Hi,
On Jan 19 2016 03:21, Ankhit Vivekananda wrote:
I am interfacing the ICS43432 MEMS microphone with McBSP interface. The
data sheet of the ICS43432 microphone shows that it takes about 4.5ms
(16kHz sampling rate) for startup. Because of this, I hear a transient
noise at the beginning of every stream. Is there in any way I can discard
the frames inside the kernel space itself before reading the samples using
snd_pcm_readi() call?
I was able to mute the first few frames after the readi() call, but would
want to know if I could do it before the readi() call itself inside the
kernel space.
If the data transmission starts in 'struct snd_pcm_ops.prepare' callback
of the driver, we can wait what we want, because ALSA PCM core
guarantees to call it in process context.
In userspace, this looks like (here I describe in alsa-lib API):
- calling snd_pcm_hw_params()
- snd_pcm_prepare() is called library internal
* struct snd_pcm_ops.prepare() is called in kernel mode.
* mute
* start data transmission
* wait for the 4.5ms or somewhat
* return
* return
- return
- PCM frame operation such as snd_pcm_writei()
* snd_pcm_ops.trigger(TRIGGER_START) is called in kernel mode.
* demute
* PCM frames starts to be transferred from userspace.
Regards
Takashi Sakamoto
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
