STM32 communication with ROS via ethernet AND Serial

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Hi! I'm trying to develop a system where I can communicate from my ROS workstation to an STM32 board via ethernet (TCP or UDP doesn't matter so much), and from there, process the same message from the UART back to the computer. I've managed to flash this STM 32 package onto the board, but I have no idea how to actually send messages to it? It seems like an excellent tool but perhaps isn't beginner-friendly.

I've also looked into using rosserial but I wouldn't even know where to start. I feel as though it's somewhat simple, the end product is a linux computer, which can send a string via ethernet (TCP or UDP) to the board, which sends a string (via serial) back to the computer.

I've lastly looked into whether it would be as simple as just setting up multiple machines but i wouldn't even be able to tell you whether it's applicable to this application.

I have the ethernet cable and the serial to USB connection back to the computer. If someone would be able to even point me in the right direction I would be incredibly grateful! :)