xref: /netbsd-src/external/bsd/ntp/dist/ntpd/refclock_chu.c (revision eabc0478de71e4e011a5b4e0392741e01d491794)

/*	$NetBSD: refclock_chu.c,v 1.11 2024/08/18 20:47:18 christos Exp $	*/

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

#include "ntp_types.h"

#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,
 * 7850 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 as propagation conditions change throughout the
 * day and season.
 *
 * The driver requires an audio codec or sound card with sampling rate 8
 * kHz and mu-law companding. This is the same standard as used by the
 * telephone industry and is supported by most hardware and operating
 * systems, including 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 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). The signal
 * consists of nine, ten-character bursts transmitted at 300 bps between
 * seconds 31 and 39 of each 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 (nibble swapped)
 *
 *	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 - 9 * 11/300 = 0.170 second. Depending on the
 * UART, character interrupts can vary somewhere between the end 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.Each line begins with the format code
 * chuA or chuB followed by the status code and signal level (0-9999).
 * The remainder of the line is as follows.
 *
 * Following is format A:
 *
 *	n b f s m code
 *
 * where n is the number of characters in the burst (0-10), 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 10 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.
 *
 * Following is format B:
 *
 *	n b s code
 *
 * where n is the number of characters in the burst (0-10), 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
 *
 *	10 40 1091891300ef6e76ec
 *
 * is interpreted as containing 10 characters with burst distance 40.
 * The nibble-swapped timecode shows DUT1 +0.1 second, year 1998 and TAI
 * - UTC 31 seconds.
 *
 * Each line is preceeded by the code chuA or chuB, as appropriate. If
 * the audio driver is compiled, the current gain (0-255) and relative
 * signal level (0-9999) follow the code. The receiver volume 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.
 *
 * 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
 *
 *	sq yyyy ddd hh:mm:ss l s dd t agc ident m b
 *
 * s	'?' before first synchronized and ' ' after that
 * q	status code (see below)
 * yyyy	year
 * ddd	day of year
 * hh:mm:ss time of day
 * l	leap second indicator (space, L or D)
 * dst	Canadian daylight code (opaque)
 * t	number of minutes since last synchronized
 * agc	audio gain (0 - 255)
 * ident identifier (CHU0 3330 kHz, CHU1 7850 kHz, CHU2 14670 kHz)
 * m	signal metric (0 - 100)
 * b	number of timecodes for the previous minute (0 - 59)
 *
 * 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.
 *
 * Alarm codes
 *
 * CEVNT_BADTIME	invalid date or time
 * CEVNT_PROP		propagation failure - no stations heard
 */
/*
 * 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 (MHz) */
#define DWELL		5	/* minutes in a dwell */
#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	MAXAMP		6000.	/* maximum signal level */
#define	MAXCLP		100	/* max clips above reference per s */
#define	SPAN		800.	/* min envelope span */
#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 BURST		11	/* max characters per burst */
#define MINCHARS		9	/* min characters per burst */
#define MINDIST		28	/* min burst distance (of 40)  */
#define MINSYNC		8	/* min sync distance (of 16) */
#define MINSTAMP	20	/* min timestamps (of 60) */
#define MINMETRIC	50	/* min channel metric (of 160) */

/*
 * The on-time synchronization point for the driver is the last stop bit
 * of the first character 170 ms. The modem delay is 0.8 ms, while the
 * receiver delay is approxmately 4.7 ms at 2125 Hz. The fudge value 1.3
 * ms due to the codec and other causes was determined by calibrating to
 * a PPS signal from a GPS receiver. The additional propagation delay
 * specific to each receiver location can be programmed in the fudge
 * time1.
 *
 * The resulting offsets with a 2.4-GHz P4 running FreeBSD 6.1 are
 * generally within 0.5 ms short term with 0.3 ms jitter. The long-term
 * offsets vary up to 0.3 ms due to ionospheric layer height variations.
 * The processor load due to the driver is 0.4 percent.
 */
#define	PDELAY	((170 + .8 + 4.7 + 1.3) / 1000)	/* system delay (s) */

/*
 * 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 */
#define	METRIC		0x0800	/* one or more stations heard */

/*
 * 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 {
	l_fp	cstamp;		/* last bit timestamp */
	double	shift[12];	/* sample shift register */
	double	span;		/* shift register envelope span */
	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	second;		/* counts the seconds of the minute */
	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;		/* radio 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 */
	double	maxsignal;	/* signal level (modem only) */
	int	gain;		/* codec gain (modem only) */

	/*
	 * 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	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 */
	int	discptr;	/* discriminator pointer */

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

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

/*
 * More function prototypes
 */
static	void	chu_decode	(struct peer *, int, l_fp);
static	void	chu_burst	(struct peer *);
static	void	chu_clear	(struct peer *);
static	void	chu_a		(struct peer *, int);
static	void	chu_b		(struct peer *, int);
static	int	chu_dist	(int, int);
static	double	chu_major	(struct peer *);
#ifdef HAVE_AUDIO
static	void	chu_uart	(struct surv *, double);
static	void	chu_rf		(struct peer *, double);
static	void	chu_gain	(struct peer *);
static	void	chu_audio_receive (struct recvbuf *rbufp);
#endif /* HAVE_AUDIO */
#ifdef ICOM
static	int	chu_newchan	(struct peer *, double);
#endif /* ICOM */
static	void	chu_serial_receive (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, 7.850, 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 */
	noentry,		/* not used (old chu_control) */
	noentry,		/* initialize driver (not used) */
	noentry,		/* not used (old chu_buginfo) */
	chu_second		/* housekeeping timer */
};


