This is an old mock-up for a dual Ethernet module. The design is simple as it is a 3-port Ethernet Switch with 2 external PHY’s and one internal RMII port, so the MCU just run lwIP using a RMII port as before and it is in effect a switch so you can connect modules in a chain on Ethernet.
What I consider is to upgrade my 3xCAN (below) with a variant that has 2 x RJ45 Ethernet ports. That way I get a fast Ethernet link between boxes. These switches are also Profinet/Ethercat capable so we could have a lot of fun. The second change I consider is to replace the 3 x CAN ports with more generic IO ports. I already have a separate CAN module, RS485 module and can easely add a RS232 module. STM32H5xx has the same FDCAN as H723. But, the daisy chained Ethernet basically need a 3 port switch to work – yes I can daisy chain in SW, but that add latency. Another observation is that LAN8742 below have a lot of passive components making the Ethernet Phy occupy a lot of space. The 3 port switches require far less space in total.
To achieve this I will need to move SD-Card and SPI-Flash to make space for 2 x RJ45. I probably can move the MCU a bit right specially as I am about to drop the 3 x CAN ports. I would like to keep SD-Card at left, but that will require some trickery.
The objective of this change is to be able to daisy chain PLC boxes using Ethernet without an Ethernet switch + it opens for better Profinet/Ethercat support. The second objective is to open for more generic usage by freeing fixed CAN ports. And then do the same on the more generic ECU Mainboard.