Arduino for STM32

You only need to define hardware serial in platformio.ini file: [env:blackpill_f401cc] platform = ststm32 board = blackpill_f401cc framework = arduino upload_protocol = dfu build_flags = -D PIO_FRAMEWORK_ARDUINO_ENABLE_CDC -D USBCON -D ENABLE_HWSERIAL2 ;Enable hardware serial2 <===== -D PIN_SERIAL2_...