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[freebsd-src/fkvm-freebsd.git] / contrib / ntp / ntpd / refclock_mx4200.c

/*
 * This software was developed by the Computer Systems Engineering group
 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66.
 *
 * Copyright (c) 1992 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Lawrence Berkeley Laboratory.
 * 4. The name of the University may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Modified: Marc Brett <marc.brett@westgeo.com>   Sept, 1999.
 *
 * 1. Added support for alternate PPS schemes, with code mostly
 *    copied from the Oncore driver (Thanks, Poul-Henning Kamp).
 *    This code runs on SunOS 4.1.3 with ppsclock-1.6a1 and Solaris 7.
 */


#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#if defined(REFCLOCK) && defined(CLOCK_MX4200) && defined(HAVE_PPSAPI)

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

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

#include "mx4200.h"

#ifdef HAVE_SYS_TERMIOS_H
# include <sys/termios.h>
#endif
#ifdef HAVE_SYS_PPSCLOCK_H
# include <sys/ppsclock.h>
#endif

#include "ntp_sprintf.h"

#ifndef HAVE_STRUCT_PPSCLOCKEV
struct ppsclockev {
# ifdef HAVE_STRUCT_TIMESPEC
        struct timespec tv;
# else
        struct timeval tv;
# endif
        u_int serial;
};
#endif /* ! HAVE_STRUCT_PPSCLOCKEV */

#ifdef HAVE_PPSAPI
# include "ppsapi_timepps.h"
#endif /* HAVE_PPSAPI */

/*
 * This driver supports the Magnavox Model MX 4200 GPS Receiver
 * adapted to precision timing applications.  It requires the
 * ppsclock line discipline or streams module described in the
 * Line Disciplines and Streams Drivers page. It also requires a
 * gadget box and 1-PPS level converter, such as described in the
 * Pulse-per-second (PPS) Signal Interfacing page.
 *
 * It's likely that other compatible Magnavox receivers such as the
 * MX 4200D, MX 9212, MX 9012R, MX 9112 will be supported by this code.
 */

/*
 * Check this every time you edit the code!
 */
#define YEAR_LAST_MODIFIED 2000

/*
 * GPS Definitions
 */
#define DEVICE          "/dev/gps%d"    /* device name and unit */
#define SPEED232        B4800           /* baud */

/*
 * Radio interface parameters
 */
#define PRECISION       (-18)   /* precision assumed (about 4 us) */
#define REFID   "GPS\0"         /* reference id */
#define DESCRIPTION     "Magnavox MX4200 GPS Receiver" /* who we are */
#define DEFFUDGETIME    0       /* default fudge time (ms) */

#define SLEEPTIME       32      /* seconds to wait for reconfig to complete */

/*
 * Position Averaging.
 */
#define INTERVAL        1       /* Interval between position measurements (s) */
#define AVGING_TIME     24      /* Number of hours to average */
#define NOT_INITIALIZED -9999.  /* initial pivot longitude */

/*
 * MX4200 unit control structure.
 */
struct mx4200unit {
        u_int  pollcnt;                 /* poll message counter */
        u_int  polled;                  /* Hand in a time sample? */
        u_int  lastserial;              /* last pps serial number */
        struct ppsclockev ppsev;        /* PPS control structure */
        double avg_lat;                 /* average latitude */
        double avg_lon;                 /* average longitude */
        double avg_alt;                 /* average height */
        double central_meridian;        /* central meridian */
        double N_fixes;                 /* Number of position measurements */
        int    last_leap;               /* leap second warning */
        u_int  moving;                  /* mobile platform? */
        u_long sloppyclockflag;         /* fudge flags */
        u_int  known;                   /* position known yet? */
        u_long clamp_time;              /* when to stop postion averaging */
        u_long log_time;                /* when to print receiver status */
        pps_handle_t    pps_h;
        pps_params_t    pps_p;
        pps_info_t      pps_i;
};

static char pmvxg[] = "PMVXG";

/* XXX should be somewhere else */
#ifdef __GNUC__
#if __GNUC__ < 2  || (__GNUC__ == 2 && __GNUC_MINOR__ < 5)
#ifndef __attribute__
#define __attribute__(args)
#endif /* __attribute__ */
#endif /* __GNUC__ < 2  || (__GNUC__ == 2 && __GNUC_MINOR__ < 5) */
#else
#ifndef __attribute__
#define __attribute__(args)
#endif /* __attribute__ */
#endif /* __GNUC__ */
/* XXX end */

/*
 * Function prototypes
 */
static  int     mx4200_start    P((int, struct peer *));
static  void    mx4200_shutdown P((int, struct peer *));
static  void    mx4200_receive  P((struct recvbuf *));
static  void    mx4200_poll     P((int, struct peer *));

static  char *  mx4200_parse_t  P((struct peer *));
static  char *  mx4200_parse_p  P((struct peer *));
static  char *  mx4200_parse_s  P((struct peer *));
#ifdef QSORT_USES_VOID_P
int     mx4200_cmpl_fp  P((const void *, const void *));
#else
int     mx4200_cmpl_fp  P((const l_fp *, const l_fp *));
#endif /* not QSORT_USES_VOID_P */
static  int     mx4200_config   P((struct peer *));
static  void    mx4200_ref      P((struct peer *));
static  void    mx4200_send     P((struct peer *, char *, ...))
    __attribute__ ((format (printf, 2, 3)));
static  u_char  mx4200_cksum    P((char *, int));
static  int     mx4200_jday     P((int, int, int));
static  void    mx4200_debug    P((struct peer *, char *, ...))
    __attribute__ ((format (printf, 2, 3)));
static  int     mx4200_pps      P((struct peer *));

/*
 * Transfer vector
 */
struct  refclock refclock_mx4200 = {
        mx4200_start,           /* start up driver */
        mx4200_shutdown,        /* shut down driver */
        mx4200_poll,            /* transmit poll message */
        noentry,                /* not used (old mx4200_control) */
        noentry,                /* initialize driver (not used) */
        noentry,                /* not used (old mx4200_buginfo) */
        NOFLAGS                 /* not used */
};



/*
 * mx4200_start - open the devices and initialize data for processing
 */
static int
mx4200_start(
        int unit,
        struct peer *peer
        )
{
        register struct mx4200unit *up;
        struct refclockproc *pp;
        int fd;
        char gpsdev[20];

