[alsa-devel] safe support for rewind in ALSA

[Raymond Yau]

2010/2/10 Clemens Ladisch <clemens at ladisch.de>

> Raymond Yau wrote:
> > ...
> > The rest of those sound cards which have period_mins = 1 are regarded as
> > broken by PA developer  (e.g. intel8x0 ,emu10k1 , ens1371 , ... ) and
> aplay
> > did not work with one period per buffer too.
> >
> > what is the hardware requirement for the driver to support one period per
> > buffer ?
>
> That the hardware can be programmed to generate only one interrupt per
> buffer.
>
> > if none of the those driver can be fixed
> >  why don't we change the period_min of all those broken drivers from 1 to
> 2
> > ?
>
> Because period_min has nothing to do with the brokenness.  PA wants to
> use as few periods as possible because it does not use period interrupts
> but the DMA pointer, and it's the latter that is broken.
>
>
> Regards,
> Clemens
>

Are the one period per buffer designed for specific purpose such as
playing/looping the pre-loaded soundfont ?

Other than pulseaudio , are there any application use this mode  properly
without glitch ?

Do you mean that PA only wake up once when configure sound card to use two
periods per buffer ?

if sound card only support non-interleaved mode and exactly two periods ,
even if you limit the rewind of application pointer to the period boundary
is not 100% safe if the sound card pre-fetch audio using DMA

Most sound cards hardware register only provide the number of  sample
processed