[time-nuts] Raspberry Pi NTP server

[Bob kb8tq]

Hi




> On Jul 6, 2020, at 11:43 AM, Matthias Welwarsky <time-nuts at welwarsky.de> wrote:
> 
> On Samstag, 4. Juli 2020 16:49:11 CEST David J Taylor via time-nuts wrote:
> 
>> Matthias, my feeling is that if you want a precision source, neither BB not
>> the RPi is a good solution.  Maybe with all the tweak you mentioned the BB
>> approaches precision (for some values of precision).  I see the RPi as
>> something which can provide far better NTP than simply using an Internet
>> source, something which will be adequate for the majority of users (for some
>> types of user!).
> 
> If your wall clock runs locked to GPS time, which it is by definition if you 
> drive its counter directly from a GPSDO, then it cannot drift away from GPS 
> time.


Sticking with the “wall clock” analogy for a bit here:

     The edge comes into the clock. 

     A device of some sort recognizes the edge

     This drives some sort of process inside that device.

     That process (eventually) gets around to talking to a stepper motor driver

     The stepper driver ramps up and “kicks” the motor based on it’s own internal design

     The stepper motor magnetizes and feeds a bit of energy to the clock mechanics. 

     There *may* be multiple kicks per second, depending on how the mechanical side was done

Everything past the “edge comes in” has variability to it. There are delays and those
delays probably are temperature and voltage dependent. Even in a *very* simple looking
system, the net result likely isn’t anywhere near 100 ns ….

Why dig into this? Pretty much every other timing device out there has the same sort
of multi layer problems ….. The sources will be different, but problems none the less. 

Bob




> ………..
> 
> As far as "for some types of users" is concerned - this list is called "time-
> nuts" for a reason, isn't it?
> 
> :-)
> 
> Best regards,
> Matthias
> 
> 
> 
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