On Wed, 03 Mar 2010 08:07:52 +0200 Eero Nurkkala ext-eero.nurkkala@nokia.com wrote:
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).
Yeah, that's interesting to find out are the XBUFFSTAT reading differences inside the DMA burst size or distributed completely randomly. I think the XBUFFSTAT should increase at the sample rate and decrease or jump down fast when the DMA burst takes place.