[time-nuts] NTP Clock suggestions?

Bob Camp lists at rtty.us
Mon May 27 14:41:52 EDT 2013


SNTP probably is ok if you are running against an NTP server hardwired on a local LAN. Running it through a home modem and out onto the internet likely isn't going to be as good as a full blown NTP stack. You could quite easily get enough lag / delay to get into the ~ 100 to 200 ms region that you can see on a clock. 


On May 27, 2013, at 2:33 PM, Graham / KE9H <TIMENUT at austin.rr.com> wrote:

> Miguel:
> If you are going to build your own, I would recommend you start with
> something like the Microchip PIC32 Ethernet Starter Kit. Comes
> with a free GCC C/C++ compiler and an Ethernet stack.
> I happened to have one for another project, that already had a
> four line serial LCD display hooked to it, as well as a serial port
> command line interface running
> Since I was already familiar with the Ethernet Stack that comes with
> the Starter Kit, all it took was turning on the SNTP function in the
> stack, and writing about ten lines of C code to get it running.
> One update of NTP sourced UTC Hours-Minutes-Seconds time on the
> display per command line request. (Anything more complicated is left as
> an exercise for the student.)
> That was after about an hour's research to find out the time
> format that NTP uses (seconds since Jan 1, 1900) and the
> (different) time format that UNIX uses (seconds since Jan 1, 1970).
> And how they both deal with leap-seconds since their
> epoch started.
> Another hour of time figuring out how to convert that to
> today's Hours, minutes, and seconds.  But that is easy,
> once it (finally) sinks in how to work with an epoch.
> Now, the real fun begins when you decide that you might
> want to convert NTP or UNIX time to Day of Week, Month,
> Calendar Year, Day of Year, Week of year, and
> adjustments for local time zone, with daylight savings time.
> That was worth about four hours research and going to bed with
> a head-ache.  Learned all about "Julian Day" and "Modified
> Julian Day", which it turns out has nothing to do with
> the Julian Calendar.  (Did you know that time started at high noon
> on January 1, 4713 BC. ?)  Finally discovered a code snippet
> in Tom Van Baak's "C" code repository that will do the
> conversion.  (Thanks, Tom.)
> A pox upon leap years, un-leap centuries, re-leap 4th centuries,
> Roman Numerals, modulus 7 weeks that do not align with the year boundary,
> months with no regular modulus structure, and no year 0.
> Who sold us this?
> Makes you appreciate the decimal time "Star Date" system used on Startrek.
> --- Graham
> ==
> On 5/27/2013 9:56 AM, Miguel Barbosa Gonçalves wrote:
>> Hi Bob!
>> On 27 May 2013 14:56, Bob Camp <lists at rtty.us> wrote:
>>> Hi
>>> Correct answer:
>>> I don't think there is such a beast. Once you get away from the radio
>>> controlled (WWVB etc) clocks the cost goes up quickly.
>> I don't understand why a microprocessor with an Ethernet controller and a 7
>> segment display would cost so much to manufacture... I think I'll build my
>> own.
>>> Also correct, but a bit of a joke answer:
>>> Raspberry PI driving your television set.  Alternatively make the Pi feed
>>> control signals to a hacked normal clock.
>> Good joke :-) I imagine the electricity bill at the end of the month.
>> I would like to have a clock sync with my super precise stratum 1 servers
>> :-) what's the point in having them if I can see the time anywhere? :-)
>> Cheers,
>> Miguel
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