetTime_us64() returns only correct values if the function

OS_Config_SysTimer() was called at initialization time. This function is not available

with all embOS ports.

294 CHAPTER 17 Time measurement

17.5.4 OS_Config_SysTimer()

Description

Configures the system time parameters for the functions OS_GetTime_us() and

OS_GetTime_us64(). This function should be called once at initialization time, e.g. in

RTOSInit.c.

Prototype

void OS_Config_SysTimer(const OS_SYSTIMER_CONFIG *pConfig)

Additional Information

OS_Config_SysTimer() uses the struct OS_SYSTIMER_CONFIG:

17.5.4.1 pfGetTimerCycles()

Description

This callback function must be implemented by the user. It returns the current hard-

ware timer count value.

Prototype

unsigned int (*pfGetTimerCycles) (void);

Return value

The current hardware timer count value.

17.5.4.2 pfGetTimerIntPending()

Description

This callback function must be implemented by the user. It returns a value unequal to

zero if the hardware timer interrupt pending flag is set.

Prototype

unsigned int (*pfGetTimerIntPending)(void);

Return value

It returns zero if the hardware timer interrupt pending flag is not set and any other

value when the pending flag is set.

Parameter Description

pConfig Pointer to a data structure of type OS_SYSTIMER_CONFIG

Table 17.8: OS_Config_SysTimer() parameter list

Member Description

TimerFreq Timer frequency in Hz

TickFreq Tick frequency in Hz

IsUpCounter 0: for hardware timer which counts down

1: for hardware timer which counts up

pfGetTimerCycles Pointer to a function which returns the current hardware

timer count value

pfGetTimerIntPending Pointer to a function which returns if the hardware timer

interrupt pending flag is set

Table 17.9: OS_Config_SysTimer() parameter list

295

17.5.4.3 Example

#define OS_FSYS 72000000u // 72 MHz CPU main clock

#define OS_PCLK_TIMER (OS_FSYS) // HW timer runs at CPU speed

#define OS_TICK_FREQ 1000u // 1 KHz => 1 msc per system tick

static unsigned int _OS_GetHWTimerCycles(void) {

return HW_TIMER_VALUE_REG;

}

static unsigned int _OS_GetHWTimer_IntPending(void) {

return HW_TIMER_INT_REG & (1uL << PENDING_BIT);

}

void OS_InitHW(void) {

OS_SYSTIMER_CONFIG Tick_Config = {OS_PCLK_TIMER,

OS_TICK_FREQ,

_OS_GetHWTimerCycles,

_OS_GetHWTimer_IntPending};

OS_Config_SysTimer(&Tick_Config);

...

}

296 CHAPTER 17 Time measurement

297

Chapter 18

System variables

The system variables are described here for a deeper understanding of how the OS

works and to make debugging easier.

298 CHAPTER 18 System va riables

18.1 Introduction

Note: Do not change the value of any system variables.

These variables are accessible and are not declared constant, but they should only be

altered by functions of embOS. However, some of these variables can be very useful,

especially the time variables.

299

18.2 Time variables

18.2.1 OS_Global

OS_Global is a structure which includes embOS internal variables. The following vari-

ables OS_Global.Time and OS_Global.TimeDex are part of OS_Global. Any other part

of OS_Global is not explained here as they are not required to use embOS.

18.2.2 OS_Global.Time

Description

This is the time variable which contains the current system time in ticks (usually

equivalent to ms).

Additional Information

The time variable has a resolution of one time unit, which is normally 1/1000 sec

(1 ms) and is normally the time between two successive calls to the embOS timer

interrupt handler. Instead of accessing this variable directly, use OS_GetTime() or

OS_GetTime32() as explained in the Chapter Time measurement on page 277.

18.2.3 OS_Global.TimeDex

Basically, for internal use only. Contains the time at which the next task switch or

timer activation is due. If ((int)(OS_Global.Time - OS_Global.TimeDex)) >= 0,

the task list and timer list will be checked for a task or timer to activate. After activa-

tion, OS_Global.TimeDex will be assigned the time stamp of the next task or timer to

be activated.

Note that the value of OS_Global.TimeDex may be invalid during task execution. it

shows correct values during execution of OS_Idle() and when used internally in the

embOS scheduler. The value of OS_Global.TimeDex should not be used by the appli-

cation.

If you need any information about the next time scheduled action from embOS, the

function OS_GetNumIdleTicks() can be used to get the number of ticks spent idle.

300 CHAPTER 18 System va riables

18.3 OS internal variables and data-structures

embOS internal variables are not explained here as they are in no way required to

use embOS. Your application should not rely on any of the internal variables, as only

the documented API functions are guaranteed to remain unchanged in future

versions of embOS.

Important

Do not alter any system variables.

301

Chapter 19

System tick

This chapter explains the concept of the system tick, generated by a hardware timer

and all options available for it.

302 CHAPTER 19 System tick

19.1 Introduction

Typically a hardware timer generates periodic interrupts used as a time base for the

OS. The interrupt service routine then calls one of the tick handlers of the OS.

embOS offers tick handlers with different functionality as well as a way to call a hook

function from within the system tick handler.

Generating timer interrupts

The hardware timer is normally initialized in the OS_InitHW() function which is deliv-

ered with the BSP. The BSP also includes the interrupt handler which is called by the

hardware timer interrupt. This interrupt handler must call one of the embOS system

tick handler functions which are explained in this chapter.

303

19.2 Tick handler

The interrupt service routine used as time base needs to call a tick handler. There are

different tick handlers available; one of these need to be called. The reason why

there are different tick handlers is simple: They differ in capabilities, code size and

execution speed. Most application use the standard tick handler OS_TICK_Handle(),

which increments the tick count by one every time it is called. This tick handler is

small and efficient, but it cannot handle situations where the interrupt rate is differ-

ent from the tick rate. OS_TICK_HandleEx() is capable of handling even fractional

interrupt rates, such as 1.6 interrupts per tick.

19.2.1 API functions

Routine Description

main

Task

ISR

Timer

OS_TICK_Handle() Standard embOS tick handler. X

OS_TICK_HandleEx() Extended embOS tick handler. X

OS_TICK_HandleNoHook() embOS tick handler without hook functionality. X

OS_TICK_Config() Configures the extended embOS tick handler. X X

Table 19.1: API functions

304 CHAPTER 19 System tick

19.2.1.1 OS_TICK_Handle()

Description

The default embOS timer tick handler which is typically called by the hardware timer

interrupt handler.

Prototype

void OS_TICK_Handle ( void );

Additional Information

The embOS tick handler must not be called by the application, it must be called from

an interrupt handler.

OS_EnterInterrupt(), or OS_EnterNestableInterrupt() must be called, before

calling the embOS tick handler

Example

/* Example of a timer interrupt handler */

/*********************************************************************

* OS_ISR_Tick

__interrupt void OS_ISR_Tick(void) {

OS_EnterNestableInterrupt();

OS_TICK_Handle();

OS_LeaveNestableInterrupt();

}

305

19.2.1.2 OS_TICK_HandleEx()

Description

An alternate tick handler which may be used instead of the standard tick handler. It

can be used in situations where the basic timer-interrupt interval (tick) is a multiple

of one ms and the time values used as parameter for delays still should use one ms

as the time base.

Prototype

void OS_TICK_HandleEx ( void );

Additional Information

The embOS tick handler must not be called by the application, it must be called from

an interrupt handler. OS_EnterInterrupt(), or OS_EnterNestableInterrupt()

must be called before calling the embOS tick handler. Refer to OS_TICK_Config() on

page 307 about how to configure OS_TICK_HandleEx().

Example

/* Example of a timer interrupt handler using OS_HandleTickEx */

/*********************************************************************

* OS_ISR_Tick

__interrupt void OS_ISR_Tick(void) {

OS_EnterNestableInterrupt();

OS_TICK_HandleEx();

OS_LeaveNestableInterrupt();

}

Assuming the hardware timer runs at a frequency of 500Hz, thus interrupting the

system every 2ms, the embOS tick handler configuration function OS_TICK_Config()

should be called as demonstrated in the Example section of OS_TICK_Config(). This

should be done during OS_InitHW(), before the embOS timer is started.

306 CHAPTER 19 System tick

19.2.1.3 OS_TICK_HandleNoHook()

Description

The alternate speed optimized embOS timer tick handler without hook function which

is typically called by the hardware timer interrupt handler.

Prototype

void OS_TICK_HandleNoHook ( void );

Additional Information

The embOS tick handler must not be called by the application, it must be called from

an interrupt handler.

OS_EnterInterrupt(), or OS_EnterNestableInterrupt() must be called before

calling the embOS tick handler

Example

/* Example of a timer interrupt handler */

/*********************************************************************

* OS_ISR_Tick

__interrupt void OS_ISR_Tick(void) {

OS_EnterNestableInterrupt();

OS_TICK_HandleNoHook();

OS_LeaveNestableInterrupt();

}

307

19.2.1.4 OS_TICK_Config()

Description

Configures the tick to interrupt ratio. The “normal” tick handler OS_TICK_Handle()

assumes a 1:1 ratio, meaning one interrupt increments the tick count (OS_Time) by

one. For other ratios, OS_TICK_HandleEx() needs to be used; the ratio is defined by

calling the OS_TICK_Config().

Prototype

void OS_TICK_Config ( unsigned FractPerInt, unsigned FractPerTick );

Additional Information

FractPerInt/FractPerTick = Time between two tick interrupts / Time for one tick

Note that fractional values are supported, such as tick is 1 ms, where an interrupt is

generated every 1.6ms. This means that FractPerInt and FractPerTick are:

FractPerInt = 16;

FractPerTick = 10;

FractPerInt = 8;

FractPerTick = 5;

Examples:

OS_TICK_Config(2, 1); // 500 Hz interrupts (2ms), 1ms tick

OS_TICK_Config(8, 5); // Interrupts once per 1.6ms, 1ms tick

OS_TICK_Config(1, 10); // 10 kHz interrupts (0.1ms), 1ms tick

OS_TICK_Config(1, 1); // 10 kHz interrupts (0.1ms), 0.1 ms tick

OS_TICK_Config(1, 100); // 10 kHz interrupts (0.1ms), 1 us tick

Parameter Description

FractPerInt Number of Fractions per interrupt

FractPerTick Number of Fractions per tick

Table 19.2: OS_TICK_Config() parameter list

308 CHAPTER 19 System tick

19.3 Hooking into the system tick

There are various situations in which it can be desirable to call a function from the

tick handler. Some examples are:

• Watchdog update

• Periodic status check

• Periodic I/O update

The same functionality can be achieved with a high-priority task or a software timer

with one tick period time.

Advantage of using a hook function

Using a hook function is much faster than performing a task switch or activating a

software timer, because the hook function is directly called from the embOS timer

interrupt handler and does not cause a context switch.

19.3.1 API functions

Routine Description

main

Task

ISR

Timer

OS_TICK_AddHook() Adds a tick hook handler. X X

OS_TICK_RemoveHook() Removes a tick hook handler. X X

Table 19.3: API functions

309

19.3.1.1 OS_TICK_AddHook()

Description

Adds a tick hook handler.

Prototype

void OS_TICK_AddHook ( OS_TICK_HOOK * pHook,

OS_TICK_HOOK_ROUTINE * pfUser );

Additional Information

The hook function is called directly from the interrupt handler.

The function therefore should execute as fast as possible.

The function called by the tick hook must not re-enable interrupts.

Parameter Description

pHook Pointer to a structure of OS_TICK_HOOK.

pfUser Pointer to an OS_TICK_HOOK_ROUTINE function.

Table 19.4: OS_TICK_AddHook() parameter list

310 CHAPTER 19 System tick

19.3.1.2 OS_TICK_RemoveHook()

Description

Removes a tick hook handler.

Prototype

void OS_TICK_RemoveHook ( const OS_TICK_HOOK * pHook );

Additional Information

The function may be called to dynamically remove a tick hook function which was

installed by a call of OS_TICK_AddHook().

Parameter Description

pHook Pointer to a structure of OS_TICK_HOOK.

Table 19.5: OS_TICK_RemoveHook() parameter list

311

19.4 Tickless support

The embOS tickless support stops the periodic system tick interrupt during idle peri-

ods. Idle periods are periods of time when there are no tasks or software timer ready

for execution. Stopping the system tick allows the microcontroller to remain in a

deep power saving state until an interrupt occurs.

embOS tickless support comes with the three functions OS_GetNumIdleTicks(),

OS_AdjustTime() and OS_StartTicklessMode(). They can be used to add tickless sup-

port to any embOS start project.

