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i.MX6 with RMII and clock externally sourced from RGMII_TX_CTL

Question asked by Ilario Gottardello on Apr 21, 2017
Latest reply on Apr 26, 2017 by igorpadykov

Good morning,

 

in our design (based on the SABRESD) we choose to connect and i.MX6 Quad to ethernet in RMII mode, sourcing clock from the PHY. I've connected this external clock signal to pad RGMII_TX_CTL (C23).

We started from the SABRESD device tree, modifing the "fsl,pins" section. And it kinda worked, but the clock signal was very distorted and ifconfig told me there were lots of framing errors.

 

We then realised that there were two clocks running! One from the PHY and one from i.MX6. So, we tried to remove "IMX6QDL_CLK_ENET_REF" from the "clocks" section of fec, and that made only the external clock present.

 

Now there are no framing errors, and ping works correctly, but it's not possible to do anything besides this. It doesn't resolve names, it doesn't connect to services. With two clocks it did those things, even if badly. With one, it doesn't.

 

So, what should we put on the "clocks" section to have fec using external clock and i.MX6 not generating one?

 

Thank you very much

Have a nice day

 

Ilario

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