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[netbsd-mini2440.git] / external / bsd / ntp / dist / ntpd / refclock_wwv.c

/*      $NetBSD$        */

/*
 * refclock_wwv - clock driver for NIST WWV/H time/frequency station
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#if defined(REFCLOCK) && defined(CLOCK_WWV)

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

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

#define ICOM 1

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

/*
 * Audio WWV/H demodulator/decoder
 *
 * This driver synchronizes the computer time using data encoded in
 * radio transmissions from NIST time/frequency stations WWV in Boulder,
 * CO, and WWVH in Kauai, HI. Transmissions are made continuously on
 * 2.5, 5, 10 and 15 MHz from WWV and WWVH, and 20 MHz from WWV. An
 * ordinary AM 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 weasons, both day and night.
 *
 * 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 demodulation and decoding algorithms used in this driver are
 * based on those developed for the TAPR DSP93 development board and the
 * TI 320C25 digital signal processor described in: Mills, D.L. A
 * precision radio clock for WWV transmissions. Electrical Engineering
 * Report 97-8-1, University of Delaware, August 1997, 25 pp., available
 * from www.eecis.udel.edu/~mills/reports.html. The algorithms described
 * in this report have been modified somewhat to improve performance
 * under weak signal conditions and to provide an automatic station
 * identification feature.
 *
 * The ICOM code is normally compiled in the driver. It isn't used,
 * unless the mode keyword on the server configuration command specifies
 * a nonzero ICOM ID select code. The C-IV trace is turned on if the
 * debug level is greater than one.
 *
 * 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.
 *
 * CEVNT_BADTIME        invalid date or time
 * CEVNT_PROP           propagation failure - no stations heard
 * CEVNT_TIMEOUT        timeout (see newgame() below)
 */
/*
 * General definitions. These ordinarily do not need to be changed.
 */
#define DEVICE_AUDIO    "/dev/audio" /* audio device name */
#define AUDIO_BUFSIZ    320     /* audio buffer size (50 ms) */
#define PRECISION       (-10)   /* precision assumed (about 1 ms) */
#define DESCRIPTION     "WWV/H Audio Demodulator/Decoder" /* WRU */
#define SECOND          8000    /* second epoch (sample rate) (Hz) */
#define MINUTE          (SECOND * 60) /* minute epoch */
#define OFFSET          128     /* companded sample offset */
#define SIZE            256     /* decompanding table size */
#define MAXAMP          6000.   /* max signal level reference */
#define MAXCLP          100     /* max clips above reference per s */
#define MAXSNR          40.     /* max SNR reference */
#define MAXFREQ         1.5     /* max frequency tolerance (187 PPM) */
#define DATCYC          170     /* data filter cycles */
#define DATSIZ          (DATCYC * MS) /* data filter size */
#define SYNCYC          800     /* minute filter cycles */
#define SYNSIZ          (SYNCYC * MS) /* minute filter size */
#define TCKCYC          5       /* tick filter cycles */
#define TCKSIZ          (TCKCYC * MS) /* tick filter size */
#define NCHAN           5       /* number of radio channels */
#define AUDIO_PHI       5e-6    /* dispersion growth factor */
#define TBUF            128     /* max monitor line length */

/*
 * Tunable parameters. The DGAIN parameter can be changed to fit the
 * audio response of the radio at 100 Hz. The WWV/WWVH data subcarrier
 * is transmitted at about 20 percent percent modulation; the matched
 * filter boosts it by a factor of 17 and the receiver response does
 * what it does. The compromise value works for ICOM radios. If the
 * radio is not tunable, the DCHAN parameter can be changed to fit the
 * expected best propagation frequency: higher if further from the
 * transmitter, lower if nearer. The compromise value works for the US
 * right coast.
 */
#define DCHAN           3       /* default radio channel (15 Mhz) */
#define DGAIN           5.      /* subcarrier gain */

/*
 * General purpose status bits (status)
 *
 * SELV and/or SELH are set when WWV or WWVH have been heard and cleared
 * on signal loss. SSYNC is set when the second sync pulse has been
 * acquired and cleared by signal loss. MSYNC is set when the minute
 * sync pulse has been acquired. DSYNC is set when the units digit has
 * has reached the threshold and INSYNC is set when all nine digits have
 * reached the threshold. The MSYNC, DSYNC and INSYNC bits are cleared
 * only by timeout, upon which the driver starts over from scratch.
 *
 * DGATE is lit if the data bit amplitude or SNR is below thresholds and
 * BGATE is lit if the pulse width amplitude or SNR is below thresolds.
 * LEPSEC is set during the last minute of the leap day. At the end of
 * this minute the driver inserts second 60 in the seconds state machine
 * and the minute sync slips a second.
 */
#define MSYNC           0x0001  /* minute epoch sync */
#define SSYNC           0x0002  /* second epoch sync */
#define DSYNC           0x0004  /* minute units sync */
#define INSYNC          0x0008  /* clock synchronized */
#define FGATE           0x0010  /* frequency gate */
#define DGATE           0x0020  /* data pulse amplitude error */
#define BGATE           0x0040  /* data pulse width error */
#define METRIC          0x0080  /* one or more stations heard */
#define LEPSEC          0x1000  /* leap minute */

/*
 * Station scoreboard bits
 *
 * These are used to establish the signal quality for each of the five
 * frequencies and two stations.
 */
#define SELV            0x0100  /* WWV station select */
#define SELH            0x0200  /* WWVH station select */

/*
 * Alarm status bits (alarm)
 *
 * These bits indicate various alarm conditions, which are decoded to
 * form the quality character included in the timecode.
 */
#define CMPERR          0x1     /* digit or misc bit compare error */
#define LOWERR          0x2     /* low bit or digit amplitude or SNR */
#define NINERR          0x4     /* less than nine digits in minute */
#define SYNERR          0x8     /* not tracking second sync */

/*
 * Watchcat timeouts (watch)
 *
 * If these timeouts expire, the status bits are mashed to zero and the
 * driver starts from scratch. Suitably more refined procedures may be
 * developed in future. All these are in minutes.
 */
#define ACQSN           6       /* station acquisition timeout */
#define DATA            15      /* unit minutes timeout */
#define SYNCH           40      /* station sync timeout */
#define PANIC           (2 * 1440) /* panic timeout */

/*
 * Thresholds. These establish the minimum signal level, minimum SNR and
 * maximum jitter thresholds which establish the error and false alarm
 * rates of the driver. The values defined here may be on the
 * adventurous side in the interest of the highest sensitivity.
 */
#define MTHR            13.     /* minute sync gate (percent) */
#define TTHR            50.     /* minute sync threshold (percent) */
#define AWND            20      /* minute sync jitter threshold (ms) */
#define ATHR            2500.   /* QRZ minute sync threshold */
#define ASNR            20.     /* QRZ minute sync SNR threshold (dB) */
#define QTHR            2500.   /* QSY minute sync threshold */
#define QSNR            20.     /* QSY minute sync SNR threshold (dB) */
#define STHR            2500.   /* second sync threshold */
#define SSNR            15.     /* second sync SNR threshold (dB) */
#define SCMP            10      /* second sync compare threshold */
#define DTHR            1000.   /* bit threshold */
#define DSNR            10.     /* bit SNR threshold (dB) */
#define AMIN            3       /* min bit count */
#define AMAX            6       /* max bit count */
#define BTHR            1000.   /* digit threshold */
#define BSNR            3.      /* digit likelihood threshold (dB) */
#define BCMP            3       /* digit compare threshold */
#define MAXERR          40      /* maximum error alarm */

/*
 * Tone frequency definitions. The increments are for 4.5-deg sine
 * table.
 */
#define MS              (SECOND / 1000) /* samples per millisecond */
#define IN100           ((100 * 80) / SECOND) /* 100 Hz increment */
#define IN1000          ((1000 * 80) / SECOND) /* 1000 Hz increment */
#define IN1200          ((1200 * 80) / SECOND) /* 1200 Hz increment */

/*
 * Acquisition and tracking time constants
 */
#define MINAVG          8       /* min averaging time */
#define MAXAVG          1024    /* max averaging time */
#define FCONST          3       /* frequency time constant */
#define TCONST          16      /* data bit/digit time constant */

/*
 * Miscellaneous status bits (misc)
 *
 * These bits correspond to designated bits in the WWV/H timecode. The
 * bit probabilities are exponentially averaged over several minutes and
 * processed by a integrator and threshold.
 */
#define DUT1            0x01    /* 56 DUT .1 */
#define DUT2            0x02    /* 57 DUT .2 */
#define DUT4            0x04    /* 58 DUT .4 */
#define DUTS            0x08    /* 50 DUT sign */
#define DST1            0x10    /* 55 DST1 leap warning */
#define DST2            0x20    /* 2 DST2 DST1 delayed one day */
#define SECWAR          0x40    /* 3 leap second warning */

/*
 * The on-time synchronization point is the positive-going zero crossing
 * of the first cycle of the 5-ms second pulse. The IIR baseband filter
 * phase delay is 0.91 ms, while the receiver delay is approximately 4.7
 * ms at 1000 Hz. The fudge value -0.45 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 and time2 values for
 * WWV and WWVH, respectively.
 *
 * The resulting offsets with a 2.4-GHz P4 running FreeBSD 6.1 are
 * generally within .02 ms short-term with .02 ms jitter. The long-term
 * offsets vary up to 0.3 ms due to ionosperhic layer height variations.
 * The processor load due to the driver is 5.8 percent.
 */
#define PDELAY  ((.91 + 4.7 - 0.45) / 1000) /* system delay (s) */

/*
 * Table of sine values at 4.5-degree increments. This is used by the
 * synchronous matched filter demodulators.
 */
double sintab[] = {
 0.000000e+00,  7.845910e-02,  1.564345e-01,  2.334454e-01, /* 0-3 */
 3.090170e-01,  3.826834e-01,  4.539905e-01,  5.224986e-01, /* 4-7 */
 5.877853e-01,  6.494480e-01,  7.071068e-01,  7.604060e-01, /* 8-11 */
 8.090170e-01,  8.526402e-01,  8.910065e-01,  9.238795e-01, /* 12-15 */
 9.510565e-01,  9.723699e-01,  9.876883e-01,  9.969173e-01, /* 16-19 */
 1.000000e+00,  9.969173e-01,  9.876883e-01,  9.723699e-01, /* 20-23 */
 9.510565e-01,  9.238795e-01,  8.910065e-01,  8.526402e-01, /* 24-27 */
 8.090170e-01,  7.604060e-01,  7.071068e-01,  6.494480e-01, /* 28-31 */
 5.877853e-01,  5.224986e-01,  4.539905e-01,  3.826834e-01, /* 32-35 */
 3.090170e-01,  2.334454e-01,  1.564345e-01,  7.845910e-02, /* 36-39 */
-0.000000e+00, -7.845910e-02, -1.564345e-01, -2.334454e-01, /* 40-43 */
-3.090170e-01, -3.826834e-01, -4.539905e-01, -5.224986e-01, /* 44-47 */
-5.877853e-01, -6.494480e-01, -7.071068e-01, -7.604060e-01, /* 48-51 */
-8.090170e-01, -8.526402e-01, -8.910065e-01, -9.238795e-01, /* 52-55 */
-9.510565e-01, -9.723699e-01, -9.876883e-01, -9.969173e-01, /* 56-59 */
-1.000000e+00, -9.969173e-01, -9.876883e-01, -9.723699e-01, /* 60-63 */
-9.510565e-01, -9.238795e-01, -8.910065e-01, -8.526402e-01, /* 64-67 */
-8.090170e-01, -7.604060e-01, -7.071068e-01, -6.494480e-01, /* 68-71 */
-5.877853e-01, -5.224986e-01, -4.539905e-01, -3.826834e-01, /* 72-75 */
-3.090170e-01, -2.334454e-01, -1.564345e-01, -7.845910e-02, /* 76-79 */
 0.000000e+00};                                             /* 80 */