/*
 * chu_start - open the devices and initialize data for processing
 */
static int
chu_start(
	int	unit,		/* instance number (not used) */
	struct peer *peer	/* peer structure pointer */
	)
{
	struct chuunit *up;
	struct refclockproc *pp;
	char device[20];	/* device name */
	int	fd;		/* file descriptor */
#ifdef ICOM
	int	temp;
#endif /* ICOM */
#ifdef HAVE_AUDIO
	int	fd_audio;	/* audio port file descriptor */
	int	i;		/* index */
	double	step;		/* codec adjustment */

	/*
	 * Open audio device. Don't complain if not there.
	 */
	fd_audio = audio_init(DEVICE_AUDIO, AUDIO_BUFSIZ, unit);

#ifdef DEBUG
	if (fd_audio >= 0 && debug)
		audio_show();
#endif

	/*
	 * If audio is unavailable, Open serial port in raw mode.
	 */
	if (fd_audio >= 0) {
		fd = fd_audio;
	} else {
		snprintf(device, sizeof(device), DEVICE, unit);
		fd = refclock_open(&peer->srcadr, device, SPEED232, LDISC_RAW);
	}
#else /* HAVE_AUDIO */

	/*
	 * Open serial port in raw mode.
	 */
	snprintf(device, sizeof(device), DEVICE, unit);
	fd = refclock_open(&peer->srcadr, device, SPEED232, LDISC_RAW);
#endif /* HAVE_AUDIO */

	if (fd < 0)
		return (0);

	/*
	 * Allocate and initialize unit structure
	 */
	up = emalloc_zero(sizeof(*up));
	pp = peer->procptr;
	pp->unitptr = up;
	pp->io.clock_recv = chu_receive;
	pp->io.srcclock = peer;
	pp->io.datalen = 0;
	pp->io.fd = fd;
	if (!io_addclock(&pp->io)) {
		close(fd);
		pp->io.fd = -1;
		free(up);
		pp->unitptr = NULL;
		return (0);
	}

	/*
	 * Initialize miscellaneous variables
	 */
	peer->precision = PRECISION;
	pp->clockdesc = DESCRIPTION;
	strlcpy(up->ident, "CHU", sizeof(up->ident));
	memcpy(&pp->refid, up->ident, 4);
	DTOLFP(CHAR, &up->charstamp);
#ifdef HAVE_AUDIO

	/*
	 * The companded samples are encoded sign-magnitude. The table
	 * contains all the 256 values in the interest of speed. We do
	 * this even if the audio codec is not available. C'est la lazy.
	 */
	up->fd_audio = fd_audio;
	up->gain = 127;
	up->comp[0] = up->comp[OFFSET] = 0.;
	up->comp[1] = 1; up->comp[OFFSET + 1] = -1.;
	up->comp[2] = 3; up->comp[OFFSET + 2] = -3.;
	step = 2.;
	for (i = 3; i < OFFSET; i++) {
		up->comp[i] = up->comp[i - 1] + step;
		up->comp[OFFSET + i] = -up->comp[i];
                if (i % 16 == 0)
                	step *= 2.;
	}
	DTOLFP(1. / SECOND, &up->tick);
#endif /* HAVE_AUDIO */
#ifdef ICOM
	temp = 0;
#ifdef DEBUG
	if (debug > 1)
		temp = P_TRACE;
#endif
	if (peer->ttl > 0) {
		if (peer->ttl & 0x80)
			up->fd_icom = icom_init("/dev/icom", B1200,
			    temp);
		else
			up->fd_icom = icom_init("/dev/icom", B9600,
			    temp);
	}
	if (up->fd_icom > 0) {
		if (chu_newchan(peer, 0) != 0) {
			msyslog(LOG_NOTICE, "icom: radio not found");
			close(up->fd_icom);
			up->fd_icom = 0;
		} else {
			msyslog(LOG_NOTICE, "icom: autotune enabled");
		}
	}
#endif /* ICOM */
	return (1);
}


/*
 * chu_shutdown - shut down the clock
 */
static void
chu_shutdown(
	int	unit,		/* instance number (not used) */
	struct peer *peer	/* peer structure pointer */
	)
{
	struct chuunit *up;
	struct refclockproc *pp;

	pp = peer->procptr;
	up = pp->unitptr;
	if (up == NULL)
		return;

	io_closeclock(&pp->io);
#ifdef ICOM
	if (up->fd_icom > 0)
		close(up->fd_icom);
#endif /* ICOM */
	free(up);
}


/*
 * chu_receive - receive data from the audio or serial device
 */
static void
chu_receive(
	struct recvbuf *rbufp	/* receive buffer structure pointer */
	)
{
#ifdef HAVE_AUDIO
	struct chuunit *up;
	struct refclockproc *pp;
	struct peer *peer;

	peer = rbufp->recv_peer;
	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * If the audio codec is warmed up, the buffer contains codec
	 * samples which need to be demodulated and decoded into CHU
	 * characters using the software UART. Otherwise, the buffer
	 * contains CHU characters from the serial port, so the software
	 * UART is bypassed. In this case the CPU will probably run a
	 * few degrees cooler.
	 */
	if (up->fd_audio > 0)
		chu_audio_receive(rbufp);
	else
		chu_serial_receive(rbufp);
#else
	chu_serial_receive(rbufp);
#endif /* HAVE_AUDIO */
}


