====== Qjackctl - DBUS ======

Since version 0.3.4.11 [[http://qjackctl.sourceforge.net/|qjackctl]] offers [[http://www.freedesktop.org/wiki/Software/dbus|DBUS]] support to start and stop the JACK audio server:

From the change-log:
  A couple of primitive D-Bus interface slots have been introduced,
  giving the option to start/stop the jackd server from the system
  bus eg. via dbus-send --system / org.rncbc.qjackctl.start (stop),
  (a nice addition supplied by Robin Gareus, thanks).
  
The DBUS addition qjackctl is mostly useful for laptops to get [[http://jackaudio.org|JACK]] back running after a suspend or hibernate cycle.

My motivation was simple: Since skype started working with jackplug in an .asoundrc I missed a couple of calls simply because I forgot to launch jackd after a suspend/resume cycle. I figured that I spend less time hacking an DBUS addition than keep re-starting jackd by hand ;)

--

//Any suggestions for when the dbus-send command doesn't work? I get the following error (with the DBUS option enabled in Setup):
**Error org.freedesktop.DBus.Error.UnknownMethod: Method "start" with signature "" on interface "org.rncbc.qjackctl" doesn't exist**//

RE: The error message is misleading. If a dbus-method is called for an object that is not documented in the dbus-schema in ''/etc/dbus-1/system.d/*'', this //error// message will be returned. It should work nevertheless. (Apparently one can configure the emission of these warnings in ''/etc/dbus-1/'' but don't call me on details about it.) The proper solution would be to file a bug report with qjackctl (or packagers thereof) to include the dbus-schema. 

===== Setup =====

The command-line to launch JACK via qjackctl is  
  dbus-send --system /org/rncbc/qjackctl org.rncbc.qjackctl.start

On resume you actually want to execute:
  (sleep 4 ; dbus-send --system /org/rncbc/qjackctl org.rncbc.qjackctl.start)&
which allows audio-devices to settle (eg USB-soundcards to power up, or ALSA settings to be restored) before restarting JACK.

This command needs to be executed when resuming from standby mode. Depending on your GNU/Linux distribution and suspend-software this can be achieved by 

  * writing a hook script in /etc/pm/sleep.d/
  * patching /usr/lib/hal/scripts/linux/hal-system-power-suspend-linux
  * adding a script in /etc/acpi/resume.d/

As a side-note, you may want to re-launch ''/etc/init.d/rtirq'' in a similar manner. Since linux-2.6.31 some IRQ-threads (may) come up with a new PID after a suspend/resume cycle. 


--

//Any suggestions for when the dbus-send command doesn't work? I get the following error (with the DBUS option enabled in Setup):

**Error org.freedesktop.DBus.Error.UnknownMethod: Method "start" with signature "" on interface "org.rncbc.qjackctl" doesn't exist**//

===== Resume Script =====

On Debian/squeeze I use the first option. Don't forget to mark the file executable (''chmod +x /etc/pm/sleep.d/90qjackctl.sh'' ) after creating it.

This works also on Ubuntu 12.04

''/etc/pm/sleep.d/90qjackctl.sh''
  #!/bin/bash
  case $1 in
    hibernate|suspend)
      dbus-send --system /org/rncbc/qjackctl org.rncbc.qjackctl.stop
      ;;
    thaw|resume)
      (sleep 4 ; dbus-send --system /org/rncbc/qjackctl org.rncbc.qjackctl.start)&
      # if you use rtirq to set IRQ priorites you should use:
      #(sleep 4 ; /etc/init.d/rtirq start; dbus-send --system /org/rncbc/qjackctl org.rncbc.qjackctl.start)&
      ;;
    *)
      ;;
  esac

===== .asoundrc =====

For lack of a better place to put it, here's the [[http://alsa.opensrc.org/.asoundrc|~/.asoundrc]] (or ''/etc/asound.conf'') that I use to run all audio through [[http://jackaudio.org|JACK]]. Works great with skype and even gives sound to Flash in every browser:

  pcm.!default {
        type plug
        slave { pcm "jack" }
  }
  
  pcm.jack {
        type jack
        playback_ports {
                0 system:playback_1
                1 system:playback_2
        }
        capture_ports {
                0 system:capture_1
                1 system:capture_2
        }
  }
  
  ctl.mixer0 {
    type hw
    card 1
  }
  
  
{{tag>audio jack documentation floss}}