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From: tell@oscar.cs.unc.edu (Stephen Tell)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: AREXX Question: Reading ser: port
Message-ID: <3397@borg.cs.unc.edu>
Date: 23 Apr 91 20:30:22 GMT
References: <17683@venera.isi.edu>
Sender: news@cs.unc.edu
Organization: University of North Carolina, Chapel Hill
Lines: 50

In article <17683@venera.isi.edu> schur@venera.isi.edu (Sean Schur) writes:
>I am trying to use AREXX to control a Lyon-Lamb Minivas. This is a single
>frame recorder controller for single framing images to videotape. The
>MiniVas has a standard RS232 port. It accepts standard ASCII characters
>for control.


>		The problem I am having with this
>(and it is probably AREXX ignorance) is that after sending a character
>with "writech" I am using "readch,1" to look for a single character.
>The program isn't receiving one and the script completely freezes, I can't
>get out of it at all without rebooting. 

>So, how do I tell AREXX to TRY to read a character, if it doesn't get
>one within a specified length of time, to return control of the program
>to me so I can type another character. It would also be desirable to
>have the script echo the character to me immediately as opposed to 
>writing it into a file to look at later.

The problem is with the SER: handler; it just isn't designed for this
"give me a character if there is one, or else time out" sort of operation.

I have had good luck writing quick & dirty serial applications from C
by opening up UUSER:, a driver that comes with the AmigaUUCP package.

I use open(), and then when I try to read() a single character the read times
out with an error if there is no character to read after the timeout specified
in the open string (somthing like "UUSER:serial.device/1/R500/C0/G0" for 500
millisecond timeout).  This should work with Arexx if it handles errors from
the AmigaDos I/O routines reasonably and lets you read and write from the same
filehandle.  From C, its easier to use the lower level I/O functions, like
open() or Open() as opposed to dealing with stdio and fopen(), which don't do
bidirectional I/O quite as gracefully.  I have Arexx, but haven't used it
enough to comment on it directly.

UUSER: is designed to run under the getty program also in the UUCP package,
but it seems to work fine by itself.

>Sean Schur		    			USENET: schur@isi.edu	
>Assistant Director Amiga/Media Lab		Compuserve: 70731,1102	
>Character Animation Department			Plink: OSS259	
>California Institute of the Arts

Steve

-- 
Steve Tell       tell@cs.unc.edu    H: +1 919 968 1792   #5L Estes Park apts
CS Grad Student, UNC Chapel Hill.   W: +1 919 962 1845   Carrboro NC 27510
Duke Blue Devils:  1991 NCAA Basketball National Champions! We're Number 1 !!
UNLV 90-91 record:  "34 and DUKE."