source: trunk/third/xntp/xntpd/refclock_mx4200.c @ 10832

/*
 * 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.
 */

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

#if defined(REFCLOCK) && defined(MX4200) && defined(PPS)

#include <stdio.h>
#include <ctype.h>
#include <sys/time.h>
#include <errno.h>

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

#include "mx4200.h"

#if __STDC__
#include <stdarg.h>
#else
#include <varargs.h>
#endif /* __STDC__ */

#ifdef PPS
#include <sys/ppsclock.h>
#endif /* PPS */

/*
 * 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.
 */

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

/*
 * The number of raw samples which we acquire to derive a single estimate.
 * NSAMPLES ideally should not exceed the default poll interval 64.
 * NKEEP must be a power of 2 to simplify the averaging process.
 */
#define NSAMPLES        64
#define NKEEP           8
#define REFCLOCKMAXDISPERSE (FP_SECOND/4) /* max sample dispersion */

/*
 * 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.
 * Reference: Dr. Thomas A. Clark's Totally Accurate Clock (TAC) files at
 * ftp://aleph.gsfc.nasa.gov/GPS/totally.accurate.clock/
 */
#define INTERVAL        1       /* Interval between position measurements (s) */
#define AVGING_TIME     24      /* Number of hours to average */
#define USUAL_EDOP      0.75    /* used for normalizing EDOP */
#define USUAL_NDOP      0.75    /* used for normalizing NDOP */
#define USUAL_VDOP      1.70    /* used for normalizing VDOP */

/*
 * Imported from the ntp_timer module
 */
extern u_long current_time;     /* current time (s) */

/*
 * Imported from ntpd module
 */
extern int debug;               /* global debug flag */

#ifdef PPS
/*
 * Imported from loop_filter module
 */
extern int fdpps;               /* ppsclock file descriptor */
#endif /* PPS */

/*
 * Imported from perror(3)
 */
extern int  sys_nerr;
extern char *sys_errlist[];
extern int  errno;

/*
 * MX4200 unit control structure.
 */
struct mx4200unit {
        u_int  pollcnt;                 /* poll message counter */
        u_int  polled;                  /* Hand in a time sample? */
#ifdef PPS
        u_int  lastserial;              /* last pps serial number */
        struct ppsclockev ppsev;        /* PPS control structure */
#endif /* PPS */
        double avg_lat;                 /* average latitude */
        double avg_lon;                 /* average longitude */
        double avg_alt;                 /* average height */
        double filt_lat;                /* latitude filter length */
        double filt_lon;                /* longitude filter length */
        double filt_alt;                /* height filter length */
        double edop;                    /* EDOP (east DOP) */
        double ndop;                    /* NDOP (north DOP) */
        double vdop;                    /* VDOP (vertical DOP) */
        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 */
        int    coderecv;                /* total received samples */
        int    nkeep;                   /* number of samples to preserve */
        int    rshift;                  /* number of rshifts for division */
        l_fp   filter[NSAMPLES];        /* offset filter */
        l_fp   lastref;                 /* last reference timestamp */
};

static char pmvxg[] = "PMVXG";

/*
 * 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_d  P((struct peer *));
static  char *  mx4200_parse_s  P((struct peer *));
static  char *  mx4200_offset   P((struct peer *));
static  char *  mx4200_process  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  void    mx4200_config   P((struct peer *));
static  void    mx4200_ref      P((struct peer *));
static  void    mx4200_send     P((struct peer *, char *, ...));
static  u_char  mx4200_cksum    P((char *, u_int));
static  int     mx4200_jday     P((int, int, int));
static  void    mx4200_debug    P((struct peer *, char *, ...));
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(unit, peer)
        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,
#ifdef PPS
                                 LDISC_PPS
#else  /* not PPS */
                                 0
#endif /* not PPS */
                                 )))
                return (0);

        /*
         * Allocate unit structure
         */
        if (!(up = (struct mx4200unit *) emalloc(sizeof(struct mx4200unit)))) {
                (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 */
        mx4200_config(peer);
        return (1);
}


