SND_SEQ_EVENT_PORT_UNSUBSCRIBED v. listconnectedto()

[Peter Billam]

Greetings. Hope you're all well :-) Erm... If I'm running an
ALSA-MIDI client, let's say called midifoo, and then someone does:
aconnect midifoo:1 TiMidity
or:
aconnect -d midifoo:1 TiMidity
then it seems to me that my client midifoo does not receive any
SND_SEQ_EVENT_PORT_SUBSCRIBED or SND_SEQ_EVENT_PORT_UNSUBSCRIBED
alsaevent. Is that right ?

Apparently these event-types only get received if an INPUT-port
is connected or disconnected ...

Is there a way of asking System to inform midifoo also about
connections and disconnections on OUTPUT-ports ?
or does midifoo have to poll listconnectedto() and look for changes ?

~> aptitude show alsa-base | grep Version
Version: 1.0.25+3~deb7u1

Hope this makes sense... greetings anyway :-)

Regards, Peter

[Clemens Ladisch]

... it seems to me that my client midifoo does not receive any
SND_SEQ_EVENT_PORT_SUBSCRIBED or SND_SEQ_EVENT_PORT_UNSUBSCRIBED
alsaevent.
Apparently these event-types only get received if an INPUT-port
is connected or disconnected ...

As you have observed, a port must be marked as INPUT to be able
to receive events.

Is there a way of asking System to inform midifoo also about
connections and disconnections on OUTPUT-ports ?

Mark that port also as INPUT. (You do not need to allow write
subscriptions to that port.)

Alternatively, listen for these notifications from the System
Announce port.


Regards,
Clemens

[Peter Billam]

Post by Clemens Ladisch

Post by Peter Billam
Is there a way of asking System to inform midifoo also about
connections and disconnections on OUTPUT-ports ?

Mark that port also as INPUT. (You do not need to allow write
subscriptions to that port.)

OK, it makes sense: those notifications are sent to the Port,
not to the Client.

For me, this arises in the context of midialsa.lua :
http://www.pjb.com.au/comp/lua/midialsa.html
I borrowed the C-code from Patricio Paez' python-module.
Is marking the OUTPUT-port also as INPUT just a matter of adding
SND_SEQ_PORT_CAP_WRITE| to the
snd_seq_create_simple_port(seq_handle, "Output port" ...
parameters ?

int portid, n;
if (snd_seq_open(&seq_handle, "default", SND_SEQ_OPEN_DUPLEX, 0) < 0) {
fprintf(stderr, "Error creating ALSA client.\n");
lua_pushboolean(L, 0); return 1;
}
snd_seq_set_client_name(seq_handle, client_name );

if ( createqueue )
queue_id = snd_seq_alloc_queue(seq_handle);
else
queue_id = SND_SEQ_QUEUE_DIRECT;

for ( n=0; n < ninputports; n++ ) {
if (( portid = snd_seq_create_simple_port(seq_handle, "Input port",
SND_SEQ_PORT_CAP_WRITE|SND_SEQ_PORT_CAP_SUBS_WRITE,
SND_SEQ_PORT_TYPE_APPLICATION)) < 0) {
fprintf(stderr, "Error creating input port %d.\n", n );
lua_pushboolean(L, 0); return 1;
}
if( createqueue ) {
/* set timestamp info of port */
snd_seq_port_info_t *pinfo;
snd_seq_port_info_alloca(&pinfo);
snd_seq_get_port_info(seq_handle, portid, pinfo);
snd_seq_port_info_set_timestamping(pinfo, 1);
snd_seq_port_info_set_timestamp_queue(pinfo, queue_id);
snd_seq_port_info_set_timestamp_real(pinfo, 1);
snd_seq_set_port_info(seq_handle, portid, pinfo);
}
}
for ( n=0; n < noutputports; n++ ) {
if (( portid = snd_seq_create_simple_port(seq_handle, "Output port",
SND_SEQ_PORT_CAP_READ|SND_SEQ_PORT_CAP_SUBS_READ,
SND_SEQ_PORT_TYPE_APPLICATION)) < 0) {
fprintf(stderr, "Error creating output port %d.\n", n );
lua_pushboolean(L, 0); return 1;
}
}
firstoutputport = ninputports;
lastoutputport = noutputports + ninputports - 1;
lua_pushboolean(L, 1); return 1;

