Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f4/STM32F446/HDMI_CEC/CEC_CR#0x0
CEC control register
CEC Enable
Tx Start Of Message
Tx End Of Message
https://github.com/modm-io/cmsis-svd-stm32