Re: serial ports

Peter Desnoyers (pjd@midnight.com)
Tue, 6 Aug 1996 10:32:22 -0400 (EDT)

>
>
> > This is not a Linux limitation. It is due to the PC architecture. Some
> > special "inteligent" cards can achieve this by mean of a special driver.
> > Read the Serial-HOWTO, which stands
> >
> > " The number of serial ports you can use is limited by the number of
> > interrupts (IRQ) and port I/O addresses we have to use. This is not a
> > Linux limitation, but a limitation of the PC bus. Each serial devices
> > must be assigned it's own interrupt and address. A serial device can
> > be a serial port, an internal modem, or a multiport serial board.
>
Magnus writes:

> But this is not true. There must be another reason why Linux' serial
> driver doesn't allow multiple ports to use the same IRQ. The serial driver
> could very well ask the serial port if it was the one to generate the
> interrupt. Don't tell me it's impossible, I have done it myself. Just
> check base+2 for a zero in bit 0.

You can write any code you want, but the electric signals on the IRQ
line on your backplane have the last word, and they say that this
solution is going to be unreliable and flaky at best if you share
interrupts between two cards in use simultaneously. Blame it on IBM.

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Peter Desnoyers : Midnight Networks Inc. 200 Fifth Avenue Waltham MA 02154
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