[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
>> this /would/ include virtual COM port devices such as RS-232/USB
>> 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
> 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.
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