source: ntrip/trunk/BNC/src/RTCM3/ephEncoder.cpp@ 6898

#include "ephEncoder.h"

using namespace std;

// Returns CRC24
////////////////////////////////////////////////////////////////////////////
static unsigned long CRC24(long size, const unsigned char *buf) {
  unsigned long crc = 0;
  int ii;
  while (size--) {
    crc ^= (*buf++) << (16);
    for(ii = 0; ii < 8; ii++) {
      crc <<= 1;
      if (crc & 0x1000000) {
        crc ^= 0x01864cfb;
      }
    }
  }
  return crc;
}

// build up RTCM3 for GPS
////////////////////////////////////////////////////////////////////////////
#define GPSTOINT(type, value) static_cast<type>(round(value))

#define GPSADDBITS(a, b) {bitbuffer = (bitbuffer<<(a)) \
                       |(GPSTOINT(long long,b)&((1ULL<<a)-1)); \
                       numbits += (a); \
                       while(numbits >= 8) { \
                       buffer[size++] = bitbuffer>>(numbits-8);numbits -= 8;}}

#define GPSADDBITSFLOAT(a,b,c) {long long i = GPSTOINT(long long,(b)/(c)); \
                             GPSADDBITS(a,i)};

int t_ephEncoder::RTCM3(const t_ephGPS& eph, unsigned char *buffer) {

  unsigned char *startbuffer = buffer;
  buffer= buffer+3;
  int size = 0;
  int numbits = 0;
  unsigned long long bitbuffer = 0;
  int ura = indexFromAccuracy(eph._ura, eph.type());
  if (eph.type() == t_eph::QZSS) {
    GPSADDBITS(12, 1044)
    GPSADDBITS(4,eph._prn.number())
    GPSADDBITS(16, static_cast<int>(eph._TOC.gpssec())>>4)
    GPSADDBITSFLOAT(8, eph._clock_driftrate, 1.0/static_cast<double>(1<<30)
    /static_cast<double>(1<<25))
    GPSADDBITSFLOAT(16, eph._clock_drift, 1.0/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITSFLOAT(22, eph._clock_bias, 1.0/static_cast<double>(1<<30)
    /static_cast<double>(1<<1))
    GPSADDBITS(8, eph._IODE)
    GPSADDBITSFLOAT(16, eph._Crs, 1.0/static_cast<double>(1<<5))
    GPSADDBITSFLOAT(16, eph._Delta_n, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITSFLOAT(32, eph._M0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
    GPSADDBITSFLOAT(16, eph._Cuc, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._e, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<3))
    GPSADDBITSFLOAT(16, eph._Cus, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._sqrt_A, 1.0/static_cast<double>(1<<19))
    GPSADDBITS(16, static_cast<int>(eph._TOEsec)>>4)
    GPSADDBITSFLOAT(16, eph._Cic, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._OMEGA0, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<1))
    GPSADDBITSFLOAT(16, eph._Cis, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._i0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
    GPSADDBITSFLOAT(16, eph._Crc, 1.0/static_cast<double>(1<<5))
    GPSADDBITSFLOAT(32, eph._omega, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<1))
    GPSADDBITSFLOAT(24, eph._OMEGADOT, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITSFLOAT(14, eph._IDOT, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITS(2,eph._L2Codes)
    GPSADDBITS(10, eph._TOC.gpsw())
    GPSADDBITS(4, ura)
    GPSADDBITS(6, eph._health)
    GPSADDBITSFLOAT(8, eph._TGD, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<1))
    GPSADDBITS(10, eph._IODC)
    GPSADDBITS(1, eph._fitInterval)
    GPSADDBITS(3, 0) /* padding */
  }
  else {
    GPSADDBITS(12, 1019)
    GPSADDBITS(6,eph._prn.number())
    GPSADDBITS(10, eph._TOC.gpsw())
    GPSADDBITS(4, ura)
    GPSADDBITS(2,eph._L2Codes)
    GPSADDBITSFLOAT(14, eph._IDOT, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITS(8, eph._IODE)
    GPSADDBITS(16, static_cast<int>(eph._TOC.gpssec())>>4)
    GPSADDBITSFLOAT(8, eph._clock_driftrate, 1.0/static_cast<double>(1<<30)
    /static_cast<double>(1<<25))
    GPSADDBITSFLOAT(16, eph._clock_drift, 1.0/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITSFLOAT(22, eph._clock_bias, 1.0/static_cast<double>(1<<30)
    /static_cast<double>(1<<1))
    GPSADDBITS(10, eph._IODC)
    GPSADDBITSFLOAT(16, eph._Crs, 1.0/static_cast<double>(1<<5))
    GPSADDBITSFLOAT(16, eph._Delta_n, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITSFLOAT(32, eph._M0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
    GPSADDBITSFLOAT(16, eph._Cuc, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._e, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<3))
    GPSADDBITSFLOAT(16, eph._Cus, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._sqrt_A, 1.0/static_cast<double>(1<<19))
    GPSADDBITS(16, static_cast<int>(eph._TOEsec)>>4)
    GPSADDBITSFLOAT(16, eph._Cic, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._OMEGA0, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<1))
    GPSADDBITSFLOAT(16, eph._Cis, 1.0/static_cast<double>(1<<29))
    GPSADDBITSFLOAT(32, eph._i0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
    GPSADDBITSFLOAT(16, eph._Crc, 1.0/static_cast<double>(1<<5))
    GPSADDBITSFLOAT(32, eph._omega, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<1))
    GPSADDBITSFLOAT(24, eph._OMEGADOT, M_PI/static_cast<double>(1<<30)
    /static_cast<double>(1<<13))
    GPSADDBITSFLOAT(8, eph._TGD, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<1))
    GPSADDBITS(6, eph._health) 
    GPSADDBITS(1, eph._L2PFlag)
    GPSADDBITS(1, eph._fitInterval)
  }

