Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!ucselx!crash!pnet01!jca
From: jca@pnet01.cts.com (John C. Archambeau)
Newsgroups: comp.os.minix
Subject: Re: Dumb Questions -- IBM Minix
Message-ID: <6113@crash.cts.com>
Date: 6 Dec 90 06:49:54 GMT
Sender: root@crash.cts.com
Organization: People-Net [pnet01], El Cajon CA
Lines: 45

ghelmer@dsuvax.uucp (Guy Helmer) writes:
>Not really.  There aren't enough interrupt request lines available
>in a PC to let COM3 and COM4 have their own interrupts, so they
>have to share interrupts with COM1 and COM2.  It would be quite
>a challenge to change the rs232 driver to handle shared interrupt
>lines, and the additional interrupt service overhead would eat
>up even more CPU cycles than it does now :-(

Not really.  You could set up the RS-232 driver to follow the COM1-COM4
conventions of the PS/2.  They are as follows:

          Base
Name     Address    IRQ
-----------------------
COM1      0x3f8      4
COM2      0x2f8      3
COM3      0x3e8      5
COM4      0x2e8      2

The only problem with that is you have to steal IRQ 5 from one of your
parallel ports (if you have more than one) and give it to COM3.  If you have a
bus mouse or 8-bit networking adaptor, that usually uses IRQ 2, so you'll have
to steal IRQ 2 from that device.
 
>It would be a much better idea to get a smart multi-port rs232 adapter
>card and try to either 1) find a driver for it or 2) write a driver
>if you really want to support four or five users.
>hour's time.

Or modify the FAS driver to work under Minix.  I don't know if it will perform
as well giving you the 38.4K baud with hardware handshaking under Minix. 
Anyone who has an AST 4 Port AT/Plus may want to try it.  The driver as is
works with that board so minimal modification would have to be done to
get it to work under Minix.

     // JCA

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