[time-nuts] LTE-Lite module
Charles Steinmetz
csteinmetz at yandex.com
Sat Oct 25 15:23:57 UTC 2014
Bob wrote:
>PHK has a roughly 6 line code snippet that does a basic PLL. Add two
>more lines to check / clamp the integrator if you wish. That's 8
>lines. If you want a D term (to give it an FLL component) add 2 more
>lines. We're up to 10 lines.
>
>It's just a control loop, not a full GPSDO. There's not a lot to it.
There's a bit more to it than that. For any loop slow (narrowband)
enough to be useful disciplining a good OCXO, I consider a dual- or
triple-rate loop filter to be essential. There is also always a fair
amount of error-trapping, and other overhead. These can add lines
fairly quickly.
I'm sure I have lots more to learn about writing efficient
code. (But note that there is a difference between coding one's
chosen algorithm more efficiently and choosing a different algorithm
that is not really what you want, just because it is more efficient.)
Best regards,
Charles
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