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From: stevem@hal.CSS.GOV (Steve Masters)
Newsgroups: comp.sys.amiga.tech
Subject: Re: ARexx and the serial port
Message-ID: <454@hal.CSS.GOV>
Date: 2 Sep 90 18:28:57 GMT
References: <33454@cup.portal.com>
Organization: ENSCO Inc., Melbourne FL
Lines: 45

dan-hankins@cup.portal.com (Daniel B Hankins) writes:


>     Can anyone provide advice on how to use ARexx to access the serial port?
>Can Arexx keep up with 2400 baud (on a stock 68K Amiga)?

I have written an Arexx system that access an electronic barometer in real
time across the Amiga serial port.  I hit several stumbling blocks you may
be interested in.   The bigest single problem was the behavior of the READCH
function.  The statement 

	     a=READCH('ser',1)  /* 'ser' was previously opened as SER: */

will hang until a character is received by the serial port.  This caused me
a major headache since my barometer does not always respond to each character
sent...you must often repeat a command two or three times to get a response.
Thus, a ( send command...wait for response) loop  would not work.  What I
needed was a function that  'read a character from an open file, return a
null string (or error indication) if no character is available.'  This behavior
would be similar to the INKEY$ function in BASIC.  I never found such a function.
If one exists (or can be easily duplicated) I would be quite interested.

My solution was to start two processes.  Process A (the main program) sends commands
to the serial port, which it has opened for output.  Process B simply listens
to the serial port, which it has opened for input.  When it receives a character,
it sends the character to process A via the ADDRESS command.  Process A periodically
checks its port via GETPKT(), which will return a null string if nothing has been
sent.  This solution taught me quite a bit about ARexx message passing, but 
was tricky to program without frequently hanging one task or the other.  I would
prefer a more straightforward approach.

Based on my experience, my solution would not keep up with a steady 2400 baud
transmission.  If a more traditional approach would work, I think it MIGHT
work as long as ARexx wasn't having to contend with too many other tasks.

>     I'd heard that Larry Phillips had written a program called SerMod which
>does at least -some- of what I'm looking for.  If so, where can I find it?

I would also be interested in any Rexx/SER: interfacing programs or info.


Steve Masters   stevem@hal.CSS.GOV
ENSCO, Inc.
Melbourne, FL  32940  USA
(407) 254 4122