/*
 * mx4200_shutdown - shut down the clock
 */
static void
mx4200_shutdown(unit, peer)
        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 void
mx4200_config(peer)
        struct peer *peer;
{
        char tr_mode;
        char add_mode;
        int i;
        register struct mx4200unit *up;
        struct refclockproc *pp;

        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->filt_lat    = 0.0;
        up->filt_lon    = 0.0;
        up->filt_alt    = 0.0;
        up->edop        = USUAL_EDOP;
        up->ndop        = USUAL_NDOP;
        up->vdop        = USUAL_VDOP;
        up->last_leap   = 0;    /* LEAP_NOWARNING */
        up->clamp_time  = current_time + (AVGING_TIME * 60 * 60);
        up->log_time    = current_time + SLEEPTIME;
        up->coderecv    = 0;
        up->nkeep       = NKEEP;
        if (up->nkeep > NSAMPLES) up->nkeep = NSAMPLES;
        if (up->nkeep >=   1) up->rshift = 0;
        if (up->nkeep >=   2) up->rshift = 1;
        if (up->nkeep >=   4) up->rshift = 2;
        if (up->nkeep >=   8) up->rshift = 3;
        if (up->nkeep >=  16) up->rshift = 4;
        if (up->nkeep >=  32) up->rshift = 5;
        if (up->nkeep >=  64) up->rshift = 6;
        up->nkeep =1;
        i = up->rshift;
        while (i > 0) {
                up->nkeep *= 2;
                i--;
        }

        /*
         * "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';
                add_mode = 0;
        } else {
                /* static: solve for pos, alt, time, while stationary */
                tr_mode = 'S';
                add_mode = 1;
        }
        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 = 0;   /* delete from list */
        } else {
                add_mode = 1;   /* add to list */
        }

        /*
         * "007" Control Port Configuration
         * Output "022" DOPs
         */
        mx4200_send(peer, "%s,%03d,%03d,%d,%d,,%d,,,", pmvxg,
            PMVXG_S_PORTCONF,
            PMVXG_D_DOPS, /* control port output block Label */
            0,          /* clear current output control list (0=no) */
            add_mode,   /* add/delete sentences from list (1=add) */
                        /* must be null */
            INTERVAL);  /* sentence output rate (sec) */
                        /* precision for position output */
                        /* nmea version for cga & gll output */
                        /* pass-through control */


        /*
         * "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) */
                        /* must be null */
            INTERVAL);  /* sentence output rate (sec) */
                        /* precision for position output */
                        /* nmea version for cga & gll output */
                        /* pass-through control */
}

/*
 * mx4200_ref - Reconfigure unit as a reference station at a known position.
 */
static void
mx4200_ref(peer)
        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;

        /*
         * "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->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) * 600.0 / 10.0;
        sprintf(lats,"%02d%02.4f", (int)lat, minute);
        minute = (lon - (double)(int)lon) * 600.0 / 10.0;
        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,        /* height */
            1);         /* Altitude Reference 1=MSL */


        /*
         * "007" Control Port Configuration
         * Stop outputting "022" DOPs
         */
        mx4200_send(peer, "%s,%03d,%03d,%d,%d,,,,,", pmvxg,
            PMVXG_S_PORTCONF,
            PMVXG_D_DOPS, /* control port output block Label */
            0,          /* clear current output control list (0=no) */
            0);         /* add/delete sentences from list (0=delete) */
                        /* must be null */
                        /* sentence output rate (sec) */
                        /* precision for position output */
                        /* nmea version for cga & gll output */
                        /* pass-through control */

        /*
         * "007" Control Port Configuration
         * Stop outputting "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) */
            0);         /* add/delete sentences from list (0=delete) */
                        /* must be null */
                        /* sentence output rate (sec) */
                        /* precision for position output */
                        /* nmea version for cga & gll output */
                        /* pass-through control */

        msyslog(LOG_DEBUG,
            "mx4200_ref: reconfig to fixed location: %s %c, %s %c, %.2f m MSL",
            lats, nsc, lons, ewc, alt );

