[LAD] alsa sequencer latency ( snd_seq_ev_schedule_real ) - need help!

[nescivi]

Hiho,

I am experiencing strange things with some code that uses the ALSA sequencer, 
with the function
 	snd_seq_ev_schedule_real(evt, mQueue, 1, &time);

The timing of this is unreliable.

At times it goes as expected for a while, but then after some time large 
delays (minutes, instead of the expected latency of 0.1 second) are 
introduced.

Does anyone have any idea what the problem could be?

I have a code snippet below. In case anyone wants to try (the app is 
SuperCollider, you need the latest svn).

I'm on a Debian kernel (2.6.24-1-amd64 #1 SMP Thu Mar 27 16:52:38 UTC 2008 
x86_64 GNU/Linux), in case that is relevant.


sincerely,
Marije



int SC_AlsaMidiClient::sendEvent(int outputIndex, int uid, snd_seq_event_t* 
evt, float late)
{
	snd_seq_real_time time;
	
	if ((outputIndex < 0) || (outputIndex >= mNumOutPorts)) return 
errIndexOutOfRange;

	snd_seq_ev_set_source(evt, mOutPorts[outputIndex]);
	if (uid == 0) {
		// send to all subscribed ports
		snd_seq_ev_set_subs(evt);
	} else {
		// send to specific port
		int cid, pid;
		SC_AlsaParseUID(uid, cid, pid);
		snd_seq_ev_set_dest(evt, cid, pid);
	}

	long latelong;
	if (late > 0.f) {
		latelong = (long) (late * 1000000000);
// new time calculation. The old one was not correct
		time.tv_sec = (long)(latelong / 1000000000); // seconds
		time.tv_nsec = (long)(latelong % 1000000000); // nanoseconds
	} else {
		time.tv_sec = time.tv_nsec = 0;
	}

// 	evt->flags = evt->flags | SND_SEQ_TIME_STAMP_REAL;

 	post("MIDI (ALSA): sending event, time %i, %i, late %f, latelong %i\n", 
time.tv_sec, time.tv_nsec, late, latelong);

	snd_seq_ev_schedule_real(evt, mQueue, 1, &time);
	snd_seq_event_output_direct(mHandle, evt);
// 	snd_seq_event_output(mHandle, evt);

	return errNone;
}