        /*
         * Open serial port
         */
        (void)sprintf(gpsdev, DEVICE, unit);
        if (!(fd = refclock_open(gpsdev, SPEED232, LDISC_PPS))) {
            return (0);
        }

        /*
         * Allocate unit structure
         */
        if (!(up = (struct mx4200unit *) emalloc(sizeof(struct mx4200unit)))) {
                perror("emalloc");
                (void) close(fd);
                return (0);
        }
        memset((char *)up, 0, sizeof(struct mx4200unit));
        pp = peer->procptr;
        pp->io.clock_recv = mx4200_receive;
        pp->io.srcclock = (caddr_t)peer;
        pp->io.datalen = 0;
        pp->io.fd = fd;
        if (!io_addclock(&pp->io)) {
                (void) close(fd);
                free(up);
                return (0);
        }
        pp->unitptr = (caddr_t)up;

        /*
         * Initialize miscellaneous variables
         */
        peer->precision = PRECISION;
        pp->clockdesc = DESCRIPTION;
        memcpy((char *)&pp->refid, REFID, 4);

        /* Ensure the receiver is properly configured */
        return mx4200_config(peer);
}


/*
 * mx4200_shutdown - shut down the clock
 */
static void
mx4200_shutdown(
        int unit,
        struct peer *peer
        )
{
        register struct mx4200unit *up;
        struct refclockproc *pp;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;
        io_closeclock(&pp->io);
        free(up);
}


/*
 * mx4200_config - Configure the receiver
 */
static int
mx4200_config(
        struct peer *peer
        )
{
        char tr_mode;
        int add_mode;
        register struct mx4200unit *up;
        struct refclockproc *pp;
        int mode;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        /*
         * Initialize the unit variables
         *
         * STRANGE BEHAVIOUR WARNING: The fudge flags are not available
         * at the time mx4200_start is called.  These are set later,
         * and so the code must be prepared to handle changing flags.
         */
        up->sloppyclockflag = pp->sloppyclockflag;
        if (pp->sloppyclockflag & CLK_FLAG2) {
                up->moving   = 1;       /* Receiver on mobile platform */
                msyslog(LOG_DEBUG, "mx4200_config: mobile platform");
        } else {
                up->moving   = 0;       /* Static Installation */
        }
        up->pollcnt             = 2;
        up->polled              = 0;
        up->known               = 0;
        up->avg_lat             = 0.0;
        up->avg_lon             = 0.0;
        up->avg_alt             = 0.0;
        up->central_meridian    = NOT_INITIALIZED;
        up->N_fixes             = 0.0;
        up->last_leap           = 0;    /* LEAP_NOWARNING */
        up->clamp_time          = current_time + (AVGING_TIME * 60 * 60);
        up->log_time            = current_time + SLEEPTIME;

        if (time_pps_create(pp->io.fd, &up->pps_h) < 0) {
                perror("time_pps_create");
                msyslog(LOG_ERR,
                        "mx4200_config: time_pps_create failed: %m");
                return (0);
        }
        if (time_pps_getcap(up->pps_h, &mode) < 0) {
                msyslog(LOG_ERR,
                        "mx4200_config: time_pps_getcap failed: %m");
                return (0);
        }

        if (time_pps_getparams(up->pps_h, &up->pps_p) < 0) {
                msyslog(LOG_ERR,
                        "mx4200_config: time_pps_getparams failed: %m");
                return (0);
        }

        /* nb. only turn things on, if someone else has turned something
         *      on before we get here, leave it alone!
         */

        up->pps_p.mode = PPS_CAPTUREASSERT | PPS_TSFMT_TSPEC;
        up->pps_p.mode &= mode;         /* only set what is legal */

        if (time_pps_setparams(up->pps_h, &up->pps_p) < 0) {
                perror("time_pps_setparams");
                msyslog(LOG_ERR,
                        "mx4200_config: time_pps_setparams failed: %m");
                exit(1);
        }

        if (time_pps_kcbind(up->pps_h, PPS_KC_HARDPPS, PPS_CAPTUREASSERT,
                        PPS_TSFMT_TSPEC) < 0) {
                perror("time_pps_kcbind");
                msyslog(LOG_ERR,
                        "mx4200_config: time_pps_kcbind failed: %m");
                exit(1);
        }


        /*
         * "007" Control Port Configuration
         * Zero the output list (do it twice to flush possible junk)
         */
        mx4200_send(peer, "%s,%03d,,%d,,,,,,", pmvxg,
            PMVXG_S_PORTCONF,
            /* control port output block Label */
            1);         /* clear current output control list (1=yes) */
        /* add/delete sentences from list */
        /* must be null */
        /* sentence output rate (sec) */
        /* precision for position output */
        /* nmea version for cga & gll output */
        /* pass-through control */
        mx4200_send(peer, "%s,%03d,,%d,,,,,,", pmvxg,
            PMVXG_S_PORTCONF, 1);

        /*
         * Request software configuration so we can syslog the firmware version
         */
        mx4200_send(peer, "%s,%03d", "CDGPQ", PMVXG_D_SOFTCONF);

        /*
         * "001" Initialization/Mode Control, Part A
         * Where ARE we?
         */
        mx4200_send(peer, "%s,%03d,,,,,,,,,,", pmvxg,
            PMVXG_S_INITMODEA);
        /* day of month */
        /* month of year */
        /* year */
        /* gmt */
        /* latitude   DDMM.MMMM */
        /* north/south */
        /* longitude DDDMM.MMMM */
        /* east/west */
        /* height */
        /* Altitude Reference 1=MSL */

        /*
         * "001" Initialization/Mode Control, Part B
         * Start off in 2d/3d coast mode, holding altitude to last known
         * value if only 3 satellites available.
         */
        mx4200_send(peer, "%s,%03d,%d,,%.1f,%.1f,%d,%d,%d,%c,%d",
            pmvxg, PMVXG_S_INITMODEB,
            3,          /* 2d/3d coast */
            /* reserved */
            0.1,        /* hor accel fact as per Steve (m/s**2) */
            0.1,        /* ver accel fact as per Steve (m/s**2) */
            10,         /* vdop */
            10,         /* hdop limit as per Steve */
            5,          /* elevation limit as per Steve (deg) */
            'U',        /* time output mode (UTC) */
            0);         /* local time offset from gmt (HHHMM) */

