[alsa-devel] ALSA: dmix: pcm status incomplete

[Dan Hordern]

I require timestamp information from the soundcard and host for our
application. However, I noticed that when using "dmix:0,0" instead of
"hw:0,0", the audio timestamp and delay frames are both zero.

Looking in to the code, it seems that the 'snd_pcm_dmix_status' function
does not populate either of these. In order to expose these, I have
modified this function to get this information from the slave pcm; patch
below.

I was hoping for some feedback on this change. I am not sure if the delay
value makes sense as yet, and whether there are consequences of using the
hardware trigger timestamp etc. I am guessing the dsnoop and dshare plugins
may also have this issue, though I have not checked.

Thanks,
Dan


diff --git a/src/pcm/pcm_dmix.c b/src/pcm/pcm_dmix.c
index babde6a..a4d7fc0 100644
--- a/src/pcm/pcm_dmix.c
+++ b/src/pcm/pcm_dmix.c
@@ -475,12 +475,12 @@ static int snd_pcm_dmix_status(snd_pcm_t *pcm,
snd_pcm_status_t * status)
                break;
        }
        memset(status, 0, sizeof(*status));
+       snd_pcm_status(dmix->spcm, status);
        status->state = snd_pcm_dmix_state(pcm);
-       status->trigger_tstamp = dmix->trigger_tstamp;
-       gettimestamp(&status->tstamp, pcm->tstamp_type);
        status->avail = snd_pcm_mmap_playback_avail(pcm);
        status->avail_max = status->avail > dmix->avail_max ? status->avail
: dmix->avail_max;
        dmix->avail_max = 0;
+       status->delay = snd_pcm_mmap_playback_delay(pcm);
        return 0;
 }