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Date: Fri, 3 Sep 1999 08:02:53 -0400 (EDT)
From: "Richard B. Johnson" <root@chaos.analogic.com>
Reply-To: root@chaos.analogic.com
To: Gerard Roudier <groudier@club-internet.fr>
cc: David Schleef <ds@stm.lbl.gov>, Paul Ashton <lk@mailandnews.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.rutgers.edu
Subject: Re: Shared interrupt (lack of) handling
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On Thu, 2 Sep 1999, Gerard Roudier wrote:
[SNIPPED]

> 
> In PCI, INTERRUPT ARE NOT SYNCHRONISATION EVENTS!  Synchronisation
> events are PCI TRANSACTIONS in the context of ordering rules defined by
> the specs,....

This sounds like something written by a lawyer. In plan language, any
hardware interrupt is a hardware request for some software to do
something. The interrupt event, itself, does not convey any
knowledge about the reason why the interrupt occurred. Software has
to inspect the hardware to determine the reason for the interrupt.

With shared interrupts, it is mandatory that the software that handles
an interrupt event (the ISR), not complain if it finds that it got
control and, upon inspecting the hardware, finds there is nothing to
do.

How the PCI controller, raises the maskable interrupt pin on the
CPU make no difference at all. One doesn't care if it's a 'PCI
TRANSACTION' or a 'PYROSYNCHROGEM'. If it happened fast enough so
the event isn't stale, nobody cares --and if the software cares,
it's broken.

> 
> G?rard.
> 


Cheers,
Dick Johnson
                   **** FILE SYSTEM WAS MODIFIED ****
Penguin : Linux version 2.3.13 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.


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