Hi all,

I am setting up chronyd on an embedded Linux device to synchronize the system 
clock using a GPS module. The GPS device sends NMEA strings over the character 
device /dev/ttyAMA1 and I have also configured /dev/pps0, both of which appear 
to be working OK.

The system is running Ubuntu 18.04 and the latest package versions are chronyd 
3.2 and gpsd 3.17.

I configured gpsd to listen to the serial device and then added these lines to 
my chrony.conf:

        refclock SHM 0 refid GPS precision 1e-1 offset 0.9999 delay 0.2
        refclock PPS /dev/pps0 refid PPS

When I run `chronyc sources` they both seem to be kind of working:

        210 Number of sources = 2
        MS Name/IP address         Stratum Poll Reach LastRx Last sample        
       
        
===============================================================================
        #- GPS                           0   4   377    12   +128ms[ +128ms] 
+/-  200ms
        #* PPS                           0   4   377    12     +6ns[ +119ns] 
+/-  203ns

However it looks like the GPS source is “not combined”. Is this a degraded 
state, e.g., it is using one of these two sources? 

Also, I am not sure why the LastRx from the PPS (or frankly either) ticks 
upwards so long—shouldn’t it constantly be receiving updates?

I am just using the precision / offset / delay figures that several examples 
use. Is there documentation on calibrating these values?

Finally, I read that using Unix sockets rather that shared memory is 
preferable, but my chronyd does not seem to create those sockets.

Thanks,
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