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Date: Wed, 07 Dec 2005 11:07:28 -0700
From: Scott Long <scottl@samsco.org>
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To: "M. Warner Losh" <imp@bsdimp.com>
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Cc: darren.pilgrim@bitfreak.org, current@freebsd.org
Subject: Re: can someone explain...[ PCI interrupts]
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M. Warner Losh wrote:

> In message: <018e01c5fafe$c9154a20$642a15ac@smiley>
>             "Darren Pilgrim" <darren.pilgrim@bitfreak.org> writes:
> : From: John Baldwin
> : > 
> : > The reason [for masking interrupts] is that PCI interrupts are level
> : > triggered, so they won't "shut up" until the ISR has run and pacified
> : > the PCI device.
> : 
> : But PCI interrupts can be programmed either level- or edge-triggered, so
> : wouldn't programming to edge-triggered interrupts solve the "they won't shut
> : up" issue?
> 
> PCI interrupts are level.  There's no way to program them otherwise.
> 
> Warner

While electrically they are level, the APIC can be programmed to pass
them on either level or edge.  Once you get into MSI, the distinction
becomes very muddy.

Scott