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Re: [gpsd-users] 1PPS not working with RPi 3 B+ and Stretch

From: Gary E. Miller
Subject: Re: [gpsd-users] 1PPS not working with RPi 3 B+ and Stretch
Date: Thu, 19 Jul 2018 11:51:49 -0700

Yo Chris!

On Thu, 19 Jul 2018 13:36:43 -0400
Chris Smith <address@hidden> wrote:

> I've followed the how-to for creating a stratum 1 NTPsec
> timeserver, but am having an issue with 1PPS.


> I am using a UM220-III N GPS receiver. It has 1PPS out at 3.3v, as
> well as 3.3v logic levels for serial (the specs sheet says TTL). It
> uses a 500ms wide pulse.

Where can we see the specs for that board?  Can you confirm the
PPS pin?

> In addition to GPS $GNGGA messages, it also outputs Beidou and GLONASS
> messages:

Who cares?  Your problem is PPS, right?  But eventually you want to
disable the BeiDou and GLONASS, they degrade the PPS quality.

> During "clockmaker --config", I chose the "Uputronics" board as it
> uses the same GPIO pin for 1PPS that I've been using for previous
> testing.

Can you confirm the contests of your /boot/config.txt and
/boot/cmdline.txt?  Just to see the script set them properly?

> Moving on, I can verify that by issuing a cat of /dev/gpsd0, I can
> see the GPS messages.

Except your problem is in the PPS, not the serial.

Can you confirm that /dev/pps0 got created on boot?

Can you confirm that /dev/pps0 is working?  It should look like this:

# ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1532025883.999999234, sequence: 169439 - clear  0.000000000, 
sequence: 0
source 0 - assert 1532025884.999999497, sequence: 169440 - clear  0.000000000, 
sequence: 0

> Additionally, here is a screen cap of my gpsmon session on my Pi:

Don't care.  The problem is the PPS.

> address@hidden:~ $ sudo ipcs -m

Why would you do that?  It tells you nothing useful.

> address@hidden:~ $ ./gpsd/ntpshmmon
> ntpshmmon version 1
> #      Name Seen@                Clock                Real
>  L Prec
> No data scrolls by.

Yeah.  You goota be root.  Stop with the 'sudo' mumbo jumbo and just
get root and stay root for gpsd testing.

> However, if I issue "sudo ./gpsd/ntpshmmon -v", I see the following:

Why would you do that?  The prper test is, as root, always as root:

# ntpshmmon
ntpshmmon version 1
#      Name Seen@                Clock                Real                 L 
sample NTP0 1532026085.784897928 1532026085.480288159 1532026085.000000000 0 -20
sample NTP1 1532026086.000474373 1532026085.999998957 1532026086.000000000 0 -30
sample NTP0 1532026086.470176017 1532026086.469552840 1532026086.000000000 0 -20
sample NTP1 1532026087.000320552 1532026086.999998782 1532026087.000000000 0 -3

> I then inspected "ntpq -p"...

Yeah, that confirms that ntpd is not getting ANY time from gpsd.

> So it appears that the SHM drivers for GPS and 1PPS are working, but
> ntpsec can't interpret the data?

Facts not in evidence.  You never showed any valid shm output from

How did you start your gpsd?

Can you verify gpsd is running now?  Like this

# pstree -paul | fgrep gpsd

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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