can't figure out how to send events via alsa_seq

can't figure out how to send events via alsa_seq

[Florian Schmidt]

Hi,

the below example code was planned for me to be a testcase to figure out
where the timing instabilities i see with different midi sequencers come
from. So i created this little program running SCHED_FIFO at prio 98
(higher than jack, so it will not be disturbed by it, etc..), mlocking
memory, yada yada

But when i hook up the created ports to some softsynth or even a midi
monitor app i don't get anything. No event is ever sent. I must be
missing something obvious, so please enlighten me (i don't need
any steenking queue's i just want to send a midi event _now_ ):

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <cstdlib>
#include <iomanip>

#include <pthread.h>
#include <linux/rtc.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <poll.h>
#include <signal.h>
#include <time.h>

#include <alsa/asoundlib.h>

#define RTC_FREQ  2048.0
#define NOTE_FREQ    1.0
#define RT_PRIO     98

int main() 
{
	int fd;

	fd = open("/dev/rtc", O_RDONLY);

	if (fd ==  -1) {
		perror("/dev/rtc");
		exit(errno);
	}

	int retval = ioctl(fd, RTC_IRQP_SET, (int)RTC_FREQ);

	if (retval == -1) {
		perror("ioctl");
		exit(errno);
	}

	std::cout << "locking memory" << std::endl;
	mlockall(MCL_CURRENT);

	// std::cout << "sleeping 1 sec" << std::endl;
	// sleep(1);

	snd_seq_t *seq_handle;

	int err, port_no;

	err = snd_seq_open(&seq_handle, "default", SND_SEQ_OPEN_OUTPUT, 0);

	if (err < 0) {
		std::cout << "error" << std::endl;
		exit(0);
	}

	std::string port_name = "midi_timer";
	// set the name to something reasonable..

	err = snd_seq_set_client_name(seq_handle, port_name.c_str());

	if (err < 0) {
		std::cout << "error" << std::endl;
		exit(0);
	}

	// this is the port others can connect to. we don't do autoconnect ourself
	err = snd_seq_create_simple_port(seq_handle, "midi_timer:output", SND_SEQ_PORT_CAP_READ|SND_SEQ_PORT_CAP_SUBS_READ, SND_SEQ_PORT_TYPE_MIDI_GENERIC);

	if (err < 0) {
		std::cout << "error" << std::endl;
		exit(0);
	}

	// on success we know our port no
	port_no = err;

	struct sched_param param;
	int policy;

	pthread_getschedparam(pthread_self(), &policy, &param);
	param.sched_priority = RT_PRIO;
	policy = SCHED_FIFO;
	pthread_setschedparam(pthread_self(), policy, &param);
	

	std::cout << "turning irq on" << std::endl;
	retval = ioctl(fd, RTC_PIE_ON, 0);

	if (retval == -1) {
		perror("ioctl");
		exit(errno);
	}

	snd_seq_event_t ev;

	unsigned long data;
	
	int ticks_passed = 0;

	while(1) {
		// then we read it
		retval = read(fd, &data, sizeof(unsigned long));
		if (retval == -1) {
			perror("read");
			exit(errno);
		}
		if ((float)ticks_passed >= (RTC_FREQ/NOTE_FREQ)) {
			std::cout << "play note" << std::endl;
			ticks_passed -= (long int)(RTC_FREQ/NOTE_FREQ);

			// play note
			snd_seq_ev_clear(&ev);
			snd_seq_ev_set_direct(&ev);
			snd_seq_ev_set_source(&ev, port_no);
			ev.type = SND_SEQ_EVENT_NOTEON;
			ev.data.note.note = 53;
			ev.data.note.velocity = 100;
			
			snd_seq_event_output_direct(seq_handle, &ev);

			snd_seq_drain_output(seq_handle);
		}
		data = (data >> 8);
		// std::cout << data << std::endl;
		ticks_passed += data;
	}
	return 0;
}


-- 
Palimm Palimm!
http://tapas.affenbande.org


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Re: can't figure out how to send events via alsa_seq

[Florian Schmidt]

On Thu, 29 Dec 2005 17:28:34 +0100
Florian Schmidt <mista.tapas@gmx.net> wrote:

> But when i hook up the created ports to some softsynth or even a midi
> monitor app i don't get anything. No event is ever sent. I must be
> missing something obvious, so please enlighten me (i don't need
> any steenking queue's i just want to send a midi event _now_ ):

Ahh, damn, i forgot to use snd_seq_ev_set_subs(). Now it works.. hmm..

Flo


-- 
Palimm Palimm!
http://tapas.affenbande.org


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