On Wed, 9 Feb 2000, Alan Cox wrote:
> > any device interrupt can be turned into an NMI interrupt - of course
> > special handlers have to be written, and careful coding is needed as no
> > other kernel facilities can be relied on.
>
> Tell me more. I have two immediate obvious uses if you can steer an ISA irq
> to NMI or generate fast timer interrupts that way
>
> 1. Z85230 sync cards at > 64Kbit without DMA
> 2. PC speaker driver
you need a system equipped with an IO-APIC (either SMP system, or UP
system with IOAPIC). Then any IRQ source (or more) can be marked to be
delivered to the NMI pin - sorting out which IRQ is which is a different
matter. If only one IRQ is redirected to NMI then it's not a problem. A
redirected IRQ is dedicated to be NMI, so it will not show up in the
do_IRQ() path.
so it's a special case, and for the 'generic ISA box' case it's not
possible without extra hardware. (but the extra hardware to generate
periodic NMI interrupts is not expensive at all)
-- mingo
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