HAL_UART_Receive_IT is not working

[KaushikSTM32]

Originally a reply in this thread - split as a separate question.

---

Hello 

My blocking mode is working with "HAL_UART_Receive(&huart4, temp, 1, 100);"

Nonblocking mode is not working

Can you suggest anything to check?

I have defined as said

/* USER CODE BEGIN 2 */

HAL_UART_Receive_IT(&huart4, temp, 1);

/* USER CODE END 2 */

and

/* USER CODE BEGIN 4 */

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
  HAL_UART_Receive_IT(&huart4, temp, 1);
  HAL_UART_Transmit(&huart4, temp, 1, 100);
}

/* USER CODE END 4 */

[Saket_Om]

Hello @KaushikSTM32 

Did you enable the UART global interrupt please?

[Andrew Neil]

---

@KaushikSTM32 wrote:

Nonblocking mode is not working

---

Define "not working"

• Does not build?
• Crashes?
• Receives junk?
• other??

Have you enabled the interrupts?

[KaushikSTM32]

Replied below

[KaushikSTM32]

Hello Andew and Saket

Well I have used putty, In blocking it was receiving what has been sent and also my toggle pin is working in while loop.

In non blocking, toggle pin stopped and also didn't received any data from controller.

What shall I do next?

[Saket_Om]

Hello @KaushikSTM32 

Could you please share your entire code? This will allow us to assist you more effectively.

[KaushikSTM32]

Sir, Please refer below code.

/* USER CODE BEGIN Header */

/**

******************************************************************************

* @file : main.c

* @brief : Main program body

******************************************************************************

* @attention

*

* Copyright (c) 2025 STMicroelectronics.

* All rights reserved.

*

* This software is licensed under terms that can be found in the LICENSE file

* in the root directory of this software component.

* If no LICENSE file comes with this software, it is provided AS-IS.

*

******************************************************************************

*/

/* USER CODE END Header */

/* Includes ------------------------------------------------------------------*/

#include "main.h"



/* Private includes ----------------------------------------------------------*/

/* USER CODE BEGIN Includes */



/* USER CODE END Includes */



/* Private typedef -----------------------------------------------------------*/

/* USER CODE BEGIN PTD */



/* USER CODE END PTD */



/* Private define ------------------------------------------------------------*/

/* USER CODE BEGIN PD */



/* USER CODE END PD */



/* Private macro -------------------------------------------------------------*/

/* USER CODE BEGIN PM */



/* USER CODE END PM */



/* Private variables ---------------------------------------------------------*/

UART_HandleTypeDef huart4;



/* USER CODE BEGIN PV */



/* USER CODE END PV */



/* Private function prototypes -----------------------------------------------*/

void SystemClock_Config(void);

static void MX_GPIO_Init(void);

static void MX_UART4_Init(void);

/* USER CODE BEGIN PFP */

unsigned char temp[2];

/* USER CODE END PFP */



/* Private user code ---------------------------------------------------------*/

/* USER CODE BEGIN 0 */

/*



/* USER CODE END 0 */



/**

* @brief The application entry point.

* @retval int

*/

int main(void)

{



/* USER CODE BEGIN 1 */



/* USER CODE END 1 */



/* MCU Configuration--------------------------------------------------------*/



/* Reset of all peripherals, Initializes the Flash interface and the Systick. */

HAL_Init();



/* USER CODE BEGIN Init */



/* USER CODE END Init */



/* Configure the system clock */

SystemClock_Config();



/* USER CODE BEGIN SysInit */



/* USER CODE END SysInit */



/* Initialize all configured peripherals */

MX_GPIO_Init();

MX_UART4_Init();

/* USER CODE BEGIN 2 */

HAL_UART_Receive_IT(&huart4, temp, 1);

/* USER CODE END 2 */



/* Infinite loop */

/* USER CODE BEGIN WHILE */

//HAL_UART_Receive_IT(&huart4, temp, 1);

while (1)

{

/* USER CODE END WHILE */

// HAL_UART_Receive(&huart4, temp, 1, 100);

// HAL_UART_Transmit(&huart4, temp, 1, 100);

HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_4);

HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_5);

/* USER CODE BEGIN 3 */

}

/* USER CODE END 3 */

}



/**

* @brief System Clock Configuration

* @retval None

*/

void SystemClock_Config(void)

{

RCC_OscInitTypeDef RCC_OscInitStruct = {0};

RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};



/** Configure the main internal regulator output voltage

*/

HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1);



/** Initializes the RCC Oscillators according to the specified parameters

* in the RCC_OscInitTypeDef structure.

