311 lines
9.0 KiB
Groff
311 lines
9.0 KiB
Groff
.TH PHC2SYS 8 "November 2012" "linuxptp"
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.SH NAME
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phc2sys \- synchronize two or more clocks
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.SH SYNOPSIS
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.B phc2sys \-a
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[
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.B \-r
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] [
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.B \-r
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] [ options ]
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.br
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.B phc2sys
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[
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.BI \-d " pps-device"
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] [
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.BI \-s " device"
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] [
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.BI \-c " device"
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] [
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.BI \-O " offset"
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] [
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.BI \-w
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] [ options ]
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.SH DESCRIPTION
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.B phc2sys
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is a program which synchronizes two or more clocks in the system. Typically,
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it is used to synchronize the system clock to a PTP hardware clock (PHC),
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which itself is synchronized by the
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.BR ptp4l (8)
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program.
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With the
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.B \-a
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option, the clocks to synchronize are fetched from the running
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.B ptp4l
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daemon and the direction of synchronization automatically follows changes of
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the PTP port states.
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Manual configuration is also possible. When using manual configuration, two
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synchronization modes are supported, one uses a pulse per second (PPS)
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signal provided by the source clock and the other mode reads time from the
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source clock directly. Some clocks can be used in both modes, the mode which
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will synchronize the slave clock with better accuracy depends on hardware
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and driver implementation.
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.SH OPTIONS
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.TP
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.BI \-a
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Read the clocks to synchronize from running
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.B ptp4l
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and follow changes in the port states, adjusting the synchronization
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direction automatically. The system clock (CLOCK_REALTIME) is not
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synchronized, unless the
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.B \-r
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option is also specified.
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.TP
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.BI \-r
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Only valid together with the
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.B \-a
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option. Instructs
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.B phc2sys
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to also synchronize the system clock (CLOCK_REALTIME). By default, the
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system clock is not considered as a possible time source. If you want the
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system clock to be eligible to become a time source, specify the
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.B \-r
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option twice.
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.TP
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.BI \-d " pps-device"
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Specify the PPS device of the master clock (e.g. /dev/pps0). With this option
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the PPS synchronization mode is used instead of the direct mode. As the PPS
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signal does not specify time and only marks start of a second, the slave clock
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should be already close to the correct time before
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.B phc2sys
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is started or the
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.B \-s
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option should be used too. With the
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.B \-s
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option the PPS signal of the master clock is enabled automatically, otherwise
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it has to be enabled before
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.B phc2sys
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is started (e.g. by running \f(CWecho 1 > /sys/class/ptp/ptp0/pps_enable\fP).
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This option can be used only with the system clock as the slave clock. Not
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compatible with the
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.B \-a
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option.
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.TP
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.BI \-s " device"
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Specify the master clock by device (e.g. /dev/ptp0) or interface (e.g. eth0) or
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by name (e.g. CLOCK_REALTIME for the system clock). When this option is used
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together with the
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.B \-d
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option, the master clock is used only to correct the offset by whole number of
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seconds, which cannot be fixed with PPS alone. Not compatible with the
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.B \-a
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option.
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.TP
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.BI \-i " interface"
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Performs the exact same function as
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.B \-s
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for compatibility reasons. Previously enabled specifying master clock by network
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interface. However, this can now be done using
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.B \-s
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and this option is no longer necessary. As such it has been deprecated, and
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should no longer be used.
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.TP
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.BI \-c " device"
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Specify the slave clock by device (e.g. /dev/ptp1) or interface (e.g. eth1) or
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by name. The default is CLOCK_REALTIME (the system clock). Not compatible
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with the
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.B \-a
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option.
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.TP
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.BI \-E " servo"
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Specify which clock servo should be used. Valid values are pi for a PI
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controller, linreg for an adaptive controller using linear regression, and
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ntpshm for the NTP SHM reference clock to allow another process to synchronize
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the local clock.
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The default is pi.
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.TP
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.BI \-P " kp"
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Specify the proportional constant of the PI controller. The default is 0.7.
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.TP
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.BI \-I " ki"
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Specify the integral constant of the PI controller. The default is 0.3.
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.TP
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.BI \-S " step"
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Specify the step threshold of the servo. It is the maximum offset that
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the servo corrects by changing the clock frequency instead of stepping the
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clock. The clock is stepped on start regardless of the option if the offset is
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larger than 20 microseconds (unless the
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.BI \-F
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option is used). It's specified in seconds. The value of 0.0 disables stepping
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after the start. The default is 0.0.
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.TP
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.BI \-F " step"
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Specify the step threshold applied only on the first update. It is the maximum
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offset that is corrected by adjusting clock. It's specified in seconds. The
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value of 0.0 disables stepping on start.
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The default is 0.00002 (20 microseconds).
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.TP
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.BI \-R " update-rate"
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Specify the slave clock update rate when running in the direct synchronization
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mode. The default is 1 per second.
