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add a new AMSG_BYE, sent by the client to requst the server to
free resources and drop the connection. This allows the client
to ensuire that at any time it's using only one connection, thus
only one MIDI control channel.

/*	$OpenBSD: amsg.h,v 1.10 2009/08/28 06:37:06 ratchov Exp $	*/
/*
 * Copyright (c) 2008 Alexandre Ratchov <alex@caoua.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#ifndef AMSG_H
#define AMSG_H

#include <stdint.h>

/*
 * WARNING: since the protocol may be simultaneously used by static
 * binaries or by different versions of a shared library, we are not
 * allowed to change the packet binary representation in a backward
 * incompatible way.
 *
 * Especially, make sure the amsg_xxx structures are not larger
 * than 32 bytes.
 */
struct amsg {
#define AMSG_ACK	0	/* ack for START/STOP */
#define AMSG_GETPAR	1	/* get the current parameters */
#define AMSG_SETPAR	2	/* set the current parameters */
#define AMSG_START	3	/* request the server to start the stream */
#define AMSG_STOP	4	/* request the server to stop the stream */
#define AMSG_DATA	5	/* data block */
#define AMSG_MOVE	6	/* position changed */
#define AMSG_GETCAP	7	/* get capabilities */
#define AMSG_SETVOL	8	/* set volume */
#define AMSG_HELLO	9	/* say hello, check versions and so ... */
#define AMSG_BYE	10	/* ask server to drop connection */
	uint32_t cmd;
	uint32_t __pad;
	union {
		struct amsg_par {
			uint8_t legacy_mode;	/* compat for old libs */
#define AMSG_IGNORE	0			/* loose sync */
#define AMSG_SYNC	1			/* resync after xrun */
#define AMSG_ERROR	2			/* kill the stream */
			uint8_t xrun;		/* one of above */
			uint8_t bps;		/* bytes per sample */
			uint8_t bits;		/* actually used bits */
			uint8_t msb;		/* 1 if MSB justified */
			uint8_t le;		/* 1 if little endian */
			uint8_t sig;		/* 1 if signed */
			uint8_t __pad1;
			uint16_t pchan;		/* play channels */
			uint16_t rchan;		/* record channels */
			uint32_t rate;		/* frames per second */
			uint32_t bufsz;		/* total buffered frames */
			uint32_t round;
			uint32_t appbufsz;	/* client side bufsz */
			uint32_t _reserved[1];	/* for future use */
		} par;
		struct amsg_cap {
			uint32_t rate;		/* native rate */
			uint32_t _reserved2[1];	/* for future use */
			uint16_t rchan;		/* native rec channels */
			uint16_t pchan;		/* native play channels */
			uint8_t bits;		/* native bits per sample */
			uint8_t bps;		/* native ytes per sample */
			uint8_t _reserved[10];	/* for future use */
		} cap;
		struct amsg_data {
#define AMSG_DATAMAX	0x1000
			uint32_t size;
		} data;
		struct amsg_ts {
			int32_t delta;
		} ts;
		struct amsg_vol {
			uint32_t ctl;
		} vol;
		struct amsg_hello {
#define AMSG_PLAY	0x1			/* audio playback */
#define AMSG_REC	0x2			/* audio recording */
#define AMSG_MIDIIN	0x4			/* MIDI thru input */
#define AMSG_MIDIOUT	0x8			/* MIDI thru output */
#define AMSG_MIXER	0x10			/* MIDI mixer */
			uint16_t proto;		/* protocol type */
			uint8_t reserved1[6];	/* for future use */
			char opt[12];		/* profile name */
			char who[12];		/* hint for leases */
		} hello;
	} u;
};

/*
 * Initialize an amsg structure: fill all fields with 0xff, so the read
 * can test which fields were set.
 */
#define AMSG_INIT(m) do { memset((m), 0xff, sizeof(struct amsg)); } while (0)

/*
 * Since the structure is memset to 0xff, the MSB can be used to check
 * if any field was set.
 */
#define AMSG_ISSET(x) (((x) & (1 << (8 * sizeof(x) - 1))) == 0)

#endif /* !defined(AMSG_H) */