refclock_chu.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_chu - clock driver for Canadian CHU time/frequency station
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#if defined(REFCLOCK) && defined(CLOCK_CHU)

#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_AUDIO
#include "audio.h"
#endif /* HAVE_AUDIO */

#define ICOM 	1		/* undefine to suppress ICOM code */

#ifdef ICOM
#include "icom.h"
#endif /* ICOM */

/*
 * Audio CHU demodulator/decoder
 *
 * This driver synchronizes the computer time using data encoded in
 * radio transmissions from Canadian time/frequency station CHU in
 * Ottawa, Ontario. Transmissions are made continuously on 3330 kHz,
 * 7335 kHz and 14670 kHz in upper sideband, compatible AM mode. An
 * ordinary shortwave receiver can be tuned manually to one of these
 * frequencies or, in the case of ICOM receivers, the receiver can be
 * tuned automatically using this program as propagation conditions
 * change throughout the day and night.
 *
 * The driver receives, demodulates and decodes the radio signals when
 * connected to the audio codec of a suported workstation hardware and
 * operating system. These include Solaris, SunOS, FreeBSD, NetBSD and
 * Linux. In this implementation, only one audio driver and codec can be
 * supported on a single machine.
 *
 * The driver can be compiled to use a Bell 103 compatible modem or
 * modem chip to receive the radio signal and demodulate the data.
 * Alternatively, the driver can be compiled to use the audio codec of
 * the Sun workstation or another with compatible audio drivers. In the
 * latter case, the driver implements the modem using DSP routines, so
 * the radio can be connected directly to either the microphone on line
 * input port. In either case, the driver decodes the data using a
 * maximum likelihood technique which exploits the considerable degree
 * of redundancy available to maximize accuracy and minimize errors.
 *
 * The CHU time broadcast includes an audio signal compatible with the
 * Bell 103 modem standard (mark = 2225 Hz, space = 2025 Hz). It consist
 * of nine, ten-character bursts transmitted at 300 bps and beginning
 * each second from second 31 to second 39 of the minute. Each character
 * consists of eight data bits plus one start bit and two stop bits to
 * encode two hex digits. The burst data consist of five characters (ten
 * hex digits) followed by a repeat of these characters. In format A,
 * the characters are repeated in the same polarity; in format B, the
 * characters are repeated in the opposite polarity.
 *
 * Format A bursts are sent at seconds 32 through 39 of the minute in
 * hex digits
 *
 *	6dddhhmmss6dddhhmmss
 *
 * The first ten digits encode a frame marker (6) followed by the day
 * (ddd), hour (hh in UTC), minute (mm) and the second (ss). Since
 * format A bursts are sent during the third decade of seconds the tens
 * digit of ss is always 3. The driver uses this to determine correct
 * burst synchronization. These digits are then repeated with the same
 * polarity.
 *
 * Format B bursts are sent at second 31 of the minute in hex digits
 *
 *	xdyyyyttaaxdyyyyttaa
 *
 * The first ten digits encode a code (x described below) followed by
 * the DUT1 (d in deciseconds), Gregorian year (yyyy), difference TAI -
 * UTC (tt) and daylight time indicator (aa) peculiar to Canada. These
 * digits are then repeated with inverted polarity.
 *
 * The x is coded
 *
 * 1 Sign of DUT (0 = +)
 * 2 Leap second warning. One second will be added.
 * 4 Leap second warning. One second will be subtracted.
 * 8 Even parity bit for this nibble.
 *
 * By design, the last stop bit of the last character in the burst
 * coincides with 0.5 second. Since characters have 11 bits and are
 * transmitted at 300 bps, the last stop bit of the first character
 * coincides with 0.5 - 10 * 11/300 = 0.133 second. Depending on the
 * UART, character interrupts can vary somewhere between the beginning
 * of bit 9 and end of bit 11. These eccentricities can be corrected
