Re: Clock Synchronization

["Marin D. Condic" <mcondic-nospam@acm.com>]

Dr. Michael Paus wrote:
> We are running a distributed application on three PowerPC boards
> which are connected via VME-Bus. The application is written in
> Ada 95 (GNAT) and we use LynxOS as our RTOS. The problem we are
> facing is that we need highly synchronized (~1ms) clocks on
> each board. We are sending messages with time-stamps back and forth
> and so it is important that each part of the application has the
> same understanding of the time. Does anybody have an idea of how
> to accomplish this without putting too much extra load on the
> system? Does anybody know of a hardware solution for this problem
> (a common clock which can be read from all CPU-boards)?

Try these guys: http://www.datum.com/

When you have multiple computers that you need to synch up to a high
degree of accuracy, nothing beats a hardware solution. The Datum guys
make network time references that are accurate enough for almost any
need. If you need better accuracy, you might want to consult with:
http://www.nist.gov/ http://www.bldrdoc.gov/timefreq/ Of course, getting
the time across the net is pointless since you can't guarantee TCP/IP
propogation delays. You'd have to go with some sort of radio source and
correct for speed of light.

Software synchronization of the different CPU's clocks could be a
problem. It depends a lot on what you have to communicate with between
the different CPUs. Lots of communication mechanisms are not
deterministic, so it becomes impossible to synchronize with any high
degree of accuracy or confidence.

Hope this helps.

MDC
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Marin David Condic - Quadrus Corporation - http://www.quadruscorp.com/
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