[ntp:questions] How do I validate my PPS clocks?

Gabs Ricalde gsricalde at gmail.com
Tue Feb 26 12:02:21 UTC 2013

The PPSAPI specification (RFC 2783) has an echo function where the PPS
driver must assert/clear an output pin after receiving the PPS event,
although the Linux PPS drivers doesn't seem to implement this.

I tried this method on a polling PPS driver but using the time mark
function of a LEA-6T GPS receiver instead of a scope or time interval
counter. The delay was about 0.7 us.

On Tue, Feb 26, 2013 at 7:45 PM, Charles Elliott <elliott.ch at verizon.net> wrote:
>         I performed the same kind of test on a commercial real-time O/S at
> the time sold by Intel, but since divested.  I put code in a program to
> output a digital pulse when the mock application program received
> notification of the parallel port interrupt and measured the interrupt
> service delay between generating the interrupt and sensing it with two
> channels of an oscilloscope, which was HIGHLY variable, although I can't
> recall the numbers.
>         You could do the same thing by patching NTPD to output a pulse when
> the PPS signal was processed and then measuring the time difference between
> the actual PPS signal and the digital pulse with an oscilloscope.  Compared
> to what I paid for one in the 1990s, oscilloscopes are dirt cheap now.
> There are people who sell them on eBay too.
> Charles Elliott

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