  startbuffer[0]=0xD3;
  startbuffer[1]=(size >> 8);
  startbuffer[2]=size;
  unsigned long  i = CRC24(size+3, startbuffer);
  buffer[size++] = i >> 16;
  buffer[size++] = i >> 8;
  buffer[size++] = i;
  size += 3;
  return size;
}

// build up RTCM3 for GLONASS
////////////////////////////////////////////////////////////////////////////
#define GLONASSTOINT(type, value) static_cast<type>(round(value))

#define GLONASSADDBITS(a, b) {bitbuffer = (bitbuffer<<(a)) \
                       |(GLONASSTOINT(long long,b)&((1ULL<<(a))-1)); \
                       numbits += (a); \
                       while(numbits >= 8) { \
                       buffer[size++] = bitbuffer>>(numbits-8);numbits -= 8;}}
#define GLONASSADDBITSFLOATM(a,b,c) {int s; long long i; \
                       if(b < 0.0) \
                       { \
                         s = 1; \
                         i = GLONASSTOINT(long long,(-b)/(c)); \
                         if(!i) s = 0; \
                       } \
                       else \
                       { \
                         s = 0; \
                         i = GLONASSTOINT(long long,(b)/(c)); \
                       } \
                       GLONASSADDBITS(1,s) \
                       GLONASSADDBITS(a-1,i)}

int t_ephEncoder::RTCM3(const t_ephGlo& eph, unsigned char *buffer)
{

  int size = 0;
  int numbits = 0;
  long long bitbuffer = 0;
  unsigned char *startbuffer = buffer;
  buffer= buffer+3;

