Interrupts

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Interrupt Code Sample

Sample Code to to toggle an LED when a button triggers an interrupt.

//Define LED and switch connections
const byte ledPin = 13;
const byte buttonPin = 2;

// Boolean to represent toggle state
volatile bool toggleState = false;

void checkSwitch@) {

  //Check status of switch
  // Toggle LED if button pressed

  if (digitalRead(buttonPin) == LOW) {
    // Switch was pressed
    // Change state of toggle 
    toggleState = !toggleState;

    // Indicate state on LED
    digitalWrite(ledPin, toggleState);
  }

}
void setup() {

  //Set LED pin as output
  pinMode(ledPin, OUTPUT) ;
  // Set switch pin as INPUT with pullup

  pinMode (buttonPin, INPUT_PULLUP) ;
  //Setup Serial Monitor
  Serial. begin (9600);

  // Attach Interrupt to Interrupt Service Routine
  attachInterrupt(digitalPinToInterrupt(buttonPin),checkSwitch, FALLING);
}

void loop() {

  // 5-second time delay
  Serial.println("Delay Started");
  delay (5000);
  Serial.println("Delay Finished");
  Serial.println(".......
}

Pin Change Interrupts

Arduino microcontrollers have a limited number of pins that are hardware interrupt compatible. 

To get around this limitation, we can use a pin change interrupts on almost all pins.

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Enable Port B

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Each port has a mask to enable particular pins.

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Activate Pin D12 on Port B

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Interrupt Service Routines are pre-defined for each port

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Define the ISR

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We must rest the interrupt by writing a "1" to the corresponding bit of the PCIFR register. This is not required when using an ISR.

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Note about Pin Change Interrupts

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Analyzing the Following Code

ATmega328P Interrupt Vector Table

• The ATmega328P provides support for 25 different interrupt sources. These interrupts and the separate Reset Vector each have a separate program vector located at the lowest addresses in the Flash program memory space.

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static uint8_t saveTCCR1A, saveTCCR1B;

static inline void capture_init(void)
{
	saveTCCR1A = TCCR1A;
	saveTCCR1B = TCCR1B;

    //reset TimerCounter 1
	TCCR1B = 0;         
    TCCR1A = 0;

	TCNT1 = 0;
	TIFR1 = (1<<ICF1) | (1<<TOV1);
	TIMSK1 = (1<<ICIE1) | (1<<TOIE1);
}
static inline void capture_start(void)
{
	TCCR1B = (1<<ICNC1) | (1<<ICES1) | (1<<CS10);
}
static inline uint16_t capture_read(void)
{
	return ICR1;
}
static inline uint8_t capture_overflow(void)
{
	return TIFR1 & (1<<TOV1);
}
static inline void capture_overflow_reset(void)
{
	TIFR1 = (1<<TOV1);
}
static inline void capture_shutdown(void)
{
	TCCR1B = 0;
	TIMSK1 = 0;
	TCCR1A = saveTCCR1A;
	TCCR1B = saveTCCR1B;
}


#define TIMER_OVERFLOW_VECTOR  TIMER1_OVF_vect
#define TIMER_CAPTURE_VECTOR   TIMER1_CAPT_vect 

References