How to ensure GPS time is working?



  • I found I have some USB GPS sensor (labelled as BU-353) and plugged it into one of USB ports on pfSense machine.

    What next? How to know it works? How to know receiver has enough signal level?

    Firs I tried to configure the device inside Services -> NTP -> Serial GPS setting port = cuaU0

    This probably caused error message in NTP log, saying

    refclock_open /dev/gps0: Device busy

    I thought this mean that device used twice, one in automatic mode, and second time via serial emulator. So, I turned OFF Serial GPS by setting port = none and have no errors.

    How to see though it is working at all?



  • For precise time syncing, you need a serial GPS receiver with PPS signal output. /dev/cuau0 is the address of the first serial port.
    USB GPSes are not suitable for precise timing, they are only good for positioning and navigation.

    A working GPS unit will display in the NTP status page a Google Maps link with the detected coordinates, and the server will become Stratum1 showing reference signal source GPS.



  • Where is NTP status page? Have only "NTP", "Serial GPS", "PPS" (see attachement)

    ![Services_ NTP.png](/public/imported_attachments/1/Services_ NTP.png)
    ![Services_ NTP.png_thumb](/public/imported_attachments/1/Services_ NTP.png_thumb)



  • Status > NTP



  • So, I have /dev/gps0 device. Who is using it, when I am trying to set it as serial GPS? Is it possible to configure it with serial GPS?

    In order to avoid talks about USB speed, please imagine, that my computer has no internet. Then any slow USB is better than nothing.


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