[alsa-devel] Set eapd to follow stream on or off

[Takashi Iwai]

At Tue, 20 May 2014 16:52:43 +0800,
Kailang wrote:
> 
> 
> > At Tue, 20 May 2014 15:15:49 +0800,
> > Kailang wrote:
> >>
> >> Hi Takashi,
> >>
> >> HP machine had pop noise via speaker.
> >> If EAPD on or off, speaker will have pop noise.
> >> So, they want to set eapd to follow with stream on or off.
> >
> > I can apply this as is, but still I wonder whether this results in
> > other problems.  Doing EAPD on/off there means that it happens far
> > more often.  For example, what happens if you do like below?
> >
> >     while true; do
> >       echo -n > /dev/snd/pcmC0D0p
> >     done
> >
> > And, what if the device is resumed from power-saving by an audio
> > playback?  Immediately after the power up, it'll start the streaming,
> > so it'll turn on EAPD.
> >
> > That said, isn't it just a need for some delay before EAPD on/off?
> 
> No, eapd on or off will cause pop noise.

Does it do always?

> Our customer just want to do eapd on when stream is open.
> The pop noise will not clear. Because music gain was biger than pop noise.

Opening a stream doesn't mean that it follows the loud sound
immediately.  The script above wouldn't produce any sound but just
does open/close the stream.  Did you try that?


Takashi