[LinuxPPS] PPS falsetick problem

[AraSim100 .]

Could you please help me with the following problem ?

Our board supports PPS & NTP . I connect & define the Garmin GPS as the
NMEA reference clock . Unfortunately  when I add the atom reference clock
to ntp in order to receive pps ,

after sometime NMEA & ATOM(pps) clocks marked as falsetick servers . I see
that it can related to the jitter and can be fixed by setserial low_latency
. But out UART doesn't support this flag .

Therefore could you please explain how I can fix pps  falsetick problem
witout use setserial . Our configuration is following :

Ntp configuration (ntpd 4.2.6p5) :

server 127.127.1.0 #lo server

fudge 127.127.1.0 stratum 7



restrict 127.127.1.0 noquery nomodify notrap

server 127.127.20.0 minpoll 4 maxpoll 4 iburst #NMEA Server

server 127.127.22.0 prefer

fudge 127.127.22.0 flag3 1 refid PPS



ntpq -p

     remote           refid      st t when poll reach   delay   offset
jitter

==============================================================================

*LOCAL(0)        .LOCL.           7 l    5   64  377    0.000    0.000
0.031

xGPS_NMEA(0)     .GPS.            0 l    4   16  377    0.000  -63.203
5.256

xPPS(0)          .PPS.            0 l    3   64  377    0.000  -347.47
7.428

root at am335x-evm:/dev# ntpdc

ntpdc> kerninfo

pll offset:           0 s

pll frequency:        0.000 ppm

maximum error:        0.013456 s

estimated error:      1e-05 s

status:               2007  pll ppsfreq ppstime nano

pll time constant:    6

precision:            1e-09 s

frequency tolerance:  500 ppm





root at am335x-evm:/dev# ntptime

ntp_gettime() returns code 0 (OK)

  time d6dd71e6.aaf4cf0c  Wed, Mar 26 2014 15:33:58.667, (.667798707),

  maximum error 23956 us, estimated error 10 us, TAI offset 0

ntp_adjtime() returns code 0 (OK)

  modes 0x0 (),

  offset 0.000 us, frequency 0.000 ppm, interval 1 s,

  maximum error 23956 us, estimated error 10 us,

  status 0x2007 (PLL,PPSFREQ,PPSTIME,NANO),

  time constant 6, precision 0.001 us, tolerance 500 ppm,



Regards

Arthur
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