Can you point to where the undocumented registers are used in the source? I don't see anything obvious that fits that definition in: https://github.com/STMicro

Can you point to where the undocumented registers are used in the source? I don't see anything obvious that fits that definition in: https://github.com/STMicroelectronics/STM32CubeF4/tree/master/Middlewares/ST/STM32_USB_Device_Library https://github.com/STMicroelectronics/STM32CubeF4/tree/maste... (I've chosen the version for STM32F4 arbitrarily; if there's something similar in one of their other USB support libraries, feel free to point to that instead.)