On Thu, 23 Mar 2017 12:40:45 +0100, sutar.mounesh@xxxxxxxxx wrote: > > From: Andreas Pape <apape@xxxxxxxxxxxxxx> > > purpose of this fix, is to read most accurate timestamps. > > From documentation of /src/pcm/pcm.c, we can see: > """" \par Timestamp mode > > The timestamp mode specifies, if timestamps are activated. Currently, only #SND_PCM_TSTAMP_NONE and #SND_PCM_TSTAMP_MMAP modes are known. > The mmap mode means that timestamp is taken on every period time boundary. Corresponding position in the ring buffer assigned to timestamp can be obtained using #snd_pcm_htimestamp() function. """" > > As snd_pcm_generic_htimestamp() internally calls snd_pcm_htimestamp() to read time, so accurate timestamp can be read from snd_pcm_generic_htimestamp(). > > Also, in case of pcm_file, if the underlying slave is hardware, then we would wish to read elapsed hardware time, as it will be the most accurate, as opposed to the elapsed wall time. > This will provide pcm_file with the most accurate timestamps. > > Following are the timesamps read with timestamp enabled, for with fix and without fix scenarios: > > 1> With fix: > :~#time aplay --enable-tstamp -Dhtstamp_test --period-time=5000 -v -fdat /dev/urandom > Playing raw data '/dev/urandom' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo > File PCM (file=/tmp/swarate_out.wav) > Final file PCM (file=/tmp/swarate_out.wav) > .. > > Slave: Hardware PCM card 0 'imx6q-sabresd-wm8962' device 0 subdevice 0 > Its setup is: > stream : PLAYBACK > access : RW_INTERLEAVED > format : S16_LE > subformat : STD > channels : 2 > rate : 48000 > exact rate : 48000 (48000/1) > msbits : 16 > buffer_size : 24000 > period_size : 240 > period_time : 5000 > tstamp_mode : ENABLE > . > . > Before sleep = 142:409.807623 > After sleep = 142:409.807623 > Before sleep = 142:414.806016 (calling snd_pcm_htimestamp(handle, &avail, &tstamp_before)) > sleep of 2 milisec > After sleep = 142:414.806016 (calling snd_pcm_htimestamp(handle, &avail, &tstamp_after) > >From the above timestamps, we can see that slave has returned the same timestamps, as --period-time choosen is 5msec. > > 2> Without this fix: > The timestamps are returned with realtime value. > > :~# time aplay --enable-tstamp -Dhtstamp_test --period-time=5000 -v -fdat /dev/urandom > Playing raw data '/dev/urandom' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo > File PCM (file=/tmp/swarate_out.wav) > Final file PCM (file=/tmp/swarate_out.wav) > . > . > Slave: Hardware PCM card 0 'imx6q-sabresd-wm8962' device 0 subdevice 0 > Its setup is: > stream : PLAYBACK > access : RW_INTERLEAVED > format : S16_LE > subformat : STD > channels : 2 > rate : 48000 > exact rate : 48000 (48000/1) > msbits : 16 > buffer_size : 24000 > period_size : 240 > period_time : 5000 > tstamp_mode : ENABLE > . > . > Before sleep = 241:136.875845 (calling snd_pcm_htimestamp(handle, &avail, &tstamp_before)) > sleep of 2 milisec > After sleep = 241:139.076376 (calling snd_pcm_htimestamp(handle, &avail, &tstamp_after) > > We can observe here, the timestamps shows time diff of ~2ms, which is the time gap of sleep duration. > Before sleep = 241:139.617588 > After sleep = 241:141.746845 > Before sleep = 241:142.291618 > After sleep = 241:144.406406 > Before sleep = 241:144.951421 > After sleep = 241:147.066118 > Before sleep = 241:147.623421 > After sleep = 241:149.740573 > > Signed-off-by: Andreas Pape <apape@xxxxxxxxxxxxxx> > Signed-off-by: Mounesh Sutar <sutar.mounesh@xxxxxxxxx> Applied now, thanks. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
