[ntp:questions] how to have offset < 1ms

Richard B. Gilbert rgilbert88 at comcast.net
Thu Apr 15 16:44:33 UTC 2010

unruh wrote:
> On 2010-04-15, Uwe Klein <uwe_klein_habertwedt at t-online.de> wrote:
>> nemo_outis wrote:
>>> It is frequently the case that OPs (for a variety of reasons) misstate or 
>>> mispecify their problem or overconstrain its solution (either in terms of 
>>> what can or must be done or what can't or mustn't).  I submit that the 
>>> current OP is a classic case.
>> The classic situation I've seen here on a regular basis is
>> that the submittant would like to have a cohesive timing situation
>> and does not care for syncronicity to the outside world.
>> The classic answer seems to be a handwaving jedi gesture.
>> You don't want that, you want "real" timekeeping.
> The easiest way to achieve cohesive timing is to have everything locked
> to real time. If everything is locked to real time, then everything is
> cohesive as well. And with the price of a GPS receiver, that is also
> often the cheapest way to do it as well. 
> Of course one can always just set on system to local time source  and have it as
> the server to everything else. That will, unless that particular machine
> suffers from severe temp variations, or other hardware problems, also
> work. Or I guess the new orphan mode of ntp. 
>> ( which imho is understandable, some here have put a significant
>>    amount of their lifetime into "real" timekeeping.
>>     The request thus is a distastefull abomination )
>> On the other hand cohesive group timing is quite sufficient in a lot of
>> applications. And lacking in agility to jump all the hoops presented
>> on the way towards "real" timekeeping this will just have to do in some
>> cases.
> What hoops? It is easy. Probably easier than worrying about cohesive
> timing in its absense. 
> Timekeeping to usec accuracy has become almost trivial. Now if someone
> would only start selling GPS18x with a usb/serial/parallel plug at the
> end of it, so one could just plug it in and not worry about soldering it
> would become totally trivial. ( Mind you some way of adding an extention
> to the 5m cable would also be useful)

My understanding is that USB is a poor choice due to large and 
unpredictable latencies.  I've never tried it because I never needed to.
My Motorola Oncore M12+T has an RS232-C serial interface that works very 

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