Re: [chrony-users] GPS stratum

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On 2014-06-13 16:27, Miroslav Lichvar wrote:
> On Fri, Jun 13, 2014 at 04:01:53PM +0200, Mattias Walström wrote:
>> Hi!
>> When I do chronyc sources the GPS is presented as a stratum 0 server,
>> shouldnt it say 1, or have I misunderstood something?
> The reference clock is handled internally as a stratum 0 server, but
> chronyd will reply to its clients as a stratum 1 server, you can see
> this in the "chronyc tracking" output.
Thanks! Thats what I was looking for, sorry that I missunderstood that part.
>> ~ # chronyc sources
>> 210 Number of sources = 1
>> MS Name/IP address         Stratum Poll Reach LastRx Last sample
>> ===============================================================================
>> #* GPS                           0   4   377    21  -6811us[-9719us]
>> +/-  253ms
>>>> According GPS shall have stratum 1
>>>> if it is connected as an external receiver, this is the case for me, I
>>>> use a GPS receiver connected with RS422.
> Were you referring to the following text of the RFC?
>   For packet stratum 0 (unspecified or invalid), this is a
>   four-character ASCII [RFC1345] string, called the "kiss code", used
>   for debugging and monitoring purposes.  For stratum 1 (reference
>   clock), this is a four-octet, left-justified, zero-padded ASCII
>   string assigned to the reference clock. 
> This is about value used in NTP packets when synchronized to a
> reference clock, chronyd is following that.
> Here is a part that might explain it better:
>   It is customary to map the stratum value 0 in received packets to
>   MAXSTRAT (16) in the peer variable p.stratum and to map p.stratum
>   values of MAXSTRAT or greater to 0 in transmitted packets. This
>   allows reference clocks, which normally appear at stratum 0, to be
>   conveniently mitigated using the same clock selection algorithms
>   used for external sources (see Appendix A.5.5.1 for an example).
>>>> But is it possible to change stratum of the GPS in chrony, so it is
>>>> correct according to the RFC?
> Currently, it's not possible to change the stratum of a refclock. An
> option could be implemented for that, but I'm not sure how useful it
> would be.
Got the question at work, requirement to separate a GPS clock with and
PPS signal with stratum.
Have now switched from ntpd( to chrony on our embedded systems
and I am
very pleased on how well it performs. Great work!


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