Re: [LAD] JACK and ALSA elucidations

On Fri, Feb 28, 2014 at 12:57 PM, Gianfranco Ceccolini <
gianfranco@email-addr-hidden> wrote:

>
> 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) ?
>

these are the number of "segments" or "periods" that the h/w buffer is
divided into. Input latency is determined by period size, playback latency
is determined by buffer size. the device will wake the CPU every time it
has 1 period of date/space available.

>
> - 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?
>

JACK starts in realtime mode by default. It can be "forced" to do that with
-R or you can turn it off with -r.

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Received on Sat Mar 1 00:15:02 2014