/*
 * Decoder operations at the end of each second are driven by a state
 * machine. The transition matrix consists of a dispatch table indexed
 * by second number. Each entry in the table contains a case switch
 * number and argument.
 */
struct progx {
        int sw;                 /* case switch number */
        int arg;                /* argument */
};

/*
 * Case switch numbers
 */
#define IDLE            0       /* no operation */
#define COEF            1       /* BCD bit */
#define COEF1           2       /* BCD bit for minute unit */
#define COEF2           3       /* BCD bit not used */
#define DECIM9          4       /* BCD digit 0-9 */
#define DECIM6          5       /* BCD digit 0-6 */
#define DECIM3          6       /* BCD digit 0-3 */
#define DECIM2          7       /* BCD digit 0-2 */
#define MSCBIT          8       /* miscellaneous bit */
#define MSC20           9       /* miscellaneous bit */         
#define MSC21           10      /* QSY probe channel */         
#define MIN1            11      /* latch time */                
#define MIN2            12      /* leap second */
#define SYNC2           13      /* latch minute sync pulse */           
#define SYNC3           14      /* latch data pulse */          

/*
 * Offsets in decoding matrix
 */
#define MN              0       /* minute digits (2) */
#define HR              2       /* hour digits (2) */
#define DA              4       /* day digits (3) */
#define YR              7       /* year digits (2) */

struct progx progx[] = {
        {SYNC2, 0},             /* 0 latch minute sync pulse */
        {SYNC3, 0},             /* 1 latch data pulse */
        {MSCBIT, DST2},         /* 2 dst2 */
        {MSCBIT, SECWAR},       /* 3 lw */
        {COEF,  0},             /* 4 1 year units */
        {COEF,  1},             /* 5 2 */
        {COEF,  2},             /* 6 4 */
        {COEF,  3},             /* 7 8 */
        {DECIM9, YR},           /* 8 */
        {IDLE,  0},             /* 9 p1 */
        {COEF1, 0},             /* 10 1 minute units */
        {COEF1, 1},             /* 11 2 */
        {COEF1, 2},             /* 12 4 */
        {COEF1, 3},             /* 13 8 */
        {DECIM9, MN},           /* 14 */
        {COEF,  0},             /* 15 10 minute tens */
        {COEF,  1},             /* 16 20 */
        {COEF,  2},             /* 17 40 */
        {COEF2, 3},             /* 18 80 (not used) */
        {DECIM6, MN + 1},       /* 19 p2 */
        {COEF,  0},             /* 20 1 hour units */
        {COEF,  1},             /* 21 2 */
        {COEF,  2},             /* 22 4 */
        {COEF,  3},             /* 23 8 */
        {DECIM9, HR},           /* 24 */
        {COEF,  0},             /* 25 10 hour tens */
        {COEF,  1},             /* 26 20 */
        {COEF2, 2},             /* 27 40 (not used) */
        {COEF2, 3},             /* 28 80 (not used) */
        {DECIM2, HR + 1},       /* 29 p3 */
        {COEF,  0},             /* 30 1 day units */
        {COEF,  1},             /* 31 2 */
        {COEF,  2},             /* 32 4 */
        {COEF,  3},             /* 33 8 */
        {DECIM9, DA},           /* 34 */
        {COEF,  0},             /* 35 10 day tens */
        {COEF,  1},             /* 36 20 */
        {COEF,  2},             /* 37 40 */
        {COEF,  3},             /* 38 80 */
        {DECIM9, DA + 1},       /* 39 p4 */
        {COEF,  0},             /* 40 100 day hundreds */
        {COEF,  1},             /* 41 200 */
        {COEF2, 2},             /* 42 400 (not used) */
        {COEF2, 3},             /* 43 800 (not used) */
        {DECIM3, DA + 2},       /* 44 */
        {IDLE,  0},             /* 45 */
        {IDLE,  0},             /* 46 */
        {IDLE,  0},             /* 47 */
        {IDLE,  0},             /* 48 */
        {IDLE,  0},             /* 49 p5 */
        {MSCBIT, DUTS},         /* 50 dut+- */
        {COEF,  0},             /* 51 10 year tens */
        {COEF,  1},             /* 52 20 */
        {COEF,  2},             /* 53 40 */
        {COEF,  3},             /* 54 80 */
        {MSC20, DST1},          /* 55 dst1 */
        {MSCBIT, DUT1},         /* 56 0.1 dut */
        {MSCBIT, DUT2},         /* 57 0.2 */
        {MSC21, DUT4},          /* 58 0.4 QSY probe channel */
        {MIN1,  0},             /* 59 p6 latch time */
        {MIN2,  0}              /* 60 leap second */
};

/*
 * BCD coefficients for maximum-likelihood digit decode
 */
#define P15     1.              /* max positive number */
#define N15     -1.             /* max negative number */

/*
 * Digits 0-9
 */
#define P9      (P15 / 4)       /* mark (+1) */
#define N9      (N15 / 4)       /* space (-1) */

double bcd9[][4] = {
        {N9, N9, N9, N9},       /* 0 */
        {P9, N9, N9, N9},       /* 1 */
        {N9, P9, N9, N9},       /* 2 */
        {P9, P9, N9, N9},       /* 3 */
        {N9, N9, P9, N9},       /* 4 */
        {P9, N9, P9, N9},       /* 5 */
        {N9, P9, P9, N9},       /* 6 */
        {P9, P9, P9, N9},       /* 7 */
        {N9, N9, N9, P9},       /* 8 */
        {P9, N9, N9, P9},       /* 9 */
        {0, 0, 0, 0}            /* backstop */
};

/*
 * Digits 0-6 (minute tens)
 */
#define P6      (P15 / 3)       /* mark (+1) */
#define N6      (N15 / 3)       /* space (-1) */

double bcd6[][4] = {
        {N6, N6, N6, 0},        /* 0 */
        {P6, N6, N6, 0},        /* 1 */
        {N6, P6, N6, 0},        /* 2 */
        {P6, P6, N6, 0},        /* 3 */
        {N6, N6, P6, 0},        /* 4 */
        {P6, N6, P6, 0},        /* 5 */
        {N6, P6, P6, 0},        /* 6 */
        {0, 0, 0, 0}            /* backstop */
};

/*
 * Digits 0-3 (day hundreds)
 */
#define P3      (P15 / 2)       /* mark (+1) */
#define N3      (N15 / 2)       /* space (-1) */

double bcd3[][4] = {
        {N3, N3, 0, 0},         /* 0 */
        {P3, N3, 0, 0},         /* 1 */
        {N3, P3, 0, 0},         /* 2 */
        {P3, P3, 0, 0},         /* 3 */
        {0, 0, 0, 0}            /* backstop */
};

/*
 * Digits 0-2 (hour tens)
 */
#define P2      (P15 / 2)       /* mark (+1) */
#define N2      (N15 / 2)       /* space (-1) */

double bcd2[][4] = {
        {N2, N2, 0, 0},         /* 0 */
        {P2, N2, 0, 0},         /* 1 */
        {N2, P2, 0, 0},         /* 2 */
        {0, 0, 0, 0}            /* backstop */
};

/*
 * DST decode (DST2 DST1) for prettyprint
 */
char dstcod[] = {
        'S',                    /* 00 standard time */
        'I',                    /* 01 set clock ahead at 0200 local */
        'O',                    /* 10 set clock back at 0200 local */
        'D'                     /* 11 daylight time */
};

/*
 * The decoding matrix consists of nine row vectors, one for each digit
 * of the timecode. The digits are stored from least to most significant
 * order. The maximum-likelihood timecode is formed from the digits
 * corresponding to the maximum-likelihood values reading in the
 * opposite order: yy ddd hh:mm.
 */
struct decvec {
        int radix;              /* radix (3, 4, 6, 10) */
        int digit;              /* current clock digit */
        int count;              /* match count */
        double digprb;          /* max digit probability */
        double digsnr;          /* likelihood function (dB) */
        double like[10];        /* likelihood integrator 0-9 */
};

/*
 * The station structure (sp) is used to acquire the minute pulse from
 * WWV and/or WWVH. These stations are distinguished by the frequency
 * used for the second and minute sync pulses, 1000 Hz for WWV and 1200
 * Hz for WWVH. Other than frequency, the format is the same.
 */
struct sync {
        double  epoch;          /* accumulated epoch differences */
        double  maxeng;         /* sync max energy */
        double  noieng;         /* sync noise energy */
        long    pos;            /* max amplitude position */
        long    lastpos;        /* last max position */
        long    mepoch;         /* minute synch epoch */

        double  amp;            /* sync signal */
        double  syneng;         /* sync signal max */
        double  synmax;         /* sync signal max latched at 0 s */
        double  synsnr;         /* sync signal SNR */
        double  metric;         /* signal quality metric */
        int     reach;          /* reachability register */
        int     count;          /* bit counter */
        int     select;         /* select bits */
        char    refid[5];       /* reference identifier */
};

/*
 * The channel structure (cp) is used to mitigate between channels.
 */
struct chan {
        int     gain;           /* audio gain */
        struct sync wwv;        /* wwv station */
        struct sync wwvh;       /* wwvh station */
};

/*
 * WWV unit control structure (up)
 */
struct wwvunit {
        l_fp    timestamp;      /* audio sample timestamp */
        l_fp    tick;           /* audio sample increment */
        double  phase, freq;    /* logical clock phase and frequency */
        double  monitor;        /* audio monitor point */
        double  pdelay;         /* propagation delay (s) */
#ifdef ICOM
        int     fd_icom;        /* ICOM file descriptor */
#endif /* ICOM */
        int     errflg;         /* error flags */
        int     watch;          /* watchcat */

        /*
         * 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 */

        /*
         * Variables used to establish basic system timing
         */
        int     avgint;         /* master time constant */
        int     yepoch;         /* sync epoch */
        int     repoch;         /* buffered sync epoch */
        double  epomax;         /* second sync amplitude */
        double  eposnr;         /* second sync SNR */
        double  irig;           /* data I channel amplitude */
        double  qrig;           /* data Q channel amplitude */
        int     datapt;         /* 100 Hz ramp */
        double  datpha;         /* 100 Hz VFO control */
        int     rphase;         /* second sample counter */
        long    mphase;         /* minute sample counter */

        /*
         * Variables used to mitigate which channel to use
         */
        struct chan mitig[NCHAN]; /* channel data */
        struct sync *sptr;      /* station pointer */
        int     dchan;          /* data channel */
        int     schan;          /* probe channel */
        int     achan;          /* active channel */

