A wild guess would be some kind of addressing clash between RAM and PCI. I
don't know where PCI address space lives on the 80321, but maybe they didn't
plan for 1GB RAM. Or maybe there's a limit to where PCI devices can DMA
from.
The address map should be in the Iyonix/Tungsten TRM. I thought a copy of it
was available on the net but I can't find it now :(
Failing that, the 80321 data sheet might give something.
It might be worth looking through the patches for Iyonix Linux and see if
they do anything like assuming RAM is 512MB or less, like chopping off
addresses at 29 bits in drivers or something.
Theo