Ubuntu Manpage: phc2sys - synchronize two or more clocks

NAME

       phc2sys - synchronize two or more clocks

SYNOPSIS

       phc2sys -a [ -r ] [ -r ] [ -f config-file ] [ options ] [ long-options ]
       phc2sys  [  -f config-file ] [ -d pps-device ] [ -s device ] [ -c device ] [ -O offset ] [
       -w ] [ options ] [ long-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  time  sink  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.

-f config
Read configuration from the specified file. No configuration file is read by
default.

-d pps-device
Specify the PPS device of the source clock (e.g. /dev/pps0). With this option the
PPS synchronization mode is used instead of the direct mode. The matching PHC must
be specified using the -s command line option. This option can be used only with
the system clock as the time sink. Not compatible with the -a option.

-s device
Specify the source 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 source 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, team0). If ptp4l
has a port on an active-backup bond or team 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 source 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 time sink 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. This option may be given up to 128 times.

-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 and
refclock_sock for the NTP SHM and chrony SOCK reference clocks respectively 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 changing the clock frequency. 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 time sink update rate when running in the direct synchronization mode.
The default is 1 per second.

-N phc-num
Specify the number of source clock readings used for each time sink update. Only
the fastest reading is used to update the 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 sink and source 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 sink and source 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.

LONG OPTIONS

       Each and every configuration file option (see below  in  section  FILE OPTIONS)  may  also
       appear as a "long" style command line argument.  For example, the transportSpecific option
       may be set using either of these two forms:

              --transportSpecific 1   --transportSpecific=1

       Option values given on the command line override values  in  the  global  section  of  the
       configuration file (which, in turn overrides default values).

CONFIGURATION FILE

       The  configuration  file  is  divided  into  sections.  Each  section  starts  with a line
       containing its name enclosed in brackets and it follows with settings.   Each  setting  is
       placed  on  a separate line, it contains the name of the option and the value separated by
       whitespace characters. Empty lines and lines starting with # are ignored.

       The global section (indicated as [global]) sets the program options. This is the only used
       option.

FILE OPTIONS

clock_servo
The servo which is used to synchronize the local clock. Valid values are "pi" for a
PI controller, "linreg" for an adaptive controller using linear regression,
"ntpshm" for the NTP SHM reference clock to allow another process to synchronize
the local clock (the SHM segment number is set to the domain number), and "nullf"
for a servo that always dials frequency offset zero (for use in SyncE nodes). The
default is "pi." Same as option -E (see above).

domainNumber
Specify the domain number used by phc2sys. The default is 0. Same as option -n (see
above).

first_step_threshold
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). Same
as option -F (see above).

free-running
Don't adjust the sink clock if enabled. The default is 0 (disabled).

kernel_leap
When a leap second is announced, let the kernel apply it by stepping the clock
instead of correcting the one-second offset with servo, which would correct the
one-second offset slowly by changing the clock frequency (unless the step_threshold
option is set to correct such offset by stepping). Relevant only with software time
stamping. The default is 1 (enabled). Same as option -x (see above).

logging_level
The maximum logging level of messages which should be printed. The default is 6
(LOG_INFO). Same as option -l (see above).

message_tag
The tag which is added to all messages printed to the standard output or system
log. The default is an empty string (which cannot be set in the configuration file
as the option requires an argument). Same as option -t (see above).

ntpshm_segment
The number of the SHM segment used by ntpshm servo. The default is 0. Same as
option -M (see above).

pi_integral_const
Specifies the integral constant of the PI controller. Same as option -I (see
above).

pi_proportional_const
Specifies the proportional constant of the PI controller. Same as option -P (see
above).

refclock_sock_address
The address of the UNIX domain socket to be used by the refclock_sock servo. The
default is /var/run/refclock.ptp.sock.

sanity_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%). Same as option -L (see above).

step_threshold
Specifies the step threshold of the servo. It is the maximum offset that the servo
corrects by changing the clock frequency (phase when using nullf servo) 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. Same as option -S (see above).

transportSpecific
The transport specific field. Must be in the range 0 to 255. The default is 0.

uds_address
Specifies the address of the server's UNIX domain socket. The default is
/var/run/ptp4 Same as option -z (see above).

use_syslog
Print messages to the system log if enabled. The default is 1 (enabled). Related
to option -q (see above).

verbose
Print messages to the standard output if enabled. The default is 0 (disabled).
Related to option -m (see above).

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  the local system clock being offset some whole number of seconds from the
       domain server's clock when in client mode, or incorect PTP time announced to  the  network
       in case the host is the domain server.

EXAMPLES

       Synchronize  time  automatically  according  to the current ptp4l state, synchronizing the
       system clock to the remote server.

              phc2sys -a -r

       Same as above, but when the host becomes the domain server, synchronize time in the domain
       to its system clock.

              phc2sys -a -rr

       Same as above, in an IEEE 802.1AS domain.

              phc2sys -a -rr --transportSpecific=1

       The host is a domain server, PTP clock is synchronized to system clock and the time offset
       is obtained from ptp4l.  Phc2sys waits for ptp4l to get at least one  port  in  server  or
       client mode before starting the synchronization.

              phc2sys -c /dev/ptp0 -s CLOCK_REALTIME -w

       Same  as  above,  time  offset  is  provided on command line and phc2sys does not wait for
       ptp4l.

              phc2sys -c /dev/ptp0 -s CLOCK_REALTIME -O 37

       The host is in client mode, system clock is synchronized from PTP clock, phc2sys waits for
       ptp4l and the offset is set automatically.

              phc2sys -s /dev/ptp0 -w

       Same  as above, PTP clock id is read from the network interface, the offset is provided on
       command line phc2sys does not wait.

              phc2sys -s eth0 -O -37

WARNING

       Be cautious when the same configuration file is used for both ptp4l and phc2sys.  Keep  in
       mind,  that  values specified in the configuration file take precedence over their default
       values. If a certain option, which is common to ptp4l and phc2sys, is specified to a  non-
       default  value  in  the  configuration file (p.e., for ptp4l), then this non-default value
       applies also for phc2sys. This might be not what is expected.

       It is recommended to use seperate configuration files for ptp4l and phc2sys  in  order  to
       avoid any unexpected behavior.