Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!apple!stevec
From: stevec@Apple.COM (Steve Christensen)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Using parameter blocks in ASM
Message-ID: <47129@apple.Apple.COM>
Date: 5 Dec 90 22:46:41 GMT
References: <0bLHodC00WBL42hVc=@andrew.cmu.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 30

gd1a+@andrew.cmu.edu (Glen M. Devries) writes:
>How does one set up a parameter block in assembly. I need a pointer to
>the block and then need to set up the contents. Where can it be? Must it
>be in the application heap or can it be in the system heap?

You can put the parameter block in a heap block as long as the block is locked
for the duration of a call.  A more common way is to allocate the space in a
stack frame, or if this is an application you're talking about, in the app's
global variable space (A5 relative).  For example, if you're talking about
a Device Manager parameter block, you could do something like this:

DoSomething	LINK	A6,#-ioQElSize		; put pb on the stack
		MOVEA.L	SP,A0			;  and point to it
		...				; do whatever with it
		UNLK	A6			; clean up the stack
		RTS

Obviously if you make an asynchronous call, you can't exit the routine until
the call completes, so in that case it would be better to allocate it on the
heap or in global space (apps only)...

steve

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