Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f1/STM32F100/AFIO/EVCR#0x0
Event Control Register (AFIO_EVCR)
Pin selection
Port selection
Event Output Enable
https://github.com/modm-io/cmsis-svd-stm32