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SubjectRe: Sharing IRQs between the first 4 serial ports.
Date
Followup to:  <Pine.LNX.3.95.971124082000.4448A-100000@chaos>
By author: "Richard B. Johnson" <root@chaos.analogic.com>
In newsgroup: linux.dev.kernel
> > A de facto standard for internal modems seems to be:
> >
> > COM1 4
> > COM2 3
> > COM3 5
> > COM4 2
> >
> > That is: no IRQ sharing.
> >
> [SNIPPED]
>
> No, No, No. This is __very__ broken!
>
> IRQ2 is the cascade from the first interrupt controller to the
> second interrupt controller. The "wire" doesn't even exist on any
> bus. It is a connection, sometimes internal, between the two
> interrupt controllers.
>

... which is why when people say IRQ 2 they really mean IRQ 9. The
ISA bus line labelled IRQ 2 is connected to IRQ 9. Linux knows about
this.

There is no way to connect anything to the "real" IRQ 2, so you can
calm down.

-hpa
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