[LinuxPPS] taming the gps18x

[tlhackque]

On 16-Mar-18 05:26, Udo van den Heuvel wrote:
> Hello,
>
> I am trying to make a Garmin GPS18x LVC work with my firewall.
> Another GPS18x *does* work, attached to this PC.
> I keep seeing 100's of ms of offset between the firewall and this
> workstation (and the rest of the world) in `ntpq -pn` output.
>
> I also see:
>
> # ppstest /chroot/ntpd/dev/pps0
> trying PPS source "/chroot/ntpd/dev/pps0"
> found PPS source "/chroot/ntpd/dev/pps0"
> ok, found 1 source(s), now start fetching data...
> source 0 - assert 1521192070.588686508, sequence: 150046 - clear
> 1521039630.201197096, sequence: 2
> source 0 - assert 1521192071.588741114, sequence: 150047 - clear
> 1521039630.201197096, sequence: 2
> source 0 - assert 1521192072.588592010, sequence: 150048 - clear
> 1521039630.201197096, sequence: 2
> source 0 - assert 1521192073.588552381, sequence: 150049 - clear
> 1521039630.201197096, sequence: 2
> source 0 - assert 1521192074.588503724, sequence: 150050 - clear
> 1521039630.201197096, sequence: 2
> source 0 - assert 1521192075.588455899, sequence: 150051 - clear
> 1521039630.201197096, sequence: 2
> source 0 - assert 1521192076.588526746, sequence: 150052 - clear
> 1521039630.201197096, sequence: 2
> ^C
>
> Why isn't the clear timestamp incrementing but /is/ the assert timestamp
> incrementing?
>
> I tried flag2 of the nmea driver (rising/falling edge) but that did not
> bring me a solution yet.
>
> What is happening here, how do I fix this?
>
>
> Udo

Start with the hardware.  If you connect the failing 18x to the same
port on this PC, does it work?
This will tell you if it's the hardware/software related to the port, or
the 18x.

If the failure goes with the 18x, did you program the pulse width?  A
narrow width might be missed, while a wider one would be caught.  This
is especially true where hardware edge detection is used - it may not be
programmed on both edges, leaving you with polling for the other edge. 
Are the firmware versions the same?

If the problem goes with the port, what, exactly is the platform and how
is the 18x interfaced?   If by PC you mean an ARM platform, such as RPi,
look at the device tree.

Finally, does the behavior change outside the chroot?



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