I was surprised how easy it was to brick my board. These ideas might be useful to somebody:
Before you start messing with PCI & I/O values that might keep their state:
- have a lspci -vvvxxx from the factory BIOS - record as much of the boot process from the factory BIOS as possible
I wanted to collect the bit masks from my factory BIOS, so I modified the filter to return 0x0 and then 0xffffffff for the PCI registers. That way I could see which bits were being changed. After some of the registers were changed, I couldn't boot the board with Coreboot or the factory BIOS. I used SerialICE to set the PCI values to what they were in a saved run of the factory BIOS, and it booted again.