ALSA sound suspend/resume
sean at mcneil.com
Wed Jun 11 08:25:08 CEST 2008
Joerg Reisenweber wrote:
> Am Mi 11. Juni 2008 schrieb Sean McNeil:
>> I had an issue with ALSA sound not coming back on resume. This looks
>> like it might have been an application error where I was setting the
>> start threshold via snd_pcm_sw_params_set_start_threshold() to the
>> buffersize. Lowering by a periodsize seems like it resolved the problem.
>> Now I would like to fix the popping noise produced when suspend or
>> resume occurs. I think it is because the amp is turned on with the
>> volume up. Is there some ramping that needs to be done when turning
>> on/off the amp?
> After a time of powerdown, the decoupling capacitors have to charge to VDD/2
> (that's what means "no signal" on output of amp) on power-return. This
> inevitably creates some sort of unwanted signal (=plop). You may drive the
> amp to GND-level before suspend by playing out minint or maxint samples
> (depends), on resume you would slowly ramp back to zero during maybe 0.5 sec
> so charging will be very smooth.
> Depending on the amp there might be meassures been taken in hardware to do the
> same, when setup and sequenced properly (on 8753 there are).
> I'll come back with more, when I read about it in the amp's specs eventually.
> Which audio output is it we talk about (hp, earphone, spk? BT even?
It is the speaker output I have set when I suspend/resume so I suspected
the speaker amp.
Thanks for the info. Any help is greatly appreciated.
More information about the openmoko-kernel