ALSA sound suspend/resume
joerg at openmoko.org
Wed Jun 11 07:40:21 CEST 2008
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?
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