  GLONASSADDBITS(12, 1020)
  GLONASSADDBITS(6, eph._prn.number())
  GLONASSADDBITS(5, 7+eph._frequency_number)
  GLONASSADDBITS(1, 0)
  GLONASSADDBITS(1, 0)
  GLONASSADDBITS(2, 0)
  eph._tki=eph._tki+3*60*60;
  GLONASSADDBITS(5, static_cast<int>(eph._tki)/(60*60))
  GLONASSADDBITS(6, (static_cast<int>(eph._tki)/60)%60)
  GLONASSADDBITS(1, (static_cast<int>(eph._tki)/30)%30)
  GLONASSADDBITS(1, eph._health) 
  GLONASSADDBITS(1, 0)
  unsigned long long timeofday = (static_cast<int>(eph._tt.gpssec()+3*60*60-eph._gps_utc)%86400);
  GLONASSADDBITS(7, timeofday/60/15)
  GLONASSADDBITSFLOATM(24, eph._x_velocity*1000, 1000.0/static_cast<double>(1<<20))
  GLONASSADDBITSFLOATM(27, eph._x_pos*1000, 1000.0/static_cast<double>(1<<11))
  GLONASSADDBITSFLOATM(5, eph._x_acceleration*1000, 1000.0/static_cast<double>(1<<30))
  GLONASSADDBITSFLOATM(24, eph._y_velocity*1000, 1000.0/static_cast<double>(1<<20))
  GLONASSADDBITSFLOATM(27, eph._y_pos*1000, 1000.0/static_cast<double>(1<<11))
  GLONASSADDBITSFLOATM(5, eph._y_acceleration*1000, 1000.0/static_cast<double>(1<<30))
  GLONASSADDBITSFLOATM(24, eph._z_velocity*1000, 1000.0/static_cast<double>(1<<20))
  GLONASSADDBITSFLOATM(27,eph._z_pos*1000, 1000.0/static_cast<double>(1<<11))
  GLONASSADDBITSFLOATM(5, eph._z_acceleration*1000, 1000.0/static_cast<double>(1<<30))
  GLONASSADDBITS(1, 0)
  GLONASSADDBITSFLOATM(11, eph._gamma, 1.0/static_cast<double>(1<<30)
  /static_cast<double>(1<<10))
  GLONASSADDBITS(2, 0) /* GLONASS-M P */
  GLONASSADDBITS(1, 0) /* GLONASS-M ln(3) */
  GLONASSADDBITSFLOATM(22, eph._tau, 1.0/static_cast<double>(1<<30))
  GLONASSADDBITS(5, 0) /* GLONASS-M delta tau */
  GLONASSADDBITS(5, eph._E)
  GLONASSADDBITS(1, 0) /* GLONASS-M P4 */
  GLONASSADDBITS(4, 0) /* GLONASS-M FT */
  GLONASSADDBITS(11, 0) /* GLONASS-M NT */
  GLONASSADDBITS(2, 0) /* GLONASS-M active? */
  GLONASSADDBITS(1, 0) /* GLONASS additional data */
  GLONASSADDBITS(11, 0) /* GLONASS NA */
  GLONASSADDBITS(32, 0) /* GLONASS tau C */
  GLONASSADDBITS(5, 0) /* GLONASS-M N4 */
  GLONASSADDBITS(22, 0) /* GLONASS-M tau GPS */
  GLONASSADDBITS(1, 0) /* GLONASS-M ln(5) */
  GLONASSADDBITS(7, 0) /* Reserved */

  startbuffer[0]=0xD3;
  startbuffer[1]=(size >> 8);
  startbuffer[2]=size;
  unsigned long i = CRC24(size+3, startbuffer);
  buffer[size++] = i >> 16;
  buffer[size++] = i >> 8;
  buffer[size++] = i;
  size += 3;
  return size;
}

// build up RTCM3 for Galileo
////////////////////////////////////////////////////////////////////////////
#define GALILEOTOINT(type, value) static_cast<type>(round(value))

#define GALILEOADDBITS(a, b) {bitbuffer = (bitbuffer<<(a)) \
                       |(GALILEOTOINT(long long,b)&((1LL<<a)-1)); \
                       numbits += (a); \
                       while(numbits >= 8) { \
                       buffer[size++] = bitbuffer>>(numbits-8);numbits -= 8;}}
#define GALILEOADDBITSFLOAT(a,b,c) {long long i = GALILEOTOINT(long long,(b)/(c)); \
                             GALILEOADDBITS(a,i)};

int t_ephEncoder::RTCM3(const t_ephGal& eph, unsigned char *buffer) {
  int size = 0;
  int numbits = 0;
  long long bitbuffer = 0;
  unsigned char *startbuffer = buffer;
  buffer= buffer+3;

  int SISA = indexFromAccuracy(eph._SISA, eph.type());