        /*
         * Variables used by the clock state machine
         */
        struct decvec decvec[9]; /* decoding matrix */
        int     rsec;           /* seconds counter */
        int     digcnt;         /* count of digits synchronized */

        /*
         * Variables used to estimate signal levels and bit/digit
         * probabilities
         */
        double  datsig;         /* data signal max */
        double  datsnr;         /* data signal SNR (dB) */

        /*
         * Variables used to establish status and alarm conditions
         */
        int     status;         /* status bits */
        int     alarm;          /* alarm flashers */
        int     misc;           /* miscellaneous timecode bits */
        int     errcnt;         /* data bit error counter */
};

/*
 * Function prototypes
 */
static  int     wwv_start       (int, struct peer *);
static  void    wwv_shutdown    (int, struct peer *);
static  void    wwv_receive     (struct recvbuf *);
static  void    wwv_poll        (int, struct peer *);

/*
 * More function prototypes
 */
static  void    wwv_epoch       (struct peer *);
static  void    wwv_rf          (struct peer *, double);
static  void    wwv_endpoc      (struct peer *, int);
static  void    wwv_rsec        (struct peer *, double);
static  void    wwv_qrz         (struct peer *, struct sync *, int);
static  void    wwv_corr4       (struct peer *, struct decvec *,
                                    double [], double [][4]);
static  void    wwv_gain        (struct peer *);
static  void    wwv_tsec        (struct peer *);
static  int     timecode        (struct wwvunit *, char *);
static  double  wwv_snr         (double, double);
static  int     carry           (struct decvec *);
static  int     wwv_newchan     (struct peer *);
static  void    wwv_newgame     (struct peer *);
static  double  wwv_metric      (struct sync *);
static  void    wwv_clock       (struct peer *);
#ifdef ICOM
static  int     wwv_qsy         (struct peer *, int);
#endif /* ICOM */

static double qsy[NCHAN] = {2.5, 5, 10, 15, 20}; /* frequencies (MHz) */

/*
 * Transfer vector
 */
struct  refclock refclock_wwv = {
        wwv_start,              /* start up driver */
        wwv_shutdown,           /* shut down driver */
        wwv_poll,               /* transmit poll message */
        noentry,                /* not used (old wwv_control) */
        noentry,                /* initialize driver (not used) */
        noentry,                /* not used (old wwv_buginfo) */
        NOFLAGS                 /* not used */
};


/*
 * wwv_start - open the devices and initialize data for processing
 */
static int
wwv_start(
        int     unit,           /* instance number (used by PCM) */
        struct peer *peer       /* peer structure pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
#ifdef ICOM
        int     temp;
#endif /* ICOM */

        /*
         * 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 /* DEBUG */

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

        /*
         * Initialize miscellaneous variables
         */
        peer->precision = PRECISION;
        pp->clockdesc = DESCRIPTION;

        /*
         * The companded samples are encoded sign-magnitude. The table
         * contains all the 256 values in the interest of speed.
         */
        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);

        /*
         * Initialize the decoding matrix with the radix for each digit
         * position.
         */
        up->decvec[MN].radix = 10;      /* minutes */
        up->decvec[MN + 1].radix = 6;
        up->decvec[HR].radix = 10;      /* hours */
        up->decvec[HR + 1].radix = 3;
        up->decvec[DA].radix = 10;      /* days */
        up->decvec[DA + 1].radix = 10;
        up->decvec[DA + 2].radix = 4;
        up->decvec[YR].radix = 10;      /* years */
        up->decvec[YR + 1].radix = 10;

#ifdef ICOM
        /*
         * Initialize autotune if available. Note that the ICOM select
         * code must be less than 128, so the high order bit can be used
         * to select the line speed 0 (9600 bps) or 1 (1200 bps). Note
         * we don't complain if the ICOM device is not there; but, if it
         * is, the radio better be working.
         */
        temp = 0;
#ifdef DEBUG
        if (debug > 1)
                temp = P_TRACE;
#endif /* DEBUG */
        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 (wwv_qsy(peer, DCHAN) != 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 */

        /*
         * Let the games begin.
         */
        wwv_newgame(peer);
        return (1);
}


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

        pp = peer->procptr;
        up = (struct wwvunit *)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);
}


/*
 * wwv_receive - receive data from the audio device
 *
 * This routine reads input samples and adjusts the logical clock to
 * track the A/D sample clock by dropping or duplicating codec samples.
 * It also controls the A/D signal level with an AGC loop to mimimize
 * quantization noise and avoid overload.
 */
static void
wwv_receive(
        struct recvbuf *rbufp   /* receive buffer structure pointer */
        )
{
        struct peer *peer;
        struct refclockproc *pp;
        struct wwvunit *up;

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

        peer = (struct peer *)rbufp->recv_srcclock;
        pp = peer->procptr;
        up = (struct wwvunit *)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 (6000) and
                 * record the number of clips to be used later by the
                 * AGC.
                 */
                if (sample > MAXAMP) {
                        sample = MAXAMP;
                        up->clipcnt++;
                } else if (sample < -MAXAMP) {
                        sample = -MAXAMP;
                        up->clipcnt++;
                }

                /*
                 * Variable frequency oscillator. The codec oscillator
                 * runs at the nominal rate of 8000 samples per second,
                 * or 125 us per sample. A frequency change of one unit
                 * results in either duplicating or deleting one sample
                 * per second, which results in a frequency change of
                 * 125 PPM.
                 */
                up->phase += (up->freq + clock_codec) / SECOND;
                if (up->phase >= .5) {
                        up->phase -= 1.;
                } else if (up->phase < -.5) {
                        up->phase += 1.;
                        wwv_rf(peer, sample);
                        wwv_rf(peer, sample);
                } else {
                        wwv_rf(peer, sample);
                }
                L_ADD(&up->timestamp, &up->tick);
        }

        /*
         * 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;
}


/*
 * wwv_poll - called by the transmit procedure
 *
 * This routine keeps track of status. If no offset samples have been
 * processed during a poll interval, a timeout event is declared. If
 * errors have have occurred during the interval, they are reported as
 * well.
 */
static void
wwv_poll(
        int     unit,           /* instance number (not used) */
        struct peer *peer       /* peer structure pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;
        if (up->errflg)
                refclock_report(peer, up->errflg);
        up->errflg = 0;
        pp->polls++;
}


/*
 * wwv_rf - process signals and demodulate to baseband
 *
 * This routine grooms and filters decompanded raw audio samples. The
 * output signal is the 100-Hz filtered baseband data signal in
 * quadrature phase. The routine also determines the minute synch epoch,
 * as well as certain signal maxima, minima and related values.
 *
 * There are two 1-s ramps used by this program. Both count the 8000
 * logical clock samples spanning exactly one second. The epoch ramp
 * counts the samples starting at an arbitrary time. The rphase ramp
 * counts the samples starting at the 5-ms second sync pulse found
 * during the epoch ramp.
 *
 * There are two 1-m ramps used by this program. The mphase ramp counts
 * the 480,000 logical clock samples spanning exactly one minute and
 * starting at an arbitrary time. The rsec ramp counts the 60 seconds of
 * the minute starting at the 800-ms minute sync pulse found during the
 * mphase ramp. The rsec ramp drives the seconds state machine to
 * determine the bits and digits of the timecode. 
 *
 * Demodulation operations are based on three synthesized quadrature
 * sinusoids: 100 Hz for the data signal, 1000 Hz for the WWV sync
 * signal and 1200 Hz for the WWVH sync signal. These drive synchronous
 * matched filters for the data signal (170 ms at 100 Hz), WWV minute
 * sync signal (800 ms at 1000 Hz) and WWVH minute sync signal (800 ms
 * at 1200 Hz). Two additional matched filters are switched in
 * as required for the WWV second sync signal (5 cycles at 1000 Hz) and
 * WWVH second sync signal (6 cycles at 1200 Hz).
 */
static void
wwv_rf(
        struct peer *peer,      /* peerstructure pointer */
        double isig             /* input signal */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        struct sync *sp, *rp;

        static double lpf[5];   /* 150-Hz lpf delay line */
        double data;            /* lpf output */
        static double bpf[9];   /* 1000/1200-Hz bpf delay line */
        double syncx;           /* bpf output */
        static double mf[41];   /* 1000/1200-Hz mf delay line */
        double mfsync;          /* mf output */

        static int iptr;        /* data channel pointer */
        static double ibuf[DATSIZ]; /* data I channel delay line */
        static double qbuf[DATSIZ]; /* data Q channel delay line */

        static int jptr;        /* sync channel pointer */
        static int kptr;        /* tick channel pointer */

        static int csinptr;     /* wwv channel phase */
        static double cibuf[SYNSIZ]; /* wwv I channel delay line */
        static double cqbuf[SYNSIZ]; /* wwv Q channel delay line */
        static double ciamp;    /* wwv I channel amplitude */
        static double cqamp;    /* wwv Q channel amplitude */

        static double csibuf[TCKSIZ]; /* wwv I tick delay line */
        static double csqbuf[TCKSIZ]; /* wwv Q tick delay line */
        static double csiamp;   /* wwv I tick amplitude */
        static double csqamp;   /* wwv Q tick amplitude */

        static int hsinptr;     /* wwvh channel phase */
        static double hibuf[SYNSIZ]; /* wwvh I channel delay line */
        static double hqbuf[SYNSIZ]; /* wwvh Q channel delay line */
        static double hiamp;    /* wwvh I channel amplitude */
        static double hqamp;    /* wwvh Q channel amplitude */

        static double hsibuf[TCKSIZ]; /* wwvh I tick delay line */
        static double hsqbuf[TCKSIZ]; /* wwvh Q tick delay line */
        static double hsiamp;   /* wwvh I tick amplitude */
        static double hsqamp;   /* wwvh Q tick amplitude */

        static double epobuf[SECOND]; /* second sync comb filter */
        static double epomax, nxtmax; /* second sync amplitude buffer */
        static int epopos;      /* epoch second sync position buffer */

        static int iniflg;      /* initialization flag */
        int     epoch;          /* comb filter index */
        double  dtemp;
        int     i;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;

        if (!iniflg) {
                iniflg = 1;
                memset((char *)lpf, 0, sizeof(lpf));
                memset((char *)bpf, 0, sizeof(bpf));
                memset((char *)mf, 0, sizeof(mf));
                memset((char *)ibuf, 0, sizeof(ibuf));
                memset((char *)qbuf, 0, sizeof(qbuf));
                memset((char *)cibuf, 0, sizeof(cibuf));
                memset((char *)cqbuf, 0, sizeof(cqbuf));
                memset((char *)csibuf, 0, sizeof(csibuf));
                memset((char *)csqbuf, 0, sizeof(csqbuf));
                memset((char *)hibuf, 0, sizeof(hibuf));
                memset((char *)hqbuf, 0, sizeof(hqbuf));
                memset((char *)hsibuf, 0, sizeof(hsibuf));
                memset((char *)hsqbuf, 0, sizeof(hsqbuf));
                memset((char *)epobuf, 0, sizeof(epobuf));
        }

