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 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
