Analog Devices EE257v01 Application Notes

Engineer-to-Engineer Note EE-257

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Technical notes on using Analog Devices DSPs, processors and development tools

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A Boot Compression/Decompression Algorithm for Blackfin® Processors

Contributed by Bob Nakib Rev 1 – December 9, 2004

Introduction

This application note describes a boot
compression/decompression algorithm for
ADSP-BF533 and ADSP-BF561 Blackfin®
processors.

The code included with this document was
verified using the VisualDSP++® 3.5 tools suite
for Blackfin processors. The project was run on
an EZ-KIT Lite® evaluation system for ADSP­BF533 Blackfin processors (ADDS-BF533­EZLITE, Rev 1.2) and on an EZ-KIT Lite
evaluation system for ADSP-BF561 Blackfin
processors (ADDS-BF561-EZLITE, Rev 1.1).

Purpose

Normally, loader files created by VisualDSP++
are not compressed, except possibly with a
simple run-length compression scheme used on
strings of 0s in the compiled code. For large
projects that must be stored in non-volatile
memory, compression provides significant
savings in hardware, such as on-board flash.
Decompression code can then be executed at
boot time by creating a 2nd-stage loader or
initialization code containing the decompression
algorithm. For more information regarding the
initialization code or any aspect of the booting
process, refer to ADSP-BF533 Blackfin Booting

Process (EE-240)

[1]

.

Boot Compression/Decompression Algorithm

This compression algorithm requires about
50 KB of overhead (extra) memory. Therefore, it
is useful only in applications of a significantly
larger size. The compression/decompression
functions are handled by a simple open-source
compression library called Zlib. For more
information, see

http://www.gzip.org/zlib/.

As an example, a compressed Blink application
is included with this EE-Note for your
convenience. It is suggested that you try the
following steps using the included Blink
application to familiarize yourself with the
compression process, then try programming the
last generated file (CompressedAppIntelHex

with the Flash Programmer to verify

.ldr)

correct functionality. Figure 3 shows the entire
process.

Step 1

You must allocate an unused area of SDRAM
memory in your user-application to store the
uncompressed user-application loader image.
The .LDF file of your user-application project
must be modified to free a section of SDRAM
memory of appropriate size. This region must be
large enough to hold an entire loader build of
your user-application, allowing uncompress() to
deflate to that area in memory.

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The user-application loader image will then be
loaded by the Boot ROM out of SDRAM.

For ADSP-BF561 processors, you must also free
L2 memory addresses 0xFEB1 FC00 through

0xFEB1 FFE7 by keeping them out of any section

in your user-application's

.LDF file. These

addresses are reserved for the 2nd-stage boot
kernel. This is done in the

.LDF file of the

example ADSP-BF561 Blink program.

Step 2

Set the UNCOMPR_ADDR field at the top of the

Init_code.c file (Init folder) to the intended

destination address for the output of the
uncompress function (that is, the starting address
of the reserved section or kept empty in the
SDRAM memory of your user-application in

Step 1). In the given example, this address is set

to 0x4000.

Step 3

Specify the user-application project to be built as
a Loader file (via Load page of Project
Options dialog box) and use SPI/ASCII/8-bit
format. Note that the SPI setting is a workaround
used to generate the output in ASCII format.

For ADSP-BF533 processors, specify the
following path to the initialization project file:

../Init/Debug/Init.dxe. (See Figure 1.)

For ADSP-BF561 processors, select Boot

kernel options
Use boot kernel, and specify the path to the

kernel file as:
under

./debug/p0.dxe.

from the Category list, select

../Init/Debug/p0.dxe. Also,

Additional options, insert:

When executed at the start of the boot process,
this object file initializes SDRAM memory, finds
the compressed user-application code, and
decompresses it to the appropriate area in
SDRAM memory.

Figure 1. Loader Options for ADSP-BF533 Processors

A Boot Compression/Decompression Algorithm for Blackfin® Processors (EE-257) Page 2 of 7

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Step 4

Build the Init code project first, and then build
your user-application. Ensure that the project to
be built is active (highlighted in the Project
window) and that project dependencies are set, if
necessary. This should create an .LDR file in the
Debug directory of your user-application.

Step 5

In the root folder, edit the compress.bat file
(use any text editor) to specify the path of the
target loader file that has just been built from
your user-application, as well as the desired level
of compression (see Table 1 in the Appendix for
compression levels). Note that the entered path
must be enclosed in double-quotes (") and must
use forward-slashes or double-backslashes. An
incorrectly specified path name or compression
level may cause undesirable results.

Step 6

Execute compress.bat (root folder) and ensure
the result of the compression (returned on line 6
of the Output window) is successful by matching

your return code with those listed in Table 2 in
the Appendix.

The Output window (Figure 2) returns important
values calculated during compression, notably:

 Source file size (line 1)
 Source buffer start address (line 2)
 Number of bytes used for the source buffer

(line 3)

 Application start address and number of

bytes used for the Init code buffer (line 4)

 Application size and output buffer start

address (line 5)

 Compression result (0 = success) and

compressed application size (line 6)

 Path of the output file (line 7)

If successful, a file called CompressedApp.ldr
is created in the same directory as your source
loader file (that is, the Debug directory of your
user-application). This ASCII format file
contains both the Init (decompression) code and
your compressed user-application code.

Figure 2. Compression Script Output Window, RESULT = 0 (SUCCESS)

A Boot Compression/Decompression Algorithm for Blackfin® Processors (EE-257) Page 3 of 7