[time-nuts] An embedded NTP server

Chris Albertson albertson.chris at gmail.com
Tue Dec 25 22:22:21 UTC 2012

This is good.  And really good that you have opened the design.  Once
a few of these get out into the "wild" you can start seeing software
contributions and the performance will improve.   We know that an ARM
based NTP server can do very well.  Hopefully it can one day beat a
low-end Linux setup which runs in the "few" uSecond range.  You should
be able to do it.

Does the uP have enough RAM to run a stripped down OS, some kind of tiny Linux?

On Tue, Dec 25, 2012 at 12:44 PM, Michael Tharp
<gxti at partiallystapled.com> wrote:
> On 12/25/2012 02:51 PM, David J Taylor wrote:
>> I think you should be able to do better on the jitter as your algorithms
>> develop.
> Yes, for starters something is causing a silly amount of extra latency hence
> the 2.4ms round-trip. I managed to cut that in half by changing compiler
> options but talking to someone using the same stack I should be able to get
> it down to ~ 400us round-trip, at worst. I have some ideas on how to achieve
> that but I want to get all the functionality working before I start
> optimizing.
> The main lack of functionality, which may or may not be the cause of the
> jitter, is that I haven't actually integrated the PLL/disciplining stuff
> yet. I just have a timer that resets with each GPS pulse, and runs at
> whatever nominal frequency the oscillator has. Not great but it succeeded at
> getting results fast. Not up to time-nuts standards though. Now I'm going
> back and adding the PLL.
>> "SNTP" does imply something else, so perhaps avoid calling it that,
>> although if it doesn't respond to all the NTP management calls I'm
>> unsure what it should be called!
> I suppose that I could call it NTP and still sleep at night since, while not
> a traditional NTP implementation, it does still feature control loops
> similar to those found in purely software-based NTP. I have not yet looked
> at what administrative/query functionality I could implement. Some of it
> like listing peers does not make sense but perhaps other commands could be
> mapped to make it more complete. I would also like to expose some of the
> internal statistics via SNMP or some other means for graphing.
>> Oh, and your Windows box is either poorly configured or
>> broken - they can work much, much better than yours illustrates as I
>> expect you know.
> Yes, it's not healthy. I installed Meinberg's NTP build and configured it
> using defaults other than the server list but it seems to not be tracking
> well. Right now it's "only" 30ms off but as shown in the forum snippet it
> makes excursions into the hundreds. Still an improvement over default
> Windows timekeeping but I'd love for it to work properly.
> -- m. tharp
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Chris Albertson
Redondo Beach, California

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