base blink changed to embedded usart3

Core/Inc/stm32f7xx_it.h

@@ -54,6 +54,7 @@ void UsageFault_Handler(void);
 void DebugMon_Handler(void);
 void TIM1_UP_TIM10_IRQHandler(void);
 void USART2_IRQHandler(void);
+void USART3_IRQHandler(void);
 /* USER CODE BEGIN EFP */
 
 /* USER CODE END EFP */

Core/Inc/usart.h

@@ -34,11 +34,14 @@ extern "C" {
 
 extern UART_HandleTypeDef huart2;
 
+extern UART_HandleTypeDef huart3;
+
 /* USER CODE BEGIN Private defines */
 
 /* USER CODE END Private defines */
 
 void MX_USART2_UART_Init(void);
+void MX_USART3_UART_Init(void);
 
 /* USER CODE BEGIN Prototypes */