Re: [Jack-Devel] sweet! (jack2 backend switching demo by robin gareus)

On 02/21/2011 12:16 PM, James Warden wrote:
> 
> --- On Mon, 2/21/11, Harry Van Haaren <[hidden]> wrote:
> 
> From: Harry Van Haaren <[hidden]> Subject: Re:
> [Jack-Devel] sweet! (jack2 backend switching demo by robin gareus) 
> To: Cc: "Jack devel" <[hidden]> Date: Monday,
> February 21, 2011, 5:31 AM
> 
> 
> 2011/2/21 Jörn Nettingsmeier <[hidden]>
> 
> http://gareus.org/blog/jack2dbu
> 
> That one gives me a broken link: http://gareus.org/blog  its
> currently the first entry...
> 
> 
> Awesome work Robin, thanks for the tip. Will be testing later in the
> week! -Harry ------------
> 
> Hey, looks interesting! Can some of the internals be used for
> suspending / resuming jack based systems ?

yes, http://rg42.org/wiki/jack2contol

However, recent work on tschack and jack2 might be more suitable for
handling suspend/resume, YMMV.

> I was thinking whether one
> could switch to the dummy backend (which would mirror the exact same
> port connectivity as the real backend is using if this dummy backend
> can be told to declare X number of fake ports), then suspend or even
> turn off the real audio device (like an RME HDSP which does not wake
> up gracefully), and then suspend the jack session. At resume time,
> the real audio device would be turned on again, the jack backend
> switching would then kick in to restore the session with this
> device.

myjackctl.sh does that exactly.
more specific: /etc/pm/sleep.d/90myjackctl.sh does it using myjackctl.sh




Here's a few quotes from an off-list exchange with Sampo:

> I have one question though: what about switching between cards with
> different amounts of I/O?

myjackctl.sh does not map ports. Currently it only restores the
previous physical port-connections, but it's a simple shell script:
change it to fit your needs.

> Say your RME/whatever gets disconnected and you don't want your
> entire setup to vanish. This mechanism switches you over to your
> builtin sound card, then you find the disconnected cable and plug it
> in. I'd expect to have all connections present, even those from/to
> ports that weren't available when using the internal sound card.

good point. the tool that does the switch will need to remember the last
connection state of _each_ interface. Currently it only remembers _the_
last state - and only very briefly :)

The idea is to go one step further: It should be possible to configure a
set of transition actions for each backend-switch.

> Does this mechanism always switch to a "new" sound interface
> connected to the system, or does it only switch back to the original
> interface jack was started with?

That is configurable.The example-commandline I posted only switches to
THIS new device once it's connected:
org/freedesktop/Hal/devices/usb_device_582_74_noserial_if0_sound_card_2
and always switches to internal card when there's a DeviceError.

Clearly, the whole mechanism, configuraion and setup will eventually
become too tricky do be done by a bash-script.

ciao,
robin

1298296505.24906_0.ltw:2,a <4D626E9D.10607 at gareus dot org>