        /*
         * "023" Time Recovery Configuration
         * Get UTC time from a stationary receiver.
         * (Set field 1 'D' == dynamic if we are on a moving platform).
         * (Set field 1 'S' == static  if we are not moving).
         * (Set field 1 'K' == known position if we can initialize lat/lon/alt).
         */

        if (pp->sloppyclockflag & CLK_FLAG2)
                up->moving   = 1;       /* Receiver on mobile platform */
        else
                up->moving   = 0;       /* Static Installation */

        up->pollcnt  = 2;
        if (up->moving) {
                /* dynamic: solve for pos, alt, time, while moving */
                tr_mode = 'D';
        } else {
                /* static: solve for pos, alt, time, while stationary */
                tr_mode = 'S';
        }
        mx4200_send(peer, "%s,%03d,%c,%c,%c,%d,%d,%d,", pmvxg,
            PMVXG_S_TRECOVCONF,
            tr_mode,    /* time recovery mode (see above ) */
            'U',        /* synchronize to UTC */
            'A',        /* always output a time pulse */
            500,        /* max time error in ns */
            0,          /* user bias in ns */
            1);         /* output "830" sentences to control port */
                        /* Multi-satellite mode */

        /*
         * Output position information (to calculate fixed installation
         * location) only if we are not moving
         */
        if (up->moving) {
                add_mode = 2;   /* delete from list */
        } else {
                add_mode = 1;   /* add to list */
        }


        /*
         * "007" Control Port Configuration
         * Output "021" position, height, velocity reports
         */
        mx4200_send(peer, "%s,%03d,%03d,%d,%d,,%d,,,", pmvxg,
            PMVXG_S_PORTCONF,
            PMVXG_D_PHV, /* control port output block Label */
            0,          /* clear current output control list (0=no) */
            add_mode,   /* add/delete sentences from list (1=add, 2=del) */
                        /* must be null */
            INTERVAL);  /* sentence output rate (sec) */
                        /* precision for position output */
                        /* nmea version for cga & gll output */
                        /* pass-through control */

        return (1);
}

/*
 * mx4200_ref - Reconfigure unit as a reference station at a known position.
 */
static void
mx4200_ref(
        struct peer *peer
        )
{
        register struct mx4200unit *up;
        struct refclockproc *pp;
        double minute, lat, lon, alt;
        char lats[16], lons[16];
        char nsc, ewc;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        /* Should never happen! */
        if (up->moving) return;

        /*
         * Set up to output status information in the near future
         */
        up->log_time    = current_time + SLEEPTIME;

        /*
         * "007" Control Port Configuration
         * Stop outputting "021" position, height, velocity reports
         */
        mx4200_send(peer, "%s,%03d,%03d,%d,%d,,,,,", pmvxg,
            PMVXG_S_PORTCONF,
            PMVXG_D_PHV, /* control port output block Label */
            0,          /* clear current output control list (0=no) */
            2);         /* add/delete sentences from list (2=delete) */
                        /* must be null */
                        /* sentence output rate (sec) */
                        /* precision for position output */
                        /* nmea version for cga & gll output */
                        /* pass-through control */

        /*
         * "001" Initialization/Mode Control, Part B
         * Put receiver in fully-constrained 2d nav mode
         */
        mx4200_send(peer, "%s,%03d,%d,,%.1f,%.1f,%d,%d,%d,%c,%d",
            pmvxg, PMVXG_S_INITMODEB,
            2,          /* 2d nav */
            /* reserved */
            0.1,        /* hor accel fact as per Steve (m/s**2) */
            0.1,        /* ver accel fact as per Steve (m/s**2) */
            10,         /* vdop */
            10,         /* hdop limit as per Steve */
            5,          /* elevation limit as per Steve (deg) */
            'U',        /* time output mode (UTC) */
            0);         /* local time offset from gmt (HHHMM) */

        /*
         * "023" Time Recovery Configuration
         * Get UTC time from a stationary receiver.  Solve for time only.
         * This should improve the time resolution dramatically.
         */
        mx4200_send(peer, "%s,%03d,%c,%c,%c,%d,%d,%d,", pmvxg,
            PMVXG_S_TRECOVCONF,
            'K',        /* known position: solve for time only */
            'U',        /* synchronize to UTC */
            'A',        /* always output a time pulse */
            500,        /* max time error in ns */
            0,          /* user bias in ns */
            1);         /* output "830" sentences to control port */
        /* Multi-satellite mode */

        /*
         * "000" Initialization/Mode Control - Part A
         * Fix to our averaged position.
         */
        if (up->central_meridian != NOT_INITIALIZED) {
                up->avg_lon += up->central_meridian;
                if (up->avg_lon < -180.0) up->avg_lon += 360.0;
                if (up->avg_lon >  180.0) up->avg_lon -= 360.0;
        }

        if (up->avg_lat >= 0.0) {
                lat = up->avg_lat;
                nsc = 'N';
        } else {
                lat = up->avg_lat * (-1.0);
                nsc = 'S';
        }
        if (up->avg_lon >= 0.0) {
                lon = up->avg_lon;
                ewc = 'E';
        } else {
                lon = up->avg_lon * (-1.0);
                ewc = 'W';
        }
        alt = up->avg_alt;
        minute = (lat - (double)(int)lat) * 60.0;
        sprintf(lats,"%02d%02.4f", (int)lat, minute);
        minute = (lon - (double)(int)lon) * 60.0;
        sprintf(lons,"%03d%02.4f", (int)lon, minute);

        mx4200_send(peer, "%s,%03d,,,,,%s,%c,%s,%c,%.2f,%d", pmvxg,
            PMVXG_S_INITMODEA,
            /* day of month */
            /* month of year */
            /* year */
            /* gmt */
            lats,       /* latitude   DDMM.MMMM */
            nsc,        /* north/south */
            lons,       /* longitude DDDMM.MMMM */
            ewc,        /* east/west */
            alt,        /* Altitude */
            1);         /* Altitude Reference (0=WGS84 ellipsoid, 1=MSL geoid)*/

        msyslog(LOG_DEBUG,
            "mx4200: reconfig to fixed location: %s %c, %s %c, %.2f m",
                lats, nsc, lons, ewc, alt );

}

/*
 * mx4200_poll - mx4200 watchdog routine
 */
static void
mx4200_poll(
        int unit,
        struct peer *peer
        )
{
        register struct mx4200unit *up;
        struct refclockproc *pp;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        /*
         * You don't need to poll this clock.  It puts out timecodes
         * once per second.  If asked for a timestamp, take note.
         * The next time a timecode comes in, it will be fed back.
         */

