2010/2/2 Jaroslav Kysela perex@perex.cz
On Mon, 1 Feb 2010, pl bossart wrote:
All, I'd like to reopen a thread on concerns with the current implementation of rewind in ALSA. This was already discussed on the mailing list last year without any progress.
I don't think that there have been no progress. The queued samples can be stored to runtime->delay now, so snd_pcm_delay() returns a correct value.
The snd_pcm_rewind() and snd_pcm_forward() functions should operate in the ring buffer and it's ok. See the USB driver for an example. Just add support for runtime->delay to the lowlevel drivers and use snd_pcm_delay() correctly in the user space and everything will work as expected.
In other words - for hardware with large FIFOs, the runtime->delay should be used for queued samples and the hw_ptr in the ring buffer should be increased as soon as the FIFO is filled with samples from the ring buffer.
Jaroslav
Are there any demo program using snd_pcm_rewind()/snd_pcm_forward() to verify the driver meet your proposal ?
For the interrupt driven model, the application fill the period while the driver playing the other period on two periods per buffer , the drivers don't need to provide accuracy up to a few sample derivation.
However It seem to me that your proposal give an impression to the application developer that all ALSA drivers can provide accuracy up to sample accuracy