#ifdef HAVE_AUDIO
/*
 * chu_audio_receive - receive data from the audio device
 */
static void
chu_audio_receive(
	struct recvbuf *rbufp	/* receive buffer structure pointer */
	)
{
	struct chuunit *up;
	struct refclockproc *pp;
	struct peer *peer;

	double	sample;		/* codec sample */
	u_char	*dpt;		/* buffer pointer */
	int	bufcnt;		/* buffer counter */
	l_fp	ltemp;		/* l_fp temp */

	peer = rbufp->recv_peer;
	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * Main loop - read until there ain't no more. Note codec
	 * samples are bit-inverted.
	 */
	DTOLFP((double)rbufp->recv_length / SECOND, &ltemp);
	L_SUB(&rbufp->recv_time, &ltemp);
	up->timestamp = rbufp->recv_time;
	dpt = rbufp->recv_buffer;
	for (bufcnt = 0; bufcnt < rbufp->recv_length; bufcnt++) {
		sample = up->comp[~*dpt++ & 0xff];

		/*
		 * Clip noise spikes greater than MAXAMP. If no clips,
		 * increase the gain a tad; if the clips are too high,
		 * decrease a tad.
		 */
		if (sample > MAXAMP) {
			sample = MAXAMP;
			up->clipcnt++;
		} else if (sample < -MAXAMP) {
			sample = -MAXAMP;
			up->clipcnt++;
		}
		chu_rf(peer, sample);
		L_ADD(&up->timestamp, &up->tick);

		/*
		 * Once each second ride gain.
		 */
		up->seccnt = (up->seccnt + 1) % SECOND;
		if (up->seccnt == 0) {
			chu_gain(peer);
		}
	}

	/*
	 * Set the input port and monitor gain for the next buffer.
	 */
	if (pp->sloppyclockflag & CLK_FLAG2)
		up->port = 2;
	else
		up->port = 1;
	if (pp->sloppyclockflag & CLK_FLAG3)
		up->mongain = MONGAIN;
	else
		up->mongain = 0;
}


/*
 * chu_rf - filter and demodulate the FSK signal
 *
 * This routine implements a 300-baud Bell 103 modem with mark 2225 Hz
 * and space 2025 Hz. It uses a bandpass filter followed by a soft
 * limiter, FM discriminator and lowpass filter. A maximum-likelihood
 * decoder samples the baseband signal at eight times the baud rate and
 * detects the start bit of each character.
 *
 * The filters are built for speed, which explains the rather clumsy
 * code. Hopefully, the compiler will efficiently implement the move-
 * and-muiltiply-and-add operations.
 */
static void
chu_rf(
	struct peer *peer,	/* peer structure pointer */
	double	sample		/* analog sample */
	)
{
	struct refclockproc *pp;
	struct chuunit *up;
	struct surv *sp;

	/*
	 * Local variables
	 */
	double	signal;		/* bandpass signal */
	double	limit;		/* limiter signal */
	double	disc;		/* discriminator signal */
	double	lpf;		/* lowpass signal */
	double	dist;		/* UART signal distance */
	int	i, j;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * Bandpass filter. 4th-order elliptic, 500-Hz bandpass centered
	 * at 2125 Hz. Passband ripple 0.3 dB, stopband ripple 50 dB,
	 * phase delay 0.24 ms.
	 */
	signal = (up->bpf[8] = up->bpf[7]) * 5.844676e-01;
	signal += (up->bpf[7] = up->bpf[6]) * 4.884860e-01;
	signal += (up->bpf[6] = up->bpf[5]) * 2.704384e+00;
	signal += (up->bpf[5] = up->bpf[4]) * 1.645032e+00;
	signal += (up->bpf[4] = up->bpf[3]) * 4.644557e+00;
	signal += (up->bpf[3] = up->bpf[2]) * 1.879165e+00;
	signal += (up->bpf[2] = up->bpf[1]) * 3.522634e+00;
	signal += (up->bpf[1] = up->bpf[0]) * 7.315738e-01;
	up->bpf[0] = sample - signal;
	signal = up->bpf[0] * 6.176213e-03
	    + up->bpf[1] * 3.156599e-03
	    + up->bpf[2] * 7.567487e-03
	    + up->bpf[3] * 4.344580e-03
	    + up->bpf[4] * 1.190128e-02
	    + up->bpf[5] * 4.344580e-03
	    + up->bpf[6] * 7.567487e-03
	    + up->bpf[7] * 3.156599e-03
	    + up->bpf[8] * 6.176213e-03;

	up->monitor = signal / 4.;	/* note monitor after filter */

	/*
	 * Soft limiter/discriminator. The 11-sample discriminator lag
	 * interval corresponds to three cycles of 2125 Hz, which
	 * requires the sample frequency to be 2125 * 11 / 3 = 7791.7
	 * Hz. The discriminator output varies +-0.5 interval for input
	 * frequency 2025-2225 Hz. However, we don't get to sample at
	 * this frequency, so the discriminator output is biased. Life
	 * at 8000 Hz sucks.
	 */
	limit = signal;
	if (limit > LIMIT)
		limit = LIMIT;
	else if (limit < -LIMIT)
		limit = -LIMIT;
	disc = up->disc[up->discptr] * -limit;
	up->disc[up->discptr] = limit;
	up->discptr = (up->discptr + 1 ) % LAG;
	if (disc >= 0)
		disc = SQRT(disc);
	else
		disc = -SQRT(-disc);

