refclock_irig.c

网络时间协议NTP 源码 版本v4.2.0b 该源码用于linux平台下

/*
 * refclock_irig - audio IRIG-B/E demodulator/decoder
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#if defined(REFCLOCK) && defined(CLOCK_IRIG)

#include "ntpd.h"
#include "ntp_io.h"
#include "ntp_refclock.h"
#include "ntp_calendar.h"
#include "ntp_stdlib.h"

#include <stdio.h>
#include <ctype.h>
#include <math.h>
#ifdef HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif /* HAVE_SYS_IOCTL_H */

#include "audio.h"

/*
 * Audio IRIG-B/E demodulator/decoder
 *
 * This driver receives, demodulates and decodes IRIG-B/E signals when
 * connected to the audio codec /dev/audio. The IRIG signal format is an
 * amplitude-modulated carrier with pulse-width modulated data bits. For
 * IRIG-B, the carrier frequency is 1000 Hz and bit rate 100 b/s; for
 * IRIG-E, the carrier frequenchy is 100 Hz and bit rate 10 b/s. The
 * driver automatically recognizes which format is in use.
 *
 * The program processes 8000-Hz mu-law companded samples using separate
 * signal filters for IRIG-B and IRIG-E, a comb filter, envelope
 * detector and automatic threshold corrector. Cycle crossings relative
 * to the corrected slice level determine the width of each pulse and
 * its value - zero, one or position identifier. The data encode 20 BCD
 * digits which determine the second, minute, hour and day of the year
 * and sometimes the year and synchronization condition. The comb filter
 * exponentially averages the corresponding samples of successive baud
 * intervals in order to reliably identify the reference carrier cycle.
 * A type-II phase-lock loop (PLL) performs additional integration and
 * interpolation to accurately determine the zero crossing of that
 * cycle, which determines the reference timestamp. A pulse-width
 * discriminator demodulates the data pulses, which are then encoded as
 * the BCD digits of the timecode.
 *
 * The timecode and reference timestamp are updated once each second
 * with IRIG-B (ten seconds with IRIG-E) and local clock offset samples
 * saved for later processing. At poll intervals of 64 s, the saved
 * samples are processed by a trimmed-mean filter and used to update the
 * system clock.
 *
 * An automatic gain control feature provides protection against
 * overdriven or underdriven input signal amplitudes. It is designed to
 * maintain adequate demodulator signal amplitude while avoiding
 * occasional noise spikes. In order to assure reliable capture, the
 * decompanded input signal amplitude must be greater than 100 units and
 * the codec sample frequency error less than 250 PPM (.025 percent).
 *
 * The program performs a number of error checks to protect against
 * overdriven or underdriven input signal levels, incorrect signal
 * format or improper hardware configuration. Specifically, if any of
 * the following errors occur for a time measurement, the data are
 * rejected.
 *
 * o The peak carrier amplitude is less than DRPOUT (100). This usually
 *   means dead IRIG signal source, broken cable or wrong input port.
 *
 * o The frequency error is greater than MAXFREQ +-250 PPM (.025%). This
 *   usually means broken codec hardware or wrong codec configuration.
 *
 * o The modulation index is less than MODMIN (0.5). This usually means
 *   overdriven IRIG signal or wrong IRIG format.
 *
 * o A frame synchronization error has occurred. This usually means
 *   wrong IRIG signal format or the IRIG signal source has lost
 *   synchronization (signature control).
 *
 * o A data decoding error has occurred. This usually means wrong IRIG
 *   signal format.
 *
 * o The current second of the day is not exactly one greater than the
 *   previous one. This usually means a very noisy IRIG signal or
 *   insufficient CPU resources.
 *
 * o An audio codec error (overrun) occurred. This usually means
 *   insufficient CPU resources, as sometimes happens with Sun SPARC
 *   IPCs when doing something useful.
 *
 * Note that additional checks are done elsewhere in the reference clock
 * interface routines.
 *
 * Debugging aids
 *
 * The timecode format used for debugging and data recording includes
 * data helpful in diagnosing problems with the IRIG signal and codec
 * connections. With debugging enabled (-d on the ntpd command line),
 * the driver produces one line for each timecode in the following
 * format:
 *
 * 00 1 98 23 19:26:52 721 143 0.694 20 0.1 66.5 3094572411.00027
 *
 * The most recent line is also written to the clockstats file at 64-s
 * intervals.
 *
 * The first field contains the error flags in hex, where the hex bits
 * are interpreted as below. This is followed by the IRIG status
 * indicator, year of century, day of year and time of day. The status
 * indicator and year are not produced by some IRIG devices. Following
 * these fields are the signal amplitude (0-8100), codec gain (0-255),
 * modulation index (0-1), time constant (2-20), carrier phase error
 * (us) and carrier frequency error (PPM). The last field is the on-time
 * timestamp in NTP format.
 *
 * The fraction part of the on-time timestamp is a good indicator of how
 * well the driver is doing. Once upon a time, an UltrSPARC 30 and
 * Solaris 2.7 kept the clock within a few tens of microseconds relative
 * to the IRIG-B signal. Accuracy with IRIG-E was about ten times worse.
 * Unfortunately, Sun broke the 2.7 audio driver in 2.8, which has a 10-
 * ms sawtooth modulation. The driver attempts to remove the modulation
 * by some clever estimation techniques which mostly work. With the
 * "mixerctl -o" command before starting the daemon, the jitter is down
 * to about 100 microseconds. Your experience may vary.
 *
 * Unlike other drivers, which can have multiple instantiations, this
 * one supports only one. It does not seem likely that more than one
 * audio codec would be useful in a single machine. More than one would
 * probably chew up too much CPU time anyway.
 *
 * Fudge factors
 *
 * Fudge flag4 causes the dubugging output described above to be
 * recorded in the clockstats file. Fudge flag2 selects the audio input
 * port, where 0 is the mike port (default) and 1 is the line-in port.
 * It does not seem useful to select the compact disc player port. Fudge
 * flag3 enables audio monitoring of the input signal. For this purpose,
 * the monitor gain is set to a default value. Fudgetime2 is used as a
 * frequency vernier for broken codec sample frequency.
 */
/*
 * Interface definitions
 */
#define	DEVICE_AUDIO	"/dev/audio" /* audio device name */
#define	PRECISION	(-17)	/* precision assumed (about 10 us) */
#define	REFID		"IRIG"	/* reference ID */
#define	DESCRIPTION	"Generic IRIG Audio Driver" /* WRU */
#define	AUDIO_BUFSIZ	320	/* audio buffer size (40 ms) */
#define SECOND		8000	/* nominal sample rate (Hz) */
#define BAUD		80	/* samples per baud interval */
#define OFFSET		128	/* companded sample offset */
#define SIZE		256	/* decompanding table size */
#define CYCLE		8	/* samples per carrier cycle */
#define SUBFLD		10	/* bits per subfield */
#define FIELD		10	/* subfields per field */
#define MINTC		2	/* min PLL time constant */
#define MAXTC		20	/* max PLL time constant max */
#define	MAXSIG		6000.	/* maximum signal level */
#define	MAXCLP		100	/* max clips above reference per s */
#define DRPOUT		100.	/* dropout signal level */
#define MODMIN		0.5	/* minimum modulation index */
#define MAXFREQ		(250e-6 * SECOND) /* freq tolerance (.025%) */
#define PI		3.1415926535 /* the real thing */
#ifdef IRIG_SUCKS
#define	WIGGLE		11	/* wiggle filter length */
#endif /* IRIG_SUCKS */

