// Button  PA2 (pin 11).
// LED     PA7 (pin 6).
#include <avr/io.h>

#define output(directions,pin) (directions |= pin) 		// macro used to set port direction for output (set to '1')
#define input(directions,pin) (directions &= (~pin)) 	// macro used to set port direction for input (set to '0')
#define set(port,pin) (port |= pin) 					// macro used to set port pin
#define clear(port,pin) (port &= (~pin)) 				// macro used to clear port pin
#define pin_test(pins,pin) (pins & pin) 				// macro used to test for port pin
#define bit_test(byte,bit) (byte & (1 << bit)) 			// macro used to test for bit set
//
//  The following definitions are specific to the particular configuration of LEDs and buttons on pins.  
//  These are the only things that need to change when you move to other pins or add devices.
//
#define input_port PORTA		// The button is on port A
#define input_direction DDRA	//  DDRA defines input/output direction for port A
#define input_pin (1 << PA2)	//  The button is on pin 2 of port A
#define input_pins PINA			//  PINA is the register that is read to detect input high or low.
#define output_port PORTA		//  port A will be used for the LED
#define output_direction DDRA	//  DDRA defines input/output direction for port A
#define output_pin (1 << PA7)	//  The LED is on pin 7 of port A



int main(void) {							//  This is the main function
	//
   	// initialize pins
   	//
   output(output_direction, output_pin);	// sets the proper bit for output to the LED	
   input(input_direction, input_pin);		// sets the appropriate bit to enable input on the input pin.
   set(input_port, input_pin);				// turn on pull-up resistor on the input (button) pin
   //
   // main loop
   //
   while (1) {								// loops forever
      if (pin_test(input_pins,input_pin))	// test to detect button push.  Result is true if button is up.
      	clear(output_port,output_pin);		// set output low if button is up.
	  else									// otherwise...	
		  set(output_port,output_pin);  	// set output high.
      }
   }