[alsa-devel] safe support for rewind in ALSA

[Lennart Poettering]

On Sun, 21.02.10 12:35, Kai Vehmanen (kvehmanen at eca.cx) wrote:

> But you can query the SNDRV_PCM_INFO_BATCH flag (it's set by e.g. the USB 
> driver) and adjust your hrtimer-based application's logic based on that 
> (if set, assume hw_ptr will jump in bursts). I know, not really ideal (you 
> essentially have to e.g. disable PA glitch-free for these cards 
> currently).
> 
> > This mean that the wake up time cannot be calculated using as number of
> > sample/rate since the fuction is not linear especially when using max buffer
> > size , min period --> max period size is much greater than the watermark
> 
> Yep, that's what SNDRV_PCM_INFO_BATCH flag warns you about.

Hmm, could you elaborate a little about SNDRV_PCM_INFO_BATCH? What
exactly does that mean in general and especially for the timer based
audio scheduling?

I am currently not making use of this, but should I?

I cannot find much documentation about this, can you enlighten me?

I assume this is exposed to userspace via
snd_pcm_hw_params_is_batch()? 

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4