Ubuntu Manpage: phc2sys - synchronize two or more clocks

Provided by: linuxptp_1.8-1ubuntu0.1_amd64

NAME

       phc2sys - synchronize two or more clocks

SYNOPSIS

       phc2sys -a [ -r ] [ -r ] [ options ]
       phc2sys [ -d pps-device ] [ -s device ] [ -c device ] [ -O offset ] [ -w ] [ options ]

DESCRIPTION

       phc2sys  is  a  program  which  synchronizes  two  or more clocks in the system. Typically, it is used to
       synchronize the system clock to a PTP hardware clock (PHC), which itself is synchronized by the  ptp4l(8)
       program.

       With the -a option, the clocks to synchronize are fetched from the running ptp4l daemon and the direction
       of synchronization automatically follows changes of the PTP port states.

       Manual configuration is also possible. When using manual configuration,  two  synchronization  modes  are
       supported, one uses a pulse per second (PPS) signal provided by the source clock and the other mode reads
       time from the source clock directly. Some clocks  can  be  used  in  both  modes,  the  mode  which  will
       synchronize the slave clock with better accuracy depends on hardware and driver implementation.

OPTIONS

-a Read the clocks to synchronize from running ptp4l and follow changes in the port states, adjusting
the synchronization direction automatically. The system clock (CLOCK_REALTIME) is not
synchronized, unless the -r option is also specified.

-r Only valid together with the -a option. Instructs phc2sys to also synchronize the system clock
(CLOCK_REALTIME). By default, the system clock is not considered as a possible time source. If you
want the system clock to be eligible to become a time source, specify the -r option twice.

-d pps-device
Specify the PPS device of the master clock (e.g. /dev/pps0). With this option the PPS
synchronization mode is used instead of the direct mode. As the PPS signal does not specify time
and only marks start of a second, the slave clock should be already close to the correct time
before phc2sys is started or the -s option should be used too. With the -s option the PPS signal
of the master clock is enabled automatically, otherwise it has to be enabled before phc2sys is
started (e.g. by running echo 1 > /sys/class/ptp/ptp0/pps_enable). This option can be used only
with the system clock as the slave clock. Not compatible with the -a option.

-s device
Specify the master clock by device (e.g. /dev/ptp0) or interface (e.g. eth0) or by name (e.g.
CLOCK_REALTIME for the system clock). When this option is used together with the -d option, the
master clock is used only to correct the offset by whole number of seconds, which cannot be fixed
with PPS alone. Not compatible with the -a option.

-i interface
Performs the exact same function as -s for compatibility reasons. Previously enabled specifying
master clock by network interface. However, this can now be done using -s and this option is no
longer necessary. As such it has been deprecated, and should no longer be used.

-c device
Specify the slave clock by device (e.g. /dev/ptp1) or interface (e.g. eth1) or by name. The
default is CLOCK_REALTIME (the system clock). Not compatible with the -a option.

-E servo
Specify which clock servo should be used. Valid values are pi for a PI controller, linreg for an
adaptive controller using linear regression, and ntpshm for the NTP SHM reference clock to allow
another process to synchronize the local clock. The default is pi.

-P kp Specify the proportional constant of the PI controller. The default is 0.7.

-I ki Specify the integral constant of the PI controller. The default is 0.3.

-S step
Specify the step threshold of the servo. It is the maximum offset that the servo corrects by
changing the clock frequency instead of stepping the clock. The clock is stepped on start
regardless of the option if the offset is larger than 20 microseconds (unless the -F option is
used). It's specified in seconds. The value of 0.0 disables stepping after the start. The default
is 0.0.

-F step
Specify the step threshold applied only on the first update. It is the maximum offset that is
corrected by adjusting clock. It's specified in seconds. The value of 0.0 disables stepping on
start. The default is 0.00002 (20 microseconds).

-R update-rate
Specify the slave clock update rate when running in the direct synchronization mode. The default
is 1 per second.

-N phc-num
Specify the number of master clock readings per one slave clock update. Only the fastest reading
is used to update the slave clock, this is useful to minimize the error caused by random delays in
scheduling and bus utilization. The default is 5.

-O offset
Specify the offset between the slave and master times in seconds. Not compatible with the -a
option. See TIME SCALE USAGE below.

-L freq-limit
The maximum allowed frequency offset between uncorrected clock and the system monotonic clock in
parts per billion (ppb). This is used as a sanity check of the synchronized clock. When a larger
offset is measured, a warning message will be printed and the servo will be reset. When set to 0,
the sanity check is disabled. The default is 200000000 (20%).

-M segment
The number of the SHM segment used by ntpshm servo. The default is 0.

-u summary-updates
Specify the number of clock updates included in summary statistics. The statistics include offset
root mean square (RMS), maximum absolute offset, frequency offset mean and standard deviation, and
mean of the delay in clock readings and standard deviation. The units are nanoseconds and parts
per billion (ppb). If zero, the individual samples are printed instead of the statistics. The
messages are printed at the LOG_INFO level. The default is 0 (disabled).

-w Wait until ptp4l is in a synchronized state. If the -O option is not used, also keep the offset
between the slave and master times updated according to the currentUtcOffset value obtained from
ptp4l and the direction of the clock synchronization. Not compatible with the -a option.

-n domain-number
Specify the domain number used by ptp4l. The default is 0.

-x When a leap second is announced, don't apply it in the kernel by stepping the clock, but let the
servo correct the one-second offset slowly by changing the clock frequency (unless the -S option
is used).

-z uds-address
Specifies the address of the server's UNIX domain socket. The default is /var/run/ptp4l.

-l print-level
Set the maximum syslog level of messages which should be printed or sent to the system logger. The
default is 6 (LOG_INFO).

-m Print messages to the standard output.

-q Don't send messages to the system logger.

-h Display a help message.

-v Prints the software version and exits.

TIME SCALE USAGE

       Ptp4l  uses  either  PTP  time  scale  or UTC (Coordinated Universal Time) time scale.  PTP time scale is
       continuous and shifted against UTC by a few tens of seconds  as  PTP  time  scale  does  not  apply  leap
       seconds.

       In  hardware  time  stamping  mode, ptp4l announces use of PTP time scale and PHC is used for the stamps.
       That means PHC must follow PTP time scale while system clock follows UTC.  Time offset between these  two
       is maintained by phc2sys.

       Phc2sys  acquires  the  offset  value  either by reading it from ptp4l when -a or -w is in effect or from
       command line when -O is supplied.  Failure to maintain the correct offset  can  result  in  local  system
       clock  being  off  some  seconds  to  domain master system clock when in slave mode, or incorect PTP time
       announced to the network in case the host is the domain master.

EXAMPLES