View source for Wiren Board 6: WBE2R-R-GPS GPS/GLONASS Extension Module:NTPD PPS Setup/en

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<!--{{DISPLAYTITLE:Настройка сервера точного времени на контроллере Wiren Board 6 с модулем WBE2R-R-GPS}}-->

'''THE ARTICLE IS IN PROGRESS!'''


The WBE2R-R-GPS module allows you to autonomously synchronize the exact time of the controller by GLONASS/GPS signals and use the controller as a source of accurate NTP time on the network.
The module supports PPS signal output to the controller's GPIO processor. Kernel modules are supported by module pps_gpio.


It is further assumed that the module is installed into the controller that is configured and functioning correctly checked (see section [[Wiren_Board 6:_WBE2R-R-GPS_GPS/GLONASS_Extension_Module/en]]

== NMEA and PPS ==

The controller module is represented by two devices - serial port /dev/ttyMOD3 and signal transmission device  pps /dev/pps2
Port /dev/ttyMOD3 transmits data from the module via standard Protocol [https://wikipedia.org/wiki/NMEA_0183 NMEA], including position, receiver speed, and time and date messages. Usually the information is updated once per second. The module is made on the chip SIM68, debugging UART-port is not available in the current hardware modification.

The pps pulse is precisely synchronized with the beginning of each second, which makes it possible to increase the accuracy of the time determination on the controller with microsecond accuracy.

=== Check for pps signal ===
At the command prompt, run <code>ppstest /dev/pps2</code>. 

[[File:Pps_ok.png|600px|thumb|right|Check for a pps signal]]

The command will sequentially display the UNIX-time timestamps with a decimal part (the timestamps can be read in the file <code>/sys/class/pps/pps2/assert</code>).

=== Check for data in NMEA format ===
To verify that the system can receive data from the GPS module in NMEA format, run the following command  
<pre>cat /dev/ttyMOD3</pre>

[[File:NMEA_ok.png|600px|thumb|right|Check for NMEA data]]

In the figure, the fragments of NMEA messages are highlighted in red, showing that the GPS module has reliably recorded its position and receives the correct data. Details see description [https://wikipedia.org/wiki/NMEA_0183 NMEA] messages.

== NTPD ==
Ntpd service is used as application SOFTWARE. By default, the ntpd server is configured to receive time from other servers on the Internet using ntp. To use the time signals from the GPS/GLONASS module, a number of configuration steps are required (see below).

=== Current accurate time sources for NPTD === 

[[File:Ntpqp_inint.png|700px|thumb|right|]]

The exact time sources are marked with special characters:

{| class="wikitable"
! Symbol !! Value
|-
| * || current source used
|-
| # || source selected but too remote
|-
| o || source selected, PPS signal used
|-
| + || source selected, ready to use
|-
| x || source rejected
|-
| . || source selected last from the list of candidates
|-
| - || source rejected by selection algorithm
|-
| space || source rejected
|}


Note that the ntpd 28 driver (shared memory driver), see below, which allows the use of gpsd functions, is not marked with an "o", even if PPS is used. If it works correctly, it will be marked with "*".

== GPSD ==
Daemon gpsd is a unified Protocol of interaction with the receivers of the satellite signals of GPS/GLONASS. In our case, we will use it as an intermediate layer between the module and the ntpd server (driver with code 28).
The daemon is installed by the command
<pre>apt-get install gpsd</pre>

=== Settings ===

=== gpsd settings ===

=== Ntpd setting ===
In ntpd server settings we need to specify two new sources of exact time: NMEA and PPS.