I have been running phase stability tests of linuxptp-1.5 using linreg
servo on an Intel i350-T2 (HP ProLiant DL120G6 RHEL 7.0 kernel 3.10)
synchronizing to an FEI-Zyfer Gsync Time and Frequency Processor. Below are
sigma-tau plots of the ptp4l phase offset between the HP server and the
Gsync PTP master, and phase offsets of CLOCK_REALTIME which is steered by
phc2sys to /dev/ptp0).
The igb driver is 5.2.5.
The sigma-tau plot for ptp4l (TDEV curve in violet) shows that we reach the
white noise flicker floor of 20 microseconds phase stability at about 8
hours. The environment is not temperature-controlled and there are
resulting frequency instabilities. But overall this looks great.
The ptp4l phase offset statistics:
min=-109 ns
max=104 ns
mean =-2.69 ns
standard deviation=35.0 ns
rate=1.32e-15 seconds/sec
drift=1.69e-16 per day
sample size 261,634 points
tau=2 sec.
The phc2sys phase offset statistics:
min=-365 ns
max=347 ns
mean=-8.31 ns
standard dev.=100.2 ns
rate=6.82e-06 drift=-1.80e-06
sample size 522,802 points
tau=1 sec.
My ptp4l.conf was:
network_transport UDPv4
logAnnounceInterval 1
logSyncInterval 1
logMinDelayReqInterval 2
logMinPdelayReqInterval 2
announceReceiptTimeout 4
clock_servo linreg
time_stamping hardware
slaveOnly 1
priority1 200
priority2 200
free_running 0
My compliments to the hard-working linuxptp team for this outstanding
performance!
Rich Schmidt
USNO
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