Looking around more, I think I'll move ahead with what is shown in Figure 99 (so option a from my previous post) of the ST datasheet. I'm pretty confused by Figure 98. because how I understand the STM32F4 is it doesn't have an option for an external ...

@LCE , @JR5 is referencing the hardware design guide from Microchip (DS00003048A).@JR5, you'll notice if you look below the table of the image you shared, you aren't using the internal RMII feedback of the KSZ as suggested by @LCE in their suggestion...

@avik.de major kudos for this great dive. Saves me a lot of time.For other's with same question as @y.rr , the ETH_MACMDIOAR... referenced in the original post comes from the reference manual. If you are looking at code generated by STM32CubeMX (stm3...