ALSA sound suspend/resume

[Sean McNeil]

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? 
> GTA01/02?)
>
> /jOERG
>   

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.