[ha] Time Synchronization

Rich (rah.at.atdot.org)
Sun, 25 Oct 1998 23:12:53 -0500

> What if two or more clocks disagree? In the same way, what if two or
> more sensors disagree on the state of something, like the openness of a
> door, or the presence of a person? Maybe the protocol needs support
> for resolving uncertainties like this.

Reading a lot of science-fiction and thriller novels (Robert Ludlum
and Tom Clancy) bring this obvious solution to mind: any critical
process must be controlled by three controllers, of which no fewer
than two can agree on what to do. If two agree, the third is marked
as 'suspect' or 'dirty' and it is more carefully watched; any further
deviation could mark the controller 'offline' (all other controllers
would ignore its commands) and generate an exception on the
control bus for someone to pick up.

> the clocks receive the MSF 60kHz radio signal transmitted
> from the national frequency standard at NPL in Rugby. Possibly a bit far
> away to much use:-) But surely NIST or someone does something similar?

Yes, NIST broadcasts time ticks on WWV in Boulder, CO and
WWVH in Honolulu, HI on various frequencies, all of which escape
me at the moment. :-{) I have seen 'fancy' clocks that can pick
up these signals, most of which are advertised in amateur radio
publications. Your report is the first I've heard of modules that can
be added to the clocks. Or am I misunderstanding this?

> The clocks are either small digital or analogue alarm clocks that
> I bought from various sources---none of them very expensive (about
> $30-$50)---or conventional clocks whose mechanisms I have replaced with
> the radio-controlled modules. These look like conventional quartz clock
> modules (55mm square, powered by a single AA battery) and cost 17 pounds
> ($28) from Maplin (a large hobby-electronics mail-order company).

"Hey, nice crysknife!"