}

/*
 * mx4200_poll - mx4200 watchdog routine
 */
static void
mx4200_poll(unit, peer)
        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(rbufp)
        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", cp);
                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", cp);
                refclock_report(peer, CEVNT_BADREPLY);
                return;
        }
        cp++;
        sentence_type = strtol(cp, &cp, 10);

        /*
         * "000" Status message
         */

        if (sentence_type == 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", cp);
                mx4200_config(peer);
                return;
        }

        /*
         * "021" Position, Height, Velocity message,
         *  if we are still averaging our position
         */
        if (sentence_type == PMVXG_D_PHV && !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 %.9f %.9f %.4f\n",
                        up->avg_lat, up->avg_lon, up->avg_alt);
                mx4200_debug(peer,
                        "mx4200_receive: position len %.4f %.4f %.4f\n",
                        up->filt_lat, up->filt_lon, up->filt_alt);
                mx4200_debug(peer,
                        "mx4200_receive: position dop %.2f %.2f %.2f\n",
                        up->ndop, up->edop, up->vdop);
                /*
                 * 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);
                }
                return;
        }

        /*
         * "022" DOPs, if we are still averaging our position
         */
        if (sentence_type == PMVXG_D_DOPS && !up->known) {
                if ((cp = mx4200_parse_d(peer)) != NULL) {
                        mx4200_debug(peer, "mx4200_receive: dop: %s\n", cp);
                        return;
                }
                return;
        }

        /*
         * Print to the syslog:
         * "004" Mode Data
         * "030" Software Configuration
         * "523" Time Recovery Parameters Currently in Use
         */
        if (sentence_type == PMVXG_D_MODEDATA ||
            sentence_type == PMVXG_D_SOFTCONF ||
            sentence_type == PMVXG_D_TRECOVUSEAGE ) {
                if ((cp = mx4200_parse_s(peer)) != NULL) {
                        mx4200_debug(peer,
                                "mx4200_receive: multi-record: %s\n", cp);
                        return;
                }
                return;
        }

        /*
         * "830" Time Recovery Results message
         */
        if (sentence_type == 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 ((cp =mx4200_offset(peer)) != NULL) {
                        mx4200_debug(peer,"mx4200_receive: offset: %s\n", cp);
                        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;

                /*
                 * It's a live one!  Remember this time.
                 */
                pp->lasttime   = current_time;

                /*
                 * Determine the reference clock offset and dispersion.
                 * NKEEP of NSAMPLE offsets are passed through a median filter.
                 * Save the (filtered) offset and dispersion in
                 * pp->offset and pp->dispersion.
                 */
                if ((cp =mx4200_process(peer)) != NULL) {
                        mx4200_debug(peer,"mx4200_receive: process: %s\n", cp);
                        refclock_report(peer, CEVNT_BADTIME);
                        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, %s\n",
                        pp->year, pp->day, pp->hour, pp->minute, pp->second,
                        prettydate(&pp->lastrec), lfptoa(&pp->offset, 6));

                refclock_receive(peer, &pp->offset, 0, pp->dispersion,
                        &pp->lastrec, &pp->lastrec, pp->leap);

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

        /*
         * Ignore all other sentence types
         */
        return;
}

/*
 * mx4200_offset - Calculate the offset, and add to the rolling filter.
 */
static char *
mx4200_offset(peer)
        struct peer *peer;
{
        register struct mx4200unit *up;
        struct refclockproc *pp;
        register int i;
        l_fp offset;

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

        /*
         * Calculate the offset
         */
        if (!clocktime(pp->day, pp->hour, pp->minute, pp->second, GMT,
                pp->lastrec.l_ui, &pp->yearstart, &offset.l_ui)) {
                return ("mx4200_process: clocktime failed");
        }
        if (pp->usec) {
                TVUTOTSF(pp->usec, offset.l_uf);
        } else {
                MSUTOTSF(pp->msec, offset.l_uf);
        }
        L_ADD(&offset, &pp->fudgetime1);
        up->lastref = offset;   /* save last reference time */
        L_SUB(&offset, &pp->lastrec); /* form true offset */

