On Sunday 28 July 2002 15.54, you wrote:
> >The way you'd do this is to link the capture and playback streams of
> >the device you use with snd_pcm_link(). They will start together and
>
> we still haven't established the timing for this. its possible that
> its not fast enough for the two streams to be started within
> <<1sample, particularly if and when 192kHz h/w appears. it might even
> be problematic with 96kHz operation. i would be suprised if this was
> true, but it needs to be measured and checked.
I've looked through some driver code, and if I understand it correctly,
it seems like some drivers, for example the ens1370, check in the
trigger function the substream is linked with other substreams on the
card, and if so, it makes sure to start/stop them at the same time, by
writing all the relevant bits to the control register at once, like
this:
snd_pcm_substream_t *s = substream;
do {
if (s == ensoniq->playback1_substream) {
what |= ES_DAC1_EN;
snd_pcm_trigger_done(s, substream);
} else if (s == ensoniq->playback2_substream) {
what |= ES_DAC2_EN;
snd_pcm_trigger_done(s, substream);
} else if (s == ensoniq->capture_substream) {
what |= ES_ADC_EN;
snd_pcm_trigger_done(s, substream);
}
s = s->link_next;
} while (s != substream);
spin_lock(&ensoniq->reg_lock);
if (cmd == SNDRV_PCM_TRIGGER_START)
ensoniq->ctrl |= what;
else
ensoniq->ctrl &= ~what;
outl(ensoniq->ctrl, ES_REG(ensoniq, CONTROL));
spin_unlock(&ensoniq->reg_lock);
So my particular problem should be solved on this card at least, am I
right? However, if the problem includes access to several different
cards, there could be a problem of course.
By the way, I tried to search for the same code in rme9652.c, and found
something similar, but it does not seem to activate both capture and
playback with a single write to the control register. I'm not sure how
the hardware works (nor the driver) though so I may be wrong. I would
very much like to know if linked playback/capture start will be
synchronised, since I will use Hammerfall cards in my particular
application.
/Anders Torger
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