        /*
         * Baseband data demodulation. The 100-Hz subcarrier is
         * extracted using a 150-Hz IIR lowpass filter. This attenuates
         * the 1000/1200-Hz sync signals, as well as the 440-Hz and
         * 600-Hz tones and most of the noise and voice modulation
         * components.
         *
         * The subcarrier is transmitted 10 dB down from the carrier.
         * The DGAIN parameter can be adjusted for this and to
         * compensate for the radio audio response at 100 Hz.
         *
         * Matlab IIR 4th-order IIR elliptic, 150 Hz lowpass, 0.2 dB
         * passband ripple, -50 dB stopband ripple, phase delay 0.97 ms.
         */
        data = (lpf[4] = lpf[3]) * 8.360961e-01;
        data += (lpf[3] = lpf[2]) * -3.481740e+00;
        data += (lpf[2] = lpf[1]) * 5.452988e+00;
        data += (lpf[1] = lpf[0]) * -3.807229e+00;
        lpf[0] = isig * DGAIN - data;
        data = lpf[0] * 3.281435e-03
            + lpf[1] * -1.149947e-02
            + lpf[2] * 1.654858e-02
            + lpf[3] * -1.149947e-02
            + lpf[4] * 3.281435e-03;

        /*
         * The 100-Hz data signal is demodulated using a pair of
         * quadrature multipliers, matched filters and a phase lock
         * loop. The I and Q quadrature data signals are produced by
         * multiplying the filtered signal by 100-Hz sine and cosine
         * signals, respectively. The signals are processed by 170-ms
         * synchronous matched filters to produce the amplitude and
         * phase signals used by the demodulator. The signals are scaled
         * to produce unit energy at the maximum value.
         */
        i = up->datapt;
        up->datapt = (up->datapt + IN100) % 80;
        dtemp = sintab[i] * data / (MS / 2. * DATCYC);
        up->irig -= ibuf[iptr];
        ibuf[iptr] = dtemp;
        up->irig += dtemp;

        i = (i + 20) % 80;
        dtemp = sintab[i] * data / (MS / 2. * DATCYC);
        up->qrig -= qbuf[iptr];
        qbuf[iptr] = dtemp;
        up->qrig += dtemp;
        iptr = (iptr + 1) % DATSIZ;

        /*
         * Baseband sync demodulation. The 1000/1200 sync signals are
         * extracted using a 600-Hz IIR bandpass filter. This removes
         * the 100-Hz data subcarrier, as well as the 440-Hz and 600-Hz
         * tones and most of the noise and voice modulation components.
         *
         * Matlab 4th-order IIR elliptic, 800-1400 Hz bandpass, 0.2 dB
         * passband ripple, -50 dB stopband ripple, phase delay 0.91 ms.
         */
        syncx = (bpf[8] = bpf[7]) * 4.897278e-01;
        syncx += (bpf[7] = bpf[6]) * -2.765914e+00;
        syncx += (bpf[6] = bpf[5]) * 8.110921e+00;
        syncx += (bpf[5] = bpf[4]) * -1.517732e+01;
        syncx += (bpf[4] = bpf[3]) * 1.975197e+01;
        syncx += (bpf[3] = bpf[2]) * -1.814365e+01;
        syncx += (bpf[2] = bpf[1]) * 1.159783e+01;
        syncx += (bpf[1] = bpf[0]) * -4.735040e+00;
        bpf[0] = isig - syncx;
        syncx = bpf[0] * 8.203628e-03
            + bpf[1] * -2.375732e-02
            + bpf[2] * 3.353214e-02
            + bpf[3] * -4.080258e-02
            + bpf[4] * 4.605479e-02
            + bpf[5] * -4.080258e-02
            + bpf[6] * 3.353214e-02
            + bpf[7] * -2.375732e-02
            + bpf[8] * 8.203628e-03;

        /*
         * The 1000/1200 sync signals are demodulated using a pair of
         * quadrature multipliers and matched filters. However,
         * synchronous demodulation at these frequencies is impractical,
         * so only the signal amplitude is used. The I and Q quadrature
         * sync signals are produced by multiplying the filtered signal
         * by 1000-Hz (WWV) and 1200-Hz (WWVH) sine and cosine signals,
         * respectively. The WWV and WWVH signals are processed by 800-
         * ms synchronous matched filters and combined to produce the
         * minute sync signal and detect which one (or both) the WWV or
         * WWVH signal is present. The WWV and WWVH signals are also
         * processed by 5-ms synchronous matched filters and combined to
         * produce the second sync signal. The signals are scaled to
         * produce unit energy at the maximum value.
         *
         * Note the master timing ramps, which run continuously. The
         * minute counter (mphase) counts the samples in the minute,
         * while the second counter (epoch) counts the samples in the
         * second.
         */
        up->mphase = (up->mphase + 1) % MINUTE;
        epoch = up->mphase % SECOND;

        /*
         * WWV
         */
        i = csinptr;
        csinptr = (csinptr + IN1000) % 80;

        dtemp = sintab[i] * syncx / (MS / 2.);
        ciamp -= cibuf[jptr];
        cibuf[jptr] = dtemp;
        ciamp += dtemp;
        csiamp -= csibuf[kptr];
        csibuf[kptr] = dtemp;
        csiamp += dtemp;

        i = (i + 20) % 80;
        dtemp = sintab[i] * syncx / (MS / 2.);
        cqamp -= cqbuf[jptr];
        cqbuf[jptr] = dtemp;
        cqamp += dtemp;
        csqamp -= csqbuf[kptr];
        csqbuf[kptr] = dtemp;
        csqamp += dtemp;

        sp = &up->mitig[up->achan].wwv;
        sp->amp = sqrt(ciamp * ciamp + cqamp * cqamp) / SYNCYC;
        if (!(up->status & MSYNC))
                wwv_qrz(peer, sp, (int)(pp->fudgetime1 * SECOND));

        /*
         * WWVH
         */
        i = hsinptr;
        hsinptr = (hsinptr + IN1200) % 80;

        dtemp = sintab[i] * syncx / (MS / 2.);
        hiamp -= hibuf[jptr];
        hibuf[jptr] = dtemp;
        hiamp += dtemp;
        hsiamp -= hsibuf[kptr];
        hsibuf[kptr] = dtemp;
        hsiamp += dtemp;

        i = (i + 20) % 80;
        dtemp = sintab[i] * syncx / (MS / 2.);
        hqamp -= hqbuf[jptr];
        hqbuf[jptr] = dtemp;
        hqamp += dtemp;
        hsqamp -= hsqbuf[kptr];
        hsqbuf[kptr] = dtemp;
        hsqamp += dtemp;

        rp = &up->mitig[up->achan].wwvh;
        rp->amp = sqrt(hiamp * hiamp + hqamp * hqamp) / SYNCYC;
        if (!(up->status & MSYNC))
                wwv_qrz(peer, rp, (int)(pp->fudgetime2 * SECOND));
        jptr = (jptr + 1) % SYNSIZ;
        kptr = (kptr + 1) % TCKSIZ;

        /*
         * The following section is called once per minute. It does
         * housekeeping and timeout functions and empties the dustbins.
         */
        if (up->mphase == 0) {
                up->watch++;
                if (!(up->status & MSYNC)) {

                        /*
                         * If minute sync has not been acquired before
                         * ACQSN timeout (6 min), or if no signal is
                         * heard, the program cycles to the next
                         * frequency and tries again.
                         */
                        if (!wwv_newchan(peer))
                                up->watch = 0;
                } else {

                        /*
                         * If the leap bit is set, set the minute epoch
                         * back one second so the station processes
                         * don't miss a beat.
                         */
                        if (up->status & LEPSEC) {
                                up->mphase -= SECOND;
                                if (up->mphase < 0)
                                        up->mphase += MINUTE;
                        }
                }
        }

        /*
         * When the channel metric reaches threshold and the second
         * counter matches the minute epoch within the second, the
         * driver has synchronized to the station. The second number is
         * the remaining seconds until the next minute epoch, while the
         * sync epoch is zero. Watch out for the first second; if
         * already synchronized to the second, the buffered sync epoch
         * must be set.
         *
         * Note the guard interval is 200 ms; if for some reason the
         * clock drifts more than that, it might wind up in the wrong
         * second. If the maximum frequency error is not more than about
         * 1 PPM, the clock can go as much as two days while still in
         * the same second.
         */
        if (up->status & MSYNC) {
                wwv_epoch(peer);
        } else if (up->sptr != NULL) {
                sp = up->sptr;
                if (sp->metric >= TTHR && epoch == sp->mepoch % SECOND)
                    {
                        up->rsec = (60 - sp->mepoch / SECOND) % 60;
                        up->rphase = 0;
                        up->status |= MSYNC;
                        up->watch = 0;
                        if (!(up->status & SSYNC))
                                up->repoch = up->yepoch = epoch;
                        else
                                up->repoch = up->yepoch;
                        
                }
        }

        /*
         * The second sync pulse is extracted using 5-ms (40 sample) FIR
         * matched filters at 1000 Hz for WWV or 1200 Hz for WWVH. This
         * pulse is used for the most precise synchronization, since if
         * provides a resolution of one sample (125 us). The filters run
         * only if the station has been reliably determined.
         */
        if (up->status & SELV)
                mfsync = sqrt(csiamp * csiamp + csqamp * csqamp) /
                    TCKCYC;
        else if (up->status & SELH)
                mfsync = sqrt(hsiamp * hsiamp + hsqamp * hsqamp) /
                    TCKCYC;
        else
                mfsync = 0;

        /*
         * Enhance the seconds sync pulse using a 1-s (8000-sample) comb
         * filter. Correct for the FIR matched filter delay, which is 5
         * ms for both the WWV and WWVH filters, and also for the
         * propagation delay. Once each second look for second sync. If
         * not in minute sync, fiddle the codec gain. Note the SNR is
         * computed from the maximum sample and the envelope of the
         * sample 6 ms before it, so if we slip more than a cycle the
         * SNR should plummet. The signal is scaled to produce unit
         * energy at the maximum value.
         */
        dtemp = (epobuf[epoch] += (mfsync - epobuf[epoch]) /
            up->avgint);
        if (dtemp > epomax) {
                int     j;

                epomax = dtemp;
                epopos = epoch;
                j = epoch - 6 * MS;
                if (j < 0)
                        j += SECOND;
                nxtmax = fabs(epobuf[j]);
        }
        if (epoch == 0) {
                up->epomax = epomax;
                up->eposnr = wwv_snr(epomax, nxtmax);
                epopos -= TCKCYC * MS;
                if (epopos < 0)
                        epopos += SECOND;
                wwv_endpoc(peer, epopos);
                if (!(up->status & SSYNC))
                        up->alarm |= SYNERR;
                epomax = 0;
                if (!(up->status & MSYNC))
                        wwv_gain(peer);
        }
}


/*
 * wwv_qrz - identify and acquire WWV/WWVH minute sync pulse
 *
 * This routine implements a virtual station process used to acquire
 * minute sync and to mitigate among the ten frequency and station
 * combinations. During minute sync acquisition the process probes each
 * frequency and station in turn for the minute pulse, which
 * involves searching through the entire 480,000-sample minute. The
 * process finds the maximum signal and RMS noise plus signal. Then, the
 * actual noise is determined by subtracting the energy of the matched
 * filter.
 *
 * Students of radar receiver technology will discover this algorithm
 * amounts to a range-gate discriminator. A valid pulse must have peak
 * amplitude at least QTHR (2500) and SNR at least QSNR (20) dB and the
 * difference between the current and previous epoch must be less than
 * AWND (20 ms). Note that the discriminator peak occurs about 800 ms
 * into the second, so the timing is retarded to the previous second
 * epoch.
 */
static void
wwv_qrz(
        struct peer *peer,      /* peer structure pointer */
        struct sync *sp,        /* sync channel structure */
        int     pdelay          /* propagation delay (samples) */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        char    tbuf[TBUF];     /* monitor buffer */
        long    epoch;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;

