I didn't want to clog up the IRC with this...
Here are some of the things I have learned about jack_control and how it
works. Here is a list of what commands it understands:
Usage: jack_control [command] [command] ...
Commands:
exit - exit jack dbus service (stops jack server
if currently running)
help - print this help text
status - check whether jack server is started,
return value is 0 if running and 1 otherwise
start - start jack server if not currently
started
stop - stop jack server if currently started
sm - switch master to currently selected
driver
dl - get list of available drivers
dg - get currently selected driver
ds <driver> - select driver
dp - get parameters of currently selected
driver
dpd <param> - get long description for driver parameter
dps <param> <value> - set driver parameter
dpr <param> - reset driver parameter to its default
value
asd <driver> - add slave driver
rsd <driver> - remove slave driver
il - get list of available internals
ip <name> - get parameters of given internal
ipd <name> <param> - get long description for internal
parameter
ips <name> <param> <value> - set internal parameter
ipr <name> <param> - reset internal parameter to its default
value
iload <name> - load internal
iunload <name> - unload internal
ep - get engine parameters
epd <param> - get long description for engine parameter
eps <param> <value> - set engine parameter
epr <param> - reset engine parameter to its default
value
I spent some time looking at the output "get" forms of these commands as
this tells you which params are available to change. The main commands
that are used are the stop, start and exit commands which are obvious. The
next most important command is sm. This is the last command to send after
changing any parameters to make them take effect. For an example, here is
the command that starts my jackdbus when I login:
---------------8<---------------
DELAY=1
DRIVER=alsa
DEV=hw:0
RATE=48000
FRAME=2048
PERIOD=2
#sleep $DELAY
jack_control ds $DRIVER dps device $DEV dps rate $RATE dps period $FRAME \
dps nperiods $PERIOD start
-----------------8<--------------
I should be using DEV=hw:D66, Frame could be 1024 or even 512 on this
machine. (I use 64 with PA still connected with no issues) USB,FW and AoIP
should probably use PERIOD=3
I have made the settings variables for now with the idea that they may
someday come from a config file or the environment. Notice the start is at
the end after all the parameters are loaded. If I was changing these
parameters "on the fly" then the start would be replaced by sm.
pretty simple. Basically, all the things jackd commandline can do
jack_command can do too. Just a different syntax and the configuration is
stored to a different place as well. So just going jack_control start will
use the same settings as last run.
To change the latency on the fly, the command to use is jack_bufsize $FRAME
As with many things if the PA system files (in /etc) are changed there are
errors when upgrading pulse because it notices the file has changed. I
need to find out where I could add a file afterwards that would not
interfere with upgrades.
--
Len Ovens
www.ovenwerks.net
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