NTP с использованием GPS и PPS в качестве часов, PPS помечен как фальшивый

Я пытаюсь добавить в свою сеть источник синхронизации на основе GPS, используя GPS, который излучает тактовый импульс 1 PPS. Он подключен к контакту GPIO.

После того, как ntpd поработал около 30 минут, часы PPS все еще не используются и отмечены как плохие, но я не могу понять, почему.

ntpq> opeer
     remote           local      st t when poll reach   delay   offset    disp
==============================================================================
-127.127.28.0    127.0.0.1        2 l    5   16  377    0.000   17.704   2.125
x127.127.22.0    127.0.0.1        0 l    4   16  377    0.000    6.546   0.260
+50.116.36.122   10.42.134.1      3 u   33   64  377   43.017    2.337   5.208
+52.0.56.137     10.42.134.1      3 u   33   64  377   52.022   -6.430   3.944
-2001:418:8405:4 _d58f:78d0:fd39  3 u   30   64  377   85.262   13.465   4.929
*104.156.99.30   10.42.134.1      2 u   32   64  377   63.671   -0.166   5.484

ntpq> assoc

ind assid status  conf reach auth condition  last_event cnt
===========================================================
  1  2139  933a   yes   yes  none   outlier    sys_peer  3
  2  2140  9134   yes   yes  none falsetick   reachable  3
  3  2141  9424   yes   yes  none candidate   reachable  2
  4  2142  9424   yes   yes  none candidate   reachable  2
  5  2143  9324   yes   yes  none   outlier   reachable  2
  6  2144  963a   yes   yes  none  sys.peer    sys_peer  3

ntpq> rv 2140
associd=2140 status=9134 conf, reach, sel_falsetick, 3 events, reachable,
srcadr=127.127.22.0, srcport=123, dstadr=127.0.0.1, dstport=123, leap=00,
stratum=0, precision=-20, rootdelay=0.000, rootdisp=0.000, refid=PPS,
reftime=da584969.00b5c330  Sun, Jan 31 2016  8:50:49.002,
rec=da584969.0f2551bb  Sun, Jan 31 2016  8:50:49.059, reach=377,
unreach=0, hmode=3, pmode=4, hpoll=4, ppoll=4, headway=0, flash=00 ok,
keyid=0, ttl=0, offset=9.551, delay=0.000, dispersion=0.260,
jitter=2.148,
filtdelay=     0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00,
filtoffset=    9.55    9.97   10.46   10.98   11.49   11.95   12.46   12.91,
filtdisp=      0.03    0.27    0.51    0.75    0.99    1.23    1.47    1.71

Сам источник PPS выглядит очень чистым и регулярным:

# ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1454230928.995087804, sequence: 7552 - clear  0.000000000, sequence: 0
source 0 - assert 1454230929.995115719, sequence: 7553 - clear  0.000000000, sequence: 0
source 0 - assert 1454230930.995144056, sequence: 7554 - clear  0.000000000, sequence: 0
source 0 - assert 1454230931.995173388, sequence: 7555 - clear  0.000000000, sequence: 0
source 0 - assert 1454230932.995202464, sequence: 7556 - clear  0.000000000, sequence: 0
source 0 - assert 1454230933.995230660, sequence: 7557 - clear  0.000000000, sequence: 0
source 0 - assert 1454230934.995258966, sequence: 7558 - clear  0.000000000, sequence: 0
source 0 - assert 1454230935.995287693, sequence: 7559 - clear  0.000000000, sequence: 0
source 0 - assert 1454230936.995317675, sequence: 7560 - clear  0.000000000, sequence: 0
source 0 - assert 1454230937.995345684, sequence: 7561 - clear  0.000000000, sequence: 0
source 0 - assert 1454230938.995375052, sequence: 7562 - clear  0.000000000, sequence: 0
source 0 - assert 1454230939.995403851, sequence: 7563 - clear  0.000000000, sequence: 0
source 0 - assert 1454230940.995433228, sequence: 7564 - clear  0.000000000, sequence: 0
source 0 - assert 1454230941.995463497, sequence: 7565 - clear  0.000000000, sequence: 0
source 0 - assert 1454230942.995491843, sequence: 7566 - clear  0.000000000, sequence: 0