23.06.2018, 14:52, "Subhashini Rao Beerisetty" <subhashbeerise...@gmail.com>:
> 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,
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