Keeping the codec running at all times

[Ricard Wanderlof]

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.

/Ricard
-- 
Ricard Wolf Wanderlof                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30