STM32F429 External Interrupt Edge

Question

I am using the STM32F429I-Discovery board, the board has a pushbutton connected to PA0, which in turn is connected to External Interrupt Line 0 (EXTI0).

Using the HAL Libraries, I can toggle a LED either on the Falling Edge or on the Rising edge using external interrupts. Eg, the LED either changes state as soon as I press the pushbutton, or only once I release the pushbutton.

What I want to do is to Interrupt on the Rising edge, start a timer, and then interrupt on the falling edge again, to stop the timer. I have got no idea how to achieve this?

There is also an option to trigger on both rising and falling edges. I do not know if there should only be one interrupt, and I then figure out if it was a rising or falling edge (probably by accessing the registers directly), or should there be two configured interrupts - One as Rising Edge and one as Falling Edge?

Below are the external interrupt code; firstly to set a GPIO up as an external interrupt, then to detect the interrupt and then to handle the interrupt (callback).

    static void EXTILine0_Config(void)
{
  GPIO_InitTypeDef   GPIO_InitStructure;

  /* Enable GPIOA clock */
  __HAL_RCC_GPIOA_CLK_ENABLE();

  /* Configure PA0 pin as input floating */
  GPIO_InitStructure.Mode = GPIO_MODE_IT_FALLING;
  GPIO_InitStructure.Pull = GPIO_NOPULL;
  GPIO_InitStructure.Pin = GPIO_PIN_0;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStructure);

  /* Enable and set EXTI Line0 Interrupt to the lowest priority */
  HAL_NVIC_SetPriority(EXTI0_IRQn, 2, 0);
  HAL_NVIC_EnableIRQ(EXTI0_IRQn);
}


/* Clears the interrupt after calling this I think */
void EXTI0_IRQHandler(void)
{
    HAL_GPIO_EXTI_IRQHandler(KEY_BUTTON_PIN);
}


/**
  * @brief EXTI line detection callbacks
  * @param GPIO_Pin: Specifies the pins connected EXTI line
  * @retval None
  */

void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
{
  if(GPIO_Pin == KEY_BUTTON_PIN)
  {
    /* Toggle LED3 */
    BSP_LED_Toggle(LED3);
  }
}

Can someone please point out how I can achieve this?

Vinci · Answer 1 · 2016-01-27T13:26:56.140

What you're looking for is called "input capture" and can be achieved with a timer directly without the need for external interrupts. On the STM32F429 PA0 is internally mapped to Timer 2 Channel 1.

The sConfigIC structure is responsible for handling input capture related configuration stuff.

The initialization looks something like this:

/* TIM2 init function */
void MX_TIM2_Init(void)
{
  TIM_ClockConfigTypeDef sClockSourceConfig;
  TIM_MasterConfigTypeDef sMasterConfig;
  TIM_IC_InitTypeDef sConfigIC;

  /* Peripheral clock enable */
  __TIM2_CLK_ENABLE();

  /* Peripheral interrupt init*/
  HAL_NVIC_SetPriority(TIM2_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(TIM2_IRQn);

  /**TIM2 GPIO Configuration    
  PA0/WKUP     ------> TIM2_CH1 
  */
  GPIO_InitStruct.Pin = GPIO_PIN_0;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
  GPIO_InitStruct.Alternate = GPIO_AF1_TIM2;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 0;
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim2.Init.Period = 0xFFFFFFFF;
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  HAL_TIM_Base_Init(&htim2);

  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig);

  HAL_TIM_IC_Init(&htim2);

  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig);

  /* Input capture stuff HERE
     Change polarity as needed */
  sConfigIC.ICPolarity = TIM_INPUTCHANNELPOLARITY_BOTHEDGE;
  sConfigIC.ICSelection = TIM_ICSELECTION_DIRECTTI;
  sConfigIC.ICPrescaler = TIM_ICPSC_DIV1;
  sConfigIC.ICFilter = 0;
  HAL_TIM_IC_ConfigChannel(&htim2, &sConfigIC, TIM_CHANNEL_1);

}

And further the interrupt function:

/* IRQ */
void TIM2_IRQHandler(void)
{
   // Check for interrupt flags here
}

Within the interrupt you've got to check for the CC1IF flag. The timer value gets stored in the capture and compare register called CCR1.

/edit

Don't forget to start the timer and input capture channel with:

HAL_TIM_IC_Start_IT(&htim2, TIM_CHANNEL_1);

This enables the timer, the according channel for input capture and the interrupt.

Hi Vinci. Thank you for this, I will definitely try that. What I ended up doing is reading the HAL_GetTick() which interrupts every 1ms. I store the value in a variable when the pin goes high and in another one when the Pin goes low. I then subtract low from high, but I have not catered for overflows yet. — AJBotha, Jan 27 '16 at 13:31

score 2 · Accepted Answer · answered Jan 26 '16 at 10:37

First, you have to setup a timer, e.g.

