phc2sys(8): 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. This option can be used up to 16 times to specify different domain numbers for different sockets specified by the -z option. The domain numbers are assigned according to the order of the options on the command line. 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. This option can be used up to 16 times in the automatic mode to synchronize clocks between multiple ptp4l instances. 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

active_key_id: Used in conjunction with spp and sa_file directives to specify which key from the spp defined Security Association should be used for outbound icv calculations. All Security Assocations are read from the file specified by sa_file. Requires spp and sa_file directives. Must be in the range of 1 to 2^{^32}-1, inclusive. The default is 0 (disabled).
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. If the tag contains the string "{level}", it will be replaced with the log level of the message as a number. 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.
sa_file: Specifies the location of the file containing Security Associations used for immediate security processing of the Authentication TLV in support of the optional security mechanism defined in ieee1588-2019 ch 14.16. See SECURITY ASSOCIATION OPTIONS for information on how this file should be formatted. spp and active_key_id should be specifed for each port to indicate which Security Association from the sa_file should be used. The default is an empty string.
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 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).
spp: Specifies the Security Parameters Pointer of the desired Security Association to be used for Authentication TLV support for a given port. Any port with an assigned spp will attach Authentication TLVs to all outbound messages and check for Authentication TLVs on all inbound messages in accordance to the corresponding security association sourced via the sa_file directive. Outbound Authentication TLVs are generated using the key specified by active_key_id. Not compatible with one step ports or advertised versions less then PTPv2.1. Requires sa_file and active_key_id directives. Must be in the range of 0 to 255, inclusive. The default is -1 (disabled).
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 (i.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.