Detailed explanation of TIM timed interrupt in STM32

 A TIM timed interrupt in STM32 (using a general-purpose timer) is one of the most powerful features in real-time embedded systems. It allows the microcontroller to perform specific tasks at precise time intervals, independent of main code execution.

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 What Is a TIM Timed Interrupt?

A TIM interrupt is an event triggered by a timer peripheral (e.g., TIM2, TIM3, etc.) when it counts to a specified value. You can configure this to fire periodically, for example, every 1 ms or every 1 second.

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 Use Cases

• Blinking LEDs at a fixed rate

• Running a real-time scheduler

• Sampling sensors at fixed intervals

• Generating PWM signals (with interrupts)

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 Key Registers in TIM

Register	Role
PSC	Prescaler (divides timer clock)
ARR	Auto-reload register (sets period)
CNT	Current counter value
DIER	Interrupt enable register
SR	Status register (flags)
CR1	Control register (start/stop)

 Basic Timing Formula

To generate an interrupt every T seconds:

ini

T = (PSC + 1) × (ARR + 1) / Timer_Clock_Frequency

So:

c

Timer Frequency = 72 MHz (example on STM32F1)
Prescaler (PSC) = 7199  → Clock = 10 kHz
ARR = 999              → Overflow every 100 ms

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 How to Set Up a TIM Timed Interrupt

Here’s how to configure it step-by-step using STM32CubeIDE:

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 1. Enable Timer in STM32CubeMX

• Open your project in STM32CubeMX or STM32CubeIDE

• Enable TIM2 (or any general-purpose timer)

• Mode: Internal Clock

• Enable Update Event Interrupt (UIE)

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 2. Set Timer Prescaler and Period

In the configuration panel:

• Prescaler (PSC): 7199 (if APB1 clock is 72 MHz)

• Counter Period (ARR): 999

This gives an interrupt every 100 ms.

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 3. Generate Code

Click Project > Generate Code. Now move to main.c.

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 4. Enable Timer and Interrupt

In main.c:

c

HAL_TIM_Base_Start_IT(&htim2);  // Start timer in interrupt mode

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 5. Write Interrupt Callback Function

In stm32f1xx_it.c or stm32xx_it.c:

c

void TIM2_IRQHandler(void)
{
  HAL_TIM_IRQHandler(&htim2);  // Handle HAL state

  // Custom code is inside HAL_TIM_PeriodElapsedCallback
}

Now implement the callback in main.c:

c

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
  if (htim->Instance == TIM2) {
    // Code to execute on each interrupt
    HAL_GPIO_TogglePin(GPIOC, GPIO_PIN_13);  // Blink LED
  }
}

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 Bare Metal (Register-Level) Example

c

// Enable TIM2 clock
RCC->APB1ENR |= RCC_APB1ENR_TIM2EN;

// Set prescaler and ARR
TIM2->PSC = 7199;       // Divide 72 MHz → 10 kHz
TIM2->ARR = 999;        // 10,000 counts → 1 second

// Enable update interrupt
TIM2->DIER |= TIM_DIER_UIE;

// Enable TIM2 counter
TIM2->CR1 |= TIM_CR1_CEN;

// Enable NVIC interrupt
NVIC_EnableIRQ(TIM2_IRQn);

In interrupt handler:

c

void TIM2_IRQHandler(void)
{
  if (TIM2->SR & TIM_SR_UIF) {
    TIM2->SR &= ~TIM_SR_UIF;  // Clear flag
    // Your code here (e.g., toggle LED)
  }
}

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 Debugging Tips

Issue	Fix
Timer not counting	Check RCC clocks and prescaler
No interrupt	Check NVIC settings and UIE bit
Interrupt too fast/slow	Adjust PSC and ARR
ISR not executing	Confirm function signature and HAL usage

 Summary

Step	Action
1	Configure timer (PSC, ARR)
2	Enable update interrupt
3	Start timer in interrupt mode
4	Write ISR or callback
5	Place time-dependent code inside ISR