        /*
         * A rolling filter.  Initialize first time around.
         */
        i = ((up->coderecv)) % NSAMPLES;

        up->filter[i] = offset;
        if (up->coderecv == 0)
                for (i = 1; (u_int) i < NSAMPLES; i++)
                        up->filter[i] = up->filter[0];
        up->coderecv++;

        return (NULL);
}

/*
 * mx4200_process - process the sample from the clock,
 * passing it through a median filter and optionally averaging
 * the samples.  Returns offset and dispersion in "up" structure.
 */
static char *
mx4200_process(peer)
        struct peer *peer;
{
        register struct mx4200unit *up;
        struct refclockproc *pp;
        register int i, n;
        int j, k;
        l_fp offset, median, lftmp;
        u_fp disp;
        l_fp off[NSAMPLES];

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

        /*
         * Copy the raw offsets and sort into ascending order
         */
        for (i = 0; i < NSAMPLES; i++)
                off[i] = up->filter[i];
        qsort((char *)off, NSAMPLES, sizeof(l_fp), mx4200_cmpl_fp);

        /*
         * Reject the furthest from the median of NSAMPLES samples until
         * NKEEP samples remain.
         */
        i = 0;
        n = NSAMPLES;
        while ((n - i) > up->nkeep) {
                lftmp = off[n - 1];
                median = off[(n + i) / 2];
                L_SUB(&lftmp, &median);
                L_SUB(&median, &off[i]);
                if (L_ISHIS(&median, &lftmp)) {
                        /* reject low end */
                        i++;
                } else {
                        /* reject high end */
                        n--;
                }
        }

        /*
         * Copy key values to the billboard to measure performance.
         */
        pp->lastref = up->lastref;
        pp->coderecv = up->coderecv;
        pp->nstages = up->nkeep + 2;
        pp->filter[0] = off[0];                 /* smallest offset */
        pp->filter[1] = off[NSAMPLES-1];        /* largest offset */
        for (j=2, k=i; k < n; j++, k++)
                pp->filter[j] = off[k];         /* offsets actually examined */

        /*
         * Compute the dispersion based on the difference between the
         * extremes of the remaining offsets. Add to this the time since
         * the last clock update, which represents the dispersion
         * increase with time. We know that NTP_MAXSKEW is 16. If the
         * sum is greater than the allowed sample dispersion, bail out.
         * If the loop is unlocked, return the most recent offset;
         * otherwise, return the median offset.
         */
        lftmp = off[n - 1];
        L_SUB(&lftmp, &off[i]);
        disp = LFPTOFP(&lftmp);
        if (disp > REFCLOCKMAXDISPERSE) {
                return("Maximum dispersion exceeded");
        }

        /*
         * Now compute the offset estimate.  If fudge flag 1
         * is set, average the remainder, otherwise pick the
         * median.
         */
        if (pp->sloppyclockflag & CLK_FLAG1) {
                L_CLR(&lftmp);
                while (i < n) {
                        L_ADD(&lftmp, &off[i]);
                        i++;
                }
                i = up->rshift;
                while (i > 0) {
                        L_RSHIFT(&lftmp);
                        i--;
                }
                offset = lftmp;
        } else {
                i = (n + i) / 2;
                offset = off[i];
        }

        /*
         * The payload: filtered offset and dispersion.
         */

        pp->offset = offset;
        pp->dispersion = disp;

        return(NULL);

}

/* Compare two l_fp's, used with qsort() */
int
#ifdef QSORT_USES_VOID_P
mx4200_cmpl_fp(p1, p2)
        const void *p1, *p2;
{
        register const l_fp *fp1 = (const l_fp *)p1;
        register const l_fp *fp2 = (const l_fp *)p2;
#else
mx4200_cmpl_fp(fp1, fp2)
        register const l_fp *fp1;
        register const l_fp *fp2;
{
#endif /* not QSORT_USES_VOID_P */

        if (!L_ISGEQ(fp1, fp2))
                return (-1);
        if (L_ISEQU(fp1, fp2))
                return (0);
        return (1);
}