  GALILEOADDBITS(12, eph._inav ? 1046 : 1045)
  GALILEOADDBITS(6, eph._prn.number())
  GALILEOADDBITS(12, eph._TOC.galw())
  GALILEOADDBITS(10, eph._IODnav)
  GALILEOADDBITS(8, SISA)
  GALILEOADDBITSFLOAT(14, eph._IDOT, M_PI/static_cast<double>(1<<30)
  /static_cast<double>(1<<13))
  GALILEOADDBITS(14, eph._TOC.gpssec()/60)
  GALILEOADDBITSFLOAT(6, eph._clock_driftrate, 1.0/static_cast<double>(1<<30)
  /static_cast<double>(1<<29))
  GALILEOADDBITSFLOAT(21, eph._clock_drift, 1.0/static_cast<double>(1<<30)
  /static_cast<double>(1<<16))
  GALILEOADDBITSFLOAT(31, eph._clock_bias, 1.0/static_cast<double>(1<<30)
  /static_cast<double>(1<<4))
  GALILEOADDBITSFLOAT(16, eph._Crs, 1.0/static_cast<double>(1<<5))
  GALILEOADDBITSFLOAT(16, eph._Delta_n, M_PI/static_cast<double>(1<<30)
  /static_cast<double>(1<<13))
  GALILEOADDBITSFLOAT(32, eph._M0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  GALILEOADDBITSFLOAT(16, eph._Cuc, 1.0/static_cast<double>(1<<29))
  GALILEOADDBITSFLOAT(32, eph._e, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<3))
  GALILEOADDBITSFLOAT(16, eph._Cus, 1.0/static_cast<double>(1<<29))
  GALILEOADDBITSFLOAT(32, eph._sqrt_A, 1.0/static_cast<double>(1<<19))
  GALILEOADDBITS(14, eph._TOEsec/60)
  GALILEOADDBITSFLOAT(16, eph._Cic, 1.0/static_cast<double>(1<<29))
  GALILEOADDBITSFLOAT(32, eph._OMEGA0, M_PI/static_cast<double>(1<<30)
  /static_cast<double>(1<<1))
  GALILEOADDBITSFLOAT(16, eph._Cis, 1.0/static_cast<double>(1<<29))
  GALILEOADDBITSFLOAT(32, eph._i0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  GALILEOADDBITSFLOAT(16, eph._Crc, 1.0/static_cast<double>(1<<5))
  GALILEOADDBITSFLOAT(32, eph._omega, M_PI/static_cast<double>(1<<30)
  /static_cast<double>(1<<1))
  GALILEOADDBITSFLOAT(24, eph._OMEGADOT, M_PI/static_cast<double>(1<<30)
  /static_cast<double>(1<<13))
  GALILEOADDBITSFLOAT(10, eph._BGD_1_5A, 1.0/static_cast<double>(1<<30)
  /static_cast<double>(1<<2))
  if(eph._inav)
  {
    GALILEOADDBITSFLOAT(10, eph._BGD_1_5B, 1.0/static_cast<double>(1<<30)
    /static_cast<double>(1<<2))
    GALILEOADDBITS(2, static_cast<int>(eph._E5bHS))
    GALILEOADDBITS(1, eph._e5bDataInValid ? 1 : 0)
    GALILEOADDBITS(2, static_cast<int>(eph._E1_bHS))
    GALILEOADDBITS(1, eph._e1DataInValid ? 1 : 0)
  }
  else
  {
    GALILEOADDBITS(2, static_cast<int>(eph._E5aHS))
    GALILEOADDBITS(1,  eph._e5aDataInValid ? 1 : 0)
  }

  GALILEOADDBITS((eph._inav ? 2 : 7), 0)

  startbuffer[0]=0xD3;
  startbuffer[1]=(size >> 8);
  startbuffer[2]=size;
  unsigned long i = CRC24(size+3, startbuffer);
  buffer[size++] = i >> 16;
  buffer[size++] = i >> 8;
  buffer[size++] = i;
  size += 3;
  return size;
}

// build up RTCM3 for SBAS
////////////////////////////////////////////////////////////////////////////
#define SBASTOINT(type, value) static_cast<type>(round(value))

#define SBASADDBITS(a, b) {bitbuffer = (bitbuffer<<(a)) \
                       |(SBASTOINT(long long,b)&((1ULL<<a)-1)); \
                       numbits += (a); \
                       while(numbits >= 8) { \
                       buffer[size++] = bitbuffer>>(numbits-8);numbits -= 8;}}
#define SBASADDBITSFLOAT(a,b,c) {long long i = SBASTOINT(long long,(b)/(c)); \
                             SBASADDBITS(a,i)};

int t_ephEncoder::RTCM3(const t_ephSBAS& eph, unsigned char* buffer) {
  int size = 0;
  int numbits = 0;
  long long bitbuffer = 0;
  unsigned char *startbuffer = buffer;
  buffer= buffer+3;

