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FRDM-K64F IEEE1588 strange timestamp resolution

Question asked by Marco Bertacci on Sep 24, 2019
Latest reply on Nov 12, 2019 by Marco Bertacci

Hi,

I'm using a FRDM-K64F board with MCUXpresso 11.0 and SDK 2.6.0.

I've slightly modified the main routine of enet ptp1588 example from SDK, in order to send 128 ptp frames and retrieve the corresponding transmit timestamps, to do some statistics.

 

I've noticed that all timestamps retrieved are multiple of 80ns.

It's a very strange behavior, because in the mentioned example the 1588 timer uses the 50Mhz board clock provided by PHY, and I would expect a 1588 timer resolution of 20ns.

If I manually read the 1588 timer, using the function ENET_Ptp1588GetTimer(...), the variation observed is correctly 20ns.

 

Where is the mistake? Some ideas?

 

Regards,

Marco

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