README.md
1KBC1126 firmware tools
2======================
3
4Many HP laptops use 8051-based SMSC KBC1098/KBC1126 as embedded
5controller. Two blobs can be found in the HP firmware images. The
6`kbc1126_ec_dump` and `kbc1126_ec_insert` tools are used to dump the
7two blobs from the factory firmware and insert them to the firmware
8image.
9
10
11Firmware format
12---------------
13
14We can easily find the BIOS region of the HP laptop firmware from the
15HP firmware update tool, which can be downloaded from the HP
16website. Now I take HP Elitebook 8470p as an example. This laptop has
17a 16MB flash chip, the last 5MB of which is the BIOS region.
18
19I use [radare2](https://radare.org) to analyze the firmware. Open the
20firmware image, and we can see 8 bytes at `$s-0x100` (`$s` means the
21image size).
22
23 [0x00000000]> x @ $s-0x100
24 - offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF
25 0x00ffff00 fff7 0008 f700 08ff 0000 0000 0000 0000 ................
26
27X86 machines map the firmware at the end of the memory address
28space. These 8 bytes tell the address of the two blobs, which we call
29FW1 (uses bytes 0-3) and FW2 (uses bytes 4-7).
30
31Let's look at FW1. The first two bytes mean the address of FW1 is
320xfff700 (these two bytes use big endian), i.e. `$s-0x900`. Byte 2 and
333 are just complements of byte 1 and 2 (in this case,
340x0008=0xffff-0xfff7).
35
36 [0x00000000]> x @ $s-0x900
37 - offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF
38 0x00fff700 fc07 c13e 02ff 1000 0000 0000 0000 0000 ...>............
39
40Both FW1 and FW2 use the same format: the first two bytes is payload
41length, then a two-byte checksum, then the payload. The payload length
42and checksum are both in little endian. The checksum is
43[SYSV checksum](https://en.wikipedia.org/wiki/SYSV_checksum).
44
45
46How to use the tools
47--------------------
48
49`kbc1126_ec_dump` is used to dump FW1 and FW2. Run `kbc1126_ec_dump
50bios.rom`, then bios.rom.fw1 and bios.rom.fw2 are generated in the
51working directory.
52
53`kbc1126_ec_insert` will overwrite a firmware image by inserting FW1
54and FW2 in it. Please run it for its usage. You need to specify the
55offsets for FW1 and FW2. Using negative offset is recommended, which
56means the distance to the end of the image. For example, if we want to
57insert FW1 and FW2 at `$s-0x900` and `$s-0x90000` as the hp/8470p
58factory firmware to coreboot.rom, you can run `kbc1126_ec_insert
59coreboot.rom bios.rom.fw1 bios.rom.fw2 -0x900 -0x90000`.
60