On Tue, 12 Jan 1999, Christoph Badura wrote:

> tomja@InnoTrac.fi (Tom Javen) writes:
> 
> >But e.g. a multi port serial card could have 8 16550s connected to the
> >same IRQ, so preventing shared irqs would not be a good idea.
> 
> But all the multi port serial cards with "interrupt sharing" I have seen
> do *not* share ISA bus IRQs.  They all have glue logic that feeds
> the individual UARTs IRQ lines to a single ISA IRQ.
The one I looked at few years ago had two modes , shared irq and separate
irq. I believe the shared irq is just a logical-or of the separate irqs.
> 
> Also, the 8250A and up UARTs can't produce real edge triggered interrupts.
> They generate level triggered interrupts and the PC interrupt controller
> triggers on the front edge of the IRQ signal being asserted.

Does it matter ? The interrupt handler has to check all devices which may
interrupt anyway.
Is there a race condition which is avoided using a edge triggered
interrupt ?


Tom
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