STM32F4 Discovery Tutorial 9 - Timer Interrupt

In this tutorial, I will share how to generate interrupt every given interval using timer on STM32F4 Discovery board. For example project, we will make orange LED toggle every 500ms interval using TIM2. In the main program we will toggle blue LED every 2500ms (blue LED toggling will not using timer interrupt, but just use delay function).

First, we write code for initialize timer. We will use TIM2. This is the block diagram for configuring the timer clock:

void TIM_INT_Init()
{
    // Enable clock for TIM2
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    // TIM2 initialization overflow every 500ms
    // TIM2 by default has clock of 84MHz
    // Here, we must set value of prescaler and period,
    // so update event is 0.5Hz or 500ms
    // Update Event (Hz) = timer_clock / ((TIM_Prescaler + 1) * 
    // (TIM_Period + 1))
    // Update Event (Hz) = 84MHz / ((4199 + 1) * (9999 + 1)) = 2 Hz
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
    TIM_TimeBaseInitStruct.TIM_Prescaler = 4199;
    TIM_TimeBaseInitStruct.TIM_Period = 9999;
    TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;

    // TIM2 initialize
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStruct);
    // Enable TIM2 interrupt
    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);
    // Start TIM2
    TIM_Cmd(TIM2, ENABLE);

    // Nested vectored interrupt settings
    // TIM2 interrupt is most important (PreemptionPriority and 
    // SubPriority = 0)
    NVIC_InitTypeDef NVIC_InitStruct;
    NVIC_InitStruct.NVIC_IRQChannel = TIM2_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct);
}

After that, we must write code for interrupt handler that will be call every timer interrupt (500ms). In this handler, we write code for toggle orange LED.

void TIM2_IRQHandler()
{
    // Checks whether the TIM2 interrupt has occurred or not
    if (TIM_GetITStatus(TIM2, TIM_IT_Update))
    {
        // Toggle orange LED (GPIO13)
        GPIO_ToggleBits(GPIOD, GPIO_Pin_13);

        // Clears the TIM2 interrupt pending bit
        TIM_ClearITPendingBit(TIM2, TIM_IT_Update);
    }
}

Finally, in the main function we can write code for toggle blue LED using delay function. The blue LED will toggle every 2500ms.

#include "stm32f4xx.h"
#include "stm32f4xx_rcc.h"
#include "stm32f4xx_gpio.h"
#include "stm32f4xx_tim.h"
#include "misc.h"
#include "clock.h"
#include "delay.h"

int main(void)
{
    // Set clock to 168MHz
    CLOCK_SetClockTo168MHz();

    // Delay initialization
    DELAY_Init();

    // Timer interrupt initialization
    TIM_INT_Init();

    // Clock for GPIOD
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

    // GPIOD initialization as an output for orange LED (GPIOD13)
    // and blue LED (GPIOD15)
    GPIO_InitTypeDef GPIO_InitStruct;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_OUT;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_13 | GPIO_Pin_15;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
    GPIO_Init(GPIOD, &GPIO_InitStruct);

    while (1)
    {
        // Toggle blue LED (GPIO15)
        GPIO_ToggleBits(GPIOD, GPIO_Pin_15);
        // Delay 2.5s
        DELAY_Ms(2500);
    }
}

This is the link for download these clock, delay library if you need.