Only for programmers and BIOS gurus with technical questions.
#56027 by nico
Thu Nov 25, 2010 12:48 pm
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#56027 by nico
Thu Nov 25, 2010 12:48 pm
Hi ,

i have a question:

i'm trying to mod the BIOS of an AsRock board.

The model is K7S41GX , bios version 2.80 , link to bios :

http://europe.asrock.com/downloadsite/b ... S41GX(2.80).zip

I'm able to succesfully replace/add modules using AMIBCP75. After modifying i checked the result file with an hex editor and all seems to be OK , modules checksums are OK.
There's only one thing i'm not sure it's ok, comparing the modded bios with the original one i can see in the hex editor that the first 4 bytes in the rom image are different. The original asrock bios has a 4 byte value that seems to be some sort of checksum , while in mod bios , generated with amibcp those bytes are set to 0xFF.

Can someone tell what's the exact meaning of those bytes ? Are thay some sort of checsum ? Are a vendor specific (ASROCK) checksum ?
I tryed all combinations for custom CRC and checksum algorithms but none of them produced the correct value .
I don't have a second board to recover bios if something goes wrong so i want to be 100% of what those bytes means .
Can they be a sort of checsum calculated at runtime then the bios is executed ?

Thanks .
Nico.