[Jack-Devel] Jack 0.120 - ALSA backend
A second quick question: have there been changes to
the ALSA backend recently ?
I can now trigger the problem reported before quite
easily.
1. Start jack using the ALSA backend and with -n 3.
2. Start and wire up jack_iodelay. Make the required
external loopback. There is already a chance that
it will show the latency for -n 2 instead of the
expected one. In any case leave it running.
3. Start a second jack client, one that will not
exit cleanly but trigger a 'subgraph time out'
when termintated with ctl-C. Jack_iodelay itself
will do fine. No need to connect its ports.
4. Terminate the second app. There is a good chance
that the measured delay will switch between the
expected values for -n 2 and -n 3.
5. When the latency is the -n 2 value, check that
the signal is still passing via the external
loopback by disconnecting it for a second.
6. Repeat 3,4,5 to taste.
Conclusions:
* Measuring the latency for -n 2 while it should be
the one for -n 3, and the signal used *is* the one
via the external loopback is possible only if there
is some error in setting up the ALSA device in the
backend. There is no way the jack engine could
'short circuit' the loop if signal being measured
is passing via the external loopback.
* This is confirmed by a 'subgraph timeout' triggering
a change in measured latency. IIRC this means a
restart of the ALSA device.
So I'm now pretty sure there is some problem in the
ALSA backend.
Ciao,
--
FA
1302947251.24326_0.ltw:2,a <20110416094718.GA12632 at linuxaudio dot org>