	/*
	 * Lowpass filter. Raised cosine FIR, Ts = 1 / 300, beta = 0.1.
	 */
	lpf = (up->lpf[26] = up->lpf[25]) * 2.538771e-02;
	lpf += (up->lpf[25] = up->lpf[24]) * 1.084671e-01;
	lpf += (up->lpf[24] = up->lpf[23]) * 2.003159e-01;
	lpf += (up->lpf[23] = up->lpf[22]) * 2.985303e-01;
	lpf += (up->lpf[22] = up->lpf[21]) * 4.003697e-01;
	lpf += (up->lpf[21] = up->lpf[20]) * 5.028552e-01;
	lpf += (up->lpf[20] = up->lpf[19]) * 6.028795e-01;
	lpf += (up->lpf[19] = up->lpf[18]) * 6.973249e-01;
	lpf += (up->lpf[18] = up->lpf[17]) * 7.831828e-01;
	lpf += (up->lpf[17] = up->lpf[16]) * 8.576717e-01;
	lpf += (up->lpf[16] = up->lpf[15]) * 9.183463e-01;
	lpf += (up->lpf[15] = up->lpf[14]) * 9.631951e-01;
	lpf += (up->lpf[14] = up->lpf[13]) * 9.907208e-01;
	lpf += (up->lpf[13] = up->lpf[12]) * 1.000000e+00;
	lpf += (up->lpf[12] = up->lpf[11]) * 9.907208e-01;
	lpf += (up->lpf[11] = up->lpf[10]) * 9.631951e-01;
	lpf += (up->lpf[10] = up->lpf[9]) * 9.183463e-01;
	lpf += (up->lpf[9] = up->lpf[8]) * 8.576717e-01;
	lpf += (up->lpf[8] = up->lpf[7]) * 7.831828e-01;
	lpf += (up->lpf[7] = up->lpf[6]) * 6.973249e-01;
	lpf += (up->lpf[6] = up->lpf[5]) * 6.028795e-01;
	lpf += (up->lpf[5] = up->lpf[4]) * 5.028552e-01;
	lpf += (up->lpf[4] = up->lpf[3]) * 4.003697e-01;
	lpf += (up->lpf[3] = up->lpf[2]) * 2.985303e-01;
	lpf += (up->lpf[2] = up->lpf[1]) * 2.003159e-01;
	lpf += (up->lpf[1] = up->lpf[0]) * 1.084671e-01;
	lpf += up->lpf[0] = disc * 2.538771e-02;

	/*
	 * Maximum-likelihood decoder. The UART updates each of the
	 * eight survivors and determines the span, slice level and
	 * tentative decoded character. Valid 11-bit characters are
	 * framed so that bit 10 and bit 11 (stop bits) are mark and bit
	 * 1 (start bit) is space. When a valid character is found, the
	 * survivor with maximum distance determines the final decoded
	 * character.
	 */
	up->baud += 1. / SECOND;
	if (up->baud > 1. / (BAUD * 8.)) {
		up->baud -= 1. / (BAUD * 8.);
		up->decptr = (up->decptr + 1) % 8;
		sp = &up->surv[up->decptr];
		sp->cstamp = up->timestamp;
		chu_uart(sp, -lpf * AGAIN);
		if (up->dbrk > 0) {
			up->dbrk--;
			if (up->dbrk > 0)
				return;

			up->decpha = up->decptr;
		}
		if (up->decptr != up->decpha)
			return;

		dist = 0;
		j = -1;
		for (i = 0; i < 8; i++) {

			/*
			 * The timestamp is taken at the last bit, so
			 * for correct decoding we reqire sufficient
			 * span and correct start bit and two stop bits.
			 */
			if ((up->surv[i].uart & 0x601) != 0x600 ||
			    up->surv[i].span < SPAN)
				continue;

			if (up->surv[i].dist > dist) {
				dist = up->surv[i].dist;
				j = i;
			}
		}
		if (j < 0)
			return;

		/*
		 * Process the character, then blank the decoder until
		 * the end of the next character.This sets the decoding
		 * phase of the entire burst from the phase of the first
		 * character.
		 */
		up->maxsignal = up->surv[j].span;
		chu_decode(peer, (up->surv[j].uart >> 1) & 0xff,
		    up->surv[j].cstamp);
		up->dbrk = 88;
	}
}


/*
 * chu_uart - maximum-likelihood UART
 *
 * This routine updates a shift register holding the last 11 envelope
 * samples. It then computes the slice level and span over these samples
 * and determines the tentative data bits and distance. The calling
 * program selects over the last eight survivors the one with maximum
 * distance to determine the decoded character.
 */
static void
chu_uart(
	struct surv *sp,	/* survivor structure pointer */
	double	sample		/* baseband signal */
	)
{
	double	es_max, es_min;	/* max/min envelope */
	double	slice;		/* slice level */
	double	dist;		/* distance */
	double	dtemp;
	int	i;

	/*
	 * Save the sample and shift right. At the same time, measure
	 * the maximum and minimum over all eleven samples.
	 */
	es_max = -1e6;
	es_min = 1e6;
	sp->shift[0] = sample;
	for (i = 11; i > 0; i--) {
		sp->shift[i] = sp->shift[i - 1];
		if (sp->shift[i] > es_max)
			es_max = sp->shift[i];
		if (sp->shift[i] < es_min)
			es_min = sp->shift[i];
	}

