Re: Keeping a VERY accurate time (within a millisecond) - Networking

This is a discussion on Re: Keeping a VERY accurate time (within a millisecond) - Networking ; On 2008-09-06, Unruh wrote: > Ignoramus10032 writes: > >>I want my ubuntu servers to keep a VERY accurate time. That is, I want >>to have a clock accurate to less than a millisecond. > > Buy a Gamin 18LVC gps ...

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Thread: Re: Keeping a VERY accurate time (within a millisecond)

  1. Re: Keeping a VERY accurate time (within a millisecond)

    On 2008-09-06, Unruh wrote:
    > Ignoramus10032 writes:
    >
    >>I want my ubuntu servers to keep a VERY accurate time. That is, I want
    >>to have a clock accurate to less than a millisecond.

    >
    > Buy a Gamin 18LVC gps receiver (about $70). Wire it up to your system and use one of
    > the refclocks for that. (eg refclock_nmea)
    > (Although I wrote my own interrupt routine to grab the pps) It can keep
    > your clock accurate to about 3usec (that is usec not msec)
    > You do need to mount the gps where it can see the sky.


    After I made my post, I realized that I have a DeLuo USB based GPS. I
    am running it right now, and I was actually very impressed. At this
    moment I am a passenger in a moving car, running gpsdrive, looking at
    the map, etc. It's all very cool.

    Man pages of gpsd suggest that I can synchronize NTP to gpsd. There
    are some warnings that it may not be very accurate, however, but I
    will see.

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  2. Re: Keeping a VERY accurate time (within a millisecond)

    Ignoramus10032 writes:

    >On 2008-09-06, Unruh wrote:
    >> Ignoramus10032 writes:
    >>
    >>>I want my ubuntu servers to keep a VERY accurate time. That is, I want
    >>>to have a clock accurate to less than a millisecond.

    >>
    >> Buy a Gamin 18LVC gps receiver (about $70). Wire it up to your system and use one of
    >> the refclocks for that. (eg refclock_nmea)
    >> (Although I wrote my own interrupt routine to grab the pps) It can keep
    >> your clock accurate to about 3usec (that is usec not msec)
    >> You do need to mount the gps where it can see the sky.


    >After I made my post, I realized that I have a DeLuo USB based GPS. I
    >am running it right now, and I was actually very impressed. At this
    >moment I am a passenger in a moving car, running gpsdrive, looking at
    >the map, etc. It's all very cool.


    Ssure, but probably useless for timing. To be useful for timing th gps MUST
    have a PPS output. AFAIK no usb one does. And almost no consumer one does.


    >Man pages of gpsd suggest that I can synchronize NTP to gpsd. There
    >are some warnings that it may not be very accurate, however, but I
    >will see.


    Sure. It will be accurate to about 10ms after a lot of fiddling to figure
    out exactly how late the time delivered actually is. (if you use it raw it
    will be out by about 500ms too slow)




  3. Re: Keeping a VERY accurate time (within a millisecond)

    On 2008-09-06, Unruh wrote:
    > Ignoramus10032 writes:
    >
    >>On 2008-09-06, Unruh wrote:
    >>> Ignoramus10032 writes:
    >>>
    >>>>I want my ubuntu servers to keep a VERY accurate time. That is, I want
    >>>>to have a clock accurate to less than a millisecond.
    >>>
    >>> Buy a Gamin 18LVC gps receiver (about $70). Wire it up to your system and use one of
    >>> the refclocks for that. (eg refclock_nmea)
    >>> (Although I wrote my own interrupt routine to grab the pps) It can keep
    >>> your clock accurate to about 3usec (that is usec not msec)
    >>> You do need to mount the gps where it can see the sky.

    >
    >>After I made my post, I realized that I have a DeLuo USB based GPS. I
    >>am running it right now, and I was actually very impressed. At this
    >>moment I am a passenger in a moving car, running gpsdrive, looking at
    >>the map, etc. It's all very cool.

    >
    > Ssure, but probably useless for timing. To be useful for timing th gps MUST
    > have a PPS output. AFAIK no usb one does. And almost no consumer one does.
    >
    >
    >>Man pages of gpsd suggest that I can synchronize NTP to gpsd. There
    >>are some warnings that it may not be very accurate, however, but I
    >>will see.

    >
    > Sure. It will be accurate to about 10ms after a lot of fiddling to figure
    > out exactly how late the time delivered actually is. (if you use it raw it
    > will be out by about 500ms too slow)


    Yes, it does not seem satisfactory...

    --
    Due to extreme spam originating from Google Groups, and their inattention
    to spammers, I and many others block all articles originating
    from Google Groups. If you want your postings to be seen by
    more readers you will need to find a different means of
    posting on Usenet.
    http://improve-usenet.org/

  4. Re: Keeping a VERY accurate time (within a millisecond)

    Unruh wrote:
    > Ignoramus10032 writes:
    >
    >> On 2008-09-06, Unruh wrote:
    >>> Ignoramus10032 writes:
    >>>
    >>>> I want my ubuntu servers to keep a VERY accurate time. That is, I want
    >>>> to have a clock accurate to less than a millisecond.
    >>> Buy a Gamin 18LVC gps receiver (about $70). Wire it up to your system and use one of
    >>> the refclocks for that. (eg refclock_nmea)
    >>> (Although I wrote my own interrupt routine to grab the pps) It can keep
    >>> your clock accurate to about 3usec (that is usec not msec)
    >>> You do need to mount the gps where it can see the sky.

    >
    >> After I made my post, I realized that I have a DeLuo USB based GPS. I
    >> am running it right now, and I was actually very impressed. At this
    >> moment I am a passenger in a moving car, running gpsdrive, looking at
    >> the map, etc. It's all very cool.

    >
    > Ssure, but probably useless for timing. To be useful for timing th gps MUST
    > have a PPS output. AFAIK no usb one does. And almost no consumer one does.
    >
    >
    >> Man pages of gpsd suggest that I can synchronize NTP to gpsd. There
    >> are some warnings that it may not be very accurate, however, but I
    >> will see.

    >
    > Sure. It will be accurate to about 10ms after a lot of fiddling to figure
    > out exactly how late the time delivered actually is. (if you use it raw it
    > will be out by about 500ms too slow)
    >
    >
    >

    You may wish to look at this:

    http://www.cis.udel.edu/%7Emills/dat...apers/fine.pdf

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    /V\ PGP-Key: 9A2FC99A Registered Machine 241939.
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