Re: hardware channel mixing [EMU10K1 DMA]

[Jaroslav Kysela <perex@suse.cz>]

On Tue, 7 Sep 2004, Lee Revell wrote:

> On Tue, 2004-09-07 at 04:23, Jaroslav Kysela wrote:
> > On Tue, 7 Sep 2004, Lee Revell wrote:
> > 
> > > The interval timer seems to be intended exactly for this use; I am a bit
> > > baffled as to why was the channel loop interrupt, a relatively obscure
> > > feature, was chosen as the playback interrupt source.
> > 
> > No, in this case you don't get exact interrupt at period boundary.
> > It seems bigger problem (wrapping) than having an extra voice.
> > 
> 
> Hmm.  If this is the case then it really seems like the OSS driver
> should not work at all then.

It works, but with higher latencies than application requested. You can 
probably write a timer scheduler code, but it will be probably 
a maintenance nightmare.

> You mentioned previously that removing the extra voice would only allow
> 2 periods per buffer.  Do you mean that the interval timer could be used

Yes, if we can do proper interrupt in the middle of voice's buffer.

> How did you figure out the use of the channel loop interrupt, as this is
> not used in the OSS driver at all?

I don't remember exactly. Maybe from old EMU8000 (because some things are 
common) and the header file from OSS driver.

> like I can implement the kX ASIO functionality without needing the extra
> voice because the efx capture device provides a very high resolution
> timer.

You can create a special playback PCM which will share efx interrupt, of
course. But I don't know, how you expect to synchronize multiple streams
for exact sample resolution, because you cannot start multiple playback
streams using one i/o transaction for emu10k? chips.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SUSE Labs


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