PHC2SYS(8)						      System Manager's Manual							PHC2SYS(8)

NAME

       phc2sys - synchronize two clocks

SYNOPSIS

       phc2sys [ -wmqvx ] [ -d pps-device ] [ -s device ] [ -c device ] [ -O offset ] [ -P kp ] [ -I ki ] [ -S step ] [ -F step ] [ -R update-rate
       ] [ -N clock-readings ] [ -u summary-updates ] [ -n domain-number ] [ -l print-level ]

DESCRIPTION

       phc2sys is a program which synchronizes two 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.

       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

       -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. This option can be used only with the system clock
	      as the slave clock.

       -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 sec-
	      onds, which cannot be fixed with PPS alone.

       -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).

       -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 PI controller. It is the maximum offset that the controller corrects by changing the clock fre-
	      quency instead of stepping the clock. The clock is stepped on start regardless of the option  if	the  offset  is  larger  than  100
	      nanoseconds (unless the -F option is used). 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 adjusting clock. The
	      value of 0.0 disables stepping on start. The default is 0.0000001 (100 nanoseconds).

       -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.  See TIME SCALE USAGE below.

       -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 mes-
	      sages 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.

       -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).

       -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).

       -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.

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 -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

       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

SEE ALSO

       ptp4l(8)

linuxptp							   November 2012							PHC2SYS(8)