[ntp:questions] Thunderbolt at NTP ref clock.

David Lord snews at lordynet.org
Tue Jul 30 20:12:28 UTC 2013

unruh wrote:
> On 2013-07-30, David Lord <snews at lordynet.org> wrote:
>> Dave Baxter wrote:
>>> Hi again.
>>> In reference to my other thread.
>>> "THunderbolt monitor/control on Win7 ?"
>>> Well, as that device seems happy in it's potential new home.
>>> I've been poking about the interweb looking for info as to getting the 
>>> TB used as a reference clock for NTP.
>>> I found this page:-
>>> http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver29.html
>>> That on the face of it, seems to tell me what I need.
>>> So, poking arround (no changes yet) my ntp.conf file, I "think" I need 
>>> this:-
>>> # Trimble Thunderbolt on /dev/gps1 (first serial port)
>>> server    mode 2  minpoll 4 maxpoll 4   prefer
>>> fudge    time1 0.020
>>> fudge    flag2 1  refid GPS
>>> server 0.uk.pool.ntp.org iburst minpoll 5 maxpoll 12
>>> server 1.uk.pool.ntp.org iburst minpoll 5 maxpoll 12
>>> server 2.uk.pool.ntp.org iburst minpoll 5 maxpoll 12
>>> Would this be suitable for general purpose local time sourcing?  With 
>>> fallback to the pool if the TB burps, dies or is otherwise compromised.
>> I'd add a few more public servers, I've been using five.
> Why not 47?
> His are backups. 3 is fine. 

Mine are backups for my gps/pps but sometimes here the internet
might not be as reliable as at your location and I've known two
or three of my backups go unreachable. My gps also has bad days
in certain weather conditions.

>>> Could all the fudge factors go on one line?
>> Shouldn't be a problem.
>> fudge    time1 0.020  flag2 1  refid GPS
> That looks like a huge time1 fudge. Are you sure that the pool servers
> do not actually give better time than does the Trimble? 

That is what is suggested in the ntp docs for the type 29
driver. The expected accuracy is given for various OS, eg
Linux 10 us.

>>> (Sorry to ask silly questions, but I don't know, so have to ask.)
>>> If so, in what (if any) order?
>>> The server currently run's FreeBSD 8.0  Uptime over 772 days now, 
>>> without a hitch! Nice...   (I do plan to configure another box, running 
>>> 9.x at some point to replace this one.)  
>>> ntpq -crv reports (among other things)...
>>> version="ntpd 4.2.4p5-a (1)"
>> I'm using 4.2.6p5 but that is fairly old (Dec 2011 maybe). One
>> of the 4.2.7pnnn may be a better choice although I tried both
>> 4.2.4p354 and p359 on NetBSD and had problems using the stom
>> driver.

I've now downloaded and installed ntp-4.2.7p377 and after a about 30 
minutes from reboot:

remote     refid  st  t  poll  reach  delay offset jitter
oPPS(2)   .PPSb.   0  l    64    377  0.000 -0.002  0.004


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