        /*
         * Find the sample with peak amplitude, which defines the minute
         * epoch. Accumulate all samples to determine the total noise
         * energy.
         */
        epoch = up->mphase - pdelay - SYNSIZ;
        if (epoch < 0)
                epoch += MINUTE;
        if (sp->amp > sp->maxeng) {
                sp->maxeng = sp->amp;
                sp->pos = epoch;
        }
        sp->noieng += sp->amp;

        /*
         * At the end of the minute, determine the epoch of the minute
         * sync pulse, as well as the difference between the current and
         * previous epoches due to the intrinsic frequency error plus
         * jitter. When calculating the SNR, subtract the pulse energy
         * from the total noise energy and then normalize.
         */
        if (up->mphase == 0) {
                sp->synmax = sp->maxeng;
                sp->synsnr = wwv_snr(sp->synmax, (sp->noieng -
                    sp->synmax) / MINUTE);
                if (sp->count == 0)
                        sp->lastpos = sp->pos;
                epoch = (sp->pos - sp->lastpos) % MINUTE;
                sp->reach <<= 1;
                if (sp->reach & (1 << AMAX))
                        sp->count--;
                if (sp->synmax > ATHR && sp->synsnr > ASNR) {
                        if (abs(epoch) < AWND * MS) {
                                sp->reach |= 1;
                                sp->count++;
                                sp->mepoch = sp->lastpos = sp->pos;
                        } else if (sp->count == 1) {
                                sp->lastpos = sp->pos;
                        }
                }
                if (up->watch > ACQSN)
                        sp->metric = 0;
                else
                        sp->metric = wwv_metric(sp);
                if (pp->sloppyclockflag & CLK_FLAG4) {
                        sprintf(tbuf,
                            "wwv8 %04x %3d %s %04x %.0f %.0f/%.1f %ld %ld",
                            up->status, up->gain, sp->refid,
                            sp->reach & 0xffff, sp->metric, sp->synmax,
                            sp->synsnr, sp->pos % SECOND, epoch);
                        record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
                        if (debug)
                                printf("%s\n", tbuf);
#endif /* DEBUG */
                }
                sp->maxeng = sp->noieng = 0;
        }
}


/*
 * wwv_endpoc - identify and acquire second sync pulse
 *
 * This routine is called at the end of the second sync interval. It
 * determines the second sync epoch position within the second and
 * disciplines the sample clock using a frequency-lock loop (FLL).
 *
 * Second sync is determined in the RF input routine as the maximum
 * over all 8000 samples in the second comb filter. To assure accurate
 * and reliable time and frequency discipline, this routine performs a
 * great deal of heavy-handed heuristic data filtering and grooming.
 */
static void
wwv_endpoc(
        struct peer *peer,      /* peer structure pointer */
        int epopos              /* epoch max position */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        static int epoch_mf[3]; /* epoch median filter */
        static int tepoch;      /* current second epoch */
        static int xepoch;      /* last second epoch */
        static int zepoch;      /* last run epoch */
        static int zcount;      /* last run end time */
        static int scount;      /* seconds counter */
        static int syncnt;      /* run length counter */
        static int maxrun;      /* longest run length */
        static int mepoch;      /* longest run end epoch */
        static int mcount;      /* longest run end time */
        static int avgcnt;      /* averaging interval counter */
        static int avginc;      /* averaging ratchet */
        static int iniflg;      /* initialization flag */
        char tbuf[TBUF];                /* monitor buffer */
        double dtemp;
        int tmp2;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;
        if (!iniflg) {
                iniflg = 1;
                memset((char *)epoch_mf, 0, sizeof(epoch_mf));
        }

        /*
         * If the signal amplitude or SNR fall below thresholds, dim the
         * second sync lamp and wait for hotter ions. If no stations are
         * heard, we are either in a probe cycle or the ions are really
         * cold. 
         */
        scount++;
        if (up->epomax < STHR || up->eposnr < SSNR) {
                up->status &= ~(SSYNC | FGATE);
                avgcnt = syncnt = maxrun = 0;
                return;
        }
        if (!(up->status & (SELV | SELH)))
                return;

        /*
         * A three-stage median filter is used to help denoise the
         * second sync pulse. The median sample becomes the candidate
         * epoch.
         */
        epoch_mf[2] = epoch_mf[1];
        epoch_mf[1] = epoch_mf[0];
        epoch_mf[0] = epopos;
        if (epoch_mf[0] > epoch_mf[1]) {
                if (epoch_mf[1] > epoch_mf[2])
                        tepoch = epoch_mf[1];   /* 0 1 2 */
                else if (epoch_mf[2] > epoch_mf[0])
                        tepoch = epoch_mf[0];   /* 2 0 1 */
                else
                        tepoch = epoch_mf[2];   /* 0 2 1 */
        } else {
                if (epoch_mf[1] < epoch_mf[2])
                        tepoch = epoch_mf[1];   /* 2 1 0 */
                else if (epoch_mf[2] < epoch_mf[0])
                        tepoch = epoch_mf[0];   /* 1 0 2 */
                else
                        tepoch = epoch_mf[2];   /* 1 2 0 */
        }


        /*
         * If the epoch candidate is the same as the last one, increment
         * the run counter. If not, save the length, epoch and end
         * time of the current run for use later and reset the counter.
         * The epoch is considered valid if the run is at least SCMP
         * (10) s, the minute is synchronized and the interval since the
         * last epoch  is not greater than the averaging interval. Thus,
         * after a long absence, the program will wait a full averaging
         * interval while the comb filter charges up and noise
         * dissapates..
         */
        tmp2 = (tepoch - xepoch) % SECOND;
        if (tmp2 == 0) {
                syncnt++;
                if (syncnt > SCMP && up->status & MSYNC && (up->status &
                    FGATE || scount - zcount <= up->avgint)) {
                        up->status |= SSYNC;
                        up->yepoch = tepoch;
                }
        } else if (syncnt >= maxrun) {
                maxrun = syncnt;
                mcount = scount;
                mepoch = xepoch;
                syncnt = 0;
        }
        if ((pp->sloppyclockflag & CLK_FLAG4) && !(up->status &
            MSYNC)) {
                sprintf(tbuf,
                    "wwv1 %04x %3d %4d %5.0f %5.1f %5d %4d %4d %4d",
                    up->status, up->gain, tepoch, up->epomax,
                    up->eposnr, tmp2, avgcnt, syncnt,
                    maxrun);
                record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
                if (debug)
                        printf("%s\n", tbuf);
#endif /* DEBUG */
        }
        avgcnt++;
        if (avgcnt < up->avgint) {
                xepoch = tepoch;
                return;
        }

        /*
         * The sample clock frequency is disciplined using a first-order
         * feedback loop with time constant consistent with the Allan
         * intercept of typical computer clocks. During each averaging
         * interval the candidate epoch at the end of the longest run is
         * determined. If the longest run is zero, all epoches in the
         * interval are different, so the candidate epoch is the current
         * epoch. The frequency update is computed from the candidate
         * epoch difference (125-us units) and time difference (seconds)
         * between updates.
         */
        if (syncnt >= maxrun) {
                maxrun = syncnt;
                mcount = scount;
                mepoch = xepoch;
        }
        xepoch = tepoch;
        if (maxrun == 0) {
                mepoch = tepoch;
                mcount = scount;
        }

        /*
         * The master clock runs at the codec sample frequency of 8000
         * Hz, so the intrinsic time resolution is 125 us. The frequency
         * resolution ranges from 18 PPM at the minimum averaging
         * interval of 8 s to 0.12 PPM at the maximum interval of 1024
         * s. An offset update is determined at the end of the longest
         * run in each averaging interval. The frequency adjustment is
         * computed from the difference between offset updates and the
         * interval between them.
         *
         * The maximum frequency adjustment ranges from 187 PPM at the
         * minimum interval to 1.5 PPM at the maximum. If the adjustment
         * exceeds the maximum, the update is discarded and the
         * hysteresis counter is decremented. Otherwise, the frequency
         * is incremented by the adjustment, but clamped to the maximum
         * 187.5 PPM. If the update is less than half the maximum, the
         * hysteresis counter is incremented. If the counter increments
         * to +3, the averaging interval is doubled and the counter set
         * to zero; if it decrements to -3, the interval is halved and
         * the counter set to zero.
         */
        dtemp = (mepoch - zepoch) % SECOND;
        if (up->status & FGATE) {
                if (abs(dtemp) < MAXFREQ * MINAVG) {
                        up->freq += (dtemp / 2.) / ((mcount - zcount) *
                            FCONST);
                        if (up->freq > MAXFREQ)
                                up->freq = MAXFREQ;
                        else if (up->freq < -MAXFREQ)
                                up->freq = -MAXFREQ;
                        if (abs(dtemp) < MAXFREQ * MINAVG / 2.) {
                                if (avginc < 3) {
                                        avginc++;
                                } else {
                                        if (up->avgint < MAXAVG) {
                                                up->avgint <<= 1;
                                                avginc = 0;
                                        }
                                }
                        }
                } else {
                        if (avginc > -3) {
                                avginc--;
                        } else {
                                if (up->avgint > MINAVG) {
                                        up->avgint >>= 1;
                                        avginc = 0;
                                }
                        }
                }
        }
        if (pp->sloppyclockflag & CLK_FLAG4) {
                sprintf(tbuf,
                    "wwv2 %04x %5.0f %5.1f %5d %4d %4d %4d %4.0f %7.2f",
                    up->status, up->epomax, up->eposnr, mepoch,
                    up->avgint, maxrun, mcount - zcount, dtemp,
                    up->freq * 1e6 / SECOND);
                record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
                if (debug)
                        printf("%s\n", tbuf);
#endif /* DEBUG */
        }

        /*
         * This is a valid update; set up for the next interval.
         */
        up->status |= FGATE;
        zepoch = mepoch;
        zcount = mcount;
        avgcnt = syncnt = maxrun = 0;
}


/*
 * wwv_epoch - epoch scanner
 *
 * This routine extracts data signals from the 100-Hz subcarrier. It
 * scans the receiver second epoch to determine the signal amplitudes
 * and pulse timings. Receiver synchronization is determined by the
 * minute sync pulse detected in the wwv_rf() routine and the second
 * sync pulse detected in the wwv_epoch() routine. The transmitted
 * signals are delayed by the propagation delay, receiver delay and
 * filter delay of this program. Delay corrections are introduced
 * separately for WWV and WWVH. 
 *
 * Most communications radios use a highpass filter in the audio stages,
 * which can do nasty things to the subcarrier phase relative to the
 * sync pulses. Therefore, the data subcarrier reference phase is
 * disciplined using the hardlimited quadrature-phase signal sampled at
 * the same time as the in-phase signal. The phase tracking loop uses
 * phase adjustments of plus-minus one sample (125 us). 
 */
static void
wwv_epoch(
        struct peer *peer       /* peer structure pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        struct chan *cp;
        static double sigmin, sigzer, sigone, engmax, engmin;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;