        /*
         * If we haven't had a response in a while, reset the receiver.
         */
        if (up->pollcnt > 0) {
                up->pollcnt--;
        } else {
                refclock_report(peer, CEVNT_TIMEOUT);

                /*
                 * Request a "000" status message which should trigger a
                 * reconfig
                 */
                mx4200_send(peer, "%s,%03d",
                    "CDGPQ",            /* query from CDU to GPS */
                    PMVXG_D_STATUS);    /* label of desired sentence */
        }

        /*
         * polled every 64 seconds. Ask mx4200_receive to hand in
         * a timestamp.
         */
        up->polled = 1;
        pp->polls++;

        /*
         * Output receiver status information.
         */
        if ((up->log_time > 0) && (current_time > up->log_time)) {
                up->log_time = 0;
                /*
                 * Output the following messages once, for debugging.
                 *    "004" Mode Data
                 *    "523" Time Recovery Parameters
                 */
                mx4200_send(peer, "%s,%03d", "CDGPQ", PMVXG_D_MODEDATA);
                mx4200_send(peer, "%s,%03d", "CDGPQ", PMVXG_D_TRECOVUSEAGE);
        }
}

static char char2hex[] = "0123456789ABCDEF";

/*
 * mx4200_receive - receive gps data
 */
static void
mx4200_receive(
        struct recvbuf *rbufp
        )
{
        register struct mx4200unit *up;
        struct refclockproc *pp;
        struct peer *peer;
        char *cp;
        int sentence_type;
        u_char ck;

        /*
         * Initialize pointers and read the timecode and timestamp.
         */
        peer = (struct peer *)rbufp->recv_srcclock;
        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        /*
         * If operating mode has been changed, then reinitialize the receiver
         * before doing anything else.
         */
        if ((pp->sloppyclockflag & CLK_FLAG2) !=
            (up->sloppyclockflag & CLK_FLAG2)) {
                up->sloppyclockflag = pp->sloppyclockflag;
                mx4200_debug(peer,
                    "mx4200_receive: mode switch: reset receiver\n");
                mx4200_config(peer);
                return;
        }
        up->sloppyclockflag = pp->sloppyclockflag;

        /*
         * Read clock output.  Automatically handles STREAMS, CLKLDISC.
         */
        pp->lencode = refclock_gtlin(rbufp, pp->a_lastcode, BMAX, &pp->lastrec);

        /*
         * There is a case where <cr><lf> generates 2 timestamps.
         */
        if (pp->lencode == 0)
                return;

        up->pollcnt = 2;
        pp->a_lastcode[pp->lencode] = '\0';
        record_clock_stats(&peer->srcadr, pp->a_lastcode);
        mx4200_debug(peer, "mx4200_receive: %d %s\n",
                     pp->lencode, pp->a_lastcode);

        /*
         * The structure of the control port sentences is based on the
         * NMEA-0183 Standard for interfacing Marine Electronics
         * Navigation Devices (Version 1.5)
         *
         *      $PMVXG,XXX, ....................*CK<cr><lf>
         *
         *              $       Sentence Start Identifier (reserved char)
         *                         (Start-of-Sentence Identifier)
         *              P       Special ID (Proprietary)
         *              MVX     Originator ID (Magnavox)
         *              G       Interface ID (GPS)
         *              ,       Field Delimiters (reserved char)
         *              XXX     Sentence Type
         *              ......  Data
         *              *       Checksum Field Delimiter (reserved char)
         *              CK      Checksum
         *              <cr><lf> Carriage-Return/Line Feed (reserved chars)
         *                         (End-of-Sentence Identifier)
         *
         * Reject if any important landmarks are missing.
         */
        cp = pp->a_lastcode + pp->lencode - 3;
        if (cp < pp->a_lastcode || *pp->a_lastcode != '$' || cp[0] != '*' ) {
                mx4200_debug(peer, "mx4200_receive: bad format\n");
                refclock_report(peer, CEVNT_BADREPLY);
                return;
        }

        /*
         * Check and discard the checksum
         */
        ck = mx4200_cksum(&pp->a_lastcode[1], pp->lencode - 4);
        if (char2hex[ck >> 4] != cp[1] || char2hex[ck & 0xf] != cp[2]) {
                mx4200_debug(peer, "mx4200_receive: bad checksum\n");
                refclock_report(peer, CEVNT_BADREPLY);
                return;
        }
        *cp = '\0';

        /*
         * Get the sentence type.
         */
        sentence_type = 0;
        if ((cp = strchr(pp->a_lastcode, ',')) == NULL) {
                mx4200_debug(peer, "mx4200_receive: no sentence\n");
                refclock_report(peer, CEVNT_BADREPLY);
                return;
        }
        cp++;
        sentence_type = strtol(cp, &cp, 10);

        /*
         * Process the sentence according to its type.
         */
        switch (sentence_type) {

        /*
         * "000" Status message
         */
        case PMVXG_D_STATUS:
                /*
                 * XXX
                 * Since we configure the receiver to not give us status
                 * messages and since the receiver outputs status messages by
                 * default after being reset to factory defaults when sent the
                 * "$PMVXG,018,C\r\n" message, any status message we get
                 * indicates the reciever needs to be initialized; thus, it is
                 * not necessary to decode the status message.
                 */
                if ((cp = mx4200_parse_s(peer)) != NULL) {
                        mx4200_debug(peer,
                                     "mx4200_receive: status: %s\n", cp);
                }
                mx4200_debug(peer, "mx4200_receive: reset receiver\n");
                mx4200_config(peer);
                break;

        /*
         * "021" Position, Height, Velocity message,
         *  if we are still averaging our position
         */
        case PMVXG_D_PHV:
                if (!up->known) {
                        /*
                         * Parse the message, calculating our averaged position.
                         */
                        if ((cp = mx4200_parse_p(peer)) != NULL) {
                                mx4200_debug(peer, "mx4200_receive: pos: %s\n", cp);
                                return;
                        }
                        mx4200_debug(peer,
                            "mx4200_receive: position avg %f %.9f %.9f %.4f\n",
                            up->N_fixes, up->avg_lat, up->avg_lon, up->avg_alt);
                        /*
                         * Reinitialize as a reference station
                         * if position is well known.
                         */
                        if (current_time > up->clamp_time) {
                                up->known++;
                                mx4200_debug(peer, "mx4200_receive: reconfiguring!\n");
                                mx4200_ref(peer);
                        }
                }
                break;

