On 27/10/16 11:52, Takashi Iwai wrote:
On Wed, 26 Oct 2016 16:30:17 +0200,
Alan Young wrote:
Hi,
When the kernel reports current (playback) delay via a call to
snd_pcm_status() or snd_pcm_delay() for a normal hardware PCM, then
the delay value reported is the sum of space used in the ring buffer
plus any delay reported from the underlying runtime driver.
snd_pcm_dshare_status() and snd_pcm_dshare_delay() discard this
refinement and simply report the use of some ring buffer. Why does it
do this and how could the reporting be improved?
The lack of delay calculation is just for simplicity. We're tracking
the different hw_avail per each d-* PCM, the delay value has to be
re-calculated for each as in the current way. But we may put the
additional delay computed from the slave PCM, indeed.
Why does it have to be re-calculated? Under what circumstances would
"snd_pcm_mmap_playback_delay(pcm)" and "slave_status.avail -
dshare->spcm->buffer_size" (from your patched source) yield different
results?
Basically d*-plugins share the same ring buffer as the underlying
slave PCM hw layer. The d-plugins have the buffers in shared memory
in addition for keeping the 32bit data for clipping.
This is only the case for dmix, right?
But in general
the ring buffer size and the position are same as the hw.
Well, basically the additional delay can be deduced from
delay - buffer_size - avail
(This is applied for playback. For capture, it's slightly different.)
A patch like below *might* work (totally untested!)
Thanks, this does seem to help but is not totally reliable.
I am wondering if the earlier call to snd_pcm_dshare_sync_ptr(pcm),
which I guess forms the basis for the result of
snd_pcm_mmap_playback_delay(pcm), may be operating on a different set of
data (because of an intervening interrupt) to that returned by
snd_pcm_status().
Thanks,
Alan.
thanks,
Takashi
---
diff --git a/src/pcm/pcm_dshare.c b/src/pcm/pcm_dshare.c
index c5b3178a4990..8e21a6ec5fc2 100644
--- a/src/pcm/pcm_dshare.c
+++ b/src/pcm/pcm_dshare.c
@@ -214,6 +214,7 @@ static int snd_pcm_dshare_sync_ptr(snd_pcm_t *pcm)
static int snd_pcm_dshare_status(snd_pcm_t *pcm, snd_pcm_status_t * status)
{
snd_pcm_direct_t *dshare = pcm->private_data;
+ snd_pcm_status_t slave_status;
switch (dshare->state) {
case SNDRV_PCM_STATE_DRAINING:
@@ -225,12 +226,15 @@ static int snd_pcm_dshare_status(snd_pcm_t *pcm, snd_pcm_status_t * status)
}
memset(status, 0, sizeof(*status));
snd_pcm_status(dshare->spcm, status);
+ slave_status = *status;
status->state = snd_pcm_state(dshare->spcm);
status->trigger_tstamp = dshare->trigger_tstamp;
status->avail = snd_pcm_mmap_playback_avail(pcm);
status->avail_max = status->avail > dshare->avail_max ? status->avail : dshare->avail_max;
dshare->avail_max = 0;
status->delay = snd_pcm_mmap_playback_delay(pcm);
+ status->delay += slave_status.delay + slave_status.avail -
+ dshare->spcm->buffer_size;
return 0;
}
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