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.TP
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.BI \-N " phc-num"
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Specify the number of master clock readings per one slave clock update. Only
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the fastest reading is used to update the slave clock, this is useful to
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minimize the error caused by random delays in scheduling and bus utilization.
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The default is 5.
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.TP
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.BI \-O " offset"
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Specify the offset between the slave and master times in seconds. Not
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compatible with the
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.B \-a
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option. See
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.SM
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.B TIME SCALE USAGE
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below.
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.TP
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.BI \-L " freq-limit"
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The maximum allowed frequency offset between uncorrected clock and the system
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monotonic clock in parts per billion (ppb). This is used as a sanity check of
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the synchronized clock. When a larger offset is measured, a warning message
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will be printed and the servo will be reset. When set to 0, the sanity check is
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disabled. The default is 200000000 (20%).
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.TP
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.BI \-M " segment"
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The number of the SHM segment used by ntpshm servo.
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The default is 0.
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.TP
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.BI \-u " summary-updates"
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Specify the number of clock updates included in summary statistics. The
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statistics include offset root mean square (RMS), maximum absolute offset,
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frequency offset mean and standard deviation, and mean of the delay in clock
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readings and standard deviation. The units are nanoseconds and parts per
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billion (ppb). If zero, the individual samples are printed instead of the
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statistics. The messages are printed at the LOG_INFO level.
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The default is 0 (disabled).
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.TP
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.B \-w
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Wait until ptp4l is in a synchronized state. If the
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.B \-O
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option is not used, also keep the offset between the slave and master
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times updated according to the currentUtcOffset value obtained from ptp4l and
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the direction of the clock synchronization. Not compatible with the
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.B \-a
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option.
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.TP
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.BI \-n " domain-number"
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Specify the domain number used by ptp4l. The default is 0.
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.TP
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.B \-x
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When a leap second is announced, don't apply it in the kernel by stepping the
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clock, but let the servo correct the one-second offset slowly by changing the
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clock frequency (unless the
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.B \-S
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option is used).
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.TP
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.BI \-z " uds-address"
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Specifies the address of the server's UNIX domain socket.
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The default is /var/run/ptp4l.
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.TP
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.BI \-l " print-level"
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Set the maximum syslog level of messages which should be printed or sent to
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the system logger. The default is 6 (LOG_INFO).
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.TP
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.BI \-t " message-tag"
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Specify the tag which is added to all messages printed to the standard output
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or system log. The default is an empty string.
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.TP
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.B \-m
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Print messages to the standard output.
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.TP
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.B \-q
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Don't send messages to the system logger.
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.TP
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.BI \-h
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Display a help message.
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.TP
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.B \-v
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Prints the software version and exits.
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.SH TIME SCALE USAGE
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.B Ptp4l
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uses either PTP time scale or UTC (Coordinated Universal Time) time
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scale. PTP time scale is continuous and shifted against UTC by a few tens of
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seconds as PTP time scale does not apply leap seconds.
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In hardware time stamping mode,
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.B ptp4l
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announces use of PTP time scale and PHC
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is used for the stamps. That means PHC must follow PTP time scale while system
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clock follows UTC. Time offset between these two is maintained by
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.BR phc2sys .
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.B Phc2sys
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acquires the offset value either by reading it from ptp4l when
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.B \-a
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or
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.B \-w
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is in effect or from command line when
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.B \-O
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is supplied. Failure to maintain the correct offset can result in local system
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clock being off some seconds to domain master system clock when in slave mode,
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or incorect PTP time announced to the network in case the host is the domain
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master.
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.SH EXAMPLES
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Synchronize time automatically according to the current
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.B ptp4l
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state, synchronize the system clock to the remote master.
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.RS
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\f(CWphc2sys \-a \-r\fP
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.RE
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Same as above, but when the host becomes the domain master, synchronize time
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in the domain to its system clock.
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.RS
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\f(CWphc2sys \-a \-rr\fP
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.RE
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The host is a domain master, PTP clock is synchronized to system clock and the
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time offset is obtained from
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.BR ptp4l .
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.B Phc2sys
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waits for
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.B ptp4l
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to get at least one port in master or slave mode before starting the
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synchronization.
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.RS
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\f(CWphc2sys \-c /dev/ptp0 \-s CLOCK_REALTIME \-w\fP
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.RE
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Same as above, time offset is provided on command line and
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.B phc2sys
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does not wait for
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.BR ptp4l .
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.RS
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\f(CWphc2sys \-c /dev/ptp0 \-s CLOCK_REALTIME \-O 35\fP
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.RE
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The host is in slave mode, system clock is synchronized from PTP clock,
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.B phc2sys
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waits for
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.B ptp4l
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and the offset is set automatically.
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.RS
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\f(CWphc2sys \-s /dev/ptp0 \-w\fP
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.RE
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Same as above, PTP clock id is read from the network interface, the offset is
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provided on command line
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.B phc2sys
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does not wait.
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.RS
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\f(CWphc2sys \-s eth0 \-O \-35\fP
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.RE
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.SH SEE ALSO
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.BR ptp4l (8)
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