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#include "range.h"

extern "C"

{

#include <avr/io.h>

#include <avr/interrupt.h>

}

/* Ultrasonic Sensor:

 * -if RX pin is left open, it will continuously take readings

 * -PW output is 147us/in.

 * -PW will be high for a maximum of 37.5ms if no target is detected

 * 

 * 37.5ms * 8 MHz / 8 prescaler = 37500 max wait

 */

// so that we can test on a 328

#if defined(__AVR_ATmega128RFA1__)

#  define read_INT0 (PIND & _BV(PD0))

#elif defined(__AVR_ATmega328P__) || defined(__AVR_ATmega328__)

#  define read_INT0 (PIND & _BV(PD2))

#else

#  error "Please define read_INT0 for this device"

#endif

unsigned int range;

ISR(INT0_vect)

{

  if (read_INT0)

  {

    // reset timer

    TCNT1 = 0;

  }

  else

  {

    range = TCNT1;

  }

}

void range_init()

{

  // ISC0 = 1, edge triggered

  EICRA |= _BV(ISC00);

  // enable INT0

  EIMSK |= _BV(INT0);

  // CS1 = 2, 1/8 prescaler

  TCCR1B = _BV(CS11);

  range = -1;

}

int range_get()

{

  int ret;

  cli();

  ret = range;

  sei();

  return ret;

}