0x00ffff00 fff7 0008 f700 08ff 0000 0000 0000 0000 ................
X86 machines map the firmware at the end of the memory address space. These 8 bytes tell the address of the two blobs, which we call FW1 (uses bytes 0-3) and FW2 (uses bytes 4-7).
Let's look at FW1. The first two bytes mean the address of FW1 is 0xfff700 (these two bytes use big endian), i.e.
$s-0x900. Byte 2 and 3 are just complements of byte 1 and 2 (in this case, 0x0008=0xffff-0xfff7).
[0x00000000]> x @ $s-0x900
Both FW1 and FW2 use the same format: the first two bytes is payload length, then a two-byte checksum, then the payload. The payload length and checksum are both in little endian. The checksum is SYSV checksum.
kbc1126_ec_dump is used to dump FW1 and FW2. Run
kbc1126_ec_dump bios.rom, then bios.rom.fw1 and bios.rom.fw2 are generated in the working directory.
kbc1126_ec_insert will overwrite a firmware image by inserting FW1 and FW2 in it. Please run it for its usage. You need to specify the offsets for FW1 and FW2. Using negative offset is recommended, which means the distance to the end of the image. For example, if we want to insert FW1 and FW2 at
$s-0x90000 as the hp/8470p factory firmware to coreboot.rom, you can run
kbc1126_ec_insert coreboot.rom bios.rom.fw1 bios.rom.fw2 -0x900 -0x90000.