Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!uunet!mcvax!kth!draken!tut!santra!jmunkki
From: jmunkki@santra.UUCP (Juri Munkki)
Newsgroups: comp.sys.mac.programmer
Subject: Having Fun? [Re: Standard File and Desk Accessories]
Keywords: Globals, Party, Enough!
Message-ID: <22694@santra.UUCP>
Date: 9 Jun 89 11:30:51 GMT
References: <4972@umd5.umd.edu> <2026@husc6.harvard.edu>
Organization: Helsinki University of Technology, Finland
Lines: 94

siegel@endor.harvard.edu (Rich Siegel) writes:
> earleh@eleazar.dartmouth.edu (Earle R. Horton) writes:
> >     This looks like fun!
> 	It IS fun.
I have to agree.

> 	For example, suppose you have an INIT and a cdev that need to
> share information with one another? How do you propose to have them
> communicate? Remember, there's no low memory you can use, and there's
> no place to place a base register. Well, you could put a block in the
> system heap with your unique signature in it, and crawl the system
> heap for it, BUT that (a) won't work when the format of heap blocks
> changes, and (b) won't work when the system heap becomes protected.

That's the technique that is described in the QuicKeys manual. I've
also used it on one occasion, but I know of a better way to do it.
There's only one problem with the better way and it's that it isn't
always possible (and it doesn't work with old systems).

The solution is to use AppleTalk. If you Mac isn't connected to a
network, this doesn't work, but in my case I was writing a program
that already required an AppleTalk network. My INIT registered itself
with name binding protocol and it also had it's own DDP socket listener.
My cdev could have set the selfsend flag, found any entity of the correct
type on the local node and sent a ddp packet to this socket. After this
the two programs can communicate by sharing memory.

There are some problems with writing socket listeners under multifinder
or using them from INITs. While writing a VBL task to control the sound
driver, I came up with a pretty good solution that works just as well
for socket listeners. The solution is LSC specific, since it uses the
inline assembler. Here are some code fragments to get you started:

/*		Note: VVars is just any structure you need
>>	If A5 points to a VVars structure, the following macro will become
>>	xx(A5), where xx is the offset into that structure element.
*/
#define VBV(field)	((int) &((VVars *) 0)->field)(A5)

VVars	Vv;	/*  Vertical blanking variables				*/

/*
>>	Setup vertical blanking variables &
>>	install vertical blanking task.
*/
void	InstallMyVBL()
{
	long	vbltask;
	
	asm	{
		lea	@myvbltask,A0	;Get address of vbltask
		move.l	A0,vbltask	;Store in local variable
		lea	@mybase,A0	;Get addr of variable base storage
		lea	Vv,A1		;Get addr of Vv record
		move.l	A1,(A0)		;Store base in base storage
		}
	
	Vv.VBL.qType=vType;		/*  Vertical blanking queue.	*/
	Vv.VBL.vblAddr=(ProcPtr)vbltask;/*  Address of task		*/
	Vv.VBL.vblCount=1;		/*  Every 1/60 seconds		*/
	Vv.VBL.vblPhase=0;		/*  0 is ok..			*/
	VInstall(&Vv.VBL);		/*  Install task in queue	*/
	if(0)				/*  Skip the following :-)	*/
asm	{	
@myvbltask
		move.l	A5,-(SP)		;Save A5
		move.l	@mybase,A5		;Get Vv address into A5
		move.w	#1,VBV(VBL.vblCount)	;Call again in 1/60 seconds

	[ Some code deleted... 
		Vv structure elements are accessed as:
		sub.w	#1,VBV(CountB)	;Decrement channel B count
		In C you would have written Vv.CountB
	]

@endvbl
		move.l	(SP)+,A5	;Restore A5
		rts			;Return from vbl routine
@mybase
		dc.l	0		;Vv record address stored here.
	}
}

To install the VBL task, you call this routine and to control what it does
you just change its variables. (Remember that this is "multitasking" so that
you have to use some sort of locking to prevent the vbl task from seeing
changes that aren't complete.)


-- 
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|     Juri Munkki jmunkki@hut.fi  jmunkki@fingate.bitnet        I Want   Ne   |
|     Helsinki University of Technology Computing Centre        My Own   XT   |
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