Arve Knudsen wrote:
> On Fri, 12 Sep 2003 16:51:26 +0200 (METDST), Clemens Ladisch
> <[EMAIL PROTECTED]> wrote:
> Maybe I should rephrase my question, now that I've got some time to think
> about it. Exactly what gets started when the start threshold is reached,
> the transfer of frames to the audio card (assuming we're writing frames)?
> Obviously it doesn't affect the state of the pcm, like snd_pcm_start does
> (SND_PCM_STATE_RUNNING).
When at least start_threshold frames have been written to the buffer,
the pcm will be started. This _will_ affect the pcm's state.
To quote alsa-kernel/core/pcm_lib.c (in snd_pcm_lib_write1):
if (runtime->status->state == SNDRV_PCM_STATE_PREPARED &&
snd_pcm_playback_hw_avail(runtime) >=
(snd_pcm_sframes_t)runtime->start_threshold) {
err = snd_pcm_start(substream);
> It seems to me a start threshold equal to buffer size would mean
> no transfer of data goes on before the buffer is filled?
Yes.
> If this is correct, what would it mean in the case of capture
> (reading frames from the card).
When, in the prepared state, you want to read at least start_threshold
frames in one call to xxx_read, the pcm will be started.
HTH
Clemens
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