THECODEPROGRAM

Let's get started.

Firstly, What is interrupt
Interrputs are one of key functions of programming. We can see interrupt system almost every programming areas. ARM based microcontrollers have NVIC. Function of NVIC is mapping the external interrupts for the MCU. NVIC has the triggers for all interrupts.

In here we are going to External Interrupt Controller to fire a function when an input activated. It controls the inputs and when a GPIO pin has an input HIGH, EXTI fires a its handler function to perform specified operation.

Now, let's start to coding

int button_counter = 0;	

Now let's write our main function. Below code block is in our main function.

• PA0 Blue Button
• PD12 Green LED
• PD13 Orange LED
• PD14 Red LED
• PD15 Blue LED

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

GPIO_InitTypeDef   GPIO_InitStructure;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT; 
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15; 
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_Init(GPIOD, &GPIO_InitStructure); 

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
GPIO_Init(GPIOA, &GPIO_InitStructure);

EXTI_InitTypeDef   EXTI_InitStructure;
EXTI_InitStructure.EXTI_Line = EXTI_Line0;
EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising;  
EXTI_InitStructure.EXTI_LineCmd = ENABLE;
EXTI_Init(&EXTI_InitStructure);

NVIC_InitTypeDef   NVIC_InitStructure;
NVIC_InitStructure.NVIC_IRQChannel = EXTI0_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0F;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0F;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

Until here our main function is ready. Now we are going to declare interrupt handler function.

void EXTI0_IRQHandler(void)
{
  if(EXTI_GetITStatus(EXTI_Line0) == SET)
  {
		button_counter++;
		if(button_counter %4 == 0){
			GPIO_SetBits(GPIOD,GPIO_Pin_12);
			GPIO_ResetBits(GPIOD,GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15);
		} 
		else if(button_counter %4 == 1){
			GPIO_SetBits(GPIOD,GPIO_Pin_13);
			GPIO_ResetBits(GPIOD,GPIO_Pin_12 | GPIO_Pin_14 | GPIO_Pin_15);
		}
		else if(button_counter %4 == 2){
			GPIO_SetBits(GPIOD,GPIO_Pin_14);
			GPIO_ResetBits(GPIOD,GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_15);
		}
    else if(button_counter %4 == 3){
			GPIO_SetBits(GPIOD,GPIO_Pin_15);
			GPIO_ResetBits(GPIOD,GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14);
		}
		
    /* Clear the EXTI line 0 pending bit */
    EXTI_ClearITPendingBit(EXTI_Line0);
  }
}

As you can see above we have never talked about a while loop. All of this operations is happening at GPIO interrupt handler.

Program is ready. You can see the working video on youtube: https://www.youtube.com/watch?v=oJFmhSvXjaA

That is all in this article.

You can reach the example code on Github : https://github.com/thecodeprogram/TheSingleFiles/blob/master/STM32F4_StdPeriph_GPIO_EXTI.c

Burak Hamdi TUFAN