[alsa-devel] [RFC] disabling ALSA period interrupts

[Raymond Yau]

2010/5/12 pl bossart <bossart.nospam at gmail.com>

> > It seems the requirement is just to have as least wakeups as possible
> > in order to
> > maximize power savings.
> > If so, then how about setting the period size slightly smaller than
> > the ring-buffer: the
> > difference being just enough to refill the ring buffer. Of course, you
> > would have to
> > enforce full-buffer-size as the start threshold.
> > We do just that to implement low-power-audio-mode for latest Samsung
> > SoC's I2S blocks.
>
> Thanks for the heads-up Jassi, this is interesting info that does show
> the need to reduce the number of wakeups in embedded low-power
> solutions...
> This might be almost equivalent to the timer approach in terms of # of
> wakeups, however the timer can be reprogrammed on-the-fly whereas
> periods can only be changed by closing and reopening the device. You
> can also adjust the timer shall underflows occur. And the timer slack
> lets the kernel group events. Not to mention that you will need
> specific apps written to make use of this mode. The only drawback of
> the timer approach is that you need to keep track of drifts between
> system and audio clock and that you need the hardware and driver to
> report the hw_ptr with precision.
>

The problem is PA require hw_ptr with precision but PA server did not
provide same precision to PA client through alsa-pulseaudio plugin , this
inaccuracy lead to underrun easily