[ntp:questions] Any chance of getting bugs 2164 and 1577 moving?

David Lord snews at lordynet.org
Thu Mar 22 02:10:19 UTC 2012

Alby VA wrote:
> On Mar 21, 8:16 pm, David Lord <sn... at lordynet.org> wrote:
>> Alby VA wrote:
>>> On Mar 21, 7:36 pm, unruh <un... at invalid.ca> wrote:
>>>> On 2012-03-21, Alby VA <alb... at empire.org> wrote:
>>>>> On Mar 21, 3:55?pm, unruh <un... at invalid.ca> wrote:
>>>>>> On 2012-03-21, David J Taylor <david-tay... at blueyonder.co.uk.invalid> wrote:
>>>>>>> "unruh" <un... at invalid.ca> wrote in message
>>>>>>> news:itmar.5841$yD7.508 at newsfe15.iad...
>>>>>>> []
>>>>>>>> But -19 is about 2 microseconds if I understand it correctly. That means
>>>>>>>> that the clocks are incapable of delivering more than about 2
>>>>>>>> microseconds of accuracy. What is you ?that last decimal digit of
>>>>>>>> accuracy in the offset is thus pure noise-- dominated by clock reading
>>>>>>>> noise. Why is it important for you then?
>>>>>>> When I can see the decimal places, then I will know whether the precision
>>>>>>> estimate is reasonable. ?Just getting values such as -1, 0, 1 microseconds
>>>>>>> is insufficient to make that call.
>>>>>> And how will the extra decimals help? The -19 was determined by making
>>>>>> successive calls to the clock and seeing how much it changed between
>>>>>> successive readings. That gives a good estimate of how long it takes to
>>>>>> make a call to the clock. Any precision in the answer beyond that is not
>>>>>> accuracy. I could give you the time to 60000 decimal places, each one of
>>>>>> the diffetent, but the last 5995 just being garbage (random numbers)
>>>>>> Would that tell yo uanything?
>>>>>> If for some reason you do not believe ntpd's estimation of your clock
>>>>>> accuracy, develope a better algorithm for determining it. It is a bug is
>>>>>> ntpd is reporting an accuracy much worse than it actually is.
>>>>>> Ie, you have no data to make that call even if you get more digits.
>>>>>>> David
>>>>> unruh:
>>>>>   My take is the precision output might say your device is -19 so you
>>>>> know its
>>>>> accuracy is around 2/microseconds. But the offset several decimal
>>>>> places
>>>>> allows you to see its ever changing accuracy within that 2/microsecond
>>>>> band
>>>> But that is not accuracy. That is presumably (if that -19 is accurate
>>>> and not a bug) is simply noise. If your measurement technique is only
>>>> good to 2us, then any additional precision is just noise. It may be fun
>>>> to see the noise, but not terribly useful. If it is not noise, then that
>>>> -19 is wrong, and one has a bug in the determination of the accuracy of
>>>> the clock reading.
>>>>> to a greater detail than just -1, 0, or 1 microseconds. I guess its
>>>>> just a matter
>>>>> of getting more granular details for cool MRTG charting. :)
>>>> It could well be that charting looks better without just bands on the
>>>> page. But is it worth it if that detail is just junk? It certainly is
>>>> not great art.
>>>  It there any good way to determine what is noise and what isn't?
>> ntpq -c rv gives output including precision= , which on
>> my server indicates precision=-19 which is 1/(2^19) or
>> approx = 2us
>> David
>  Yup. I'm getting the same thing, precision = -19
> In the math, I get 0.0000019073486328125 (1.907/microseconds).
>  To improve this to better precision, would the only path of success
> be
> in getting a better stratum 0 device?

Probably not but it depends on the specification of
your GPS. The problem is in getting the PPS pulse into
the computer.

Take a look at www.ko4bb.com and www.febo.com.

I'm not sure if it's a soekris board that can be modified
to accept a PPS signal via an input pin rather than via
rs232 and interrupt.


> assID=0 status=0415 leap_none, sync_uhf_clock, 1 event,
> event_clock_reset,
> version="ntpd 4.2.6p5 at 1.2349-o Mon Feb 20 22:00:33 UTC 2012 (1)",
> processor="amd64", system="FreeBSD/9.0-RELEASE", leap=00, stratum=1,
> precision=-19, rootdelay=0.000, rootdisp=0.297, refid=PPS,
> reftime=d314f812.ee1ec4ca  Wed, Mar 21 2012 21:00:02.930,
> clock=d314f817.b13ef313  Wed, Mar 21 2012 21:00:07.692, peer=21829,
> tc=4, mintc=3, offset=0.002, frequency=-24.569, sys_jitter=0.002,
> clk_jitter=0.002, clk_wander=0.001

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