        /*
         * Print to the syslog:
         * "004" Mode Data
         * "030" Software Configuration
         * "523" Time Recovery Parameters Currently in Use
         */
        case PMVXG_D_MODEDATA:
        case PMVXG_D_SOFTCONF:
        case PMVXG_D_TRECOVUSEAGE:

                if ((cp = mx4200_parse_s(peer)) != NULL) {
                        mx4200_debug(peer,
                                     "mx4200_receive: multi-record: %s\n", cp);
                }
                break;

        /*
         * "830" Time Recovery Results message
         */
        case PMVXG_D_TRECOVOUT:

                /*
                 * Capture the last PPS signal.
                 * Precision timestamp is returned in pp->lastrec
                 */
                if (mx4200_pps(peer) != NULL) {
                        mx4200_debug(peer, "mx4200_receive: pps failure\n");
                        refclock_report(peer, CEVNT_FAULT);
                        return;
                }


                /*
                 * Parse the time recovery message, and keep the info
                 * to print the pretty billboards.
                 */
                if ((cp = mx4200_parse_t(peer)) != NULL) {
                        mx4200_debug(peer, "mx4200_receive: time: %s\n", cp);
                        refclock_report(peer, CEVNT_BADREPLY);
                        return;
                }

                /*
                 * Add the new sample to a median filter.
                 */
                if (!refclock_process(pp)) {
                        mx4200_debug(peer,"mx4200_receive: offset: %.6f\n",
                            pp->offset);
                        refclock_report(peer, CEVNT_BADTIME);
                        return;
                }

                /*
                 * The clock will blurt a timecode every second but we only
                 * want one when polled.  If we havn't been polled, bail out.
                 */
                if (!up->polled)
                        return;

                /*
                 * Return offset and dispersion to control module.  We use
                 * lastrec as both the reference time and receive time in
                 * order to avoid being cute, like setting the reference time
                 * later than the receive time, which may cause a paranoid
                 * protocol module to chuck out the data.
                 */
                mx4200_debug(peer, "mx4200_receive: process time: ");
                mx4200_debug(peer, "%4d-%03d %02d:%02d:%02d at %s, %.6f\n",
                    pp->year, pp->day, pp->hour, pp->minute, pp->second,
                    prettydate(&pp->lastrec), pp->offset);
                pp->lastref = pp->lastrec;
                refclock_receive(peer);

                /*
                 * We have succeeded in answering the poll.
                 * Turn off the flag and return
                 */
                up->polled = 0;
                break;

        /*
         * Ignore all other sentence types
         */
        default:
                break;

        } /* switch (sentence_type) */

        return;
}


/*
 * Parse a mx4200 time recovery message. Returns a string if error.
 *
 * A typical message looks like this.  Checksum has already been stripped.
 *
 *    $PMVXG,830,T,YYYY,MM,DD,HH:MM:SS,U,S,FFFFFF,PPPPP,BBBBBB,LL
 *
 *      Field   Field Contents
 *      -----   --------------
 *              Block Label: $PMVXG
 *              Sentence Type: 830=Time Recovery Results
 *                      This sentence is output approximately 1 second
 *                      preceding the 1PPS output.  It indicates the
 *                      exact time of the next pulse, whether or not the
 *                      time mark will be valid (based on operator-specified
 *                      error tolerance), the time to which the pulse is
 *                      synchronized, the receiver operating mode,
 *                      and the time error of the *last* 1PPS output.
 *      1  char Time Mark Valid: T=Valid, F=Not Valid
 *      2  int  Year: 1993-
 *      3  int  Month of Year: 1-12
 *      4  int  Day of Month: 1-31
 *      5  int  Time of Day: HH:MM:SS
 *      6  char Time Synchronization: U=UTC, G=GPS
 *      7  char Time Recovery Mode: D=Dynamic, S=Static,
 *                      K=Known Position, N=No Time Recovery
 *      8  int  Oscillator Offset: The filter's estimate of the oscillator
 *                      frequency error, in parts per billion (ppb).
 *      9  int  Time Mark Error: The computed error of the *last* pulse
 *                      output, in nanoseconds.
 *      10 int  User Time Bias: Operator specified bias, in nanoseconds
 *      11 int  Leap Second Flag: Indicates that a leap second will
 *                      occur.  This value is usually zero, except during
 *                      the week prior to the leap second occurrence, when
 *                      this value will be set to +1 or -1.  A value of
 *                      +1 indicates that GPS time will be 1 second
 *                      further ahead of UTC time.
 *
 */
static char *
mx4200_parse_t(
        struct peer *peer
        )
{
        struct refclockproc *pp;
        struct mx4200unit *up;
        char   time_mark_valid, time_sync, op_mode;
        int    sentence_type, valid;
        int    year, day_of_year, month, day_of_month;
        int    hour, minute, second, leapsec;
        int    oscillator_offset, time_mark_error, time_bias;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        leapsec = 0;  /* Not all receivers output leap second warnings (!) */
        sscanf(pp->a_lastcode,
                "$PMVXG,%d,%c,%d,%d,%d,%d:%d:%d,%c,%c,%d,%d,%d,%d",
                &sentence_type, &time_mark_valid, &year, &month, &day_of_month,
                &hour, &minute, &second, &time_sync, &op_mode,
                &oscillator_offset, &time_mark_error, &time_bias, &leapsec);

        if (sentence_type != PMVXG_D_TRECOVOUT)
                return ("wrong rec-type");

        switch (time_mark_valid) {
                case 'T':
                        valid = 1;
                        break;
                case 'F':
                        valid = 0;
                        break;
                default:
                        return ("bad pulse-valid");
        }

        switch (time_sync) {
                case 'G':
                        return ("synchronized to GPS; should be UTC");
                case 'U':
                        break; /* UTC -> ok */
                default:
                        return ("not synchronized to UTC");
        }

        /*
         * Check for insane time (allow for possible leap seconds)
         */
        if (second > 60 || minute > 59 || hour > 23 ||
            second <  0 || minute <  0 || hour <  0) {
                mx4200_debug(peer,
                    "mx4200_parse_t: bad time %02d:%02d:%02d",
                    hour, minute, second);
                if (leapsec != 0)
                        mx4200_debug(peer, " (leap %+d\n)", leapsec);
                mx4200_debug(peer, "\n");
                refclock_report(peer, CEVNT_BADTIME);
                return ("bad time");
        }
        if ( second == 60 ) {
                msyslog(LOG_DEBUG,
                    "mx4200: leap second! %02d:%02d:%02d",
                    hour, minute, second);
        }