19.4.1 OS_Idle()

In order to use the tickless support the OS_Idle() function needs to be modified. The

default OS_Idle() function is just an endless loop which starts a low power mode:

void OS_Idle(void) {

while (1) {

_EnterLowPowerMode();

}

The tickless OS_Idle() function depends on the actual hardware:

void OS_Idle(void) {

OS_TIME IdleTicks;

OS_DI();

IdleTicks = OS_GetNumIdleTicks();

if (IdleTicks > 1) {

if ((OS_U32)IdleTicks > TIMER1_MAX_TICKS) {

IdleTicks = TIMER1_MAX_TICKS;

}

OS_StartTicklessMode(IdleTicks, &_EndTicklessMode);

_SetHWTimer(IdleTicks);

}

OS_EI();

while (1) {

_EnterLowPowerMode();

}

The following description explains the tickless OS_Idle() function step by step:

void OS_Idle(void) {

OS_TIME IdleTicks;

OS_DI();

Interrupts are disabled to avoid a timer interrupt.

IdleTicks = OS_GetNumIdleTicks();

if (IdleTicks > 1) {

The OS_Idle() function reads the idle ticks with OS_GetNumIdleTicks(). The tickless

mode is only used when there is more than one idle tick. If there are zero or one idle

ticks the scheduler is executed at the next system tick hence it makes no sense to

enter the tickless mode.

if ((OS_U32)IdleTicks > TIMER_MAX_TICKS) {

IdleTicks = TIMER_MAX_TICKS;

}

If it is not possible due to hardware timer limitations to generate the timer interrupt

at the specified time the idle ticks can be reduced to any lower value. For example

OS_GetNumIdleTicks() returns 200 idle ticks but the hardware timer is limited to 100

ticks. The variable IdleTicks will be set to 100 ticks and the system will wake up after

312 CHAPTER 19 System tick

100 ticks. OS_Idle() will be again executed and OS_GetNumIdleTicks() returns the

remaining 100 idle ticks. This means that the system wakes up two times before the

complete 200 idle ticks are expired.

if (IdleTicks > 1) {

...

OS_StartTicklessMode(IdleTicks, &_EndTicklessMode);

_SetHWTimer(IdleTicks);

}

OS_StartTicklessMode() sets the idle ticks and the callback function. The idle ticks

information is later used in the callback function. The callback function is described

below. _SetHWTimer() is a hardware dependend function which reprograms the

hardware timer to generate a system tick interrupt at the time defined by idle ticks.

OS_EI();

while (1) {

_EnterLowPowerMode();

}

Interrupts are reenabled and the CPU enters in the endless while loop the low power

mode. _EnterLowPowerMode() is a hardware depending function which activates the

low power mode.

19.4.2 Callback Function

The callback function calculates how long we actually stayed in low power mode and

corrects the system time accordingly. The hardware timer will be reset to the default

system tick time.

static void _EndTicklessMode(void) {

OS_U32 NumTicks;

if (OS_Global.TicklessExpired) {

OS_AdjustTime(OS_Global.TicklessFactor);

} else {

NumTicks = _GetLowPowerTicks();

OS_AdjustTime(NumTicks);

}

_SetHWTimer(OS_TIMER_RELOAD);

}

The following description explains the callback function step by step:

static void _EndTicklessMode(void) {

OS_U32 NumTicks;

if (OS_Global.TicklessExpired) {

OS_AdjustTime(OS_Global.TicklessFactor);

If the hardware timer expired and the system tick interrupt was executed the flag

OS_Global.TicklessExpired is set to 1. This can be used to determine if the system

stayed in low power mode for the complete idle time. If this flag is set we can use the

value in OS_Global.TicklessFactor to adjust the system time.

} else {

NumTicks = _GetLowPowerTicks();

OS_AdjustTime(NumTicks);

}

_GetLowPowerTicks() is a hardware depending function which returns the expired

idle ticks if the low power mode was interrupted by any other interrupt than the sys-

tem tick. We use that value to adjust the system time.

_SetHWTimer(OS_TIMER_RELOAD);

}

_SetHWTimer() is a hardware depending function which reprograms the hardware

timer to it’s default value for one system tick.

313

19.4.3 API functions

Routine Description

OS_GetNumIdleTicks() Retrieves the number of embOS timer ticks until the next

time scheduled action will be started.

OS_AdjustTime() Adjusts the embOS internal time.

OS_StartTicklessMode() Starts the tickless mode.

OS_StopTicklessMode() Stops the tickless mode.

Table 19.6: API functions

314 CHAPTER 19 System tick

19.4.3.1 OS_GetNumIdleTicks()

Description

Retrieves the number of embOS timer ticks until the next time scheduled action will

be started.

Prototype

OS_TIME OS_GetNumIdleTicks(void)

Return value

The number of ticks until the next time scheduled action.

Additional Information

The function may be useful when the embOS timer and CPU shall be halted by the

application and restarted after the idle time to save power.

This works, when the application has its own time base and a special interrupt that

can wake up the CPU.

When the embOS timer is started again the internal time must be adjusted to guar-

antee time scheduled actions to be executed. This can be done by a call of

OS_AdjustTime().

315

19.4.3.2 OS_AdjustTime()

Description

This function may be used to adjust the embOS internal time by adding an amount of

time to the internal time variable.

Prototype

void OS_AdjustTicks(OS_TIME Time)

Additional Information

The function may be useful when the embOS timer was halted by the application for

a certain known interval of time.

When the embOS timer is started again the internal time must be adjusted to guar-

antee time scheduled actions to be executed.

Parameter Description

Time The amount of time which should be added to the embOS internal

time variable.

Table 19.7: OS_AdjsutTime() parameter list

316 CHAPTER 19 System tick

19.4.3.3 OS_StartTicklessMode()

Description

This function may be used to start the tickless mode.

Prototype

void OS_StartTicklessMode(OS_TIME Time, voidRoutine *Callback)

Additional Information

This function starts the tickless mode. It must be called in OS_Idle() before the CPU

enters a low power mode.

The callback function must stop the tickless mode. It must calculate how many sys-

tem ticks are actually spent in lower power mode and adjust the system time by call-

ing OS_AdjustTime(). It also must reset the system tick timer to it’s default tick

period.

Parameter Description

Time Time in ticks which will be spent in low power mode.

Callback Callback function to stop the tickless mode.

Table 19.8: OS_StartTicklessMode() parameter list

317

19.4.3.4 OS_StopTicklessMode()

Description

This function may be used to stop the tickless mode.

Prototype

void OS_StopTicklessMode(void)

Additional Information

This function stops the tickless mode. It calls the callback function when the tickless

mode was enabled.

318 CHAPTER 19 System tick

19.4.4 Frequently Asked Questions

1. Q: Where can I find more information about tickless support for a specific CPU?

A: Segger provides Application Notes for tickless support for different CPUs.

2. Q: Can I use embOS without tickless support?

A: Yes, you can use embOS without tickless support. There is no change required

in your project.

3. Q: What hardware depending functions must be implemented and where?

A: OS_Idle() must be modified and the callback function must be implemented.

OS_Idle() is part of the RTOSInit.c file. We suppose to implement the callback

function in the same file.

4. Q: What triggers the callback function?

A: The callback function is executed once from the scheduler when the tickless

operation ends and normal operation resumes.

319

Chapter 20

Configuration of target system

(BSP)

This chapter explains the target system specific parts of embOS, also called BSP

(board support package).

If the system is up and running on your target system, there is no need to read this

chapter.

320 CHAPTER 20 Configuration of target system (BSP)

20.1 Introduction

You do not need to configure anything to get started with embOS. The start project

supplied will execute on your system. Small changes in the configuration will be nec-

essary at a later point for system frequency or for the UART used for communication

with the optional embOSView.

The file RTOSInit.c is provided in source code and can be modified to match your

target hardware needs. It is compiled and linked with your application program.

321

20.2 Hardware-specific routines

20.2.1 OS_Idle()

The embOS function OS_Idle() is called when no task is ready for execution.

The function OS_Idle() is part of the target CPU specific RTOSInit.c file delivered

with embOS.

Normally it is programmed as an endless loop without any functionality.

In most embOS ports, it activates a power saving sleep mode of the target CPU.

The embOS OS_Idle() function is not a task, it has no task context and does not

have its own stack.

The OS_Idle() function runs on the normal CSTACK which is also used for the kernel.

Exceptions and interrupts which occur during OS_Idle() are no problem as long as

they don't trigger a task switch.

They return into OS_Idle() and the code is continued where it was interrupted.

When a task switch occurs during the execution of OS_Idle(), the OS_Idle() func-

tion is interrupted and does not continue execution when it is activated again.

When OS_Idle() is activated, it always starts from the beginning. Interrupted code

is not continued.

You might create your own idle task running as endless loop with the lowest task pri-

ority in the system.

When you don't call any blocking or suspending function in this idle task, you will

never arrive in OS_Idle().

Routine Description

main

Task

ISR

Timer

Required for embOS

OS_InitHW()

Initializes the hardware timer used for gener-

ating interrupts. embOS needs a timer-inter-

rupt to determine when to activate tasks that

wait for the expiration of a delay, when to call

a software timer, and to keep the time variable

up-to-date.

OS_Idle()

The idle loop is always executed whenever no

other task (and no interrupt service routine) is

ready for execution.

OS_ISR_Tick()

The embOS timer-interrupt handler. When

using a different timer, always check the spec-

ified interrupt vector.

OS_ConvertCycles2us() Converts cycles into µs (used with profiling

only). XXXX

OS_GetTime_Cycles()

Reads the timestamp in cycles. Cycle length

depends on the system. This function is used

for system information sent to embOSView.

XXXX

Optional for run-time OS-View

OS_COM_Init() Initializes communication for embOSView

(used with embOSView only). X

OS_ISR_rx() Rx Interrupt service handler for embOSView

(used with embOSView only).

OS_ISR_tx() Tx Interrupt service handler for embOSView

(used with embOSView only).

OS_COM_Send1()

Send one byte via a UART (used with embOS-

View only).

Do not call this function from your application.

Table 20.1: Hardware specific routines

322 CHAPTER 20 Configuration of target system (BSP)

You might alternatively use OS_EnterRegion() and OS_LeaveRegion() to avoid task

switches during the execution of your ..doStuff() in OS_Idle().

Running in a critical region does not block interrupts, but disables task switches until

OS_LeaveRegion() is called.

Using a critical region during OS_Idle() will affect task activation time, but will not

affect interrupt latency.

323

20.3 Configuration defines

For most embedded systems, configuration is done by simply modifying the following

defines, located at the top of the RTOSInit.c file:

Define Description

OS_FSYS System frequency (in Hz).

Example: 20000000 for 20MHz.

OS_UART Selection of UART to be used with embOSView

(-1 will disable communication),

OS_BAUDRATE Selection of baudrate for communication with embOSView.

Table 20.2: Configuration defines overview

324 CHAPTER 20 Configuration of target system (BSP)

20.4 How to change settings

The only file which you may need to change is RTOSInit.c. This file contains all

hardware-specific routines. The one exception is that some ports of embOS require

an additional interrupt vector table file (details can be found in the CPU & Compiler

Specifics manual of embOS documentation).

20.4.1 Setting the system frequency OS_FSYS

Relevant defines

OS_FSYS

Relevant routines

OS_ConvertCycles2us() (used with profiling only)

For most systems it should be sufficient to change the OS_FSYS define at the top of

RTOSInit.c. When using profiling, certain values may require a change in

OS_ConvertCycles2us(). The RTOSInit.c file contains more information about in

which cases this is necessary and what needs to be done.

20.4.2 Using a different timer to generate the tick-interrupts for

embOS

Relevant routines

OS_InitHW()

embOS usually generates one interrupt per ms, making the timer-interrupt, or tick,

normally equal to 1 ms. This is done by a timer initialized in the routine

OS_InitHW(). If you want to use a different timer for your application, you must

modify OS_InitHW() to initialize the appropriate timer. For details about initialization,

read the comments in RTOSInit.c.

20.4.3 Using a different UART or baudrate for embOSView

Relevant defines

OS_UART

OS_BAUDRATE

Relevant routines:

OS_COM_Init()

OS_COM_Send1()

OS_ISR_rx()

OS_ISR_tx()

In some cases, this is done by simply changing the define OS_UART. Refer to the con-

tents of the RTOSInit.c file for more information about which UARTS that are sup-

ported for your CPU.

20.4.4 Changing the tick frequency

Relevant defines

OS_FSYS

As noted above, embOS usually generates one interrupt per ms. OS_FSYS defines the

clock frequency of your system in Hz (times per second). The value of OS_FSYS is

used for calculating the desired reload counter value for the system timer for 1000

interrupts/sec. The interrupt frequency is therefore normally 1 kHz.

