Detecting new alsa sequencer clients (with some event loop) so that i can subscribe them

Detecting new alsa sequencer clients (with some event loop) so that i can subscribe them

[R. Dresens]

Hello,

I'm currently writing an application that will be able to 'auto
subscribe' itself to a certain sequencer client when that client
becomes available to the system. I want (for example) to be able to 
plug in a USB MIDI interface, and when I do that then my application
detects this and does a subscription on it, just like aconnect would
do.

A possible solution is polling; every second or so, i could generate a
list of clients with snd_seq_query_next_client and look for a certain
client name (libpcre comes to mind here;), but I was wondering if there
is a better solution? ..in other words, is it possible to get such
events from the system in a similar way like one would receive regular
MIDI events?

http://www.alsa-project.org/alsa-doc/alsa-lib/structsnd__seq__event.html
list all the events; an interesting one could be snd_seq_connect_t
for monitoring connections on my own ports, but that's not what I'm
looking for. I can't seem to find an event related to this
functionality. Is there something what I'm currently overlooking?

Such functionality may be usefull for GUI versions of aconnect. I
looked in the source of qjackctl (it has an alsa patchbay), but I
haven't found nothing usefull yet since it seems to me that this
software also does polling/refresh on a certain interval.

Has anyone a usefull tip for me?

Thanks in advance,

Greetings,

Raymond Dresens.

Re: Detecting new alsa sequencer clients (with some event loop) so that i can subscribe them

[Clemens Ladisch]

R. Dresens wrote:
> I'm currently writing an application that will be able to 'auto
> subscribe' itself to a certain sequencer client when that client
> becomes available to the system. I want (for example) to be able to
> plug in a USB MIDI interface, and when I do that then my application
> detects this and does a subscription on it, just like aconnect would
> do.
>
> A possible solution is polling; every second or so, i could generate a
> list of clients with snd_seq_query_next_client and look for a certain
> client name (libpcre comes to mind here;), but I was wondering if there
> is a better solution? ..in other words, is it possible to get such
> events from the system in a similar way like one would receive regular
> MIDI events?

Subscribe to SND_SEQ_CLIENT_SYSTEM:SND_SEQ_PORT_SYSTEM_ANNOUNCE.
Try "aseqdump -p 0:1" to see what events you get.


HTH
Clemens

Re: Detecting new alsa sequencer clients (with some event loop) so that i can subscribe them

[R. Dresens]

On Tue, 01 Apr 2008 09:01:50 +0200
Clemens Ladisch <clemens@ladisch.de> wrote:

> > A possible solution is polling; every second or so, i could
> > generate a list of clients with snd_seq_query_next_client and
> > look for a certain client name (libpcre comes to mind here;), but
> > I was wondering if there is a better solution? ..in other words, is
> > it possible to get such events from the system in a similar way
> > like one would receive regular  MIDI events?
> 
> Subscribe to SND_SEQ_CLIENT_SYSTEM:SND_SEQ_PORT_SYSTEM_ANNOUNCE.
> Try "aseqdump -p 0:1" to see what events you get.

Yes, that did the trick: this is exactly what I'm looking for.

Thanks for your help!

Greetings,

Raymond Dresens.