 * along with the radio propagation delay using fudge time 1.
 *
 * Debugging aids
 *
 * The timecode format used for debugging and data recording includes
 * data helpful in diagnosing problems with the radio signal and serial
 * connections. With debugging enabled (-d on the ntpd command line),
 * the driver produces one line for each burst in two formats
 * corresponding to format A and B. Following is format A:
 *
 *	n b f s m code
 *
 * where n is the number of characters in the burst (0-11), b the burst
 * distance (0-40), f the field alignment (-1, 0, 1), s the
 * synchronization distance (0-16), m the burst number (2-9) and code
 * the burst characters as received. Note that the hex digits in each
 * character are reversed, so the burst
 *
 *	10 38 0 16 9 06851292930685129293
 *
 * is interpreted as containing 11 characters with burst distance 38,
 * field alignment 0, synchronization distance 16 and burst number 9.
 * The nibble-swapped timecode shows day 58, hour 21, minute 29 and
 * second 39.
 *
 * When the audio driver is compiled, format A is preceded by
 * the current gain (0-255) and relative signal level (0-9999). The
 * receiver folume control should be set so that the gain is somewhere
 * near the middle of the range 0-255, which results in a signal level
 * near 1000.
 *
 * Following is format B:
 * 
 *	n b s code
 *
 * where n is the number of characters in the burst (0-11), b the burst
 * distance (0-40), s the synchronization distance (0-40) and code the
 * burst characters as received. Note that the hex digits in each
 * character are reversed and the last ten digits inverted, so the burst
 *
 *	11 40 1091891300ef6e76ecff
 *
 * is interpreted as containing 11 characters with burst distance 40.
 * The nibble-swapped timecode shows DUT1 +0.1 second, year 1998 and TAI
 * - UTC 31 seconds.
 *
 * In addition to the above, the reference timecode is updated and
 * written to the clockstats file and debug score after the last burst
 * received in the minute. The format is
 *
 *	qq yyyy ddd hh:mm:ss nn dd tt
 *
 * where qq are the error flags, as described below, yyyy is the year,
 * ddd the day, hh:mm:ss the time of day, nn the number of format A
 * bursts received during the previous minute, dd the decoding distance
 * and tt the number of timestamps. The error flags are cleared after
 * every update.
 *
 * Fudge factors
 *
 * For accuracies better than the low millisceconds, fudge time1 can be
 * set to the radio propagation delay from CHU to the receiver. This can
 * be done conviently using the minimuf program.
 *
 * Fudge flag4 causes the dubugging output described above to be
 * recorded in the clockstats file. When the audio driver is compiled,
 * 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.
 *
 * The audio codec code is normally compiled in the driver if the
 * architecture supports it (HAVE_AUDIO defined), but is used only if
 * the link /dev/chu_audio is defined and valid. The serial port code is
 * always compiled in the driver, but is used only if the autdio codec
 * is not available and the link /dev/chu%d is defined and valid.
 *
 * The ICOM code is normally compiled in the driver if selected (ICOM
 * defined), but is used only if the link /dev/icom%d is defined and
 * valid and the mode keyword on the server configuration command
 * specifies a nonzero mode (ICOM ID select code). The C-IV speed is
 * 9600 bps if the high order 0x80 bit of the mode is zero and 1200 bps
 * if one. The C-IV trace is turned on if the debug level is greater
 * than one.
 */
/*
 * Interface definitions
 */
#define	SPEED232	B300	/* uart speed (300 baud) */
#define	PRECISION	(-10)	/* precision assumed (about 1 ms) */
#define	REFID		"CHU"	/* reference ID */
#define	DEVICE		"/dev/chu%d" /* device name and unit */
#define	SPEED232	B300	/* UART speed (300 baud) */
#ifdef ICOM
#define TUNE		.001	/* offset for narrow filter (kHz) */
#define DWELL		5	/* minutes in a probe cycle */
#define NCHAN		3	/* number of channels */
#define ISTAGE		3	/* number of integrator stages */
#endif /* ICOM */

