vetz wrote on 2026-07-29, 07:31:

EDIT: Figured it out, its due to 4.x using LH4 compression.

Ohhh, so it's LH4! I don't think I tried that one when I was looking into this a while back. I assumed it had to do with the sliding window size or other compression param since the decoding had no problems, but due to lack of time I didn't get around to try the different compression methods. Thanks!!!

vetz wrote on 2026-07-28, 23:13:

TheMobRules wrote on 2026-07-28, 22:55:

vetz wrote on 2026-07-28, 16:38:

Funny you mention WinBIOS 5.x. I've been experimenting with it on my own before these tools surfaced. I can decompress and recompile it.

How did you manage to re-compress the BIOS blocks? I remember figuring out that it used some variant of the LZH format, with simplified/minimal headers... I was able to decompress them in a similar way to what AMIDECO does, but when using a tool like LHA to compress them again (even if I didn't tamper with them) the resulting BIOS would always hang up during the POST decompression phase.

Correct, its LHA (LH5 to be precise). It needs a little customization for it to repackage again, AMI's own 8-byte length header and correct offset. I haven't tested a repacked BIOS on real hardware yet, but it decodes byte-exact. I can share the python script if you want it.

Please do!

BurnedPinguin wrote on 2026-08-01, 12:02:

vetz wrote on 2026-07-28, 23:13:

TheMobRules wrote on 2026-07-28, 22:55:

How did you manage to re-compress the BIOS blocks? I remember figuring out that it used some variant of the LZH format, with simplified/minimal headers... I was able to decompress them in a similar way to what AMIDECO does, but when using a tool like LHA to compress them again (even if I didn't tamper with them) the resulting BIOS would always hang up during the POST decompression phase.

Correct, its LHA (LH5 to be precise). It needs a little customization for it to repackage again, AMI's own 8-byte length header and correct offset. I haven't tested a repacked BIOS on real hardware yet, but it decodes byte-exact. I can share the python script if you want it.

Please do!

I'll do once I've confirmed the rebuilt BIOS actually boots in my M921. I hope to do that tonight. I see little point in releasing something here if it's not been confirmed working on real hardware.