[time-nuts] FreeBSD, NetBSD, or Minix-III?

Hal Murray hmurray at megapathdsl.net
Sun May 24 18:13:55 UTC 2009


> Also, someone I was discussing this with at work reminded me of a
> common problem.  We often run tests in a testbed where we need to have
> the entire testbed running at some time *not the actual time*.. E.g.
> If you're simulating a Mars entry,descent,landing scenario, you want
> the spacecraft running with "time" at the expected EDL time.  But, you
> want to have everybody sync'd to a common source.

> So, it's easy to get all the computers controlling the test gear
> sync'd to UTC or TAI using something like NTP, but you need a way to
> have precision "simulated time" as well. 

Is the "entire testbed" isolated from the rest of the network?  (If not, what 
do you do about the time warp?)

Just setup a ntpd running with the local clock (127.127.1.0).  Set the time 
manually and point all of your other boxes at it.  Details TBD.  You will 
probably have to restart ntpd since they won't jump more than 1000 seconds 
once it is running.

It local-server box keep (much) better time if you let it run normally for a 
while to calibrate the drift factor.

You can also use one of the refclock drivers that supports an offset fudge 
factor.  Just set the fudge factor to shift by the desired amount.  (I 
haven't tried it.  Please let me know if it does or doesn't work.)



-- 
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