*BSD News Article 22930


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From: vandys@cisco.com (Andrew Valencia)
Newsgroups: comp.os.386bsd.questions
Subject: Re: The reason for stray interrupts
Date: 27 Oct 93 18:10:53 GMT
Organization: cisco Systems
Lines: 16
Message-ID: <vandys.751745453@cisco.com>
References: <2ais9gINN2t8@xs4all.hacktic.nl> <2alpnh$1cm@werple.apana.org.au>
NNTP-Posting-Host: glare.cisco.com

>ptuomola@hacktic.nl (Petri Tuomola) writes:

>>Many people have been asking why their machines display "ISA strayintr 7"
>>messages. This is an extract from /sys/arch/i386/isa/isa.c:

Sigh.

I seem to post this every month or so.

The problem is the way interrupts are cleared from the two chained
PIC's.  If you disable the chained IRQ to the second PIC, or if you
use auto-EIO mode, or if you use selective EOI to finish a pending
interrupt, it doesn't happen.  The simplistic code which shotguns
the two PICs in a row unconditionally is at fault.

					Andy