This page describes how to use coreboot on the GIGABYTE GA-MA785GMT-UD2H mainboard.
This board exists in 4 versions: v1.0, v1.1, v1.3 and v3.3.
This documentation applies to v1.1. If you have a different version of the board, YMMV.
This board has a dual BIOS chip. Both chips are 8Mbit; the main BIOS is called M_BIOS, the backup BIOS is called B_BIOS. GIGABYTE claims the backup BIOS can not be flashed by the user. It contains code that will overwrite M_BIOS if it determines that M_BIOS is corrupted.
The M_BIOS chip is a Macronix MX25L8005.
If you flash coreboot into M_BIOS and something goes wrong, you can force B_BIOS to boot and reflash M_BIOS by bridging pins 4 (GND) and 7 (#HOLD) on the M_BIOS chip, powering up the machine, and then releasing your bridge after a few seconds. The B_BIOS will take over at that point — you will hear a beep, and see the B_BIOS boot and forcibly re-flash M_BIOS.