*/

RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;

RCC_OscInitStruct.HSIState = RCC_HSI_ON;

RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;

RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;

RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;

RCC_OscInitStruct.PLL.PLLM = RCC_PLLM_DIV4;

RCC_OscInitStruct.PLL.PLLN = 75;

RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;

RCC_OscInitStruct.PLL.PLLQ = RCC_PLLQ_DIV2;

RCC_OscInitStruct.PLL.PLLR = RCC_PLLR_DIV2;

if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)

{

Error_Handler();

}



/** Initializes the CPU, AHB and APB buses clocks

*/

RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK

|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;

RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;

RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;

RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;

RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;



if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)

{

Error_Handler();

}

}



/**

* @brief UART4 Initialization Function

* @PAram None

* @retval None

*/

static void MX_UART4_Init(void)

{



/* USER CODE BEGIN UART4_Init 0 */



/* USER CODE END UART4_Init 0 */



/* USER CODE BEGIN UART4_Init 1 */



/* USER CODE END UART4_Init 1 */

huart4.Instance = UART4;

huart4.Init.BaudRate = 115200;

huart4.Init.WordLength = UART_WORDLENGTH_8B;

huart4.Init.StopBits = UART_STOPBITS_1;

huart4.Init.Parity = UART_PARITY_NONE;

huart4.Init.Mode = UART_MODE_TX_RX;

huart4.Init.HwFlowCtl = UART_HWCONTROL_NONE;

huart4.Init.OverSampling = UART_OVERSAMPLING_16;

huart4.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;

huart4.Init.ClockPrescaler = UART_PRESCALER_DIV1;

huart4.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;

if (HAL_UART_Init(&huart4) != HAL_OK)

{

Error_Handler();

}

if (HAL_UARTEx_SetTxFifoThreshold(&huart4, UART_TXFIFO_THRESHOLD_1_8) != HAL_OK)

{

Error_Handler();

}

if (HAL_UARTEx_SetRxFifoThreshold(&huart4, UART_RXFIFO_THRESHOLD_1_8) != HAL_OK)

{

Error_Handler();

}

if (HAL_UARTEx_DisableFifoMode(&huart4) != HAL_OK)

{

Error_Handler();

}

/* USER CODE BEGIN UART4_Init 2 */



/* USER CODE END UART4_Init 2 */



}



/**

* @brief GPIO Initialization Function

* @PAram None

* @retval None

*/

static void MX_GPIO_Init(void)

{

GPIO_InitTypeDef GPIO_InitStruct = {0};

/* USER CODE BEGIN MX_GPIO_Init_1 */

/* USER CODE END MX_GPIO_Init_1 */



/* GPIO Ports Clock Enable */

__HAL_RCC_GPIOA_CLK_ENABLE();

__HAL_RCC_GPIOC_CLK_ENABLE();



/*Configure GPIO pin Output Level */

HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4|GPIO_PIN_5, GPIO_PIN_RESET);



/*Configure GPIO pins : PA4 PA5 */

GPIO_InitStruct.Pin = GPIO_PIN_4|GPIO_PIN_5;

GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;

GPIO_InitStruct.Pull = GPIO_NOPULL;

GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;

HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);



/* USER CODE BEGIN MX_GPIO_Init_2 */

/* USER CODE END MX_GPIO_Init_2 */

}



/* USER CODE BEGIN 4 */

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)

{

HAL_UART_Receive_IT(&huart4, temp, 1);

HAL_UART_Transmit(&huart4, temp, 1, 100);

}

/* USER CODE END 4 */



/**

* @brief This function is executed in case of error occurrence.

* @retval None

*/

void Error_Handler(void)

{

/* USER CODE BEGIN Error_Handler_Debug */

/* User can add his own implementation to report the HAL error return state */

__disable_irq();

while (1)

{

}

/* USER CODE END Error_Handler_Debug */

}



#ifdef USE_FULL_ASSERT

/**

* @brief Reports the name of the source file and the source line number

* where the assert_param error has occurred.

* @PAram file: pointer to the source file name

* @PAram line: assert_param error line source number

* @retval None

*/

void assert_failed(uint8_t *file, uint32_t line)

{

/* USER CODE BEGIN 6 */

/* User can add his own implementation to report the file name and line number,

ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */

/* USER CODE END 6 */

}

#endif /* USE_FULL_ASSERT */

[Andrew Neil]

---

@KaushikSTM32 wrote:

Below is another thread posted by me---

---

Please don't post multiple threads on the same question. Please give a link to that post.

For how to properly post source code, see: 

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

[KaushikSTM32]

Agreed, Noted Thanks

[Saket_Om]

@KaushikSTM32 

It is better to add a flag in HAL_UART_RxCpltCallback() and check it in the main. Please see the snippet code below.

if(RXcplt)
{
HAL_UART_Transmit(&huart4, temp, 1, 100);
HAL_UART_Receive_IT(&huart4, temp, 1);
}



void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)

{
RXcplt =1;
}