Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!usc!apple!well!cbm
From: cbm@well.sf.ca.us (Chris Muir)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MIDI Manager/Think C/A5 Register
Summary: Look in OSUtil.h
Message-ID: <17249@well.sf.ca.us>
Date: 14 Apr 90 20:28:49 GMT
References: <9004121500.AA00697@canoe.cis.ohio-state.edu>
Reply-To: cbm@well.UUCP (Chris Muir)
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 44

In message <9004121500.AA00697@canoe.cis.ohio-state.edu>,
james_kent@CIS.OHIO-STATE.EDU writes:
>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


This is a little cryptic, but:

/* From OSUtil.h */
/*  access A5 from interrupt level (new way)  */
pascal long SetCurrentA5(void) = { 0x2E8D, 0x2A78, 0x0904 }; 
/* MOVE.L     A5,(A7)   	;2E8D */
/* MOVEA.L    CurrentA5,A5	;2A78 0904  */

pascal long SetA5(long) = { 0x2F4D, 0x0004, 0x2A5F }; 
/* MOVE.L     A5,$0004(A7)	;2F4D 0004 */
/* MOVEA.L    (A7)+,A5		;2A5F */


/* in your MIDI setup routine  */
	myMidiInputParams.refCon = SetCurrentA5();	
        /* stash the real A5 in refcon */


/* in your read hook (which gets passed the refcon) */
 long	oldA5;

	oldA5 = SetA5(myRefCon);			/* set A5 to "my" A5 */
	/* do stuff that needs globals */
	oldA5 = SetA5(oldA5);				/* set A5 to old A5 */



-- 
__________________________________________________________________________
Chris Muir                              |   "There is no language in our
cbm@well.sf.ca.us                       |    lungs to tell the world just
{hplabs,pacbell,ucbvax,apple}!well!cbm  |    how we feel"  - A. Partridge