From owner-freebsd-hardware  Fri Jun 27 02:58:48 1997
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To: Stefan Esser <se@freebsd.org>
cc: Jon Inouye <jinouye@cse.ogi.edu>, freebsd-hardware@freebsd.org
Subject: Re: IRQ assignment for PII motherboards 
In-reply-to: Your message of "Fri, 27 Jun 1997 11:40:22 +0200."
             <19970627114022.32725@mi.uni-koeln.de> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Fri, 27 Jun 1997 02:59:46 -0700
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>On Jun 26, David Greenman <dg@root.com> wrote:
>>    I was able to get the Pro/100B, in a system with a pair of ahc3940's, to
>> get assigned to a non-shared interrupt by playing around with which slots
>> the cards were plugged into. It took about 3 tries to find the right order
>> (including leaving a slot empty), but I finally found an arrangement that
>> worked. My understanding is that the shared irq assignment isn't a function
>> of the BIOS, but rather a function of the slot the card is in and how it
>> is wired compared to the others. The motherboard I did this in wasn't made
>> by Intel, but the same principles should still apply.
>
>Interrupts should not be shared, unless at least one PCI card 
>in the system either:
>
>1) contains a PCI to PCI bridge, or
>2) contains a multi-function PCI chip.

   Yes, the aha3940's are dual-channel SCSI adapters and have a bridge chip on
each card to connect the two SCSI chips. This seems to make the determination
of which interrupts will be shared on how they are shared very difficult or
impossible. Is there a scheme to the sharing when bridge chips are involved?

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project