/*
 * 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       Time Mark Valid: T=Valid, F=Not Valid
 *      2       Year: 1993-
 *      3       Month of Year: 1-12
 *      4       Day of Month: 1-31
 *      5       Time of Day: HH:MM:SS
 *      6       Time Synchronization: U=UTC, G=GPS
 *      7       Time Recovery Mode: D=Dynamic, S=Static,
 *                      K=Known Position, N=No Time Recovery
 *      8       Oscillator Offset: The filter's estimate of the oscillator
 *                      frequency error, in parts per billion (ppb).
 *      9       Time Mark Error: The computed error of the *last* pulse
 *                      output, in nanoseconds.
 *      10      User Time Bias: Operator specified bias, in nanoseconds
 *      11      Leap Second Flag: Indicates that a leap second will
 *                      occur.  This value is usually zero, except during
 *                      the week prior to the leap second occurence, 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(peer)
        struct peer *peer;
{
        struct refclockproc *pp;
        struct mx4200unit *up;
        int sentence_type, valid;
        int year, yearday, month, monthday, hour, minute, second, leapsec;
        char *cp;

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

        cp = pp->a_lastcode;

        if ((cp = strchr(cp, ',')) == NULL)
                return ("no rec-type");
        cp++;

        /* Sentence type */
        sentence_type = strtol(cp, &cp, 10);
        if (sentence_type != PMVXG_D_TRECOVOUT)
                return ("wrong rec-type");

        /* Pulse valid indicator */
        if (*cp++ != ',')
                return ("no pulse-valid");
        if (*cp == 'T')
                valid = 1;
        else if (*cp == 'F')
                valid = 0;
        else
                return ("bad pulse-valid");
        cp++;

        /* Year */
        if (*cp++ != ',')
                return ("no year");
        year = strtol(cp, &cp, 10);

        /* Month of year */
        if (*cp++ != ',')
                return ("no month");
        month = strtol(cp, &cp, 10);

        /* Day of month */
        if (*cp++ != ',')
                return ("no month day");
        monthday = strtol(cp, &cp, 10);

        /* Hour */
        if (*cp++ != ',')
                return ("no hour");
        hour = strtol(cp, &cp, 10);

        /* Minute */
        if (*cp++ != ':')
                return ("no minute");
        minute = strtol(cp, &cp, 10);

        /* Second */
        if (*cp++ != ':')
                return ("no second");
        second = strtol(cp, &cp, 10);

        /* Time indicator */
        if (*cp++ != ',')
                return ("no time indicator");
        if (*cp == 'G')
                return ("synchronized to GPS; should be UTC");
        else if (*cp != 'U')
                return ("not synchronized to UTC");
        cp++;

        /* Time recovery mode */
        if (*cp++ != ',' || *cp++ == '\0')
                return ("no time mode");

        /* Oscillator offset */
        if ((cp = strchr(cp, ',')) == NULL)
                return ("no osc off");
        cp++;

        /* Time mark error */
        /* (by request, always less than 0.5 usec (500 nsec), so ignore) */
        if ((cp = strchr(cp, ',')) == NULL)
                return ("no time mark err");
        cp++;

        /* User time bias */
        /* (by request, always zero, so ignore */
        if ((cp = strchr(cp, ',')) == NULL)
                return ("no user bias");
        cp++;

        /* Leap second flag */
        if ((cp = strchr(cp, ',')) == NULL)
                return ("no leap");
        cp++;
        leapsec = strtol(cp, &cp, 10);


        /*
         * 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_parse_t: leap second! %02d:%02d:%02d",
                         hour, minute, second);
        }

        /*
         * Check for insane date
         * (Certainly can't be a year before this code was last altered!)
         */
        if (monthday > 31 || month > 12 ||
            monthday <  1 || month <  1 || year < 1997) {
                mx4200_debug(peer,
                        "mx4200_parse_t: bad date (%4d-%02d-%02d)\n",
                        year, month, monthday);
                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;
                                monthday--;
                                if (monthday < 1) {
                                        return ("sorry, month boundary");
                                }
                        }
                }
        }

