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RXM – SVSI (0x02 0x20)
It periodically polls the information of SV status.
Header ID Data Length Data Checksum
0xB5 0x62 0x02 0x20 8+N*6 See below CK_A CK_B
Data
Offset bytes Format Descriptions Notes
0 I4 GPS time of week (ms)
4 I2 GPS week number
6 U1 Number of observable satellites
7 U1 Number of satellite data
following
The following data will be repeated N times (number of satellites).
8+N*6 U1 PRN number
9+N*6 U1 Flags 0x01 – health SV
0x02 – ephemeris valid
0x04 – almanac valid
10+N*6 I2 Azimuth (degrees)
12+N*6 I1 Elevation (degrees)
13+N*6 U1 Age of almanac (ALM) and
ephemeris (EPH)
Bits 0 ~ 3 – age of ALM in days
offset by 4,
Bits 4 ~ 7 – age of EPH in hours
offset by 4.
i.e. the reference time may be in
the future:
age_of_alm = (Age & 0x0f) – 4
age_of_eph = ((Age & 0xf0) >>
4) - 4