Bill Studenmund <wrstuden@zembu.com> writes:

> > > > Err... do those isa bi (busses?) share their address space?
> 
> I doubt it. I suspect the BIOS has programmed one of them to bridge a
> specific set of devices and nothing else.

Not that the OS can tell anything about that from the ISA
universe. The only way to sensibly handle this is with a upper-layer
direct bus, and I think ACPI covers this problem.

> Right, but you can really only have one subtractive-decoding bus in a
> system. So one of these two isa busses has to be postitive-addressing
> only.

To be picky, that's a rule for a single PCI bus tree. There wouldn't
be anything wrong with having multiple primary PCI buses, each with
its own independent address space, and each one of those having a
single subtractive bridge. Mutliple-primary-PCI systems certainly
exist.

        - Nathan