Re: [chrony-users] help - UTC time of PPS pulses

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

0 seconds

If you trigger on the wrong edge of the pulse (the trailing, descending edge)
you will get an number like you suggest, but that edge is not to be used as
its timing is horrible.

The GPS leanding edge is, depending on your GPS card, within about 10 nano
seconds of true UTC second. It may have a sawtooth deviation (Ie increases for
a while-- in the nanosecond range-- and then corrected down back to 0. That
infomation for each sattelite can be found afterwards to correct times if
needed. No common computer however has a sufficiently good interrupt handler
to be able to see nanosecond type accuracy.

William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/

On Tue, 13 Oct 2020, Yoed Stavi wrote:

> Hi,
>
>  
>
> I use Chrony as our NTP client and also for PPS synchronization.
>
> This works great.
>
> The same server creates a DVB-T transport (MPEG-2 TS with MIP packets). The DVB-T protocol includes timestamps that should be relative to
> GPS pulses.
>
> Since the DVB-T software doesnʼt know when the GPS pulses are (only Chrony knows that), I set the timestamps to be relative to whole UTC
> seconds instead of GPS pulses.
>
>  
>
> I would like to improve by knowing the offset between GPS pulses and UTC seconds as it is measured by Chrony  (from my measurements the
> result should be between 230-250 milliseconds).
>
>  
>
> Can this data be found anywhere?
>
>  
>
> Thanks,
>
>   Yoed.
>
>  
 pulse 
>