unruh wrote:
On 2010-04-15, Uwe Klein <[email protected]> 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.
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.
uwe
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