PPSCHECK(8)		      GPSD Documentation		   PPSCHECK(8)

NAME
       ppscheck - tool to check a serial port for PPS

SYNOPSIS
       ppscheck [-?] [--help] [-p] [--pps] [--version] [-h] [-V]

       ppscheck [-m] device

DESCRIPTION
       ppscheck watches a specified serial port for transitions that might be
       PPS. It looks for changes in handshake lines CD, CTS, DSR, and RI by
       running ioctl(...., TIOCMIWAIT, ...) in a loop. When it sees a state
       change it emits a timestamped line of output dumping the state of the
       handshake signals. It’s useful for checking whether a device is
       emitting PPS.

       ppscheck can run as a normal user, but that user must have permissions
       to read the target device.  Running under sudo may, or may not, work.
       Running as root will always work.

       To check the first serial port do this:

	   # ppscheck /dev/ttyS0

       As a side effect, ppscheck will try to create the matching /dev/ppsX by
       setting the tty line discipline (ldisc) to N_PPS (18).  You should then
       have a device /dev/pps0.	 Note that not all serial devices support
       ldisc N_PPS.

       You can now use ppscheck to see if the KPPS (RFC 2783) interface is
       working:

	   # ppscheck /dev/pps0

       ppscheck is not intended for routine use, but rather for diagnostic
       purposes. Once you have verified a particular device can output PPS
       signals you will never need to use it again on that device.

OPTIONS
       The program accepts the following options:

       -?, `-h, `--help
	   Print help message, then exit.

       -m, `--match
	   Find PPS device that matches device.

       -p, `--pps
	   Print active PPS devices, then exit.

       -V, `--version
	   Dump version, then exit.

       -x SEC, --seconds SEC
	   Exit after delay of SEC seconds.

ARGUMENTS
       The device argument should be the pathname of a device. Such as
       /dev/ttyS0 or /dev/pps0. It will be the device monitored.

       For a tty device, each output line is the second and nanosecond parts
       of a timestamp followed by the names of the handshake signals then
       asserted. Off transitions may generate lines with no signals asserted.

       For a pps device, each output line will contain the assert and clear
       times last detected by KPPS.

       If you don’t see output within a second, use cgps, xgps, or some other
       equivalent tool to check that your device has a satellite lock and is
       getting 3D fixes before giving up on the possibility of PPS.

       Check your cable. Cheap DB9 to DB9 cables such as those issued with
       UPSes often carry TXD/RXD/GND only, omitting handshake lines such as
       CD. Suspect this especially if the cable jacket looks too skinny to
       hold more than three leads!

       Most GPS that have built in USB do not support PPS. When in doubt,
       contact the vendor for confirmation that your device does supply PPS.

RETURN VALUES
       0
	   OK

       1
	   if the device could not be opened, or some other failure

SEE ALSO
       cgps(1), xgps(1), gpsd(8)

RESOURCES
       Project web site:  <https://gpsd.io/>

COPYING
       This file is Copyright 2013 by the GPSD project
       SPDX-License-Identifier: BSD-2-clause

AUTHOR
       Eric S. Raymond

GPSD, Version 3.26.1		  2025-05-15			   PPSCHECK(8)