SwitchDebounce.ino

/****************************************************************************************************************************
  SwitchDebounce.ino
  RPi_Pico_ISR_Timer-Impl.h
  For RP2040-based boards such as RASPBERRY_PI_PICO, ADAFRUIT_FEATHER_RP2040 and GENERIC_RP2040.
  Written by Khoi Hoang

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

  The RPI_PICO system timer peripheral provides a global microsecond timebase for the system, and generates
  interrupts based on this timebase. It supports the following features:
    • A single 64-bit counter, incrementing once per microsecond
    • This counter can be read from a pair of latching registers, for race-free reads over a 32-bit bus.
    • Four alarms: match on the lower 32 bits of counter, IRQ on match: TIMER_IRQ_0-TIMER_IRQ_3

  Now even you use all these new 16 ISR-based timers,with their maximum interval practically unlimited (limited only by
  unsigned long miliseconds), you just consume only one RPI_PICO timer and avoid conflicting with other cores' tasks.
  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_Generic.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         1
#define _TIMERINTERRUPT_LOGLEVEL_     4

// Can be included as many times as necessary, without `Multiple Definitions` Linker Error
#include "RPi_Pico_TimerInterrupt.h"

#define PIN_D1              1         // Pin D1 mapped to pin GPIO1 of RPI_PICO

unsigned int SWPin = PIN_D1;

#define TIMER1_INTERVAL_MS        20
#define DEBOUNCING_INTERVAL_MS    100
#define LONG_PRESS_INTERVAL_MS    5000

#define LOCAL_DEBUG               2

// Init RPI_PICO_Timer, can use any from 0-15 pseudo-hardware timers
RPI_PICO_Timer ITimer1(1);

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

bool TimerHandler1(struct repeating_timer *t)
{ 
  (void) t;
  
  static unsigned int debounceCountSWPressed  = 0;
  static unsigned int debounceCountSWReleased = 0;

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

  unsigned long currentMillis = millis();
#endif

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

    if (++debounceCountSWPressed >= DEBOUNCING_INTERVAL_MS / TIMER1_INTERVAL_MS)
    {
      // Call and flag SWPressed
      if (!SWPressed)
      {
#if (LOCAL_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 / TIMER1_INTERVAL_MS)
      {
        // Call and flag SWLongPressed
        if (!SWLongPressed)
        {
#if (LOCAL_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 / TIMER1_INTERVAL_MS))
    {
#if (LOCAL_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 (LOCAL_DEBUG > 1)
      Serial.print("SW Pressed total time ms = ");
      Serial.println(SWReleasedTime - SWPressedTime);
#endif

      debounceCountSWPressed = 0;
    }
  }

  return true;
}

void setup()
{
  pinMode(SWPin, INPUT_PULLUP);
  
  Serial.begin(115200);
  while (!Serial);

  delay(100);
  
  Serial.print(F("\nStarting SwitchDebounce on ")); Serial.println(BOARD_NAME);
  Serial.println(RPI_PICO_TIMER_INTERRUPT_VERSION);
  Serial.print(F("CPU Frequency = ")); Serial.print(F_CPU / 1000000); Serial.println(F(" MHz"));

  // Interval in microsecs
  if (ITimer1.attachInterruptInterval(TIMER1_INTERVAL_MS * 1000, TimerHandler1))
  {
    Serial.print(F("Starting ITimer1 OK, millis() = ")); Serial.println(millis());
  }
  else
    Serial.println(F("Can't set ITimer1. Select another freq. or timer"));
}

void loop()
{

}