setting the time using gps-time and pps withoutntpd? - NTP

This is a discussion on setting the time using gps-time and pps withoutntpd? - NTP ; Hello, recently I tried building a microsecond precision timeserver using a gps-device with pps signal. The gps-data is transmitted via usb, the pps signal via the rs232 carrier detect line. I tried several drivers and they all worked, but I ...

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Thread: setting the time using gps-time and pps withoutntpd?

  1. setting the time using gps-time and pps withoutntpd?

    Hello,

    recently I tried building a microsecond precision timeserver using a
    gps-device with pps signal.

    The gps-data is transmitted via usb, the pps signal via the rs232
    carrier detect line.

    I tried several drivers and they all worked, but I had to figure that
    obviously my mainboard (via epia en12000EG) has terrible jitter. - unusable!

    To solve the problem I think about simply setting the time every n
    seconds according to the collected gps time and the pps-signal. My
    system will run off for far less than a microsecond in an interval of
    let's say, 20 seconds or so. Like this I would implement a constantly
    jumping time, but the amount of jumps would be extremely small.

    Since I learned that timekeeping is a very complex topic, I thought, I'd
    better ask on this list, before I build something troublesome without
    even knowing..

    What do you think?

    With best regards,
    .../nico berndt

  2. Re: setting the time using gps-time and pps without ntpd?

    >>> In article <480DB716.1000404@komeda-berlin.de>, nb@komeda-berlin.de (Nicola Berndt) writes:

    Nicola> Hello, recently I tried building a microsecond precision timeserver
    Nicola> using a gps-device with pps signal.

    Nicola> The gps-data is transmitted via usb, the pps signal via the rs232
    Nicola> carrier detect line.

    Nicola> I tried several drivers and they all worked, but I had to figure
    Nicola> that obviously my mainboard (via epia en12000EG) has terrible
    Nicola> jitter. - unusable!

    Your best hope will be to get that PPS signal delivered to either a real
    serial port (no USB) or a pin on a parallel port.

    The jitter on USB serial is large, as you have seen.

    --
    Harlan Stenn
    http://ntpforum.isc.org - be a member!

  3. Re: setting the time using gps-time and pps without ntpd?

    nb@komeda-berlin.de (Nicola Berndt) writes:

    >Hello,


    >recently I tried building a microsecond precision timeserver using a
    >gps-device with pps signal.


    >The gps-data is transmitted via usb, the pps signal via the rs232
    >carrier detect line.


    >I tried several drivers and they all worked, but I had to figure that
    >obviously my mainboard (via epia en12000EG) has terrible jitter. - unusable!


    Are you sure that it is not the reading of the time that is the problem.
    What gps do you use? Are you sure it really has and is using PPS?
    And what do you call "terrible"



    >To solve the problem I think about simply setting the time every n
    >seconds according to the collected gps time and the pps-signal. My
    >system will run off for far less than a microsecond in an interval of
    >let's say, 20 seconds or so. Like this I would implement a constantly
    >jumping time, but the amount of jumps would be extremely small.


    Just use ntp to discipline your clock. No need to try to bacly reinvent
    something.


    >Since I learned that timekeeping is a very complex topic, I thought, I'd
    >better ask on this list, before I build something troublesome without
    >even knowing..


  4. Re: setting the time using gps-time and pps withoutntpd?

    Unruh schrieb:
    > nb@komeda-berlin.de (Nicola Berndt) writes:
    >
    >> Hello,

    >
    >> recently I tried building a microsecond precision timeserver using a
    >> gps-device with pps signal.

    >
    >> The gps-data is transmitted via usb, the pps signal via the rs232
    >> carrier detect line.

    >
    >> I tried several drivers and they all worked, but I had to figure that
    >> obviously my mainboard (via epia en12000EG) has terrible jitter. - unusable!

    >
    > Are you sure that it is not the reading of the time that is the problem.
    > What gps do you use? Are you sure it really has and is using PPS?
    > And what do you call "terrible"
    >


    I use a Conrad USB-Receiver that contains a U-Blox board. I took the
    PPS-Signal from the according pins inside the device myself and tested,
    if it sends a pulse every second and it does. So that looks ok to me.

    "Terrible" I call that I can watch the jitter with ntpq -p jump from -50
    to 50. I assume those are microseconds, so +/-50 ms makes 1/10 seconds.
    I can set any clock that precise using my bare hands

    The next problem I actually stumbled across is the long time ntpd needs
    to settle. The system I inted to build has to be ready right after the
    start, because the pc lies in a shelf, off, and is switched on right
    when needed. There is no way to let it run, since it is battery-driven.
    >
    >
    >> To solve the problem I think about simply setting the time every n
    >> seconds according to the collected gps time and the pps-signal. My
    >> system will run off for far less than a microsecond in an interval of
    >> let's say, 20 seconds or so. Like this I would implement a constantly
    >> jumping time, but the amount of jumps would be extremely small.

    >
    > Just use ntp to discipline your clock. No need to try to bacly reinvent
    > something.


    Oh, I happily would, I just didn't get it to work and gave up at some
    point (after days..)

    best regards,
    .../nico

  5. Re: setting the time using gps-time and pps without ntpd?

    Nicola Berndt wrote:

    > I use a Conrad USB-Receiver that contains a U-Blox board. I took the
    > PPS-Signal from the according pins inside the device myself and tested,


    It's still unclear to me. In your original post you wrote that you used
    USB for the gps data and the RS232 CD line for the PPS pulse, but now it
    seems like maybe you also feed the PPS through USB (bad idea).

    A quick glance over the specs tells me that your mainboard has a serial
    port. Do you use it?

    N

  6. Re: setting the time using gps-time and pps withoutntpd?

    Nero Imhard schrieb:
    > Nicola Berndt wrote:
    >
    >> I use a Conrad USB-Receiver that contains a U-Blox board. I took the
    >> PPS-Signal from the according pins inside the device myself and tested,

    >
    > It's still unclear to me. In your original post you wrote that you used
    > USB for the gps data and the RS232 CD line for the PPS pulse, but now it
    > seems like maybe you also feed the PPS through USB (bad idea).
    >
    > A quick glance over the specs tells me that your mainboard has a serial
    > port. Do you use it?
    >
    > N
    >
    > _______________________________________________
    > questions mailing list
    > questions@lists.ntp.org
    > https://lists.ntp.org/mailman/listinfo/questions

    Hi all,

    just wanted to let everyone that answered me, that I will be gone until
    monday and have a further look into things then.

    I'm in a rush right now, but in short: I used rs232 for pps and usb for
    gps. I used the shm-driver and two others, just forgot the name and have
    no time to look them up.

    Thx, anyway and I'll report back monday..

    Nice weekend!
    .../nico


    --
    Nico Berndt
    KOMEDA

    Reichenberger Strasse 8
    10999 Berlin

    nb@komeda-berlin.de

    +49 30 / 6730 1395
    +49 177 / 335 3562

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