[LinuxPPS] NMEA Refclock in ntp-dev does not work

[William S. Brasher]

The NMEA refclock, refclock_nmea.c, from ntp-dev-4.2.5p233-RC does not 
work for me.  NTP refuses to use it as a time source and rejects it and 
PPS.

If I use another time source as the "prefer" source, then NTP appears to 
sync to PPS, so it appears to me that either refclock_nmea.c has a problem 
using the Linux PPS or I've mis-configured NTP.





Excerpt from /etc/ntp.conf:

server 127.127.20.0 prefer minpoll 4      # NMEA clock  refid GPS 
fudge 127.127.20.0 flag3 1 flag2 0 time1 0.0

server 127.127.22.0 minpoll 4 maxpoll 4    # PPS clock  refid PPS  
fudge 127.127.22.0 flag3 1 flag2 0

server 192.168.48.2  iburst     # chronos
server 192.168.48.18 iburst     # tick


     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
xGPS_NMEA(0)     .GPS.            0 l   11   16  377    0.000  -343.40  37.321
xPPS(0)          .PPS.            0 l   15   16  377    0.000   -1.784   0.289
*chronos         .PPS.            1 u   24   64  377    0.184   -1.227   1.316
+tick            .PPS.            1 u   38   64  377    0.161   -1.066   1.303




Excerpt from /etc/ntp.conf:

server 127.127.22.0 minpoll 4 maxpoll 4    # PPS clock  refid .PPS
fudge 127.127.22.0 flag3 1 flag2 0

server 192.168.48.2  prefer  iburst     # chronos
server 192.168.48.18 iburst     # tick


     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
oPPS(0)          .PPS.            0 l    3   16  377    0.000    0.001   0.001
*chronos         .PPS.            1 u   57   64  377    0.170    0.008   0.004
+tick            .PPS.            1 u   64   64  377    0.145   -0.004   0.024