Different (lower or higher) interrupt rates are possible. If you choose an interrupt

frequency different from 1 kHz, the value of the time variable OS_Time will no longer

be equivalent to multiples of 1 ms. However, if you use a multiple of 1 ms as tick

325

time, the basic time unit can be made 1 ms by using the function OS_TICK_Config().

The basic time unit does not need to be 1 ms; it might just as well be 100 µs or 10

ms or any other value. For most applications, 1 ms is an appropriate value.

326 CHAPTER 20 Configuration of target system (BSP)

20.5 STOP / HALT / IDLE modes

Most CPUs support power-saving STOP, HALT, or IDLE modes. Using these types of

modes is one possible way to save power consumption during idle times. As long as

the timer-interrupt will wake up the system with every embOS tick, or as long as

other interrupts will activate tasks, these modes may be used for saving power con-

sumption.

If required, you may modify the OS_Idle() routine, which is part of the hardware-

dependant module RTOSInit.c, to switch the CPU to power-saving mode during idle

times. Refer to the CPU & Compiler Specifics manual of embOS documentation for

details about your processor.

327

Chapter 21

Profiling

This chapter explains the profiling functions that can be used by an application.

328 CHAPTER 21 Profiling

21.0.1 API functions

Routine Description

main

Task

ISR

Timer

OS_STAT_Sample() Starts a new task cpu load measurement. X X X X

OS_STAT_GetLoad() Returns the task-specific cpu load. X X X X

OS_AddLoadMeasurement() Adds total CPU load measurement functi-

nality. XX

OS_GetLoadMeasurement() Returns the total CPU load. X X X X

OS_STAT_Enable() Enables profiling X X X X

OS_STAT_Disable() Disables profiling X X X X

OS_STAT_GetTaskExecTime() Returns the total task execution time X X X X

Table 21.1: API functions

329

21.0.1.1 OS_STAT_Sample()

Description

OS_STAT_Sample() starts profiling and calculates the absolute task run time since

the last call to OS_STAT_Sample().

Prototype

void OS_STAT_Sample ( void );

Additional Information

OS_STAT_Sample() starts the profiling for 5 seconds, the next call to

OS_STAT_Sample() must be within this 5 seconds. Please use the embOS function

OS_STAT_GetLoad() to get the task-specific cpu load in 1/10 percent.

OS_STAT_Sample() cannot be used from multiple tasks at a time, because it uses a

global variable.

330 CHAPTER 21 Profiling

21.0.1.2 OS_STAT_GetLoad()

Description

OS_STAT_GetLoad() calculates the current tasks cpu load in 1/10 percent.

Prototype

int OS_STAT_GetLoad(OS_TASK * pTask);

Return value

OS_STAT_GetLoad() returns the current tasks cpu load in 1/10 percent.

Additional Information

OS_STAT_GetLoad() requires that OS_STAT_Sample() is called periodically.

OS_STAT_GetLoad() cannot be used from multiple tasks at a time, because it uses a

global variable.

Parameter Description

pTask Pointer to task control block

Table 21.2: OS_STAT_GetLoad() parameter list

331

21.0.1.3 Sample application for OS_STAT_Sample() and

OS_STAT_GetLoad()

#include "RTOS.h"

#include "stdio.h"

OS_STACKPTR int StackHP[128], StackLP[128], StackMP[128]; /* Task stacks */

OS_TASK TCBHP, TCBLP, TCBMP; /* Task-control-blocks */

static void HPTask(void) {

volatile int r;

while (1) {

OS_Delay (1000);

OS_STAT_Sample();

r = OS_STAT_GetLoad(&TCBMP);

printf("CPU Usage of MP Task: %d\n", r);

}

static void MPTask(void) {

while (1) {

}

static void LPTask(void) {

while (1) {

}

int main(void) {

OS_IncDI(); /* Initially disable interrupts */

OS_InitKern(); /* Initialize OS */

OS_InitHW(); /* Initialize Hardware for OS */

/* You need to create at least one task before calling OS_Start() */

OS_CREATETASK(&TCBHP, "HP Task", HPTask, 100, StackHP);

OS_CREATETASK(&TCBMP, "MP Task", MPTask, 50, StackMP);

OS_CREATETASK(&TCBLP, "LP Task", LPTask, 50, StackLP);

OS_Start(); /* Start multitasking */

return 0;

}

Output:

500

499

501

500

...

332 CHAPTER 21 Profiling

21.0.1.4 OS_AddLoadMeasurement()

Description

OS_AddLoadMeasurement() may be used to start calculation of the total CPU load of

an application.

Prototype

void OS_AddLoadMeasurement(int Period,

OS_U8 AutoAdjust,

int DefaultMaxValue);

Additional Information

OS_AddLoadMeasurement() creates a task running at highest priority. The task sus-

pends itself periodically by calling OS_Delay(Period). When the task is resumed after

the delay, it calculates the CPU load by comparison of two counter values.

The CPU load is the percentage not spent in OS_Idle().

For the calculation, it is required that OS_Idle() is called.

OS_Idle() must increment a counter by calling OS_INC_IDLE_CNT();

The maximum value of this counter is stored and is compared against the current

value of the counter, every time the measurement task is activated.

It is assumed, that the maximum value of the counter reperesents a CPU load of 0,

all time spent in OS_Idle().

When AutoAdjust is set, the task will initially suspend all other tasks for the Period-

time and than call OS_Delay(Period). This way, the whole period is spent in

OS_Idle() and the counter incremented in OS_Idle() reaches its maximum value

initially.

If this behavior is not wanted, because it blocks all tasks for the Period-time once ini-

tially, the maximum value for the counter may be examined once and then be set by

the parameter DefaultMaxValue with AutoAdjust disabled.

The value for DefaultMaxValue can be examined once from one task before any

other tasks are created:

void MainTask(void) {

OS_I32 DefaultMax;

OS_Delay(100);

DefaultMax = OS_IdleCnt; /* This value can be used as DefaultMaxValue. */

/* Now other tasks can be created and started. */

The calculation does not work when OS_Idle() puts the CPU in Low-power (Stop)

mode.

OS_Idle() must look like follows:

void OS_Idle(void) { /* Idle loop: No task is ready to execute */

while (1) {

OS_INC_IDLE_CNT();

}

Parameter Description

Period Period for measurement in embOS timer ticks

AutoAdjust When != 0, the measurement is autoadjusted once initially.

DefaultMaxValue May be used to set a default counter value when AutoAdjust is

not used. (See additional information)

Table 21.3: OS_STAT_GetLoad() parameter list

333

21.0.1.5 OS_GetLoadMeasurement()

Description

OS_GetLoadMeasurement() can be called from the application to retrieve the result of

the CPU load measurement.

Prototype

int OS_GetLoadMeasurement(void)

Return value

OS_GetLoadMeasurement returns the total CPU load in percent.

Additional Information

OS_GetLoadMeasurement() delivers correct results when the CPU load measurement

was started by calling OS_AddLoadMeasurement() with auot-adjustment before, and

OS_Idle() updates the measurement by calling OS_INC_IDLE_CNT().

The calculation does not work when OS_Idle() puts the CPU in Low-power (Stop)

mode.

OS_Idle() must look like follows:

void OS_Idle(void) { /* Idle loop: No task is ready to execute */

while (1) {

OS_INC_IDLE_CNT();

}

334 CHAPTER 21 Profiling

21.0.1.6 OS_CPU_Load

Description

This global variable shows the total CPU load in percent. It may be usefull to show

the variable in a debugger with life-watch capability during programm development.

Declaration

volatile OS_INT OS_CPU_Load;

Additional Information

This variable may not exist and will not show correct results, when the CPU load

measurement was not started by a call of OS_AddLoadMeasurement().

As an additional condition embOS must be running and OS_Idle must call

OS_INC_IDLE_CNT() to update the CPU load measurement.

335

21.0.1.7 OS_STAT_Enable()

Description

OS_STAT_Enable() may be used to start the profiling for an infinite time.

Prototype

void OS_STAT_Enable(void);

Additional Information

The profiling is started and does not disable itself after 5 seconds. The function

OS_STAT_Disable() may be used to stop the profiling.

336 CHAPTER 21 Profiling

21.0.1.8 OS_STAT_Disable()

Description

OS_STAT_Disable() may be used to stop the profiling.

Prototype

void OS_STAT_Disable(void);

Additional Information

The function OS_STAT_Enable() may be used to start the profiling.

337

21.0.1.9 OS_STAT_GetTaskExecTime()

Description

OS_STAT_GetTaskExecTime() may be used to return the total task execution time.

Prototype

OS_U32 OS_STAT_GetTaskExecTime(const OS_TASK *pTask);

Return value

OS_STAT_GetTaskExecTime() returns the total task execution time.

Additional Information

This function only returns valid values when the profiling is enabled before with

OS_STAT_Enable(). If pTask is the NULL pointer, the function returns the total task

execution time of the currently running task. If pTask does not specify a valid task, a

debug build of embOS calls OS_Error(). A release build of embOS cannot check the

validity of pTask and may therefore return invalid values if pTask does not specify a

valid task.

Example

OS_U32 ExecTime;

void MyTask(void) {

OS_STAT_Enable();

while (1) {

ExecTime = OS_STAT_GetTaskExecTime(NULL);

OS_Delay(100);

}

Parameter Description

pTask Pointer to a task control block.

338 CHAPTER 21 Profiling

339

Chapter 22

embOSView: Profiling and analyz-

ing

340 CHAPTER 22 embOSView: Profiling and analyzing

22.1 Overview

embOSView displays the state of a running application using embOS. A serial

interface (UART) is normally used for communication with the target. But there are

also other communication channels like ethernet or memory read/write for Cortex M

CPUs or DCC for ARM7/9 CPUs. The hardware-dependent routines and defines avail-

able for communication with embOSView are located in RTOSInit.c. This file must be

configured properly. For details on how to configure this file, refer the CPU & Com-

piler Specifics manual of embOS documentation. The embOSView utility is shipped as

embOSView.exe with embOS and runs under Windows 9x / NT / 2000 / Vista and Win-

dows 7/8. The latest version is available on our website at www.segger.com

embOSView is a very helpful tool for analysis of the running target application.

The CPU load feature assumes that an embOS library with profiling feature is used

like “stack-check plus profiling”, “debug plus profiling” or “debug including trace plus

profiling”.

Table 22.1: embOS libraries with support for profiling used for CPU load

Name Description

SP Stack-checking plus profiling

DP Debug plus profiling

DT Debug including trace plus profiling

341

22.2 Task list window

embOSView shows the state of every created task of the target application in the

Task list window. The information shown depends on the library used in your

application.

The Task list window is helpful in analysis of stack usage and CPU load for every

running task.

Item Description Builds

Prio Current priority of task. All

Id Task ID, which i s t he address of the task control

block. All

Name Name assigned during creation. All

Status Current state of task (ready, executing, delay,

reason for suspension). All

Data Depends on status. All

Timeout Time of next activation. All

Stack Used stack size/max. stack size/stack location. S, SP, D, DP, DT

CPULoad Percentage CPU load caused by task. SP, DP, DT

Context

Switches Number of activations since reset. SP, DP, DT

Table 22.2: Task list window overview

342 CHAPTER 22 embOSView: Profiling and analyzing

22.3 System variables window

embOSView shows the actual state of major system variables in the System vari-

ables window. The information shown also depends on the library used in your

application:

Item Description Builds

OS_VERSION Current version of embOS. All

CPU Target CPU and compiler. All

LibMode Library mode used for target application. All

OS_Time Current system time in timer ticks. All

OS_NUM_TASKS Current number of defined tasks. All

OS_Status Current error code (or O.K.). All

OS_pActiveTask Active task that should be running. SP, D, DP, DT

OS_pCurrentTask Actual currently running task. SP, D, DP, DT

SysStack Used size/max. size/location of system

stack. SP, DP, DT

IntStack Used size/max. size/location of interrupt

stack. SP, DP, DT

TraceBuffer Current count/maximum size and current

state of trace buffer. All trace builds

Table 22.3: System variables window overview

343

22.4 Sharing the SIO for terminal I/O

The serial input/output (SIO) used by embOSView may also be used by the

application at the same time for both input and output. This can be very helpful.

Terminal input is often used as keyboard input, where terminal output may be used

for outputting debug messages. Input and output is done via the Terminal window,

which can be shown by selecting View/Terminal from the menu.

To ensure communication via the Terminal window in parallel with the viewer

functions, the application uses the function OS_SendString() for sending a string to

the Terminal window and the function OS_SetRxCallback() to hook a recep-

tion routine that receives one byte.

