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From: moyman@ecn.purdue.edu (James M Moya)
Newsgroups: comp.sys.mac.programmer
Subject: Calling "OpenDriver" from LightSpeed C
Message-ID: <1990Aug17.215833.15273@ecn.purdue.edu>
Date: 17 Aug 90 21:58:33 GMT
Sender: news@ecn.purdue.edu (USENET news)
Organization: Purdue University Engineering Computer Network
Lines: 21

This is interesting.  I wrote a simple Device Driver from LSC that simply does
a SysBeep every 2 seconds.  I select the "Build Device Driver" menu item.
I then attach the resources created to an application that just calls 
"Open Driver".  Here is the interesting part:  If the DRVR resource is
0 then everything works fine, you get a SysBeep every 2 seconds.  If you
use an DRVR ID inside the IM range 0-31 other than zero, the driver starts
up but nothing else (the driver Open routine gets called but nothing else).  
If you use a number > 31 I get a -21 error returned from the OpenDriver call.  
Something seems very wrong.  I figured OpenDriver would select a free unit 
number and assign the refnumber accordingly, it doesn't, It always uses the 
DRVR resource ID whether it's being used or not.

I have looked at several DRVR resource in my system, all use numbers like 63,
124, etc... (>31)???  Am I missing something??  Also, shouldn't the driver
continue to run until I call a CloseDriver?? This isn't the case either, It
only runs until I quit the application that called the OpenDriver...Maybe
this behavior is from running the app within the LSC debugger...Any ideas

Mike Moya
Engineering Computer Network
Purdue University