[ntp:hackers] Question about "howto.html"

David L. Mills mills at udel.edu
Fri Jan 9 14:13:03 PST 2004


Confused,

I assume you do know about the filegen facility. The reference clock
drivers report status to the clockstats file. The flag4 enables a driver
to do that. However, there are almost four dozen drivers written by
folks with varying degrees of personal art, and the flag4 convention is
not universal.

A few drivers respect the flag1 convention. For those that do and when a
PPS signal disciplines the clock the measured clock offset is copied
with sign inverted to the time1 value. When the system time stabilizes
after a few hours, you read that value using ntpq, edit the
configuration file with that value and reset flag1.

I very much prefer general questions like this to be directed to the
newsgroup rather than the hackers list, which I do not read. In this way
your question and my answer appear to lots of folks and I don't have to
answer the question multiple times.

Dave

reg at dwf.com wrote:
> 
> In the howto.html (How to write a Reference Clock Driver), down under
> Conventions, Fudge Factors and Flags, it says:
> 
> ---
> 
> Most drivers support manual or automatic calibration for systematic offset
> bias using values encoded in the fudge configuration command. By convention,
> the time1 value defines the calibration offset in seconds. For those drivers
> that support statistics collection using the filegen utility and the
> clockstats file, the flag4 switch enables the utility. When a PPS signal is
> available, a special automatic calibration facility is provided. If the flag1
> switch is set and the PPS signal is actively disciplining the system time, the
> calibration value is automatically adjusted to maintain a residual offset of
> zero. Should the PPS signal or the prefer peer fail, the adjustment is frozen
> and the remaining drivers continue to discipline the system clock with a
> minimum of residual error.
> 
> ---
> 
> I had not noticed this section till I read the HOWTO recently, and I am
> definately missing something.
> 
> So some questions.
> I understand manual setting of the offset, but what about this automagic stuff?
> Does it work?  And what does:
> 
>     "For those drivers that support statistics collection using the
>      filegen utility and the clockstats file"
> 
> imply?  If it is based on the clockstats file, It would seem to be an external
> program that perhaps scans the file, but what is it looking for and just
> What/Where is the filegen Utility mentioned above?
> 
> Does this try to (re)set the offset assuming that the GPS or TCP/IP clock
> offsets are zero?  A few more details would help.
> 
> Confused.
> 
> --
>                                         Reg.Clemens
>                                         reg at dwf.com
> 
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