        /*
         * Find the maximum minute sync pulse energy for both the
         * WWV and WWVH stations. This will be used later for channel
         * and station mitigation. Also set the seconds epoch at 800 ms
         * well before the end of the second to make sure we never set
         * the epoch backwards.
         */
        cp = &up->mitig[up->achan];
        if (cp->wwv.amp > cp->wwv.syneng) 
                cp->wwv.syneng = cp->wwv.amp;
        if (cp->wwvh.amp > cp->wwvh.syneng) 
                cp->wwvh.syneng = cp->wwvh.amp;
        if (up->rphase == 800 * MS)
                up->repoch = up->yepoch;

        /*
         * Use the signal amplitude at epoch 15 ms as the noise floor.
         * This gives a guard time of +-15 ms from the beginning of the
         * second until the second pulse rises at 30 ms. There is a
         * compromise here; we want to delay the sample as long as
         * possible to give the radio time to change frequency and the
         * AGC to stabilize, but as early as possible if the second
         * epoch is not exact.
         */
        if (up->rphase == 15 * MS)
                sigmin = sigzer = sigone = up->irig;

        /*
         * Latch the data signal at 200 ms. Keep this around until the
         * end of the second. Use the signal energy as the peak to
         * compute the SNR. Use the Q sample to adjust the 100-Hz
         * reference oscillator phase.
         */
        if (up->rphase == 200 * MS) {
                sigzer = up->irig;
                engmax = sqrt(up->irig * up->irig + up->qrig *
                    up->qrig);
                up->datpha = up->qrig / up->avgint;
                if (up->datpha >= 0) {
                        up->datapt++;
                        if (up->datapt >= 80)
                                up->datapt -= 80;
                } else {
                        up->datapt--;
                        if (up->datapt < 0)
                                up->datapt += 80;
                }
        }


        /*
         * Latch the data signal at 500 ms. Keep this around until the
         * end of the second.
         */
        else if (up->rphase == 500 * MS)
                sigone = up->irig;

        /*
         * At the end of the second crank the clock state machine and
         * adjust the codec gain. Note the epoch is buffered from the
         * center of the second in order to avoid jitter while the
         * seconds synch is diddling the epoch. Then, determine the true
         * offset and update the median filter in the driver interface.
         *
         * Use the energy at the end of the second as the noise to
         * compute the SNR for the data pulse. This gives a better
         * measurement than the beginning of the second, especially when
         * returning from the probe channel. This gives a guard time of
         * 30 ms from the decay of the longest pulse to the rise of the
         * next pulse.
         */
        up->rphase++;
        if (up->mphase % SECOND == up->repoch) {
                up->status &= ~(DGATE | BGATE);
                engmin = sqrt(up->irig * up->irig + up->qrig *
                    up->qrig);
                up->datsig = engmax;
                up->datsnr = wwv_snr(engmax, engmin);

                /*
                 * If the amplitude or SNR is below threshold, average a
                 * 0 in the the integrators; otherwise, average the
                 * bipolar signal. This is done to avoid noise polution.
                 */
                if (engmax < DTHR || up->datsnr < DSNR) {
                        up->status |= DGATE;
                        wwv_rsec(peer, 0);
                } else {
                        sigzer -= sigone;
                        sigone -= sigmin;
                        wwv_rsec(peer, sigone - sigzer);
                }
                if (up->status & (DGATE | BGATE))
                        up->errcnt++;
                if (up->errcnt > MAXERR)
                        up->alarm |= LOWERR;
                wwv_gain(peer);
                cp = &up->mitig[up->achan];
                cp->wwv.syneng = 0;
                cp->wwvh.syneng = 0;
                up->rphase = 0;
        }
}


/*
 * wwv_rsec - process receiver second
 *
 * This routine is called at the end of each receiver second to
 * implement the per-second state machine. The machine assembles BCD
 * digit bits, decodes miscellaneous bits and dances the leap seconds.
 *
 * Normally, the minute has 60 seconds numbered 0-59. If the leap
 * warning bit is set, the last minute (1439) of 30 June (day 181 or 182
 * for leap years) or 31 December (day 365 or 366 for leap years) is
 * augmented by one second numbered 60. This is accomplished by
 * extending the minute interval by one second and teaching the state
 * machine to ignore it.
 */
static void
wwv_rsec(
        struct peer *peer,      /* peer structure pointer */
        double bit
        )
{
        static int iniflg;      /* initialization flag */
        static double bcddld[4]; /* BCD data bits */
        static double bitvec[61]; /* bit integrator for misc bits */
        struct refclockproc *pp;
        struct wwvunit *up;
        struct chan *cp;
        struct sync *sp, *rp;
        char    tbuf[TBUF];     /* monitor buffer */
        int     sw, arg, nsec;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;
        if (!iniflg) {
                iniflg = 1;
                memset((char *)bitvec, 0, sizeof(bitvec));
        }

        /*
         * The bit represents the probability of a hit on zero (negative
         * values), a hit on one (positive values) or a miss (zero
         * value). The likelihood vector is the exponential average of
         * these probabilities. Only the bits of this vector
         * corresponding to the miscellaneous bits of the timecode are
         * used, but it's easier to do them all. After that, crank the
         * seconds state machine.
         */
        nsec = up->rsec;
        up->rsec++;
        bitvec[nsec] += (bit - bitvec[nsec]) / TCONST;
        sw = progx[nsec].sw;
        arg = progx[nsec].arg;

        /*
         * The minute state machine. Fly off to a particular section as
         * directed by the transition matrix and second number.
         */
        switch (sw) {

        /*
         * Ignore this second.
         */
        case IDLE:                      /* 9, 45-49 */
                break;

        /*
         * Probe channel stuff
         *
         * The WWV/H format contains data pulses in second 59 (position
         * identifier) and second 1, but not in second 0. The minute
         * sync pulse is contained in second 0. At the end of second 58
         * QSY to the probe channel, which rotates in turn over all
         * WWV/H frequencies. At the end of second 0 measure the minute
         * sync pulse. At the end of second 1 measure the data pulse and
         * QSY back to the data channel. Note that the actions commented
         * here happen at the end of the second numbered as shown.
         *
         * At the end of second 0 save the minute sync amplitude latched
         * at 800 ms as the signal later used to calculate the SNR. 
         */
        case SYNC2:                     /* 0 */
                cp = &up->mitig[up->achan];
                cp->wwv.synmax = cp->wwv.syneng;
                cp->wwvh.synmax = cp->wwvh.syneng;
                break;

        /*
         * At the end of second 1 use the minute sync amplitude latched
         * at 800 ms as the noise to calculate the SNR. If the minute
         * sync pulse and SNR are above thresholds and the data pulse
         * amplitude and SNR are above thresolds, shift a 1 into the
         * station reachability register; otherwise, shift a 0. The
         * number of 1 bits in the last six intervals is a component of
         * the channel metric computed by the wwv_metric() routine.
         * Finally, QSY back to the data channel.
         */
        case SYNC3:                     /* 1 */
                cp = &up->mitig[up->achan];

                /*
                 * WWV station
                 */
                sp = &cp->wwv;
                sp->synsnr = wwv_snr(sp->synmax, sp->amp);
                sp->reach <<= 1;
                if (sp->reach & (1 << AMAX))
                        sp->count--;
                if (sp->synmax >= QTHR && sp->synsnr >= QSNR &&
                    !(up->status & (DGATE | BGATE))) {
                        sp->reach |= 1;
                        sp->count++;
                }
                sp->metric = wwv_metric(sp);

                /*
                 * WWVH station
                 */
                rp = &cp->wwvh;
                rp->synsnr = wwv_snr(rp->synmax, rp->amp);
                rp->reach <<= 1;
                if (rp->reach & (1 << AMAX))
                        rp->count--;
                if (rp->synmax >= QTHR && rp->synsnr >= QSNR &&
                    !(up->status & (DGATE | BGATE))) {
                        rp->reach |= 1;
                        rp->count++;
                }
                rp->metric = wwv_metric(rp);
                if (pp->sloppyclockflag & CLK_FLAG4) {
                        sprintf(tbuf,
                            "wwv5 %04x %3d %4d %.0f/%.1f %.0f/%.1f %s %04x %.0f %.0f/%.1f %s %04x %.0f %.0f/%.1f",
                            up->status, up->gain, up->yepoch,
                            up->epomax, up->eposnr, up->datsig,
                            up->datsnr,
                            sp->refid, sp->reach & 0xffff,
                            sp->metric, sp->synmax, sp->synsnr,
                            rp->refid, rp->reach & 0xffff,
                            rp->metric, rp->synmax, rp->synsnr);
                        record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
                        if (debug)
                                printf("%s\n", tbuf);
#endif /* DEBUG */
                }
                up->errcnt = up->digcnt = up->alarm = 0;

                /*
                 * If synchronized to a station, restart if no stations
                 * have been heard within the PANIC timeout (2 days). If
                 * not and the minute digit has been found, restart if
                 * not synchronized withing the SYNCH timeout (40 m). If
                 * not, restart if the unit digit has not been found
                 * within the DATA timeout (15 m).
                 */
                if (up->status & INSYNC) {
                        if (up->watch > PANIC) {
                                wwv_newgame(peer);
                                return;
                        }
                } else if (up->status & DSYNC) {
                        if (up->watch > SYNCH) {
                                wwv_newgame(peer);
                                return;
                        }
                } else if (up->watch > DATA) {
                        wwv_newgame(peer);
                        return;
                }
                wwv_newchan(peer);
                break;

        /*
         * Save the bit probability in the BCD data vector at the index
         * given by the argument. Bits not used in the digit are forced
         * to zero.
         */
        case COEF1:                     /* 4-7 */ 
                bcddld[arg] = bit;
                break;

        case COEF:                      /* 10-13, 15-17, 20-23, 25-26,
                                           30-33, 35-38, 40-41, 51-54 */
                if (up->status & DSYNC) 
                        bcddld[arg] = bit;
                else
                        bcddld[arg] = 0;
                break;

        case COEF2:                     /* 18, 27-28, 42-43 */
                bcddld[arg] = 0;
                break;

        /*
         * Correlate coefficient vector with each valid digit vector and
         * save in decoding matrix. We step through the decoding matrix
         * digits correlating each with the coefficients and saving the
         * greatest and the next lower for later SNR calculation.
         */
        case DECIM2:                    /* 29 */
                wwv_corr4(peer, &up->decvec[arg], bcddld, bcd2);
                break;

        case DECIM3:                    /* 44 */
                wwv_corr4(peer, &up->decvec[arg], bcddld, bcd3);
                break;

        case DECIM6:                    /* 19 */
                wwv_corr4(peer, &up->decvec[arg], bcddld, bcd6);
                break;

        case DECIM9:                    /* 8, 14, 24, 34, 39 */
                wwv_corr4(peer, &up->decvec[arg], bcddld, bcd9);
                break;

