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AML-IMAGE-FORMAT.md

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Amlogic Image Firmware (Amlogic Upgrade Package) Format

The firmware file consists of a header and an array of elements (descriptors) that describe the files stored in the firmware. The byte order is Little Endian.

Header Description

Offset Size (bytes) Description
0x0000 4 crc - checksum of the entire firmware image, excluding the first 4 bytes
0x0004 4 version - currently only two versions are known, so version can contain 0 or 1
0x0008 4 magic - contains 0x27B51956
0x000c 8 size - size of the firmware image
0x0014 4 item align - possibly the alignment between file descriptors
0x0018 4 number of items - number of files in the firmware
0x001c 36 reserved

The crc can be calculated in Python as follows:

from zlib import crc32

data = open('aml_image.img', 'rb').read()
crc = crc32(data[4:]) ^ 0xffffffff
print(hex(crc))

File Descriptor

The file descriptor varies depending on the version. For version 1, it looks like this:

Offset1 Size (bytes) Description
0x0000 4 id - file identifier
0x0004 4 file type - type of file
0x0008 8 offset - the purpose of this field is unclear. It is typically set to 0
0x0010 8 offset in image - absolute offset in the firmware image to the start of the file
0x0018 8 size - size of the file
0x0020 32 main type - taken from the packing configuration file
0x0040 32 sub type - taken from the packing configuration file
0x0060 4 verify - indicates whether the checksum needs to be checked after burning
0x0064 2 is backup
0x0066 2 backup id
0x0068 24 reserved

For version 2:

Offset1 Size (bytes) Description
0x0000 4 id - file identifier
0x0004 4 file type - type of file
0x0008 8 offset - the purpose of this field is unclear. It is typically set to 0
0x0010 8 offset in image - absolute offset in the firmware image to the start of the file
0x0018 8 size - size of the file
0x0020 256 main type - taken from the packing configuration file
0x0120 256 sub type - taken from the packing configuration file
0x0220 4 verify - indicates whether the checksum needs to be checked after burning
0x0224 2 is backup
0x0226 2 backup id
0x0228 24 reserved

For version 2, the sizes for main type and sub type have been increased from 32 bytes to 256 bytes.

Currently known file type:

Name Value
normal 0x000
sparse 0x0fe
ubi 0x1fe
ubifs 0x2fe

Currently known main type:

  • USB - files (bootloader) for writing to memory
  • PARTITION - firmware file
  • dtb - device-tree file
  • VERIFY - checksum file. sub type indicates which file it belongs to
  • conf - configuration file for SoC (platform.conf)

Footnotes

  1. Offset relative to the header. To get the absolute offset, add the header size (64 bytes) to Offset. ↩ ↩2