344 CHAPTER 22 embOSView: Profiling and analyzing

22.5 API functions

Routine Description

main

Task

ISR

Timer

OS_SendString() Sends a string over SIO to the Terminal win-

dow.XX

OS_SetRxCallback() Sets a callback hook to a routine for receiving

one character. XX X

Table 22.4: Shared SIO API functions

345

22.5.1 OS_SendString()

Description

Sends a string over SIO to the embOSView terminal window.

Prototype

void OS_SendString (const char* s);

Additional Information

This function uses OS_COM_Send1() which is defined in RTOSInit.c.

Parameter Description

sPointer to a zero-terminated string that should be sent to the

Terminal window.

Table 22.5: OS_SendString() parameter list

346 CHAPTER 22 embOSView: Profiling and analyzing

22.5.2 OS_SetRxCallback()

Description

Sets a callback hook to a routine for receiving one character.

Prototype

typedef void OS_RX_CALLBACK (OS_U8 Data)

OS_RX_CALLBACK* OS_SetRxCallback (OS_RX_CALLBACK* cb);

Return value

OS_RX_CALLBACK* as described above. This is the pointer to the callback function that

was hooked before the call.

Additional Information

The user function is called from embOS. The received character is passed as parame-

ter. See the example below.

Example

void GUI_X_OnRx(OS_U8 Data); /* Callback ... called from Rx-interrupt */

void GUI_X_Init(void) {

OS_SetRxCallback( &GUI_X_OnRx);

}

Parameter Description

cb Pointer to the application routine that should be called when one

character is received over the serial interface.

Table 22.6: OS_SetRxCallback() parameter list

347

22.6 Using the API trace

embOS versions 3.06 or higher contain a trace feature for API calls. This requires the

use of the trace build libraries in the target application.

The trace build libraries implement a buffer for 100 trace entries. Tracing of API calls

can be started and stopped from embOSView via the Trace menu, or from within the

application by using the functions OS_TraceEnable() and OS_TraceDiasable().

Individual filters may be defined to determine which API calls should be traced for

different tasks or from within interrupt or timer routines.

Once the trace is started, the API calls are recorded in the trace buffer, which is peri-

odically read by embOSView. The result is shown in the Trace window:

Every entry in the Trace list is recorded with the actual system time. In case of calls

or events from tasks, the task ID (TaskId) and task name (TaskName) (limited to

15 characters) are also recorded. Parameters of API calls are recorded if possible,

and are shown as part of the APIName column. In the example above, this can be

seen with OS_Delay(3). Once the trace buffer is full, trace is automatically stopped.

The Trace list and buffer can be cleared from embOSView.

Setting up trace from embOSView

Three different kinds of trace filters are defined for tracing. These filters can be set

up from embOSView via the menu Options/Setup/Trace.

Filter 0 is not task-specific and records all specified events regardless of the task. As

the Idle loop is not a task, calls from within the idle loop are not traced.

Filter 1 is specific for interrupt service routines, software timers and all calls that

occur outside a running task. These calls may come from the idle loop or during star-

tup when no task is running.

Filters 2 to 4 allow trace of API calls from named tasks.

348 CHAPTER 22 embOSView: Profiling and analyzing

To enable or disable a filter, simply check or uncheck the corresponding checkboxes

labeled Filter 4 Enable to Filter 0 Enable.

For any of these five filters, individual API functions can be enabled or disabled by

checking or unchecking the corresponding checkboxes in the list. To speed up the

process, there are two buttons available:

•Select all - enables trace of all API functions for the currently enabled (checked)

filters.

•Deselect all - disables trace of all API functions for the currently enabled

(checked) filters.

Filter 2, Filter 3, and Filter 4 allow tracing of task-specific API calls. A task name

can therefore be specified for each of these filters. In the example above, Filter 4 is

configured to trace calls of OS_Delay() from the task called MainTask. After the set-

tings are saved (via the Apply or OK button), the new settings are sent to the target

application.

349

22.7 Trace filter setup functions

Tracing of API or user function calls can be started or stopped from embOSView. By

default, trace is initially disabled in an application program. It may be very helpful to

control the recording of trace events directly from the application, using the following

functions.

350 CHAPTER 22 embOSView: Profiling and analyzing

22.8 API functions

Routine Description

main

Task

ISR

Timer

OS_TraceEnable() Enables tracing of filtered API calls. X X X X

OS_TraceDisable() Disables tracing of API and user function

calls. XXXX

OS_TraceEnableAll()

Sets up Filter 0 (any task), enables trac-

ing of all API calls and then enables the

trace function.

XXXX

OS_TraceDisableAll()

Sets up Filter 0 (any task), disables trac-

ing of all API calls and also disables

trace.

XXXX

OS_TraceEnableId()

Sets the specified ID value in Filter 0

(any task), thus enabling trace of the

specified function, but does not start

trace.

XXXX

OS_TraceDisableId()

Resets the specified ID value in Filter 0

(any task), thus disabling trace of the

specified function, but does not stop

trace.

XXXX

OS_TraceEnableFilterId()

Sets the specified ID value in the speci-

fied trace filter, thus enabling trace of the

specified function, but does not start

trace.

XXXX

OS_TraceDisableFilterId()

Resets the specified ID value in the spec-

ified trace filter, thus disabling trace of

the specified function, but does not stop

trace.

XXXX

Table 22.7: Trace filter API functions

351

22.8.1 OS_TraceEnable()

Description

Enables tracing of filtered API calls.

Prototype

void OS_TraceEnable (void);

Additional Information

The trace filter conditions should have been set up before calling this function. This

functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

352 CHAPTER 22 embOSView: Profiling and analyzing

22.8.2 OS_TraceDisable()

Description

Disables tracing of API and user function calls.

Prototype

void OS_TraceDisable (void);

Additional Information

This functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

353

22.8.3 OS_TraceEnableAll()

Description

Sets up Filter 0 (any task), enables tracing of all API calls and then enables the trace

function.

Prototype

void OS_TraceEnableAll (void);

Additional Information

The trace filter conditions of all the other trace filters are not affected.

This functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

354 CHAPTER 22 embOSView: Profiling and analyzing

22.8.4 OS_TraceDisableAll()

Description

Sets up Filter 0 (any task), disables tracing of all API calls and also disables trace.

Prototype

void OS_TraceDisableAll (void);

Additional Information

The trace filter conditions of all the other trace filters are not affected, but tracing is

stopped.

This functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

355

22.8.5 OS_TraceEnableId()

Description

Sets the specified ID value in Filter 0 (any task), thus enabling trace of the specified

function, but does not start trace.

Prototype

void OS_TraceEnableId (OS_U8 Id);

Additional Information

To enable trace of a specific embOS API function, you must use the correct Id value.

These values are defined as symbolic constants in RTOS.h.

This function may also enable trace of your own functions.

This functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

Parameter Description

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

Table 22.8: OS_TraceEnableId() parameter list

356 CHAPTER 22 embOSView: Profiling and analyzing

22.8.6 OS_TraceDisableId()

Description

Resets the specified ID value in Filter 0 (any task), thus disabling trace of the speci-

fied function, but does not stop trace.

Prototype

void OS_TraceDisableId (OS_U8 Id);

Additional Information

To disable trace of a specific embOS API function, you must use the correct Id value.

These values are defined as symbolic constants in RTOS.h.

This function may also be used for disabling trace of your own functions.

This functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

Parameter Description

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

Table 22.9: OS_TraceDisabledId() parameter list

357

22.8.7 OS_TraceEnableFilterId()

Description

Sets the specified ID value in the specified trace filter, thus enabling trace of the

specified function, but does not start trace.

Prototype

void OS_TraceEnableFilterId (OS_U8 FilterIndex,

OS_U8 Id)

Additional Information

To enable trace of a specific embOS API function, you must use the correct Id value.

These values are defined as symbolic constants in RTOS.h.

This function may also be used for enabling trace of your own functions.

This functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

Parameter Description

FilterIndex

Index of the filter that should be affected:

0 <= FilterIndex <= 4

0 affects Filter 0 (any task) and so on.

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

Table 22.10: OS_TraceEnabledFilterId() parameter list

358 CHAPTER 22 embOSView: Profiling and analyzing

22.8.8 OS_TraceDisableFilterId()

Description

Resets the specified ID value in the specified trace filter, thus disabling trace of the

specified function, but does not stop trace.

Prototype

void OS_TraceDisableFilterId (OS_U8 FilterIndex,

OS_U8 Id)

Additional Information

To disable trace of a specific embOS API function, you must use the correct Id value.

These values are defined as symbolic constants in RTOS.h.

This function may also be used for disabling trace of your own functions.

This functionality is available in trace builds only. In non-trace builds, the API call is

removed by the preprocessor.

Parameter Description

FilterIndex

Index of the filter that should be affected:

0 <= FilterIndex <= 4

0 affects Filter 0 (any task) and so on.

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

Table 22.11: OS_TraceDisableFilterId() parameter list

359

22.9 Trace record functions

The following functions are used for writing (recording) data into the trace buffer. As

long as only embOS API calls should be recorded, these functions are used internally

by the trace build libraries. If, for some reason, you want to trace your own functions

with your own parameters, you may call one of these routines.

All of these functions have the following points in common:

• To record data, trace must be enabled.

• An ID value in the range from 100 to 127 must be used as the ID parameter. ID

values from 0 to 99 are internally reserved for embOS.

• The events specified as ID must be enabled in any of the trace filters.

• Active system time and the current task are automatically recorded together with

the specified event.

360 CHAPTER 22 embOSView: Profiling and analyzing

22.10 API functions

Routine Description

main

Task

ISR

Timer

OS_TraceVoid() Writes an entry identified only by its ID into

the trace buffer. XXXX

OS_TracePtr() Writes an entry with ID and a pointer as

parameter into the trace buffer. XXXX

OS_TraceData() Writes an entry with ID and an integer as

parameter into the trace buffer. XXXX

OS_TraceDataPtr() Writes an entry with ID, an integer, and a

pointer as parameter into the trace buffer. XXXX

OS_TraceU32Ptr()

Writes an entry with ID, a 32-bit unsigned

integer, and a pointer as parameter into the

trace buffer.

XXXX

Table 22.12: Trace record API functions

361

22.10.1 OS_TraceVoid()

Description

Writes an entry identified only by its ID into the trace buffer.

Prototype

void OS_TraceVoid (OS_U8 Id);

Additional Information

This functionality is available in trace builds only, and the API call is not removed by

the preprocessor.

Parameter Description

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

Table 22.13: OS_TraceVoid() parameter list

362 CHAPTER 22 embOSView: Profiling and analyzing

22.10.2 OS_TracePtr()

Description

Writes an entry with ID and a pointer as parameter into the trace buffer.

Prototype

void OS_TracePtr (OS_U8 Id,

void* p);

Additional Information

The pointer passed as parameter will be displayed in the trace list window of

embOSView. This functionality is available in trace builds only. In non-trace builds,

the API call is removed by the preprocessor.

Parameter Description

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

pAny void pointer that should be recorded as parameter.

Table 22.14: OS_TracePtr() parameter list

363

22.10.3 OS_TraceData()

Description

Writes an entry with ID and an integer as parameter into the trace buffer.

Prototype

void OS_TraceData (OS_U8 Id,

int v);

Additional Information

The value passed as parameter will be displayed in the trace list window of

embOSView.This functionality is available in trace builds only. In non-trace builds,

the API call is removed by the preprocessor.

Parameter Description

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

vAny integer value that should be recorded as parameter.

Table 22.15: OS_TraceData() parameter list

364 CHAPTER 22 embOSView: Profiling and analyzing

22.10.4 OS_TraceDataPtr()

Description

Writes an entry with ID, an integer, and a pointer as parameter into the trace buffer.

Prototype

void OS_TraceDataPtr (OS_U8 Id,

int v,

void* p);

Additional Information

The values passed as parameters will be displayed in the trace list window of embOS-

View. This functionality is available in trace builds only. In non-trace builds, the API

call is removed by the preprocessor.

Parameter Description

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

vAny integer value that should be recorded as parameter.

pAny void pointer that should be recorded as parameter.

Table 22.16: OS_TraceDataPtr() parameter list

365

22.10.5 OS_TraceU32Ptr()

Description

Writes an entry with ID, a 32-bit unsigned integer, and a pointer as parameter into

the trace buffer.

Prototype

void OS_TraceU32Ptr (OS_U8 Id,

OS_U32 p0,

void* p1);

Additional Information

This function may be used for recording two pointers. The values passed as parame-

ters will be displayed in the trace list window of embOSView. This functionality is

available in trace builds only. In non-trace builds, the API call is removed by the pre-

processor.

