[alsa-devel] [PATCH 3/3] ASoC: omap-mcbsp: Add period size protection mode

Grazvydas Ignotas notasas at gmail.com
Wed Mar 21 12:55:24 CET 2012

On Wed, Mar 21, 2012 at 10:23 AM, Peter Ujfalusi <peter.ujfalusi at ti.com> wrote:
> On 03/20/2012 06:15 PM, Grazvydas Ignotas wrote:
>> I wouldn't really call them broken, it's enough to set period size to
>> 512 with smaller start_threshold (something like 50ms) to have
>> problems, those parameters are perfectly valid for a program trying to
>> achieve low latency.
> Where this 50ms comes from?
> The McBSP2 FIFO length is:
> 48KHz/mono:     26.66ms
> 48KHz/stereo:   13.33ms
> 44.1KHz/mono:   29.02ms
> 44.1KHz/stereo: 14.51ms
> 8Khz/mono:      160ms
> 8Khz/stereo:    80ms
> Does Pandora uses 8Khz?

Nope, 50ms+8kHz was just to illustrate the problem easier. 22/44kHz
are used most often, some games that tend to set low thresholds and
OSS emulation are ones with problems.

> The same thing applies to the start_threshold as to the period size. It
> has to be bigger than the FIFO size.
>> It's a shame this still won't work out-of-the box, but at least there
>> will be some solution.
> Defaulting this behavior would break other distributions for OMAP
> platforms. I know, Pandora is bitten by this, but MeeGo, ubuntu, Linaro
> is fine (as far as I know).

I wonder about that, if they are already ok they must be using larger
period/start_threshold anyway and should not be affected?


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