VisualDSP++ 4.5 Loader and Utilities Manual - Analog Devices

Loader for ADSP-2126x/2136x/2137x SHARC Processors
The kernel code with the decompression engine is on the top of the loader
file. This section is loaded into the processor first and is executed first
when a boot process starts. Once the kernel code is executed, the rest of
the stream is brought into the processor. The kernel code calls the decompression
routine to perform the decompression operation on the stream,
and then loads the decompressed stream into the processor’s memory in
the same manner a conventional kernel does when it encounters a compressed
stream.
Figure 5-6 shows the structure of a compressed boot stream.
COMPRESSED BLOCK HEADER
COMPRESSED STREAM
Figure 5-6. Compressed Block
Compressed Block Headers
A compressed stream always has a header, followed by the payload compressed
stream.
The compressed block header is comprised of three 32-bit words. The
structure of a compressed block header is shows in Figure 5-7.
0X00002000 COMPRESSION TAG/FLAG
0XWBIT0PAD WINDOW SIZE/PADDED WORD COUNT
0XBYTEBYTE COMPRESSED BYTE COUNT
Figure 5-7. Compressed Block Header
The first 32-bit word of the compressed block header holds the compression
flag, 0x00002000, which indicates that it is a compressed block
header.
VisualDSP++ 4.5 Loader and Utilities Manual 5-37