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

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

#include "ntp_types.h"

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

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

#include <stdio.h>
#include <ctype.h>
#include <math.h>

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

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

#ifdef ICOM
#include "icom.h"
#endif /* ICOM */
/*
* Audio CHU demodulator/decoder
*
* This driver synchronizes the computer time using data encoded in
* radio transmissions from Canadian time/frequency station CHU in
* Ottawa, Ontario. Transmissions are made continuously on 3330 kHz,
* 7850 kHz and 14670 kHz in upper sideband, compatible AM mode. An
* ordinary shortwave receiver can be tuned manually to one of these
* frequencies or, in the case of ICOM receivers, the receiver can be
* tuned automatically as propagation conditions change throughout the
* day and season.
*
* The driver requires an audio codec or sound card with sampling rate 8
* kHz and mu-law companding. This is the same standard as used by the
* telephone industry and is supported by most hardware and operating
* systems, including Solaris, SunOS, FreeBSD, NetBSD and Linux. In this
* implementation, only one audio driver and codec can be supported on a
* single machine.
*
* The driver can be compiled to use a Bell 103 compatible modem or
* modem chip to receive the radio signal and demodulate the data.
* Alternatively, the driver can be compiled to use the audio codec of
* the workstation or another with compatible audio drivers. In the
* latter case, the driver implements the modem using DSP routines, so
* the radio can be connected directly to either the microphone on line
* input port. In either case, the driver decodes the data using a
* maximum-likelihood technique which exploits the considerable degree
* of redundancy available to maximize accuracy and minimize errors.
*
* The CHU time broadcast includes an audio signal compatible with the
* Bell 103 modem standard (mark = 2225 Hz, space = 2025 Hz). The signal
* consists of nine, ten-character bursts transmitted at 300 bps between
* seconds 31 and 39 of each minute. Each character consists of eight
* data bits plus one start bit and two stop bits to encode two hex
* digits. The burst data consist of five characters (ten hex digits)
* followed by a repeat of these characters. In format A, the characters
* are repeated in the same polarity; in format B, the characters are
* repeated in the opposite polarity.
*
* Format A bursts are sent at seconds 32 through 39 of the minute in
* hex digits (nibble swapped)
*
*      6dddhhmmss6dddhhmmss
*
* The first ten digits encode a frame marker (6) followed by the day
* (ddd), hour (hh in UTC), minute (mm) and the second (ss). Since
* format A bursts are sent during the third decade of seconds the tens
* digit of ss is always 3. The driver uses this to determine correct
* burst synchronization. These digits are then repeated with the same
* polarity.
*
* Format B bursts are sent at second 31 of the minute in hex digits
*
*      xdyyyyttaaxdyyyyttaa
*
* The first ten digits encode a code (x described below) followed by
* the DUT1 (d in deciseconds), Gregorian year (yyyy), difference TAI -
* UTC (tt) and daylight time indicator (aa) peculiar to Canada. These
* digits are then repeated with inverted polarity.
*
* The x is coded
*
* 1 Sign of DUT (0 = +)
* 2 Leap second warning. One second will be added.
* 4 Leap second warning. One second will be subtracted.
* 8 Even parity bit for this nibble.
*
* By design, the last stop bit of the last character in the burst
* coincides with 0.5 second. Since characters have 11 bits and are
* transmitted at 300 bps, the last stop bit of the first character
* coincides with 0.5 - 9 * 11/300 = 0.170 second. Depending on the
* UART, character interrupts can vary somewhere between the end of bit
* 9 and end of bit 11. These eccentricities can be corrected along with
* the radio propagation delay using fudge time 1.
*
* Debugging aids
*
* The timecode format used for debugging and data recording includes
* data helpful in diagnosing problems with the radio signal and serial
* connections. With debugging enabled (-d on the ntpd command line),
* the driver produces one line for each burst in two formats
* corresponding to format A and B.Each line begins with the format code
