Ubuntu Manpage: phc2sys - synchronize two or more clocks

Provided by: linuxptp_1.9.2-1ubuntu0.1_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. This option does not support bonded interface (e.g. bond0). If ptp4l has a
port on an active-backup bond interface, the -a option can be used to track the
active interface.

-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).

-t message-tag
Specify the tag which is added to all messages printed to the standard output or
system log. The default is an empty string.

-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