Arduino for STM32

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This is because the usb port is not configured as a composite usb device. A USB Composite Device is a peripheral device that supports more than one device class (source: keil.com). For example, using the usb port as a composite device you can have a usb serial port, mouse and keyboard, all at the same time.

Currently, the HID bootloader does not run as a composite usb device. When running your sketch, only the USB Serial port is available. The Arduino IDE uses the serial port to restart the MCU in HID bootloader mode. If there is no serial port, the loader cannot restart the MCU. When you replace:

USB support from CDC generic supersede U (S) ART

to

HID keyboard and mouse

automatically turn off the serial port needed to restart the MCU in the next programming.

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