[ntp:questions] Re: HowTo calibrate system clock frequency using NTP

David L. Mills mills at udel.edu
Mon Feb 6 22:15:39 UTC 2006


Daniel,

The peer offset is recorded for each client/server exchange. Let it run 
for a few hours and record the time of day and the offsets at the 
beginning and end. Subtract and divide by the interval. It's really not 
complicated.

Dave

Daniel Kabs wrote:
> Good afternoon David,
> 
> I think we are talking at cross-purposes: in case of Plan B, you 
> suggested to use the option "disable ntp" (so there should be no 
> frequency correction) and to read the time offset at intervals using
>    ntpq -c 'rv <assoc_id_of_peer>'
> 
> If I configure ntp that way, this is how the billboard looks on my 
> system after some days of running time:
> 
> # ntpq -c 'rv 16532'
> status=9634 reach, conf, sel_sys.peer, 3 events, event_reach,
> srcadr=10.0.0.254, srcport=123, dstadr=0.0.0.0, dstport=123, keyid=0,
> stratum=1, precision=-18, rootdelay=0.000, rootdispersion=6.989,
> refid=DCFa, reftime=c7919b26.416249a1  Mon, Feb  6 2006 10:53:42.255,
> delay=0.688, offset=-114389.792, jitter=75.264, dispersion=0.947,
> reach=377, valid=7, hmode=3, pmode=4, hpoll=6, ppoll=6, leap=00,
> flash=00 ok, org=c7919b4f.ed9e6256  Mon, Feb  6 2006 10:54:23.928,
> rec=c7919bc2.517e5647  Mon, Feb  6 2006 10:56:18.318,
> xmt=c7919bc2.514cec41  Mon, Feb  6 2006 10:56:18.317,
> filtdelay= 0.69    0.68    0.77    0.79    0.88    0.77    0.69    0.69,
> filtoffset= -114389 -114372 -114353 -114335 -114316 -114299 -114282 
> -114264,
> filtdisp=  0.01    0.97    1.96    2.92    3.91    4.87    5.83    6.82
> 
> 
> I was asking about reading the "offset" variable:
>     offset=-114389.792
> What is the corresponding time when this variable was set? The
> billboard show several candidates ("reftime", "org", "rec" or "xmt"), 
> but I don't know which one is the correct one.
> 
> 
> Cheers
> Daniel
> 
> 
> David L. Mills wrote:
> 
>> Daniel,
>>
>> Your question does not parse. The frequency correction has nothing to 
>> do with the state variables you quote. The time the frequency 
>> correction is monitored is prominently displayed on the ntpq rv 
>> billboard.
>>
>> Dave




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