Hardware Setup
Components Used
Software Architecture
Background Tasks (Interrupts
Foreground Tasks (Main Loop
Implementation
Timer Configuration
Interrupt Callback
External Interrupt
Result
Analysis

Vincent Adrian QUITORIANO

•

Paul Rodolf Castor

•

Paul Rodolf P. Castor

Published June 13, 2026

STM32 Timer Interrupts and Task Scheduling

A real-time embedded system built on the STM32F407ZGT6 that demonstrates timer interrupts, cyclic executive scheduling, and event-driven pro

IntermediateShowcase (no instructions)20

STM32 Timer Interrupts and Task Scheduling

Things used in this project

Hardware components

RT-Thread RT-Spark Development Board (STM32F407ZGT6)

Software apps and online services

stm32CubeIDE 2.0.0

STMicroelectronics STM32CUBEPROG

Github

Story

IntroductionIn this era embedded systems must handle multiple tasks at the same time while maintaining timing. This project, a time driven foreground/background scheduling system is built on STM32F407ZGT6 microcontroller using the RT-Thread RT-Spark development board and demonstrate the use of hardware timers, interrupt service routines, cyclic executive scheduling and event triggered interrupts.

Hardware Setup

Components Used

RT-Thread RT-Sparkk Development Board
STM32CubeIDE
STM32CubeMX

Pin Configuration

figure 1. GPIO mode and Configuration

figure 2. NVIC mode and Configuration

Software Architecture

This project uses a foreground/Background system architecture.

Background Tasks (Interrupts)

TIM2 Interrupt (1 Hz)

Toggles the Red LED
Sets the task_adc_ready flag
Increments the system tick counter
TIM2 Interrupt (1 Hz)Toggles the Red LEDSets the task_adc_ready flagIncrements the system tick counter

TIM3 Interrupt (2 Hz)

Toggles the Blue LED
Sets the task_display_ready flag
TIM3 Interrupt (2 Hz)Toggles the Blue LEDSets the task_display_ready flag

EXTI Interrupt (Button Press)

Immediately toggles both LEDs
EXTI Interrupt (Button Press)Immediately toggles both LEDs

Foreground Tasks (Main Loop)

Task A

Triggered by TIM2
Simulates ADC processing
Execution Time: 50 ms
Task ATriggered by TIM2Simulates ADC processingExecution Time: 50 ms

Task B

Triggered by TIM3
Simulates display update
Execution Time: 20 ms
Task BTriggered by TIM3Simulates display updateExecution Time: 20 ms

Implementation

Timer Configuration

TIM2

Prescaler: 8399
Auto Reload Register: 9999
Frequency: 1 Hz
Priority: 0 (Highest)

TIM3

Clock Source: Internal Clock
Prescaler: 8399
Auto Reload Register: 4999
Frequency: 2 Hz
Priority: 1

Interrupt Callback

The timer callback function determines which timer generated the interrupt and executes the appropriate background task.

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
    if(htim->Instance == TIM2)
    {
        HAL_GPIO_TogglePin(LED_RED_GPIO_Port, LED_RED_Pin);
        task_adc_ready = 1;
        tick_count++;
    }

    if(htim->Instance == TIM3)
    {
        HAL_GPIO_TogglePin(LED_BLUE_GPIO_Port, LED_BLUE_Pin);
        task_display_ready = 1;
    }
}

External Interrupt

The user button was configure as an external interrupt source.

void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin) 
{     if(GPIO_Pin == GPIO_PIN_0)     
    {         
        HAL_GPIO_TogglePin(LED_RED_GPIO_Port, LED_RED_Pin);         
        HAL_GPIO_TogglePin(LED_BLUE_GPIO_Port, LED_BLUE_Pin);     
    } 
}

Result

After uploading the firmware to the RT-Spark board, the following behavior was observed:

Red LED blinked every 1 second
Blue LED blinked every 0.5 second
Task A executed when the TIM2 interrupt flag was set
Task B executed when the TIM3 interrupt flag was set
Button presses immediately toggled both LEDs
Interrupt priorities functioned correctly

Analysis

Measured latency for task A was approximately 72ms. This latency happens because the cyclic executive architecture requires the main loop to complete any currently running tasks.The response time was calculated as:

TResponse = TLatency + TTask

TResponse = 72 ms + 50 ms = 122 ms

Github repo link: https://github.com/Dian-qit/QUITORIAN_Timer_Interrupts_Lab1

QUITORIAN_Timer_Interrupts_Lab1

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2026 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 ---------------------------------------------------------*/
TIM_HandleTypeDef htim2;
TIM_HandleTypeDef htim3;

/* USER CODE BEGIN PV */
volatile uint8_t task_adc_ready = 0;
volatile uint8_t task_display_ready = 0;
volatile uint32_t tick_count = 0;
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_TIM2_Init(void);
static void MX_TIM3_Init(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

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

// Timer 2 Interrupt Callback - called every 1 second
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
    // Background Task 1: TIM2 @ 1 Hz (high priority)
	if (htim->Instance == TIM2)
	{
	    HAL_GPIO_WritePin(DEBUG_PIN_GPIO_Port, DEBUG_PIN_Pin, GPIO_PIN_SET);
	    HAL_GPIO_TogglePin(LED_RED_GPIO_Port, LED_RED_Pin);
	    task_adc_ready = 1;
	    HAL_GPIO_WritePin(DEBUG_PIN_GPIO_Port, DEBUG_PIN_Pin, GPIO_PIN_RESET);
	}