	/*
	 * Determine the span as the maximum less the minimum and the
	 * slice level as the minimum plus a fraction of the span. Note
	 * the slight bias toward mark to correct for the modem tendency
	 * to make more mark than space errors. Compute the distance on
	 * the assumption the last two bits must be mark, the first
	 * space and the rest either mark or space.
	 */
	sp->span = es_max - es_min;
	slice = es_min + .45 * sp->span;
	dist = 0;
	sp->uart = 0;
	for (i = 1; i < 12; i++) {
		sp->uart <<= 1;
		dtemp = sp->shift[i];
		if (dtemp > slice)
			sp->uart |= 0x1;
		if (i == 1 || i == 2) {
			dist += dtemp - es_min;
		} else if (i == 11) {
			dist += es_max - dtemp;
		} else {
			if (dtemp > slice)
				dist += dtemp - es_min;
			else
				dist += es_max - dtemp;
		}
	}
	sp->dist = dist / (11 * sp->span);
}
#endif /* HAVE_AUDIO */


/*
 * chu_serial_receive - receive data from the serial device
 */
static void
chu_serial_receive(
	struct recvbuf *rbufp	/* receive buffer structure pointer */
	)
{
	struct peer *peer;

	u_char	*dpt;		/* receive buffer pointer */

	peer = rbufp->recv_peer;

	dpt = (u_char *)&rbufp->recv_space;
	chu_decode(peer, *dpt, rbufp->recv_time);
}


/*
 * chu_decode - decode the character data
 */
static void
chu_decode(
	struct peer *peer,	/* peer structure pointer */
	int	hexhex,		/* data character */
	l_fp	cstamp		/* data character timestamp */
	)
{
	struct refclockproc *pp;
	struct chuunit *up;

	l_fp	tstmp;		/* timestamp temp */
	double	dtemp;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * If the interval since the last character is greater than the
	 * longest burst, process the last burst and start a new one. If
	 * the interval is less than this but greater than two
	 * characters, consider this a noise burst and reject it.
	 */
	tstmp = up->timestamp;
	if (L_ISZERO(&up->laststamp))
		up->laststamp = up->timestamp;
	L_SUB(&tstmp, &up->laststamp);
	up->laststamp = up->timestamp;
	LFPTOD(&tstmp, dtemp);
	if (dtemp > BURST * CHAR) {
		chu_burst(peer);
		up->ndx = 0;
	} else if (dtemp > 2.5 * CHAR) {
		up->ndx = 0;
	}

	/*
	 * Append the character to the current burst and append the
	 * character timestamp to the timestamp list.
	 */
	if (up->ndx < BURST) {
		up->cbuf[up->ndx] = hexhex & 0xff;
		up->cstamp[up->ndx] = cstamp;
		up->ndx++;

	}
}


/*
 * chu_burst - search for valid burst format
 */
static void
chu_burst(
	struct peer *peer
	)
{
	struct chuunit *up;
	struct refclockproc *pp;

	int	i;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * Correlate a block of five characters with the next block of
	 * five characters. The burst distance is defined as the number
	 * of bits that match in the two blocks for format A and that
	 * match the inverse for format B.
	 */
	if (up->ndx < MINCHARS) {
		up->status |= RUNT;
		return;
	}
	up->burdist = 0;
	for (i = 0; i < 5 && i < up->ndx - 5; i++)
		up->burdist += chu_dist(up->cbuf[i], up->cbuf[i + 5]);

	/*
	 * If the burst distance is at least MINDIST, this must be a
	 * format A burst; if the value is not greater than -MINDIST, it
	 * must be a format B burst. If the B burst is perfect, we
	 * believe it; otherwise, it is a noise burst and of no use to
	 * anybody.
	 */
	if (up->burdist >= MINDIST) {
		chu_a(peer, up->ndx);
	} else if (up->burdist <= -MINDIST) {
		chu_b(peer, up->ndx);
	} else {
		up->status |= NOISE;
		return;
	}

	/*
	 * If this is a valid burst, wait a guard time of ten seconds to
	 * allow for more bursts, then arm the poll update routine to
	 * process the minute. Don't do this if this is called from the
	 * timer interrupt routine.
	 */
	if (peer->outdate != current_time)
		peer->nextdate = current_time + 10;
}


/*
 * chu_b - decode format B burst
 */
static void
chu_b(
	struct peer *peer,
	int	nchar
	)
{
	struct	refclockproc *pp;
	struct	chuunit *up;

	u_char	code[11];	/* decoded timecode */
	char	tbuf[80];	/* trace buffer */
	char *	p;
	size_t	chars;
	size_t	cb;
	int	i;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * In a format B burst, a character is considered valid only if
	 * the first occurence matches the last occurence. The burst is
	 * considered valid only if all characters are valid; that is,
	 * only if the distance is 40. Note that once a valid frame has
	 * been found errors are ignored.
	 */
	snprintf(tbuf, sizeof(tbuf), "chuB %04x %4.0f %2d %2d ",
		 up->status, up->maxsignal, nchar, -up->burdist);
	cb = sizeof(tbuf);
	p = tbuf;
	for (i = 0; i < nchar; i++) {
		chars = strlen(p);
		if (cb < chars + 1) {
			msyslog(LOG_ERR, "chu_b() fatal out buffer");
			exit(1);
		}
		cb -= chars;
		p += chars;
		snprintf(p, cb, "%02x", up->cbuf[i]);
	}
	if (pp->sloppyclockflag & CLK_FLAG4)
		record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
	if (debug)
		printf("%s\n", tbuf);
#endif
	if (up->burdist > -40) {
		up->status |= BFRAME;
		return;
	}

