Firmware format

Structure

Firmware file consists of header and body.

Header

All strings are null-terminated and pure ASCII (unless specified otherwise), string size includes terminating '\0'. Integers are unsigned and little-endian.

4 bytes	magic string 0x4f 0x49 0x46 0x57	–
4 bytes	size of file header (from start of file to end of blocks list)	integer

List of properties:

4 bytes	size of property name	integer
4 bytes	size of property	integer
N bytes	property name	string
N bytes	property value	string

List ends with the property with empty name (0 bytes of length).

List of blocks:

4 bytes	size of block name	integer
8 bytes	block offset from the start of file (required to be 4-bytes aligned)	integer
8 bytes	block size	integer
N bytes	block name	string
M bytes	List of block-specific properties (see above for the format of the properties list)	–

List ends with block with empty name (0 bytes of length)

Body

Body of firmware consists of data, according to the blocks information in header.

Known properties

• device - name of device the firmware is suitable for.
  • Required. Bootloader should not consider firmware file with wrong device property or without this property as a valid update file.
  • Known values:
    • n516 for N516
• hwrev - hardware revision.
  • Optional. Per-device rules apply.
  • Not required for N516.
• description - free-formed description of firmware.
  • Optional. Presentation-only.
• date - firmware build time, unixtime (decimal number).
  • Optional. Presentation-only.
• epoch - "epoch" of firmware, determining the layout and size of blocks.
  • Absence of this property is equal to epoch 0.

Known block-level properties

• crc32 - CRC32 checksum (polynomial used in IEEE 802.3 to be precise)
  • 4-byte little-endian integer for N516 bootloader with epoch 0
  • ASCII string of digits for N516 bootloader with epoch > 0 and for all other bootloaders
• raw - If yes, then block should be flashed to MTD partition. By default blocks are flashed to UBI.
• compression - compression method. The only supported value is gzip. If this property is not present, then block data is assumed to be uncompressed. Supported since epoch 1 of N516 bootloader.

N516 firmware epochs

• 0
  • first firmware revision
• 1
  • added support for compression=gzip on block level
  • crc32 block-level property changed into ASCII string