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From: warwick@cs.uq.oz.au (Warwick Allison)
Newsgroups: comp.sys.atari.st,comp.sys.atari.st.tech
Subject: Re: Help with timerA [disassembling play.prg]
Keywords: digitzed samples
Message-ID: <1180@uqcspe.cs.uq.oz.au>
Date: 6 May 91 04:03:34 GMT
References: <TSAKOGIA.91May1154459@r6.uk.ac.man.cs> <1147@uqcspe.cs.uq.oz.au> <1991May3.173853.15078@wam.umd.edu>
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I wrote:

>>Check out what TimerB, C and D do, check Internals (though from memory
>>there was a bug in that part :-( ), or grab play.arc from atari.archive
>>and look for the interrupt code that writes to the Yamaha chip.

I'd like to appologise to Dave for seeming to suggest anyone use his code.
I meant only to indicate a place to see interrupt code.  I was talking
about the couple of lines of hand waving the systems requires - you have
to reset interrupt pending flags or something.  The last thing I would
suggest is for someone to grab Dave's code verbatim - or grab anyone's.
Nobody learns anything by just copying code.

Now, to write a Timer A interrupt:

Use the XBIOS function Xbtimer to set the vector to your handler.
Your handler should:
	1. Save and restore ANY registers it uses.
	2. Before you exit, clear bit 5 of $fffffa0f, the Interrupt in-service
		bit for timer A.
	3. Exit using RTE

That, I think, is the bare essentials.  Dave would nodoubt do exactly that.
So would any other program used Timer A.

Warwick.
--
  _-_|\       warwick@cs.uq.oz.au
 /     *  <-- Computer Science Department,
 \_.-._/      University of Queensland,
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