8.1.4 Time Initialisation
Time initialisation completes once the system has determined time accurately. This occurs as soon as the
GNSS receiver obtains its first fix. For this to occur the system must receive rough time as well as a 1PPS signal
on one of the GPIO pins. It is also possible to acquire time from an external source, see
for more information.
Until the time has initialised, the Unix or formatted time that Boreas outputs will be flagged as invalid.
8.2 Hot Start
Advanced Navigation GNSS/INS devices were the first on the market with hot-start functionality. This hot-start
functionality allows Boreas to start inertial navigation within 500 ms to 1 s, and obtain a GNSS fix in as little as 2
seconds. The hot-start functionality is always on and fully automatic. See
for
details.
A next generation backup battery system within Boreas provides the hot-start ability for more than 48 hours
without power. When Boreas hot-starts, it assumes that it is in the same state it was when it lost power and
begins navigating from that position. The hot-start also provides ephemeris, almanac and time information to the
GNSS receiver which allows it to achieve a GNSS fix far more quickly than it otherwise could. When the GNSS
achieves its first fix, Boreas will jump to the new position without disturbing the filter.
Whenever Boreas is without power it continues to accurately keep time so that it is immediately valid for a hot-
start.
The hot-start functionality is of particular benefit to vehicle tracking and robotics applications. The primary
benefits are immunity and fast recovery from power failure as well as fast start up time.
8.3 Time
Boreas has been designed to provide a highly accurate time reference. It contains a temperature compensated
disciplined oscillator that corrects itself very precisely using GNSS time. When a GNSS fix is available, the
Boreas time is accurate to within 20 nanoseconds.
When the GNSS fix is lost, the Boreas time will slowly lose accuracy at a rate of approximately 3 microseconds
per hour.
If greater accuracy is required for your application, Advanced Navigation may be able to offer Boreas with a
temperature compensated disciplined oscillator that has greater time accuracy than 20 nanoseconds and less
than 3 μs/hr of drift. Contact Advanced Navigation's sales department at [email protected] for
more information.
When Boreas hot-starts the time accuracy is typically within 1 second immediately on startup and corrected to
within 50 nanoseconds as soon as a GNSS fix is achieved.
The time can be accessed via the following means:
l
A dedicated
. This is the preferred means to obtaining the most accurate timing output.
l
A 1PPS output over GPIO or the Auxiliary port, see
of the Dynamic Pin Functions.
l
A built-in Precision Time Protocol (PTP) version 2 server for synchronisation with network-connected
devices which require high accuracy time. The PTP server broadcasts PTP messages (Sync, Follow Up,
Announce) to multicast IP address 224.0.1.129. The PTP broadcasts are sent whenever an Ethernet
connection is established and cannot be disabled.
l
A built-in Network Time Protocol (NTP) server.
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Boreas Reference Manual • Using Boreas
