On 4/2/18 3:14 PM, Georg Chini wrote:
On 02.04.2018 21:35, Pierre-Louis Bossart wrote:
On 04/02/2018 07:54 AM, Georg Chini wrote:
The current code does not call snd_pcm_status_set_audio_htstamp_config()
to configure the way timestamps are updated in ALSA. This leads to
incorrect time stamps in the status object returned by snd_pcm_status(),
so the computed latencies are wrong.
This patch uses snd_pcm_status_set_audio_htstamp_config() to set the
ALSA report_delay flag to 1 before the call to snd_pcm_status(). With
this, time stamps are updated as expected.
---
src/modules/alsa/alsa-util.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/src/modules/alsa/alsa-util.c b/src/modules/alsa/alsa-util.c
index 61fb4903..b91a0e98 100644
--- a/src/modules/alsa/alsa-util.c
+++ b/src/modules/alsa/alsa-util.c
@@ -1187,6 +1187,7 @@ int pa_alsa_safe_delay(snd_pcm_t *pcm,
snd_pcm_status_t *status, snd_pcm_sframes
size_t abs_k;
int err;
snd_pcm_sframes_t avail = 0;
+ snd_pcm_audio_tstamp_config_t tstamp_config;
pa_assert(pcm);
pa_assert(delay);
@@ -1200,6 +1201,12 @@ int pa_alsa_safe_delay(snd_pcm_t *pcm,
snd_pcm_status_t *status, snd_pcm_sframes
* avail, delay and timestamp values in a single kernel call to
improve
* timer-based scheduling */
+ /* The time stamp configuration needs to be set so that the
+ * ALSA code will use the internal delay reported by the driver */
+ tstamp_config.type_requested = 1; /* ALSA default time stamp
type */
+ tstamp_config.report_delay = 1;
+ snd_pcm_status_set_audio_htstamp_config(status, &tstamp_config);
+
are you sure it's necessary or is this possibly a misunderstanding of
what audio_tstamps are?
this command is only for the audio timestamp, and to the best of my
knowledge you are not using the results using one of the
snd_pcm_status_get_audio_htstamp_* commands
the typical usage (see alsa-lib/test/audio_time.c) is this:
snd_pcm_status_set_audio_htstamp_config(status, audio_tstamp_config);
if ((err = snd_pcm_status(handle, status)) < 0) {
printf("Stream status error: %s\n", snd_strerror(err));
exit(0);
}
snd_pcm_status_get_trigger_htstamp(status, trigger_timestamp);
snd_pcm_status_get_htstamp(status, timestamp);
snd_pcm_status_get_audio_htstamp(status, audio_timestamp);
snd_pcm_status_get_audio_htstamp_report(status, audio_tstamp_report);
if you are not using the _get_audio_hstamp() then the config has
essentially no effect, and the delay is available separately in the
status command as before.
if ((err = snd_pcm_status(pcm, status)) < 0)
return err;
See this bug report, why it is needed:
https://bugzilla.kernel.org/show_bug.cgi?id=199235
It finally turned out that there was not a bug but just the flag missing.
We are using snd_pcm_status_get_htstamp() with the time smoother
to calculate sink/source latency.
Humm, that looks more like a bug in the fix (20e3f9 'ALSA: pcm: update
tstamp only in audio_tstamp changed'). I don't think we intended that
changes in the way the audio_tstamp is calculated (with or without
delay) would impact when the system timestamp is updated. I am pretty
sure we only wanted to update the timestamp when the hw_ptr changed with
this fix so as to go back to the traditional behavior before kernel 4.1.
Can you check if just using tstamp_config.type_requested = 1; isn't
enough for PulseAudio? If not, we have two conflicting desires on when
the system timestamp should be updated.
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