TIM_HandleTypeDef htim1;

void TIM1_Init(void)
{

  TIM_ClockConfigTypeDef sClockSourceConfig;
  TIM_MasterConfigTypeDef sMasterConfig;

  htim1.Instance = TIM1;
  htim1.Init.Prescaler = 71;
  htim1.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim1.Init.Period = 65535;
  htim1.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim1.Init.RepetitionCounter = 0;
  HAL_TIM_Base_Init(&htim1);

  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  HAL_TIM_ConfigClockSource(&htim1, &sClockSourceConfig);

  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  HAL_TIMEx_MasterConfigSynchronization(&htim1, &sMasterConfig);

}

Code is taken from an STM32F1, so maybe you have to adapt a little, just have a look in the HAL handbook.

The interrupt for rising and falling edge is the same, so you have to check the state of the pin in your interrupt handler.

To start the timer

  HAL_TIM_Base_Start(&htim1);

and to stop

  HAL_TIM_Base_Stop(&htim1);

the counter value is stored in

TIM1->CNT

"The interrupt for rising and falling edge is the same, so you have to check the state of the pin in your interrupt handler." I don't know why I did not think of that! Thank you. — AJBotha, Jan 26 '16 at 10:45

score 1 · Answer 3 · answered Jan 27 '16 at 13:44

A bit of background: Using the STM32F429I the code below is to display how long you press the blue user button for, the count is given as milliseconds. The PCB has a hardware debounce circuit so the fastest response I was able to get is around 50ms.

As stated earlier PA0 is connected to EXTILine0. I set the PA0 line up to interrupt on both rising and falling edges.

static void EXTILine0_Config(void)
{
  GPIO_InitTypeDef   GPIO_InitStructure;

  /* Enable GPIOA clock */
  __HAL_RCC_GPIOA_CLK_ENABLE();

  /* Configure PA0 pin as input floating */
  GPIO_InitStructure.Mode = GPIO_MODE_IT_RISING_FALLING;
  GPIO_InitStructure.Pull = GPIO_NOPULL;
  GPIO_InitStructure.Pin = GPIO_PIN_0;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStructure);

  /* Enable and set EXTI Line0 Interrupt to the lowest priority */
  HAL_NVIC_SetPriority(EXTI0_IRQn, 2, 0);
  HAL_NVIC_EnableIRQ(EXTI0_IRQn);
}

When a interrupt then occurs, I read the amount of counts that are currently stored in HAL_GetTick(), this function clocks every 1 millisecond. I also read whether the pin is high or low to determine if the interrupt was on a falling or on a rising edge.

uint16_t beginCount;
uint16_t stopCount;

void EXTI0_IRQHandler(void)
{

uint16_t var;
var = HAL_GetTick();
uint16_t calcCount = 0;
unsigned char buffer[10];
BSP_LCD_Clear(LCD_COLOR_WHITE);
        // The Pin Goes high when the pushbutton is pressed. 
        if (HAL_GPIO_ReadPin(GPIOA, KEY_BUTTON_PIN) == 0x01)
            {
                  beginCount = 0;
                  beginCount = var;
                  BSP_LCD_SetTextColor(LCD_COLOR_GREEN);
                  BSP_LCD_DisplayStringAtLine(6, "Rising Edge" );
            }
        else 
            {
                    stopCount = 0;
                    stopCount = var;
                    BSP_LCD_SetTextColor(LCD_COLOR_RED);
                    BSP_LCD_DisplayStringAtLine(7, (uint8_t*)"Falling Edge");

                    // Calculate Counts and covert to seconds - What if the counter overflows?
                    calcCount = stopCount - beginCount;
                    sprintf(buffer, "%d", calcCount); // Convert the integer to string and put it in variable buffer

                    BSP_LCD_DisplayStringAtLine(8, (&buffer) ); // Display the value stored at buffer's location

            }



    HAL_GPIO_EXTI_IRQHandler(KEY_BUTTON_PIN);

}

Lastly the interrupt callback triggers and just toggles the LED on the board. The counter can only go to something like 65 seconds, after that it would overflow and my 'calculated' time would be incorrect. This methods works OK for what I intend to do with it. I want to measure 20-300 milliseconds with a accuracy of a few milliseconds. I still have to put in a catch for if the timer overflows between two measurements.

Anything fundamentally wrong with this approach? I am not very experienced with C, and not at all with STM32.

Please correct the variable 'var' size to uint32_t to match the SysTick, else it will not work. Also, there is no need to assign 0 to beginCount or to stopCount, if the very next line assigns to it new value. Just erase those lines, even if they do no harm. And yes, every two months the counter overflows :) check if there is overflow in order to have reliable code. And one more: calCount is in msec, in order to have it in seconds you must divide it by 1000. — EmbeddedGuy, Jul 28 '20 at 16:16

STM32F429 External Interrupt Edge

3 Answers3