[ntp:questions] ntp & system without a rtc
David Lord
snews at lordynet.org
Wed May 15 19:46:39 UTC 2013
David Lord wrote:
> unruh wrote:
>> On 2013-05-14, David Woolley <david at ex.djwhome.demon.invalid> wrote:
>>> Richard B. Gilbert wrote:
>>>
>>>> NTPD is NOT designed for fast convergence. From start up to get the
>>>> minutes correct, NTPD will need about thirty minutes! To get the
>>>> best time you are going to get, you will need to wait for about ten
>>>> hours!
>>>>
>>> Convergence to within 128ms should take a lot less than that. With
>>> iburst, I believe it should be less than one minute.
>>
>> Since ntpd steps ( changes the rate by an infinite slope) if the time is
>> out by 128 ms, yes, convergence IS faster than that. ( however it has to
>> make sure that the clock really is out by that much and that takes a few
>> cycles of clock querrying).
>>
>> For a ms accuracy your could expect a couple of hours. for 10
>> microsecond, about 10 hr.
>>>>
>
> Hi
>
> I posted a reply on May 11, but did not give the ntpq stats
> as they'd already been archived away.
>
> After three reboots to replace kernel and userland taking
> around 10-15 minutes 'ntpq -p' with polling at 6 minutes gave
> the following:
>
> min reach offset jitter
>
> -18 377 -0.001 0.004
> -12 377 0.007 0.007
Ouch! I've checked with the actual times logged and there
was no poll logged at 19:30
19:24 -6 377 -0.001 0.006
19:30
19:36 0 0 0.000 0.000
19:42 6 17 -0.036 275.881
> 12 377 0.126 0.125
> 18 377 0.173 0.049
> 24 377 0.047 0.092
> 30 377 0.007 0.028
> 36 377 -0.001 0.007
> 42 377 -0.001 0.004
>
> There was a well established ntp.drift file and my rc.conf starts
> ntpd with flags="-g -N -p /var/run/ntpd.pid"
>
> NetBSD/6.1_RC3
> ntpd 4.2.6p5-o
> PPS from Sure demo board
>
>
> David
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