Path: utzoo!attcan!uunet!snorkelwacker!apple!han
From: han@Apple.COM (Byron Han, scapegoat)
Newsgroups: comp.sys.mac.programmer
Subject: Re: RAM serial driver and event handling
Message-ID: <10326@goofy.Apple.COM>
Date: 20 Sep 90 22:50:35 GMT
References: <1990Sep20.143626.23475@midway.uchicago.edu>
Organization: Apple Computer, Inc.
Lines: 35

In article <1990Sep20.143626.23475@midway.uchicago.edu> rfl@oddjob.UChicago.EDU () writes:
>
>> As a further note, when opening the serial driver, it is best to check to see
>> if the driver is already open before opening - this prevents one application
>> from "stealing" the serial driver from another under MultiFinder.
>
>How do you mean "steal"? 

Application A opens the serial driver.  User switches to Finder and opens
Application B which also opens the serial driver.  Data is not shared in a
totally nondeterministic manner between the two applications.

>If my application checks to see if the driver is
>already open, what happens if my application changes the baud rate? Or what
>happens if someone clicks to another application in MultiFinder that uses
>the port at another baudrate? How does an application handle things like this?

Appications B (a A for that matter) should check to see if the serial driver
to be opened is already opened or not.  If it is already open, it should
put up an alert saying that the serial port is already in use.  If the  driver
is not open, _PBOpen should then be called.  If _PBOpen returns portInUse,
the application should also post an alert.  This is what the Serial Connection
Tool does.

Oh also, do not assume that the only drivers available are .Ain, .Aout, .BIn,
and .Bout.  If the CommToolbox is installed, perform a lookup of the serial
devices that are installed to get the names of all of the ports and the 
names of the associated input and output drivers (which should all support the
same control calls that the existing .A/B In/Out drivers do.

Hope this helps.

Byron Han
Occasional Wizard
.