Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!CIS.OHIO-STATE.EDU!james_kent
From: james_kent@CIS.OHIO-STATE.EDU
Newsgroups: comp.sys.mac.programmer
Subject: MIDI Manager/Think C/A5 Register
Message-ID: <9004121500.AA00697@canoe.cis.ohio-state.edu>
Date: 12 Apr 90 15:36:36 GMT
Sender: james_kent@tut.cis.ohio-state.edu
Lines: 29



I've been trying to use MIDI manager with Think C and have come across the
following problem (at least as I understand it).

MIDI manager uses interrupt routines to perform some types of tasks.  When
the interrupt routine is called, the A5 register does not necessarily contain
the application's A5 value.  A5 is used to point to an application's global
variables.  

I need a method of doing the following, using Think C :

1) save the application's A5 value somewhere when the application starts
        (Location X)
2) when the interrupt routine is called, save the current A5 value (Location Y)
    and move the value from Location X into A5
3) when the interrupt routine completes, move the value from Location Y back
    into A5 before returning

The problem is Location X can not be a global variable, since the interrupt
routine cannot access the global variables until A5 has been properly set.

I'd appreciate any code and/or comments about my understanding of this
problem.  Any pointers to Apple guidelines for methods of doing such
a thing would also be appreciated.

thanks
Jim Kent
(kent@cis.ohio-state.edu)