int main(void)
{

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
  /* Configure the system clock */
  SystemClock_Config();
  /* Initialize all configured peripherals */
  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOD_CLK_ENABLE();

    GPIO_InitStruct.Pin = GPIO_PIN_13 ;
    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
    HAL_GPIO_Init(GPIOD, &GPIO_InitStruct);

    /*Configure GPIO pin : PA2 Tx */
  	GPIO_InitStruct.Pin = GPIO_PIN_2 ;
  	GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  	GPIO_InitStruct.Pull = GPIO_PULLUP;
  	GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
  	GPIO_InitStruct.Alternate = GPIO_AF7_USART2;
  	HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  	/*Configure GPIO pin : PA3 Rx */
  	GPIO_InitStruct.Pin = GPIO_PIN_3 ;
  	GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  	GPIO_InitStruct.Pull = GPIO_PULLUP;
  	GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
  	GPIO_InitStruct.Alternate = GPIO_AF7_USART2;
  	HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

    huart2.Instance = USART2;
    huart2.Init.BaudRate = 9600;
    huart2.Init.WordLength = UART_WORDLENGTH_8B;
    huart2.Init.StopBits = UART_STOPBITS_1;
    huart2.Init.Parity = UART_PARITY_NONE;
    huart2.Init.Mode = UART_MODE_TX_RX;
    huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
    huart2.Init.OverSampling = UART_OVERSAMPLING_16;
    HAL_UART_Init(&huart2);
    HAL_UART_MspInit(&huart2);
  /* USER CODE BEGIN WHILE */
    int i = 0;
    while (1){
    	if(i < 10000)
    		HAL_GPIO_WritePin(GPIOD, GPIO_PIN_13, GPIO_PIN_SET);
    	else
    		HAL_GPIO_WritePin(GPIOD, GPIO_PIN_13, GPIO_PIN_RESET);
    	i++;
    	HAL_UART_Transmit(&huart2, (uint8_t*)"Hello world\n", strlen("Hello world\n"), HAL_MAX_DELAY);
	  //printf("Hello World\n");
    }
}

/** System Clock Configuration
*/
void SystemClock_Config(void)
{

  RCC_OscInitTypeDef RCC_OscInitStruct;
  RCC_ClkInitTypeDef RCC_ClkInitStruct;

  __HAL_RCC_PWR_CLK_ENABLE();

  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);

  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = 16;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  HAL_RCC_OscConfig(&RCC_OscInitStruct);

  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
  HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0);

  HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);

  HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);

  /* SysTick_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
}