[alsa-devel] ALSA always writes _whole_ periods, right?

Joachim Förster mls.JOFT at gmx.de
Wed Jun 13 18:23:38 CEST 2007

Hi ALSA devs,

I have a quick question regarding the filling of the usual ring buffer
in RAM (used by sound controllers via DMA), just to be really sure:

Is it true, that ALSA always writes (via mmap'ing) _whole_ periods?

I took snd-dummy and modified it to use "ack()" method and tried to
confirm, if the above is true _without_ memory mapping (classical
read/write). It seem's to be true, ALSA is "filling up" the last (not
always complete) period - e.g. if the played wav file is not a multiple
of periodsize in length.
But well, with mmap, I cannot see the copying action (done by ALSA
library, right?) ... so, thus my question ;-) .


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