        /*
         * Check for insane date
         * (Certainly can't be any year before this code was last altered!)
         */
        if (day_of_month > 31 || month > 12 ||
            day_of_month <  1 || month <  1 || year < YEAR_LAST_MODIFIED) {
                mx4200_debug(peer,
                    "mx4200_parse_t: bad date (%4d-%02d-%02d)\n",
                    year, month, day_of_month);
                refclock_report(peer, CEVNT_BADDATE);
                return ("bad date");
        }

        /*
         * Silly Hack for MX4200:
         * ASCII message is for *next* 1PPS signal, but we have the
         * timestamp for the *last* 1PPS signal.  So we have to subtract
         * a second.  Discard if we are on a month boundary to avoid
         * possible leap seconds and leap days.
         */
        second--;
        if (second < 0) {
                second = 59;
                minute--;
                if (minute < 0) {
                        minute = 59;
                        hour--;
                        if (hour < 0) {
                                hour = 23;
                                day_of_month--;
                                if (day_of_month < 1) {
                                        return ("sorry, month boundary");
                                }
                        }
                }
        }

        /*
         * Calculate Julian date
         */
        if (!(day_of_year = mx4200_jday(year, month, day_of_month))) {
                mx4200_debug(peer,
                    "mx4200_parse_t: bad julian date %d (%4d-%02d-%02d)\n",
                    day_of_year, year, month, day_of_month);
                refclock_report(peer, CEVNT_BADDATE);
                return("invalid julian date");
        }

        /*
         * Setup leap second indicator
         */
        switch (leapsec) {
                case 0:
                        pp->leap = LEAP_NOWARNING;
                        break;
                case 1:
                        pp->leap = LEAP_ADDSECOND;
                        break;
                case -1:
                        pp->leap = LEAP_DELSECOND;
                        break;
                default:
                        pp->leap = LEAP_NOTINSYNC;
        }

        /*
         * Any change to the leap second warning status?
         */
        if (leapsec != up->last_leap ) {
                msyslog(LOG_DEBUG,
                    "mx4200: leap second warning: %d to %d (%d)",
                    up->last_leap, leapsec, pp->leap);
        }
        up->last_leap = leapsec;

        /*
         * Copy time data for billboard monitoring.
         */

        pp->year   = year;
        pp->day    = day_of_year;
        pp->hour   = hour;
        pp->minute = minute;
        pp->second = second;

        /*
         * Toss if sentence is marked invalid
         */
        if (!valid || pp->leap == LEAP_NOTINSYNC) {
                mx4200_debug(peer, "mx4200_parse_t: time mark not valid\n");
                refclock_report(peer, CEVNT_BADTIME);
                return ("pulse invalid");
        }

        return (NULL);
}

/*
 * Calculate the checksum
 */
static u_char
mx4200_cksum(
        register char *cp,
        register int n
        )
{
        register u_char ck;

        for (ck = 0; n-- > 0; cp++)
                ck ^= *cp;
        return (ck);
}

/*
 * Tables to compute the day of year.  Viva la leap.
 */
static int day1tab[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
static int day2tab[] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

/*
 * Calculate the the Julian Day
 */
static int
mx4200_jday(
        int year,
        int month,
        int day_of_month
        )
{
        register int day, i;
        int leap_year;

        /*
         * Is this a leap year ?
         */
        if (year % 4) {
                leap_year = 0; /* FALSE */
        } else {
                if (year % 100) {
                        leap_year = 1; /* TRUE */
                } else {
                        if (year % 400) {
                                leap_year = 0; /* FALSE */
                        } else {
                                leap_year = 1; /* TRUE */
                        }
                }
        }

        /*
         * Calculate the Julian Date
         */
        day = day_of_month;

        if (leap_year) {
                /* a leap year */
                if (day > day2tab[month - 1]) {
                        return (0);
                }
                for (i = 0; i < month - 1; i++)
                    day += day2tab[i];
        } else {
                /* not a leap year */
                if (day > day1tab[month - 1]) {
                        return (0);
                }
                for (i = 0; i < month - 1; i++)
                    day += day1tab[i];
        }
        return (day);
}

/*
 * Parse a mx4200 position/height/velocity sentence.
 *
 * A typical message looks like this.  Checksum has already been stripped.
 *
 * $PMVXG,021,SSSSSS.SS,DDMM.MMMM,N,DDDMM.MMMM,E,HHHHH.H,GGGG.G,EEEE.E,WWWW.W,MM
 *
 *      Field   Field Contents
 *      -----   --------------
 *              Block Label: $PMVXG
 *              Sentence Type: 021=Position, Height Velocity Data
 *                      This sentence gives the receiver position, height,
 *                      navigation mode, and velocity north/east.
 *                      *This sentence is intended for post-analysis
 *                      applications.*
 *      1 float UTC measurement time (seconds into week)
 *      2 float WGS-84 Lattitude (degrees, minutes)
 *      3  char N=North, S=South
 *      4 float WGS-84 Longitude (degrees, minutes)
 *      5  char E=East, W=West
 *      6 float Altitude (meters above mean sea level)
 *      7 float Geoidal height (meters)
 *      8 float East velocity (m/sec)
 *      9 float West Velocity (m/sec)
 *      10  int Navigation Mode
 *                  Mode if navigating:
 *                      1 = Position from remote device
 *                      2 = 2-D position
 *                      3 = 3-D position
 *                      4 = 2-D differential position
 *                      5 = 3-D differential position
 *                      6 = Static
 *                      8 = Position known -- reference station
 *                      9 = Position known -- Navigator
 *                  Mode if not navigating:
 *                      51 = Too few satellites
 *                      52 = DOPs too large
 *                      53 = Position STD too large
 *                      54 = Velocity STD too large
 *                      55 = Too many iterations for velocity
 *                      56 = Too many iterations for position
 *                      57 = 3 sat startup failed
 *                      58 = Command abort
 */
static char *
mx4200_parse_p(
        struct peer *peer
        )
{
        struct refclockproc *pp;
        struct mx4200unit *up;
        int sentence_type, mode;
        double mtime, lat, lon, alt, geoid, vele, veln;
        char   north_south, east_west;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        /* Should never happen! */
        if (up->moving) return ("mobile platform - no pos!");

        sscanf ( pp->a_lastcode,
                "$PMVXG,%d,%lf,%lf,%c,%lf,%c,%lf,%lf,%lf,%lf,%d",
                &sentence_type, &mtime, &lat, &north_south, &lon, &east_west,
                &alt, &geoid, &vele, &veln, &mode);

