[ntp:questions] Peer Review of ntpq -c rv

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Thu Mar 8 03:06:43 UTC 2012

On 3/7/2012 7:10 PM, David Lord wrote:
> Ron Frazier (NTP) wrote:
>> I'm a little confused.  Are you currently getting offsets in the 10's 
>> of milliseconds range or in the 10's of microseconds range.  Also, 
>> how are you measuring offset from UTC, as opposed to offset from the 
>> GPS board?
>> Sincerely,
>> Ron
>> On 3/7/2012 7:26 AM, Alby VA wrote:
>>>   I'm looking to get a little feedback on if the following output of my
>>> Sure GPS / FreeBSD
>>> setup looks like its running smoothly and keeping time correctly.
>>> assID=0 status=0115 leap_none, sync_atomic, 1 event,
>>> event_clock_reset,
>>> version="ntpd 4.2.6p5 at 1.2349-o Mon Feb 20 22:00:33 UTC 2012 (1)",
>>> processor="amd64", system="FreeBSD/9.0-RELEASE", leap=00, stratum=1,
>>> precision=-19, rootdelay=0.000, rootdisp=0.269, refid=PPS,
>>> reftime=d301d22f.dc1393c2  Wed, Mar  7 2012  7:25:19.859,
>>> clock=d301d230.cc08bad9  Wed, Mar  7 2012  7:25:20.797, peer=41909,
>>> tc=4, mintc=3, offset=-0.034, frequency=-25.214, sys_jitter=0.002,
>>> clk_jitter=0.002, clk_wander=0.001
> From above the offset is -0.034 msec, ie 34 usec
> David

At first I was confused and thought he was ms off.  However, if he's 
within 34 us, that's pretty good.  Sounds like his board is working OK, 
but could possibly be a bit better.  If he were communicating 
exclusively on the serial port and the PPS were not working, would he be 
getting performance this good?

Even though it's not as critical with PPS, I thought I'd pass a long a 
couple of tips to making the serial NMEA connection perform as good a 

My advice to stabilize the NMEA data as much as possible, do the following:

A) maximize the baud rate, as long as it doesn't destabilize the system.
B) minimize the number of NMEA sentences, to preferably one.
C) make that NMEA sentence one that doesn't vary much, if at all, in 
length, like GPZDA or maybe GPZDG.  I don't know much about GPZDG.  
However, the manual for the Trimble Resolution T recommends GPZDA for 
D) Set ntp.conf to read only the desired sentence.

Here's something else that could be affecting his results, or possibly, 
I could be all wet.  It occurred to me that BSD (which I know nothing 
about, but am assuming it's a linux like system) might be automatically 
loading the virtual com port driver for the USB connection, like Ubuntu 
did when I plugged in the USB GPS that I have, which is a Globalsat 
BU-353.  So, my thought was, if it were trying to communicate both by 
USB and serial, that it might be causing a problem.  Or, it could be 
totally unrelated.  But, I just thought I'd throw it out there.



>>>   Here are my website graphs/stats I've been keeping since day 1.
>>> NTP Clock Offset: http://godzilla.empire.org:9999/
>>> NTP Offset from UTC: 
>>> http://godzilla.empire.org:9999/godzilla_ntp-b.html


(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such.  I don't always see new messages very quickly.  If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT c3energy.com

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