I have another question there, too, only slightly off-topic:
If I want to create an Input/Output port, so that both input and
output go through midifoo:0 , do I have to use snd_seq_create_port()
or is that possible within snd_seq_create_simple_port() using
different "caps = capability bits" parameters ?
http://alsa-project.org/alsa-doc/alsa-lib/group___seq_port.html
That is: do I just add SND_SEQ_PORT_CAP_DUPLEX| to the
snd_seq_create_simple_port() call ? Does it make sense to specify
both SND_SEQ_PORT_CAP_WRITE and SND_SEQ_PORT_CAP_READ, without
also specifying SND_SEQ_PORT_CAP_DUPLEX ? or vice versa ?
I'm not sure how they interrelate ...

Post by Clemens Ladisch
Alternatively, listen for these notifications from the System
Announce port.

Good low-tech workaround :-)

Thanks, Regards, Peter

[Clemens Ladisch]

Post by Peter Billam
Is marking the OUTPUT-port also as INPUT just a matter of adding
SND_SEQ_PORT_CAP_WRITE| to the
snd_seq_create_simple_port(seq_handle, "Output port" ...
parameters ?

Yes.

Post by Peter Billam
If I want to create an Input/Output port, so that both input and
output go through midifoo:0 , do I have to use snd_seq_create_port()
or is that possible within snd_seq_create_simple_port() using
different "caps = capability bits" parameters ?

Just specify both READ and WRITE.

Post by Peter Billam
That is: do I just add SND_SEQ_PORT_CAP_DUPLEX| to the
snd_seq_create_simple_port() call ? Does it make sense to specify
both SND_SEQ_PORT_CAP_WRITE and SND_SEQ_PORT_CAP_READ, without
also specifying SND_SEQ_PORT_CAP_DUPLEX ? or vice versa ?

If you want to allow other clients to send events to the port, set the
WRITE flag.

If you want to allow other clients to create a subscription to the port,
set the WRITE and SUBS_WRITE flags.

If you want to allow other clients to create a subscription from the
port, set the READ and SUBS_READ flags.

(Setting only the READ flag does not make sense because these flags
specify what *other* clients are allowed to do.)

The DUPLEX flag is purely informational, but you should set it if the
port supports both directions.


Regards,
Clemens

[Peter Billam]

Post by Clemens Ladisch

Post by Peter Billam
Is marking the OUTPUT-port also as INPUT just a matter of adding
SND_SEQ_PORT_CAP_WRITE| to the
snd_seq_create_simple_port(seq_handle, "Output port" ...
parameters ?

Yes.

Post by Peter Billam
If I want to create an Input/Output port, so that both input
and output go through midifoo:0

Just specify both READ and WRITE.

Post by Peter Billam
That is: do I just add SND_SEQ_PORT_CAP_DUPLEX| to the
snd_seq_create_simple_port() call ? Does it make sense to specify
both SND_SEQ_PORT_CAP_WRITE and SND_SEQ_PORT_CAP_READ, without
also specifying SND_SEQ_PORT_CAP_DUPLEX ? or vice versa ?

If you want to allow other clients to send events to the port,
set the WRITE flag.
If you want to allow other clients to create a subscription to
the port, set the WRITE and SUBS_WRITE flags.
If you want to allow other clients to create a subscription from
the port, set the READ and SUBS_READ flags.
(Setting only the READ flag does not make sense because these flags
specify what *other* clients are allowed to do.)
The DUPLEX flag is purely informational, but you should set it if
the port supports both directions.

That's excellent, Clemens, very helpful, many thanks :-)

Regards, Peter