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

        /*
         * Setup leap second indicator
         */
        if (leapsec == 0)
                pp->leap = LEAP_NOWARNING;
        else if (leapsec == 1)
                pp->leap = LEAP_ADDSECOND;
        else if (leapsec == -1)
                pp->leap = LEAP_DELSECOND;
        else
                pp->leap = LEAP_NOTINSYNC;      /* shouldn't happen */

        /*
         * Any change to the leap second warning status?
         */
        if (leapsec != up->last_leap ) {
                msyslog(LOG_DEBUG,
                        "mx4200_parse_t: 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    = yearday;
        pp->hour   = hour;
        pp->minute = minute;
        pp->second = second;
        pp->msec   = 0;
        pp->usec   = 0;

        /*
         * 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(cp, n)
        register char *cp;
        register u_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 day1tab[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
static day2tab[] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

/*
 * Calculate the the Julian Day
 */
static int
mx4200_jday(year, month, monthday)
        int year;
        int month;
        int monthday;
{
        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 = monthday;

        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       UTC measurement time (seconds into week)
 *      2       WGS-84 Lattitude (degrees, minutes)
 *      3       N=North, S=South
 *      4       WGS-84 Longitude (degrees, minutes)
 *      5       E=East, W=West
 *      6       Altitude (meters above mean sea level)
 *      7       Geoidal height (meters)
 *      8       East velocity (m/sec)
 *      9       West Velocity (m/sec)
 *      10      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(peer)
        struct peer *peer;
{
        struct refclockproc *pp;
        struct mx4200unit *up;
        int sentence_type, mode;
        double dtemp, dtemp2, mtime, lat, lon, alt, geoid, vele, veln, weight;
        char *cp;

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

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

        cp = pp->a_lastcode;

        if ((cp = strchr(cp, ',')) == NULL)
                return ("no rec-type");
        cp++;

        /* Sentence type */
        sentence_type = strtol(cp, &cp, 10);
        if (sentence_type != PMVXG_D_PHV)
                return ("wrong rec-type");

        /* Measurement Time */
        if (*cp++ != ',')
                return ("no measurement time");
        mtime = strtod(cp,&cp);

        /* Latitude (always +ve) */
        if (*cp++ != ',')
                return ("no latitude");
        dtemp = atof(cp);
        dtemp2 = strtod(cp,&cp);
        if (dtemp < 0.0)
                return ("negative latitude");
        lat = (double) ( (int)dtemp / 100);
        lat += (dtemp - (lat*100.0)) * 10.0 / 600.0;

        /* North/South */
        if (*cp++ != ',')
                return ("no north/south indicator");
        if (*cp == 'N')
                lat = lat;
        else if (*cp == 'S')
                lat *= -1.0;
        else
                return ("invalid north/south indicator");
        cp++;

        /* Longitude (always +ve) */
        if (*cp++ != ',')
                return ("no longitude");
        dtemp = atof(cp);
        dtemp2 = strtod(cp,&cp);
        if (dtemp < 0.0)
                return ("negative latitude");
        lon = (double) ( (int)dtemp / 100);
        lon += (dtemp - (lon*100.0)) * 10.0 / 600.0;

        /* East/West */
        if (*cp++ != ',')
                return ("no east/west indicator");
        if (*cp == 'E')
                lon = lon;
        else if (*cp == 'W')
                lon *= -1.0;
        else
                return ("invalid east/west indicator");
        cp++;

        /* Altitude */
        if (*cp++ != ',')
                return ("no altitude");
        alt = atof(cp);
        dtemp2 = strtod(cp,&cp);

        /* geoid height */
        if (*cp++ != ',')
                return ("no geoid height");
        geoid = strtod(cp,&cp);

        /* East velocity */
        if (*cp++ != ',')
                return ("no east velocity");
        vele = strtod(cp,&cp);

        /* north velocity */
        if (*cp++ != ',')
                return ("no north velocity");
        veln = strtod(cp,&cp);

        /* nav mode */
        if (*cp++ != ',')
                return ("no nav mode");
        mode = strtol(cp, &cp, 10);


        /*
         * return if not navigating
         */
        if (mode > 10)
                return ("not navigating");

