[Linuxptp-devel] Question: LinuxPTP cannot be convergent after ethernet cable hot-plug

[Richard Cochran]

I found there have one issue while running LinuxPTP stack (1.5/1.6,
all versions) on i.MX6/7x platform. The issue is PTP cannot be
convergent after PTP slave Ethernet cable plug-out and then
plug-in. Of course, networking works fine after hot-plugin. If kill
Linuxptp progress, and then run it again, it can be convergent after
some time sync.

It looks like the driver is resetting the PHC time on link down/up.
Check the driver and fix it, if needed. To work around this behavior,
you can use the 'step_threshold' configuration option.

Thanks,
Richard

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[Richard Cochran]

Thanks for your response. Set 'step_threhold' can workaround the
issue even if ifconfig eth0 down/up. The driver after link down and
interface down will reset the MAC that cause ptp timer register
reset to zero, so after link up, stack still think it is locked, in
fact, two ptp timer is out of lock. So driver need keep ptp timer
work during link down ?

Yes, it should keep the time continuous if possible. Some HW does not
allow this, but I don't know whether the imx6 has this problem.

And there have another question is that ptp convergence range is
large while running iperf between master and slave. That is to say,
ptp convergence is not good when add networking loading in the
traffic. Do you think it is reasonable ?

Using SW time stamping, this is reasonable, but it should not happen
with HW time stamping.

Thanks,
Richard

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