STM32F070F6P6 bootloader peripheral selection

[RBukk]

Hi,

As per app note AN2606, STM32F070x6 bootloader supports USART1/2, I2C1 and USB peripherals. However for STM32F070F6P6 (TSSOP 20pins), only USART1 and USB are feasible but they are also mutually exclusive due to PA9/10 (USART1) and PA11/12 (USB) sharing same pin numbers 17/18.

Now the question is for STM32F070F6P6 when bootloader detects HSE clock does it also remaps PA11/12 on pins 17/18 for USB DFU or USART1 is the only choice irrespective of HSE clock?

Thanks.

[RBukk]

My custom boards arrived, based on observation I will answer my own question, it might be useful for someone planning to use STM32F070F6P6: If HSE clock is present then PA11/12 also gets remapped and USB DFU is the only option for bootloader. If no HSE clock then USART1 is the only option. If you want to use HSE clock but not USB then keep SWD pins free.

[DDziu.1]

Thank you for your answer! I got the same exact problem, also had another MCU available on board - and generating external clock instantly worked!