Message-ID: <03a701c2ccf6$5ccd6160$0600000a@broadpark.no>
From: "Gisle Vanem" <giva AT bgnett DOT no>
To: <djgpp AT delorie DOT com>
References: <b1qcar$16070j$1 AT ID-83062 DOT news DOT dfncis DOT de>
Subject: Re: Determining interrupt vector for serial port
Date: Wed, 5 Feb 2003 10:10:00 +0100
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Reply-To: djgpp AT delorie DOT com

"John Henderson" <jhenRemoveThis AT bigpond DOT com> said:

> But I've been unable to discover how to "read" the associated IRQ
> value for each port.  So far I've found them hardcoded as 4, 3,
> 4, 3 respectively in all examples.  But I've got to look no
> further than my own PC to find COM3 using IRQ5 (on an ISA card).
> How does a program discover this?

Only way I know is to 
1. mask off all interrupts in the PIC (to prevent false positives)
2. clear the in-service bits
3. issue an UART command that raises it's IRQ line (e.g. an internal 
  loopback test)
4. poll all in-service bits in the PIC
5. and finally restore the PIC mask.

A lot of work to automate. A IMHO nicer approach would be to
use an environment variable so the user can override default assumptions.
E.g. COM1_SETTINGS=irq 5, base 0x3f8

Gisle V.