problem on APIC with PCI

["Han Woo Jong" <wjhan@pear.etri.re.kr>]

Hi all,

We are building a quad-PPro board including PCI bus i/f on board.
This design includes APIC,i82379 , to interface the interrupt bus of PPro
and
PCI arbitration.  The ISA i/f function of it is not utilized in this
design.
OPB(S82494) is used to interfcae PCI.

The problem is the APIC responds all IO cycles generated by PPro.
When there is no PCI device on board, it works fine.  When there is
a PCI device such as SCSI i/f card, PPro can not access the card through
IO cycle since APIC considers as it is his cycle, of course not in fact.
For the SCSI card we are using is accessbile via memory cycle also.
So when PPro uses the memory cycle for SCSI i/f, it works fine.

Now, it is quite strange to me.
I believe the APIC is designed to be used with PCI bus, reminding it has
PCI arbitor. Then, is it recommended for all PCI cards to be accessed
via memory cycle, not IO cycle ?
I could not find such recommendation in any part of PCI spec.
Naturally, OS engineers do not want to change their driver in OS to
utilize memory cycle rather than IO cycle, since they can not be sure
all PCI cards can be accessed via memory cycle and it is natural to be
accessed via IO cycle more.

Is it possibly a problem of OPB, 82494 ?

Does anyone know about this problem ?
Any information or reference shall be greatly appreciated.

Thanks in advance.

Woo-Jong Hahn
(wjhan@com.etri.re.kr)
Processor Section, ETRI.


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