#ifdef HAVE_AUDIO
/*
 * Audio demodulator definitions
 */
#define SECOND		8000	/* nominal sample rate (Hz) */
#define BAUD		300	/* modulation rate (bps) */
#define OFFSET		128	/* companded sample offset */
#define SIZE		256	/* decompanding table size */
#define	MAXSIG		6000.	/* maximum signal level */
#define	MAXCLP		100	/* max clips above reference per s */
#define LIMIT		1000.	/* soft limiter threshold */
#define AGAIN		6.	/* baseband gain */
#define LAG		10	/* discriminator lag */
#define	DEVICE_AUDIO	"/dev/audio" /* device name */
#define	DESCRIPTION	"CHU Audio/Modem Receiver" /* WRU */
#define	AUDIO_BUFSIZ	240	/* audio buffer size (30 ms) */
#else
#define	DESCRIPTION	"CHU Modem Receiver" /* WRU */
#endif /* HAVE_AUDIO */

/*
 * Decoder definitions
 */
#define CHAR		(11. / 300.) /* character time (s) */
#define	FUDGE		.185	/* offset to first stop bit (s) */
#define BURST		11	/* max characters per burst */
#define MINCHAR		9	/* min characters per burst */
#define MINDIST		28	/* min burst distance (of 40)  */
#define MINBURST	4	/* min bursts in minute */
#define MINSYNC		8	/* min sync distance (of 16) */
#define MINSTAMP	20	/* min timestamps (of 60) */
#define METRIC		50.	/* min channel metric */
#define PANIC		1440	/* panic timeout (m) */
#define HOLD		30	/* reach hold (m) */

/*
 * Hex extension codes (>= 16)
 */
#define HEX_MISS	16	/* miss _ */
#define HEX_SOFT	17	/* soft error * */
#define HEX_HARD	18	/* hard error = */

/*
 * Status bits (status)
 */
#define RUNT		0x0001	/* runt burst */
#define NOISE		0x0002	/* noise burst */
#define BFRAME		0x0004	/* invalid format B frame sync */
#define BFORMAT		0x0008	/* invalid format B data */
#define AFRAME		0x0010	/* invalid format A frame sync */
#define AFORMAT		0x0020	/* invalid format A data */
#define DECODE		0x0040	/* invalid data decode */
#define STAMP		0x0080	/* too few timestamps */
#define AVALID		0x0100	/* valid A frame */
#define BVALID		0x0200	/* valid B frame */
#define INSYNC		0x0400	/* clock synchronized */

/*
 * Alarm status bits (alarm)
 *
 * These alarms are set at the end of a minute in which at least one
 * burst was received. SYNERR is raised if the AFRAME or BFRAME status
 * bits are set during the minute, FMTERR is raised if the AFORMAT or
 * BFORMAT status bits are set, DECERR is raised if the DECODE status
 * bit is set and TSPERR is raised if the STAMP status bit is set.
 */
#define SYNERR		0x01	/* frame sync error */
#define FMTERR		0x02	/* data format error */
#define DECERR		0x04	/* data decoding error */
#define TSPERR		0x08	/* insufficient data */

#ifdef HAVE_AUDIO
/*
 * Maximum likelihood UART structure. There are eight of these
 * corresponding to the number of phases.
 */ 
struct surv {
	double	shift[12];	/* mark register */
	double	es_max, es_min;	/* max/min envelope signals */
	double	dist;		/* sample distance */
	int	uart;		/* decoded character */
};
#endif /* HAVE_AUDIO */

#ifdef ICOM
/*
 * CHU station structure. There are three of these corresponding to the
 * three frequencies.
 */
struct xmtr {
	double	integ[ISTAGE];	/* circular integrator */
	double	metric;		/* integrator sum */
	int	iptr;		/* integrator pointer */
	int	probe;		/* dwells since last probe */
};
#endif /* ICOM */

