OXTS xNAV650, Руководство по оборудованию

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Oxford Technical Solutions Ltd. http://www.oxts.com Page 35 of 42
PTP
Currently (March 2021), there is no GUI way of configuring PTP settings but this will be implemented in
a future release of NAVsuite.
Use the link above to access the PTP Quick Start Guide on our support site that has more details.
To use PTP on your xNAV650 device ensure that you have the PTP feature code purchased and
enabled and do the following:
1. Upgrade the firmware of the OxTS INS.
2. Upload a ptpd.conf file and the leap-seconds.list file to the unit.
3. Ensure the PTP feature code is enabled.
4. Append -enable_ptp to mobile.cfg.
5. Reboot the unit.
For the PTP functionality to work, the unit must have the primary GNSS antenna connected and be
tracking satellites. For optimum performance, the unit must also be initialised.
All of the other PTP settings are configured w
ith the “ptpd.conf” file. All the options are documented (for
example, https://manpages.debian.org/testing/ptpd/ptpd.conf.5.en.html ), though some are not
supported. See the support article for an example of this. To edit the configuration, edit the ptpd.conf
file and then upload it again to the unit and reboot it.
PTP packets will be viewable in software such as Wireshark as PTPv2 protocol packets.
OxTS devices get their time solution from GNSS satellites which use very accurate atomic clocks. The
time that OxTS devices receive from the satellites is the number of seconds since midnight January 5th
- January 6th 1980. This is known as the GPS epoch and from this the device can calculate the current
date and time. By default, when an OxTS device is used with PTP, it will be using the GPS epoch.
Not all devices expect timestamps to be in the GPS epoch. Here is a list of commonly used time modes:
Table 16: Epoch time configurations
GPS Time in seconds since the GPS epoch (1980-01-01 00:00:00 UTC), same as NCOM.
Unix Time in seconds since the Unix epoch (1970-01-01 00:00:00 UTC).
UTC
Time in seconds since the Unix epoch (1970-01-01 00:00:00 UTC),
including leap seconds.
PTP
Time in seconds since the PTP epoch (1969-12-31 23:59:51 TAI),
including leap seconds.
To get the correct date and time from a timestamp, it is important to know which epoch is being used.
If the PTP device being synchronised to the OxTS device does not use the GPS epoch, it is possible to
configure the OxTS device to output PTP timestamps from a different epoch (this will not change the
timestamps in the NCOM stream). This is done by adding the relevant advanced command in
NAVconfig (Modify Configuration>Advanced>Commands):