STM32 uses ordinary IO ports to measure the frequency of PWM

There are many ways for STM32 to measure the frequency of external input signals:

Use the internal timer input capture function.

Use ordinary IO port to set external interrupt + timer to measure the frequency of PWM signal. 

Of these two methods, the first one is recommended, as it uses internal resources to save CPU resources. 

Of course, when the internal resources are insufficient, or when the corresponding pins are not connected during hardware circuit design, only the second method can be used.

Due to the inadequacy of hardware circuit design, the pins for measuring PWM input signals were not connected to the corresponding channels. The second method was used: 

Note: The priority of the timer interrupt here is higher than the priority of the external interrupt

The idea is as follows:

Set the PWM input signal pin to external interrupt mode, and the trigger mode is GPIO_MODE_IT_RISING_FALLING. Both rising and falling edges can be triggered.

Next, enable a timer TIM4, and set the timer interrupt time according to the frequency you need to measure. (This time it is set to 2us –> the maximum measurable frequency is 50KHz)

In the external interrupt, when the rising edge arrives, the counter TIM4->CNT=0 is cleared, and the rising edge flag is set to 1, which represents the start of calculating the PWM time tim4_PWM_cnt++.

When a falling edge arrives, set a falling edge flag to 1.

When the next rising edge comes, check whether the previous one was a falling edge. If yes, it means that the time of one PWM cycle has arrived. Read the time. PWM_Cycle = timer4_PWM_cnt*2. And clear the count variable tim4_PWM_cnt = 0

Then the next falling edge comes, and it is determined whether the previous one was a rising edge. If it is, it means that a cycle of high level has ended, and the time is read, which is the pulse width PWM_Duty = timer4_PWM_cnt*2. 

The specific C language implementation code is as follows:

if(__HAL_GPIO_EXTI_GET_IT(GPIO_PIN_11) != RESET)

{                           

    HAL_GPIO_EXTI_IRQHandler(GPIO_PIN_11); //Call interrupt handling common function  

    if(PWM_EN()==1) // rising edge trigger

    {

        TIM4->CNT=0; // Clear TIM4 count here. Restart counting

        if((PWM_FLAG_DOWM==1)&&(PWM_FLAG_UP==2))//Judge whether the last time was a falling edge

        {

            PWM_Cycle = timer4_PWM_cnt*2;

            timer4_PWM_cnt=0;

        }

        PWM_FLAG_CNT = 1;

        PWM_FLAG_UP = 1; // rising edge flag

        PWM_FLAG_DOWM = 2; // rising edge flag

    }

    else //Falling edge trigger

    {

      if((PWM_FLAG_DOWM==2)&&(PWM_FLAG_UP == 1))//The falling edge determines whether the previous state is a rising edge

      {

        PWM_Duty = timer4_PWM_cnt*2;

      }

     PWM_FLAG_DOWM=1; //Falling edge flag

     PWM_FLAG_UP=2; //Falling edge flag

}

void TIM4_Init(u16 arr,u16 psc)

{  

    TIM4_Handler.Instance=TIM4; //General timer 4

    TIM4_Handler.Init.Prescaler=psc; //Frequency division coefficient

    TIM4_Handler.Init.CounterMode=TIM_COUNTERMODE_UP; //Up counter

    TIM4_Handler.Init.Period=arr; //Automatically load value

    TIM4_Handler.Init.ClockDivision=TIM_CLOCKDIVISION_DIV1; //Clock division factor

    HAL_TIM_Base_Init(&TIM4_Handler);

    HAL_TIM_Base_Start_IT(&TIM4_Handler); //Enable timer 4 and timer 4 update interrupt: TIM_IT_UPDATE   

}

void TIM4_IRQHandler(void)

{

    HAL_TIM_IRQHandler(&TIM4_Handler);

    if(PWM_FLAG_CNT == 1) //PWM rising edge arrival flag

    {

        timer4_PWM_cnt++;

    }

}