refclock_nmea.c   [plain text]

/*
 * refclock_nmea.c - clock driver for an NMEA GPS CLOCK
 *		Michael Petry Jun 20, 1994
 *		 based on refclock_heathn.c
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#if defined(REFCLOCK) && defined(CLOCK_NMEA)

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

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

/*
 * This driver supports the NMEA GPS Receiver with
 *
 * Protype was refclock_trak.c, Thanks a lot.
 *
 * The receiver used spits out the NMEA sentences for boat navigation.
 * And you thought it was an information superhighway.  Try a raging river
 * filled with rapids and whirlpools that rip away your data and warp time.
 */

/*
 * Definitions
 */
#define	DEVICE		"/dev/gps%d"	/* name of radio device */
#define	SPEED232	B4800	/* uart speed (4800 bps) */
#define	PRECISION	(-9)	/* precision assumed (about 2 ms) */
#define	DCD_PRECISION	(-20)	/* precision assumed (about 1 us) */
#define	REFID		"GPS\0"	/* reference id */
#define	DESCRIPTION	"NMEA GPS Clock" /* who we are */

#define LENNMEA		75	/* min timecode length */

/*
 * Tables to compute the ddd of year form icky dd/mm timecode. 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};

/*
 * Unit control structure
 */
struct nmeaunit {
	int	pollcnt;	/* poll message counter */
	int	polled;		/* Hand in a sample? */
	l_fp	tstamp;		/* timestamp of last poll */
};

/*
 * Function prototypes
 */
static	int	nmea_start	P((int, struct peer *));
static	void	nmea_shutdown	P((int, struct peer *));
static	void	nmea_receive	P((struct recvbuf *));
static	void	nmea_poll	P((int, struct peer *));
static	void	gps_send	P((int, const char *, struct peer *));
static	char	*field_parse	P((char *, int));

/*
 * Transfer vector
 */
struct	refclock refclock_nmea = {
	nmea_start,		/* start up driver */
	nmea_shutdown,	/* shut down driver */
	nmea_poll,		/* transmit poll message */
	noentry,		/* handle control */
	noentry,		/* initialize driver */
	noentry,		/* buginfo */
	NOFLAGS			/* not used */
};

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

	/*
	 * Open serial port. Use CLK line discipline, if available.
	 */
	(void)sprintf(device, DEVICE, unit);
	if (!(fd = refclock_open(device, SPEED232, LDISC_CLK)))
	    return (0);

	/*
	 * Allocate and initialize unit structure
	 */
	if (!(up = (struct nmeaunit *)
	      emalloc(sizeof(struct nmeaunit)))) {
		(void) close(fd);
		return (0);
	}
	memset((char *)up, 0, sizeof(struct nmeaunit));
	pp = peer->procptr;
	pp->io.clock_recv = nmea_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 = DCD_PRECISION;
	pp->clockdesc = DESCRIPTION;
	memcpy((char *)&pp->refid, REFID, 4);
	up->pollcnt = 2;
	gps_send(pp->io.fd,"$PMOTG,RMC,0000*1D\r\n", peer);

	return (1);
}

/*
 * nmea_shutdown - shut down a GPS clock
 */
static void
nmea_shutdown(
	int unit,
	struct peer *peer
	)
{
	register struct nmeaunit *up;
	struct refclockproc *pp;

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

/*
 * nmea_receive - receive data from the serial interface
 */
static void
nmea_receive(
	struct recvbuf *rbufp
	)
{
	register struct nmeaunit *up;
	struct refclockproc *pp;
	struct peer *peer;
	l_fp trtmp;
	int month, day;
	int i;
	char *cp, *dp;
	int cmdtype;

	/*
	 * Initialize pointers and read the timecode and timestamp
	 */
	peer = (struct peer *)rbufp->recv_srcclock;
	pp = peer->procptr;
	up = (struct nmeaunit *)pp->unitptr;
	pp->lencode = refclock_gtlin(rbufp, pp->a_lastcode, BMAX, &trtmp);

	/*
	 * There is a case that a <CR><LF> gives back a "blank" line
	 */
	if (pp->lencode == 0)
	    return;

	/*
	 * We get a buffer and timestamp for each <cr>.
	 */
	pp->lastrec = up->tstamp = trtmp;
	up->pollcnt = 2;
#ifdef DEBUG
	if (debug)
	    printf("nmea: timecode %d %s\n", pp->lencode,
		   pp->a_lastcode);
#endif

