[LAD] JACK and ALSA elucidations

[Jeremy Jongepier]

On 02/28/2014 06:57 PM, Gianfranco Ceccolini wrote:
> When starting it on the Beaglebone Black I get:
> 
> 
> /usr/bin/jackd --realtime -P80 -dalsa -r48000 -p128 -n2 -Xraw
> 
> 
> creating alsa driver ... hw:0|hw:0|128|2|48000|0|0|nomon|swmeter|-|32bit
> 
> configuring for 48000Hz, period = 128 frames (2.7 ms), buffer = 2 periods
> 
> ALSA: final selected sample format for capture: 32bit integer little-endian
> 
> ALSA: use 16 periods for capture
> 
> ALSA: final selected sample format for playback: 32bit integer little-endian
> 
> ALSA: use 16 periods for playback
> 
> 
> - what are those "periods" in the ALSA lines? (2 for the PC and 16 for the
> BBB) ? I read a post by Jeremy Jongepier about the Cubieboard2 stating that
> the hardcoded values for the Cubie (Minimum number of periods was 4 and
> minimum buffer size was 1024) where unfit for realtime operation. Why is
> that so?

Hello Gianfranco,

What kind of audio interface are you using with the BBB? I'm no ALSA
expert but it seems as if the minimum period size of the driver has been
set to 16. If you have access to the source code of the driver you could
experiment with lower default values for .period_bytes_min and .periods_min.

Bye,

Jeremy

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