Using parse driver rather then nmea driver? - NTP

This is a discussion on Using parse driver rather then nmea driver? - NTP ; Hi All I have a NMEA GPS device that outputs the correct strings. However due to where I have to position the device it doesn't always have a lock on three satellites and then goes into Void mode. However the ...

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  1. Using parse driver rather then nmea driver?

    Hi All

    I have a NMEA GPS device that outputs the correct strings. However
    due to where I have to position the device it doesn't always have a
    lock on three satellites and then goes into Void mode. However the
    time values are still being collected (It always sees at least one
    satellite).

    Is it possible to write a parse (127,127,8,0) driver to read only the
    time values and ignore the void message and thereby make it the
    stratum 0 source?

    Thanks in advance.

  2. Re: Using parse driver rather then nmea driver?


    >I have a NMEA GPS device that outputs the correct strings. However
    >due to where I have to position the device it doesn't always have a
    >lock on three satellites and then goes into Void mode. However the
    >time values are still being collected (It always sees at least one
    >satellite).


    Which particular NMEA unit are you using?


    >Is it possible to write a parse (127,127,8,0) driver to read only the
    >time values and ignore the void message and thereby make it the
    >stratum 0 source?


    If your unit is doing what I think it's doing, you probably don't
    want to do that. The GPS unit is telling you that it doesn't really
    know the time, but its best guess is xxxx. Why would you want to
    use time that's known not to be good? It would work OK if you
    didn't have to coast for very long. But then your PC can coast
    just as well for short times, maybe even better.

    --
    These are my opinions, not necessarily my employer's. I hate spam.


  3. Re: Using parse driver rather then nmea driver?

    hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) writes:


    >>I have a NMEA GPS device that outputs the correct strings. However
    >>due to where I have to position the device it doesn't always have a
    >>lock on three satellites and then goes into Void mode. However the
    >>time values are still being collected (It always sees at least one
    >>satellite).


    >Which particular NMEA unit are you using?



    >>Is it possible to write a parse (127,127,8,0) driver to read only the
    >>time values and ignore the void message and thereby make it the
    >>stratum 0 source?


    >If your unit is doing what I think it's doing, you probably don't
    >want to do that. The GPS unit is telling you that it doesn't really
    >know the time, but its best guess is xxxx. Why would you want to
    >use time that's known not to be good? It would work OK if you
    >didn't have to coast for very long. But then your PC can coast
    >just as well for short times, maybe even better.


    IF you know your position, then a single satellite is sufficient to give
    the time to high precision (ie, microseconds assuming you know your position to 300m acccuracy). However, I suspect that your unit will not differentiate between seeing no satellites whatsoever or seeing just one or 2. Many have an on board oscillator which they use to interpolate between valid sightings.
    Ie, it will depend entirely on your gps unit.




  4. Re: Using parse driver rather then nmea driver?

    >>>I have a NMEA GPS device that outputs the correct strings. However
    >>>due to where I have to position the device it doesn't always have a
    >>>lock on three satellites and then goes into Void mode. However the
    >>>time values are still being collected (It always sees at least one
    >>>satellite).

    >
    >>Which particular NMEA unit are you using?

    >
    >
    >>>Is it possible to write a parse (127,127,8,0) driver to read only the
    >>>time values and ignore the void message and thereby make it the
    >>>stratum 0 source?

    >
    >>If your unit is doing what I think it's doing, you probably don't
    >>want to do that. The GPS unit is telling you that it doesn't really
    >>know the time, but its best guess is xxxx. Why would you want to
    >>use time that's known not to be good? It would work OK if you
    >>didn't have to coast for very long. But then your PC can coast
    >>just as well for short times, maybe even better.

    >
    > IF you know your position, then a single satellite is sufficient to give
    > the time to high precision (ie, microseconds assuming you know your position to 300m acccuracy). However, I suspect that your unit will not differentiate between seeing no satellites whatsoever or seeing just one or 2. Many have an on board oscillator which they use to interpolate between valid sightings.
    > Ie, it will depend entirely on your gps unit.
    >
    >
    >
    > _______________________________________________
    > questions mailing list
    > questions@lists.ntp.org
    > https://lists.ntp.org/mailman/listinfo/questions
    >


    Hi Guys

    I am actually using three seperate BU 303 GPS devices pointing in
    different directions.

    I know my position to within 10m (got from a roof reading with 9 sats
    in view) so my confidence in the readings is high.

    I only need accuracy to about half a second but then need that machine
    to be the stratum 1 server for the other machines in the environment.
    For reasons I won''t bore you with they can't connect to an external
    network connection so this seems the best solution?

    It's a shame no-one makes a GPS device that allows multiple sources at
    the same time (I suppose an old garmin GPS III plus unit with multiple
    external antennas I have might do it....if I could power it from the
    mains).

    Any other ideas?

    Thanks

  5. Re: Using parse driver rather then nmea driver?

    >I am actually using three seperate BU 303 GPS devices pointing in
    >different directions.


    Beware of the leap-second bug.

    I don't have a BU 303, but all the other SiRF units I've tried
    are off by a second for some strange pattern.
    http://www.megapathdsl.net/~hmurray/ntp/leap-gps.gif
    That happens when a leap-second is pending.

    >I know my position to within 10m (got from a roof reading with 9 sats
    >in view) so my confidence in the readings is high.
    >
    >I only need accuracy to about half a second but then need that machine
    >to be the stratum 1 server for the other machines in the environment.
    >For reasons I won''t bore you with they can't connect to an external
    >network connection so this seems the best solution?


    In theory, one satellite should be good enough if you know your
    location. That only works if the software in the GPS box supports
    that mode.

    --
    These are my opinions, not necessarily my employer's. I hate spam.


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