* chuA or chuB followed by the status code and signal level (0-9999).
* The remainder of the line is as follows.
*
* Following is format A:
*
*      n b f s m code
*
* where n is the number of characters in the burst (0-10), b the burst
* distance (0-40), f the field alignment (-1, 0, 1), s the
* synchronization distance (0-16), m the burst number (2-9) and code
* the burst characters as received. Note that the hex digits in each
* character are reversed, so the burst
*
*      10 38 0 16 9 06851292930685129293
*
* is interpreted as containing 10 characters with burst distance 38,
* field alignment 0, synchronization distance 16 and burst number 9.
* The nibble-swapped timecode shows day 58, hour 21, minute 29 and
* second 39.
*
* Following is format B:
*
*      n b s code
*
* where n is the number of characters in the burst (0-10), b the burst
* distance (0-40), s the synchronization distance (0-40) and code the
* burst characters as received. Note that the hex digits in each
* character are reversed and the last ten digits inverted, so the burst
*
*      10 40 1091891300ef6e76ec
*
* is interpreted as containing 10 characters with burst distance 40.
* The nibble-swapped timecode shows DUT1 +0.1 second, year 1998 and TAI
* - UTC 31 seconds.
*
* Each line is preceeded by the code chuA or chuB, as appropriate. If
* the audio driver is compiled, the current gain (0-255) and relative
* signal level (0-9999) follow the code. The receiver volume control
* should be set so that the gain is somewhere near the middle of the
* range 0-255, which results in a signal level near 1000.
*
* In addition to the above, the reference timecode is updated and
* written to the clockstats file and debug score after the last burst
* received in the minute. The format is
*
*      sq yyyy ddd hh:mm:ss l s dd t agc ident m b
*
* s    '?' before first synchronized and ' ' after that
* q    status code (see below)
* yyyy year
* ddd  day of year
* hh:mm:ss time of day
* l    leap second indicator (space, L or D)
* dst  Canadian daylight code (opaque)
* t    number of minutes since last synchronized
* agc  audio gain (0 - 255)
* ident identifier (CHU0 3330 kHz, CHU1 7850 kHz, CHU2 14670 kHz)
* m    signal metric (0 - 100)
* b    number of timecodes for the previous minute (0 - 59)
*
* Fudge factors
*
* For accuracies better than the low millisceconds, fudge time1 can be
* set to the radio propagation delay from CHU to the receiver. This can
* be done conviently using the minimuf program.
*
* Fudge flag4 causes the dubugging output described above to be
* recorded in the clockstats file. When the audio driver is compiled,
* fudge flag2 selects the audio input port, where 0 is the mike port
* (default) and 1 is the line-in port. It does not seem useful to
* select the compact disc player port. Fudge flag3 enables audio
* monitoring of the input signal. For this purpose, the monitor gain is
* set to a default value.
*
* The audio codec code is normally compiled in the driver if the
* architecture supports it (HAVE_AUDIO defined), but is used only if
* the link /dev/chu_audio is defined and valid. The serial port code is
* always compiled in the driver, but is used only if the autdio codec
* is not available and the link /dev/chu%d is defined and valid.
*
* The ICOM code is normally compiled in the driver if selected (ICOM
* defined), but is used only if the link /dev/icom%d is defined and
* valid and the mode keyword on the server configuration command
* specifies a nonzero mode (ICOM ID select code). The C-IV speed is
* 9600 bps if the high order 0x80 bit of the mode is zero and 1200 bps
* if one. The C-IV trace is turned on if the debug level is greater
* than one.
*
* Alarm codes
*
* CEVNT_BADTIME        invalid date or time
* CEVNT_PROP           propagation failure - no stations heard
*/
/*
* Interface definitions
*/
#define SPEED232        B300    /* uart speed (300 baud) */
#define PRECISION       (-10)   /* precision assumed (about 1 ms) */
#define REFID           "CHU"   /* reference ID */
#define DEVICE          "/dev/chu%d" /* device name and unit */
#define SPEED232        B300    /* UART speed (300 baud) */
#ifdef ICOM
#define TUNE            .001    /* offset for narrow filter (MHz) */
#define DWELL           5       /* minutes in a dwell */
#define NCHAN           3       /* number of channels */
#define ISTAGE          3       /* number of integrator stages */
#endif /* ICOM */

