[ntp:questions] ntpd on embedded risc

Unruh unruh-spam at physics.ubc.ca
Wed Feb 18 04:12:06 UTC 2009


cnm3332 at gmail.com (Christopher Mire) writes:

>I have a small embedded linux machine. Moxa UC-7112 Plus that I want to
>use as NTP server. http://www.moxa.com/product/UC-7110-LX.htm
>Its has MOXA ART ARM9 32-bit 192 MHz processor CPU.

>Here are statistics I collected after using it a bit.  This is using gpsd
>2.33 to collect NMEA, PPS.

"a bit" means what? Remember that ntpd takes 1 hour to cut the error by
half. Thus unless you ran this for more than 10 hours, these offsets mean
nothing.




>     remote           refid      st t when poll reach   delay   offset
>jitter
>==============================================================================
>+SHM(0)          .NMEA.           0 l    8   16  377    0.000  -21.691
>7.812
>*SHM(1)          .PPS.            0 l    1   16  377    0.000  -17.105
>7.81

>ntpq> cv
>status=0101 clk_noreply, last_clk_noreply,
>device="SHM/Shared memory interface", timecode=, poll=54, noreply=78,
>badformat=0, baddata=0, fudgetime1=0.000, stratum=0, refid=PPS, flags=0
>ntpq> rv
>status=09e4 leap_none, sync_telephone, 14 events, event_peer/strat_chg,
>version="ntpd 4.1.1 at 1.786 Tue Sep 11 19:14:27 CDT 2007 (1)",
>processor="armv4tl", system="Linux2.6.9-uc0", leap=00, stratum=1,
>precision=-7, rootdelay=0.000, rootdispersion=32.592, peer=4253,
>refid=PPS, reftime=cd44982f.b9359791  Tue, Feb 17 2009  9:58:07.723,
>poll=4, clock=cd449838.649a9973  Tue, Feb 17 2009  9:58:16.392, state=4,
>offset=-13.494, frequency=142.853, jitter=7.908, stability=4.197

>root at Moxa:~# cat /proc/cpuinfo
>Processor    : ARM922Tid(wb) rev 1 (v4l)
>BogoMIPS    : 76.59
>Features    : swp half thumb
>CPU implementer    : 0x66
>CPU architecture: 4
>CPU variant    : 0x0
>CPU part    : 0x526
>CPU revision    : 1
>Cache type    : VIVT write-back
>Cache clean    : cp15 c7 ops
>Cache lockdown    : format B
>Cache format    : Harvard
>I size        : 16384
>I assoc        : 2
>I line length    : 16
>I sets        : 512
>D size        : 16384
>D assoc        : 2
>D line length    : 16
>D sets        : 512

>Some gpsd messages in case :
>gpsd: <= GPS: $GPZDA,020012.000,17,02,2009,,*58
>gpsd: carrier-detect on /dev/ttyM1 changed to 0
>gpsd: carrier-detect on /dev/ttyM1 changed to 1
>gpsd: ntpshm_pps: precision -6

>ntp.conf
>server 127.127.28.0 minpoll 4 maxpoll 4
>fudge 127.127.28.0 time1 0.411 refid NMEA
>server 127.127.28.1 minpoll 4 maxpoll 4 prefer
>fudge 127.127.28.1 refid PPS

>I am curious if the platform is the limitation, or if there are things that
>can be done to make this work well as a NTP server, because now the accuracy
>is unacceptable.  Ideas?




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