Technology Background - Advanced Micro Devices

July 2003

The following document refers to Spansion memory products that are now offered by both Advanced

Micro Devices and Fujitsu. Although the document is marked with the name of the company that orig-

inally developed the specification, these products will be offered to customers of both AMD and

Fujitsu.

Continuity of Specifications

There is no change to this document as a result of offering the device as a Spansion product. Any

changes that have been made are the result of normal documentation improvements and are noted

in the document revision summary, where supported. Future routine revisions will occur when appro-

priate, and changes will be noted in a revision summary.

Continuity of Ordering Part Numbers

AMD and Fujitsu continue to support existing part numbers beginning with “Am” and “MBM”. To order

these products, please use only the Ordering Part Numbers listed in this document.

For More Information

Please contact your local AMD or Fujitsu sales office for additional information about Spansion

memory solutions.

Data Management Software (DMS)

for AMD Simultaneous Read/Write

Flash Memory Devices

Technology Background

Publication Number 22274 Revision AAmendment 0 Issue Date November 1, 1998

TECHNOLOGY BACKGROUND

Data Ma nagement Software (DMS)

for AMD Simultaneous Read/Write

Flash Memor y Devices

2 DMS (Data Management Software) Technology Background

Introduction

A wide variety of applications use Flash memory to store embedded control code. Most of

these applications (including cellular phones, modems, and automobile engine control) have

traditionally utilized an EEPROM to store factory, system, and/or user data. Replacing

EEPROM with Flash memory simplifies hardware and software design, reduces board space

requirements, and decreases system cost. Removing EEPROM can also increase system

performance since Flash memory is both faster and more reliable than EEPROM.

Replacing an EEPROM with Flash memory presents a new set of problems, however. First,

comple x task management software will usually be needed, since most Flash devices can only

perform one operation at a time. Secondly, some form of data management software must be

de veloped to manipulate data within the sectors of Flash memory de vices.

Task Manag ers

When storing code and data in a tr aditional flash device, the system cannot read operating

code while data is being written or erased. This can cause unacceptable delays in syst em

operation while w aiting for the wri te to complete. To get around this limitation requires

complex task management soft ware . Thi s software must constantly monitor priorities of

operations, to suspend lo wer priority commands (such as erase and write) and activate higher

priority one s (lik e read syste m code). While this softwa r e solution enables EEPROM

replacement, it is very dif f icult to integra te the task management software with system

software. This software solution also results in signif icant system overhead that impacts

system performance, especially in real time applications.

The Am29DLxxx family of Simultaneous Read/Write Flash provides a unique performance

adva ntage over other flash products. The de vice can read data while it is performing a write or

erase operation. This simulta neous operation eli mina tes the need for complicated task

managers, resulting in simpler software and increased performance. However, data

manageme nt software is still required to manage data storage .

DMS (Data Managem ent Software ) Technolog y Backgro und 3

Data Manag ement Software

AMD pr ovi des Data Management S oftw are ( DMS) to work together with Simultaneous Read-

Write flash devices to make it easy for customers to store code and data in a single flash

device1. DMS takes advantage of the Simult a neous Read/Write devices by storing the system

software (including DMS) in one bank of the flash, and storing data in the other bank.

Partitioning the memory this way allows code to be read out of one ba nk while the system

updates and manages data in the other. Systems that use a traditional flash device must copy

code to RAM to run the s ystem while writing data to the flash memory.

DMS provides all the tools necessary to update data in a fl a sh device. The system software

only has to call one of se ve n functions to utilize DMS. Because the system only needs to

access these few functions, DMS requires as few as 20 hours of integration time. Other

solutions based on traditional flash devices require a minimum of 500 hours.

DMS stores and tr acks data as virtual cells and blocks within the physical boundaries of the

flash bank. Since a byte in flash may not be overwritten, an old occurrence of data is marked

“dirty” when the data is updated. DMS continues to store data until there is not enough

“clean” space in the bank t o write ne w records. At this point, DMS initiates a cleanup process,

saving the latest valid occurrence of each data in another sector, then erasing the old dirty

sector. System software can be greatly simplified because it doesn’t have to perform this

comple x bookkeeping. DMS so ftware even handles variable length parameter storage, which

allow s for data streaming applications like voice recording. With the introduction of DMS,

AMD offers a s imple and complete solution for data storage.

1. DMS als o su pport s non- sim ulta neo us de vic es if c ustomer s on ly wa nt to util i ze its dat a manag emen t ca pabil it ies. In

this case, DMS must execute from an external memory device other than the flash device storing the data, and will

require a user written task manager.

4 DMS (Data Management Software) Technology Background

DMS Overview

DMS is brok en up into four layers: the application layer , the cell layer , the block layer , and the

device layer. These layers interact with each other, maintaining a minimum level of coupling

and a maximum lev el of data abstraction. This simpli f ies the integration process by requiring

the system soft ware to only acces s one layer of DMS, hiding all complex data management

tasks in t he other layers of DMS. (See Figure 1.)

The applica tion inter face layer handles all

communication between the DMS libr ary and

the user’ s application. From an object oriented

perspe ctive this is the public interfac e to t he

DMS object. A vendor or integr ator can

perform all necessary DMS operations by

calling the routines in this layer.

The cell layer provides an interface to DMS

that is similar to an EEPROM. Each cell is

composed of one or more data blocks. The

data blocks are read from the data block layer

and combined to form a cell. To prevent cell

corr uption, a compile time switch is provide d

that assures cell integrity at the e xpense of

restrictions on cell si ze and fr ee s pace. If the c ompile time cell integrity switch is not utilize d,

cell data may be corrupted during a po wer outage. F or example, if po wer was lost during a cell

update operation, the cell may be corrupted. Half of the blocks in the cell may contain new

data, while the other half contain old data. While these blocks all contain va lid data, this

hy brid cell does not contain va lid cell data. (See Figure 2). When re-i nitializ ed (cell inte grity

switch acti ve), DMS detects the corrupted cell and reverts all data in the cell to old cell data.

