Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!cs.utexas.edu!uunet!ccavax!lmrc!hassinger
From: hassinger@lmrc.uucp (Bob Hassinger)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Problems with serial device in shared mode
Message-ID: <851@lmrc.uucp>
Date: 23 Oct 89 13:43:03 GMT
References: <1989Oct19.163629.9047@dvinci.usask.ca>
Distribution: na
Organization: Liberty Mutual Research Center, Hopkinton, MA
Lines: 50

In article <1989Oct19.163629.9047@dvinci.usask.ca>, aries@skorpio.usask.ca (Aries Project) writes:
> I am having trouble with what seems to be a bug in the serial device.  What
> I am doing is opening up the serial device a second time in shared mode while
> someone is online.  I'm almost positive I am doing things correctly (only
> one incarnation of the device is active at a time).  The problem is that about
> 1/10 times, dtr is dropped when the serial device is opened the second time.
> I can get around this by forcing dtr, but I don't want to.
> 
> This is not just a problem with my software.  Every program that I have tried
> that uses the serial device in shared mode does the same this.
> 
> Any solutions??
> 
> 		-Mike Oliphant

I have been looking for information on the general subject of the shared mode
for the serial device.  I have been unable to find anything about it so far and
hardly anyone seems to know it even exists.  Some exposition on exactly how it
works and interacts would be greatly appreciated.

My particular problem is that I need to come up with a small program that I can
use to issue commands from the keyboard out the serial port to make a
connection (via a DECserver 200) to a printer.  After the connection is made I
need to hold the modem control signals so the connection is not broken while I
run a program such as Pro Page and do output to the printer, then additional
commands need to be sent to the port to break the connection to the printer.
Powering off the Amiga should break the connection too by dropping the modem
control signals (DTR I think).

Since I have not found a way to do this yet, my current work around is to
program the DECserver to ignore the modem control signals on the Amiga port. 
However, that means that if the user forgets to go back and issue the commands
to release the printer then even when the Amiga is turned off the printer
remains connected to the Amiga port and other users (two VAXs worth in this
case) can not get access to it.

There are several questions here such as what can be expected of programs like
Pro Page with respect to sharing of the serial port in this way and what
options does the shared mode offer in situations like this?  Do all programs
sharing the port have to open it in shared mode or could my little program open
it shared first and then another one like Pro Page open it without being
required to specify the shared option.

Oh, and BTW - anyone know of a suitable program (i.e. not a big full functioned
terminal emulator, just a lean and mean keyboard to port and port to screen
tool with sharing or some other way of controlling the modem control signals)?

Bob Hassinger
508-435-9061
UUCP:  ...uunet!ccavax!lmrc!hassinger