Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!asuvax!stjhmc!p12.f56.n114.z1.fidonet.org!Chris.Gehlker
From: Chris.Gehlker@p12.f56.n114.z1.fidonet.org (Chris Gehlker)
Newsgroups: comp.sys.mac.programmer
Subject: RE: Problems installing interrupt handler (INIT part 2)
Message-ID: <30417.27493A91@stjhmc.fidonet.org>
Date: 20 Nov 90 14:14:31 GMT
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In a message
> From: nugteren@pttrnl.nl

Nils Nugteren asks:

> I have written an interrupt handler in Think C, that catches incoming 
> characters from the serial port and manipulates these in the background 
> (i.e. invisible to the user). It works fine as an application, but I
> am having troubles installing it in the background (memory resident etc.).
> I'm new to MacIntosh programming so I would appreciate any help greatly.

Nils, my serial drivers patch themselves into the level 2 dispand reprogram the SCC completely.  What you are trying to do is somewhat
different so take these suggestions with a grain of salt.

> Also, the program must be combined with an INIT somehow, because it has to
> startup and install itself in the background in startup time. Should I 
convert
> the whole program to an INIT or create a loader INIT that loads the code in
> separately ?

Use an INIT that loads the driver and then calls DetachResource() on it
so that the driver won't get purged by the INIT31 mechanism.  The part
of the INIT that does the ShowIcon stuff can go away. Also set the
SysHeap and Locked bits in the driver.

> The program uses global variables (but not QuickDraw).
> I gather this may be somewhat of a problem in an INIT. Or does Think C take
> care of this problem by using register A4 to address globals ?

Using A4 works for me.

> The program should stay resident indefinitely and not be reinitialised.
> Do I have to load it into the system heap? How do I do this with Think C ?

For some reason THINK C gives you a pop-up menu to set the resource bits
for code resources but not for drivers. What I do is compile my cdev to
disk. Then I compile the INIT that opens the driver and merge like it
into the cdev.  Then I compile my driver into a file of type rsrc with
creator RSED. When I double click this file it launches ResEdit and I have
the ResEdit menu customized to open my cdev-INIT from the Open Special
Menu.  I set both the DRVR and the DATA resources to SysHeap and Locked
and paste them into the INIT-cdev.  Then I just shove the DRVR-INIT-cdev
file into the system folder and reboot.

 

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