[time-nuts] Lowest Power NTP Server

[Hal Murray]

kb8tq at n1k.org said:
> For a server (that gets inquiries at any time) the “wake up” process is going
> to be a problem with a deep sleep approach. The GPS on the server also would
> need to wake  up and get going. That combo is going to give you a mighty long
> turn around time on a request. I also suspect that the requests will come in
> often enough (compared to a  minute or two long GPS lockup) that it would
> never go into deep sleep anyway.

Handwave.  Probably more work than you want to do, but ...

I could imagine a setup where everybody wakes up at the same time, does some 
work, then goes back to sleep.  The NTP server might have to wake up earlier 
in order to get the GPS going.

You should be able to keep time at the ms level for an hour or 6 without GPS.  
Longer if you do temperature compensation.

Do you need time synced to UTC or just everybody dancing in step?

----------

In the old days, systems used a periodic interrupt from the RTC for 
timekeeping.  The next step was to use a cycle-counter running off the CPU 
clock to interpolate between ticks.  Modern systems just use the CPU clock.  
For ms level accuracy at low power, I could imagine going back to timing based 
on the RTC.

It may be simpler to keep your own clock in parallel with the OS rather than 
beat the OS into recovering good time after sleeping.  One of the problems 
with RTCs is that you can only read them to the second.  You can get much 
better time by polling to watch for the second to change.  Better would be to 
set them up to interrupt on the second boundary and run the interrupt line 
into a GPIO setup as a PPS input.  (Maybe newer RTCs have a sub-second 
register.)



-- 
These are my opinions.  I hate spam.