snd_seq_sync_output_queue does not work

snd_seq_sync_output_queue does not work

[Bengt Mÿffffe5nsson]

I'm trying to make an app where I need to exchange an
18k sysex. I use Rh9.
I think I've worked out the receiving part, but
sending will not work.
I chop the big sysex into 256 byte blocks and send in
a sequence. This seems to work fine when I run it
stepwise in the debugger, but crash when I run it at
full speed.
I think I've traced the problem down to the call to
snd_seq_sync_output_queue. I expect that call to hang
until the output is drained, and return a 0.
What happens is that the call seems to return
immediately with a 1.
Tried to use snd_seq_nonblock(0) but that didn't
change anything.
Does anyone have any hint?
/Bengt



		
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Re: snd_seq_sync_output_queue does not work

[Clemens Ladisch]

Bengt Månsson wrote:
> I'm trying to make an app where I need to exchange an
> 18k sysex. I use Rh9.
> I think I've worked out the receiving part, but
> sending will not work.
> I chop the big sysex into 256 byte blocks and send in
> a sequence. This seems to work fine when I run it
> stepwise in the debugger, but crash when I run it at
> full speed.

The sequencer isn't designed to handle big sysexs.  Due to the
message-based architecture it's difficult to signal back to the
sending application that the output buffer is full.

I'd guess some message couldn't be delivered and was thrown away.

Try to limit the rate of messages so that you don't exceed the MIDI
data rate.

> I think I've traced the problem down to the call to
> snd_seq_sync_output_queue. I expect that call to hang
> until the output is drained, and return a 0.
> What happens is that the call seems to return
> immediately with a 1.

The documentation is wrong, any nonnegative return value indicates
success (the current implementation always returns 1).

snd_seq_sync_output_queue waits until all events have been sent.  At
this point, it's too late to detect events than cannot be delivered at
the destination.


The documentation, if it actually existed, would tell you to use the
rawmidi API for big chunks of sysex data.  See the amidi program for
an example.


HTH
Clemens



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Re: snd_seq_sync_output_queue does not work

[Bengt Mÿffffe5nsson]

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Thank you for your quick reply.
I've looked at amidi and maybe that is a solution.
It's a little bit annoying though, since receiving
works so fine. I would prefer a symetrical solution
that is easy to map to tha java api.
Maybe a sleep is easiest, but I'll consider that when
I've had some myself.
/Bengt

--- Clemens Ladisch <clemens@ladisch.de> wrote:

> Bengt Månsson wrote:
> > I'm trying to make an app where I need to exchange
> an
> > 18k sysex. I use Rh9.
> > I think I've worked out the receiving part, but
> > sending will not work.
> > I chop the big sysex into 256 byte blocks and send
> in
> > a sequence. This seems to work fine when I run it
> > stepwise in the debugger, but crash when I run it
> at
> > full speed.
> 
> The sequencer isn't designed to handle big sysexs. 
> Due to the
> message-based architecture it's difficult to signal
> back to the
> sending application that the output buffer is full.
> 
> I'd guess some message couldn't be delivered and was
> thrown away.
> 
> Try to limit the rate of messages so that you don't
> exceed the MIDI
> data rate.
> 
> > I think I've traced the problem down to the call
> to
> > snd_seq_sync_output_queue. I expect that call to
> hang
> > until the output is drained, and return a 0.
> > What happens is that the call seems to return
> > immediately with a 1.
> 
> The documentation is wrong, any nonnegative return
> value indicates
> success (the current implementation always returns
> 1).
> 
> snd_seq_sync_output_queue waits until all events
> have been sent.  At
> this point, it's too late to detect events than
> cannot be delivered at
> the destination.
> 
> 
> The documentation, if it actually existed, would
> tell you to use the
> rawmidi API for big chunks of sysex data.  See the
> amidi program for
> an example.
> 
> 
> HTH
> Clemens
> 
> 



		
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