Resolved! Can't set USART_CR1_RXNEIE to enable
I tried to enable RXNEIE with following code: USART2->CR1 = (USART_CR1_TE | USART_CR1_UE | USART_CR1_RE | USART_CR1_RXNEIE); But when I checked CR1 register, it's still set to 0: gdb: x /8ub 0x40004400 0x40004400: 45 0 0 0 0 0 0 0 I checked the manu...