/* ========================================================================== */
/*                                                                            */
/*   UltraSonicSensorModule.c                                                 */
/*   (c) 2007 Frazras                                                         */
/*   CHIP: ATMega8535L  8MHz clock                                                      */
/*                                                                            */
/*   Description: The following code will send a pulse to the SRF04 ultrsonic */
/*                Ranger(sensor) and output the range in centimeters          */
/*                                                                            */
/*       This code is free software; you can redistribute it and/or           */
/*       modify it under the terms of the GNU Library General Public          */
/*       License as published by the Free Software Foundation; either         */
/*       version 2 of the License, or (at your option) any later version.     */
/*                                                                            */
/* ========================================================================== */
#define F_CPU 1000000UL

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


//define times for start and end of signal
uint16_t rising, falling;

//this function sleeps s seconds (if F_CPU is set to frequency of processor)
void sleep_sec(uint8_t s)
{
  uint8_t i;
  while (s--) for (i = 0; i < 100; i++) _delay_ms(10);
}


//Timer1 capture interrupt service subroutine
ISR(TIMER1_CAPT_vect)
{
	/*This subroutine checks to see if itwas start of pulse (rising edge)
	or was it end (fallingedge)and performs required operations*/

	//if high level detected
	if ((bit_is_set(PIND, 6))){ 
	
	//save start time
	rising=ICR1;

	//set to trigger next  on falling edge
	TCCR1B = _BV(CS10);

}else{

	//save falling time
	falling=ICR1;
	
    //rising edge triggers next
	TCCR1B = _BV(CS10)|_BV(ICES1);
	
	//variable to display values on LED
	int led;

	//calculate the pulse width
	led = falling - rising;

	//convert to centimeters (cm)
	led /=58;

	//output range on LEDs
	DDRB = 0xFF;
	PORTB = (uint8_t)led;
	
	//display for 4 seconds
	//sleep_sec(4);

  	}	
}


void pulse(){

	//send pulse throught PIN 1
	DDRD = 0b00000001;
	PORTD= 0b00000001;

	//12 us delay
	asm volatile(
	"ldi r16, 31\n\t"
	"loop: dec r16\n\t"
	"brne loop\n\t"
	);

	//Set PIN1 to LOW and end pulse
	PORTD= 0b00000000;

}

int main()
{	
	//Input Capture Interrupt Enable
	TIMSK = _BV(TICIE1); 
  	
	//Enable Global interrupt
    sei();
	
	//Send pulse to SRF04 ultrasonic sensor		
	pulse();
				
	//Start timer counter and Enable input capture on rising edge
	TCCR1B = _BV(CS10)|_BV(ICES1); 
		
  	while(1);
}