[ntp:questions] step and stepout

David Woolley david at ex.djwhome.demon.invalid
Sun Jun 30 11:49:12 UTC 2013


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Orna Sumszyk wrote:

> My last question is how can I monitor the time offset from my ntp server
> during the running of ntpd to make sure this happens?

Use a PCI parallel port, or possibly a modem control signal on a PCI 
serial port.  Output a pulse on that port and also record the 
interpolated system time at that time.  Use a hardware counter to 
measure the the time difference between the pulses form the two machines 
and combine that with the information they output about their view of 
the time when they output the pulses.

Although loopstats will give you the "offset" used as input to the ntpd 
clock discipline algorithm, this includes various random and systematic 
errors that cannot be measured without special instrumentation, like 
that described above.  If they could be accurately measured in real 
time, ntpd would be using them to correct the time to a level at which 
the errors could no longer be corrected in that way.



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