/*
 * CHU unit control structure
 */
struct chuunit {
	u_char	decode[20][16];	/* maximum likelihood decoding matrix */
	l_fp	cstamp[BURST];	/* character timestamps */
	l_fp	tstamp[MAXSTAGE]; /* timestamp samples */
	l_fp	timestamp;	/* current buffer timestamp */
	l_fp	laststamp;	/* last buffer timestamp */
	l_fp	charstamp;	/* character time as a l_fp */
	int	errflg;		/* error flags */
	int	status;		/* status bits */
	char	ident[5];	/* station ID and channel */
#ifdef ICOM
	int	fd_icom;	/* ICOM file descriptor */
	int	chan;		/* data channel */
	int	achan;		/* active channel */
	int	dwell;		/* dwell cycle */
	struct xmtr xmtr[NCHAN]; /* station metric */
#endif /* ICOM */

	/*
	 * Character burst variables
	 */
	int	cbuf[BURST];	/* character buffer */
	int	ntstamp;	/* number of timestamp samples */
	int	ndx;		/* buffer start index */
	int	prevsec;	/* previous burst second */
	int	burdist;	/* burst distance */
	int	syndist;	/* sync distance */
	int	burstcnt;	/* format A bursts this minute */

	/*
	 * Format particulars
	 */
	int	leap;		/* leap/dut code */
	int	dut;		/* UTC1 correction */
	int	tai;		/* TAI - UTC correction */
	int	dst;		/* Canadian DST code */

#ifdef HAVE_AUDIO
	/*
	 * Audio codec variables
	 */
	int	fd_audio;	/* audio port file descriptor */
	double	comp[SIZE];	/* decompanding table */
	int	port;		/* codec port */
	int	gain;		/* codec gain */
	int	mongain;	/* codec monitor gain */
	int	clipcnt;	/* sample clip count */
	int	seccnt;		/* second interval counter */

	/*
	 * Modem variables
	 */
	l_fp	tick;		/* audio sample increment */
	double	bpf[9];		/* IIR bandpass filter */
	double	disc[LAG];	/* discriminator shift register */
	double	lpf[27];	/* FIR lowpass filter */
	double	monitor;	/* audio monitor */
	double	maxsignal;	/* signal level */
	int	discptr;	/* discriminator pointer */

	/*
	 * Maximum likelihood UART variables
	 */
	double	baud;		/* baud interval */
	struct surv surv[8];	/* UART survivor structures */
	int	decptr;		/* decode pointer */
	int	dbrk;		/* holdoff counter */
#endif /* HAVE_AUDIO */
};

/*
 * Function prototypes
 */
static	int	chu_start	P((int, struct peer *));
static	void	chu_shutdown	P((int, struct peer *));
static	void	chu_receive	P((struct recvbuf *));
static	void	chu_poll	P((int, struct peer *));

/*
 * More function prototypes
 */
static	void	chu_decode	P((struct peer *, int));
static	void	chu_burst	P((struct peer *));
static	void	chu_clear	P((struct peer *));
static	void	chu_a		P((struct peer *, int));
static	void	chu_b		P((struct peer *, int));
static	int	chu_dist	P((int, int));
static	double	chu_major	P((struct peer *));
#ifdef HAVE_AUDIO
static	void	chu_uart	P((struct surv *, double));
static	void	chu_rf		P((struct peer *, double));
static	void	chu_gain	P((struct peer *));
static	void	chu_audio_receive P((struct recvbuf *rbufp));
#endif /* HAVE_AUDIO */
#ifdef ICOM
static	int	chu_newchan	P((struct peer *, double));
#endif /* ICOM */
static	void	chu_serial_receive P((struct recvbuf *rbufp));

/*
 * Global variables
 */
static char hexchar[] = "0123456789abcdef_*=";

#ifdef ICOM
/*
 * Note the tuned frequencies are 1 kHz higher than the carrier. CHU
 * transmits on USB with carrier so we can use AM and the narrow SSB
 * filter.
 */
static double qsy[NCHAN] = {3.330, 7.335, 14.670}; /* freq (MHz) */
#endif /* ICOM */

/*
 * Transfer vector
 */
struct	refclock refclock_chu = {
	chu_start,		/* start up driver */
	chu_shutdown,		/* shut down driver */
	chu_poll,		/* transmit poll message */