> Since he is used to machines that have operating systems, with system
> clocks and that sort of thing available to users, he might be able to
> do it on those.  But I do not think there is any way whatsoever on a
> PIC to do this.  (No peripherals -- just the raw chip running, with his
> program).

I can do this without writing any code at all.  Your PIC is running at
20MHz +-20MHz.  Without an accuracy constraint you lose immediately.

You also didn't specify what the external circuit constraints are.  The
watchdog timer can be used to measure the processor clock without any
external timing hardware required.  It's not very accurate, but it depends
on what your accuracy requirements are.


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