@Fotofieber
I was more talking about Atmel M0 mcu which are well integrated into Arduino.
So your boards are ST mcu. They seems to be nice (but a bit memory limited), and cheap. I have a nucleo board from ST which is also very nice because they are cheap (10$) and they have the programmer&debugger embedded and you can detach it.
But even if this ST mcu is M0, Arduino boards core files can differ.
That said, there is STM32duino for arduino, but I've never used it with Mysensors. And I'm not playing actually with ST.
It could work out of the box depending of mysensors features used (compiling) but not really sure, I don't know the state of integration for these module in Arduino.
You would need to use at least the spi port referenced by your board and the STM32duino. SPi port is spi port. For other pins like interrupt, CS etc.., that would need to check how pin are defined in STM32duino.
I'm not sure if that will work easily out of the box...(https://www.hackster.io/rayburne/4-dollar-90-mips-32-bit-72-mhz-arm-arduino-f6e5c9)
I know there are few other people working on ATSAM boards for mysensors
On my side, few months ago I have designed a lipo charger board for ATSAM. sort of featherM0 that i have improved for using with mysensors (spi flash for ota, eeprom for mysensors config, etc..)..I will release it if it can help
My project was looking to this https://forum.mysensors.org/topic/3551/my-32bits-atsam-node-project
Since, i have made other atsam boards for fun and I can't wait my esp32 module order which could change the game and my opinion...
I could try a bit later (actually busy), with my nucleo board...but i can't tell when for the moment..