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Date: Fri, 5 Apr 1996 13:46:05 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199604050346.NAA15285@godzilla.zeta.org.au>
To: nate@sri.MT.net, rgrimes@GndRsh.aac.dev.com
Subject: Re: tty-level buffer overflows - what to do?
Cc: current@FreeBSD.org, jgreco@brasil.moneng.mei.com, root@deadline.snafu.de
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>> This is a pretty good indication that something is mis-confugred.  IRQ 7
>> is the 'junk' interrupt, which means it gets all of the interrupts not
>> otherwise assigned to a particular piece of hardware.  Something is
>> generating interrupts on your system bogusly and you need to find out
>> what.

>This is not quite correct, IRQ 7 is signal when someone asserts an IRQ singal
>then removes that signal _before_ the CPU runs the interrupt acknowledge
>cycle to the 8259 PIC.

This is not quite correct :-).  IRQ7 is signaled when an IRQ signal is
removed _during_ the interrupt acknowledge cycle for that IRQ.  It isn't
signaled if the cycle never begins.

>Often the cause of stray IRQ7's is noisy or floating IRQ signals from boards
>that are not recognized by FreeBSD.

The cause has to be a signal on one of the IRQ lines enabled by FreeBSD
(because masked lines are completely ignored).  The signal can then interfere
with the signal from the enabled board.

Bruce