Meinberg LANTIME M600 Technical Information download pdf (Page 19)

Booting the GPS receiver

If both, the antenna and the power supply, have been connected the system is ready

to operate. About 2 minutes 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.

If the receiver position has changed by some hundred kilometers 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. two minutes. During

this time the following message appears on the display:

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 synchronization with the reference clocks (usual the hardware clock of

the single board computer and the GPS receiver). Until synchronization is finished the

following message is displayed:

GPS: NORMAL OPERATION Mon, 28.08.2006

NTP: sync to local UTC 14:33:10

GPS: NORMAL OPERATION Mon, 28.08.2006

NTP: not sync UTC 14:33:10

MEINBERG TIMESERVER please wait...

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Meinberg LANTIME M600 Technical Information Page 19