[time-nuts] Trimble Resolution SMT GG weirdness
Hal Murray
hmurray at megapathdsl.net
Mon Apr 22 22:15:15 UTC 2013
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.
--
These are my opinions. I hate spam.
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