[time-nuts] Thunderbolt GPS TimeKeeper

Javier Herrero jherrero at hvsistemas.es
Mon Jan 23 14:05:50 EST 2012

El 23/01/2012 19:29, Chris Albertson escribió:
> So back to time.   If the goal is keeping good time then it is best
> not to use Microsoft Windows.  There are good technical reasons having
> to do with the way MS Win. keeps and adjusts time.  The bottom line is
> that you will never be able to do better then about the millisecond
> level even with a directly attached GPS.   Using another OS, BSD or
> Linux you can do almost three orders of magnitude better.  (Three
> orders is huge.)  The OS and software is free and all you need is any
> computer that has a physical serial port, not USB but a real DB9
> connector.  This is a good use for a 10 year old notebook PC.  (The
> computational load is trivial so even a 486 class computer is OK)

I agree at all at not thinking on MS Windows for any precision timing 
task (even low precision). We have some systems with a Windows based 
workstation and Meinberg ntp distribution, and several linux embedded 
processors taking the time from the workstation using ntp in a LAN (with 
very very low traffic, also). This works well if you only need relative 
precision (i.e. 1 second) time difference to the workstation, but once 
we tried an application that required a synchronization between the 
linux processors and the windows system in the order of 10ms, and this 
never worked reliably. This is trivial to put into work in a LAN using 
ntp or chrony. By orders of magnitude.

And that to not speak about the windows time server, not fully ntp 
compatible but partially (to make things more confusing - the usual MS 
way of taking an industry standard and pervert it on its own way - 
rather imaginative also). You only need to have a look to this: 
http://support.microsoft.com/kb/939322 amd particularly to the 
paragraphs "We do not guarantee and we do not support the accuracy of 
the W32Time service between nodes on a network" and "The W32Time service 
cannot reliably maintain sync time to the range of 1 to 2 seconds". This 
explains all...



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