/*
 * Experimentally determined filter delays
 */
#define IRIG_B		.0019	/* IRIG-B filter delay */
#define IRIG_E		.0019	/* IRIG-E filter delay */

/*
 * Data bit definitions
 */
#define BIT0		0	/* zero */
#define BIT1		1	/* one */
#define BITP		2	/* position identifier */

/*
 * Error flags (up->errflg)
 */
#define IRIG_ERR_AMP	0x01	/* low carrier amplitude */
#define IRIG_ERR_FREQ	0x02	/* frequency tolerance exceeded */
#define IRIG_ERR_MOD	0x04	/* low modulation index */
#define IRIG_ERR_SYNCH	0x08	/* frame synch error */
#define IRIG_ERR_DECODE	0x10	/* frame decoding error */
#define IRIG_ERR_CHECK	0x20	/* second numbering discrepancy */
#define IRIG_ERR_ERROR	0x40	/* codec error (overrun) */
#define IRIG_ERR_SIGERR	0x80	/* IRIG status error (Spectracom) */

/*
 * IRIG unit control structure
 */
struct irigunit {
	u_char	timecode[21];	/* timecode string */
	l_fp	timestamp;	/* audio sample timestamp */
	l_fp	tick;		/* audio sample increment */
	double	integ[BAUD];	/* baud integrator */
	double	phase, freq;	/* logical clock phase and frequency */
	double	zxing;		/* phase detector integrator */
	double	yxing;		/* cycle phase */
	double	exing;		/* envelope phase */
	double	modndx;		/* modulation index */
	double	irig_b;		/* IRIG-B signal amplitude */
	double	irig_e;		/* IRIG-E signal amplitude */
	int	errflg;		/* error flags */
	/*
	 * Audio codec variables
	 */
	double	comp[SIZE];	/* decompanding table */
	int	port;		/* codec port */
	int	gain;		/* codec gain */
	int	mongain;	/* codec monitor gain */
	int	clipcnt;	/* sample clipped count */
	int	seccnt;		/* second interval counter */

