From: alane AT wozzle DOT linet DOT org
Subject: com handler for djgpp
To: imageek!saturn.SDSU.Edu!akrause (Alan Krause)
Date: Fri, 20 Aug 1993 17:41:36 -0500 (EDT)
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu

> 
> Subject: Async libraries.. 
> 
>   D J, I was wondering if the aeasync library would be easily modifiable for use
> of the COM3 and COM4 ports??  Is it difficult to program code for COM3 and COM4
> due to the shared interrupts with COM1 and COM2??  I know next to nothing about
> programming the RS-232 on the IBM, but I always notice that most libraries only
> support COM1 and COM2.

Hello, 'AE' here. :)

I'm not actively supporting any of the things that I wrote for DJGPP, as
I now run Linux at home (great OS!). But, I can guide you a bit.

1. The COM1 handler has to also handle COM3. The same is true for 2 and 4.

2. Make two sets of buffers, etc, rather than one. First set is for COMn,
second for COMn+2.

3. Check which UART generated the interrupt, load the address of the 
appropriate shared space, and then jump to common code to handle it.

4. The C interface to read things has to be similarly modified.

I don't really think any of this should be terribly difficult. Good luck.

If you do modify it, please mail me a copy as that handler is just as
good for real mode C programs as for djgpp, and I'd like to keep a
current copy. Thanks.

-- 
J. Alan Eldridge (alane AT wozzle DOT linet DOT org)