[ntp:questions] SIRF time output wobble, GPS or NTP fault?

David J Taylor david-taylor at blueyonder.co.uk.invalid
Thu Mar 8 10:00:39 UTC 2012

"Dave Hart" <hart at ntp.org> wrote in message 
news:CAMbSiYDtftww+Jov8XPSSzpfZx9+wWgCkVj5C5Au5ntjcN08hA at mail.gmail.com...
> On Thu, Mar 8, 2012 at 08:17, David J Taylor
> <david-taylor at blueyonder.co.uk.invalid> wrote:
>> Dave, perhaps you could clarify one thing on Windows about the 
>> user-mode PPS
>> timestamping.  When you say "serial I/O layer", my understanding is 
>> that
>> this /would/ include virtual COM port devices such as RS-232/USB 
>> adapters.
> Correct.


>> Perhaps the Linux port could also benefit from a user-mode DCD 
>> timestamp, or
>> is there not the justification for the effort?
> It's an ugly hack, and one that fortunately will be migrating out of
> the ntpd Windows port serial I/O code and into its own PPSAPI provider
> DLL, thanks to a suggestion by Juergen Perlinger which I should have
> considered myself.
> There's no provision to enable or disable it currently, for example.
> By putting it in an optional DLL, only those who want end-of-line
> timestamps replaced with PPS timestamps taken in user mode would get
> them.  It's particularly confusing for drivers that have different
> fudge factors for PPS and serial, as NMEA does, and putting it in a
> PPSAPI provider DLL will correct that confusion.
> Apparently no one has had the right mix of idea and motivation to
> modify the POSIX ntpd serial I/O code to watch for DCD transitions to
> accomplish similar.  It's not hard to find proper PPS support in free
> OSes.
> Cheers,
> Dave Hart

That's good news, Dave, as anything which reduces confusion is welcome.  I 
have a variety of boxes here I can test with should you need, and it will 
allow me to measure my own GPS devices as well.


More information about the questions mailing list