Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!hao!hull
From: hull@hao.UUCP (Howard Hull)
Newsgroups: net.micro.amiga
Subject: Mechanics of dropping DTR
Message-ID: <257@hao.UUCP>
Date: Wed, 15-Oct-86 14:32:23 EDT
Article-I.D.: hao.257
Posted: Wed Oct 15 14:32:23 1986
Date-Received: Wed, 15-Oct-86 20:43:19 EDT
References: <305@pttesac.UUCP>
Organization: High Altitude Obs./NCAR, Boulder CO
Lines: 33
Summary: tally of device open calls affects dropping DTR

In article <305@pttesac.UUCP>, vanam@pttesac.UUCP (Marnix van Ammers) writes:
>                    ... according to Wecker, the [VT100] program does
> *not* leave DTR on.  So now I've found that this thing that I thought
> was a feature, actually only happens under certain circumstances.  I'm
> trying to isolate just when I get this feature.  For some reason I
> could not get the feature to work at all last night (DTR kept going off
> when I quit the program) but I swear, the night before it was working
> just as I've said: DTR remained on...

Ah ha... I had the same sensation of inconsistency about Wecker's VT100 and
the behavior of DTR dependent interfaces.  I finally discovered that what I
had done was to invoke another terminal program which doesn't reset DTR,
quit that, and then fire up VT100.  I read somewhere that the serial device
keeps a cumulative count of the number of devices that have requested use
of the port.  Those that open the device properly increment the count, and
those that close the device properly decrement the count.  If you have a
program that fails to close properly when it quits, then the device count
is already at least one when VT100 starts up.  Thus when VT100 quits, the
count remains greater than zero and DTR remains asserted.

However two things remain a mystery to me.  The first is that I wonder why
I can't blast the count to zero by repeatedly hitting the "hang up" menu
option in the VT100 program.  The second is the matter of the meaning of
"Exclusive Use" of the port.  It seems to me that if a program requests
exclusive use of the port, and the count is already up by one, then the
AmigaDOS response had ought to be to return an error for the dev Open call.
I really have no idea what it does do, as I haven't yet had a chance to
look at it.  But as I say, I am beginning to wonder...

						                Howard Hull
[If yet unproven concepts are outlawed in the range of discussion...
                   ...Then only the deranged will discuss yet unproven concepts]
	{ucbvax!hplabs | decvax!noao | mcvax!seismo | ihnp4!seismo} !hao!hull