[time-nuts] simple, cheap clock for the local LAN

Bob Camp lists at rtty.us
Mon Apr 5 10:10:11 EDT 2010


Hi

You have two basic routes if you are trying to do what I *think* you are.

1) Set up an NTP server 

2) Set up a 1588 grand master clock

Both require client software on the other machines on your LAN. If you want the ultimate level of performance 1588 requires hardware time stamping in your LAN adapters. 

I'd suggest setting up NTP on something like a Soekris 45xx box. Run it on a battery and it's going to be a pretty reliable backup time source. Without a lot of effort it will give you milisecond level time. Hack an OCXO into the motherboard clock, do some tweaking and you can get into the 100's of nanoseconds. 

1588 without hardware time stamps will do microseconds. With hardware time stamps it will do nanoseconds. With some tweaking and 1588 aware switches it will do 10's of nanoseconds. 

Both systems have to get a time reference from somewhere. 1588 can take a pulse per second input. NTP has all sorts of drivers to hook to things like cesium standards and VLF time receivers. 

Of course I may have completely misunderstood what you are trying to do. 

Bob


On Apr 5, 2010, at 9:47 AM, Eugen Leitl wrote:

> 
> Hi, 
> 
> I'm thinking about putting a local clock standard (nothing too fancy,
> quartz would probably do) for the local LAN so that I have more or
> less stable clocks when GPS is down for whatever reason.
> 
> I have zero clue about time standards for the low end. Can anyone
> recommend anything affordable? Thanks.
> 
> -- 
> Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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