Garmin GPS 17HVS - Receiver Module Technical Specifications page 33

An example function to do the parsing is shown below. Note that the double data types are converted by the function
cnvt_ieee_double(). This function merely swaps the upper and lower words of the double. This is necessary
on GPS 15, 16, 17 series sensors due to a compatibility issue with the IEEE floating point standard): In this example,
the array m_TempArray contains the data portion of the ephemeris packet (with DLE stuffing removed).
/****************************************************************************
*
* PROCEDURE NAME:
* copyData - ephemeris data unpacker
*
* DESCRIPTION:
* unpacks data from ephemeris packet DATA field after extraneous DLEs
* have been removed.
* integer type.
*
****************************************************************************/
void GPM_ephList::copyData
(
GPM_ephData* pTemp
)
{
pTemp->EphStruct.wn
pTemp->EphStruct.toc = *(float*)&m_TempArray[IDX_EPH_TOC];
pTemp->EphStruct.toe = *(float*)&m_TempArray[IDX_EPH_TOE];
pTemp->EphStruct.af0 = *(float*)&m_TempArray[IDX_EPH_AF0];
pTemp->EphStruct.af1 = *(float*)&m_TempArray[IDX_EPH_AF1];
pTemp->EphStruct.af2 = *(float*)&m_TempArray[IDX_EPH_AF2];
pTemp->EphStruct.ura = *(float*)&m_TempArray[IDX_EPH_URA];
cnvt_ieee_double((long *)&m_TempArray[IDX_EPH_E]);
pTemp->EphStruct.e = *(double*)&m_TempArray[IDX_EPH_E];
cnvt_ieee_double((long *)&m_TempArray[IDX_EPH_SQRTA]);
pTemp->EphStruct.sqrta = *(double*)&m_TempArray[IDX_EPH_SQRTA];
cnvt_ieee_double((long *)&m_TempArray[IDX_EPH_DN]);
pTemp->EphStruct.dn = *(double*)&m_TempArray[IDX_EPH_DN];
cnvt_ieee_double((long *)&m_TempArray[IDX_EPH_M0]);
pTemp->EphStruct.m0 = *(double*)&m_TempArray[IDX_EPH_M0];
cnvt_ieee_double((long *)&m_TempArray[IDX_EPH_W]);
pTemp->EphStruct.w = *(double*)&m_TempArray[IDX_EPH_W];
cnvt_ieee_double((long *)&m_TempArray[IDX_EPH_OMG0]);
pTemp->EphStruct.omg0 = *(double*)&m_TempArray[IDX_EPH_OMG0];
cnvt_ieee_double((long *)&m_TempArray[IDX_EPH_I0]);
pTemp->EphStruct.i0 = *(double*)&m_TempArray[IDX_EPH_I0];
pTemp->EphStruct.odot = *(float*)&m_TempArray[IDX_EPH_ODOT];
pTemp->EphStruct.idot = *(float*)&m_TempArray[IDX_EPH_IDOT];
pTemp->EphStruct.cus = *(float*)&m_TempArray[IDX_EPH_CUS];
pTemp->EphStruct.cuc = *(float*)&m_TempArray[IDX_EPH_CUC];
pTemp->EphStruct.cis = *(float*)&m_TempArray[IDX_EPH_CIS];
pTemp->EphStruct.cic = *(float*)&m_TempArray[IDX_EPH_CIC];
pTemp->EphStruct.crs = *(float*)&m_TempArray[IDX_EPH_CRS];
pTemp->EphStruct.crc = *(float*)&m_TempArray[IDX_EPH_CRC];
pTemp->EphStruct.iod = *(unsigned char*)&m_TempArray[IDX_EPH_IOD];
return;
} /* copyData */
190-00228-21
Note that sint16 refers to a signed 16-bit
/* ephemeris data unpacker
/* pointer to ephemeris data array
= *(sint16*)&m_TempArray[IDX_EPH_WN];
GPS 16/17 Technical Specifications
Page 29
*/
*/
Rev. A