Buffer underrun in a not empty playback buffer

[Christian Gruber <christian.gruber@voiceinterconnect.de>]

I had a problem with an ALSA-driver, which causes an underrun in the playback stream 
before the playback buffer was completely empty (snd_pcm_avail() < playback buffer size). 
The driver developer told me, that this is correct, since for correct DMA transfer a 
minimum buffer filling level is required.

Is this an allowed ALSA-driver behaviour or does the ALSA-driver developer has to hide all 
DMA internals to the application developer so that an underrun just occurs, when the 
playback buffer is empty? If yes, how can I get to know about the required minimum buffer 
filling level before an underrun occurs?

Regards,
Christian

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