[alsa-devel] [RFC 3/4] OMAP3: McBSP: Add interface for transmit FIFO state query

Jarkko Nikula jhnikula at gmail.com
Wed Mar 3 08:03:24 CET 2010

On Wed, 03 Mar 2010 08:07:52 +0200
Eero Nurkkala <ext-eero.nurkkala at 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.


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