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FRDM-K64F mdio clock

Question asked by David Sherman on Jan 19, 2018
Latest reply on Jan 20, 2018 by Mark Butcher

I'm having a little trouble with the mdio clock on the FRDM K64F.  According to the K64 reference manual, the MDIO clock is derived from the bus clock.  Is this correct?  I can get the ethernet working under FreeRTOS and FreeRTOS-TCP, but only if I run the FRDM-K64F at 50MHz with a 50MHz bus clock.  If I try to use it at 120 MHz with a 60MHz bus clock (FLL engaged external mode), I calculate the MDIO clock and use 11 for the ENET MSCR MII_SPEED register (60/2.5 = 24, (24/2) - 1 = 11).  However, I get 5 MHz out for the MDIO clock, and I cannot read the phy ID correctly.  I'm pretty sure the bus clock is correct, as I have set the clock divider registers accordingly.  I did see an older thread about MDIO communication problems on the FRDM-K64F, so I have the pull up enabled on the MDIO line.