	/*
	 * Convert the burst data to internal format. Don't bother with
	 * the timestamps.
	 */
	for (i = 0; i < 5; i++) {
		code[2 * i] = hexchar[up->cbuf[i] & 0xf];
		code[2 * i + 1] = hexchar[(up->cbuf[i] >>
		    4) & 0xf];
	}
	if (sscanf((char *)code, "%1x%1d%4d%2d%2x", &up->leap, &up->dut,
	    &pp->year, &up->tai, &up->dst) != 5) {
		up->status |= BFORMAT;
		return;
	}
	up->status |= BVALID;
	if (up->leap & 0x8)
		up->dut = -up->dut;
}


/*
 * chu_a - decode format A burst
 */
static void
chu_a(
	struct peer *peer,
	int nchar
	)
{
	struct refclockproc *pp;
	struct chuunit *up;

	char	tbuf[80];	/* trace buffer */
	char *	p;
	size_t	chars;
	size_t	cb;
	l_fp	offset;		/* timestamp offset */
	int	val;		/* distance */
	int	temp;
	int	i, j, k;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * Determine correct burst phase. There are three cases
	 * corresponding to in-phase, one character early or one
	 * character late. These cases are distinguished by the position
	 * of the framing digits 0x6 at positions 0 and 5 and 0x3 at
	 * positions 4 and 9. The correct phase is when the distance
	 * relative to the framing digits is maximum. The burst is valid
	 * only if the maximum distance is at least MINSYNC.
	 */
	up->syndist = k = 0;
	// val = -16;
	for (i = -1; i < 2; i++) {
		temp = up->cbuf[i + 4] & 0xf;
		if (i >= 0)
			temp |= (up->cbuf[i] & 0xf) << 4;
		val = chu_dist(temp, 0x63);
		temp = (up->cbuf[i + 5] & 0xf) << 4;
		if (i + 9 < nchar)
			temp |= up->cbuf[i + 9] & 0xf;
		val += chu_dist(temp, 0x63);
		if (val > up->syndist) {
			up->syndist = val;
			k = i;
		}
	}

	/*
	 * Extract the second number; it must be in the range 2 through
	 * 9 and the two repititions must be the same.
	 */
	temp = (up->cbuf[k + 4] >> 4) & 0xf;
	if (temp < 2 || temp > 9 || k + 9 >= nchar || temp !=
	    ((up->cbuf[k + 9] >> 4) & 0xf))
		temp = 0;
	snprintf(tbuf, sizeof(tbuf),
		 "chuA %04x %4.0f %2d %2d %2d %2d %1d ", up->status,
		 up->maxsignal, nchar, up->burdist, k, up->syndist,
		 temp);
	cb = sizeof(tbuf);
	p = tbuf;
	for (i = 0; i < nchar; i++) {
		chars = strlen(p);
		if (cb < chars + 1) {
			msyslog(LOG_ERR, "chu_a() fatal out buffer");
			exit(1);
		}
		cb -= chars;
		p += chars;
		snprintf(p, cb, "%02x", up->cbuf[i]);
	}
	if (pp->sloppyclockflag & CLK_FLAG4)
		record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
	if (debug)
		printf("%s\n", tbuf);
#endif
	if (up->syndist < MINSYNC) {
		up->status |= AFRAME;
		return;
	}

	/*
	 * A valid burst requires the first seconds number to match the
	 * last seconds number. If so, the burst timestamps are
	 * corrected to the current minute and saved for later
	 * processing. In addition, the seconds decode is advanced from
	 * the previous burst to the current one.
	 */
	if (temp == 0) {
		up->status |= AFORMAT;
	} else {
		up->status |= AVALID;
		up->second = pp->second = 30 + temp;
		offset.l_ui = 30 + temp;
		offset.l_uf = 0;
		i = 0;
		if (k < 0)
			offset = up->charstamp;
		else if (k > 0)
			i = 1;
		for (; i < nchar && (i - 10) < k; i++) {
			up->tstamp[up->ntstamp] = up->cstamp[i];
			L_SUB(&up->tstamp[up->ntstamp], &offset);
			L_ADD(&offset, &up->charstamp);
			if (up->ntstamp < MAXSTAGE - 1)
				up->ntstamp++;
		}
		while (temp > up->prevsec) {
			for (j = 15; j > 0; j--) {
				up->decode[9][j] = up->decode[9][j - 1];
				up->decode[19][j] =
				    up->decode[19][j - 1];
			}
			up->decode[9][j] = up->decode[19][j] = 0;
			up->prevsec++;
		}
	}

	/*
	 * Stash the data in the decoding matrix.
	 */
	i = -(2 * k);
	for (j = 0; j < nchar; j++) {
		if (i < 0 || i > 18) {
			i += 2;
			continue;
		}
		up->decode[i][up->cbuf[j] & 0xf]++;
		i++;
		up->decode[i][(up->cbuf[j] >> 4) & 0xf]++;
		i++;
	}
	up->burstcnt++;
}


