Path: utzoo!attcan!uunet!cadnetix.COM!cadnetix!pem
From: pem@cadnetix.COM (Paul Meyer)
Newsgroups: comp.sys.mac.programmer
Subject: Checking Serial drivers for pending chars
Message-ID: <10346@cadnetix.COM>
Date: 20 Nov 89 23:09:18 GMT
Sender: news@cadnetix.COM
Reply-To: pem@cadnetix.COM (Paul Meyer)
Organization: Cadnetix Corp.,  Boulder, CO
Lines: 42

[]
	I'm writing a "door" for Red Ryder Host, and am trying to implement
the RRH "hot menus" feature.  The idea is that while a menu is printing
out a keystroke (a command from the menu) will interrupt the printout and
immediately do the command.  (This can save a lot of time on slow connections.)

	I'm not using the CommToolbox (yet), because I'm not sure how well
I can interface it to RRH which doesn't use it either.  (I'm also as leery
of the configuration by script options as some of the other posters have
been.)

	The easiest thing would be to check if there is pending stuff in
the serial driver's buffer.  A couple of calls in IM looked like they *might*
give this info, but both looked more likely not to (please pardon any
misremembered call names; I don't have my IM at work):
	SerGetBufSize? returns the size of the serial buffer.  I suspect this
is the size it was allocated (default or by the set-buffer call), not the
amount in use or amount left.
	SerGetStatus has bits for pending reads and writes, but I suspect this
is for whether any incomplete asynchronous calls are running.

	Failing a simple way to do this, my next thought would be to always
have a 1-byte asynchronous call going, and use the completion routine to
add the incoming characters to the buffer I keep locally-generated keystrokes
in.  The problem is that a technote says that major switches will not happen
while File Manager asynchronous calls are pending; PBRead is a File Manager
call, not a Device Manager one.  It would be unacceptable to have a BBS-
related application not backgroundable.

	I also looked for a PBRead call that would return with an error
if no characters were available; this didn't seem to be there either.

	I know this can be done; if nothing else, RRH does it.  (I hope
SW didn't write his own serial driver!)  Could somebody tell me a way to
do this, or even a DTS-blessed way?

Thanks in advance, etc.

Paul Meyer                      pem@cadnetix.COM
Daisy/Cadnetix Inc. (DAZIX)	{uunet,boulder}!cadnetix!pem
5775 Flatirons Pkwy.            GEnie P.MEYER   CI$ 73627,1274
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