STM32f4 timer interrupt experimental code

Let's take a look at our time.c file. The code of the timer.c file is as follows:

//General timer 3 interrupt initialization

//arr: automatic reload value. psc: clock pre-division number

//Timer overflow time calculation method: Tout=((arr+1)*(psc+1))/Ft us.

//Ft=timer operating frequency, unit: Mhz

//Timer 3 is used here!

void TIM3_Int_Init(u16 arr,u16 psc)

{

  TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;

  NVIC_InitTypeDef NVIC_InitStructure;

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE); //Enable TIM3 clock

   TIM_TimeBaseInitStructure.TIM_Period = arr; //Automatically reload value

  TIM_TimeBaseInitStructure.TIM_Prescaler=psc; //Timer frequency division

  TIM_TimeBaseInitStructure.TIM_CounterMode=TIM_CounterMode_Up; //Upward counting mode

  TIM_TimeBaseInitStructure.TIM_ClockDivision=TIM_CKD_DIV1;  

  TIM_TimeBaseInit(TIM3,&TIM_TimeBaseInitStructure); // Initialize timer TIM3

  TIM_ITConfig(TIM3,TIM_IT_Update,ENABLE); //Enable timer 3 update interrupt

  NVIC_InitStructure.NVIC_IRQChannel=TIM3_IRQn; //Timer 3 interrupt

  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0x01; //Preemption priority 1

  NVIC_InitStructure.NVIC_IRQChannelSubPriority=0x03; //Response priority 3

  NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;

  NVIC_Init(&NVIC_InitStructure); // Initialize NVIC  

TIM_Cmd(TIM3,ENABLE); //Enable timer 3  

}

//Timer 3 interrupt service function

void TIM3_IRQHandler(void)

{

  if(TIM_GetITStatus(TIM3,TIM_IT_Update)==SET) // Overflow interrupt

  {

    LED1=!LED1;

  }

  TIM_ClearITPendingBit(TIM3,TIM_IT_Update); //Clear interrupt flag

}

This file contains an interrupt service function and a timer 3 interrupt initialization function. The interrupt service function is relatively simple. After each interrupt, the interrupt type of TIM3 is determined. If the interrupt type is correct, the flip of LED1 (DS1) is executed. The TIM3_Int_Init function executes the 5 steps we introduced above to make TIM3 start working and enable interrupts. Here we use the label ~ to mark the five steps of timer initialization. The 2 parameters of this function are used to set the overflow time of TIM3. Because the APB1 clock has been initialized to 4 divisions in the system initialization SystemInit function, the APB1 clock is 42M. From the internal clock tree diagram of STM32F4 (Figure 4.3.1.1), we know that when the APB1 clock division number is 1, the clocks of TIM2~7 and TIM12~14 are the clocks of APB1. If the APB1 clock division number is not 1, the clock frequencies of TIM2~7 and TIM12~14 will be twice the APB1 clock. Therefore, the clock of TIM3 is 84M. Based on the values ​​of arr and psc we designed, we can calculate the interrupt time. The calculation formula is as follows:

Tout= ((arr+1)*(psc+1))/Tclk;

in:

Tclk: Input clock frequency of TIM3 (in MHz).

Tout: TIM3 overflow time (in us).

  The content of the timer.h header file is relatively simple, so we will not explain it here.

Finally, let's look at the main function code as follows:

int main(void)

{  

  NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2); //Set system interrupt priority group 2

  delay_init(168); //Initialize delay function

  LED_Init(); //Initialize LED port

    TIM3_Int_Init(5000-1,8400-1); //Timer clock 84M, frequency division factor 8400, so 84M/8400=10Khz

//Counting frequency, counting 5000 times is 500ms      

  while(1)

  {

    LED0=!LED0;

    delay_ms(200); //delay 200ms

  };

}

The code here is similar to the previous one. After initializing TIM3, this code enters an infinite loop waiting for the TIM3 overflow interrupt. When the value of TIM3_CNT is equal to the value of TIM3_ARR, a TIM3 update interrupt is generated, and then LED1 is negated in the interrupt, and TIM3_CNT starts counting from 0 again.

Here, the timer timing duration of 500ms is calculated as follows: the timer clock is 84Mhz, and the division factor is 8400, so the counting frequency after division is 84Mhz/8400=10KHz, and then it counts to 5000, so the duration is 5000/10000=0.5s, which is 500ms.