[alsa-devel] audio samples data flow from user mode to kernel mode

[Subhashini Rao Beerisetty]

Hello All,



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?



Thanks,