/* 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 SWITCH_DDR DDRB
#define SWITCH_PULL_UP PORTB
#define SWITCH_PORT_IN PINB
#define SWITCH_0_PIN PB4
#define SWITCH_1_PIN PB3

#define SYNC_DDR DDRB
#define SYNC_PORT_IN PINB
#define SYNC_0_PIN PB0
#define SYNC_1_PIN PB1

#define LED_DDR DDRB
#define LED_PORT_OUT PORTB
#define LED_PIN PB2

#define SET_BIT(byte, bit) ((byte) |= (1UL << (bit)))
#define CLEAR_BIT(byte,bit) ((byte) &= ~(1UL << (bit)))
#define IS_SET(byte,bit) (((byte) & (1UL << (bit))) >> (bit)) 
#define IS_PRESSED(byte,bit) (!(((byte) & (1UL << (bit))) >> (bit)))  


volatile uint8_t frequency, mode, frequency_old, mode_old, sequence=0, duration, duty, c, d, timer_overflow_count=0, timer_overflow_target=6;

ISR(TIM0_OVF_vect) {

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

    timer_overflow_target=6; // by default every 82ms

    /* If SWITCH_1 is pressed, change device's frequency */
    if (IS_PRESSED(SWITCH_PORT_IN,SWITCH_1_PIN)) { 
      frequency ++; 
      timer_overflow_target=12; // wait 164ms after a button is pressed
    }
    if (frequency > 4) { frequency = 0; }

    /* If SWITCH_0 is pressed,  change device's duty cycle     */
    if (IS_PRESSED(SWITCH_PORT_IN,SWITCH_0_PIN)) { 
      mode++; 
      timer_overflow_target=12; // wait 164ms after a button is pressed
    }
    if (mode > 4) { mode = 0; }


    /* If two buttons are pressed at the same time, reset to default settings */
    if((IS_PRESSED(SWITCH_PORT_IN,SWITCH_1_PIN)) && (IS_PRESSED(SWITCH_PORT_IN,SWITCH_0_PIN))) {  
      frequency=4;
      mode=2;
      eeprom_update_byte((uint8_t*)ADDRESS_1, frequency); // update EEPROM with defaults
      eeprom_update_byte((uint8_t*)ADDRESS_2, mode);
      CLEAR_BIT(LED_PORT_OUT,LED_PIN); // and make LEDs go dark
      _delay_ms(1000); // for one second
    }

    timer_overflow_count = 0;

  }
}    
      

void advance_sequence(void) { // this function drives LEDs 

  switch(sequence) {

    case 0: 
    /* light LEDs only when eye is occluded and mode is not 0*/
    if(((IS_SET(SYNC_PORT_IN,SYNC_0_PIN)) || (IS_SET(SYNC_PORT_IN,SYNC_1_PIN))) && mode) {  
      SET_BIT(LED_PORT_OUT,LED_PIN);
    }
    break;

    case 1: 
    CLEAR_BIT(LED_PORT_OUT,LED_PIN);
    break;

    break;

  }

  sequence++;
  if(sequence>1) sequence=0;

}


int main(void) {


  uint8_t i;
  uint16_t delay;

  CLEAR_BIT(SWITCH_DDR,SWITCH_0_PIN); // set switches pins as inputs, pulled-up by internal resistors
  CLEAR_BIT(SWITCH_DDR,SWITCH_1_PIN);
  SET_BIT(SWITCH_PULL_UP,SWITCH_0_PIN);
  SET_BIT(SWITCH_PULL_UP,SWITCH_1_PIN);

  CLEAR_BIT(SYNC_DDR,SYNC_0_PIN); // set SYNC pins as inputs
  CLEAR_BIT(SYNC_DDR,SYNC_1_PIN);

  SET_BIT(LED_DDR,LED_PIN); // set LEDs pin as output

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

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

  SET_BIT(TCCR0B,CS01); // prescale timer to 1/64th the clock rate
  SET_BIT(TCCR0B,CS00);
  SET_BIT(TIMSK0,TOIE0); // enable timer overflow interrupt
  sei();


  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=1; break;
    }

    d = d + duration;

    if(d > 100) {  // Check approximately every 100 ms.
                   // duration is in 0.1 ms, in one cycle of main while loop duration is executed 10
                   // times (in this particular device 4 times), hence 10 "milliseconds" in 100 ms 

      if((frequency == frequency_old) && (mode == mode_old)) c++; // check if settings are permanent
      else c= 0;
      if(c==100) {  // 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;

    switch(frequency) { // determines how much time each fourth of main while loop cycle will take
      case 0: delay=3000; break;
      case 1: delay=1500; break;
      case 2: delay=1000; break;
      case 3: delay=750; break;
      case 4: delay=75; break;
    }


    /* Puts 4 blocks of _delay_loop_2 to properly   */
    /* control LEDs duty cycle. First blocks set    */
    /* LED_PIN to 1, next blocks set LED_PIN to 0.  */
    /* 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 < (4-duty); i++) _delay_loop_2(delay);

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


  }


}