@runger111 reports:

Welcome to RosmoESC, v0.1
Startup complete.
Iteration/s: 2003
Iteration/s: 2002
Iteration/s: 2002

That’s from the serial output of a RosmoESC, via USB. So USB is working, the MCU is working, I can program it and its getting power. Was a little work to get the completely custom board up and running in platformIO - needs all kinds of setup stuff you don’t have to think about when using one of the standard pre-selectable boards.

I’ll check the other stuff (SPI sensors, motor drivers!) in the next few days.