Garmin 15L Technical Specifications - Page 33

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Next, the unit will send the specified number of packets containing the ephemeris information. An
example packet is shown below. Each packet should be acknowledged as before. (Be sure to
modify the ACK packet to indicate what type of packet being acknowledged. For ephemeris data,
the ID is 0x35.)
RX Packet: Ephemeris Data
Byte Description
Delimiter
Ephemeris data ID
Number of bytes in data
Ephemeris data
.
.
.
Checksum calculation
Delimiter
End of packet
The data portion of each packet can then be parsed into an instance of the following structure.
Each of these structures represents data from a single satellite.
typedef struct
{
sint16
wn;
float
toc;
float
toe;
float
af0;
float
af1;
float
af2;
float
ura;
double
e;
double
sqrta;
double
dn;
double
m0;
double
w;
double
omg0;
double
i0;
float
odot;
float
idot;
float
cus;
float
cuc;
float
cis;
float
cic;
float
crs;
float
crc;
unsigned char
iod; /* issue of data
} SDM_spc_eph_type;
Name
DLE
IOP_SPC_EPH_DATA
SIZE
DATA
.
.
.
CHKSUM
DLE
ETX
/* ephemeris data record for SPC
/* week number (weeks)
/* reference time of clock parameters (s)
/* reference time of ephemeris parameters (s)
/* clock correction coefficient - group delay
/* clock correction coefficient
/* clock correction coefficient
/* user range accuracy
/* eccentricity
/* square root of semi-major axis (a)
/* mean motion correction
/* mean anomaly at reference time
/* argument of perigee
/* right ascension
/* inclination angle at reference time
/* rate of right ascension
/* rate of inclination angle
/* argument of latitude correction, sine
/* argument of latitude correction, cosine
/* inclination correction, sine
/* inclination correction, cosine
/* radius correction, sine
/* radius correction, cosine
33
HEX Value
0x10
0x35
0x78
----
.
.
.
----
0x10
0x03
*/
*/
*/
*/
(s)
*/
(s/s)
*/
(s/s/s)
*/
(m)
*/
(-)
*/
(m**1/2)
*/
(r/s)
*/
(r)
*/
(r)
*/
(r)
*/
(r)
*/
(r/s)
*/
(r/s)
*/
(r)
*/
(r)
*/
(r)
*/
(r)
*/
(m)
*/
(m)
*/
*/