RE: PCI-ISA bridges and ISAPNP

[Dan Mick <Dan.Mick@West.Sun.COM>]

> However, it seems that the PCI bridge responds to address 279h for writes
> and reads (on some mainboards), which obviously causes a conflict.
> Since PCI tends not to have two devices at the same location, one responding
> to reads and one responding to writes, does this basically mean that I can't
> use location 279h?

Ah, I see the point.  If the PCI-ISA bridge *and* your PCI device
both respond, that could be bad.

But I thought that "subtractive decode" on the PCI-ISA bridge was
supposed to stop this...namely, if your PCI device responds before
the PCI-ISA bridge does, then the PCI-ISA bridge will not decode the
cycle, write, read, whatever.

On the other hand, if your PCI device is responding to writes to port
279, then it's probably behaving wrongly; you should not decode those
cycles, and then the subtractive decode in the PCI-ISA bridge should
claim the write.