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i need to know how to write (and read) eeprom from most popular motherboards. (ami and award/phoenix)
im most interested in reads, but i guess its simmilar.
i understand i need to use some sequence of magic pio requests, right?

i dont want to access shadowed rom, only real rom.



- how much will cost me cheapest eeprom programmer (so i can recover from error while testing my new bios).

Reading is always the same, just read the area from FFFx0000 - FFFFFFFF depending on the size of the ROM. Often, unmapped addresses will just read as FF.

As for writing, it's probably not documented, so you'll have to disassemble the updating program to find out.

But, writing a new PC BIOS is just as demanding as it sounds. You should be very familiar with how the chipset works. And remember that the startup code can't use memory until the memory controller has been configured, and in the BIOSes I've looked at, there are very many steps that take place beforehand. This, of course means, that everything must be stored in registers, including return addresses for subroutine calls.

EEPROM programmers can cost as low as 45 dollars, depending on how advanced they are.

The memory mapped region isn't always the complete contents of the ROM/Flash, either.

The flashrom program from the coreboot project is probably the single most collective resource for reading and writing BIOS firmware.. it's very chipset/vendor specific, doing it all in one tool is even more complicated.

You can find more information on their website.