Greetings. I have been struggling with this problem in a Lab of PCs for a very long time… 4+ years if im being honest… Finally with my tail between my legs I am here to ask for help after failing to figure this out myself. I do hope this is where I am to post.
I Extracted the BIOS from an ASUS P5G41C-M-LX Motherboard and injected the CPU microcode for lga775 Xeon cpus using mmtool. I then flashed the bios and all was successful. so far so good… It detected the XEON and booted to Windows.
Then I made the error of using the very same modded bios to flash the remaining lab PCS.
and no… I did not back up the BIOS for each PC… Derp!
Since then It has been a hassle imaging these devices from pxe. I spoof the MAC in windows so that these PCs are at least useable… but, you know its still not ideal.
I revisit this issue from time to time scouring the forums trying to find how I can correct my mistake but I fail every time and have to move on to other things.
If I could please get some guidance I would be grateful.
Thank you for your attention lfb6. Attached is a RAR file containing a ROM dump from the BIOS chip using a CH341A periperal and an image of the PXE boot screen showing the MAC and GUID. P5G41C-M-LX-ASUS-0702_MOD.rar (5.8 MB)
Afaik Realtek adapters do have a one time writable memory for storing the MAC, see f.ex. here:
For a short look of the functions watch from ca. 10:50 I assume the MAC and UUID stored in the efuse is still the same. Be careful rewriting it, it’s just around some 100 or 200 bytes, every time rewriting a MAC costs you 17 bytes(?) and if all bytes are written there’s no option for further changes.
A little unclear to me which way you want to go, but I’m not very knowledgeable with these old non- UEFI bioses, so that’s what I can come with.
First off I would like to express my gratitude to you lfb6.
Secondly I would like to express my embarassment… I never once considered searching the actual rom instead I extracted sections and searched them for hours… the solution was so simple.
I have completed the entire lab by reading each chip using the programmer and modifying the 4 entries as shown by lfb6 and writing back to the chip.
Thank you lfb6 for your guidance and effort to help me.