/*
 * chu_poll - called by the transmit procedure
 */
static void
chu_poll(
	int unit,
	struct peer *peer	/* peer structure pointer */
	)
{
	struct refclockproc *pp;

	pp = peer->procptr;
	pp->polls++;
}


/*
 * chu_second - process minute data
 */
static void
chu_second(
	int unit,
	struct peer *peer	/* peer structure pointer */
	)
{
	struct refclockproc *pp;
	struct chuunit *up;
	l_fp	offset;
	char	synchar, qual, leapchar;
	int	minset, i;
	double	dtemp;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * This routine is called once per minute to process the
	 * accumulated burst data. We do a bit of fancy footwork so that
	 * this doesn't run while burst data are being accumulated.
	 */
	up->second = (up->second + 1) % 60;
	if (up->second != 0)
		return;

	/*
	 * Process the last burst, if still in the burst buffer.
	 * If the minute contains a valid B frame with sufficient A
	 * frame metric, it is considered valid. However, the timecode
	 * is sent to clockstats even if invalid.
	 */
	chu_burst(peer);
	minset = ((current_time - peer->update) + 30) / 60;
	dtemp = chu_major(peer);
	qual = 0;
	if (up->status & (BFRAME | AFRAME))
		qual |= SYNERR;
	if (up->status & (BFORMAT | AFORMAT))
		qual |= FMTERR;
	if (up->status & DECODE)
		qual |= DECERR;
	if (up->status & STAMP)
		qual |= TSPERR;
	if (up->status & BVALID && dtemp >= MINMETRIC)
		up->status |= INSYNC;
	synchar = leapchar = ' ';
	if (!(up->status & INSYNC)) {
		pp->leap = LEAP_NOTINSYNC;
		synchar = '?';
	} else if (up->leap & 0x2) {
		pp->leap = LEAP_ADDSECOND;
		leapchar = 'L';
	} else if (up->leap & 0x4) {
		pp->leap = LEAP_DELSECOND;
		leapchar = 'l';
	} else {
		pp->leap = LEAP_NOWARNING;
	}
	snprintf(pp->a_lastcode, sizeof(pp->a_lastcode),
	    "%c%1X %04d %03d %02d:%02d:%02d %c%x %+d %d %d %s %.0f %d",
	    synchar, qual, pp->year, pp->day, pp->hour, pp->minute,
	    pp->second, leapchar, up->dst, up->dut, minset, up->gain,
	    up->ident, dtemp, up->ntstamp);
	pp->lencode = strlen(pp->a_lastcode);

	/*
	 * If in sync and the signal metric is above threshold, the
	 * timecode is ipso fatso valid and can be selected to
	 * discipline the clock.
	 */
	if (up->status & INSYNC && !(up->status & (DECODE | STAMP)) &&
	    dtemp > MINMETRIC) {
		if (!clocktime(pp->day, pp->hour, pp->minute, 0, GMT,
		    up->tstamp[0].l_ui, &pp->yearstart, &offset.l_ui)) {
			up->errflg = CEVNT_BADTIME;
		} else {
			offset.l_uf = 0;
			for (i = 0; i < up->ntstamp; i++)
				refclock_process_offset(pp, offset,
				up->tstamp[i], PDELAY +
				    pp->fudgetime1);
			pp->lastref = up->timestamp;
			refclock_receive(peer);
		}
	}
	if (dtemp > 0)
		record_clock_stats(&peer->srcadr, pp->a_lastcode);
#ifdef DEBUG
	if (debug)
		printf("chu: timecode %d %s\n", pp->lencode,
		    pp->a_lastcode);
#endif
#ifdef ICOM
	chu_newchan(peer, dtemp);
#endif /* ICOM */
	chu_clear(peer);
	if (up->errflg)
		refclock_report(peer, up->errflg);
	up->errflg = 0;
}


/*
 * chu_major - majority decoder
 */
static double
chu_major(
	struct peer *peer	/* peer structure pointer */
	)
{
	struct refclockproc *pp;
	struct chuunit *up;

	u_char	code[11];	/* decoded timecode */
	int	metric;		/* distance metric */
	int	val1;		/* maximum distance */
	int	synchar;	/* stray cat */
	int	temp;
	int	i, j, k;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * Majority decoder. Each burst encodes two replications at each
	 * digit position in the timecode. Each row of the decoding
	 * matrix encodes the number of occurences of each digit found
	 * at the corresponding position. The maximum over all
	 * occurrences at each position is the distance for this
	 * position and the corresponding digit is the maximum-
	 * likelihood candidate. If the distance is not more than half
	 * the total number of occurences, a majority has not been found
	 * and the data are discarded. The decoding distance is defined
	 * as the sum of the distances over the first nine digits. The
	 * tenth digit varies over the seconds, so we don't count it.
	 */
	metric = 0;
	for (i = 0; i < 9; i++) {
		val1 = 0;
		k = 0;
		for (j = 0; j < 16; j++) {
			temp = up->decode[i][j] + up->decode[i + 10][j];
			if (temp > val1) {
				val1 = temp;
				k = j;
			}
		}
		if (val1 <= up->burstcnt)
			up->status |= DECODE;
		metric += val1;
		code[i] = hexchar[k];
	}

	/*
	 * Compute the timecode timestamp from the days, hours and
	 * minutes of the timecode. Use clocktime() for the aggregate
	 * minutes and the minute offset computed from the burst
	 * seconds. Note that this code relies on the filesystem time
	 * for the years and does not use the years of the timecode.
	 */
	if (sscanf((char *)code, "%1x%3d%2d%2d", &synchar, &pp->day,
	    &pp->hour, &pp->minute) != 4)
		up->status |= DECODE;
	if (up->ntstamp < MINSTAMP)
		up->status |= STAMP;
	return (metric);
}


