/* ATtiny13 1.2MHz */

#define F_CPU 1200000L

#include <avr/io.h>
#include <util/delay.h>  
#include <avr/interrupt.h>
#include <avr/eeprom.h>

#define ADDRESS_1 8
#define ADDRESS_2 16

#define PANEL_DDR DDRB
#define PANEL_PORT_OUT PORTB
#define PANEL_L_PIN PB4
#define PANEL_R_PIN PB2
#define PANEL_C_PIN PB3

volatile uint8_t sequence, adc, frequency, mode, frequency_old, mode_old, duration, duty, c, d, i;
volatile uint16_t timer_overflow_count, timer_overflow_target=384, delay;


ISR(TIM0_OVF_vect) {  // Read buttons state in interrupt, using ADC

  if(++timer_overflow_count > timer_overflow_target) { // check if any button is pressed

    timer_overflow_target = 384; // by default every 82ms
    timer_overflow_count = 0;

    ADCSRA |= (1 << ADSC);  // start analog-to-digital conversion
    while (ADCSRA & (1 << ADSC));  // wait for it to finish
    adc = ADCH;

    /* If two buttons are pressed at the same time, reset to default settings */
    if(adc < 150) {  
      frequency=1;
      mode=2;
      eeprom_update_byte((uint8_t*)ADDRESS_1, frequency); // update EEPROM with defaults
      eeprom_update_byte((uint8_t*)ADDRESS_2, mode);
      PANEL_PORT_OUT &= ~( (1 << PANEL_L_PIN) | (1 << PANEL_R_PIN) | (1 << PANEL_C_PIN) ); // and make LC panels transparent
      _delay_ms(1000); // for one second
      return;
    }

    /* If SWITCH_1 is pressed, change device's occlusions frequency */
    if (adc < 176) { 
      frequency ++; 
      timer_overflow_target = 768; // wait 164ms after a button is pressed
      return;
    }
    if (frequency > 4) { frequency = 0; }

    /* If SWITCH_0 is pressed,  change device's eyes occlusion rate     */
    /* (with eye is occluded longer in each main while loop execution) */
    if (adc < 210) { 
      mode++; 
      timer_overflow_target=768; // wait 164ms after a button is pressed
      return;
    }
    if (mode > 4) { mode = 0; }


  }

}  

void advance_sequence(void) { // This function drives outputs 

  switch(sequence) {

    case 0: 
    PANEL_PORT_OUT |= (1 << PANEL_L_PIN);
    PANEL_PORT_OUT &= ~( (1 << PANEL_R_PIN) | (1 << PANEL_C_PIN) );
    break;

    case 1: 
    PANEL_PORT_OUT |= (1 << PANEL_L_PIN) | (1 << PANEL_C_PIN);
    PANEL_PORT_OUT &= ~(1 << PANEL_R_PIN);
    break;

    case 2: 
    PANEL_PORT_OUT |= (1 << PANEL_R_PIN) | (1 << PANEL_C_PIN);
    PANEL_PORT_OUT &= ~(1 << PANEL_L_PIN);
    break;

    case 3: 
    PANEL_PORT_OUT |= (1 << PANEL_R_PIN);
    PANEL_PORT_OUT &= ~( (1 << PANEL_L_PIN) | (1 << PANEL_C_PIN) );
    break;

  }

  sequence++;
  if(sequence>3) sequence=0;

}


int main(void) {


  /* PB1 and PB0 as outputs, PWM;  LC panels driver pins as outputs*/
  PANEL_DDR |= (1 << PB1) | (1 << PB0) | (1 << PANEL_L_PIN) | (1 << PANEL_R_PIN) | (1 << PANEL_C_PIN);

  /* Use 8-bit timer/counter to generate two 4687.5 Hz waves that drive voltage multiplier (charge pump)*/
  TCCR0B |= (1 << CS00); // 8-bit timer/counter prescaler to 1
  TCCR0A |= (1 << WGM01) | (1 << WGM00); // set to 'Fast PWM' mode
  TCCR0A |= (1 << COM0A1) | (1 << COM0A0) | (1 << COM0B1); // OC0A output is in antiphase to OC0B
  OCR0A = 127; // duty 50%
  OCR0B = 127;

  TIMSK0 |= (1 << TOIE0); // enable timer overflow interrupt
  sei();

  /* Set up ADC, default ADC input is PB5/ADC0 */
  ADMUX |= (1 << ADLAR);  //left adjust result
  ADCSRA |= (1 << ADPS2) | (1 << ADEN);  // prescaler to 16, enable ADC

  /* Read previous state of device */
  frequency = eeprom_read_byte((uint8_t*)ADDRESS_1);
  mode = eeprom_read_byte((uint8_t*)ADDRESS_2);

  if (frequency > 4) { frequency = 1; } // if EEPROM stored settings outside of range, set defaults
  if (mode > 4) { mode = 2; }


  while (1) {


    switch(frequency) { // calculate how much time every main while loop execution will take
      case 0: duration=40; break;
      case 1: duration=20; break;
      case 2: duration=13; break;
      case 3: duration=10; break;
      case 4: duration=8; break;
    }

    d = d + duration;

    if(d > 100) {  // Check approximately every second.
                   // duration is in ms, in one cycle of main while loop duration is executed 10 times, 
                   // hence 100 "milliseconds" in a second 

      if((frequency == frequency_old) && (mode == mode_old)) c++; // check if settings are permanent
      else c= 0;
      if(c==10) {  // after approximately 10 seconds of settings being permanent
        
        eeprom_update_byte((uint8_t*)ADDRESS_1, frequency); //start updating EEPROM with stable setting
        eeprom_update_byte((uint8_t*)ADDRESS_2, mode);

        c = 0;

      }

      frequency_old = frequency;
      mode_old = mode;

      d = 0;

    }


    duty = mode * 2; // if you multiply duty value by 10 and add 10,
                     // you get percentage of time left eye is occluded in each main while loop execution

    switch(frequency) { // determines how much time each tenth of main while loop cycle will take
      case 0: delay=12000; break;
      case 1: delay=6000; break;
      case 2: delay=4000; break;
      case 3: delay=3000; break;
      case 4: delay=2400; break;
    }


    /* Puts 10 blocks of _delay_loop_2 to properly  */
    /* synchronize eyes occlusions. First blocks    */
    /* occlude left eye, next blocks occlude right  */
    /* eye. Each execution of _delay_loop_2 takes   */
    /* four clock cycles.                           */
    /* -------------------------------------------- */

    advance_sequence();

    for(i = 0; i <= (duty); i++) _delay_loop_2(delay);

    advance_sequence();

    for(i = 0; i < (9-duty); i++) _delay_loop_2(delay);

    /* -------------------------------------------- */


  }


}