SwitchDebounce.ino

/****************************************************************************************************************************
  SwitchDebounce.ino
  For AVR ATmega164, ATmega324, ATmega644, ATmega1284 with MightyCore
  Written by Khoi Hoang

  Built by Khoi Hoang https://github.com/khoih-prog/ATmega_TimerInterrupt
  Licensed under MIT license

  Now with we can use these new 16 ISR-based timers, while consuming only 1 hwarware Timer.
  Their independently-selected, maximum interval is practically unlimited (limited only by unsigned long miliseconds)
  The accuracy is nearly perfect compared to software timers. The most important feature is they're ISR-based timers
  Therefore, their executions are not blocked by bad-behaving functions / tasks.
  This important feature is absolutely necessary for mission-critical tasks.

  Notes:
  Special design is necessary to share data between interrupt code and the rest of your program.
  Variables usually need to be "volatile" types. Volatile tells the compiler to avoid optimizations that assume
  variable can not spontaneously change. Because your function may change variables while your program is using them,
  the compiler needs this hint. But volatile alone is often not enough.
  When accessing shared variables, usually interrupts must be disabled. Even with volatile,
  if the interrupt changes a multi-byte variable between a sequence of instructions, it can be read incorrectly.
  If your data is multiple variables, such as an array and a count, usually interrupts need to be disabled
  or the entire sequence of your code which accesses the data.
 *****************************************************************************************************************************/
/****************************************************************************************************************************
   Switch Debouncing uses high frequency hardware timer 50Hz == 20ms) to measure the time from the SW is pressed,
   debouncing time is 100ms => SW is considered pressed if timer count is > 5, then call / flag SW is pressed
   When the SW is released, timer will count (debounce) until more than 50ms until consider SW is released.
   We can set to flag or call a function whenever SW is pressed more than certain predetermined time, even before
   SW is released.
 *****************************************************************************************************************************/

// These define's must be placed at the beginning before #include "TimerInterrupt.h"
// _TIMERINTERRUPT_LOGLEVEL_ from 0 to 4
// Don't define _TIMERINTERRUPT_LOGLEVEL_ > 0. Only for special ISR debugging only. Can hang the system.
#define TIMER_INTERRUPT_DEBUG         0
#define _TIMERINTERRUPT_LOGLEVEL_     0
// Select just 1 TIMER to be true
#define USE_TIMER_1     true
#define USE_TIMER_2     false
// TIMER_3 Only valid for ATmega1284 and ATmega324PB (not ready in core yet)
#define USE_TIMER_3     false
// TIMER_4 Only valid for ATmega324PB, not ready in core yet
#define USE_TIMER_4     false

#if USE_TIMER_1
  #define CurrentTimer   ITimer1
#elif USE_TIMER_2
  #define CurrentTimer   ITimer2
#elif USE_TIMER_3
  #define CurrentTimer   ITimer3
#elif USE_TIMER_4
  #define CurrentTimer   ITimer4
#else
  #error You must select one Timer  
#endif

#if (_TIMERINTERRUPT_LOGLEVEL_ > 3)
  #if (USE_TIMER_1)
    #warning Using Timer1  
  #elif (USE_TIMER_2)
    #warning Using Timer2
  #elif (USE_TIMER_3)
    #warning Using Timer3
  #elif (USE_TIMER_4)
    #warning Using Timer4
  #endif
#endif

// To be included only in main(), .ino with setup() to avoid `Multiple Definitions` Linker Error
#include "ATmega_TimerInterrupt.h"

unsigned int SWPin = A0;

#define TIMER_INTERVAL_MS        20
#define DEBOUNCING_INTERVAL_MS    100
#define LONG_PRESS_INTERVAL_MS    5000

volatile bool SWPressed     = false;
volatile bool SWLongPressed = false;

void TimerHandler()
{
  static unsigned int debounceCountSWPressed  = 0;
  static unsigned int debounceCountSWReleased = 0;

