Dne 26.9.2014 v 10:45 Kuninori Morimoto napsal(a):
Hi Jaroslav
We noticed that DMA seems transfered +1 time when Ctrl-C happen. But, is this correct ? is this our driver bug ? [...] 7. DMA transfer interrupt happen
It calls snd_pcm_period_elapsed() and try to transfer next 2048 byte snd_pcm_playback_avail() in snd_pcm_update_state() return 8192 this time. then, it calls snd_pcm_drain_done()
snd_soc_dai_ops :: trigger called with SNDRV_PCM_TRIGGER_STOP
driver stops DMA transfer
There is no strong synchronization between snd_pcm_drain() and the rest of the system; snd_pcm_drain() just waits for an underrun to happen.
In other words, the last actual DMA transfer is likely to contain invalid (outdated) samples, but gets aborted immediately.
I wonder why we need drain ? This "likely to contain invalid samples" will be solved if we can skip "complete drain" ?
The user app should do the flush instead the drain in this case...
Thank you about this help. Can you show me how to do this in app side ? (Calling some alsa-lib function ?)
Yes, the function is snd_pcm_drop() .
Jaroslav