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To: Steve Passe <smp@csn.net>
cc: hackers@freefall.freebsd.org, smp@freefall.freebsd.org
Subject: Re: ed0 timeouts 
In-reply-to: Your message of "Sat, 02 Nov 1996 23:43:56 MST."
             <199611030643.XAA25052@clem.systemsix.com> 
From: David Greenman <dg@Root.COM>
Reply-To: dg@Root.COM
Date: Sun, 03 Nov 1996 00:43:51 -0800
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>Question:
>
>Is it possible for a new INT to be asserted by the if_ed driver WHILE
>it is currently being serviced by the edintr() routine?
>
>What I have discovered is that unlike the 8259, the IO APIC will ignore
>(ie NOT delivered or held pending) an edge level INT if it currently is
>masked.  The routine in vector.s masks the INT, calls edintr(), then after
>edintr() returns it unmasks the INT.  If another INT fired as a result
>of ed_start() being called in edintr() BEFORE the INT was unmasked it
>would be LOST.

   Yes, you can get another interrupt while servicing one. The driver loops
until all interrupts are serviced, but there would be a window between when it
thinks there are no more interrupts to service and returning to vector.s to
unmask the interrupts. This window will exist in all ISA drivers.

-DG

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