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From: adrie@philica.ica.philips.nl (Adrie Koolen)
Newsgroups: comp.os.minix
Subject: Re: >>Dumb Questions -- IBM Minix
Message-ID: <719@philica.ica.philips.nl>
Date: 7 Dec 90 14:05:43 GMT
References: <3719@rwthinf.UUCP>
Reply-To: adrie@beitel.ica.philips.nl (Adrie Koolen)
Organization: Philips TDS, Innovation Centre Aachen
Lines: 18

In article <3719@rwthinf.UUCP> u31b3hs@cip-s01.informatik.rwth-aachen.de (Michael Haardt) writes:
>It is not difficult to modify the serial card for shared interrupts if it
>uses open collector drivers.

I'm no PC expert, but the PC uses edge-triggered interrupts, so you can only
benefit from open collector drivers (and thus interrupt sharing) when using
level-sensitive interrupts. You can program the 8259a PIC for that. If you
don't reprogram the PIC for level sensitivity, it will still work, but you'll
probably lose interrupts!

BTW, long time ago, I ported Minix 1.2 to the IBM PS/2 Model 60. The driver
I wrote for the 3 RS232c channels, still suffered from lost interrupts when
getting much send and receive interrupts at the same time. The design of the
8250 is such that you can't (or at least it's very hard to) design a driver
that is *guaranteed* not to lose interrupts!

Adrie Koolen (adrie@ica.philips.nl)
Philips Innovation Centre Aachen