hello,
obviously there is a small bug in CMSIS USART Driver STM32F4xx Rev 2.3:
line 1808: else if (usart->reg == USART3) { __HAL_RCC_USART2_CLK_ENABLE(); }
correction: else if (usart->reg == USART3) { __HAL_RCC_USART3_CLK_ENABLE(); }
Thanks for reporting this. Updated driver, with corrected this and some other typos, will be available in next pack release.