A few questions about EFI (BIOS)

[PhilipC]

I've been reading up on flashing the bios and seem to be getting conflicting information if someone could clear this up it would really be appreciated.

If you got a machine in without a bios chip is it possible to get one from a donor board?
I read stuff like you have to get the ME region from the old chip etc. Then I also read stuff about "clean" ME regions.
Does a clean ME region mean it will adopt whatever the ME of the machine is? if so how is "cleaning" the ME region work.

Some people were talking about changing the serial in the donor chips to match the machine serial. And they were replacing it with "SystemSerial" then flashing a new serial with serializer.
Can't you just put in the new serial instead of putting "SystemSerial"?

It seems like to flash a bios chip it is recommended to take them off the board, but most of the videos i see use clamps while the chips are on the board.

Why is it important to keep the old bios chip's data when putting a new chip on.

I've also seen people say "you'll need to clean this bios file before using it" what does that mean?

Also seen "this bios is locked so only good for testing"

Some "guides" say to install a new OSX after messing with the bios or entering single-user mode, are these required?

I saw somewhere that hosted a load of bios files which you just had to replace the serial number, what about the ME region?



Maybe a sticky with this info would also be helpful to new members

 

[dukefawks]

You cannot use a chip from another board because of ME region. You need to use a clean ME if the original one was lost as it "mates" itself to the PCH on the very first boot.

I usually don't change the serial, it breaks the "override" file and gives an ASD error. Replacing serial with SystenSerial and using the serializer tool doesn't work as far as I know.

Take chips off the board, don't risk corruption by having the board mess with the data lines.

You MUST backup the old to save your ME region and serial number override file.

There are lots of BIOSes out there which already have a "clean" ME and can be used as-is, optional is to change the serial.

 

[PhilipC]

So you can use a chip from a donor board as long as you program it with a "clean" ME region bin file? Are the chips interchangeable between models? as long as pinout and package is the same?

Is it right that the clean ME regions are specific to each board so even though it is clean you can still only use it for the specified board

So an "unclean" bios just means that it has already been paired to a board, and that's why you would have to copy it from the original chip?

what repercussions does the "override" file being broken have? as I have seen videos of people doing it and looks to be working

And finally why MUST you backup the ME region if you can just use a clean ME region,


Thanks for taking the time to answer my questions

 

[dukefawks]

Don't swap chips between board models unless they have the same part number.

ME is specific to each board model.

Unclean BIOS cannot be used on another board unless you swap over the PCH from the donor too.

Override file corruption gives ASD error. No idea what further issues it may cause that is why I don't mess with it. Manually editing the serial # does show it correct in OSX but as said the override file will checksum fail.

Why would you not backup the old BIOS and risk messing something up? Clean ME is just adding another risk.

 

[PhilipC]

So to sum it all up

Desolder chip from boards for reading/writing

Backup BIOS and modify if possible else use clean ME region BIOS file for that board

Changing serial is a no no


Thank you, I feel I have enough knowledge now.

 

[dukefawks]

There is usually no need to even touch these chips. Only time I need to do anything to them is when someone fucked with it prior or after swapping the PCH. When swapping a PCH I try to take them from a donor that has BIOS chip on it so I can pull the ME region from there.