        /*
         * Miscellaneous bits. If above the positive threshold, declare
         * 1; if below the negative threshold, declare 0; otherwise
         * raise the BGATE bit. The design is intended to avoid
         * integrating noise under low SNR conditions.
         */
        case MSC20:                     /* 55 */
                wwv_corr4(peer, &up->decvec[YR + 1], bcddld, bcd9);
                /* fall through */

        case MSCBIT:                    /* 2-3, 50, 56-57 */
                if (bitvec[nsec] > BTHR) {
                        if (!(up->misc & arg))
                                up->alarm |= CMPERR;
                        up->misc |= arg;
                } else if (bitvec[nsec] < -BTHR) {
                        if (up->misc & arg)
                                up->alarm |= CMPERR;
                        up->misc &= ~arg;
                } else {
                        up->status |= BGATE;
                }
                break;

        /*
         * Save the data channel gain, then QSY to the probe channel and
         * dim the seconds comb filters. The www_newchan() routine will
         * light them back up.
         */
        case MSC21:                     /* 58 */
                if (bitvec[nsec] > BTHR) {
                        if (!(up->misc & arg))
                                up->alarm |= CMPERR;
                        up->misc |= arg;
                } else if (bitvec[nsec] < -BTHR) {
                        if (up->misc & arg)
                                up->alarm |= CMPERR;
                        up->misc &= ~arg;
                } else {
                        up->status |= BGATE;
                }
                up->status &= ~(SELV | SELH);
#ifdef ICOM
                if (up->fd_icom > 0) {
                        up->schan = (up->schan + 1) % NCHAN;
                        wwv_qsy(peer, up->schan);
                } else {
                        up->mitig[up->achan].gain = up->gain;
                }
#else
                up->mitig[up->achan].gain = up->gain;
#endif /* ICOM */
                break;

        /*
         * The endgames
         *
         * During second 59 the receiver and codec AGC are settling
         * down, so the data pulse is unusable as quality metric. If
         * LEPSEC is set on the last minute of 30 June or 31 December,
         * the transmitter and receiver insert an extra second (60) in
         * the timescale and the minute sync repeats the second. Once
         * leaps occurred at intervals of about 18 months, but the last
         * leap before the most recent leap in 1995 was in  1998.
         */
        case MIN1:                      /* 59 */
                if (up->status & LEPSEC)
                        break;

                /* fall through */

        case MIN2:                      /* 60 */
                up->status &= ~LEPSEC;
                wwv_tsec(peer);
                up->rsec = 0;
                wwv_clock(peer);
                break;
        }
        if ((pp->sloppyclockflag & CLK_FLAG4) && !(up->status &
            DSYNC)) {
                sprintf(tbuf,
                    "wwv3 %2d %04x %3d %4d %5.0f %5.1f %5.0f %5.1f %5.0f",
                    nsec, up->status, up->gain, up->yepoch, up->epomax,
                    up->eposnr, up->datsig, up->datsnr, bit);
                record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
                if (debug)
                        printf("%s\n", tbuf);
#endif /* DEBUG */
        }
        pp->disp += AUDIO_PHI;
}

/*
 * The radio clock is set if the alarm bits are all zero. After that,
 * the time is considered valid if the second sync bit is lit. It should
 * not be a surprise, especially if the radio is not tunable, that
 * sometimes no stations are above the noise and the integrators
 * discharge below the thresholds. We assume that, after a day of signal
 * loss, the minute sync epoch will be in the same second. This requires
 * the codec frequency be accurate within 6 PPM. Practical experience
 * shows the frequency typically within 0.1 PPM, so after a day of
 * signal loss, the time should be within 8.6 ms.. 
 */
static void
wwv_clock(
        struct peer *peer       /* peer unit pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        l_fp    offset;         /* offset in NTP seconds */

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;
        if (!(up->status & SSYNC))
                up->alarm |= SYNERR;
        if (up->digcnt < 9)
                up->alarm |= NINERR;
        if (!(up->alarm))
                up->status |= INSYNC;
        if (up->status & INSYNC && up->status & SSYNC) {
                if (up->misc & SECWAR)
                        pp->leap = LEAP_ADDSECOND;
                else
                        pp->leap = LEAP_NOWARNING;
                pp->second = up->rsec;
                pp->minute = up->decvec[MN].digit + up->decvec[MN +
                    1].digit * 10;
                pp->hour = up->decvec[HR].digit + up->decvec[HR +
                    1].digit * 10;
                pp->day = up->decvec[DA].digit + up->decvec[DA +
                    1].digit * 10 + up->decvec[DA + 2].digit * 100;
                pp->year = up->decvec[YR].digit + up->decvec[YR +
                    1].digit * 10;
                pp->year += 2000;
                L_CLR(&offset);
                if (!clocktime(pp->day, pp->hour, pp->minute,
                    pp->second, GMT, up->timestamp.l_ui,
                    &pp->yearstart, &offset.l_ui)) {
                        up->errflg = CEVNT_BADTIME;
                } else {
                        up->watch = 0;
                        pp->disp = 0;
                        pp->lastref = up->timestamp;
                        refclock_process_offset(pp, offset,
                            up->timestamp, PDELAY + up->pdelay);
                        refclock_receive(peer);
                }
        }
        pp->lencode = timecode(up, pp->a_lastcode);
        record_clock_stats(&peer->srcadr, pp->a_lastcode);
#ifdef DEBUG
        if (debug)
                printf("wwv: timecode %d %s\n", pp->lencode,
                    pp->a_lastcode);
#endif /* DEBUG */
}


/*
 * wwv_corr4 - determine maximum-likelihood digit
 *
 * This routine correlates the received digit vector with the BCD
 * coefficient vectors corresponding to all valid digits at the given
 * position in the decoding matrix. The maximum value corresponds to the
 * maximum-likelihood digit, while the ratio of this value to the next
 * lower value determines the likelihood function. Note that, if the
 * digit is invalid, the likelihood vector is averaged toward a miss.
 */
static void
wwv_corr4(
        struct peer *peer,      /* peer unit pointer */
        struct decvec *vp,      /* decoding table pointer */
        double  data[],         /* received data vector */
        double  tab[][4]        /* correlation vector array */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        double  topmax, nxtmax; /* metrics */
        double  acc;            /* accumulator */
        char    tbuf[TBUF];     /* monitor buffer */
        int     mldigit;        /* max likelihood digit */
        int     i, j;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;

        /*
         * Correlate digit vector with each BCD coefficient vector. If
         * any BCD digit bit is bad, consider all bits a miss. Until the
         * minute units digit has been resolved, don't to anything else.
         * Note the SNR is calculated as the ratio of the largest
         * likelihood value to the next largest likelihood value.
         */
        mldigit = 0;
        topmax = nxtmax = -MAXAMP;
        for (i = 0; tab[i][0] != 0; i++) {
                acc = 0;
                for (j = 0; j < 4; j++)
                        acc += data[j] * tab[i][j];
                acc = (vp->like[i] += (acc - vp->like[i]) / TCONST);
                if (acc > topmax) {
                        nxtmax = topmax;
                        topmax = acc;
                        mldigit = i;
                } else if (acc > nxtmax) {
                        nxtmax = acc;
                }
        }
        vp->digprb = topmax;
        vp->digsnr = wwv_snr(topmax, nxtmax);

        /*
         * The current maximum-likelihood digit is compared to the last
         * maximum-likelihood digit. If different, the compare counter
         * and maximum-likelihood digit are reset.  When the compare
         * counter reaches the BCMP threshold (3), the digit is assumed
         * correct. When the compare counter of all nine digits have
         * reached threshold, the clock is assumed correct.
         *
         * Note that the clock display digit is set before the compare
         * counter has reached threshold; however, the clock display is
         * not considered correct until all nine clock digits have
         * reached threshold. This is intended as eye candy, but avoids
         * mistakes when the signal is low and the SNR is very marginal.
         */
        if (vp->digprb < BTHR || vp->digsnr < BSNR) {
                up->status |= BGATE;
        } else {
                if (vp->digit != mldigit) {
                        up->alarm |= CMPERR;
                        if (vp->count > 0)
                                vp->count--;
                        if (vp->count == 0)
                                vp->digit = mldigit;
                } else {
                        if (vp->count < BCMP)
                                vp->count++;
                        if (vp->count == BCMP) {
                                up->status |= DSYNC;
                                up->digcnt++;
                        }
                }
        }
        if ((pp->sloppyclockflag & CLK_FLAG4) && !(up->status &
            INSYNC)) {
                sprintf(tbuf,
                    "wwv4 %2d %04x %3d %4d %5.0f %2d %d %d %d %5.0f %5.1f",
                    up->rsec - 1, up->status, up->gain, up->yepoch,
                    up->epomax, vp->radix, vp->digit, mldigit,
                    vp->count, vp->digprb, vp->digsnr);
                record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
                if (debug)
                        printf("%s\n", tbuf);
#endif /* DEBUG */
        }
}


/*
 * wwv_tsec - transmitter minute processing
 *
 * This routine is called at the end of the transmitter minute. It
 * implements a state machine that advances the logical clock subject to
 * the funny rules that govern the conventional clock and calendar.
 */
static void
wwv_tsec(
        struct peer *peer       /* driver structure pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        int minute, day, isleap;
        int temp;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;

        /*
         * Advance minute unit of the day. Don't propagate carries until
         * the unit minute digit has been found.
         */
        temp = carry(&up->decvec[MN]);  /* minute units */
        if (!(up->status & DSYNC))
                return;

        /*
         * Propagate carries through the day.
         */ 
        if (temp == 0)                  /* carry minutes */
                temp = carry(&up->decvec[MN + 1]);
        if (temp == 0)                  /* carry hours */
                temp = carry(&up->decvec[HR]);
        if (temp == 0)
                temp = carry(&up->decvec[HR + 1]);

        /*
         * Decode the current minute and day. Set leap day if the
         * timecode leap bit is set on 30 June or 31 December. Set leap
         * minute if the last minute on leap day, but only if the clock
         * is syncrhronized. This code fails in 2400 AD.
         */
        minute = up->decvec[MN].digit + up->decvec[MN + 1].digit *
            10 + up->decvec[HR].digit * 60 + up->decvec[HR +
            1].digit * 600;
        day = up->decvec[DA].digit + up->decvec[DA + 1].digit * 10 +
            up->decvec[DA + 2].digit * 100;

        /*
         * Set the leap bit on the last minute of the leap day.
         */
        isleap = up->decvec[YR].digit & 0x3;
        if (up->misc & SECWAR && up->status & INSYNC) {
                if ((day == (isleap ? 182 : 183) || day == (isleap ?
                    365 : 366)) && minute == 1439)
                        up->status |= LEPSEC;
        }

        /*
         * Roll the day if this the first minute and propagate carries
         * through the year.
         */
        if (minute != 1440)
                return;

        minute = 0;
        while (carry(&up->decvec[HR]) != 0); /* advance to minute 0 */
        while (carry(&up->decvec[HR + 1]) != 0);
        day++;
        temp = carry(&up->decvec[DA]);  /* carry days */
        if (temp == 0)
                temp = carry(&up->decvec[DA + 1]);
        if (temp == 0)
                temp = carry(&up->decvec[DA + 2]);

        /*
         * Roll the year if this the first day and propagate carries
         * through the century.
         */
        if (day != (isleap ? 365 : 366))
                return;

        day = 1;
        while (carry(&up->decvec[DA]) != 1); /* advance to day 1 */
        while (carry(&up->decvec[DA + 1]) != 0);
        while (carry(&up->decvec[DA + 2]) != 0);
        temp = carry(&up->decvec[YR]);  /* carry years */
        if (temp == 0)
                carry(&up->decvec[YR + 1]);
}


