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Re: gpsd time service: PPS-synchronised SHM samples rare, both sources g

From: Marek Szuba
Subject: Re: gpsd time service: PPS-synchronised SHM samples rare, both sources gradually less and less frequent
Date: Fri, 18 Sep 2020 21:36:04 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0

On 2020-09-18 14:39, Marek Szuba wrote:

> 1. 'chronyc sources' shows no data AT ALL has been received from the
> 'PPS' refclock. Moreover, the last time the 'GPS' clock sent anything
> was just under two hours earlier. The refclocks log confirms this - no
> PPS lines, and GPS lines ceased abruptly about 40 minutes after start-up.

Following up on this, I switched from chrony back to ntpsec and
configured it to use the received in generic-NMEA mode (server, with /dev/gps0 pointing to ttyAMA0 and /dev/gpspps0 to
pps0). It has been running like this for 6 hours now and the samples
keep on coming. Most likely not a hardware problem, then... I wonder
what causes gpsd to suddenly try and switch to 4800 bps. Is there any
way of forcing it to stay in specific serial mode?

Regarding the PPS signal, I have decided to bring out the big guns and
connected the receiver to an oscilloscope. Result - unless I have wired
something wrong, the PPS waveform has exactly the same shape as what the
receiver sends out on the TX line... That can't be right, can it? The
odd thing is, I have checked both the computer-side connectors and (just
to be extra sure) the pins of the chip (whose label by the way says
NEO-M8N after all) for short circuits and there seem to be none.
Something wrong with the configuration of the TIMEPULSE signal?


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