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19.7. Verifying Time Synchronization

When PTP time synchronization is working correctly, new messages with offsets and frequency adjustments are printed periodically to the ptp4l and phc2sys outputs if hardware time stamping is used. The output values converge shortly. You can see these messages in the /var/log/messages file.
The following examples of the ptp4l and the phc2sys output contain:
  • offset (in nanoseconds)
  • frequency offset (in parts per billion (ppb))
  • path delay (in nanoseconds)
Example of the ptp4l output:
ptp4l[352.359]: selected /dev/ptp0 as PTP clock
ptp4l[352.361]: port 1: INITIALIZING to LISTENING on INITIALIZE
ptp4l[352.361]: port 0: INITIALIZING to LISTENING on INITIALIZE
ptp4l[353.210]: port 1: new foreign master 00a069.fffe.0b552d-1
ptp4l[357.214]: selected best master clock 00a069.fffe.0b552d
ptp4l[357.214]: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l[359.224]: master offset       3304 s0 freq      +0 path delay      9202
ptp4l[360.224]: master offset       3708 s1 freq  -29492 path delay      9202
ptp4l[361.224]: master offset      -3145 s2 freq  -32637 path delay      9202
ptp4l[361.224]: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l[362.223]: master offset       -145 s2 freq  -30580 path delay      9202
ptp4l[363.223]: master offset       1043 s2 freq  -29436 path delay      8972
ptp4l[364.223]: master offset        266 s2 freq  -29900 path delay      9153
ptp4l[365.223]: master offset        430 s2 freq  -29656 path delay      9153
ptp4l[366.223]: master offset        615 s2 freq  -29342 path delay      9169
ptp4l[367.222]: master offset       -191 s2 freq  -29964 path delay      9169
ptp4l[368.223]: master offset        466 s2 freq  -29364 path delay      9170
ptp4l[369.235]: master offset         24 s2 freq  -29666 path delay      9196
ptp4l[370.235]: master offset       -375 s2 freq  -30058 path delay      9238
ptp4l[371.235]: master offset        285 s2 freq  -29511 path delay      9199
ptp4l[372.235]: master offset        -78 s2 freq  -29788 path delay      9204
Example of the phc2sys output:
phc2sys[526.527]: Waiting for ptp4l...
phc2sys[527.528]: Waiting for ptp4l...
phc2sys[528.528]: phc offset     55341 s0 freq      +0 delay   2729
phc2sys[529.528]: phc offset     54658 s1 freq  -37690 delay   2725
phc2sys[530.528]: phc offset       888 s2 freq  -36802 delay   2756
phc2sys[531.528]: phc offset      1156 s2 freq  -36268 delay   2766
phc2sys[532.528]: phc offset       411 s2 freq  -36666 delay   2738
phc2sys[533.528]: phc offset       -73 s2 freq  -37026 delay   2764
phc2sys[534.528]: phc offset        39 s2 freq  -36936 delay   2746
phc2sys[535.529]: phc offset        95 s2 freq  -36869 delay   2733
phc2sys[536.529]: phc offset      -359 s2 freq  -37294 delay   2738
phc2sys[537.529]: phc offset      -257 s2 freq  -37300 delay   2753
phc2sys[538.529]: phc offset       119 s2 freq  -37001 delay   2745
phc2sys[539.529]: phc offset       288 s2 freq  -36796 delay   2766
phc2sys[540.529]: phc offset      -149 s2 freq  -37147 delay   2760
phc2sys[541.529]: phc offset      -352 s2 freq  -37395 delay   2771
phc2sys[542.529]: phc offset       166 s2 freq  -36982 delay   2748
phc2sys[543.529]: phc offset        50 s2 freq  -37048 delay   2756
phc2sys[544.530]: phc offset       -31 s2 freq  -37114 delay   2748
phc2sys[545.530]: phc offset      -333 s2 freq  -37426 delay   2747
phc2sys[546.530]: phc offset       194 s2 freq  -36999 delay   2749
To reduce the ptp4l output and print only the values, use the summary_interval directive. The summary_interval directive is specified as 2 to the power of n in seconds. For example, to reduce the output to every 1024 seconds, add the following line to the /etc/ptp4l.conf file:
summary_interval 10
An example of the ptp4l output, with summary_interval set to 6:
ptp4l: [615.253] selected /dev/ptp0 as PTP clock
ptp4l: [615.255] port 1: INITIALIZING to LISTENING on INITIALIZE
ptp4l: [615.255] port 0: INITIALIZING to LISTENING on INITIALIZE
ptp4l: [615.564] port 1: new foreign master 00a069.fffe.0b552d-1
ptp4l: [619.574] selected best master clock 00a069.fffe.0b552d
ptp4l: [619.574] port 1: LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l: [623.573] port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l: [684.649] rms  669 max 3691 freq -29383 ± 3735 delay  9232 ± 122
ptp4l: [748.724] rms  253 max  588 freq -29787 ± 221 delay  9219 ± 158
ptp4l: [812.793] rms  287 max  673 freq -29802 ± 248 delay  9211 ± 183
ptp4l: [876.853] rms  226 max  534 freq -29795 ± 197 delay  9221 ± 138
ptp4l: [940.925] rms  250 max  562 freq -29801 ± 218 delay  9199 ± 148
ptp4l: [1004.988] rms  226 max  525 freq -29802 ± 196 delay  9228 ± 143
ptp4l: [1069.065] rms  300 max  646 freq -29802 ± 259 delay  9214 ± 176
ptp4l: [1133.125] rms  226 max  505 freq -29792 ± 197 delay  9225 ± 159
ptp4l: [1197.185] rms  244 max  688 freq -29790 ± 211 delay  9201 ± 162
By default, summary_interval is set to 0, so messages are printed once per second, which is the maximum frequency. The messages are logged at the LOG_INFO level. To disable messages, use the -l option to set the maximum log level to 5 or lower:
~]# phc2sys -l 5
You can use the -u option to reduce the phc2sys output:
~]# phc2sys -u summary-updates
Where summary-updates is the number of clock updates to include in summary statistics. An example follows:
~]# phc2sys -s eth3 -w -m -u 60
phc2sys[700.948]: rms 1837 max 10123 freq -36474 ± 4752 delay  2752 ±  16
phc2sys[760.954]: rms  194 max  457 freq -37084 ± 174 delay  2753 ±  12
phc2sys[820.963]: rms  211 max  487 freq -37085 ± 185 delay  2750 ±  19
phc2sys[880.968]: rms  183 max  440 freq -37102 ± 164 delay  2734 ±  91
phc2sys[940.973]: rms  244 max  584 freq -37095 ± 216 delay  2748 ±  16
phc2sys[1000.979]: rms  220 max  573 freq -36666 ± 182 delay  2747 ±  43
phc2sys[1060.984]: rms  266 max  675 freq -36759 ± 234 delay  2753 ±  17
When used with these options, the interval for updating the statistics is set to 60 seconds (-u), phc2sys waits until ptp4l is in synchronized state (-w), and messages are printed to the standard output (-m). For further details about the phc2sys options, see the phc2sys(5) man page.
The output includes:
  • offset root mean square (rms)
  • maximum absolute offset (max)
  • frequency offset (freq): its mean, and standard deviation
  • path delay (delay): its mean, and standard deviation