On Tue, 2010-03-02 at 15:06 +0100, ext Jarkko Nikula wrote: > On Tue, 02 Mar 2010 15:52:00 +0200 > Eero Nurkkala <ext-eero.nurkkala@xxxxxxxxx> wrote: > > > Reading the XBUFFSTAT register is by no means accurate. > > IIRC, it reports the buffer status incorrectly about 1/50 times > > on average (@ 48000khz); with simple math, it may be read during the DMA > > burst. Or is it guaranteed not being read during DMA transfer / have > > you otherwise verified the behavior? > > > Do you remember how big was this variation? Was it near the burst size > or some arbitrary difference? > > Mostly the samples were good (49/50, @48khz, 2 channels, value polled from userpace), but the remaining 1/50 were garbage - and actually matched the probability of a simultaneous DMA burst. So the problem is - if you read at time t0, and the DMA burst is taking place at the same time - you get a value that looks rather random, as when (if) you poll the position @ t0 + n uS, the value is (after some usecs) a lot different. Or maybe the XBUFFSTAT just isn't reliable at all (regardless of DMA bursts etc). It's easy to check - at DMA IRQ, read out the XBUFFSTAT... if the range is not valid, print a message...(to rule out the DMA bursts). - Eero _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
