PCI-ISA bridges and ISAPNP

["Andy Green" <andy.green@oxsemi.com>]

Regarding PCI on Wintel PCs:-

To place ISAPNP cards into configuration mode, the OS writes a stream of
bytes to I/O port 279h.
Therefore the PCI-ISA bridge must respond to that location, even though it's
a write-only port for ISAPNP.

However I expect the resource should really be available for devices since
no 'real' device is present at 279h.

Does having ISAPNP therefore preclude the use of I/O location 279 for PCI
devices? This gives us a problem since legacy software expects parallel
ports to sit at 278h (and 378h is usually taken by the port on the
mainboard). Our device doesn't work at 278, and the logic analyser trace
shows a bus contention!

Has anyone else seen this? Could any BIOS guys tell me what to expect?

--
Andy Green

Design Engineer
Oxford Semiconductor Ltd