Parameter Description

ID value of API call that should be enabled for trace:

0 <= Id <= 127

Values from 0 to 99 are reserved for embOS.

p0 Any unsigned 32-bit value that should be recorded as parameter.

p1 Any void pointer that should be recorded as parameter.

Table 22.17: OS_TraceU32Ptr() parameter list

366 CHAPTER 22 embOSView: Profiling and analyzing

22.11 Application-controlled trace example

As described in the previous section, the user application can enable and set up the

trace conditions without a connection or command from embOSView. The trace

record functions can also be called from any user function to write data into the trace

buffer, using ID numbers from 100 to 127.

Controlling trace from the application can be very helpful for tracing API and user

functions just after starting the application, when the communication to embOSView

is not yet available or when the embOSView setup is not complete.

The example below shows how a trace filter can be set up by the application. The

function OS_TraceEnableID() sets the trace filter 0 which affects calls from any

running task. Therefore, the first call to SetState() in the example would not be

traced because there is no task running at that moment. The additional filter setup

routine OS_TraceEnableFilterId() is called with filter 1, which results in tracing

calls from outside running tasks.

Example code

#include "RTOS.h"

#ifndef OS_TRACE_FROM_START

#define OS_TRACE_FROM_START 1

#endif

/* Application specific trace id numbers */

#define APP_TRACE_ID_SETSTATE 100

char MainState;

/* Sample of application routine with trace */

void SetState(char* pState, char Value) {

#if OS_TRACE

OS_TraceDataPtr(APP_TRACE_ID_SETSTATE, Value, pState);

#endif

* pState = Value;

}

/* Sample main routine, that enables and setup API and function call trace

from start */

void main(void) {

OS_InitKern();

OS_InitHW();

#if (OS_TRACE && OS_TRACE_FROM_START)

/* OS_TRACE is defined in trace builds of the library */

OS_TraceDisableAll(); /* Disable all API trace calls */

OS_TraceEnableId(APP_TRACE_ID_SETSTATE); /* User trace */

OS_TraceEnableFilterId(0, APP_TRACE_ID_SETSTATE); /* User trace */

OS_TraceEnable();

#endif

/* Application specific initialization */

SetState(&MainState, 1);

OS_CREATETASK(&TCBMain, "MainTask", MainTask, PRIO_MAIN, MainStack);

OS_Start(); /* Start multitasking -> MainTask() */

}

By default, embOSView lists all user function traces in the trace list window as Rou-

tine, followed by the specified ID and two parameters as hexadecimal values. The

example above would result in the following:

Routine100(0xabcd, 0x01)

where 0xabcd is the pointer address and 0x01 is the parameter recorded from

OS_TraceDataPtr().

367

22.12 User-defined functions

To use the built-in trace (available in trace builds of embOS) for application program

user functions, embOSView can be customized. This customization is done in the

setup file embOS.ini.

This setup file is parsed at the startup of embOSView. It is optional; you will not see

an error message if it cannot be found.

To enable trace setup for user functions, embOSView needs to know an ID number,

the function name and the type of two optional parameters that can be traced. The

format is explained in the following sample embOS.ini file:

Example code

# File: embOS.ini

# embOSView Setup file

# embOSView loads this file at startup. It must reside in the same

# directory as the executable itself.

# Note: The file is not required to run embOSView. You will not get

# an error message if it is not found. However, you will get an error message

# if the contents of the file are invalid.

# Define add. API functions.

# Syntax: API( <Index>, <Routinename> [parameters])

# Index: Integer, between 100 and 127

# Routinename: Identifier for the routine. Should be no more than 32 characters

# parameters: Optional paramters. A max. of 2 parameters can be specified.

# Valid parameters are:

# int

# ptr

# Every parameter must be placed after a colon.

API( 100, "Routine100")

API( 101, "Routine101", int)

API( 102, "Routine102", int, ptr)

368 CHAPTER 22 embOSView: Profiling and analyzing

369

Chapter 23

Performance and resource usage

This chapter covers the performance and resource usage of embOS. It explains how

to benchmark embOS and contains information about the memory requirements in

typical systems which can be used to obtain sufficient estimates for most target sys-

tems.

370 CHAPTER 23 Performance and resource usage

23.1 Introduction

High performance combined with low resource usage has always been a major design

consideration. embOS runs on 8/16/32-bit CPUs. Depending on which features are

being used, even single-chip systems with less than 2 Kbytes ROM and 1 Kbyte RAM

can be supported by embOS. The actual performance and resource usage depends on

many factors (CPU, compiler, memory model, optimization, configuration, etc.).

371

23.2 Memory requirements

The memory requirements of embOS (RAM and ROM) differs depending on the used

features of the library. The following table shows the memory requirements for the

different modules.

* These values are typical values for a 32 bit cpu and depends on CPU, compiler, and

library model used.

Module Memory type Memory requirements

embOS kernel ROM 1100 - 1600 bytes *

embOS kernel RAM 18 - 50 bytes *

Mailbox RAM 8 - 20 bytes *

Semaphore RAM 2 bytes

Resource semaphore RAM 8 bytes *

Timer RAM 8 - 20 bytes *

Event RAM 0 bytes

Table 23.1: embOS memory requirements

372 CHAPTER 23 Performance and resource usage

23.3 Performance

The following section shows how to benchmark embOS with the supplied example

programs.

23.4 Benchmarking

embOS is designed to perform fast context switches. This section describes two dif-

ferent methods to calculate the execution time of a context switch from a task with

lower priority to a task with a higher priority.

The first method uses port pins and requires an oscilloscope. The second method

uses the high-resolution measurement functions. Example programs for both meth-

ods are supplied in the \Sample directory of your embOS shipment.

Segger uses these programs to benchmark the embOS performance. You can use

these examples to evaluate the benchmark results. Note, that the actual perfor-

mance depends on many factors (CPU, clock speed, toolchain, memory model, opti-

mization, configuration, etc.).

Please be aware that the amount of cycles are not equal to the amount of instruc-

tions. Many instructions on ARM7 need two or three cycles even at zero waitstates,

e.g. LDR needs 3 cycles.

The following table gives an overview about the variations of the context switch time

depending on the memory type and the CPU mode:

All named example performance values in the following section are determined with

the following system configuration:

All sources are compiled with IAR Embedded Workbench version 5.40 using thumb or

arm mode, XR library and high optimization level. embOS version 3.82 has been

used; values may differ for different builds.

Target Memory CPU mode Time / Cycles

ATMEL AT91SAM7S256 @ 48Mhz RAM ARM 4.09us / 196

ATMEL AT91SAM7S256 @ 48Mhz Flash ARM 6.406us / 307

ATMEL AT91SAM7S256 @ 48Mhz RAM Thumb 5.28us / 253

ATMEL AT91SAM7S256 @ 48Mhz Flash Thumb 6.823us / 327

NXP LPC3180 @ 208Mhz RAM ARM 0.948us / 197

Table 23.2: embOS context switch times

373

23.4.1 Measurement with port pins and oscilloscope

The example file MeasureCST_Scope.c uses the LED.c module to set and clear a port

pin. This allows measuring the context switch time with an oscilloscope.

The following source code is excerpt from MeasureCST_Scope.c:

#include "RTOS.h"

#include "LED.h"

static OS_STACKPTR int StackHP[128], StackLP[128]; // Task stacks

static OS_TASK TCBHP, TCBLP; // Task-control-blocks

/*********************************************************************

* HPTask

static void HPTask(void) {

while (1) {

OS_Suspend(NULL); // Suspend high priority task

LED_ClrLED0(); // Stop measurement

}

/*********************************************************************

* LPTask

static void LPTask(void) {

while (1) {

OS_Delay(100); // Synchronize to tick to avoid jitter

// Display measurement overhead

LED_SetLED0();

LED_ClrLED0();

// Perform measurement

LED_SetLED0(); // Start measurement

OS_Resume(&TCBHP); // Resume high priority task to force task switch

}

/*********************************************************************

* main

int main(void) {

OS_IncDI(); // Initially disable interrupts

OS_InitKern(); // Initialize OS

OS_InitHW(); // Initialize Hardware for OS

LED_Init(); // Initialize LED ports

OS_CREATETASK(&TCBHP, "HP Task", HPTask, 100, StackHP);

OS_CREATETASK(&TCBLP, "LP Task", LPTask, 99, StackLP);

OS_Start(); // Start multitasking

return 0;

}

374 CHAPTER 23 Performance and resource usage

23.4.1.1 Oscilloscope analysis

The context switch time is the time between switching the LED on and off. If the LED

is switched on with an active high signal, the context switch time is the time between

the rising and the falling edge of the signal. If the LED is switched on with an active

low signal, the signal polarity is reversed.

The real context switch time is shorter, because the signal also contains the overhead

of switching the LED on and off. The time of this overhead is also displayed on the

oscilloscope as a small peak right before the task switch time display and must be

subtracted from the displayed context switch time. The picture below shows a simpli-

fied oscilloscope signal with an active-low LED signal (low means LED is illuminated).

There are switching points to determine:

• A = LED is switched on for overhead measurement

• B = LED is switched off for overhead measurement

• C = LED is switched on right before context switch in low-prio task

• D = LED is switched off right after context switch in high-prio task

The time needed to switch the LED on and off in subroutines is marked as time tAB.

The time needed for a complete context switch including the time needed to switch

the LED on and off in subroutines is marked as time tCD.

The context switching time tCS is calculated as follows:

tCS = tCD - tAB

Voltage [V]

A B C D

tAB tCD

375

23.4.1.2 Example measurements AT91SAM7S, ARM code in RAM

Task switching time has been measured with the parameters listed below:

embOS Version V3.82

Application program: MeasureCST_Scope.c

Hardware: AT91SAM7SE512 processor with 48MHz

Program is executing in RAM

ARM mode is used

Compiler used: IAR V5.40

CPU frequency (fCPU): 47.9232MHz

CPU clock cycle (tCycle): tCycle = 1 / fCPU = 1 / 47.9232MHz = 20,866ns

Measuring tAB and tCD

Resulting context switching time and number of cycles

The time which is required for the pure context switch is:

tCS = tCD - tAB = 212Cycles - 16Cycles = 196Cycles

=> 196Cycles (4.09us @48MHz).

tAB is measured as 312ns.

The number of cycles calcu-

lates as follows:

CyclesAB = tAB / tCycle

=332ns / 20.866ns

= 15.911Cycles

=> 16Cycles

tCD is measured as 4420.0ns.

The number of cycles calcu-

lates as follows:

CyclesCD = tCD / tCycle

= 4420.0ns / 20.866ns

= 211.83Cycles

=> 212Cycles

376 CHAPTER 23 Performance and resource usage

23.4.1.3 Example measurements AT91SAM7S, Thumb code in FLASH

Task switching time has been measured with the parameters listed below:

embOS Version V3.82

Application program: MeasureCST_Scope.c

Hardware: AT91SAM7E512 processor with 48MHz

Program is executing in FLASH

Thumb mode is used

Compiler used: IAR V5.40

CPU frequency (fCPU): 47.9232MHz

CPU clock cycle (tCycle): tCycle = 1 / fCPU = 1 / 47.9232MHz = 20,866ns

Measuring tAB and tCD

Resulting context switching time and number of cycles

The time which is required for the pure context switch is:

tCS = tCD - tAB = 347Cycles - 20Cycles = 327Cycles

=> 327Cycles (6.83us @48MHz).

tAB is measured as 436.8ns.

The number of cycles calcu-

lates as follows:

CyclesAB = tAB / tCycle

=416.0ns / 20.866ns

= 19.937Cycles

=> 20Cycles

tCD is measured as 7250ns.

The number of cycles calcu-

lates as follows:

CyclesCD = tCD / tCycle

= 7250ns / 20.866ns

= 347.46Cycles

=> 347Cycles

377

23.4.1.4 Measurement with high-resolution timer

The context switch time may be measured with the high-resolution timer. Refer to

section High-resolution measurement on page 283 for detailed information about the

embOS high-resolution measurement.

The example MeasureCST_HRTimer_embOSView.c uses a high resolution timer to

measure the context switch time from a low priority task to a high priority task and

displays the results on embOSView.

