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

Bob kb8tq kb8tq at n1k.org
Wed Nov 1 20:07:15 EDT 2017


The normal NTP kernel does a pretty good job in “flywheel” mode. For modest 
outages, it’s quite adequate. 


> On Nov 1, 2017, at 7:21 PM, MLewis <mlewis000 at rogers.com> wrote:
> 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.
> Thanks,
> Michael
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