  int ura = indexFromAccuracy(eph._ura, eph.type());
  SBASADDBITS(12, 1043)
  SBASADDBITS(6, eph._prn.number()-20)
  SBASADDBITS(8, eph._IODN)
  SBASADDBITS(13, static_cast<int>(eph._TOC.daysec())>>4)
  SBASADDBITS(4, ura)
  SBASADDBITSFLOAT(30, eph._x_pos, 0.08)
  SBASADDBITSFLOAT(30, eph._y_pos, 0.08)
  SBASADDBITSFLOAT(25, eph._z_pos, 0.4)
  SBASADDBITSFLOAT(17, eph._x_velocity, 0.000625)
  SBASADDBITSFLOAT(17, eph._y_velocity, 0.000625)
  SBASADDBITSFLOAT(18, eph._z_velocity, 0.004)
  SBASADDBITSFLOAT(10, eph._x_acceleration, 0.0000125)
  SBASADDBITSFLOAT(10, eph._y_acceleration, 0.0000125)
  SBASADDBITSFLOAT(10, eph._z_acceleration, 0.0000625)
  SBASADDBITSFLOAT(12, eph._agf0, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  SBASADDBITSFLOAT(8, eph._agf1, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<10))
  SBASADDBITS(2,0);

  startbuffer[0]=0xD3;
  startbuffer[1]=(size >> 8);
  startbuffer[2]=size;
  unsigned long i = CRC24(size+3, startbuffer);
  buffer[size++] = i >> 16;
  buffer[size++] = i >> 8;
  buffer[size++] = i;
  size += 3;
  return size;
}

// build up RTCM3 for BDS
////////////////////////////////////////////////////////////////////////////
#define BDSTOINT(type, value) static_cast<type>(round(value))

#define BDSADDBITS(a, b) {bitbuffer = (bitbuffer<<(a)) \
                       |(BDSTOINT(long long,b)&((1ULL<<a)-1)); \
                       numbits += (a); \
                       while(numbits >= 8) { \
                       buffer[size++] = bitbuffer>>(numbits-8);numbits -= 8;}}
#define BDSADDBITSFLOAT(a,b,c) {long long i = BDSTOINT(long long,(b)/(c)); \
                             BDSADDBITS(a,i)};

int t_ephEncoder::RTCM3(const t_ephBDS& eph, unsigned char* buffer) {
  int size = 0;
  int numbits = 0;
  long long bitbuffer = 0;
  unsigned char *startbuffer = buffer;
  buffer= buffer+3;

  int URA = indexFromAccuracy(eph._URA, eph.type());
  BDSADDBITS(12, RTCM3ID_BDS)
  BDSADDBITS(6, eph._prn.number())
  BDSADDBITS(13, eph._TOC.bdsw() - 1356.0)
  BDSADDBITS(4, URA);
  BDSADDBITSFLOAT(14, eph._IDOT, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<13))
  BDSADDBITS(5, eph._AODE)
  BDSADDBITS(17, static_cast<int>(eph._TOC.bdssec())>>3)
  BDSADDBITSFLOAT(11, eph._clock_driftrate, 1.0/static_cast<double>(1<<30)
      /static_cast<double>(1<<30)/static_cast<double>(1<<6))
  BDSADDBITSFLOAT(22, eph._clock_drift, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<20))
  BDSADDBITSFLOAT(24, eph._clock_bias, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<3))
  BDSADDBITS(5, eph._AODC)
  BDSADDBITSFLOAT(18, eph._Crs, 1.0/static_cast<double>(1<<6))
  BDSADDBITSFLOAT(16, eph._Delta_n, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<13))
  BDSADDBITSFLOAT(32, eph._M0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(18, eph._Cuc, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(32, eph._e, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<3))
  BDSADDBITSFLOAT(18, eph._Cus, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(32, eph._sqrt_A, 1.0/static_cast<double>(1<<19))
  BDSADDBITS(17, static_cast<int>(eph._TOE.bdssec())>>3)
  BDSADDBITSFLOAT(18, eph._Cic, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(32, eph._OMEGA0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(18, eph._Cis, 1.0/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(32, eph._i0, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(18, eph._Crc, 1.0/static_cast<double>(1<<6))
  BDSADDBITSFLOAT(32, eph._omega, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<1))
  BDSADDBITSFLOAT(24, eph._OMEGADOT, M_PI/static_cast<double>(1<<30)/static_cast<double>(1<<13))
  BDSADDBITSFLOAT(10, eph._TGD1, 0.0000000001)
  BDSADDBITSFLOAT(10, eph._TGD2, 0.0000000001)
  BDSADDBITS(1, eph._SatH1)
  BDSADDBITS(1, 0) /* reserved bit, fill up 8 bits */

  startbuffer[0]=0xD3;
  startbuffer[1]=(size >> 8);
  startbuffer[2]=size;
  unsigned long i = CRC24(size+3, startbuffer);
  buffer[size++] = i >> 16;
  buffer[size++] = i >> 8;
  buffer[size++] = i;
  size += 3;
  return size;
}