Meinberg LANTIME, Operating Instructions Manual, Page: 26 / 153

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:
NORMAL OPERATION
NTP: Not Ready
Tue, 05.06.2001
MESZ 14:23:03
Once per second the GPS compares the GPS time with the PZF5xx time. Both the
pulses per second and the serial time strings are compared. If the calculated deviation
exceeds the configured time limit or one of the receiver stops generating time strings
or pulses, the hybridsystem stops sending time information to the NTP server. Once
the hybridsystem sent a time string, the NTP daemon is started with the
corresponding parameters. After that the NTPD starts synchronisation with the
references. The references are usually the RTC of the single board computer, the
serial time string and the pulse per second (PPS) from the hybridsystem. If the NTPD
is started but not synchronous with the hybridsystem yet, the following message is
displayed:
NORMAL OPERATION
NTP: Not Sync
Tue, 05.06.2001
MESZ 12:00:00
For the synchronisation of the NTPD with the GPS it is necessary that the GPS
receiver is synchronous with the GPS time (LOCK LED is turned on). Also the time
difference between the GPS und PZF receiver must be less then the time limit error.
In this case the following message is monitored on the display:
NORMAL OPERATION
NTP: Offs:3ms
Thu, 05.06.2001
MESZ 12:00:00
The second line shows the user that the NTPD is synchronized with the GPS with an
offset of -3 ms. Because of the internal time of the NTP which is adjusted by a
software PLL (phase locked loop) it takes a certain time to optimise this offset. The
NTPD tries to keep the offset below ±128 ms; if the offset becomes too large the
system time is set with the GPS time. Typically values for the offset are +-5 ms after
the NTPD has already synchronized. If NTPD is not synchronised and GPS receiver
is then, the green LOCK-LED is blinking.
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