#include "RTOS.h"

#include "stdio.h"

static OS_STACKPTR int StackHP[128], StackLP[128]; // Task stacks

static OS_TASK TCBHP, TCBLP; // Task-control-blocks

static OS_U32 _Time; // Timer values

/*********************************************************************

* HPTask

static void HPTask(void) {

while (1) {

OS_Suspend(NULL); // Suspend high priority task

OS_Timing_End(&_Time); // Stop measurement

}

/*********************************************************************

* LPTask

static void LPTask(void) {

char acBuffer[100]; // Output buffer

OS_U32 MeasureOverhead; // Time for Measure Overhead

OS_U32 v;

// Measure Overhead for time measurement so we can take

// this into account by subtracting it

OS_Timing_Start(&MeasureOverhead);

OS_Timing_End(&MeasureOverhead);

// Perform measurements in endless loop

while (1) {

OS_Delay(100); // Sync. to tick to avoid jitter

OS_Timing_Start(&_Time); // Start measurement

OS_Resume(&TCBHP); // Resume high priority task to force task switch

v = OS_Timing_GetCycles(&_Time) - OS_Timing_GetCycles(&MeasureOverhead);

v = OS_ConvertCycles2us(1000 * v); // Convert cycles to nano-seconds

sprintf(acBuffer, "Context switch time: %u.%.3u usec\r", v / 1000, v % 1000);

OS_SendString(acBuffer);

}

The example program calculates and subtracts the measurement overhead itself, so

there is no need to do this. The results will be transmitted to embOSView, so the

example runs on every target that supports UART communication to embOSView.

The example program MeasureCST_HRTimer_Printf.c is equal to the example pro-

gram MeasureCST_HRTimer_embOSView.c but displays the results with the printf()

function for those debuggers which support terminal output emulation.

378 CHAPTER 23 Performance and resource usage

379

Chapter 24

Debugging

380 CHAPTER 24 Debugging

24.1 Runtime errors

Some error conditions can be detected during runtime. These are:

• Usage of uninitialized data structures

• Invalid pointers

• Unused resource that has not been used by this task before

•OS_LeaveRegion() called more often than OS_EnterRegion()

• Stack overflow (this feature is not available for some processors)

Which runtime errors that can be detected depend on how much checking is per-

formed. Unfortunately, additional checking costs memory and speed (it is not that

significant, but there is a difference). If embOS detects a runtime error, it calls the

following routine:

void OS_Error(int ErrCode);

This routine is shipped as source code as part of the module OS_Error.c. It simply

disables further task switches and then, after re-enabling interrupts, loops forever as

follows:

Example

Run time error reaction

void OS_Error(int ErrCode) {

OS_EnterRegion(); /* Avoid further task switches */

OS_DICnt =0; /* Allow interrupts so we can communicate */

OS_EI();

OS_Status = ErrCode;

while (OS_Status);

}

If you are using embOSView, you can see the value and meaning of OS_Status in the

system variable window.

When using an emulator, you should set a breakpoint at the beginning of this routine

or simply stop the program after a failure. The error code is passed to the function as

parameter.

You can modify the routine to accommodate your own hardware; this could mean

that your target hardware sets an error-indicating LED or shows a little message on

the display.

Note: When modifying the OS_Error() routine, the first statement needs

to be the disabling of scheduler via OS_EnterRegion(); the last statement

needs to be the infinite loop.

If you look at the OS_Error() routine, you will see that it is more complicated than

necessary. The actual error code is assigned to the global variable OS_Status. The

program then waits for this variable to be reset. Simply reset this variable to 0 using

your in circuit-emulator, and you can easily step back to the program sequence caus-

ing the problem. Most of the time, looking at this part of the program will make the

problem clear.

24.1.1 OS_DEBUG_LEVEL

The define OS_DEBUG_LEVEL defines the embOS debug level. The default value is 1.

With higher debug level more debug code is included. The debug level 2 checks if

OS_RegionCnt overflows.

381

24.2 List of error codes

Value Define Explanation

100 OS_ERR_ISR_INDEX

Index value out of bounds during

interrupt controller initialization or

interrupt installation.

101 OS_ERR_ISR_VECTOR Default interrupt handler called, but

interrupt vector not initialized.

102 OS_ERR_ISR_PRIO Wrong interrupt priority

103 OS_ERR_WRONG_STACK Wrong stack used before main()

104 OS_ERR_ISR_NO_HANDLER No interrupt handler was defined for

this interrupt

105 OS_ERR_TLS_INIT

OS_TLS_Init() called multiple times

for one task. (Port specific error

message)

106 OS_ERR_MB_BUFFER_SIZE

The maximum buffer size of 64KB for

one mailbox buffer is exceed by call

of OS_CreateMB(). This limit exists

on 8 and 16bit CPUs only.

116 OS_ERR_EXTEND_CONTEXT OS_ExtendTaskContext called multi-

ple times from one task

117 OS_ERR_TIMESLICE

An illegal time slice value of zero was

used when calling OS_CreateTask(),

OS_CreateTaskEx() or

OS_SetTimeSlice().

Since version 3.86f of embOS, a time

slice of zero is legal (as described in

chapter 4). The error is not gener-

ated when a task is created with a

time slice value of zero.

118 OS_ERR_INTERNAL

OS_ChangeTask called without

RegionCnt set (or other internal

error)

119 OS_ERR_IDLE_RETURNS Idle loop should not return

120 OS_ERR_STACK Stack overflow or invalid stack.

121 OS_ERR_CSEMA_OVERFLOW Counting semaphore overflow.

122 OS_ERR_POWER_OVER Counter overflows when calling

OS_POWER_UsageInc()

123 OS_ERR_POWER_UNDER Counter underflows when calling

OS_POWER_UsageDec()

124 OS_ERR_POWER_INDEX Index to high, exceeds

(OS_POWER_NUM_COUNTERS - 1)

125 OS_ERR_SYS_STACK System stack overflow

126 OS_ERR_INT_STACK Interrupt stack overflow

128 OS_ERR_INV_TASK Task control block invalid, not initial-

ized or overwritten.

129 OS_ERR_INV_TIMER Timer control block invalid, not ini-

tialized or overwritten.

130 OS_ERR_INV_MAILBOX Mailbox control block invalid, not ini-

tialized or overwritten.

132 OS_ERR_INV_CSEMA

Control block for counting sema-

phore invalid, not initialized or over-

written.

Table 24.1: Error code list

382 CHAPTER 24 Debugging

133 OS_ERR_INV_RSEMA

Control block for resource sema-

phore invalid, not initialized or over-

written.

135 OS_ERR_MAILBOX_NOT1

One of the following 1-byte mailbox

functions has been used on a multi-

byte mailbox:

OS_PutMail1()

OS_PutMailCond1()

OS_GetMail1()

OS_GetMailCond1().

136 OS_ERR_MAILBOX_DELETE OS_DeleteMB() was called on a mail-

box with waiting tasks.

137 OS_ERR_CSEMA_DELETE

OS_DeleteCSema() was called on a

counting semaphore with waiting

tasks.

138 OS_ERR_RSEMA_DELETE

OS_DeleteRSema() was called on a

resource semaphore which is claimed

by a task.

140 OS_ERR_MAILBOX_NOT_IN_LIST

The mailbox is not in the list of mail-

boxes as expected. Possible reasons

may be that one mailbox data struc-

ture was overwritten.

142 OS_ERR_TASKLIST_CORRUPT The OS internal task list is

destroyed.

143 OS_ERR_QUEUE_INUSE Queue in use

144 OS_ERR_QUEUE_NOT_INUSE Queue not in use

145 OS_ERR_QUEUE_INVALID Queue invalid

146 OS_ERR_QUEUE_DELETE

A queue was deleted by a call of

OS_Q_Delete() while tasks are wait-

ing at the queue.

150 OS_ERR_UNUSE_BEFORE_USE OS_Unuse() has been called before

OS_Use().

151 OS_ERR_LEAVEREGION_BEFORE_ENTERR

EGION

OS_LeaveRegion() has been called

before OS_EnterRegion().

152 OS_ERR_LEAVEINT Error in OS_LeaveInterrupt().

153 OS_ERR_DICNT

The interrupt disable counter

(OS_DICnt) is out of range (0-15).

The counter is affected by the follow-

ing API calls:

OS_IncDI()

OS_DecRI()

OS_EnterInterrupt()

OS_LeaveInterrupt()

154 OS_ERR_INTERRUPT_DISABLED

OS_Delay() or OS_DelayUntil()

called from inside a critical region

with interrupts disabled.

155 OS_ERR_TASK_ENDS_WITHOUT_TERMINA

Task routine returns without

0S_TerminateTask()

156 OS_ERR_RESOURCE_OWNER

OS_Unuse() has been called from a

task which does not own the

resource.

157 OS_ERR_REGIONCNT The Region counter overflows (>255)

Value Define Explanation

Table 24.1: Error code list (Continued)

383

160 OS_ERR_ILLEGAL_IN_ISR

Illegal function call in an interrupt

service routine: A routine that must

not be called from within an ISR has

been called from within an ISR.

161 OS_ERR_ILLEGAL_IN_TIMER

Illegal function call in an interrupt

service routine: A routine that must

not be called from within a software

timer has been called from within a

timer.

162 OS_ERR_ILLEGAL_OUT_ISR

embOS timer tick handler or UART

handler for embOSView was called

without a call of

OS_EnterInterrupt().

163 OS_ERR_NOT_IN_ISR OS_EnterInterrupt() has been called,

but CPU is not in ISR state

164 OS_ERR_IN_ISR OS_EnterInterrupt() has not been

called, but CPU is in ISR stat

165 OS_ERR_INIT_NOT_CALLED OS_InitKern() was not called

166 OS_ERR_CPU_STATE_ISR_ILLEGAL OS-function called from ISR with

high priority

167 OS_ERR_CPU_STATE_ILLEGAL CPU runs in illegal mode

168 OS_ERR_CPU_STATE_UNKNOWN CPU runs in unknown mode or mode

could not be read

170 OS_ERR_2USE_TASK

Task control block has been initial-

ized by calling a create function

twice.

171 OS_ERR_2USE_TIMER

Timer control block has been initial-

ized by calling a create function

twice.

172 OS_ERR_2USE_MAILBOX

Mailbox control block has been ini-

tialized by calling a create function

twice.

174 OS_ERR_2USE_CSEMA

Counting semaphore has been initial-

ized by calling a create function

twice.

175 OS_ERR_2USE_RSEMA

Resource semaphore has been ini-

tialized by calling a create function

twice.

176 OS_ERR_2USE_MEMF

Fixed size memory pool has been ini-

tialized by calling a create function

twice.

180 OS_ERR_NESTED_RX_INT

OS_Rx interrupt handler for embOS-

View is nested. Disable nestable

interrupts.

190 OS_ERR_MEMF_INV Fixed size memory block control

structure not created before use.

191 OS_ERR_MEMF_INV_PTR Pointer to memory block does not

belong to memory pool on Release

192 OS_ERR_MEMF_PTR_FREE

Pointer to memory block is already

free when calling

OS_MEMF_Release(). Possibly, same

pointer was released twice.

Value Define Explanation

Table 24.1: Error code list (Continued)

384 CHAPTER 24 Debugging

The latest version of the defined error table is part of the comment just before the

OS_Error() function declaration in the source file OS_Error.c.

193 OS_ERR_MEMF_RELEASE

OS_MEMF_Release() was called for a

memory pool, that had no memory

block allocated (all available blocks

were already free before).

194 OS_ERR_POOLADDR

OS_MEMF_Create() was called with a

memory pool base address which is

not located at a word aligned base

address

195 OS_ERR_BLOCKSIZE

OS_MEMF_Create() was called with a

data block size which is not a multi-

ple of processors word size.

200 OS_ERR_SUSPEND_TOO_OFTEN Nested call of OS_Suspend()

exceeded OS_MAX_SUSPEND_CNT

201 OS_ERR_RESUME_BEFORE_SUSPEND OS_Resume() called on a task that

was not suspended.

202 OS_ERR_TASK_PRIORITY

OS_CreateTask() was called with a

task priority which is already

assigned to another task. This error

can only occur when embOS was

compiled without round robin sup-

port.

203 OS_ERR_TASK_PRIORITY_INVALID The value 0 was used as task prior-

ity.

210 OS_ERR_EVENT_INVALID An OS_EVENT object was used before

it was created.

211 OS_ERR_2USE_EVENTOBJ

An OS_EVENT object was created

twice.

This error should not be reported.

Contact Segger support.

212 OS_ERR_EVENT_DELETE An OS_EVENT object was deleted with

waiting tasks

223 OS_ERR_TICKHOOK_INVALID Invalid tick hook.

224 OS_ERR_TICKHOOK_FUNC_INVALID Invalid tick hook function

230 OS_ERR_NON_ALIGNED_INVALIDATE Cache invalidation needs to be cache

line aligned

235 OS_ERR_NON_TIMERCYCLES_FUNC

Callback function for timer counter

value has not been set.

