Re: 3.22 not sending PPS to SHM

[Gary E. Miller]

Yo David!

On Tue, 12 Jan 2021 11:33:26 +0000
David Taylor <gm8arv@yahoo.co.uk> wrote:

> On 11/01/2021 19:31, Gary E. Miller wrote:
> > It means you only have one time source being sent to ntpd (or
> > chronyd).. Which could be only serial time or only PPS time.
> 
> So in the case of the Raspberry Pi, with no DCD or whatever serial
> PPS signal, the only source of PPS is the GPIO pin 18 (in my case). 

Yes.

> ntpshmmon shows just NTP0.

Which means gpsd saw no valid PPS.

>  When I use servers 127.127.28.0 and 
> 127.127.28.1, SHM0 shows a valid non-zero offset (serial output
> delay), but SHM1 shows no connection:

Exactly as you would expect since you have an NTP0, and will never have
an NTP1.

>    remote        refid   st t when poll reach   delay offset jitter
> ==============================================================================
> x127.127.28.0    .SHM0.   0 l    6   16  377    0.000 43.709 0.940

And notice the SHM0 (NTP0) jitter is terrible.  As you would expect.

> My expectation was that for a stand-alone Raspberry Pi I could use
> 28.0 as the "time of day" ref-clock, and 28.1 as the "PPS" ref-clock.

Both are providing "time of day" to ntpd.  When they work.

Your other chimers will provide much better time then NTP0.  NTP0
should always be the lst item in ntp.conf to have it only for
last resort.

>  Is it correct that the 28.1 ref-clock in that RPi configuration will
> not provide PPS.

Correct.  It will be NTP2, when you fix it.

> and I should use a combination of 28.0 and 22.0
> instead? Or am I missing something?

Yes, you are missing that ntpd is doing no "combining".  gpsd did the
"combining".  Do not think of this like the ntpd built in PPS driver.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

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