Can't get GPS/PPS to work

[Philipp Ammann]

Hi List,

I'm trying to get ntpsec (1.2.1; running on a Raspberry Pi 4 / Gentoo)
to sync to a GPS module connected via GPIO. The GPS module a
run-of-the-mill (Whadda branded) uBlox Neo-7M based board. `gpsmon`
reports "Quality: 1 / Sats: 10" so everything seems to be working
perfectly fine here. `ppstest` also reports that everything is on order.
However, I am unable to use the GPS signal in ntpd. I have the following
devices:

 * /dev/pps0
 * /dev/ttyAMA0 # the GPS device
 * /dev/gps0 -> /dev/ttyAMA0
 * /dev/gpspps0 -> /dev/pps0

ntp.conf:

```
driftfile /var/lib/ntp/ntp.drift
statsdir /var/log/ntp/stats

restrict default kod limited nomodify nopeer noquery
restrict -4 127.0.0.1
restrict -6 ::1

# tried that, didn't work
#refclock pps unit 0 flag2 0 1
#refclock nmea baud 9600 path /dev/ttyAMA0 ppspath /dev/pps0

#server ptbtime1.ptb.de. iburst
#server ptbtime2.ptb.de. iburst
#server ptbtime3.ptb.de. iburst

server 127.127.20.0 minpoll 2 maxpoll 4
fudge 127.127.20.0 time1 1 refid GPS

server 127.127.22.0 minpoll 4 maxpoll 4 prefer
fudge 127.127.22.0 refid PPS
```

I did try many variations in the config. But no matter what, I always get:

```
ntpq> peers
     remote      refid st t when poll reach   delay   offset   jitter
=====================================================================
 NMEA(0)    .GPS.       0 l    -    4    0   0.0000   0.0000   1.9531
 PPS(0)     .PPS.       0 l    -   16    0   0.0000   0.0000   0.0002

ntpq> associations

ind assid status  conf reach auth condition  last_event cnt
===========================================================
  1 17767  80fb   yes    no  none    reject clock_alarm 15
  2 17768  8011   yes    no  none    reject    mobilize  1
```

HOWEVER it did work once (yesterday), reporting:

```
$ ntpq -p
     remote      refid st t when poll reach   delay   offset   jitter
=====================================================================
*NMEA(0)    .GPS.       0 l    2    4  377   0.0000 218.7745   1.5621
 PPS(0)     .PPS.       0 l    -   16    0   0.0000   0.0000   0.0002
```

After restarting ntpd it was back to where it was before -- without
changing anything it the config. Let it run over night -- no change.

Can you guys give me any pointers as to what is going on here?

Thank you
Philipp