ogr_msgdump.c

The OpenGPSRec receiver software runs on the real time operating system RTAI-Linux. It compiles with

             exactly by one second (511500 units of c_511500). 
             However, after enough sats have been acquired, the GPS 
             gets an idea of its internal clock drift, and (in my unit)
             511500 units of c_511500 correspond to about 1.00002 sec 
             of the receiver time. These 20 microseconds per second
             correspond to aprox. 6000 m/sec, the drift of the internal
             clock reflected in the pseudoranges. Monitoring this field
             we can check our clock drift. Also, as I have already said,
             the increments of c_511500 are not exactly 511500, as the 
             GPS tries to take each measurement synced to a GPS second.   

Name         svid
Position     Byte 37  
Type         Byte
Description  Space Vehicle ID (PRN-1) 

Statistics:

Record 0x0d  (  345) L=  8 bytes 
Record 0x0e  (    1) L= 12 bytes 
Record 0x11  (    1) L= 16 bytes 
Record 0x14  (  304) L= 84 bytes 
Record 0x17  (   55) L= 52 bytes 
Record 0x27  (  209) L=  2 bytes 
Record 0x28  (  209) L=  4 bytes 
Record 0x36  ( 6998) L=  9 bytes 
Record 0x37  (  523) L= 33 bytes 
Record 0x38  ( 2376) L= 37 bytes 
Record 0xff  (    1) L= 27 bytes 

-----------------------------------------------------------------

*/


/* ------------------------------ includes -------------------------------- */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <time.h>
#include <assert.h>
#include <unistd.h>

//#include <sys/io.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>

#include <fcntl.h>
#include <signal.h>

#include "port.h"
#include "ogr_defines.h"
#include "ogr_structs.h"
#include "ogr_prototypes.h"

#include  "ogr_globals.h"

/* ------------------------------- defines -------------------------------- */

/* ----------------------------- prototypes ------------------------------- */

/* ------------------------------ globals --------------------------------- */

/* ----------------------------- procedures ------------------------------- */

int write_msg_0x11( FILE *fp, double lat, double lon)
{
  char id, len;
  int nof = 0;

  if ( !fp)
    return (0);

  id = 0x11;
  nof = fwrite ( &id, sizeof( char), 1, fp);
  
  len = 16;
  nof += fwrite ( &len, sizeof( char), 1, fp);

  nof += sizeof( double) * fwrite ( &lat, sizeof( double), 1, fp);

  nof += sizeof( double) * fwrite ( &lon, sizeof( double), 1, fp);

  return (0);
}

int write_msg_0xff( FILE *fp)
{
  char id, len, str[14];
  UINT16 shrt;
  int nof = 0;

  if ( !fp)
    return (0);

  id = 0xff;
  nof = fwrite ( &id, sizeof( char), 1, fp);
  
  len = 18;
  nof += fwrite ( &len, sizeof( char), 1, fp);

  shrt = 0x17;
  nof += fwrite ( &shrt, sizeof( UINT16), 1, fp);

  shrt = 0x1;
  nof += fwrite ( &shrt, sizeof( UINT16), 1, fp);

  strncpy( str, "OpenGPSRec  ", 13);
  str[13] = '\0';
  nof += fwrite ( str, sizeof( char), 14, fp);

  return (0);
}

/*
 * date & time info 
 */
int write_msg_0x0e( FILE *fp, struct tm *gmt)
{
  char id, len, chr;
  UINT16 shrt;
  int nof = 0;
  
  if ( !fp)
    return (0);

  id = 0x0e;
  nof = fwrite ( &id, sizeof( char), 1, fp);
  
  len = 8;
  nof += fwrite ( &len, sizeof( char), 1, fp);

  chr = (char) gmt->tm_mon+1;
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  chr = (char) gmt->tm_mday;
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  shrt = (UINT16) gmt->tm_year + 1900;
  nof += fwrite ( &shrt, sizeof( UINT16), 1, fp);

  chr = (char) gmt->tm_hour;
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  chr = 0;
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  chr = (char) gmt->tm_min;
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  chr = (char) gmt->tm_sec;
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  return (0);
}

