[LAD] JACK and ALSA elucidations

From: Gianfranco Ceccolini <gianfranco@email-addr-hidden>
Date: Fri Feb 28 2014 - 19:57:37 EET

Hi LADs

We are working on an ARM based MOD device and while fiddling with JACK some
questions appeared.

I didn't know whether to post on the ALSA os JACK lists, so I decided to
post here :-)

When I start Jack in my PC I get the well know message:

/usr/bin/jackd -P80 -dalsa -r48000 -p128 -n2 -D -Chw:0 -Phw:0

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 2 periods for capture

ALSA: final selected sample format for playback: 32bit integer little-endian

ALSA: use 2 periods for playback

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?

- on the ArchWiki page on Jack there is a D-bus call

jack_control eps realtime true

stating that it "Sets JACK to realtime mode in its own internal setup."
What is this internal setup? How do I address this when not using D-Bus?

King regards all

Gianfranco Ceccolini
The MOD Team

PS: We will be at LAC againd this year. I'm very eager to meet most of this
distinguished community members there. We have lots of good new for the MOD
in 2014.

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Received on Sat Mar 1 00:15:02 2014

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