Firmware Format
Firmware can be divided into a single .img file and a .fls file composed of multiple .img files:
.img file is the smallest burning unit, and a .img file can be burned to a certain address in flash.
.fls is a complete firmware package composed of multiple .img files, and the order of .img files is not required.
.img File Format
An image is composed of three parts: Header, Body, and Digital Signature (as shown in the figure).
Image Header
The W800 Image Header contains information such as the magic number, image attributes, image start address, image length, image header location, image upgrade address, image CRC check, image decryption information, digital signature, and compression information.
Description of Each Image Header Field
Field |
Description |
magic_no |
Magic number, fixed value 0xA0FFFF9F |
img_attr |
Image attribute type, IMAGE Attribute |
img_addr |
Image running position in flash |
img_len |
Length of the image area in bytes |
img_header_addr |
Position of the IMAGE header in flash |
upgrade_img_addr |
Upgrade area address, storage location of the upgrade IMAGE header in flash |
org_checksum |
CRC32 result of the image body |
upd_no |
Upgrade version number, larger value indicates a newer version; when the version number is 0xFFFFFFFF, any version of firmware can be upgraded |
ver |
Image version number, string |
next |
Position of the next image header in flash (optional) |
hd_checksum |
CRC32 value of the above fields in the image header |
Image Attribute
Field |
Bit |
Description |
img_type |
4 |
0x0: SECBOOT; 0x1: User Image; 0xE: test program; other values: user-defined |
code_encrypt |
1 |
0: Firmware stored in plaintext; 1: Firmware stored encrypted by the customer |
pricey_sel |
3 |
The chip has 8 sets of built-in RSA private keys for decrypting the encrypted firmware key, users can choose any set to use, the range is 0~7 |
signature |
1 |
0: IMAGE does not contain a signature; 1: IMAGE contains a 128-byte signature |
zip_type |
1 |
0: Not compressed; 1: image area is compressed: currently only GZIP is supported |
reserved |
1 |
Reserved |
erase_block_en |
1 |
0: Does not support 64KB block erase; 1: Supports block erase |
erase_always |
1 |
0: Check if the flash is all F before sector or block erase, sectors or blocks that are all F are not erased; 1: Always erase before writing |
Image Body
Encrypted |
Compressed |
Image Body Content |
Purpose |
X |
X |
Original image content |
SECBOOT, User Image |
X |
√ |
Compressed original image content |
User Image |
√ |
X |
Encrypted original image content + encryption information |
SECBOOT |
√ |
√ |
Compressed and encrypted original image content + encryption information |
User Image |
Digital Signature
If the signature attribute in the image header is set, it means that the firmware contains a digital signature.
The digital signature is for the file composed of the image header and image body.
.fls File Format
The SOC distinguishes the current burning location based on the header.