[time-nuts] Trimble Resolution SMT GG weirdness

[Hal Murray]

dginsburg at gmail.com said:
> First, the frequency offset of the microcontroller. I use a built-in
> counting timer in the uC which runs at 84MHz to measure the duration between
> 2 PPS. What I get is ~84008000 timer ticks between two pulses, which
> corresponds to about 95ppm offset. While the crystal on the board is of the
> cheapest variety, I think 95ppm is just too much. Is that correct, and 95ppm
> offset even for a the most crappy oscillator is not a reasonable value? 

It isn't totally unreasonable.

Yes, 95 PPM is the high end of even cheap crystals, but it could easily be a 
design error.  The capacitive loading of the circuit might not match the 
specs on the crystal.

There is also the possibility of a software bug.  OSes have a long history of 
not getting that quite right.  They are usually close enough so that nobody 
cares unless some geek starts monitoring the details.

-- 
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