Re: [chrony-users] Forcing chrony to use the clear (falling) edge of negative PPS

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Since it is gpsd that is servicing the interrupt, not chrony, surely you have
to look at gpsd as to how to get it, not chrony, to regard the proper edge of
the pulse.
Or get a non-inverting converter (many serial ports can read ttl fine, despite
what the RS232 standards say, so it is not clear that you need the converter).

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On Sat, 3 Jul 2021, ZB wrote:

[CAUTION: Non-UBC Email]Hi Everyone,

I have a Novatel FlexPak G2 that puts out a Negative PPS (because it's going through a TTL to RS232
converter, which flips the pulse). The pulse width is 1ms. I have gpsd (v3.22) and chrony (v4.1) working
together on my Linux Mint 19.1 machine. 

I have configured chrony to be fed from gpsd as follows in the /etc/chrony.conf file:

refclock SHM 0 delay 0.5 refid NMEA 
refclock SOCK /var/run/chrony.ttyS0.sock precision 1e-7 refid PPS

Question:  how can I tell Chrony to use the falling edge (clear edge, which is the first leading edge of
the negative PPS) ? 

In the manual it says that you can use the keyword "clear" if you are using the PPS reflcock i.e.
reflclock PPS /dev/pps0:clear but since I am using gpsd, I am supposed to use the SOCK method, correct

Putting refclock SOCK /var/run/chrony.ttyS0.sock:clear causes chronyd to error out. 

Any help appreciated, thanks!

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