#ifdef HAVE_AUDIO
/*
* Audio demodulator definitions
*/
#define SECOND          8000    /* nominal sample rate (Hz) */
#define BAUD            300     /* modulation rate (bps) */
#define OFFSET          128     /* companded sample offset */
#define SIZE            256     /* decompanding table size */
#define MAXAMP          6000.   /* maximum signal level */
#define MAXCLP          100     /* max clips above reference per s */
#define SPAN            800.    /* min envelope span */
#define LIMIT           1000.   /* soft limiter threshold */
#define AGAIN           6.      /* baseband gain */
#define LAG             10      /* discriminator lag */
#define DEVICE_AUDIO    "/dev/audio" /* device name */
#define DESCRIPTION     "CHU Audio/Modem Receiver" /* WRU */
#define AUDIO_BUFSIZ    240     /* audio buffer size (30 ms) */
#else
#define DESCRIPTION     "CHU Modem Receiver" /* WRU */
#endif /* HAVE_AUDIO */

/*
* Decoder definitions
*/
#define CHAR            (11. / 300.) /* character time (s) */
#define BURST           11      /* max characters per burst */
#define MINCHARS                9       /* min characters per burst */
#define MINDIST         28      /* min burst distance (of 40)  */
#define MINSYNC         8       /* min sync distance (of 16) */
#define MINSTAMP        20      /* min timestamps (of 60) */
#define MINMETRIC       50      /* min channel metric (of 160) */

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

/*
* Status bits (status)
*/
#define RUNT            0x0001  /* runt burst */
#define NOISE           0x0002  /* noise burst */
#define BFRAME          0x0004  /* invalid format B frame sync */
#define BFORMAT         0x0008  /* invalid format B data */
#define AFRAME          0x0010  /* invalid format A frame sync */
#define AFORMAT         0x0020  /* invalid format A data */
#define DECODE          0x0040  /* invalid data decode */
#define STAMP           0x0080  /* too few timestamps */
#define AVALID          0x0100  /* valid A frame */
#define BVALID          0x0200  /* valid B frame */
#define INSYNC          0x0400  /* clock synchronized */
#define METRIC          0x0800  /* one or more stations heard */

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

#ifdef HAVE_AUDIO
/*
* Maximum-likelihood UART structure. There are eight of these
* corresponding to the number of phases.
*/
struct surv {
       l_fp    cstamp;         /* last bit timestamp */
       double  shift[12];      /* sample shift register */
       double  span;           /* shift register envelope span */
       double  dist;           /* sample distance */
       int     uart;           /* decoded character */
};
#endif /* HAVE_AUDIO */

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

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

       /*
        * Character burst variables
        */
       int     cbuf[BURST];    /* character buffer */
       int     ntstamp;        /* number of timestamp samples */
       int     ndx;            /* buffer start index */
       int     prevsec;        /* previous burst second */
       int     burdist;        /* burst distance */
       int     syndist;        /* sync distance */
       int     burstcnt;       /* format A bursts this minute */
       double  maxsignal;      /* signal level (modem only) */
       int     gain;           /* codec gain (modem only) */

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

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

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

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

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

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

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

#ifdef ICOM
/*
* Note the tuned frequencies are 1 kHz higher than the carrier. CHU
* transmits on USB with carrier so we can use AM and the narrow SSB
* filter.
*/
static double qsy[NCHAN] = {3.330, 7.850, 14.670}; /* freq (MHz) */
#endif /* ICOM */

/*
* Transfer vector
*/
struct  refclock refclock_chu = {
       chu_start,              /* start up driver */
       chu_shutdown,           /* shut down driver */
       chu_poll,               /* transmit poll message */
       noentry,                /* not used (old chu_control) */
       noentry,                /* initialize driver (not used) */
       noentry,                /* not used (old chu_buginfo) */
       chu_second              /* housekeeping timer */
};


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

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

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

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

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

       if (fd < 0)
               return (0);

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

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

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


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

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

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


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

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

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


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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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


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

       u_char  *dpt;           /* receive buffer pointer */

       peer = rbufp->recv_peer;

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


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

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

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

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

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

       }
}


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

       int     i;

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

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

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

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


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

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

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

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

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


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

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

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

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

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

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

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


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

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


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

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

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

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

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


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

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

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

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

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


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

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

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

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

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

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

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

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

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


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

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


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

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

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


#else
NONEMPTY_TRANSLATION_UNIT
#endif /* REFCLOCK */