[time-nuts] Lowest Power NTP Server

[Bob kb8tq]

Hi

There are a bunch of devices out each doing their own thing. Some are running
100% of the time, others get power cycled “as needed”. There also are a range
of OS’s involved. Having everybody wake up at once …. not practical.  However 
if the “broadcast” NTP approach was the method of choice, then a wake up and
do it would work. for. the server.

Bob



> On Dec 4, 2019, at 5:23 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> 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.
> 
> 
>