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

        /*
         * Calculate running weighted averages
         */

        weight = (USUAL_EDOP/up->edop);
        weight = weight * weight;
        up->avg_lon = up->filt_lon * up->avg_lon + weight * lon;
        up->filt_lon += weight;
        up->avg_lon = up->avg_lon / up->filt_lon;

        weight = (USUAL_NDOP/up->ndop);
        weight = weight * weight;
        up->avg_lat = up->filt_lat * up->avg_lat + weight * lat;
        up->filt_lat += weight;
        up->avg_lat = up->avg_lat / up->filt_lat;

        weight = (USUAL_VDOP/up->vdop);
        weight = weight * weight;
        up->avg_alt = up->filt_alt * up->avg_alt + weight * alt;
        up->filt_alt += weight;
        up->avg_alt = up->avg_alt / up->filt_alt;

        return (NULL);
}

/*
 * Parse a mx4200 DOP sentence.
 *
 * A typical message looks like this.  Checksum has already been stripped.
 *
 * $PMVXG,022,SSSSSS.SSEE.E,NN.N,VV.V,XX,XX,XX,XX,XX,XX
 *
 *      Field   Field Contents
 *      -----   --------------
 *              Block Label: $PMVXG
 *              Sentence Type: 022=DOPs.  The DOP values in this sentence
 *                      correspond to the satellites listed.  The PRNs in
 *                      the message are listed in receiver channel number order
 *      1       UTC measurement time (seconds into week)
 *      2       EDOP (east DOP)
 *      3       NDOP (north DOP)
 *      4       VDOP (vertical DOP)
 *      5       PRN on channel 1
 *      6       PRN on channel 2
 *      7       PRN on channel 3
 *      8       PRN on channel 4
 *      9       PRN on channel 5
 *      10      PRN on channel 6
 */
static char *
mx4200_parse_d(peer)
        struct peer *peer;
{
        struct refclockproc *pp;
        struct mx4200unit *up;
        int sentence_type;
        double mtime, dtemp2, edop, ndop, vdop;
        char *cp;

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

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

        cp = pp->a_lastcode;

        if ((cp = strchr(cp, ',')) == NULL)
                return ("no rec-type");
        cp++;

        /* Sentence type */
        sentence_type = strtol(cp, &cp, 10);
        if (sentence_type != PMVXG_D_DOPS)
                return ("wrong rec-type");

        /* Measurement Time */
        if (*cp++ != ',')
                return ("no measurement time");
        mtime = strtod(cp,&cp);

        /* EDOP */
        if (*cp++ != ',')
                return ("no edop");
        edop = atof(cp);
        dtemp2 = strtod(cp,&cp);

        /* NDOP */
        if (*cp++ != ',')
                return ("no ndop");
        ndop = atof(cp);
        dtemp2 = strtod(cp,&cp);

        /* VDOP */
        if (*cp++ != ',')
                return ("no vdop");
        vdop = atof(cp);
        dtemp2 = strtod(cp,&cp);

        /* Ignore the PRNs... */


        /* Update values */
        if (ndop <= 0.0 || ndop<= 0.0 || vdop <= 0.0)
                return ("nonpositive dop");
        up->edop = edop;
        up->ndop = ndop;
        up->vdop = vdop;

        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(peer)
        struct peer *peer;
{
        struct refclockproc *pp;
        struct mx4200unit *up;
        int sentence_type;
        char *cp;

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

        cp = pp->a_lastcode;

        if ((cp = strchr(cp, ',')) == NULL)
                return ("no rec-type");
        cp++;

        /* Sentence type */
        sentence_type = strtol(cp, &cp, 10);
        if (sentence_type != PMVXG_D_STATUS &&
            sentence_type != PMVXG_D_MODEDATA &&
            sentence_type != PMVXG_D_SOFTCONF &&
            sentence_type != PMVXG_D_TRECOVUSEAGE )
                return ("wrong rec-type");
        cp++;

        /* Log the Status */
        if (sentence_type == PMVXG_D_STATUS) {
                msyslog(LOG_DEBUG,
                "mx4200_parse_s: status: %s", cp);
        }

