23.2.3. Starting ptp4l
The ptp4l program tries to use hardware time stamping by default. To use ptp4l with hardware time stamping capable drivers and NICs, you must provide the network interface to use with the
-ioption. Enter the following command as
~]#Where eth3 is the interface you want to configure. Below is example output from ptp4l when the
ptp4l -i eth3 -m
PTPclock on the NIC is synchronized to a master:
~]#The master offset value is the measured offset from the master in nanoseconds. The
ptp4l -i eth3 -mselected eth3 as PTP clock port 1: INITIALIZING to LISTENING on INITIALIZE port 0: INITIALIZING to LISTENING on INITIALIZE port 1: new foreign master 00a069.fffe.0b552d-1 selected best master clock 00a069.fffe.0b552d port 1: LISTENING to UNCALIBRATED on RS_SLAVE master offset -23947 s0 freq +0 path delay 11350 master offset -28867 s0 freq +0 path delay 11236 master offset -32801 s0 freq +0 path delay 10841 master offset -37203 s1 freq +0 path delay 10583 master offset -7275 s2 freq -30575 path delay 10583 port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED master offset -4552 s2 freq -30035 path delay 10385
s2strings indicate the different clock servo states:
s1is clock step and
s2is locked. Once the servo is in the locked state (
s2), the clock will not be stepped (only slowly adjusted) unless the
pi_offset_constoption is set to a positive value in the configuration file (described in the
ptp4l(8)man page). The
freqvalue is the frequency adjustment of the clock in parts per billion (ppb). The path delay value is the estimated delay of the synchronization messages sent from the master in nanoseconds. Port 0 is a Unix domain socket used for local
PTPmanagement. Port 1 is the
eth3interface (based on the example above.) INITIALIZING, LISTENING, UNCALIBRATED and SLAVE are some of possible port states which change on the INITIALIZE, RS_SLAVE, MASTER_CLOCK_SELECTED events. In the last state change message, the port state changed from UNCALIBRATED to SLAVE indicating successful synchronization with a
The ptp4l program can also be started as a service by running:
~]#When running as a service, options are specified in the
service ptp4l start
/etc/sysconfig/ptp4lfile. More information on the different ptp4l options and the configuration file settings can be found in the
By default, messages are sent to
/var/log/messages. However, specifying the
-moption enables logging to standard output which can be useful for debugging purposes.
To enable software time stamping, the
-Soption needs to be used as follows:
ptp4l -i eth3 -m -S
126.96.36.199. Selecting a Delay Measurement Mechanism
There are two different delay measurement mechanisms and they can be selected by means of an option added to the
ptp4lcommand as follows:
-Pselects the peer-to-peer (P2P) delay measurement mechanism.The P2P mechanism is preferred as it reacts to changes in the network topology faster, and may be more accurate in measuring the delay, than other mechanisms. The P2P mechanism can only be used in topologies where each port exchanges PTP messages with at most one other P2P port. It must be supported and used by all hardware, including transparent clocks, on the communication path.
-Eselects the end-to-end (E2E) delay measurement mechanism. This is the default.The E2E mechanism is also referred to as the delay “request-response” mechanism.
-Aenables automatic selection of the delay measurement mechanism.The automatic option starts ptp4l in E2E mode. It will change to P2P mode if a peer delay request is received.
All clocks on a single
PTPcommunication path must use the same mechanism to measure the delay. A warning will be printed when a peer delay request is received on a port using the E2E mechanism. A warning will be printed when a E2E delay request is received on a port using the P2P mechanism.