Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!hp4nl!phigate!ehviea!leo
From: leo@ehviea.ine.philips.nl (Leo de Wit)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Using Timer A to replay a sample
Message-ID: <891@ehviea.ine.philips.nl>
Date: 26 Sep 90 11:40:56 GMT
References: <1990Sep24.122920.15704@irscscm.UUCP>
Reply-To: leo@ehviea.UUCP (Leo de Wit)
Organization: Philips I&E Eindhoven
Lines: 51

In article <1990Sep24.122920.15704@irscscm.UUCP> mlake@irscscm.UUCP (Marshall Lake) writes:
|
|I have a programming problem and I'm hoping someone here can help me.
|
|I am attempting to play back a sample via timer A while allowing other
|things to go on as it plays.  When the program attempts to start the
|actual playback it blows, sometimes displaying 4 bombs and sometimes
|6.  I have also tried to place the interrupt code into the main flow
|of the program to see what would happen.  The bombs don't occur but
|nothing is emitted by the sound chip either.  What am I doing wrong?
[...]
|do_snd () {
|    if (buff_cnt > buff_end)
|        return;
|
|    snd_value = (*buff_cnt + 128) * 8;*/
|    *sound_chip = snd_out[snd_value];
|    *sound_chip = snd_out[snd_value + 4];
|
|    buff_cnt++;
|}

[...]
|main () {
[...]
|    Xbtimer (0, 7, 0, &do_snd);
[...]
|}

Your do_snd routine must be coded as an interrupt routine; that is, it
must end in a rte instruction; not only that, it must also mark
(clear?) a bit in the I/O range (sorry, have to look this up),
otherwise the system will think the interrupt is still pending
(actually, I think the peripheral chip is thinking this 8-). For an
example, take a peek into the ROMs to see how the system timer (timer
C) is coded (the I/O address I mentioned is different, but you'll get
the picture).

Alternatively, you can do it the easy way, forget about programming it
yourself and use the Xbios function Dosound() (but I assume there is a
special reason you cannot use this?).

And if you experience spurious interrupts using Xbtimer(), I got a
solution for this too (8-).

Cheers,
        Leo.

P.S. The 4 bombs (illegal instruction) confirm that a wild jump was
taken; this is because your code pops a return address off the stack
where there is a status word and a return address.