Hi,
Takashi Iwai wrote:
>> At least this is the behaviour I experienced.
>
> It's your mis-interpretation of START/STOP concenpt in the ALSA
> framework. The trigger START and STOP mean the start/stop of the
> whole streaming operation. It's basically called from the outside,
> i.e. the application starts/stops the stream. If you need to keep
> some DMA start/stop operations internally, do it in the driver
> lowlevel side internally.
thanks for reply but as already stated this is the behaviour I
_experienced_. I don't know why also continuously calls trigger START,
play one period, trigger STOP. Here is some pseudo code:
---snip---
pcm_trigger()
{
case SNDRV_PCM_TRIGGER_START:
/* start the DMA Transfer */
ret = startTransfer(dma_devaddr, params->ch_num,
num_blocks, vi1888_pcm_dma_userCallback, substream);
break;
...
}
vi1888_pcm_dma_userCallback() // gets called upon completion of DMA
transfer
{
prtd->period_ptr += prtd->period_size;
if (prtd->period_ptr >= prtd->dma_buffer_end) {
prtd->period_ptr = prtd->dma_buffer;
}
/* reconfigure channel according to new period pointer */
/* start the next DMA Transfer */
ret = startTransfer(dma_devaddr, params->ch_num, num_blocks,
vi1888_pcm_dma_userCallback, substream();
/* notify Alsa for the elapsed periods */
snd_pcm_period_elapsed(substream);
}
---snap---
After each call to snd_pcm_period_elapsed() Alsa calls
pcm_trigger(TRIGGER_STOP).
Please tell me what I am doing wrong in these callbacks?
Thanks in advance,
Markus
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