Re: Variations on XTAL clock AND time synchronization

From: Peter (moocowmoo_at_newprovidence.demon.co.uk)
Date: 02/19/05 

Date: Sat, 19 Feb 2005 12:35:09 -0000

<Sunwaesh> wrote in message
news:4217214a$0$1998$afc38c87@news.optusnet.com.au...
> Jerry G.,
>
> Thank you for your valuable answer.
> In a project I need to have time synchronization between a set of
> computers where some of them are networked together on a LAN (no internet)
> and some others are running stand alone. I am planning to use the
> one-pulse-per-second (1PPS) signal from the GPS receivers. The networked
> computers will have one GPS receiver and all the other stand alone
> computers will have their own GPS receivers. GPS receivers will generate
> 1PPS signals to interrupt the computers to set their internal time clocks.
> Applications will use the computer timer (get the time of the day). I want
> to model (some how, but I do not know how) the probable variation that a
> computer clock may have between 1PPS signals.
>
> Would anyone comment/argue/recommend/suggest/propose how one can model the
> variation on a PC clock frequency ?
>

You should have mentioned your project in your first post.

For the networked PCs you can use Network Time Protocol. Run an NTP server
on your time standard PC and run clients on all the others. This learns the
error rate of the PC clock and gently slews the time of the client to keep
it in sync. This ensures that the time is monotonic (always goes forwards)
and doesn't have discontinuities. It also has the great advantage that you
just have to install it as everything has been written for it already.

For the standalone PCs the simplest model that I can think of is that the PC
clock runs at fairly constant but slightly incorrect speed. When you have
measured the rate of time drift you can estimate what the offset you need
for the correct time. You will have to average it out over a long time to
get an accurate value. You should always be measuring the drift so that you
can adapt to change in the rate of drift. This should be stable enough for
anything that a PC needs to do.

Peter

Relevant Pages

  • Re: Variations on XTAL clock AND time synchronization
    ... > computers where some of them are networked together on a LAN (no internet) ... > computers will have their own GPS receivers. ... > computer clock may have between 1PPS signals. ...
    (comp.arch.embedded)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers where some of them are networked together on a LAN (no internet) ... > computers will have their own GPS receivers. ... > computer clock may have between 1PPS signals. ...
    (sci.electronics.misc)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers where some of them are networked together on a LAN (no internet) ... > computers will have their own GPS receivers. ... > computer clock may have between 1PPS signals. ...
    (sci.electronics.components)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers will have one GPS receiver and all the other stand alone computers ... GPS receivers will generate 1PPS signals ... > variation on a PC clock frequency? ... >>install the hardware and software in your computer to work with it. ...
    (sci.electronics.misc)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers will have one GPS receiver and all the other stand alone computers ... GPS receivers will generate 1PPS signals ... > variation on a PC clock frequency? ... >>install the hardware and software in your computer to work with it. ...
    (sci.electronics.components)