phc2sys.8

.TH PHC2SYS 8 "February 2023" "linuxptp"
.SH NAME
phc2sys \- synchronize two or more clocks

.SH SYNOPSIS
.B phc2sys \-a
[
.B \-r
] [
.B \-r
] [
.BI \-f " config-file"
] [ options ] [
.I long-options
]
.br
.B phc2sys
[
.BI \-f " config-file"
] [
.BI \-d " pps-device"
] [
.BI \-s " device"
] [
.BI \-c " device"
] [
.BI \-O " offset"
] [
.BI \-w
] [ options ] [
.I long-options
]
.I .\|.\|.


.SH DESCRIPTION
.B 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
.BR ptp4l (8)
program.

With the
.B \-a
option, the clocks to synchronize are fetched from the running
.B 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.

.SH OPTIONS
.TP
.BI \-a
Read the clocks to synchronize from running
.B ptp4l
and follow changes in the port states, adjusting the synchronization
direction automatically. The system clock (CLOCK_REALTIME) is not
synchronized, unless the
.B \-r
option is also specified.
.TP
.BI \-r
Only valid together with the
.B \-a
option. Instructs
.B 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
.B \-r
option twice.
.TP
.BI \-f " config"
Read configuration from the specified file. No configuration file is read by
default.
.TP
.BI \-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
.B \-s
command line option.
This option can be used only with the system clock as the time sink. Not
compatible with the
.B \-a
option.
.TP
.BI \-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
.B \-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
.B \-a
option. This option does not support bonded interface (e.g. bond0, team0). If
.B ptp4l
has a port on an active-backup bond or team interface, the
.B \-a
option can be used to track the active interface.
.TP
.BI \-i " interface"
Performs the exact same function as
.B \-s
for compatibility reasons. Previously enabled specifying source clock by network
interface. However, this can now be done using
.B \-s
and this option is no longer necessary. As such it has been deprecated, and
should no longer be used.
.TP
.BI \-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
.B \-a
option. This option may be given up to 128 times.
.TP
.BI \-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.
.TP
.BI \-P " kp"
Specify the proportional constant of the PI controller. The default is 0.7.
.TP
.BI \-I " ki"
Specify the integral constant of the PI controller. The default is 0.3.
.TP
.BI \-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
.BI \-F
option is used). It's specified in seconds. The value of 0.0 disables stepping
after the start. The default is 0.0.
.TP
.BI \-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).
.TP
.BI \-R " update-rate"
Specify the time sink update rate when running in the direct synchronization
mode. The default is 1 per second.
.TP
.BI \-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.
.TP
.BI \-O " offset"
Specify the offset between the sink and source times in seconds. Not
compatible with the
.B \-a
option.  See
.SM
.B TIME SCALE USAGE
below.
.TP
.BI \-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%).
.TP
.BI \-M " segment"
The number of the SHM segment used by ntpshm servo.
The default is 0.
.TP
.BI \-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).
.TP
.B \-w
Wait until ptp4l is in a synchronized state. If the
.B \-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
.B \-a
option.
.TP
.BI \-n " domain-number"
Specify the domain number used by ptp4l. This option can be used up to 16 times
to specify different domain numbers for different sockets specified by the
.B \-z
option. The domain numbers are assigned according to the order of the options
on the command line.
The default is 0.
.TP
.B \-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
.B \-S
option is used).
.TP
.BI \-z " uds-address"
Specifies the address of the server's UNIX domain socket. This option can be
used up to 16 times in the automatic mode to synchronize clocks between multiple
.B ptp4l
instances.
The default is /var/run/ptp4l.
.TP
.BI \-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).
.TP
.BI \-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.
.TP
.B \-m
Print messages to the standard output.
.TP
.B \-q
Don't send messages to the system logger.
.TP
.BI \-h
Display a help message.
.TP
.B \-v
Prints the software version and exits.

.SH LONG OPTIONS

Each and every configuration file option (see below in section
.BR 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:

.RS
\f(CW\-\-transportSpecific 1   \-\-transportSpecific=1\fP
.RE

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

.SH 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
.BR [global] )
sets the program options. This is the only used option.

.SH FILE OPTIONS

.TP
.B 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
.B \-E
(see above).

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

.TP
.B 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
.B \-F
(see above).

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

.TP
.B 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
.B \-x
(see above).

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

.TP
.B 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
.B \-t
(see above).

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

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

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

.TP
.B 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.

.TP
.B 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
.B \-L
(see above).

.TP
.B 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
.B \-S
(see above).

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

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

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

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

.SH TIME SCALE USAGE

.B 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,
.B 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
.BR phc2sys .

.B Phc2sys
acquires the offset value either by reading it from ptp4l when
.B \-a
or
.B \-w
is in effect or from command line when
.B \-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.

.SH EXAMPLES

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

.RS
\f(CWphc2sys \-a \-r\fP
.RE

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

.RS
\f(CWphc2sys \-a \-rr\fP
.RE

Same as above, in an IEEE 802.1AS domain.

.RS
\f(CWphc2sys \-a \-rr --transportSpecific=1\fP
.RE

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

.RS
\f(CWphc2sys \-c /dev/ptp0 \-s CLOCK_REALTIME \-w\fP
.RE

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

.RS
\f(CWphc2sys \-c /dev/ptp0 \-s CLOCK_REALTIME \-O 37\fP
.RE

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

.RS
\f(CWphc2sys \-s /dev/ptp0 \-w\fP
.RE

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

.RS
\f(CWphc2sys \-s eth0 \-O \-37\fP
.RE

.SH 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.

.SH SEE ALSO
.BR ptp4l (8)