Notices

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>

void set_gps(int fd, int msg_type, int mode, int rate, char *buf, int buf_len);

int
main(int argc, char **argv)
{
   
   char cmdbuf[1024]={0};
   char buf[64];
   char *real_gpsd = "/usr/sbin/gpsd_real ";
   int i;

   //the real gpsd executable:
   snprintf(cmdbuf, 1024, "%s", "/usr/sbin/gpsd_real ");

   for ( i=1; i<argc; i++)
   {
      strncat(cmdbuf, argv[i], 1024);
      strncat(cmdbuf, " ", 1);
   }
   strncat(cmdbuf, "&", 1);
   printf("Executing: %s\n", cmdbuf);
   system(cmdbuf);

   //poll for the bluetooh to be ready 
   while (system ("ls /dev/rfcomm0 >> /dev/null") != 0)
   {
       sleep(2);
   }
   
   
   while (1)
   {
      int fd=open("/dev/rfcomm0", O_RDWR);
      set_gps(fd, 1, 0, 1, buf, 64);
      set_gps(fd, 2, 0, 5, buf, 64);
      set_gps(fd, 3, 0, 1, buf, 64);
      set_gps(fd, 5, 0, 1, buf, 64);

      //quit if the gps module has gone
      if (system ("ls /dev/rfcomm0 >> /dev/null") != 0)
      {
         system("killall gpsd_real");
         return 0;
      }

      sleep(60);
   }
}

/*
 * fd: the file to write
 * msg_type: NMEA msg type: 1-9
 * mode: query or setRate: 0=setRate, 1=Query
 * rate: off=0, max=255, unit: second
 * buf: output buffer
 * buf_len: output buffer len
 */
void set_gps(int fd, int msg_type, int mode, int rate, char *buf, int buf_len)
{
   char *sptr=0;
   char *ptail=0;
   int csum=0;
   int buf_tmp_size=0;

   memset(buf, 0, buf_len);
   snprintf(buf, buf_len, "%s,0%d,0%d,0%d,01*", "$PSRF103", msg_type, mode, rate);

   sptr=buf+1; /*skip the $*/
   buf_tmp_size=strlen(buf);
   ptail=buf+buf_tmp_size;

   while(*sptr && *sptr != '*')
     csum ^= *sptr++;

   snprintf(ptail, buf_len-buf_tmp_size, "%x\r\n", csum);
   printf("%s", buf);
   write(fd, buf, strlen(buf));
}

gcc -o gpsd gps_set.c

cp /usr/sbin/gpsd /usr/sbin/gpsd_real

cp gpsd /usr/sbin