I am using KSZ8863RLL to achieve dual Ethernet, This is a 3 port switch and it basically just replace the LAN8742. The MCU will just see an ordinary Ethernet not realizing that it is a switch. My initial idea was to re-use the ECU main board with minimal changes, but I underestimated the amout of extra components needed + many of the pins need a strap since they have one purpose during boot and another during operation. The result is that with 0603 components I run out of space, I can start pushing trancient caps to the back side, but I also have 2 cm space left on the right side so I can push the MCU to right and re-route the entire board. What I can’t move is the M connectors because they are aligned with the sub-boards, but I can move MCU w/components and route more to the right to free space for dual Ethernet.
The schematics on this is not 100% yet – I have found 2 good references that I am using, but it is a fiddle then you want to reduce components. I am using a trick to strap Ethernet to RESET as it power up so that it don’t boot before the MCU wants it to. I will also use a 2nd 3.3V PSU that can be switched on/off for this. I preffer to leave all components on top layer, but I will consider putting straps and trancient caps on the bottom. It is an interesting routing experimen, so will be interesting to see if I get this working. TBH the complexity on this is at the level where I expect I will need two PCB runs – actually I always do.