This quick guide will show you how to use DFU mode to flash firmware onto your flight controller using zadig drivers
If you ever have any issues when connecting your STM32 based flight controller to your PC, chances are you are using the wrong drivers for your board. This commonly occurs when you try to connect to your board, or flash firmware and you get an error message saying
failed to open serial port.
Read Full article on dronetrest - http://www.dronetrest.com/t/zadig-drivers-for-cleanflight-betaflight-stm32-flight-controllers-dfu-mode/2719