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 counld 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