[time-nuts] Holdover, RTC for Pi as NTP GPS source
hmurray at megapathdsl.net
Wed Nov 1 17:04:20 EDT 2017
>> How are you planning on making ntp use the RTC as a secondary
>> time source? I don't see that as a supported refclk driver.
> hadn't got there yet likely using NTPsec, as the codebase is available if a
> driver or generic driver won't work
The PPS driver expects the pulse to be on the second. You won't get that
from a RTC.
If I was doing it, I use the SHM driver. Then you can do all your work in a
separate program and feed an offset to ntpd.
I haven't looked at RTC chips recently. You want a pulse that you can feed
to the kernel's PPS capture logic. 60Hz works on a PC. 32KHz is probably
too fast. (might be worth a try) You might have to add a divider.
If you use the GPS HAT from Adafruit, it has a prototyping area where you
could drop in a RTC and wire it up to various GPIO pins. DIP package would
be convenient. The Ethernet on the PI is via USB, so it's crappy for making
a nutty-good NTP server. But the PI is convenient and good enough for all
but nutty uses.
These are my opinions. I hate spam.
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