On 29 Jun 1997, somebody wrote:
> You can also end auto-initialized mode by reprogrammering the DSP for
> single-cycle mode. The card then switches from A/I mode to S/C mode after the
> next interrupt. It will then continue to play or record for the length
> specified, generate an interrupt and stop.

I've never tried this method myself, but it it listed in the Creative
Labs SDK, so I'm assuming it will work if done correctly.  I usually
just fill the rest of the last buffer with silence and let it run out.
 
> First a question, what do you mean with "reprogrammering"? The
> SoundBlaster seems to ignore the command "start single cycle" ($B0) mode,
> if one have not given command "stop at end" ($D9) AND waited till stop.
> (Sorry for my bad english). "The card then switches from A/I ... ", do
> you mean the card itself, or my interrupt-routine? After the last A/I
> interrupt (if i've give stop command earlier) i could use a normal single
> cycle mode to play the rest of data, but as you know it makes a click to
> reprogram the card "on the fly". Can the SB16 card itself switch from a/i
> to single-cycle mode on the interrupt after i programmed it? How?..

I've never really thought about how to do it.  Here's what the SDK says:
  There are two ways to terminate auto-initialize DMA mode transfer:
    1.	Program the DSP to switch to single-cycle DMA mode transfer.  At
	the end of the current block transfer, the DSP will exit from the
	auto-initialize DMA mode and continue to transfer using the 
	specified single-ylce DMA mode.
    2.	Send the exit auto-initialize command; the DSP will exit
	auto-initialize DMA mode and the end of the current block
	and terminate the transfer.

What I get from this is that, since you know ahead of time when you
will run out of data, you can program the sound card for single-cycle
two blocks ahead of time.  When you load the final block of data (this
should be happening as the next-to-last block of data begins to play), 
you reprogram it for single-cycle.  It finishes playing the next-to-last
block with a/i, then switches to s/c to play the last block.  The DMA
controller remains in a/i mode, but that doesn't matter, since the sound
card isn't asking for samples any more.

> Or, is the best method to always stop at end of block and fill the rest
> with silence? I don't mean if the user press escape and i use the PAUSE
> command, but i mean if i'm at the ens of the soundfile etc.. 

I think this is the best way to do it.  If you're using auto-initialized
DMA, it's likely that you have a pretty small buffer, probably lasting
only 1/10, 1/100 second, or less.  The main use for the switch to s/c
method, as I see it, is to reduce long delays of you try to play a sound
of size n*64k+5 with a DMA buffer of 64k.  Then, instead of waiting for
64k-5 samples of silence to play, you can get it to stop immediately.
When there are only a few hundred or thousand samples of silence to play,
it isn't a problem.

    Ethan Brodsky

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<A HREF="http://www.pobox.com/~ebrodsky/"> Ethan Brodsky </A>