linux/sound/core/seq/seq_system.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *   ALSA sequencer System services Client
 *   Copyright (c) 1998-1999 by Frank van de Pol <[email protected]>
 */

#include <linux/init.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <sound/core.h>
#include "seq_system.h"
#include "seq_timer.h"
#include "seq_queue.h"

/* internal client that provide system services, access to timer etc. */

/*
 * Port "Timer"
 *      - send tempo /start/stop etc. events to this port to manipulate the 
 *        queue's timer. The queue address is specified in
 *	  data.queue.queue.
 *      - this port supports subscription. The received timer events are 
 *        broadcasted to all subscribed clients. The modified tempo
 *	  value is stored on data.queue.value.
 *	  The modifier client/port is not send.
 *
 * Port "Announce"
 *      - does not receive message
 *      - supports supscription. For each client or port attaching to or 
 *        detaching from the system an announcement is send to the subscribed
 *        clients.
 *
 * Idea: the subscription mechanism might also work handy for distributing 
 * synchronisation and timing information. In this case we would ideally have
 * a list of subscribers for each type of sync (time, tick), for each timing
 * queue.
 *
 * NOTE: the queue to be started, stopped, etc. must be specified
 *	 in data.queue.addr.queue field.  queue is used only for
 *	 scheduling, and no longer referred as affected queue.
 *	 They are used only for timer broadcast (see above).
 *							-- iwai
 */


/* client id of our system client */
static int sysclient = …;

/* port id numbers for this client */
static int announce_port = …;



/* fill standard header data, source port & channel are filled in */
static int setheader(struct snd_seq_event * ev, int client, int port)
{ … }


/* entry points for broadcasting system events */
void snd_seq_system_broadcast(int client, int port, int type)
{ … }
EXPORT_SYMBOL_GPL(…);

/* entry points for broadcasting system events */
int snd_seq_system_notify(int client, int port, struct snd_seq_event *ev)
{ … }

/* call-back handler for timer events */
static int event_input_timer(struct snd_seq_event * ev, int direct, void *private_data, int atomic, int hop)
{ … }

/* register our internal client */
int __init snd_seq_system_client_init(void)
{ … }


/* unregister our internal client */
void snd_seq_system_client_done(void)
{ … }