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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: Mon, 21 Sep 2020 14:46:34 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0

On 2020-09-19 17:40, Mike Simpson wrote:

> Just to let you know that if you disable GLONASS then the 4second
> pps offset will disappear.

THAT'S IT! Two quick constellation changes (disabled GLONASS, and since
that released a frequency re-enabled BeiDou - even though as previously
mentioned here I hardly ever pick up either BeiDou or Galileo satellites
from my location) and I have now had a PPS-synchronised time source
running without issues for over 24 hours, with both offset and jitter in
the order of < 100 us under idle conditions. Overall there is still room
for some improvement because the receiver is currently connected via USB
and there is a handful of other services running on that machine, in
particular I have noticed that the jitter becomes noticeably higher when
there is significant I/O activity - but even the way things are now I've
got worst-case of time accuracy of better than one millisecond, i.e. 1-2
orders of magnitude better than what NTP gives me.

Thank you very much for this tip, Mike!

> I’m sumosing it’s because my GPS firmware is very old but I don’t run
> any Windows so can’t run the proprietary ublox software to update
> it.

As already mentioned here yesterday u-center does work fine under Wine,
after all it does as far as communication with the hardware is concerned
is writing to and reading from a serial port. I understand why one might
not want to run firmware updates that way, though; I am not sure if *I*


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