// Jeffery Durand

// 
// v_06: The brightness also decreases, adding a custom defines for modularity
// 

//
// Head: taken from Neil Gershenfeld's programs, with added functions
//

// Button   PA3 (pin 10)
// LED      PA7 (pin 6)
// Cristal  Xtal 1 & 2 (pin 2 & 3)
#include <avr/io.h> // basic library
#include <util/delay.h> /* Functions to waste time */
#include <stdbool.h> // contains the booleans
#include <math.h> // contains math functions, but is big!

// Certain functions are the same in fact but conceptually different hance the different names
// pin x is always one bit shifted x times
// DDRx manipulation
#define output(directions,pin) (directions |= pin) // set port direction for output (make 1)
#define input(directions,pin) (directions &= (~pin)) // set port direction for input, default (make 0)
// PORTx manipulation
#define set(port,pin) (port |= pin) // set port pin
#define clear(port,pin) (port &= (~pin)) // clear port pin
#define all_set(port) (port = 0xff) // set all port pins, not recommended as different names may be given to same port
#define all_clear(port) (port = 0x00) // clear all port pins
// PINx reading
#define pin_test(pins,pin) (pins & pin) // test for port pin
#define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set

// PROGRAM specific
// the button or input
#define button_port PORTA
#define button_direction DDRA
#define button_pins PINA
#define button_pin (1 << PA3)
// the LED or output
#define LED_port PORTA
#define LED_direction DDRA
#define LED_pins PINA
#define LED_pin (1 << PA7)

// delaying set out explicitly
#define power_levels 12 // different levels of power
#define delay_on 1 // number of us the LED is left on 

int main (void)
{
  /* Initialization */
  output (LED_direction, LED_pin);
  set (button_port, button_pin); 

  // full brightness at first
  int delay = 0;
  uint8_t count = 0; // unsigned 8-bit integer
  // need to declare i here, does not work in for loop
  int i;
  // tells if the button has just been pressed
  bool pressed = false;

  /* Event Loop */
  while (1)
  {
    /* action */
    if (pin_test (button_pins, button_pin) == 0 && pressed == false) // meaning the input on PA3 is low, so ground is connected, so button is pressed
    { 
      // clear to avoid flash at beginning
      clear (LED_port, LED_pin); 
      // increase count and use exponential growth for the delay
      count = (count + 1) % power_levels;
      delay = pow (2, count);
      // set to pressed true so that the delay is not changed again while button remains pressed
      pressed = true;
    }
    else 
    {
      // only change back to false once the button is up again
      if (pin_test(button_pins, button_pin) != 0)
      {
        pressed = false;
      } 

      clear (LED_port, LED_pin); // turn the led pin off
      // need the for loop, cannot use variables inside _delay
      for (i = 0; i < delay; i++)
      {
        _delay_us(delay_on);
      }
      set (LED_port, LED_pin); // turn the LED pin on
      _delay_us(delay_on); // wait
    }
  }
  return (0); // never reached 
}