        /* Sentence type */
        if (sentence_type != PMVXG_D_PHV)
                return ("wrong rec-type");

        /*
         * return if not navigating
         */
        if (mode > 10)
                return ("not navigating");
        if (mode != 3 && mode != 5)
                return ("not navigating in 3D");

        /* Latitude (always +ve) and convert DDMM.MMMM to decimal */
        if (lat <  0.0) return ("negative latitude");
        if (lat > 9000.0) lat = 9000.0;
        lat *= 0.01;
        lat = ((int)lat) + (((lat - (int)lat)) * 1.6666666666666666);

        /* North/South */
        switch (north_south) {
                case 'N':
                        break;
                case 'S':
                        lat *= -1.0;
                        break;
                default:
                        return ("invalid north/south indicator");
        }

        /* Longitude (always +ve) and convert DDDMM.MMMM to decimal */
        if (lon <   0.0) return ("negative longitude");
        if (lon > 180.0) lon = 180.0;
        lon *= 0.01;
        lon = ((int)lon) + (((lon - (int)lon)) * 1.6666666666666666);

        /* East/West */
        switch (east_west) {
                case 'E':
                        break;
                case 'W':
                        lon *= -1.0;
                        break;
                default:
                        return ("invalid east/west indicator");
        }

        /*
         * Normalize longitude to near 0 degrees.
         * Assume all data are clustered around first reading.
         */
        if (up->central_meridian == NOT_INITIALIZED) {
                up->central_meridian = lon;
                mx4200_debug(peer,
                    "mx4200_receive: central meridian =  %.9f \n",
                    up->central_meridian);
        }
        lon -= up->central_meridian;
        if (lon < -180.0) lon += 360.0;
        if (lon >  180.0) lon -= 360.0;

        /*
         * Calculate running averages
         */

        up->avg_lon = (up->N_fixes * up->avg_lon) + lon;
        up->avg_lat = (up->N_fixes * up->avg_lat) + lat;
        up->avg_alt = (up->N_fixes * up->avg_alt) + alt;

        up->N_fixes += 1.0;

        up->avg_lon /= up->N_fixes;
        up->avg_lat /= up->N_fixes;
        up->avg_alt /= up->N_fixes;

        mx4200_debug(peer,
            "mx4200_receive: position rdg %.0f: %.9f %.9f %.4f (CM=%.9f)\n",
            up->N_fixes, lat, lon, alt, up->central_meridian);

        return (NULL);
}

/*
 * Parse a mx4200 Status sentence
 * Parse a mx4200 Mode Data sentence
 * Parse a mx4200 Software Configuration sentence
 * Parse a mx4200 Time Recovery Parameters Currently in Use sentence
 * (used only for logging raw strings)
 *
 * A typical message looks like this.  Checksum has already been stripped.
 *
 * $PMVXG,000,XXX,XX,X,HHMM,X
 *
 *      Field   Field Contents
 *      -----   --------------
 *              Block Label: $PMVXG
 *              Sentence Type: 000=Status.
 *                      Returns status of the receiver to the controller.
 *      1       Current Receiver Status:
 *              ACQ = Satellite re-acquisition
 *              ALT = Constellation selection
 *              COR = Providing corrections (for reference stations only)
 *              IAC = Initial acquisition
 *              IDL = Idle, no satellites
 *              NAV = Navigation
 *              STS = Search the Sky (no almanac available)
 *              TRK = Tracking
 *      2       Number of satellites that should be visible
 *      3       Number of satellites being tracked
 *      4       Time since last navigation status if not currently navigating
 *              (hours, minutes)
 *      5       Initialization status:
 *              0 = Waiting for initialization parameters
 *              1 = Initialization completed
 *
 * A typical message looks like this.  Checksum has already been stripped.
 *
 * $PMVXG,004,C,R,D,H.HH,V.VV,TT,HHHH,VVVV,T
 *
 *      Field   Field Contents
 *      -----   --------------
 *              Block Label: $PMVXG
 *              Sentence Type: 004=Software Configuration.
 *                      Defines the navigation mode and criteria for
 *                      acceptable navigation for the receiver.
 *      1       Constrain Altitude Mode:
 *              0 = Auto.  Constrain altitude (2-D solution) and use
 *                  manual altitude input when 3 sats avalable.  Do
 *                  not constrain altitude (3-D solution) when 4 sats
 *                  available.
 *              1 = Always constrain altitude (2-D solution).
 *              2 = Never constrain altitude (3-D solution).
 *              3 = Coast.  Constrain altitude (2-D solution) and use
 *                  last GPS altitude calculation when 3 sats avalable.
 *                  Do not constrain altitude (3-D solution) when 4 sats
 *                  available.
 *      2       Altitude Reference: (always 0 for MX4200)
 *              0 = Ellipsoid
 *              1 = Geoid (MSL)
 *      3       Differential Navigation Control:
 *              0 = Disabled
 *              1 = Enabled
 *      4       Horizontal Acceleration Constant (m/sec**2)
 *      5       Vertical Acceleration Constant (m/sec**2) (0 for MX4200)
 *      6       Tracking Elevation Limit (degrees)
 *      7       HDOP Limit
 *      8       VDOP Limit
 *      9       Time Output Mode:
 *              U = UTC
 *              L = Local time
 *      10      Local Time Offset (minutes) (absent on MX4200)
 *
 * A typical message looks like this.  Checksum has already been stripped.
 *
 * $PMVXG,030,NNNN,FFF
 *
 *      Field   Field Contents
 *      -----   --------------
 *              Block Label: $PMVXG
 *              Sentence Type: 030=Software Configuration.
 *                      This sentence contains the navigation processor
 *                      and baseband firmware version numbers.
 *      1       Nav Processor Version Number
 *      2       Baseband Firmware Version Number
 *
 * A typical message looks like this.  Checksum has already been stripped.
 *
 * $PMVXG,523,M,S,M,EEEE,BBBBBB,C,R
 *
 *      Field   Field Contents
 *      -----   --------------
 *              Block Label: $PMVXG
 *              Sentence Type: 523=Time Recovery Parameters Currently in Use.
 *                      This sentence contains the configuration of the
 *                      time recovery feature of the receiver.
 *      1       Time Recovery Mode:
 *              D = Dynamic; solve for position and time while moving
 *              S = Static; solve for position and time while stationary
 *              K = Known position input, solve for time only
 *              N = No time recovery
 *      2       Time Synchronization:
 *              U = UTC time
 *              G = GPS time
 *      3       Time Mark Mode:
 *              A = Always output a time pulse
 *              V = Only output time pulse if time is valid (as determined
 *                  by Maximum Time Error)
 *      4       Maximum Time Error - the maximum error (in nanoseconds) for
 *              which a time mark will be considered valid.
 *      5       User Time Bias - external bias in nanoseconds
 *      6       Time Message Control:
 *              0 = Do not output the time recovery message
 *              1 = Output the time recovery message (record 830) to
 *                  Control port
 *              2 = Output the time recovery message (record 830) to
 *                  Equipment port
 *      7       Reserved
 *      8       Position Known PRN (absent on MX 4200)
 *
 */
static char *
mx4200_parse_s(
        struct peer *peer
        )
{
        struct refclockproc *pp;
        struct mx4200unit *up;
        int sentence_type;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        sscanf ( pp->a_lastcode, "$PMVXG,%d", &sentence_type);

