[time-nuts] Brooks Shera

Chris Albertson albertson.chris at gmail.com
Mon Mar 25 14:18:06 EDT 2013

> Ie the output of the counter becomes
> (more or less) random. Which in turn means the lower 4 bit of the
> input to the PI control loop are wrong[1]. Or in terms of time, we
> might be off by +/-2^4*42ns=672ns, which is a major hit against the
> PI loop (like knocking it with a sledge hammer).

But these numbers don't go directly to the PI loop, there is a
software layer between that can inspect for outliers.

This is how engineers can reduce costs by knowing when something needs
to be perfect and when it does not need to be.   In the end the
controller works about as good as it needs to.    What saves this is
the unstably of the cheap 24MHz clock.  If the clock problem happens
the randomness will make it soon stop happening and the software can
just ignore the outliers.  You have to look at the whole system and
not just the hardware.  Much of the functionality is in the software.


Chris Albertson
Redondo Beach, California

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