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 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.

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

-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, 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
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 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 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.

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

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

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).

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

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).

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).

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

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).

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

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

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).

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

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

       Synchronize time automatically according to the current ptp4l state, synchronize the system clock to  the
       remote master.

              phc2sys -a -r

       Same  as above, but when the host becomes the domain master, 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 master, 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 master or slave 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 35

       The  host  is in slave 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 -35

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.