	/*
	 * We check the timecode format and decode its contents. The
	 * we only care about a few of them.  The most important being
	 * the $GPRMC format
	 * $GPRMC,hhmmss,a,fddmm.xx,n,dddmmm.xx,w,zz.z,yyy.,ddmmyy,dd,v*CC
	 */
#define GPRMC	0
#define GPXXX	1
	cp = pp->a_lastcode;
	cmdtype=0;
	if(strncmp(cp,"$GPRMC",6)==0) {
		cmdtype=GPRMC;
	}
	else if(strncmp(cp,"$GPXXX",6)==0) {
		cmdtype=GPXXX;
	}
	else
	    return;

	switch( cmdtype ) {
	    case GPRMC:
		/*
		 *	Check time code format of NMEA
		 */

		dp = field_parse(cp,1);
		if( !isdigit((int)dp[0]) ||
		    !isdigit((int)dp[1]) ||
		    !isdigit((int)dp[2]) ||
		    !isdigit((int)dp[3]) ||
		    !isdigit((int)dp[4]) ||
		    !isdigit((int)dp[5])	
		    ) {
			refclock_report(peer, CEVNT_BADREPLY);
			return;
		}

		/*
		 * Test for synchronization.  Check for quality byte.
		 */
		dp = field_parse(cp,2);
		if( dp[0] != 'A')  {
			refclock_report(peer, CEVNT_BADREPLY);
			return;
		}
		break;
	    case GPXXX:
		return;
	    default:
		return;

	}

	dp = field_parse(cp,9);
	/*
	 * Convert date and check values.
	 */
	day = dp[0] - '0';
	day = (day * 10) + dp[1] - '0';
	month = dp[2] - '0';
	month = (month * 10) + dp[3] - '0';
	pp->year = dp[4] - '0';
	pp->year = (pp->year * 10) + dp[5] - '0';

	if (month < 1 || month > 12 || day < 1) {
		refclock_report(peer, CEVNT_BADTIME);
		return;
	}

	if (pp->year % 4) {
		if (day > day1tab[month - 1]) {
			refclock_report(peer, CEVNT_BADTIME);
			return;
		}
		for (i = 0; i < month - 1; i++)
		    day += day1tab[i];
	} else {
		if (day > day2tab[month - 1]) {
			refclock_report(peer, CEVNT_BADTIME);
			return;
		}
		for (i = 0; i < month - 1; i++)
		    day += day2tab[i];
	}
	pp->day = day;

	dp = field_parse(cp,1);
	/*
	 * Convert time and check values.
	 */
	pp->hour = ((dp[0] - '0') * 10) + dp[1] - '0';
	pp->minute = ((dp[2] - '0') * 10) + dp[3] -  '0';
	pp->second = ((dp[4] - '0') * 10) + dp[5] - '0';
	pp->msec = 0; 

	if (pp->hour > 23 || pp->minute > 59 || pp->second > 59) {
		refclock_report(peer, CEVNT_BADTIME);
		return;
	}

	/*
	 * Process the new sample in the median filter and determine the
	 * reference clock offset and dispersion. 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.
	 */
	if (!refclock_process(pp)) {
		refclock_report(peer, CEVNT_BADTIME);
		return;
	}

	/*
	 * Only go on if we had been polled.
	 */
	if (!up->polled)
	    return;
	up->polled = 0;

	refclock_receive(peer);

	record_clock_stats(&peer->srcadr, pp->a_lastcode);
}

/*
 * nmea_poll - called by the transmit procedure
 *
 * We go to great pains to avoid changing state here, since there may be
 * more than one eavesdropper receiving the same timecode.
 */
static void
nmea_poll(
	int unit,
	struct peer *peer
	)
{
	register struct nmeaunit *up;
	struct refclockproc *pp;

	pp = peer->procptr;
	up = (struct nmeaunit *)pp->unitptr;
	if (up->pollcnt == 0)
	    refclock_report(peer, CEVNT_TIMEOUT);
	else
	    up->pollcnt--;
	pp->polls++;
	up->polled = 1;

	/*
	 * usually nmea_receive can get a timestamp every second
	 */

	gps_send(pp->io.fd,"$PMOTG,RMC,0000*1D\r\n", peer);
}

/*
 *
 *	gps_send(fd,cmd, peer)  Sends a command to the GPS receiver.
 *	 as	gps_send(fd,"rqts,u\r", peer);
 *
 *	We don't currently send any data, but would like to send
 *	RTCM SC104 messages for differential positioning. It should
 *	also give us better time. Without a PPS output, we're
 *	Just fooling ourselves because of the serial code paths
 *
 */
static void
gps_send(
	int fd,
	const char *cmd,
	struct peer *peer
	)
{

	if (write(fd, cmd, strlen(cmd)) == -1) {
		refclock_report(peer, CEVNT_FAULT);
	}
}

static char *
field_parse(
	char *cp,
	int fn
	)
{
	char *tp;
	int i = fn;

	for (tp = cp; *tp != '\0'; tp++) {
		if (*tp == ',')
		    i--;
		if (i == 0)
		    break;
	}
	return (++tp);
}
#else
int refclock_nmea_bs;
#endif /* REFCLOCK */