#if (TIMER_INTERRUPT_DEBUG > 1)
  static unsigned long SWPressedTime;
  static unsigned long SWReleasedTime;

  unsigned long currentMillis = millis();
#endif

  static bool started = false;

  if (!started)
  {
    started = true;
    pinMode(SWPin, INPUT_PULLUP);
  }

  if ( (!digitalRead(SWPin)) )
  {
    // Start debouncing counting debounceCountSWPressed and clear debounceCountSWReleased
    debounceCountSWReleased = 0;

    if (++debounceCountSWPressed >= DEBOUNCING_INTERVAL_MS / TIMER_INTERVAL_MS)
    {
      // Call and flag SWPressed
      if (!SWPressed)
      {
#if (TIMER_INTERRUPT_DEBUG > 1)   
        SWPressedTime = currentMillis;
        
        Serial.print("SW Press, from millis() = "); Serial.println(SWPressedTime);
#endif

        SWPressed = true;
        // Do something for SWPressed here in ISR
        // But it's better to use outside software timer to do your job instead of inside ISR
        //Your_Response_To_Press();
      }

      if (debounceCountSWPressed >= LONG_PRESS_INTERVAL_MS / TIMER_INTERVAL_MS)
      {
        // Call and flag SWLongPressed
        if (!SWLongPressed)
        {
#if (TIMER_INTERRUPT_DEBUG > 1)
          Serial.print("SW Long Pressed, total time ms = "); Serial.print(currentMillis);
          Serial.print(" - "); Serial.print(SWPressedTime);
          Serial.print(" = "); Serial.println(currentMillis - SWPressedTime);                                           
#endif

          SWLongPressed = true;
          // Do something for SWLongPressed here in ISR
          // But it's better to use outside software timer to do your job instead of inside ISR
          //Your_Response_To_Long_Press();
        }
      }
    }
  }
  else
  {
    // Start debouncing counting debounceCountSWReleased and clear debounceCountSWPressed
    if ( SWPressed && (++debounceCountSWReleased >= DEBOUNCING_INTERVAL_MS / TIMER_INTERVAL_MS))
    {
#if (TIMER_INTERRUPT_DEBUG > 1)      
      SWReleasedTime = currentMillis;

      // Call and flag SWPressed
      Serial.print("SW Released, from millis() = "); Serial.println(SWReleasedTime);
#endif

      SWPressed     = false;
      SWLongPressed = false;

      // Do something for !SWPressed here in ISR
      // But it's better to use outside software timer to do your job instead of inside ISR
      //Your_Response_To_Release();

      // Call and flag SWPressed
#if (TIMER_INTERRUPT_DEBUG > 1)
      Serial.print("SW Pressed total time ms = ");
      Serial.println(SWReleasedTime - SWPressedTime);
#endif

      debounceCountSWPressed = 0;
    }
  }
}

void setup()
{
  Serial.begin(115200);
  while (!Serial && millis() < 5000);

  Serial.print(F("\nStarting SwitchDebounce on ")); Serial.println(BOARD_TYPE);
  Serial.println(ATMEGA_TIMER_INTERRUPT_VERSION);
  Serial.print(F("CPU Frequency = ")); Serial.print(F_CPU / 1000000); Serial.println(F(" MHz"));

  // Timer0 is already used for micros(), millis(), delay(), etc and can't be used
  // Select Timer 1-2
  // Timer 2 is 8-bit timer, only for higher frequency
  
  CurrentTimer.init();

  // Using ATmega324 with 16MHz CPU clock ,
  // For 16-bit timer 1, set frequency from 0.2385 to some KHz
  // For 8-bit timer 2 (prescaler up to 1024, set frequency from 61.5Hz to some KHz

  if (CurrentTimer.attachInterruptInterval(TIMER_INTERVAL_MS, TimerHandler))
  {
    Serial.print(F("Starting ITimer OK, millis() = ")); Serial.println(millis());
  }
  else
    Serial.println(F("Can't set ITimer. Select another freq. or timer"));
}

void loop()
{

}