/*
 *  50 Hz counter and navigation word (30 bit)
 */
static int write_msg_0x36( FILE *fp, unsigned long tow, int sfm, 
  int word, INT16 prn, unsigned long msg)
{
  char id, len, chr;
  int nof = 0;
  unsigned long count50hz;
  
  if ( !fp)
    return (0);

  id = 0x36;
  nof = fwrite ( &id, sizeof( char), 1, fp);
  
  len = 9;
  nof += fwrite ( &len, sizeof( char), 1, fp);

//  count50hz = tow * 50 + (word - 1) * 30 + (sfm-1) * 300;
// *** FIXME: week roll-over? ***
//  count50hz = tow * 50 + word * 30 + (sfm-1) * 300 - 300;
  count50hz = tow * 50 + word * 30 - 300;

  nof += sizeof( long) * fwrite ( &count50hz, sizeof( long), 1, fp);

  nof += sizeof( long) * fwrite ( &msg, sizeof( long), 1, fp);
  
  chr = (char) (prn-1);
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  if ( nof != 11)
    return (-1);
    

  return (0);
}

/*
     0    long   phase counter
     4    char   track byte
     5    char   unknown
     6    char   unknown
     7    char   unknown
     8    word   doppler
    10    long   integrated phase
    14    double pseudorange
    22    long   511500 Hz counter
    26    word   signal strength
    28    double time of week
    36    char   PRN-1
 */
 
/*
 * tracking info
 */
int write_msg_0x38( FILE *fp, int ch, double pseudorange, 
  unsigned long phase_counter, double rec_time)
{
  char id, len, chr;
  int nof = 0;
  INT16 strength, doppler;
  static unsigned long counter_511500Hz[NOFCHN];
  unsigned long intphase;

  static double tow_init = -1.0;

  if ( !fp)
    return (0);

  if ( tow_init < 0.0)
    tow_init = RT_Ctrl->tow_tic_count / 10.0;

  id = 0x38;
  nof = fwrite ( &id, sizeof( char), 1, fp);
  
  len = 37;
  nof += fwrite ( &len, sizeof( char), 1, fp);

//   now the data ...

  nof += sizeof( long) * fwrite ( &phase_counter, sizeof( long), 1, fp);

  chr = 0xff;
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  chr = 0;
  nof += fwrite ( &chr, sizeof( char), 1, fp);
  nof += fwrite ( &chr, sizeof( char), 1, fp);
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  doppler = 0;
  nof += sizeof( INT16) * fwrite ( &doppler, sizeof( INT16), 1, fp);

  intphase = 0;
  nof += sizeof( long) * fwrite ( &intphase, sizeof( long), 1, fp);

  nof += sizeof( double) * fwrite ( &pseudorange, sizeof( double), 1, fp);

  counter_511500Hz[ch] += 511500;
  nof += sizeof( long) * fwrite ( &(counter_511500Hz[ch]), sizeof( long), 1, fp);

  strength = 9;
  nof += sizeof( INT16) * fwrite ( &strength, sizeof( INT16), 1, fp);

//  tow = Ctrl->tow_tic_count / 10.0;
  nof += sizeof( double) * fwrite ( &rec_time, sizeof( double), 1, fp);

  chr = (char) (Chan[ch].prn-1);
  nof += fwrite ( &chr, sizeof( char), 1, fp);

  if ( nof != 39)
    return (-1);
    
  return (0);
}

void write_frames_to_file( FILE *fp, int ch, int sfm, 
  unsigned long tow, unsigned long sf[])
{
  int word;
  
  if ( !fp)
    return;

#if 0
  gotoxy( 1, 22+ch);
  printf( "(%d) sfr = %d, tow = %ld", ch, sfm, tow);
  printf( "\n");
#endif

  for ( word=1; word<=10; word++)
  {
    write_msg_0x36( fp, tow, sfm, word, Chan[ch].prn, sf[word]);
  }


#if 0
  {
    int j;
    gotoxy( 1, 22+ch);
    printf( "(%d)", ch);
    for(j=1;j<=10;j++)
      printf( " %08lx", Msg[ch].subframe_parity[j]);
    printf( "\n");
    for(j=1;j<=10;j++)
      printf( " %08lx", sf[j]);
    printf( "\n");
  }
#endif


  return;
}

/* ------------------------------- end of file ---------------------------- */