	/*
	 * RF variables
	 */
	double	hpf[5];		/* IRIG-B filter shift register */
	double	lpf[5];		/* IRIG-E filter shift register */
	double	intmin, intmax;	/* integrated envelope min and max */
	double	envmax;		/* peak amplitude */
	double	envmin;		/* noise amplitude */
	double	maxsignal;	/* integrated peak amplitude */
	double	noise;		/* integrated noise amplitude */
	double	lastenv[CYCLE];	/* last cycle amplitudes */
	double	lastint[CYCLE];	/* last integrated cycle amplitudes */
	double	lastsig;	/* last carrier sample */
	double	fdelay;		/* filter delay */
	int	decim;		/* sample decimation factor */
	int	envphase;	/* envelope phase */
	int	envptr;		/* envelope phase pointer */
	int	carphase;	/* carrier phase */
	int	envsw;		/* envelope state */
	int	envxing;	/* envelope slice crossing */
	int	tc;		/* time constant */
	int	tcount;		/* time constant counter */
	int	badcnt;		/* decimation interval counter */

	/*
	 * Decoder variables
	 */
	int	pulse;		/* cycle counter */
	int	cycles;		/* carrier cycles */
	int	dcycles;	/* data cycles */
	int	xptr;		/* translate table pointer */
	int	lastbit;	/* last code element length */
	int	second;		/* previous second */
	int	fieldcnt;	/* subfield count in field */
	int	bits;		/* demodulated bits */
	int	bitcnt;		/* bit count in subfield */
#ifdef IRIG_SUCKS
	l_fp	wigwag;		/* wiggle accumulator */
	int	wp;		/* wiggle filter pointer */
	l_fp	wiggle[WIGGLE];	/* wiggle filter */
	l_fp	wigbot[WIGGLE];	/* wiggle bottom fisher*/
#endif /* IRIG_SUCKS */
	l_fp	wuggle;
};

/*
 * Function prototypes
 */
static	int	irig_start	P((int, struct peer *));
static	void	irig_shutdown	P((int, struct peer *));
static	void	irig_receive	P((struct recvbuf *));
static	void	irig_poll	P((int, struct peer *));

/*
 * More function prototypes
 */
static	void	irig_base	P((struct peer *, double));
static	void	irig_rf		P((struct peer *, double));
static	void	irig_decode	P((struct peer *, int));
static	void	irig_gain	P((struct peer *));

/*
 * Transfer vector
 */
struct	refclock refclock_irig = {
	irig_start,		/* start up driver */
	irig_shutdown,		/* shut down driver */
	irig_poll,		/* transmit poll message */
	noentry,		/* not used (old irig_control) */
	noentry,		/* initialize driver (not used) */
	noentry,		/* not used (old irig_buginfo) */
	NOFLAGS			/* not used */
};

/*
 * Global variables
 */
static char	hexchar[] = {	/* really quick decoding table */
	'0', '8', '4', 'c',	/* 0000 0001 0010 0011 */
	'2', 'a', '6', 'e',	/* 0100 0101 0110 0111 */
	'1', '9', '5', 'd',	/* 1000 1001 1010 1011 */
	'3', 'b', '7', 'f'	/* 1100 1101 1110 1111 */
};


/*
 * irig_start - open the devices and initialize data for processing
 */
static int
irig_start(
	int	unit,		/* instance number (used for PCM) */
	struct peer *peer	/* peer structure pointer */
	)
{
	struct refclockproc *pp;
	struct irigunit *up;

	/*
	 * Local variables
	 */
	int	fd;		/* file descriptor */
	int	i;		/* index */
	double	step;		/* codec adjustment */

	/*
	 * Open audio device
	 */
	fd = audio_init(DEVICE_AUDIO, AUDIO_BUFSIZ, unit);
	if (fd < 0)
		return (0);
#ifdef DEBUG
	if (debug)
		audio_show();
#endif

	/*
	 * Allocate and initialize unit structure
	 */
	if (!(up = (struct irigunit *)
	      emalloc(sizeof(struct irigunit)))) {
		(void) close(fd);
		return (0);
	}
	memset((char *)up, 0, sizeof(struct irigunit));
	pp = peer->procptr;
	pp->unitptr = (caddr_t)up;
	pp->io.clock_recv = irig_receive;
	pp->io.srcclock = (caddr_t)peer;
	pp->io.datalen = 0;
	pp->io.fd = fd;