Keeping the codec running at all times

[Jaroslav Kysela]

Dne 06. 05. 20 v 17:15 Ricard Wanderlof napsal(a):
> 
> In certain system-on-chip systems, with separate ADCs and DACs for
> instance, the ADC could generate clocks for the DAC, where it not for the
> fact that ALSA shuts down whatever device is not being used in order to
> conserve power. Is it possible to instruct ALSA not to do this, i.e. once
> a codec has been configured to operate at a given sample rate, it will
> continue to do so, even after all streams have stopped.
> 
> I suppose one way to do this would be to change the codec set_bias_level()
> callback so that the BIAS_OFF and BIAS_STANDBY cases don't do anything but
> leave the codec running. But it doesn't sound like a clean way of doing
> this.
> 
> Of course, one complication is that at system startup, before any capture
> or playback operations have been attempted, ALSA doesn't know which sample
> rate should be configured, as there is no concept of a 'default sample
> rate'; the sample rate is always set when a stream is opened.

The driver may limit the available rates (thus it may be possible to set the 
one accepted rate via the module parameter or so which may be used for the 
codec initialization before an application uses the PCM device).

						Jaroslav

> 
> /Ricard
> 


-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.