/*
 * carry - process digit
 *
 * This routine rotates a likelihood vector one position and increments
 * the clock digit modulo the radix. It returns the new clock digit or
 * zero if a carry occurred. Once synchronized, the clock digit will
 * match the maximum-likelihood digit corresponding to that position.
 */
static int
carry(
        struct decvec *dp       /* decoding table pointer */
        )
{
        int temp;
        int j;

        dp->digit++;
        if (dp->digit == dp->radix)
                dp->digit = 0;
        temp = dp->like[dp->radix - 1];
        for (j = dp->radix - 1; j > 0; j--)
                dp->like[j] = dp->like[j - 1];
        dp->like[0] = temp;
        return (dp->digit);
}


/*
 * wwv_snr - compute SNR or likelihood function
 */
static double
wwv_snr(
        double signal,          /* signal */
        double noise            /* noise */
        )
{
        double rval;

        /*
         * This is a little tricky. Due to the way things are measured,
         * either or both the signal or noise amplitude can be negative
         * or zero. The intent is that, if the signal is negative or
         * zero, the SNR must always be zero. This can happen with the
         * subcarrier SNR before the phase has been aligned. On the
         * other hand, in the likelihood function the "noise" is the
         * next maximum down from the peak and this could be negative.
         * However, in this case the SNR is truly stupendous, so we
         * simply cap at MAXSNR dB (40).
         */
        if (signal <= 0) {
                rval = 0;
        } else if (noise <= 0) {
                rval = MAXSNR;
        } else {
                rval = 20. * log10(signal / noise);
                if (rval > MAXSNR)
                        rval = MAXSNR;
        }
        return (rval);
}


/*
 * wwv_newchan - change to new data channel
 *
 * The radio actually appears to have ten channels, one channel for each
 * of five frequencies and each of two stations (WWV and WWVH), although
 * if not tunable only the DCHAN channel appears live. While the radio
 * is tuned to the working data channel frequency and station for most
 * of the minute, during seconds 59, 0 and 1 the radio is tuned to a
 * probe frequency in order to search for minute sync pulse and data
 * subcarrier from other transmitters.
 *
 * The search for WWV and WWVH operates simultaneously, with WWV minute
 * sync pulse at 1000 Hz and WWVH at 1200 Hz. The probe frequency
 * rotates each minute over 2.5, 5, 10, 15 and 20 MHz in order and yes,
 * we all know WWVH is dark on 20 MHz, but few remember when WWV was lit
 * on 25 MHz.
 *
 * This routine selects the best channel using a metric computed from
 * the reachability register and minute pulse amplitude. Normally, the
 * award goes to the the channel with the highest metric; but, in case
 * of ties, the award goes to the channel with the highest minute sync
 * pulse amplitude and then to the highest frequency.
 *
 * The routine performs an important squelch function to keep dirty data
 * from polluting the integrators. In order to consider a station valid,
 * the metric must be at least MTHR (13); otherwise, the station select
 * bits are cleared so the second sync is disabled and the data bit
 * integrators averaged to a miss. 
 */
static int
wwv_newchan(
        struct peer *peer       /* peer structure pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        struct sync *sp, *rp;
        double rank, dtemp;
        int i, j, rval;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;

        /*
         * Search all five station pairs looking for the channel with
         * maximum metric.
         */
        sp = NULL;
        j = 0;
        rank = 0;
        for (i = 0; i < NCHAN; i++) {
                rp = &up->mitig[i].wwvh;
                dtemp = rp->metric;
                if (dtemp >= rank) {
                        rank = dtemp;
                        sp = rp;
                        j = i;
                }
                rp = &up->mitig[i].wwv;
                dtemp = rp->metric;
                if (dtemp >= rank) {
                        rank = dtemp;
                        sp = rp;
                        j = i;
                }
        }

        /*
         * If the strongest signal is less than the MTHR threshold (13),
         * we are beneath the waves, so squelch the second sync and
         * advance to the next station. This makes sure all stations are
         * scanned when the ions grow dim. If the strongest signal is
         * greater than the threshold, tune to that frequency and
         * transmitter QTH.
         */
        up->status &= ~(SELV | SELH);
        if (rank < MTHR) {
                up->dchan = (up->dchan + 1) % NCHAN;
                if (up->status & METRIC) {
                        up->status &= ~METRIC;
                        refclock_report(peer, CEVNT_PROP);
                }
                rval = FALSE;
        } else {
                up->dchan = j;
                up->sptr = sp;
                memcpy(&pp->refid, sp->refid, 4);
                peer->refid = pp->refid;
                up->status |= METRIC;
                if (sp->select & SELV) {
                        up->status |= SELV;
                        up->pdelay = pp->fudgetime1;
                } else if (sp->select & SELH) {
                        up->status |= SELH;
                        up->pdelay = pp->fudgetime2;
                } else {
                        up->pdelay = 0;
                }
                rval = TRUE;
        }
#ifdef ICOM
        if (up->fd_icom > 0)
                wwv_qsy(peer, up->dchan);
#endif /* ICOM */
        return (rval);
}


/*
 * wwv_newgame - reset and start over
 *
 * There are three conditions resulting in a new game:
 *
 * 1    After finding the minute pulse (MSYNC lit), going 15 minutes
 *      (DATA) without finding the unit seconds digit.
 *
 * 2    After finding good data (DSYNC lit), going more than 40 minutes
 *      (SYNCH) without finding station sync (INSYNC lit).
 *
 * 3    After finding station sync (INSYNC lit), going more than 2 days
 *      (PANIC) without finding any station. 
 */
static void
wwv_newgame(
        struct peer *peer       /* peer structure pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;
        struct chan *cp;
        int i;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;

        /*
         * Initialize strategic values. Note we set the leap bits
         * NOTINSYNC and the refid "NONE".
         */
        if (up->status)
                up->errflg = CEVNT_TIMEOUT;
        peer->leap = LEAP_NOTINSYNC;
        up->watch = up->status = up->alarm = 0;
        up->avgint = MINAVG;
        up->freq = 0;
        up->gain = MAXGAIN / 2;

        /*
         * Initialize the station processes for audio gain, select bit,
         * station/frequency identifier and reference identifier. Start
         * probing at the strongest channel or the default channel if
         * nothing heard.
         */
        memset(up->mitig, 0, sizeof(up->mitig));
        for (i = 0; i < NCHAN; i++) {
                cp = &up->mitig[i];
                cp->gain = up->gain;
                cp->wwv.select = SELV;
                sprintf(cp->wwv.refid, "WV%.0f", floor(qsy[i])); 
                cp->wwvh.select = SELH;
                sprintf(cp->wwvh.refid, "WH%.0f", floor(qsy[i])); 
        }
        up->dchan = (DCHAN + NCHAN - 1) % NCHAN;
        wwv_newchan(peer);
        up->schan = up->dchan;
}

/*
 * wwv_metric - compute station metric
 *
 * The most significant bits represent the number of ones in the
 * station reachability register. The least significant bits represent
 * the minute sync pulse amplitude. The combined value is scaled 0-100.
 */
double
wwv_metric(
        struct sync *sp         /* station pointer */
        )
{
        double  dtemp;

        dtemp = sp->count * MAXAMP;
        if (sp->synmax < MAXAMP)
                dtemp += sp->synmax;
        else
                dtemp += MAXAMP - 1;
        dtemp /= (AMAX + 1) * MAXAMP;
        return (dtemp * 100.);
}


#ifdef ICOM
/*
 * wwv_qsy - Tune ICOM receiver
 *
 * This routine saves the AGC for the current channel, switches to a new
 * channel and restores the AGC for that channel. If a tunable receiver
 * is not available, just fake it.
 */
static int
wwv_qsy(
        struct peer *peer,      /* peer structure pointer */
        int     chan            /* channel */
        )
{
        int rval = 0;
        struct refclockproc *pp;
        struct wwvunit *up;

        pp = peer->procptr;
        up = (struct wwvunit *)pp->unitptr;
        if (up->fd_icom > 0) {
                up->mitig[up->achan].gain = up->gain;
                rval = icom_freq(up->fd_icom, peer->ttl & 0x7f,
                    qsy[chan]);
                up->achan = chan;
                up->gain = up->mitig[up->achan].gain;
        }
        return (rval);
}
#endif /* ICOM */


/*
 * timecode - assemble timecode string and length
 *
 * Prettytime format - similar to Spectracom
 *
 * sq yy ddd hh:mm:ss ld dut lset agc iden sig errs freq avgt
 *
 * s    sync indicator ('?' or ' ')
 * q    error bits (hex 0-F)
 * yyyy year of century
 * ddd  day of year
 * hh   hour of day
 * mm   minute of hour
 * ss   second of minute)
 * l    leap second warning (' ' or 'L')
 * d    DST state ('S', 'D', 'I', or 'O')
 * dut  DUT sign and magnitude (0.1 s)
 * lset minutes since last clock update
 * agc  audio gain (0-255)
 * iden reference identifier (station and frequency)
 * sig  signal quality (0-100)
 * errs bit errors in last minute
 * freq frequency offset (PPM)
 * avgt averaging time (s)
 */
static int
timecode(
        struct wwvunit *up,     /* driver structure pointer */
        char *ptr               /* target string */
        )
{
        struct sync *sp;
        int year, day, hour, minute, second, dut;
        char synchar, leapchar, dst;
        char cptr[50];
        

        /*
         * Common fixed-format fields
         */
        synchar = (up->status & INSYNC) ? ' ' : '?';
        year = up->decvec[YR].digit + up->decvec[YR + 1].digit * 10 +
            2000;
        day = up->decvec[DA].digit + up->decvec[DA + 1].digit * 10 +
            up->decvec[DA + 2].digit * 100;
        hour = up->decvec[HR].digit + up->decvec[HR + 1].digit * 10;
        minute = up->decvec[MN].digit + up->decvec[MN + 1].digit * 10;
        second = 0;
        leapchar = (up->misc & SECWAR) ? 'L' : ' ';
        dst = dstcod[(up->misc >> 4) & 0x3];
        dut = up->misc & 0x7;
        if (!(up->misc & DUTS))
                dut = -dut;
        sprintf(ptr, "%c%1X", synchar, up->alarm);
        sprintf(cptr, " %4d %03d %02d:%02d:%02d %c%c %+d",
            year, day, hour, minute, second, leapchar, dst, dut);
        strcat(ptr, cptr);

        /*
         * Specific variable-format fields
         */
        sp = up->sptr;
        sprintf(cptr, " %d %d %s %.0f %d %.1f %d", up->watch,
            up->mitig[up->dchan].gain, sp->refid, sp->metric,
            up->errcnt, up->freq / SECOND * 1e6, up->avgint);
        strcat(ptr, cptr);
        return (strlen(ptr));
}


/*
 * wwv_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
 * monitor.
 */
static void
wwv_gain(
        struct peer *peer       /* peer structure pointer */
        )
{
        struct refclockproc *pp;
        struct wwvunit *up;

        pp = peer->procptr;
        up = (struct wwvunit *)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;
#if DEBUG
        if (debug > 1)
                audio_show();
#endif
}


#else
int refclock_wwv_bs;
#endif /* REFCLOCK */