[time-nuts] Holdover, RTC for Pi as NTP GPS source

MLewis mlewis000 at rogers.com
Wed Nov 1 19:21:43 EDT 2017

Is this a workable or worthwhile strategy?:
- RTC providing date & time to second to system on boot
- RTC frequency output driving a counter/divider to produce PPS
- GPS module providing UTC PPS
- GPS module's secondary PPS disciplining the RTC-counter-divider PPS by 
resetting the RTC's counter/divider (I'm assuming there's one that will 
rest fast enough to sync; I've never looked into these...)

If GPS PPS is lost, then the RTC counter/divider is producing a recently 
disciplined PPS.

Valid or invalid?

And the DS3231 has:
- a 32K output, and
- an Active-Low-Interrupt/SQW output that can be set to PPS.
It's unclear to me how to sync the DS3231 PPS to the GPS PPS, or if that 
can be done.



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