[ntp:questions] TrueTime refclock Users?

Jason Rabel jason at extremeoverclocking.com
Fri Apr 20 03:13:52 UTC 2007


Yes, the driver appears to walk-through several old TrueTime devices, some
of which I don't think are even functional these days. The 468DC GOES
receiver will not work (GOES stopped transmitting time back in 05 I think)
unless you use a special antenna that converts a GPS signal into something
the unit can read. But that's another story.

One of the reasons the driver did not work for me was the code is too
generic when checking for a TrueTime device. It just assumes anything with a
string "TRUETIME Mk III" is a GPS model and sends a F50 & F51 code to get
some GPS specific satellite info. Since those codes are specific to GPS
models only, my receiver sends back a "ERROR 05 NO SUCH FUNCTION" which
throws the code into a different state making it impossible to proceed with
the time-output. Those two codes that are sent (F50 & F51) are never checked
against anything in the code to ensure satellite validity and such, I guess
the somebody started the implementation but never got around to finishing

I was hoping someone with a GPS model would be able to post their version
string and see if it was different from mine, also it would be nice to get
the GPS info to complete those checks. A little less elaborate method could
be used by assuming if the Truetime string passes, but the F50 & F51 strings
fail then it has to be a IRIG or PPS model. Or the whole F50 & F51 strings
could be skipped entirely since they don't actually do anything.

I noticed too if I first start the once-a-second time output from the NTS
serial port then start NTP, it works just fine. The debug shows it stops at
the first receiver check (Omega I believe) and since it's receiving time in
a format it can parse (just falls through the code until the time parse
routine) it is happy.

Anyhow, I'm not complaining or anything, the whole experience of
communicating through the NTS serial port was just a "for fun" experiment.
Anyone using this method would have to adjust their offset slightly, but the
jitter is quite reasonable. In the end though, it's not really a practical
means of a time source for the NTS series since they have a built-in NTP
server and even a PPS output. 


> I recall that Paul Vixie was the author of that much-mangled driver. He 
> intended to support a number of TrueTime devices, including the GOES and 
> WWVB clocks which are no longer manufactured. The code has little 
> wiggles designed to support most if not all historic TrueTime devices 
> with one driver. Should you make serious changes to adapt your a model 
> not supported by the driver, it might lose the valuable feature of one 
> driver fits all.
> TrueTime of course has been eaten by Symmetricom and it appears all 
> except the GPS receivers have become extinct except on eBay. What I'm 
> saying is that it might be better to clone another driver and leave the 
> TrueTime one alone. The best choice would be to find a driver that with 
> minimal compile or configuration changes could support both the original 
> and your driver. Several drivers now automatically detect which radio is 
> hot and configure accordingly.

More information about the questions mailing list