[time-nuts] an interesting problem

[Hal Murray]

> I've got a system at work with an internal clock oscillator that I want  to
> get some statistics on, but there's no direct visibility for the
> oscillator, nor do I have a convenient test point that I can probe. 
...


Fun problem.  Thanks for tossing it out.

I see two approaches.  Are there others?

One is to generate something like a PPS pulse and capture timestamps.  Then 
crunch the data and hope you see N buckets so you can ignore anything that 
isn't in bucket 0.  (or correct them by shifting by N ticks)

The other approach would be to measure the time between pairs of pulses.  You 
can probably do that much faster than once per second.  This should give you 
2*N buckets.

I can't quite figure out how far apart the pulses should be for best results. 
 (It will probably be simple after I see it.)  I expect it will depend on the 
ADEV of the measuring system and the ADEV of the clock you are trying to 
measure.

I assume you can get a rough ADEV of the clock you want to measure by 
measuring a similar part on a typical lab setup.

It's probably worth sanity checking the divide step to make sure it's 
dividing by M rather than M-1 or M+1.  (Digital geeks are often off by one, 
especially if nobody has checked carefully.)  I'm not sure how to do that.  
Probably something like divide by 2*M and see if it matches.  Or divide by a 
small M and measure the frequency.

-----------

Plan B would be to use an inconvenient test point. (or make one)

Years ago, my boss gave a neat talk about how to prototype hardware.  Step 0 
was hire a good technician.  :)



-- 
These are my opinions, not necessarily my employer's.  I hate spam.