libgpsd_core.c

很好的一个gps daemon驱动,简单实用

/*
 * This provides the interface to the library that supports direct access to
 * GPSes on serial or USB devices.
 */
#include "config.h"
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <sys/ioctl.h>
#ifdef HAVE_SYS_FILIO_H
#include <sys/filio.h>	/* for FIONREAD on BSD systems */
#endif

#include "gpsd.h"

struct gps_session_t *gpsd_init(char devicetype, char *dgpsserver)
/* initialize GPS polling */
{
    time_t now = time(NULL);
    struct gps_session_t *session = (struct gps_session_t *)calloc(sizeof(struct gps_session_t), 1);
    if (!session)
	return NULL;

    session->gpsd_device = DEFAULT_DEVICE_NAME;
    session->device_type = gpsd_drivers[0];
#ifdef NON_NMEA_ENABLE
    {
    struct gps_type_t **dp;
    for (dp = gpsd_drivers; *dp; dp++)
	if ((*dp)->typekey == devicetype) {
	    gpsd_report(3, "Selecting %s driver...\n", (*dp)->typename);
	    session->device_type = *dp;
	    goto foundit;
	}
    gpsd_report(1, "invalid GPS type \"%s\", using NMEA instead\n");
    foundit:;
    }
#endif /* NON_NMEA_ENABLE */
    session->baudrate = session->device_type->baudrate;
    session->dsock = -1;
    if (dgpsserver) {
	char hn[256], buf[BUFSIZE];
	char *colon, *dgpsport = "rtcm-sc104";

	if ((colon = strchr(dgpsserver, ':'))) {
	    dgpsport = colon+1;
	    *colon = '\0';
	}
	if (!getservbyname(dgpsport, "tcp"))
	    dgpsport = "2101";

	session->dsock = netlib_connectsock(dgpsserver, dgpsport, "tcp");
	if (session->dsock < 0)
	    gpsd_report(1, "Can't connect to dgps server, netlib error %d\n", session->dsock);
	else {
	    gethostname(hn, sizeof(hn));
	    sprintf(buf, "HELO %s gpsd %s\r\nR\r\n", hn, VERSION);
	    write(session->dsock, buf, strlen(buf));
	}
    }

    /* mark GPS fd closed */
    session->gNMEAdata.gps_fd = -1;

    INIT(session->gNMEAdata.online_stamp, now);
    INIT(session->gNMEAdata.latlon_stamp, now);
    INIT(session->gNMEAdata.altitude_stamp, now);
    INIT(session->gNMEAdata.track_stamp, now);
    INIT(session->gNMEAdata.speed_stamp, now);
    INIT(session->gNMEAdata.status_stamp, now);
    INIT(session->gNMEAdata.mode_stamp, now);
    INIT(session->gNMEAdata.fix_quality_stamp, now);
    INIT(session->gNMEAdata.satellite_stamp, now);
    session->gNMEAdata.mode = MODE_NO_FIX;

    return session;
}

void gpsd_deactivate(struct gps_session_t *session)
/* temporarily release the GPS device */
{
    session->gNMEAdata.online = 0;
    REFRESH(session->gNMEAdata.online_stamp);
    session->gNMEAdata.mode = MODE_NO_FIX;
    session->gNMEAdata.status = STATUS_NO_FIX;
    gpsd_close(session);
    session->gNMEAdata.gps_fd = -1;
    if (session->device_type->wrapup)
	session->device_type->wrapup(session);
    gpsd_report(1, "closed GPS\n");
}

int gpsd_activate(struct gps_session_t *session)
/* acquire a connection to the GPS device */
{
    if ((session->gNMEAdata.gps_fd = gpsd_open(session->baudrate, session->device_type->stopbits, session)) < 0)
	return -1;
    else {
	session->gNMEAdata.online = 1;
	REFRESH(session->gNMEAdata.online_stamp);
	gpsd_report(1, "gpsd_activate: opened GPS (%d)\n", session->gNMEAdata.gps_fd);

	/* if there is an initializer and no trigger string, invoke it */
	if (session->device_type->initializer && !session->device_type->trigger)
	    session->device_type->initializer(session);
	return session->gNMEAdata.gps_fd;
    }
}

static int is_input_waiting(int fd)
{
    int	count;
    if (fd < 0 || ioctl(fd, FIONREAD, &count) < 0)
	return -1;
    return count;
}

int gpsd_poll(struct gps_session_t *session)
/* update the stuff in the scoreboard structure */
{
    int waiting;

    /* accept a DGPS correction if one is pending */
    if (is_input_waiting(session->dsock) > 0) {
	char buf[BUFSIZE];
	int rtcmbytes;

	if ((rtcmbytes=read(session->dsock,buf,BUFSIZE))>0 && (session->gNMEAdata.gps_fd !=-1)) {
	    if (session->device_type->rtcm_writer(session, buf, rtcmbytes) <= 0)
		gpsd_report(1, "Write to rtcm sink failed\n");
	    else
		gpsd_report(2, "<= DGPS: %d bytes of RTCM relayed.\n", rtcmbytes);
	} else
	    gpsd_report(1, "Read from rtcm source failed\n");
    }

    /* update the scoreboard structure from the GPS */
    waiting = is_input_waiting(session->gNMEAdata.gps_fd);
    gpsd_report(4, "GPS has %d chars waiting\n", waiting);
    if (waiting < 0)
	return waiting;
    else if (!waiting) {
	if (time(NULL) <= session->gNMEAdata.online_stamp.last_refresh + session->device_type->interval+1) {
	    return 0;
	} else {
	    session->gNMEAdata.online = 0;
	    REFRESH(session->gNMEAdata.online_stamp);
	    return -1;
	}
    } else {
	session->gNMEAdata.online = 1;
	REFRESH(session->gNMEAdata.online_stamp);

	/* call the input routine from the device-specific driver */
	session->device_type->handle_input(session);

	/* count the good fixes */
	if (session->gNMEAdata.status > STATUS_NO_FIX) 
	    session->fixcnt++;

	/* may be time to ship a DGPS correction to the GPS */
	if (session->fixcnt > 10 && !session->sentdgps) {
	    session->sentdgps++;
	    if (session->dsock > -1) {
		char buf[BUFSIZE];
		sprintf(buf, "R %0.8f %0.8f %0.2f\r\n", 
			session->gNMEAdata.latitude,
			session->gNMEAdata.longitude, 
			session->gNMEAdata.altitude);
		write(session->dsock, buf, strlen(buf));
		gpsd_report(2, "=> dgps %s", buf);
	    }
	}
    }
    return waiting;
}

void gpsd_wrap(struct gps_session_t *session)
/* end-of-session wrapup */
{
    gpsd_deactivate(session);
    if (session->dsock >= 0)
	close(session->dsock);
}