Garmin 15L Technical Specifications - Page 34

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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 for GPS 15, 15x. 16, 16x. 17, 18 and 18x 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 */

Note that sint16 refers to a signed 16-bit

/* ephemeris data unpacker

/* pointer to ephemeris data array

= *(sint16*)&m_TempArray[IDX_EPH_WN];