[time-nuts] Lowest Power NTP Server
Bob kb8tq
kb8tq at n1k.org
Wed Dec 4 22:45:39 UTC 2019
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.
>
>
>
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