*BSD News Article 63187


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From: james@raid.us.dell.com (James R. Van Artsdalen)
Newsgroups: comp.unix.bsd.bsdi.misc
Subject: Re: multiple pci cards [shared IRQs]
Date: 10 Mar 1996 00:09:37 -0600
Organization: Dell Computer Corporation
Lines: 23
Message-ID: <4htrn1$otm@raid.us.dell.com>
References: <313E5821.6D78@execpc.com>
Reply-To: james@raid.us.dell.com (James R. Van Artsdalen)
NNTP-Posting-Host: raid.us.dell.com

In <313E5821.6D78@execpc.com>, Craig Hapanovich <chapan@execpc.com> wrote:

> DEC FDDI card unless I remove the other two cards.  BSD tech support
> said the problem is all three cards are using the same interrupt(9)
> and that I should use different interrupts for each card. Does this
> make any sense?  The zenith setup program will not allow me to
> change pci interrupts anyway, so now what?

BSDi Tech Support is confused: PCI devices will often share the
same IRQ, and BSDi _must_ support this.  This is just a basic
part of the PCI spec.  There's really no way for the user to
prevent sharing.

Most BIOSs will try to use different IRQs for different PCI devices.
But if there aren't enough IRQs to go around, then the BIOS will begin
sharing PCI IRQs, potentially putting ever PCI INT on the same IRQ.
(PCI IDE excepted - these are never shared and aren't really PCI anyway)

If nothing else, most multi-channel NICs or SCSI controllers will
use the same IRQ for each device behind the onboard PCI-PCI bridge.
-- 
James R. Van Artsdalen          james@dell.com            "Live Free or Die"
Dell Computer Co    9505 Arboretum Blvd Austin TX 78759-7299    512-728-8789