I2C between two NUCLEO-F446RE boards

Asif17r · ‎2025-02-05

Hi, I am trying to use a Nucleo-F446re as master and another one as slave. But the master is probably being timed out (not sure). Can you guys please have a look at my code and configuration. Thanks in advance <3

My Wiring:

1. I connected PB8 & PB9 of both master and slave via direct wire as I used then as SCL and SDA

2. Connected GND of master and slave

My code:

Master 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 */
#include "i2cMaster.h"
/* 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 ---------------------------------------------------------*/
I2C_HandleTypeDef hi2c1;

UART_HandleTypeDef huart2;

/* USER CODE BEGIN PV */
char msgToSend[] = "MsgFromMaster";
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART2_UART_Init(void);
static void MX_I2C1_Init(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

int sz = 50;
uint8_t sndData[50];

void writeData(uint8_t* msg, uint8_t len){
	sndData[0] = len;
	memcpy(&sndData[1],msg,len);
	if(HAL_I2C_Master_Transmit(&hi2c1, (0x27 << 1), sndData, len+1, 10000) != HAL_OK){
		sz = 100;
	}
	sz = -1;
}


/* 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_USART2_UART_Init();
  MX_I2C1_Init();
  /* USER CODE BEGIN 2 */

  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */
	  HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_5);
	  writeData((uint8_t*)msgToSend,13);
	  HAL_Delay(1000);
    /* 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_RCC_PWR_CLK_ENABLE();
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);

  /** 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 = 16;
  RCC_OscInitStruct.PLL.PLLN = 336;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV4;
  RCC_OscInitStruct.PLL.PLLQ = 2;
  RCC_OscInitStruct.PLL.PLLR = 2;
  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_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief I2C1 Initialization Function
  *  None
  * @retval None
  */
static void MX_I2C1_Init(void)
{

  /* USER CODE BEGIN I2C1_Init 0 */

  /* USER CODE END I2C1_Init 0 */

  /* USER CODE BEGIN I2C1_Init 1 */

  /* USER CODE END I2C1_Init 1 */
  hi2c1.Instance = I2C1;
  hi2c1.Init.ClockSpeed = 100000;
  hi2c1.Init.DutyCycle = I2C_DUTYCYCLE_2;
  hi2c1.Init.OwnAddress1 = 0;
  hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
  hi2c1.Init.OwnAddress2 = 0;
  hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
  hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
  if (HAL_I2C_Init(&hi2c1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN I2C1_Init 2 */

  /* USER CODE END I2C1_Init 2 */

}

/**
  * @brief USART2 Initialization Function
  *  None
  * @retval None
  */
static void MX_USART2_UART_Init(void)
{

  /* USER CODE BEGIN USART2_Init 0 */

  /* USER CODE END USART2_Init 0 */

  /* USER CODE BEGIN USART2_Init 1 */

  /* USER CODE END USART2_Init 1 */
  huart2.Instance = USART2;
  huart2.Init.BaudRate = 115200;
  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;
  if (HAL_UART_Init(&huart2) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN USART2_Init 2 */

  /* USER CODE END USART2_Init 2 */

}

/**
  * @brief GPIO Initialization Function
  *  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_GPIOC_CLK_ENABLE();
  __HAL_RCC_GPIOH_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOB_CLK_ENABLE();

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin : B1_Pin */
  GPIO_InitStruct.Pin = B1_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_IT_FALLING;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(B1_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pin : LD2_Pin */
  GPIO_InitStruct.Pin = LD2_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(LD2_GPIO_Port, &GPIO_InitStruct);

/* USER CODE BEGIN MX_GPIO_Init_2 */
/* USER CODE END MX_GPIO_Init_2 */
}

/* USER CODE BEGIN 4 */

/* 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.
  *   file: pointer to the source file name
  *   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 */

Slave Code:

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Minimal I2C Slave Example with LED indication (Address: 0x27)
  ******************************************************************************
  * This code sets up an I2C slave that waits for a transmission from a master.
  * The master is expected to send N+1 bytes:
  *   - The first byte is the number of payload bytes (N)
  *   - Followed by N payload bytes.
  * The onboard LED (LD2) will be lit when the slave is actively listening.
  * When the master starts a transmission, the LED is turned off.
  ******************************************************************************
  */
/* USER CODE END Header */

/* Includes ------------------------------------------------------------------*/
#include "main.h"

/* Private variables ---------------------------------------------------------*/
I2C_HandleTypeDef hi2c1;  // I2C used for the slave

// Global reception buffer and state variables.
#define BUFFER_SIZE 50
uint8_t rxBuffer[BUFFER_SIZE];       // Buffer for incoming data.
volatile uint8_t rxPayloadLength = 0;  // Expected payload length (first byte)
volatile uint8_t rxStage = 0;          // 0: waiting for length, 1: receiving payload