/*
 * chu_clear - clear decoding matrix
 */
static void
chu_clear(
	struct peer *peer	/* peer structure pointer */
	)
{
	struct refclockproc *pp;
	struct chuunit *up;
	int	i, j;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * Clear stuff for the minute.
	 */
	up->ndx = up->prevsec = 0;
	up->burstcnt = up->ntstamp = 0;
	up->status &= INSYNC | METRIC;
	for (i = 0; i < 20; i++) {
		for (j = 0; j < 16; j++)
			up->decode[i][j] = 0;
	}
}

#ifdef ICOM
/*
 * chu_newchan - called once per minute to find the best channel;
 * returns zero on success, nonzero if ICOM error.
 */
static int
chu_newchan(
	struct peer *peer,
	double	met
	)
{
	struct chuunit *up;
	struct refclockproc *pp;
	struct xmtr *sp;
	int	rval;
	double	metric;
	int	i;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * The radio can be tuned to three channels: 0 (3330 kHz), 1
	 * (7850 kHz) and 2 (14670 kHz). There are five one-minute
	 * dwells in each cycle. During the first dwell the radio is
	 * tuned to one of the three channels to measure the channel
	 * metric. The channel is selected as the one least recently
	 * measured. During the remaining four dwells the radio is tuned
	 * to the channel with the highest channel metric.
	 */
	if (up->fd_icom <= 0)
		return (0);

	/*
	 * Update the current channel metric and age of all channels.
	 * Scan all channels for the highest metric.
	 */
	sp = &up->xmtr[up->chan];
	sp->metric -= sp->integ[sp->iptr];
	sp->integ[sp->iptr] = met;
	sp->metric += sp->integ[sp->iptr];
	sp->probe = 0;
	sp->iptr = (sp->iptr + 1) % ISTAGE;
	metric = 0;
	for (i = 0; i < NCHAN; i++) {
		up->xmtr[i].probe++;
		if (up->xmtr[i].metric > metric) {
			up->status |= METRIC;
			metric = up->xmtr[i].metric;
			up->chan = i;
		}
	}

	/*
	 * Start the next dwell. If the first dwell or no stations have
	 * been heard, continue round-robin scan.
	 */
	up->dwell = (up->dwell + 1) % DWELL;
	if (up->dwell == 0 || metric == 0) {
		rval = 0;
		for (i = 0; i < NCHAN; i++) {
			if (up->xmtr[i].probe > rval) {
				rval = up->xmtr[i].probe;
				up->chan = i;
			}
		}
	}

	/* Retune the radio at each dwell in case somebody nudges the
	 * tuning knob.
	 */
	rval = icom_freq(up->fd_icom, peer->ttl & 0x7f, qsy[up->chan] +
	    TUNE);
	snprintf(up->ident, sizeof(up->ident), "CHU%d", up->chan);
	memcpy(&pp->refid, up->ident, 4);
	memcpy(&peer->refid, up->ident, 4);
	if (metric == 0 && up->status & METRIC) {
		up->status &= ~METRIC;
		refclock_report(peer, CEVNT_PROP);
	}
	return (rval);
}
#endif /* ICOM */


/*
 * chu_dist - determine the distance of two octet arguments
 */
static int
chu_dist(
	int	x,		/* an octet of bits */
	int	y		/* another octet of bits */
	)
{
	int	val;		/* bit count */
	int	temp;
	int	i;

	/*
	 * The distance is determined as the weight of the exclusive OR
	 * of the two arguments. The weight is determined by the number
	 * of one bits in the result. Each one bit increases the weight,
	 * while each zero bit decreases it.
	 */
	temp = x ^ y;
	val = 0;
	for (i = 0; i < 8; i++) {
		if ((temp & 0x1) == 0)
			val++;
		else
			val--;
		temp >>= 1;
	}
	return (val);
}


#ifdef HAVE_AUDIO
/*
 * chu_gain - adjust codec gain
 *
 * This routine is called at the end of each second. During the second
 * the number of signal clips above the MAXAMP threshold (6000). If
 * there are no clips, the gain is bumped up; if there are more than
 * MAXCLP clips (100), it is bumped down. The decoder is relatively
 * insensitive to amplitude, so this crudity works just peachy. The
 * routine also jiggles the input port and selectively mutes the
 */
static void
chu_gain(
	struct peer *peer	/* peer structure pointer */
	)
{
	struct refclockproc *pp;
	struct chuunit *up;

	pp = peer->procptr;
	up = pp->unitptr;

	/*
	 * Apparently, the codec uses only the high order bits of the
	 * gain control field. Thus, it may take awhile for changes to
	 * wiggle the hardware bits.
	 */
	if (up->clipcnt == 0) {
		up->gain += 4;
		if (up->gain > MAXGAIN)
			up->gain = MAXGAIN;
	} else if (up->clipcnt > MAXCLP) {
		up->gain -= 4;
		if (up->gain < 0)
			up->gain = 0;
	}
	audio_gain(up->gain, up->mongain, up->port);
	up->clipcnt = 0;
}
#endif /* HAVE_AUDIO */


#else
NONEMPTY_TRANSLATION_UNIT
#endif /* REFCLOCK */