    // Background Task 2: TIM3 @ 2 Hz (lower priority)
    if (htim->Instance == TIM3)
    {
        HAL_GPIO_TogglePin(LED_BLUE_GPIO_Port, LED_BLUE_Pin);
        task_display_ready = 1;  // tell foreground to update display
    }
}

/* 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_TIM2_Init();
  MX_TIM3_Init();
  /* USER CODE BEGIN 2 */

  HAL_TIM_Base_Start_IT(&htim2);
  HAL_TIM_Base_Start_IT(&htim3);

  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
	  // Task A: ADC processing (triggered by TIM2 every 1s)
		  if (task_adc_ready)
		  {
			  HAL_GPIO_WritePin(DEBUG_PIN_GPIO_Port, DEBUG_PIN_Pin, GPIO_PIN_SET);
			  task_adc_ready = 0;
			  HAL_Delay(50);
			  HAL_GPIO_WritePin(DEBUG_PIN_GPIO_Port, DEBUG_PIN_Pin, GPIO_PIN_RESET);
		  }

	      // Task B: Display update (triggered by TIM3 every 0.5s)
	      if (task_display_ready)
	      {
	          task_display_ready = 0;
	          HAL_Delay(20);   // simulate 20ms display update
	      }

	      // Task C: 10-second periodic monitoring
	      if (tick_count >= 10)
	      {
	          tick_count = 0;
	          // perform 10-second task here
	      }
  }
  /* 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_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 = 8;
  RCC_OscInitStruct.PLL.PLLN = 168;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = 4;
  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_DIV4;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief TIM2 Initialization Function
  * @param None
  * @retval None
  */
static void MX_TIM2_Init(void)
{

  /* USER CODE BEGIN TIM2_Init 0 */

  /* USER CODE END TIM2_Init 0 */

  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
  TIM_MasterConfigTypeDef sMasterConfig = {0};

  /* USER CODE BEGIN TIM2_Init 1 */

  /* USER CODE END TIM2_Init 1 */
  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 8399;
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim2.Init.Period = 9999;
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim2) != HAL_OK)
  {
    Error_Handler();
  }
  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  if (HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM2_Init 2 */

  /* USER CODE END TIM2_Init 2 */

}

/**
  * @brief TIM3 Initialization Function
  * @param None
  * @retval None
  */
static void MX_TIM3_Init(void)
{

  /* USER CODE BEGIN TIM3_Init 0 */

  /* USER CODE END TIM3_Init 0 */

  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
  TIM_MasterConfigTypeDef sMasterConfig = {0};

  /* USER CODE BEGIN TIM3_Init 1 */

  /* USER CODE END TIM3_Init 1 */
  htim3.Instance = TIM3;
  htim3.Init.Prescaler = 8399;
  htim3.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim3.Init.Period = 4999;
  htim3.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim3.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim3) != HAL_OK)
  {
    Error_Handler();
  }
  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  if (HAL_TIM_ConfigClockSource(&htim3, &sClockSourceConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim3, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM3_Init 2 */

  /* USER CODE END TIM3_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_GPIOF_CLK_ENABLE();
  __HAL_RCC_GPIOE_CLK_ENABLE();

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOF, LED_RED_Pin|LED_BLUE_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(DEBUG_PIN_GPIO_Port, DEBUG_PIN_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin : PA0 */
  GPIO_InitStruct.Pin = GPIO_PIN_0;
  GPIO_InitStruct.Mode = GPIO_MODE_IT_RISING;
  GPIO_InitStruct.Pull = GPIO_PULLDOWN;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  /*Configure GPIO pins : LED_RED_Pin LED_BLUE_Pin */
  GPIO_InitStruct.Pin = LED_RED_Pin|LED_BLUE_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOF, &GPIO_InitStruct);

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

  /* EXTI interrupt init*/
  HAL_NVIC_SetPriority(EXTI0_IRQn, 2, 0);
  HAL_NVIC_EnableIRQ(EXTI0_IRQn);

  /* USER CODE BEGIN MX_GPIO_Init_2 */

  /* USER CODE END MX_GPIO_Init_2 */
}

/* USER CODE BEGIN 4 */
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
{
    if (GPIO_Pin == GPIO_PIN_0)
    {
        // Button pressed — toggle both LEDs immediately
        HAL_GPIO_TogglePin(LED_RED_GPIO_Port, LED_RED_Pin);
        HAL_GPIO_TogglePin(LED_BLUE_GPIO_Port, LED_BLUE_Pin);
    }
}
/* 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 */

STM32 Timer Interrupts and Task Scheduling

Things used in this project

Hardware components

Software apps and online services

Story

Hardware Setup

Components Used

Software Architecture

Background Tasks (Interrupts)

Foreground Tasks (Main Loop)

Implementation

Timer Configuration

Interrupt Callback

External Interrupt

Result

Analysis

Code

QUITORIAN_Timer_Interrupts_Lab1

QUITORIAN_Timer_Interrupts_Lab1

Credits

Vincent Adrian QUITORIANO

Paul Rodolf Castor

Paul Rodolf P. Castor

Comments

Embed the widget on your own site

STM32 Timer Interrupts and Task Scheduling

STM32 Timer Interrupts and Task Scheduling

Things used in this project

Hardware components

Software apps and online services

Story

Hardware Setup

Components Used

Software Architecture

Background Tasks (Interrupts)

Foreground Tasks (Main Loop)

Implementation

Timer Configuration

Interrupt Callback

External Interrupt

Result

Analysis

Code

QUITORIAN_Timer_Interrupts_Lab1

QUITORIAN_Timer_Interrupts_Lab1

Credits

Vincent Adrian QUITORIANO

Paul Rodolf Castor

Paul Rodolf P. Castor

Comments

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