Required by OS_GetTime_us().

236 OS_ERR_NON_TIMERINTPENDING_FUNC

Callback function for timer interrupt

pending flag has not been set.

Required by OS_GetTime_us().

254 OS_ERR_TRIAL_LIMIT Trial time limit reached

Value Define Explanation

Table 24.1: Error code list (Continued)

385

24.3 Application defined error codes

The embOS error codes begin at 100. The range 1 - 99 can be used for application

defined error codes. With it you can call OS_Error() with you own defined error code

from your application.

Example

#define OS_ERR_APPL 0x02

void UserAppFunc(void) {

int r;

r = DoSomething()

if (r == 0) {

OS_Error(OS_ERR_APPL)

}

386 CHAPTER 24 Debugging

387

Chapter 25

Supported development tools

388 CHAPTER 25 Supported development to ols

25.1 Overview

embOS has been developed with and for a specific C compiler version for the selected

target processor. Check the file RELEASE.HTML for details. It works with the specified

C compiler only, because other compilers may use different calling conventions

(incompatible object file formats) and therefore might be incompatible. However, if

you prefer to use a different C compiler, contact us and we will do our best to satisfy

your needs in the shortest possible time.

Reentrance

All routines that can be used from different tasks at the same time must be fully

reentrant. A routine is in use from the moment it is called until it returns or the task

that has called it is terminated.

All routines supplied with your real-time operating system are fully reentrant. If for

some reason you need to have non-reentrant routines in your program that can be

used from more than one task, it is recommended to use a resource semaphore to

avoid this kind of problem.

C routines and reentrance

Normally, the C compiler generates code that is fully reentrant. However, the com-

piler may have options that force it to generate non-reentrant code. It is recom-

mended not to use these options, although it is possible to do so under certain

circumstances.

Assembly routines and reentrance

As long as assembly functions access local variables and parameters only, they are

fully reentrant. Everything else needs to be thought about carefully.

389

Chapter 26

Limitations

390 CHAPTER 26 Limitati ons

The following limitations exist for embOS:

We appreciate your feedback regarding possible additional functions and we will do

our best to implement these functions if they fit into the concept.

Do not hesitate to contact us. If you need to make changes to embOS, the full source

code is available.

Max. no. of tasks: limited by available RAM only

Max. no. of priorities: 255

Max. no. of semaphores: limited by available RAM only

Max. no. of mailboxes: limited by available RAM only

Max. no. of queues: limited by available RAM only

Max. size. of queues: limited by available RAM only

Max. no. of timers limited by available RAM only

Task-specific event flags: 8 bits / task (32 bits on 32 bit CPU)

391

Chapter 27

Source code of kernel and library

392 CHAPTER 27 Source code of kernel and library

27.1 Introduction

embOS is available in two versions:

1. Object version: Object code + hardware initialization source.

2. Full source version: Complete source code.

Because this document describes the object version, the internal data structures are

not explained in detail. The object version offers the full functionality of embOS

including all supported memory models of the compiler, the debug libraries as

described and the source code for idle task and hardware initialization. However, the

object version does not allow source-level debugging of the library routines and the

kernel.

The full source version gives you the ultimate options: embOS can be recompiled for

different data sizes; different compile options give you full control of the generated

code, making it possible to optimize the system for versatility or minimum memory

requirements. You can debug the entire system and even modify it for new memory

models or other CPUs.

The source code distribution of embOS contains the following additional files:

•The CPU folder contains all CPU and compiler specific source code and header

files used for building the embOS libraries. It also contains the sample start

project, workspace, and source files for the embOS demo project delivered in the

Start folder. Normally, you should not modify any of the files in the CPU folder.

•The GenOSSrc folder contains all embOS sources and a batch file used for compil-

ing all of them in batch mode as described in the following section.

393

27.2 Building embOS libraries

The embOS libraries can only be built if you have purchased a source code version of

embOS.

In the root path of embOS, you will find a DOS batch file PREP.BAT, which needs to

be modified to match the installation directory of your C compiler. Once this is done,

you can call the batch file M.BAT to build all embOS libraries for your CPU.

Note: Rebuilding the embOS libraries using the M.bat file will delete and

rebuild the entire Start folder. If you made any modifications or built own

projects in the Start folder, make a copy of your start folder before rebuild-

ing embOS.

The build process should run without any error or warning message. If the build

process reports any problem, check the following:

• Are you using the same compiler version as mentioned in the file RELEASE.HTML?

• Can you compile a simple test file after running PREP.BAT and does it really use

the compiler version you have specified?

• Is there anything mentioned about possible compiler warnings in the

RELEASE.HTML?

If you still have a problem, let us know.

The whole build process is controlled with a few amount of batch files which are

located in the root directory of your source code distribution:

•Prep.bat: Sets up the environment for the compiler, assembler, and linker.

Ensure, that this file sets the path and additional include directories which are

needed for your compiler. Normally, this batch file is the only one which might

need to be modified to build the embOS libraries. Normally, this file is called from

M.bat during the build process of all libraries.

•Clean.bat: Deletes the whole output of the embOS library build process. It is

called automatically during the build process, before new libraries are generated.

Normally it deletes the Start folder. Therefore, be careful not to call this batch

file accidentally. Normally, this file is called initially by M.bat during the build

process of all libraries.

•cc.bat: This batch file calls the compiler and is used for compiling one embOS

source file without debug information output. Most compiler options are defined

in this file and should normally not be modified. For your purposes, you might

activate debug output and may also modify the optimization level. All modifica-

tions should be done with care. Normally, this file is called from the embOS inter-

nal batch file CC_OS.bat and cannot be called directly.

•ccd.bat: This batch file calls the compiler and is used for compiling OS_Global.c

which contains all global variables. All compiler settings are equal to those used

in cc.bat, except debug output is activated to enable debugging of global vari-

ables when using embOS libraries. Normally, this file is called from the embOS

internal batch file CC_OS.bat and cannot be called directly.

•asm.bat: This batch file calls the assembler and is used for assembling the

assembly part of embOS which normally contains the task switch functionality.

Normally this file is called from the embOS internal batch file CC_OS.bat and can-

not be called directly.

•MakeH.bat: Builds the embOS header file RTOS.h which is composed from the

CPU/compiler-specific part OS_Chip.h and the generic part OS_RAW.h. Normally,

RTOS.h is output in the subfolder Start\Inc.

•M1.bat: This batch file is called from M.bat and is used for building one specific

embOS library, it cannot be called directly.

•M.bat: This batch file must be called to generate all embOS libraries. It initially

calls Clean.bat and therefore deletes the whole Start folder. The generated

libraries are then placed in a new Start folder which contains start projects,

libraries, header, and sample start programs.

394 CHAPTER 27 Source code of kernel and library

27.3 Major compile time switches

Many features of embOS may be modified by compile-time switches. All of them are

predefined to reasonable values in the distribution of embOS. The compile-time

switches must not be changed in RTOS.h. When the compile-time switches should be

modified to alter any of the embOS features, the modification must be done in

OS_RAW.h or must be passed as parameters during the library build process. embOS

sources must be recompiled and RTOS.h must be rebuilt with the modified switches.

27.3.1 OS_RR_SUPPORTED

This switch defines whether round robin scheduling algorithm is supported. All

embOS versions enable round robin scheduling by default. If you never use round

robin scheduling and all of your tasks run on different individual priorities, you may

disable round robin scheduling by defining this switch to 0. This will save RAM and

ROM and will also speed up the task-switching process. Ensure that none of your

tasks ever run on the same priority when you disable round robin scheduling. This

compile time switch must not be modified in RTOS.h. It must be modified in OS_RAW.h

before embOS libraries are rebuilt.

395

Chapter 28

FAQ (frequently asked questions)

396 CHAPTER 28 FAQ (frequently asked questions)

Q: Can I implement different priority scheduling algorithms?

A: Yes, the system is fully dynamic, which means that task priorities can be changed

while the system is running (using OS_SetPriority()). This feature can be used

for changing priorities in a way so that basically every desired algorithm can be

implemented. One way would be to have a task control task with a priority higher

than that of all other tasks that dynamically changes priorities. Normally, the

priority-controlled round-robin algorithm is perfect for real-time applications.

Q: Can I use a different interrupt source for embOS?

A: Yes, any periodic signal can be used, that is any internal timer, but it could also be

an external signal.

Q: What interrupt priorities can I use for the interrupts my program uses?

A: Any.

397

Chapter 29

Support

This chapter should help if any problem occurs. This could be a problem with the tool

chain, with the hardware or the use of the embOS functions and it describes how to

contact the embOS support.

398 CHAPTER 29 Support

29.1 Contacting support

If you are a registered embOS user and you need to contact the embOS support

please send the following information via email to support_embos@segger.com:

• Which embOS do you use? (CPU, compiler).

• The embOS version.

• Your embOS registration number.

• If you are unsure about the above information you can also use the name of the

embOS zip file (which contains the above information).

• A detailed description of the problem.

• Optionally a project with which we can reproduce the problem.

399

Chapter 30

Glossary

400 CHAPTER 30 Glossary

Cooperative multi-

tasking

A scheduling system in which each task is allowed to run until

it gives up the CPU; an ISR can make a higher priority task

ready, but the interrupted task will be returned to and finished

first.

Counting sema-

phore

A type of semaphore that keeps track of multiple resources.

Used when a task must wait for something that can be sig-

naled more than once.

CPU Central Processing Unit. The “brain” of a microcontroller; the

part of a processor that carries out instructions.

Critical region A section of code which must be executed without interrup-

tion.

Event A message sent to a single, specified task that something has

occurred. The task then becomes ready.

Interrupt Handler Interrupt Service Routine. The routine is called automatically

by the processor when an interrupt is acknowledged. ISRs

must preserve the entire context of a task (all registers).

ISR Interrupt Service Routine. The routine is called automatically

by the processor when an interrupt is acknowledged. ISRs

must preserve the entire context of a task (all registers).

Mailbox A data buffer managed by the RTOS, used for sending mes-

sages to a task or interrupt handler.

Message An item of data (sent to a mailbox, queue, or other container

for data).

Multitasking The execution of multiple software routines independently of

one another. The OS divides the processor's time so that the

different routines (tasks) appear to be happening simulta-

neously.

NMI Non-Maskable Interrupt. An interrupt that cannot be masked

(disabled) by software. Example: Watchdog timer-interrupt.

Preemptive multi-

tasking

A scheduling system in which the highest priority task that is

ready will always be executed. If an ISR makes a higher prior-

ity task ready, that task will be executed before the inter-

rupted task is returned to.

Process Processes are tasks with their own memory layout. 2 pro-

cesses cannot normally access the same memory locations.

Different processes typically have different access rights and

(in case of MMUs) different translation tables.

Processor Short for microprocessor. The CPU core of a controller

401

Priority The relative importance of one task to another. Every task in

an RTOS has a priority.

Priority inversion A situation in which a high priority task is delayed while it

waits for access to a shared resource which is in use by a

lower priority task. A task with medium priority in the ready

state may run, instead of the high priority task. embOS avoids

this situation by priority inheritance.

Queue Like a mailbox, but used for sending larger messages, or mes-

sages of individual size, to a task or an interrupt handler.

Ready Any task that is in “ready state” will be activated when no

other task with higher priority is in “ready state”.

Resource Anything in the computer system with limited availability (for

example memory, timers, computation time). Essentially, any-

thing used by a task.

Resource sema-

phore

A type of semaphore used for managing resources by ensuring

that only one task has access to a resource at a time.

RTOS Real-time Operating System.

Running task Only one task can execute at any given time. The task that is

currently executing is called the running task.

Scheduler The program section of an RTOS that selects the active task,

based on which tasks are ready to run, their relative priorities,

and the scheduling system being used.

Semaphore A data structure used for synchronizing tasks.

Software timer A data structure which calls a user-specified routine after a

specified delay.

Stack An area of memory with LIFO storage of parameters, auto-

matic variables, return addresses, and other information that

needs to be maintained across function calls. In multitasking

systems, each task normally has its own stack.

Superloop A program that runs in an infinite loop and uses no real-time

kernel. ISRs are used for real-time parts of the software.

Task A program running on a processor. A multitasking system

allows multiple tasks to execute independently from one

another.

Thread Threads are tasks which share the same memory layout. 2

threads can access the same memory locations. If virtual

memory is used, the same virtual to physical translation and

access rights are used

(-> Thread, Process)

402 CHAPTER 30 Glossary

Tick The OS timer interrupt. Usually equals 1 ms.

Time slice The time (number of ticks) for which a task will be executed

until a round-robin task change may occur.

