can someone explain...[ PCI interrupts]

John Baldwin jhb at
Thu Dec 8 06:57:04 PST 2005

On Wednesday 07 December 2005 06:11 pm, Darren Pilgrim wrote:
> From: John Baldwin
> > No, PCI interrupts are level triggered.  Individual APIC pins
> > can be programmed to be edge-triggered, sure.  However, then
> > interrupts stop working if 2 devices are sharing a line and
> > one interrupts after the other has already interrupted and
> > after the second device's ISR has already run.  In this case,
> > the ithread will finish and go back to sleep waiting for an
> > interrupt.  However, since the ISR for the second device
> > wasn't run after that device asserted its interrupt pin, the
> > second device will keep the pin pulled low forever, so there
> > will never be a hi -> low transition that the APIC pin would
> > post an interrupt for and that intpin and all attached
> > devices are effectively dead.
> What if the APIC was programmed to be edge-triggered just before the
> ithread runs and programmed back to level-trigger when the ithread
> completes?

I'd rather work on my other solution which might be about 5 lines of code 
rather than screw around with the APICs when that might have other side 

John Baldwin <jhb at>  <><
"Power Users Use the Power to Serve"  =

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