Colony » Colony Scout » Colony Scout OS

extern "C"

{

#include <avr/io.h>

#include <avr/interrupt.h>

#include <util/delay.h>

}

#include "range.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

 * 37.5ms * 16 MHz / 8 prescaler = problem

 * 37.5ms * 16 MHz / 64 prescaler = 9375 max wait

 * 147us/in * 16 MHz / 64 prescaler = 1.44685039 ticks / mm

 */

struct range_t {

  unsigned int start; // timer value on rising edge

  unsigned int value; // last measured range

  char busy;

} volatile range[2];

static void on_edge(int which)

{

  unsigned char int_high;

  unsigned int time = TCNT5;

  if (which)

  {

    int_high = PIN_SONAR_PWM & _BV(P_SONAR_PWM1);

  }

  else

  {

    int_high = PIN_SONAR_PWM & _BV(P_SONAR_PWM0);

  }

  if (int_high)

  {

    range[which].start = time;

    range[which].busy = 1;

  }

  else

  {

    // if timer overflowed since start, this arithmetic should still work out

    range[which].value = time - range[which].start;

    range[which].busy = 0;

  }

}

ISR(INT3_vect)

{

  on_edge(0);

}

ISR(INT2_vect)

{

  on_edge(1);

}

void range_init()

{

  // ISCx = 1, edge triggered

  EICRA |= _BV(ISC20) | _BV(ISC30);

  // enable INT2 and INT3

  EIMSK |= _BV(INT2) | _BV(INT3);

  // CS1 = 3, 1/64 prescaler

  // if this is changed, remember to change recv_edge in bom.cpp!

  TCCR5B = _BV(CS50) | _BV(CS51);

  // set tx as output

  DDRG |= _BV(DDG1);

  PORT_SONAR_TX &= ~ _BV(P_SONAR_TX);

}

void range_measure(unsigned int *values)

{

  int i;

  for (i = 0; i < 2; i++)

  {

    range[i].value = RANGE_ERR;

    range[i].busy = 0;

  }

  // TODO ensure that one interrupt won't be delayed because of the other

  PORT_SONAR_TX |= _BV(P_SONAR_TX);

  _delay_ms(40);

  PORT_SONAR_TX &= ~ _BV(P_SONAR_TX);

  for (i = 0; i < 2; i++)

  {

    while (range[i].busy) {}

    values[i] = range[i].value;

  }

}