The data block laye r is responsible for most of the f ile structure functionality of DMS. An ID

number uniquely identifies each data block. Cells consist of data blocks linked by ID

numbers. To increase performance, data block information is sorted upon initialization and

cached in an external memory table. If po wer is terminated while a data block is being written,

the data block will re vert to the previous v ersion of itself. To provide wear leveling of the

de vice , each data block is mo ved to a different location when written.

Figure 1. DMS Block Diagram

DMS (Data Managem ent Software ) Technolog y Backgro und 5

Figu re 2. Corru pt Gl ob a l Cel l Table

The device layer of DMS encapsulates the device interface, providing a generic interface that

does not depend on a specific processor or operating system. This approach allows other

layers to remain unchanged from one environment to another. Platform specific information,

such as memory mapping, is handled by a small sub-set of the device layer, the vendor

specific module. The v endor specific module is unique to each DMS platform.

The functions that reside in the vendor specific module integrate DMS and the hardware

platform. Therefore these are the only functions in DMS not necessarily written in ANSI C.

Each time DMS is ported to a new platform these functions need to be modified. Because this

module provides for rigid hardwar e abstraction, the remainder of DMS is not platform

dependent and thus is written in ANSI C.

The seven functions in the top layer (Application Interface Layer) are the only f unctions that

the system software needs to call. This layer abstracts the DMS into seven functions: Forma t,

Initialize, Write, Cleanup, Read, IsBusy, and Shutdown.

Cell 1 1

Valid

Available

Blocks

(index 0)

Cell 2

Erased

Cell 3

Valid

Cell 4 18

Valid

Cell 5 23

Valid

New Block

Old Block

licate Blocks

6 DMS (Data Management Software) Technology Background

Format

Format allows users to choos e which sectors to manage with DM S. It then divides those

allocated sectors into cells, and in turn partitions those cells into blocks. The Format function

must be called before using DMS the fir st time, since it prepares the flash d evice for use by

DMS. It formats the areas of the flash allocated for use by DMS into the device layout

specified by the user. (See Figure 3.) First, Format erases all sect ors allocated for DMS

management. Then those sectors are partiti oned into the cell lengths according to the cell

structure the user specified. This is done on two levels, cell length and block length. In the

header file, the user specifies the cell length, while the blocks are set at a default length (for

e xample, 512 bytes). The cell is then brok en up into an integer number of these blocks. When

a sector is erased, Format must again be called to reformat tha t sector only.

Figu re 3. Form at ted FFS

Cells and blocks are managed via two different means: Sector Erase header, and Global Cell

Table. The Sector Erase header includes the following:

❏sector index

❏number of blocks that fit into the sector

❏number of cells stored in the device

❏number of blocks stored in the sector

Every time the global ce ll table is modified, the s ector header is modified accordingly.

DMS (Data Managem ent Software ) Technolog y Backgro und 7

Initialize

Initialize creates the Global Cell Table based upon the cell structure defined by the user to

manage data and track where data is physically located in the flash memory. Initialize should

be called when booting up the de vice. Each cell stored in the flash has a corresponding entry

in the Global Cell Table. Each entry consists of a number of nodes, which contain information

about the blocks that constitute the cell. This information (unique block number, status of

block (valid, invalid), and a pointer to the next block in the cell) is represented below in the

global cell table, where each numbered block is a node. The nodes are added to the correct

inde x ( based on t he Cell Number) in a s orted order based on the data block number withi n the

node.

After all of the cells are defined and all ocated in the flash, an integrity check is performed to

ensure that the Global Cell table only points to valid data.

Write

The Write function writes data to a cell, after format and initialize are comple te. Data is

copied from the user buff er and stored in the flash device. This function will only return to the

calling program a fter the write completes.

System soft wa re must send two paramete rs each time it calls the Write function. The firs t is

the cell number to be written. The second parameter is a pointer to the current location of the

data the user wants written to the de vice. Based upon the cell number sent, DMS will modify

or add an entry in the Global Cell Table. DMS then calls the Cleanup function to ensure there

is enough space av ailable to write the entire cell without a cleanup having to occur during the

write operation. Once this is ensured, DMS traces through the data to be copied, then writes

this data block by block to the flash. If an existing cell is being updated, the status flag for

each node in the Global Cell Table is updated with the ne w location of the data. If a ne w cell is

being added, additional entries and nodes are added to the Global Cell Table.

Cleanup

As mentioned above, the Cleanup function defragments the sectors managed by DMS. First,

it identifie s the sector with the most dirty blocks. Next, all valid blocks in this sector are

moved to another sector in the devi ce. Finally, the entire “dirty” sector is erased and

automatic a lly re-formatted.

8 DMS (Data Management Software) Technology Background

System code may call this function dire ctly if it determine s that it is in an idle s tate and would

like to take care of the Cleanup and garbage collection process. This reduces the possibility of

the user waiting for this cleanup to occur before data is written, causing an unacceptable delay.

Read

The Read operation reads the contents of a specific cell and stores the data in the user buff er.

The cell number is used to index the Global Cell Table. DMS tr aces through that entry in the

Table, node by node, and will output the data into the user buffer block by block, until the

entire cell has been read.

IsBusy

IsBusy checks to see if the flash device i s currently performing an operation. This is

accomplished through the standard method of polling the DQ7 - Data Polling bit.

Shutdown

Shutdown deallocates static memory used by DMS. It should be called when shutting off the

DMS functionality.

TECHNOLOGY BACKGROUND

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