        /* Log the Mode Data */
        if (sentence_type == PMVXG_D_MODEDATA) {
                msyslog(LOG_DEBUG,
                "mx4200_parse_s: mode data: %s", cp);
        }

        /* Log the Software Version */
        if (sentence_type == PMVXG_D_SOFTCONF) {
                msyslog(LOG_DEBUG,
                "mx4200_parse_s: firmware configuration: %s", cp);
        }

        /* Log the Time Recovery Parameters */
        if (sentence_type == PMVXG_D_TRECOVUSEAGE) {
                msyslog(LOG_DEBUG,
                "mx4200_parse_s: time recovery parms: %s", cp);
        }

        return (NULL);
}

/*
 * Process a PPS signal, returning a timestamp.
 */
static int
mx4200_pps(peer)
        struct peer *peer;
{
#ifdef PPS
        struct refclockproc *pp;
        struct mx4200unit *up;

        int temp_serial;

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


        /*
         * Grab the timestamp of the PPS signal.
         */
        temp_serial = up->ppsev.serial;
        if (ioctl(fdpps, CIOGETEV, (caddr_t)&up->ppsev) < 0) {
                /* XXX Actually, if this fails, we're pretty much screwed */
                mx4200_debug(peer, "mx4200_pps: CIOGETEV: ");
                if (errno < sys_nerr)
                        mx4200_debug(peer, "%s", sys_errlist[errno]);
                mx4200_debug(peer, "\n");
                refclock_report(peer, CEVNT_FAULT);
                return(1);
        }
        if (temp_serial == up->ppsev.serial) {
                mx4200_debug(peer,
                        "mx4200_pps: ppsev serial not incrementing: %d\n",
                                up->ppsev.serial);
                refclock_report(peer, CEVNT_FAULT);
                return(1);
        }

        /*
         * Check pps serial number against last one
         */
        if (up->lastserial + 1 != up->ppsev.serial && up->lastserial != 0) {
                if (up->ppsev.serial == up->lastserial)
                        mx4200_debug(peer, "mx4200_pps: no new pps event\n");
                else
                        mx4200_debug(peer, "mx4200_pps: missed %d pps events\n",
                                up->ppsev.serial - up->lastserial - 1);
                refclock_report(peer, CEVNT_FAULT);
        }
        up->lastserial = up->ppsev.serial;

        /*
         * Return the timestamp in pp->lastrec
         */
        up->ppsev.tv.tv_sec += (u_int32) JAN_1970;
        TVTOTS(&up->ppsev.tv,&pp->lastrec);

#endif /* PPS */

        return(0);
}

/*
 * mx4200_debug - print debug messages
 */
#if __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
{
        va_list ap;
        struct refclockproc *pp;
        struct mx4200unit *up;

        if (debug) {

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

                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);
        }
}

/*
 * Send a character string to the receiver.  Checksum is appended here.
 */
static void
#if __STDC__
mx4200_send(struct peer *peer, char *fmt, ...)
#else
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 __STDC__
        va_start(ap, fmt);
#else
        va_start(ap);
#endif /* __STDC__ */

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

        cp = buf;
        *cp++ = '$';
#ifdef notdef
        /* BSD is rational */
        n = vsnprintf(cp, sizeof(buf) - 1, fmt, ap);
#else
        /* SunOS sucks */
        (void)vsprintf(cp, fmt, ap);
        n = strlen(cp);
#endif /* notdef */
        ck = mx4200_cksum(cp, n);
        cp += n;
        ++n;
#ifdef notdef
        /* BSD is rational */
        n += snprintf(cp, sizeof(buf) - n - 5, "*%02X\r\n", ck);
#else
        /* SunOS sucks */
        sprintf(cp, "*%02X\r\n", ck);
        n += strlen(cp);
#endif /* notdef */

        m = write(pp->io.fd, buf, 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 /* not (REFCLOCK && MX4200 && PPS) */
int refclock_mx4200_bs;
#endif /* not (REFCLOCK && MX4200 && PPS) */