This is how to load a Fcode ROM form the hard disk in Open Firmware, while they still have a PC VBios on them. If you want to test a AGP card, it is best to have a Mac PCI video card, but it can be done without one.
We can only boot OS 9 at this time if the card you are testing is nVidia. I'll update this when I test an ATI card.
With a PCI Video card:
Install the latest drivers for the card you want to test.
Open your ROM in Hexedit and remove the PCI Header, everything to 0x40. We shouldn't have to do this, but Apple screwed around with their Open Firmware implementation, so we have to.
Place the Fcode ROM file you want to test in a folder at the root of your drive, name the folder ppc.
Shut Down.
Put in your Mac PCI card, and your PC AGP card into your Mac. Connect a display to both cards, if you have 2 displays, if not connect you display to the PCI card.
Boot into Open Firmware, Command+Opt+O+F. It may take a few seconds as the Mac probes the APG card, then redirects video to the PCI card.
If all goes well, you will be greeted with the Open Firmware prompt.
Now we want to load the FCode Rom we want to test, for this example I named mine GFM.rom, and my hard drive partition number is 10.
load hd:10,\ppc\GFM.rom
dev agp/@10
800000 1 byte-load
" agp/@10" open-dev to my-self
800000 1 byte-load
boot hd:10,\\:tbxi
If you get no errors, then you should see the screen light up on the AGP card, if you have a display connected to it, and OS 9 should boot.
Enjoy!
I tested it on the Gainwood dual DVI GeForce 4ti 4600 PC Bios card, with a Mac Radeon 9200 PCI. Everything worked 2D/3D and DVD Player.
If things go wrong, and you get no display, ensure your card works in a PC, if it does, you haven't edited the FCode ROM correctly.
I also tried it with the Quadro 900 GXL that MacTron sent me, one with a dead eeprom, however the display stared up out of sync/range, then went dark, and OS 9 never finished booting.
Once we can boot OS X with this, we should be able to flash the cards without the need for a PC at all.
I'll update when I test ATI cards, and PCI Cards, if anyone is interested?