Unable to Get RMII Link on KSZ8863RLL Port 3 (STM32F746)
I am developing a device based on an STM32F746VET6 with two Ethernet ports. To implement this, I chose the KSZ8863RLL, as it provides two external Ethernet PHY ports and an RMII interface to the STM32.
At the moment, Port 1 and Port 2 are both working correctly at 100 Mbps full duplex. I can successfully transmit and receive data through both ports. However, I cannot get Port 3 (the RMII CPU port) to establish a link.
I'm a bit confused about the correct RMII interface connections. I am using Clock Mode 5, and my understanding is that the external 25 MHz crystal is internally multiplied to 50 MHz, with REFCLKO_3 providing the 50 MHz reference clock to the STM32. Is that interpretation correct?
This is how I originally routed the RMII signals:
After reading through the datasheet and application notes, I also came across the following information:
Based on that, I bodged my PCB to match the recommended connections, but I still cannot get a link on Port 3.
Has anyone successfully used the KSZ8863RLL in RMII Mode 5 with an STM32? Am I misunderstanding how the RMII interface or clocking should be connected, or is there something obvious I'm missing?
Original schematics of the PCB are attached bellow
