Hello,

For years I’ve have ntpd+NMEA+PPS working great.  My OS was Ubuntu server 12.04 
- and then (currently) 14.04.  GPS is a Garmin LVC 18x.

I use setserial to set low_latency, I’ve reduced the NMEA sentence to bare 
minimum, etc.  All the usual tweaks.  All of this going into a real UART serial 
PCI slot board (no USB) on a full size PC.

My relevant ntp.conf for this:

server 127.127.20.0 mode 1 minpoll 4 maxpoll 4
fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 time2 0.600

I decided to try to upgrade, and hit nothing but roadblocks.  So far I’ve tried 
both Debian 9 and Ubuntu 18.04.  What I observe is that my GPS offset steadily 
climbs and climbs.  It never seems to decrease.  I’ve also tried the above 
config with flag3 set to 0 (“soft” PPS).  In all of these cases I’ve verified 
with ppswatch that I have pps coming in on the port.  It really seems like 
something has changed in the kernel in the past few years that’s causing this.  
It’s about the only thing I can think of as a variable.  I’ve tried distro ntpd 
packages as well as compiling a few versions of the latest source.  All with 
the same behavior.

Anyone have any ideas what could cause this behavior ?

--
Brandon Applegate - CCIE 10273
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"For thousands of years men dreamed of pacts with demons.
Only now are such things possible."

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