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

Uwe Klein uwe_klein_habertwedt at t-online.de
Thu Apr 15 16:09:36 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
> What hoops? It is easy. Probably easier than worrying about cohesive
> timing in its absense. 

You are thinking in terms of experimental lab utility.
( and I tend to do that for experimental setups too, but:)

You should think in terms of reproduceability / qualification / certification
and the need for breaching management firewalling.

If I needed to closely sync the set of two, later three embedded pc104/linux
based spectrometers, my customer has installed on a SOFIA backend, I would
either need to push for ntp service from the aircraft infrastructure or find a
contained solution. Nailing a Garmin unit to the frames wouldn't really cut it ;-)

The paperwork for the enclosures readily consumed a small orchard and took
more than a year of time to get past all obstacles.

Additionally you get dependencies on external infrastructure.
Your setup no longer is a contained system.


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