.TH PHC2SYS 8 "November 2012" "linuxptp"
.SH NAME
phc2sys \- synchronize two clocks

.SH SYNOPSIS
.B phc2sys
{
.BI \-d " pps-device"
[
.BI \-s " phc-device"
|
.BI \-i " interface"
] |
.BI \-s " phc-device"
|
.BI \-i " interface"
} [
.BI \-c " phc-device"
] [
.BI \-P " kp"
] [
.BI \-I " ki"
] [
.BI \-R " update-rate"
] [
.BI \-N " clock-readings"
] [
.BI \-O " offset"
] [
.B \-v
]

.SH DESCRIPTION
.B 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
.BR 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. The PPS mode is usually preferred, because reading the
PHC is slow and introduces an unknown error in the readings, but not all PHCs
provide the PPS signal.

.SH OPTIONS
.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. 
.TP
.BI \-s " phc-device"
Specify the master clock by device (e.g. /dev/ptp0) or name (e.g. CLOCK_REALTIME
for the system clock). When this option is used together with the
.B \-d
option, the master clock is read only on start to fix an offset over 0.5
seconds which cannot be fixed with PPS alone.
.TP
.BI \-i " interface"
Similar to the
.B \-s
option, but specified by the interface which provides the master clock. 
.TP
.BI \-c " phc-device"
Specify the slave clock by device (e.g. /dev/ptp1) or name. The default is
CLOCK_REALTIME (the system clock).
.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 \-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.
The default is 0 seconds.
.TP
.BI \-h
Display a help message.
.TP
.B \-v
Prints the software version and exits.

.SH SEE ALSO
.BR ptp4l (8)