Hi Anis, Gonzalo,
To complete what Gonzalo has said, to subscribe to AVMD messages you will do in Perl:
$con->events("plain", "CUSTOM avmd::start");
$con->events("plain", "CUSTOM avmd::stop");
$con->events("plain", "CUSTOM avmd::beep");
Please take a look into src/mod/applications/mod_avmd/scripts/ folder for complete examples.
cheers,
Piotr