[ntp:questions] ntp & system without a rtc
snews at lordynet.org
Wed May 15 19:18:25 UTC 2013
> 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.
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as they'd already been archived away.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
min reach offset jitter
-18 377 -0.001 0.004
-12 377 0.007 0.007
-6 377 -0.001 0.006
0 0 0.000 0.000
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"
PPS from Sure demo board
More information about the questions