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_I2C1_Init(void);

/* USER CODE BEGIN 0 */
// For clarity, we'll define helper functions to set the LED state.
void LED_On(void)
{
  HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_SET);
}

void LED_Off(void)
{
  HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_RESET);
}
/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{
  /* MCU Configuration--------------------------------------------------------*/
  HAL_Init();

  SystemClock_Config();

  MX_GPIO_Init();
  MX_I2C1_Init();

  // Enable I2C listen mode (interrupt based) so that the slave responds to address match.
  if (HAL_I2C_EnableListen_IT(&hi2c1) != HAL_OK)
  {
    while(1);
  }
  // Turn the LED on to indicate the device is actively listening.
  LED_On();

  /* Infinite loop */
  while (1)
  {

  }
}

/* --- I2C Slave Callbacks --- */

/**
  * @brief  Address Match Callback.
  * Called when the slave address is matched.
  *   hi2c: Pointer to the I2C handle.
  *   TransferDirection: Direction requested by master.
  *   AddrMatchCode: Matched address.
  * @retval None
  */
void HAL_I2C_AddrCallback(I2C_HandleTypeDef *hi2c, uint8_t TransferDirection, uint16_t AddrMatchCode)
{
  if (hi2c->Instance == I2C1)
  {
    // Turn off LED when the master starts transmission (i.e. we're no longer just listening)
    LED_Off();

    if (TransferDirection == I2C_DIRECTION_TRANSMIT)
    {
      // Start reception: first, receive one byte (the length)
      rxStage = 0;  // Waiting for length byte.
      if (HAL_I2C_Slave_Seq_Receive_IT(hi2c, rxBuffer, 1, I2C_FIRST_FRAME) != HAL_OK)
      {
        while(1);
      }
    }
    else
    {
      // We do not support master reading from slave in this example.
      while(1);
    }
  }
}

/**
  * @brief  Slave Reception Complete Callback.
  * Called when the requested number of bytes have been received.
  *   hi2c: Pointer to the I2C handle.
  * @retval None
  */
void HAL_I2C_SlaveRxCpltCallback(I2C_HandleTypeDef *hi2c)
{
  if (hi2c->Instance == I2C1)
  {
    if (rxStage == 0)
    {
      // First byte (length) received.
      rxPayloadLength = rxBuffer[0];
      rxStage = 1;
      if (rxPayloadLength > 0)
      {
        // Now receive the payload (rxPayloadLength bytes) in the last frame.
        if (HAL_I2C_Slave_Seq_Receive_IT(hi2c, &rxBuffer[1], rxPayloadLength, I2C_LAST_FRAME) != HAL_OK)
        {
          while(1);
        }
      }
      else
      {
        // If payload length is 0, re-enable listening.
        if (HAL_I2C_EnableListen_IT(hi2c) != HAL_OK)
        {
          while(1);
        }
        // Turn the LED on again (active listening)
        LED_On();
      }
    }
    else
    {
      // Payload reception complete.
      // (Data is now stored in rxBuffer[1] to rxBuffer[rxPayloadLength])

      // Re-enable listen mode to accept the next transmission.
      if (HAL_I2C_EnableListen_IT(hi2c) != HAL_OK)
      {
        while(1);
      }
      // Turn the LED on again.
      LED_On();
    }
  }
}

/**
  * @brief  I2C Error Callback.
  * Called when an error occurs.
  *   hi2c: Pointer to the I2C handle.
  * @retval None
  */
void HAL_I2C_ErrorCallback(I2C_HandleTypeDef *hi2c)
{
  if (hi2c->Instance == I2C1)
  {
    // Attempt to re-enable listen mode in case of error.
    if (HAL_I2C_EnableListen_IT(hi2c) != HAL_OK)
    {
      while(1);
    }
    // Turn the LED on to indicate listening mode is re-established.
    LED_On();
  }
}

/* --- Peripheral Initialization Functions --- */

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  __HAL_RCC_PWR_CLK_ENABLE();
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);

  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       = 16;
  RCC_OscInitStruct.PLL.PLLN       = 336;
  RCC_OscInitStruct.PLL.PLLP       = RCC_PLLP_DIV4;
  RCC_OscInitStruct.PLL.PLLQ       = 2;
  RCC_OscInitStruct.PLL.PLLR       = 2;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    while(1);
  }

  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_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  {
    while(1);
  }
}

