NTPsec flags my GPS as a falseticker
Nick Burkitt
nick.burkitt at nanotok.com
Thu Mar 19 17:15:44 UTC 2020
Hi Hal.
>
>users at ntpsec.org said:
>> 2020-03-19T02:39:11 ntpd[19607]: CONFIG: configpeers: Ignoring duplicate '127.127.28.2'
>> 2020-03-19T02:39:11 ntpd[19607]: CONFIG: configpeers: Ignoring duplicate '127.127.28.0'
>
>Something fishy there. I'd fix that just to make sure you are using the
>correct lines from the config file.
Yeah - I have no idea where that's coming from. The PPS and GPS devices
are each mentioned only once in my ntpd.conf file.
>
>The combination of 0 and 2 is a bit strange. The usual pairing is 0 and 1 for
>the first GPS device and 2 and 3 for the second GPS device.
That one cost me a lot of time. :-) gpsd assigns two shared memory
segments to each device listed on its command line. Since my PPS device
is separate from my GPS device, I have to pass both devices on the gpsd
command line, GPS (/dev/ttyACMx) followed by PPS (/dev/pps0). gpsd
assigns shm unit 0 to the GPS and shm unit 1 to the (non-existent)
associated PPS, shm unit 2 to the PPS, and it's not clear what it does
with the shm unit 3.
ntpshmmon does a good job of detecting active shm units, though.
>I'm not a gpsd wizard. If you don't need it for some other reason, try using
>the NMEA and PPS drivers. This works for me on a Raspberry Pi.
I do need the capabilities of gpsd, and it allows me to support
different GPS devices. At the moment that's only two, but you never
know. But both the GPS and PPS times are recognized by ntpd. The only
issue (I think) is that ntpd declares my GPS as a falseticker, at least
most of the time. I'd like to understand why that is. So far, I've
managed to improve things a bit by adjust the GPS offset
># PPS via GPIO, Adafruit GPS card with ???? NMEA driver: GPRMC, 9600, stats
>server 127.127.20.0 prefer path /dev/ttyAMA0 mode 0x010011
>fudge 127.127.20.0 flag1 0 # disable PPS
>fudge 127.127.20.0 time2 0.600 # Fixup offset
>server 127.127.22.0 # PPS signal, needs prefer
>fudge 127.127.22.0 flag2 0 # Rising edge
>
> remote refid st t when poll reach delay offset jitter
>===============================================================================
>*NMEA(0) .GPS. 0 l 59 64 377 0.0000 -31.9530 35.5048
>oPPS(0) .PPS. 0 l 58 64 377 0.0000 -0.1953 1.6976
>
So you define your GPS and PPS as peer servers, rather than refclocks.
How does that affect the way ntpd handles them?
Thanks,
-Nick
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