I already posted much of this information at
http://forum.giga-byte.co.uk/index.php/topic,4157.0.html but didn't get a reply after a few days.
I'm using a GA-P67A-UD3 rev 1.1, updated to the most recent release BIOS, F6.
The system is not overclocked and otherwise very stable.
When I insert a Kworld PI610 DVB-T & 1394 card, the system goes into a similar boot loop to that previously described. The system never comes up with the BIOS screen, but seems to power down after about 10 seconds or so, then tries to power up again, repeat forever.
When I insert a gerneric 1394 card, or other PCI cards without a bridge, the system boots fine.
These cards also work fine in an old Dell Optiplex 755 which is based around the IntelQ35/ICH9, but I don't want to use that anymore.
I'm sure that this isn't a PSU problem as I have two video cards installed, one PCIeX16 and the other PCIeX4. If I remove one of the video cards, the system still won't boot.
So, some more detail about the cards...
The working 1394 card is 3v3 and the main component is a TI TSB12LV23 chip, which is compliant with the PCI 2.2 specification.
The card which upsets the P67A-UD3 is also 3v3 and has a PLX PCI6140 PCI-PCI bridge chip. On the far side, there is a TSB43AB22A (PCI 2.2) and an NXP SAA7131E (PCI 2.2).
I believe that the GeForce 9400 and 8400 (mentioned in topic 4157) are basically PCIe based GPUs and that the PCI versions of these cards use a PCI-PCIe bridge.
My best guess as to what is happening is that the BIOS isn't expecting to see another PCI-PCI bridge, so can't allocate space for the BARs in the devices on the far side and just gives up.
I'd like some confirmation that the BIOS has a soft limit on the depth/span of bridges that results from this configuration. I'd really, really like a BIOS update which would fix this.
Thanks,
Julian