.TH PHC2SYS 8 "April 2018" "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 slave clock 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 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

.B phc2sys

is started or the

.B \-s

option should be used too. With the

.B \-s

option the PPS signal of the master clock is enabled automatically, otherwise

it has to be enabled before

.B phc2sys

is started (e.g. by running \f(CWecho 1 > /sys/class/ptp/ptp0/pps_enable\fP).

This option can be used only with the system clock as the slave clock. Not

compatible with the

.B \-a

option.

.TP

.BI \-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

.B \-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

.B \-a

option. This option does not support bonded interface (e.g. bond0). If

.B ptp4l

has a port on an active-backup bond 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 master 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 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

.B \-a

option.

.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 for the NTP SHM reference clock 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 slave clock update rate when running in the direct synchronization

mode. The default is 1 per second.

.TP

.BI \-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.

.TP

.BI \-O " offset"

Specify the offset between the slave and master 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 slave and master

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. 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.

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 domainNumber

Specify the domain number used by phc2sys. The default is 0. Same as option

.B \-n

(see above).

.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).

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 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 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 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 transportSpecific

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

The default is 0.

.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).

.TP

.B pi_proportional_const

Specifies the proportional constant of the PI controller.

Same as option

.B \-P

(see above).

.TP

.B pi_integral_const

Specifies the integral constant of the PI controller.

Same as option

.B \-I

(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 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 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 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 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).

.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 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.

.SH EXAMPLES

Synchronize time automatically according to the current

.B ptp4l

state, synchronize the system clock to the remote master.

.RS

\f(CWphc2sys \-a \-r\fP

.RE

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

.RE

The host is in slave 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 \-35\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)