Booting The Gps Receiver; Booting The Single Board Computer - Meinberg LANTIME/GPS Operating Instructions Manual

Booting the GPS receiver

If both, the antenna and the power supply, have been connected the system is ready
to operate. About 10 seconds after power-up the receiver's oscillator has warmed up
and operates with the required accuracy. If the receiver finds valid almanac and
ephemeris data in its battery buffered memory and the receiver's position has not
changed significantly since its last operation the receiver can find out which satellites
are in view now. Only a single satellite needs to be received to synchronize and
generate output pulses, so synchronization can be achieved maximally one minute
after power-up.
SERVER NOT READY
NTP: Not Ready
If the receiver position has changed by some hundred kilometres since last operation,
the satellites´ real elevation and Doppler might not match those values expected by
the receiver thus forcing the receiver to start scanning for satellites. This mode is
called Warm Boot because the receiver can obtain ID numbers of existing satellites
from the valid almanac. When the receiver has found four satellites in view it can
update its new position and switch to Normal Operation. If the almanac has been
lost because the battery had been disconnected the receiver has to scan for a satellite
and read in the current almanacs. This mode is called Cold Boot. It takes 12 minutes
until the new almanac is complete and the system switches to Warm Boot mode
scanning for other satellites.

Booting the Single Board Computer

The LINUX operating system is loaded from a packed file on the flash disk of the
single board computer to a RAM disk. All files of the flash disk are stored in the
RAM disk after booting. Because of that it is guaranteed that the file system is in a
defined condition after restart. This boot process takes approx. one minute. During
this time the following message appears on the display:
GPS: NORMAL OPERATION
NTP: Not Ready
After starting up the LINUX system the network function is initiated and the program
for communication with the GPS and the NTPD (NTP daemon) is started. After that
NTPD starts synchronisation with the reference clocks (usual the hardware clock of
the single board computer and the GPS receiver). Until synchronisation is finished the
following message is displayed:
GPS: NORMAL OPERATION
NTP: Not Sync
Wed, 18.11.1998
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