GameCounter/Source/src/buttons.c

#include "buttons.h"
#include <avr/interrupt.h>
#include <util/atomic.h>


ButtonState buttonUp;
ButtonState buttonDown;
ButtonState buttonOption;


void button_init(ButtonState* state)
{
  (*state).flags = BSFLastReported;
  (*state).debounceTicks = 0;
  (*state).repeatTicks = 0;
}


void buttons_init()
{
  button_init(&buttonUp);
  button_init(&buttonDown);
  button_init(&buttonOption);

  // Input with internal pull-up resistor
  DDRB &= ~BUTTON_ALL;
  PORTB |= BUTTON_ALL;

  // Mode 2: CTC
  TCCR0A = _BV(WGM01);

  // Set prescaler to divide by 1024
  TCCR0B = _BV(CS02) | _BV(CS00);

  // 10ms
  OCR0A = XTAL / 1024.0 * 10e-3 - 1;

  // Enable timer interrupt
  TIMSK = _BV(OCIE0A);

  sei();
}



// Since it's a pull-up, the value is low when the button is pressed.
// This macro just helps make the code more readable.
#define isPressed(state) (!state)

#define flagSet(flags, value) ((flags & value) != 0)
#define setFlag(flags, value) flags |= (value)
#define clearFlag(flags, value) flags &= ~(value)



void button_check(ButtonState* state, uint8_t readState)
{
  #define stateRef (*state)

  uint8_t lastState = flagSet(stateRef.flags, BSFLastReported);
  uint8_t newState = lastState;

  // Debounce
  if (readState != lastState)
  {
    stateRef.debounceTicks++;
    if (stateRef.debounceTicks >= DEBOUNCE_TIME)
    {
      // Pressed / released
      newState = readState;

      if (newState)
        setFlag(stateRef.flags, BSFLastReported);
      else
        clearFlag(stateRef.flags, BSFLastReported);
    }
  }
  else
  {
    // State changed, reset debounce timer
    stateRef.debounceTicks = 0;
  }


  // Check new state
  if (isPressed(newState))
  {
    if (!isPressed(lastState))
    {
      // Pressed
      clearFlag(stateRef.flags, BSFRepeated | BSFReleased);
      setFlag(stateRef.flags, BSFPressed | BSFRepeatEnabled);
      stateRef.repeatTicks = REPEAT_START;
    }
    else if (flagSet(stateRef.flags, BSFRepeatEnabled))
    {
      // Held pressed
      stateRef.repeatTicks--;

      if (stateRef.repeatTicks == 0)
      {
        stateRef.repeatTicks = REPEAT_NEXT;
        setFlag(stateRef.flags, BSFRepeated);
      }
    }
  }
  else if (isPressed(lastState))
  {
    // Released
    setFlag(stateRef.flags, BSFReleased);
  }

  #undef stateRef
}



// every 10ms
ISR(TIMER0_COMPA_vect)
{
  uint8_t pinState = PINB;

  button_check(&buttonUp, flagSet(pinState, _BV(BUTTON_UP)));
  button_check(&buttonDown, flagSet(pinState, _BV(BUTTON_DOWN)));
  button_check(&buttonOption, flagSet(pinState, _BV(BUTTON_OPTION)));
}



inline uint8_t readAndClearFlag(ButtonState* state, uint8_t flag)
{
  uint8_t result;

  ATOMIC_BLOCK(ATOMIC_FORCEON)
  {
    result = flagSet((*state).flags, flag);
    (*state).flags &= ~(flag);
  }

  return result;
}


uint8_t button_is_pressed(ButtonState* state)
{
  return readAndClearFlag(state, BSFPressed);
}

uint8_t button_is_released(ButtonState* state)
{
  return readAndClearFlag(state, BSFReleased);
}

uint8_t button_is_repeated(ButtonState* state)
{
  return readAndClearFlag(state, BSFRepeated);
}


uint8_t button_is_pressed_or_repeated(ButtonState* state)
{
  return readAndClearFlag(state, BSFPressed | BSFRepeated);
}


uint8_t button_is_released_short(ButtonState* state)
{
  uint8_t result;

  ATOMIC_BLOCK(ATOMIC_FORCEON)
  {
    result = flagSet((*state).flags, BSFReleased) &&
             (!flagSet((*state).flags, BSFRepeated));

    if (result)
      (*state).flags &= ~BSFReleased;
  }

  return result;
}

uint8_t button_is_pressed_long(ButtonState* state)
{
  uint8_t result;

  ATOMIC_BLOCK(ATOMIC_FORCEON)
  {
    result = flagSet((*state).flags, BSFPressed) &&
             flagSet((*state).flags, BSFRepeated);

    // Remove RepeatEnabled as well to prevent further repeat events
    if (result)
      (*state).flags &= ~(BSFPressed | BSFRepeated | BSFRepeatEnabled);
  }

  return result;
}