On Sat, Jun 23, 2018 at 4:41 PM, <o@xxxxxxxxxx> wrote: > > > 23.06.2018, 14:52, "Subhashini Rao Beerisetty" < > subhashbeerisetty@xxxxxxxxx>: > > Hello All, > > Hello, > > > > I’m trying to understand how audio samples transferred between user mode > to kernel mode during playback and capture. I’m using aplay & arecord alsa > utilities for playback and capture. > > > > Let us take a PCM wav file of sample rate 48000 and it has a total > number of samples 480000 (Approx.Duration in seconds=10). Size of each > sample is 8 bytes(two channels). After invocation of aplay from user mode, > how does these audio samples gets copied to kernel mode? Can someone > explain me on this? > > > > Is it possible to capture the timestamps for the first and last audio > samples that arrive at the driver level? > > > > Can I consider the .trigger(for playback & capture) callback in > SNDRV_PCM_TRIGGER_START case is timestamp for the first audio sample? > > > > Similarly does .trigger callbacks SNDRV_PCM_TRIGGER_STOP gives the last > audio sample timestamp? > > I think no, because the SNDRV_PCM_TRIGGER_START and SNDRV_PCM_TRIGGER_STOP > functions only system call to the PCM transmitted. > So, will want two different functions as playback / capture and the method > depends on you use alsa or pulse. > > I think you want to: > > snd_mychip_playback_open > snd_mychip_playback_close > > snd_mychip_capture_open > snd_mychip_capture_close > Are these part of "struct snd_pcm_ops" .open & .close? If so timestamps captured at these API's gives the first and last audio sample timestamps? Trigger funcs times are not real playback or capture time-stamps. Regards Ozgur > Thanks, _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
