But trailing isn't the same as falling. The leading edge can be of either polarity.
On Wed, Nov 9, 2016 at 11:28 PM, Bob Stewart <b...@evoria.net> wrote: > Tom, > How many times have people posted here, on time-nuts, not to trust the > trailing edge of a 1PPS pulse? > > Bob ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > From: Tom Van Baak <t...@leapsecond.com> > To: Discussion of precise time and frequency measurement < > time-nuts@febo.com> > Sent: Wednesday, November 9, 2016 4:44 PM > Subject: Re: [time-nuts] How to get PPS from ublox mini-PCI GPS to APU2 > SoC serial port for ntpd > > Bob, > > The PIC's I use have essentially no jitter. If they generate a 1PPS the > edge and the pulse width are perfect, down to picoseconds. The talk about > "other stuff" and "priority" and "number of compares" and "ambiguity" is > worrisome. It sounds like a design or coding flaw to me, like what happens > when people try to do precise time with a high level language. > > /tvb > > ----- Original Message ----- > From: "Bob Stewart" <b...@evoria.net> > To: "Discussion of precise time and frequency measurement" < > time-nuts@febo.com> > Sent: Wednesday, November 09, 2016 9:30 AM > Subject: Re: [time-nuts] How to get PPS from ublox mini-PCI GPS to APU2 > SoC serial port for ntpd > > > I'd like to comment on the idea of measuring the width of the pulse. My > experience with creating the 1PPS from an interrupt is that it's fairly > straightforward how to do the set interrupt: The interrupt happens, you > execute one, maybe two instructions to raise the output pin, and you leave > the interrupt routine. But, resetting the pin is a different story. Unless > you've got a lot of interrupt vectors to play with, the reset part of the > 1PPS signal is delegated to a general purpose timing interrupt where you're > doing a lot of other stuff - and it has a somewhat lower priority. So, you > wind up doing a number of compares to see if you should reset the pin, > which adds some ambiguity to the set/reset times. > Granted, I'm doing this on a general purpose PIC, but I have read comments > about various receivers having some jitter on the reset side of their 1PPS > pulse. > Bob > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.