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130
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