        /* Sentence type */
        switch (sentence_type) {

                case PMVXG_D_STATUS:
                        msyslog(LOG_DEBUG,
                          "mx4200: status: %s", pp->a_lastcode);
                        break;
                case PMVXG_D_MODEDATA:
                        msyslog(LOG_DEBUG,
                          "mx4200: mode data: %s", pp->a_lastcode);
                        break;
                case PMVXG_D_SOFTCONF:
                        msyslog(LOG_DEBUG,
                          "mx4200: firmware configuration: %s", pp->a_lastcode);
                        break;
                case PMVXG_D_TRECOVUSEAGE:
                        msyslog(LOG_DEBUG,
                          "mx4200: time recovery parms: %s", pp->a_lastcode);
                        break;
                default:
                        return ("wrong rec-type");
        }

        return (NULL);
}

/*
 * Process a PPS signal, placing a timestamp in pp->lastrec.
 */
static int
mx4200_pps(
        struct peer *peer
        )
{
        int temp_serial;
        struct refclockproc *pp;
        struct mx4200unit *up;

        struct timespec timeout;

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        /*
         * Grab the timestamp of the PPS signal.
         */
        temp_serial = up->pps_i.assert_sequence;
        timeout.tv_sec  = 0;
        timeout.tv_nsec = 0;
        if (time_pps_fetch(up->pps_h, PPS_TSFMT_TSPEC, &(up->pps_i),
                        &timeout) < 0) {
                mx4200_debug(peer,
                  "mx4200_pps: time_pps_fetch: serial=%ul, %s\n",
                     (unsigned long)up->pps_i.assert_sequence, strerror(errno));
                refclock_report(peer, CEVNT_FAULT);
                return(1);
        }
        if (temp_serial == up->pps_i.assert_sequence) {
                mx4200_debug(peer,
                   "mx4200_pps: assert_sequence serial not incrementing: %ul\n",
                        (unsigned long)up->pps_i.assert_sequence);
                refclock_report(peer, CEVNT_FAULT);
                return(1);
        }
        /*
         * Check pps serial number against last one
         */
        if (up->lastserial + 1 != up->pps_i.assert_sequence &&
            up->lastserial != 0) {
                if (up->pps_i.assert_sequence == up->lastserial) {
                        mx4200_debug(peer, "mx4200_pps: no new pps event\n");
                } else {
                        mx4200_debug(peer, "mx4200_pps: missed %ul pps events\n",
                            up->pps_i.assert_sequence - up->lastserial - 1UL);
                }
                refclock_report(peer, CEVNT_FAULT);
        }
        up->lastserial = up->pps_i.assert_sequence;

        /*
         * Return the timestamp in pp->lastrec
         */

        pp->lastrec.l_ui = up->pps_i.assert_timestamp.tv_sec +
                           (u_int32) JAN_1970;
        pp->lastrec.l_uf = ((double)(up->pps_i.assert_timestamp.tv_nsec) *
                           4.2949672960) + 0.5;

        return(0);
}

/*
 * mx4200_debug - print debug messages
 */
#if defined(__STDC__)
static void
mx4200_debug(struct peer *peer, char *fmt, ...)
#else
static void
mx4200_debug(peer, fmt, va_alist)
     struct peer *peer;
     char *fmt;
#endif /* __STDC__ */
{
#ifdef DEBUG
        va_list ap;
        struct refclockproc *pp;
        struct mx4200unit *up;

        if (debug) {

#if defined(__STDC__)
                va_start(ap, fmt);
#else
                va_start(ap);
#endif /* __STDC__ */

                pp = peer->procptr;
                up = (struct mx4200unit *)pp->unitptr;


                /*
                 * Print debug message to stdout
                 * In the future, we may want to get get more creative...
                 */
                vprintf(fmt, ap);

                va_end(ap);
        }
#endif
}

/*
 * Send a character string to the receiver.  Checksum is appended here.
 */
#if defined(__STDC__)
static void
mx4200_send(struct peer *peer, char *fmt, ...)
#else
static void
mx4200_send(peer, fmt, va_alist)
     struct peer *peer;
     char *fmt;
     va_dcl
#endif /* __STDC__ */
{
        struct refclockproc *pp;
        struct mx4200unit *up;

        register char *cp;
        register int n, m;
        va_list ap;
        char buf[1024];
        u_char ck;

#if defined(__STDC__)
        va_start(ap, fmt);
#else
        va_start(ap);
#endif /* __STDC__ */

        pp = peer->procptr;
        up = (struct mx4200unit *)pp->unitptr;

        cp = buf;
        *cp++ = '$';
        n = VSNPRINTF((cp, sizeof(buf) - 1, fmt, ap));
        ck = mx4200_cksum(cp, n);
        cp += n;
        ++n;
        n += SNPRINTF((cp, sizeof(buf) - n - 5, "*%02X\r\n", ck));

        m = write(pp->io.fd, buf, (unsigned)n);
        if (m < 0)
                msyslog(LOG_ERR, "mx4200_send: write: %m (%s)", buf);
        mx4200_debug(peer, "mx4200_send: %d %s\n", m, buf);
        va_end(ap);
}

#else
int refclock_mx4200_bs;
#endif /* REFCLOCK */