[gpsd-users] count of satellites_used is incorrect

[Ralph Nemitz]

Hi everybody,

when I try to get the count of "satellites_used" by the following little 
program:

/*
 * Copyright (c) 2010 by the GPSD project
 * Copyright (c) 2012,2013,2014,2015 LogicWay GmbH
 * BSD terms apply: see the file COPYING in the distribution root for 
details.
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <syslog.h>
#include <math.h>
#include <time.h>
#include <errno.h>
#include <libgen.h>
#include <signal.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <unistd.h>
#include <sys/wait.h>

#include <gps.h>

unsigned char loglevel = 0;

int gpsdc_mainloop ( void )
{
    struct gps_data_t gpsdata;
    unsigned long cycle = 0, outtimed = 0;

    fprintf ( stderr, "%s: starting%s\n", __FILE__, (loglevel ? "" : " 
(log is off)"));
    if ( gps_open ( "localhost", "2947", &gpsdata ) != 0 ) {
        fprintf ( stderr, "%s: No gpsd is running or network error: %d, 
%s.\n", __FILE__, errno, gps_errstr(errno) );
        return -1;
    } else {
        if ( gps_stream ( &gpsdata, WATCH_ENABLE, NULL ) >= 0 ) {
            for (;;) {
                cycle++;
                if ( gps_waiting ( &gpsdata, 5000000 ) ) {
                    if ( gps_read ( &gpsdata ) == -1 ) {
                        fprintf ( stderr, "%s: gpsd read error\n", 
__FILE__ );
                        break;
                    } else {
                        if ( loglevel ) {
                            fprintf ( stderr, "%s (%lu/%lu) fix: %d 
lat/lon/alt: %f/%f/%f status: %d deviations: %f/%f satellites: %d\n",
                                      __FILE__, outtimed, cycle,
                                      gpsdata.fix.mode, 
gpsdata.fix.latitude, gpsdata.fix.longitude, gpsdata.fix.altitude,
                                      gpsdata.status, gpsdata.dop.pdop, 
gpsdata.dop.hdop, gpsdata.satellites_used );
                        }
                    }
                } else {
                    fprintf ( stderr, "%s: gpsd read timeout 
(%lu/%lu)\n", __FILE__, outtimed, cycle );
                    outtimed++;
                }
            }
        }
        gps_stream ( &gpsdata, WATCH_DISABLE, NULL );
        gps_close ( &gpsdata );
        fprintf ( stderr, "%s: finished\n", __FILE__);
    }
    return 0;
}

int main ( int argc, char **argv )
{
    int opt;
    while ( ( opt = getopt ( argc, argv, "v" ) ) != -1 ) {
        switch ( opt ) {
        case 'v':
            loglevel++;
            break;
        default:
            printf ( "gpsd_c [-v]\n  -v ... verbose\n" );
            exit ( -1 );
            break;
        }
    }
    gpsdc_mainloop();
    return 0;
}

the count of "satellites_used" decreases to one after about half an 
hour. The count of "satellites_used" in the program "gpsmon" stays 
meanwhile nearly constant at eigth to ten. The other values from the 
gpsdata structure correspond to the values on "gpsmon".

What can be the reason for decreasing "satellites_used"?

I use gpsd-3.16 with linux (buildroot), the gps-chip is "GNS1301" from 
Unitronics.

Thanks for your help!

Ralph

--

--
###############################################################
Dipl.-Phys. Ralph Nemitz    Tel.:    (0385) 3993 9354
Logic Way GmbH              Fax:     (0385) 3993 458
Hagenower Strasse 73        HTTP:    http://www.logicway.de
19061 Schwerin              E-Mail:  address@hidden
###############################################################