[ntp:questions] pps breaks when nmea is enabled for ntpd

David Lord snews at lordynet.org
Sun Jun 16 09:20:47 UTC 2013


Richard Cagley wrote:
> hmm, timeX is just a calibration factor so I don't think adding it will fix
> my pps breakage. But, I do think it's important and I'm not using it.
> 
> So, question to you, I have a U-Blox NEO-6P module. How would I go about
> determining the time1/time2 values for the 127.127.20.0 server? The key
> words "offset" and "calibration" don't show up here
> http://www.u-blox.com/images/downloads/Product_Docs/NEO-6_DataSheet_%28GPS.G6-HW-09005%29.pdf
> 

I initially used "noselect" for 127.127.20.n and had one
of my other servers marked as "prefer"

I also have "tos mindist 0.4"

 From peer_summary over several days I selected the mean
to use for time2.

Peer_summary for nmea over past 20 days shows wide spreads
of values: mean = -3 to 12, rms = 16 to 22, max = 63 to 88

The type 20 nmea driver can be used alone without problem
but I had been comparing pps to parallel vs serial inputs
(and did not find any significant difference).


David

> 
> On Sat, Jun 15, 2013 at 8:54 AM, David Lord <snews at lordynet.org> wrote:
> 
>> Richard Cagley wrote:
>>
>>> I have a TI DM8168 processor and a u-blox gps.
>>>
>>> If I enable an internet server and pps, then pps works great
>>>
>>> server clock.redhat.com iburst prefer minpoll 4 maxpoll 4
>>> server 127.127.22.0 minpoll 4 maxpoll 4
>>> fudge 127.127.22.0 flag3 1
>>>
>>> However, if I add an NMEA server to my ntp.conf file like this
>>>
>>> server 127.127.20.0 mode 1
>>> fudge 127.127.20.0 flag1 1
>>> server 127.127.22.0 minpoll 4 maxpoll 4
>>> fudge 127.127.22.0 flag3 1
>>>
>>> then pps stops working. I can kill ntpd and ppstest no longer works. It's
>>> as though nmea is clobbering the serial port.
>>>
>>> It sorta feels like this, but there was no resolution
>>> http://lists.ntp.org/**pipermail/questions/2011-**September/030347.html<http://lists.ntp.org/pipermail/questions/2011-September/030347.html>
>>>
>>> Can anyone help me. I've really been struggling with this.
>>>
>> I'm using NetBSD-6.1 ntpd 4.2.6p5 but have also had pps + nmea
>> working on ubuntu.
>>
>> You probably need to determine then add time2 0.xyz sec to
>> your config. The time2 value is for your particular gps and
>> gps firmware version.
>>
>> For my "Sure" gps I have:
>>
>> server 127.127.20.2 mode 18 prefer
>> fudge  127.127.20.2 stratum 4 time2 0.417 flag1 0 refid GPSb
>> server 127.127.22.2
>> fudge  127.127.22.2 flag2 0 flag3 1 refid PPSb
>>
>> From peer summary I have:
>> 127.127.22.2 mean=0.000 rms=0.004 max=0.038
>>
>> The 0.038 is mostly due to load from two cron jobs each evening.
>>
>>
>> David
>>
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