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From: alain@atr-la.atr.co.jp (Alain de Cheveigne)
Newsgroups: comp.sys.mac.programmer
Subject: Opening the serial driver.
Message-ID: <3903@atr-la.atr.co.jp>
Date: 31 Dec 89 07:06:27 GMT
Organization: ATR International,Japan
Lines: 63



I'm updating some code according to TN 249 to use OpenDriver() instead
of RamSDOpen().  I hope in this way to detect when some other terminal
program has opened the line, to avoid opening twice.  The code I use is:

	/* MPW C 3.0 */
	/* test to see if another program owns the serial port */
	short refnum = aoutRefNum;
	result = opendriver("AOut",&refnum);
	if (result == portInUse) {		/* port already open */
		dont_close_serial = true;	/* no need to close on exit */
		return;
	} 

	[test for portNotCf]

	if (result != noErr) {
		errMsg("result: %d", result);	/* say what's wrong */
		error = true;
		return;
	}

	[code to open "AIn"]

The result of opendriver() is always -43, which corresponds to fnfErr
in Errors.h of CInterfaces.  I don't know what that means.  I tried
installing the SERD resources in the program file, with no success.

Questions:

1) What am I doing wrong?

2) If I get OpenDriver() to work, should I still use SerSetBuf(),
SerHShake(), SerReset(), etc., or are they also superseded?

3) If I don't get it to work, is there any objection to keeping with
RamSDOpen()?  

I think Tim Maroney suggested some time back that one can test whether
the port is open with a status call, and open only if that call fails.

4) If the port is already open, I don't need to open, and I don't
close on exit.  I expect other programs to act the same.  What happens
if I opened first, then the other program starts, then I quit.  Is
there anyway of knowing if the other program still needs the port?

5) My program works fine over serial lines.  I'd like it to work over
ethernet, and maybe AppleTalk.  Is there any chance that someone will
come out with a piece of software that will emulate a serial port over
ethernet or AppleTalk?  It would open a window, establish a connection
to a host and let me log in, and from then on the serial port (A or B)
would be redirected through this channel.  I wouldn't need to modify
my code.  

Is this in the CTB?  If so, is there something I should do to be
compatible?  Or shall I really have to modify my code?

Thanks for any help.  If I get good e-mail, I'll summarize.


Alain de Cheveigne,
alain@atr-la.atr.co.jp