/**
  * @brief I2C1 Initialization Function (Slave)
  *  None
  * @retval None
  */
static void MX_I2C1_Init(void)
{
  hi2c1.Instance = I2C1;
  hi2c1.Init.ClockSpeed      = 100000;
  hi2c1.Init.DutyCycle       = I2C_DUTYCYCLE_2;
  hi2c1.Init.OwnAddress1     = 0x27;  // Slave address set to 0x27
  hi2c1.Init.AddressingMode   = I2C_ADDRESSINGMODE_7BIT;
  hi2c1.Init.DualAddressMode  = I2C_DUALADDRESS_DISABLE;
  hi2c1.Init.OwnAddress2      = 0;
  hi2c1.Init.GeneralCallMode  = I2C_GENERALCALL_DISABLE;
  hi2c1.Init.NoStretchMode    = I2C_NOSTRETCH_DISABLE;
  if (HAL_I2C_Init(&hi2c1) != HAL_OK)
  {
    while(1);
  }
}

/**
  * @brief GPIO Initialization Function
  *  None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};

  /* Enable GPIO clocks */
  __HAL_RCC_GPIOB_CLK_ENABLE();  // Adjust if your I2C pins are on a different port.
  __HAL_RCC_GPIOA_CLK_ENABLE();  // For LED if needed (depends on board)

  /* Configure I2C1 SCL and SDA pins */
  /* Adjust the pins if your board uses different ones */
  GPIO_InitStruct.Pin       = GPIO_PIN_6 | GPIO_PIN_7; // Example: PB6 (SCL) & PB7 (SDA)
  GPIO_InitStruct.Mode      = GPIO_MODE_AF_OD;
  GPIO_InitStruct.Pull      = GPIO_PULLUP;
  GPIO_InitStruct.Speed     = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF4_I2C1;
  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

  /* Configure LED pin (LD2) */
  /* Adjust port/pin names to match your board's configuration */
  GPIO_InitStruct.Pin   = LD2_Pin;
  GPIO_InitStruct.Mode  = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull  = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(LD2_GPIO_Port, &GPIO_InitStruct);
}

/**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */
void Error_Handler(void)
{
  __disable_irq();
  while (1)
  {
    // Stay here in case of error.
  }
}

Can anyone please verify why my code is not working ? I am a beginner, trying to make it work for 3 days. I appreciate your attention. Thank you.

Andrew Neil · ‎2025-02-05

@Asif17r wrote:
the master is probably being timed out (not sure).

So what have you done to confirm whether that is or is not the case?

Used an oscilloscope and/or logic analyser to see what's happening on the wires?
Used the debugger to see what's happening in the code?

Have you verified that your Master works with a known-good slave?

https://community.st.com/t5/stm32-mcus-products/i2c-communication-between-two-different-stm32-evk-boards/m-p/755042/highlight/true#M268963

General debugging tips:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/tac-p/706966/highlight/true#M49

PS:

Have you tried any of the provided I2C examples:

https://www.st.com/resource/en/application_note/an4739-stm32cube-firmware-examples-for-stm32f4-series-stmicroelectronics.pdf#page=12

https://github.com/STMicroelectronics/STM32CubeF4/tree/master/Projects/STM32446E-Nucleo/Examples/I2C

PS:

@Asif17r wrote:
My Wiring:
1. I connected PB8 & PB9 of both master and slave via direct write (sic) as I used then as SCL and SDA
2. Connected GND of master and slave

I guess "write" there means "wire" ?

Note that describing wiring in words never works well - a diagram is far more effective.

You didn't mention pullups?

Pavel A. · ‎2025-02-05

Here you can find someone to review your code and jump-start your project going.

Asif17r · ‎2025-02-05

Thank you for those samples. I am new, I have not tried those samples yet. I will try now.

Do we need pull up resistors? I used the internal one with this line

GPIO_InitStruct.Pull      = GPIO_PULLUP;

Is this OK or we need to actually add a pullup resistors ?

As per the diagram, I have not found any diagram website with that chip till now. As a result I could not add the diagram. I just had 3 direct wires,

1. Master SCL -> Slave SCL

2. Master SDA -> Slave SDA

3. Master GND -> Slave GND

That's all.

Also, the master code can send I2C signal when I connect it to LCD display. That means the Master Code is good. But in debug mode I observed it gets timed out when connected to Nucleo-F446re slave.

Let me know what you are thinking.

Andrew Neil · ‎2025-02-05

@Asif17r wrote:
I am new, .

Just new to the STM32, or new to microcontrollers in general? Programming in general?

@Asif17r wrote:
Do we need pull up resistors? I used the internal one with this line.

Microcontroller internal pullups are too "weak" for reliable I2C - you should always use appropriate external pullups.

https://community.st.com/t5/stm32-mcus-products/stm32g071g8u6tr-trying-to-use-i2c-communication/m-p/769341/highlight/true#M272348

See https://electronics.stackexchange.com/a/473799 for an illustration of the effect of pullup values

@Asif17r wrote:
As per the diagram, I have not found any diagram website with that chip till now. As a result I could not add the diagram.

So draw the diagram!

A hand-drawn sketch would be sufficient