403

Index

Baudrate for embOSView .................... 324

C startup ............................................37

Compiler .......................................... 388

Configuration defines ......................... 323

Configuration, of embOS .......301, 319–327

Counting Semaphores ........................ 125

Critical regions ......................30, 271–275

Debug build, of embOS .........................38

Debugging ................................. 379–384

error codes ..............................381, 385

runtime errors ................................ 380

Development tools ............................. 387

embOS

building libraries of .......................... 393

different builds of ..............................38

features of .......................................21

embOS features ..................................21

embOS profiling ..................................38

embOSView ............................... 339–367

API trace ........................................ 347

overview ........................................ 340

SIO ............................................... 343

system variables window .................. 342

task list window .............................. 341

trace filter setup functions ................ 349

trace record functions ...................... 359

Error codes ................................381, 385

Events ................... 33, 177–187, 189–206

Internal data-structures ...................... 300

Interrupt control macros ..................... 261

Interrupt level .....................................25

Interrupt service routines ..............25, 245

Interrupts ..................................245–270

enabling/disabling ............................258

interrupt handler .............................252

ISR ..................................................245

Libraries, building ..............................393

Limitations, of embOS ........................389

Mailboxes ............................. 33, 139–158

basics ............................................141

single-byte .....................................143

Measurement ....................................279

high-resolution ................................283

low-resolution .................................279

Memory management

fixed block size ................................213

heap memory ..................................207

Memory pools .............................213–227

Multitasking systems ........................... 27

cooperative multitasking .................... 29

preemptives multitasking ................... 28

Nesting interrupts ..............................262

Non-maskable interrupts ............. 266, 270

OS_AddLoadMeasurement() ................332

OS_AddOnTerminateHook() .................. 50

OS_AdjustTime() ...............................315

OS_BAUDRATE ..................................323

OS_CallISR() .....................................254

OS_CallNestableISR() .........................255

OS_ClearEvents() ..............................187

OS_ClearMB() ...................................156

OS_COM_Init() ..................................321

OS_COM_Send1() ..............................321

OS_ConvertCycles2us() ......................321

OS_CPU_Load ...................................334

OS_CREATECSEMA() ..........................128

404 Index

OS_CreateCSema() ........................... 129

OS_CREATEMB() ............................... 145

OS_CREATERSEMA() .......................... 115

OS_CREATETASK() .............................. 51

OS_CreateTask() ................................. 53

OS_CREATETASK_EX() ......................... 55

OS_CreateTaskEx() .............................. 57

OS_CREATETIMER() ............................. 88

OS_CreateTimer() ............................... 89

OS_CREATETIMER_EX() ....................... 99

OS_CreateTimerEx() .......................... 100

OS_CSemaRequest() ......................... 134

OS_DecRI() ...................................... 259

OS_Delay() ........................................ 58

OS_DelayUntil() .................................. 59

OS_Delayus() ..................................... 60

OS_DeleteCSema() ........................... 137

OS_DeleteMB() ................................. 158

OS_DeleteTimer() ............................... 94

OS_DeleteTimerEx() .......................... 105

OS_DI() ........................................... 260

OS_EI() ........................................... 260

OS_EnterInterrupt() .......................... 256

OS_EnterNestableInterrupt() .............. 263

OS_EnterRegion() ............................. 274

OS_EVENT_Create() .......................... 192

OS_EVENT_CreateEx() ....................... 193

OS_EVENT_Delete() .......................... 201

OS_EVENT_Get() .............................. 200

OS_EVENT_GetResetMode() ............... 203

OS_EVENT_Pulse() ............................ 199

OS_EVENT_Reset() ............................ 198

OS_EVENT_RESET_MODE_AUTO .. 193, 202

OS_EVENT_RESET_MODE_MANUAL 193, 202

OS_EVENT_RESET_MODE_SEMIAUTO . 193,

202

OS_EVENT_Set() ............................... 197

OS_EVENT_SetResetMode() ................ 202

OS_EVENT_Wait() ............................. 194

OS_EVENT_WaitTimed() ..................... 195

OS_ExtendTaskContext() ...................... 61

OS_free() ......................................... 209

OS_FSYS .......................................... 323

OS_GetCSemaValue() ........................ 135

OS_GetEventsOccurred() .................... 186

OS_GetIntStackBase() ....................... 241

OS_GetIntStackSize() ........................ 242

OS_GetIntStackSpace() ..................... 243

OS_GetIntStackUsed() ....................... 244

OS_GetLoadMeasurement() ................ 333

OS_GetMail() .................................... 150

OS_GetMail1() .................................. 150

OS_GetMailCond() ............................. 151

OS_GetMailCond1() ........................... 151

OS_GetMailTimed() ........................... 152

OS_GetMessageCnt() ......................... 157

OS_GetNumIdleTicks() ....................... 314

OS_GetpCurrentTask() ......................... 64

OS_GetpCurrentTimer() ....................... 98

OS_GetpCurrentTimerEx() .................. 109

OS_GetPriority() ................................. 65

OS_GetResourceOwner() .................... 122

OS_GetSemaValue() .......................... 121

OS_GetStackBase() ........................... 233

OS_GetStackSize() ............................ 234

OS_GetStackSpace() ......................... 235

OS_GetStackUsed() ........................... 236

OS_GetSysStackBase() ...................... 237

OS_GetSysStackSize() ....................... 238

OS_GetSysStackSpace() ..................... 239

OS_GetSysStackUsed() ...................... 240

OS_GetTaskID() ..................................67

OS_GetTaskName() .............................68

OS_GetTime() ................................... 281

OS_GetTime_Cycles() ........................ 321

OS_GetTime32() ............................... 282

OS_GetTimerPeriod() ...........................95

OS_GetTimerPeriodEx() ...................... 106

OS_GetTimerStatus() ........................... 97

OS_GetTimerStatusEx() ..................... 108

OS_GetTimerValue() ............................96

OS_GetTimerValueEx() ....................... 107

OS_GetTimeSliceRem() ........................ 69

OS_Global.Time ................................ 299

OS_Global.TimeDex ........................... 299

OS_Idle() .................................. 321, 326

OS_IncDI() ....................................... 259

OS_InInterrupt() ............................... 265

OS_InitHW() ..................................... 321

OS_INTERRUPT_MaskGlobal() ............. 267

OS_INTERRUPT_PreserveAndMaskGlobal() .

269

OS_INTERRUPT_PreserveGlobal() ........ 268

OS_INTERRUPT_RestoreGlobal() .......... 269

OS_INTERRUPT_UnmaskGlobal() ......... 267

OS_ISR_rx() ..................................... 321

OS_ISR_tx() ..................................... 321

OS_IsRunning() .................................. 70

OS_IsTask() ........................................71

OS_LeaveInterrupt() .......................... 257

OS_LeaveNestableInterrupt() .............. 264

OS_LeaveRegion() ............................. 275

OS_malloc() ..................................... 209

OS_MEMF_Alloc() .............................. 218

OS_MEMF_AllocTimed() ...................... 219

OS_MEMF_Create() ............................ 216

OS_MEMF_Delete() ............................ 217

OS_MEMF_FreeBlock() ....................... 222

OS_MEMF_GetBlockSize() ................... 224

OS_MEMF_GetMaxUsed() ................... 226

OS_MEMF_GetNumBlocks() ................. 223

OS_MEMF_GetNumFreeBlocks() ........... 225

OS_MEMF_IsInPool() ......................... 227

OS_MEMF_Release() .......................... 221

OS_MEMF_Request() .......................... 220

OS_ON_TERMINATE_FUNC ....................50

OS_PeekMail() .................................. 155

OS_PutMail() .................................... 146

OS_PutMail1() ................................... 146

OS_PutMailCond() ............................. 147

OS_PutMailCond1() ............................ 147

OS_PutMailFront() ............................. 148

OS_PutMailFront1() ........................... 148

OS_PutMailFrontCond() ...................... 149

OS_PutMailFrontCond1() .................... 149

OS_Q_Clear() ................................... 171

OS_Q_Create() ................................. 163

OS_Q_Delete() .................................. 173

OS_Q_GetMessageCnt() ..................... 172

OS_Q_GetPtr() ........................... 167, 175

OS_Q_GetPtrCond() ........................... 168

OS_Q_GetPtrTimed() ......................... 169

OS_Q_IsInUse() ................................ 174

OS_Q_Purge() ................................... 170

Index 405

OS_Q_Put() ...............................164, 335

OS_Q_PutTimed() .............................. 166

OS_realloc() ..................................... 209

OS_Request() ................................... 120

OS_RestoreI() ................................... 260

OS_Resume() ......................................72

OS_ResumeAllSuspendedTasks() ...........73

OS_RetriggerTimer() ............................92

OS_RetriggerTimerEx() ...................... 103

OS_SendString() ............................... 345

OS_SetCSemaValue() ......................... 136

OS_SetInitialSuspendCnt() ...................74

OS_SetPriority() ..................................75

OS_SetRxCallback() ........................... 346

OS_SetTaskName() ..............................76

OS_SetTimerPeriod() ...........................93

OS_SetTimerPeriodEx() ...................... 104

OS_SetTimeSlice() ...............................77

OS_SignalCSema() ............................ 130

OS_SignalCSemaMax() ....................... 131

OS_SignalEvent() .............................. 184

OS_Start() ..........................................78

OS_StartTimer() ..................................90

OS_StartTimerEx() ............................ 101

OS_STAT_GetLoad() .......................... 330

OS_STAT_Sample() ............................ 329

OS_StopTimer() ..................................91

OS_StopTimerEx() ............................. 102

OS_Suspend() .....................................79

OS_SuspendAllTasks() ..........................80

OS_TASK_EVENT ............................... 178

OS_TerminateTask() .............................81

OS_TICK_AddHook() .......................... 309

OS_TICK_Config() ............................. 307

OS_TICK_Handle() ............................ 304

OS_TICK_HandleEx() ......................... 305

OS_TICK_HandleNoHook() .................. 306

OS_TICK_RemoveHook() .................... 310

OS_Timing_End() .............................. 286

OS_Timing_GetCycles() ...................... 288

OS_Timing_Getus() ........................... 287

OS_Timing_Start() ............................. 285

OS_TraceData() ................................. 363

OS_TraceDataPtr() ............................. 364

OS_TraceDisable() ............................. 352

OS_TraceDisableAll() .......................... 354

OS_TraceDisableFilterId() ................... 358

OS_TraceDisableId() .......................... 356

OS_TraceEnable() .............................. 351

OS_TraceEnableAll() ........................... 353

OS_TraceEnableFilterId() .................... 357

OS_TraceEnableId() ........................... 355

OS_TracePtr() ................................... 362

OS_TraceU32Ptr() .............................. 365

OS_TraceVoid() ................................. 361

OS_UART .......................................... 323

OS_Unuse() ...................................... 119

OS_Use() ......................................... 116

OS_UseTimed() ................................. 118

OS_WaitCSema() ............................... 132

OS_WaitCSemaTimed() ...................... 133

OS_WaitEvent() ................................. 180

OS_WaitEventTimed() ........................ 182

OS_WaitMail() ................................... 153

OS_WaitMailTimed() .......................... 154

OS_WaitSingleEvent() ........................ 181

OS_WaitSingleEventTimed() ................ 183

OS_WakeTask() .................................. 82

Preemptive multitasking ....................... 28

Priority .............................................. 30

Priority inheritance .............................. 31

priority inversion ................................. 31

Profiling ............................................. 38

Queues ................................ 33, 159–174

Reentrance ........................................388

Release build, of embOS ...................... 38

Resource semaphores .........................111

Round-robin ....................................... 30

RTOSInit.c configuration .....................320

Runtime errors ..................................380

Scheduler .......................................... 30

Semaphores ....................................... 33

Counting .................................125–137

Resource .................................111–123

Software timer .............................. 85–98

Software timer API functions ................ 87

Stack .................................. 34, 229–244

Stack pointer ...................................... 34

Stacks

switching ......................................... 35

Superloop .......................................... 25

Switching stacks ................................. 35

Syntax, conventions used ....................... 9

System variables ........................297–300

Task communication ............................ 33

Task control block .......................... 34, 44

Task routines ??– ................................. 83

Tasks .......................................24, 42–43

communication ................................. 33

global variables ................................ 33

multitasking systems ........................ 27

periodic polling ................................. 33

single-task systems .......................... 25

status ............................................. 36

superloop ........................................ 25

switching ......................................... 34

TCB ................................................... 34

Time measurement .....................277–291

Time variables ...................................299

UART ................................................340

UART, for embOS ...............................324

Vector table file .................................324

406 Index