ultrasonic.c

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/*
 * 
 * code needs to be moved in asuro.c to be compilable
 */

#include <util/delay.h>
#include "asuro.h"
#include "ultrasonic.h"

int count40kHz;

ISR(TIMER2_COMP_vect)
{
        count40kHz++;
}

void InitUltrasonics(void)
{
        // Change Oscillator-frequency of Timer 2
        // to 40kHz, no toggling of IO-pin:
  cli();
  TCCR2  = (1 << WGM21) | (1 << CS20);
        OCR2   = 100;              // 40kHz @8MHz crystal
        TIMSK  = (1 << OCIE2);     // OCIE2:  Timer/Counter2 Output Compare Match Interrupt Enable
        
        ADCSRA = (0 << ADEN);      // deactivate ADC
        ACSR  |= (1 << ACIS1);     // Comparator Interrupt on Falling Output Edge

        ADMUX  = 0x03;             // connect ADC3-input with comparator
        SFIOR |= (1 << ACME);      // connect ADC multiplexer to comparator
        DDRD  &= ~(1 << 6);        // use Port D Pin 6 as input (AIN0)
  sei();
}

void RestoreAsuro(void)
{
  cli();
  TCCR2 = (1 << WGM20) | (1 << WGM21) | (1 << COM20) | (1 << COM21) | (1 << CS20);
        OCR2  = 0x91;              // duty cycle for 36kHz
        TIMSK &= ~(1 << OCIE2);     // OCIE2:  Timer/Counter2 Output Compare Match Interrupt Disable

        ADCSRA = (1 << ADEN) | (1 << ADPS2) | (1 << ADPS1); // clk/64
        ACSR  |= (0 << ACIS1);

        if(autoencode) {
                EncoderInit();
        }
        sei();
        _delay_us(1);
}

int Chirp(void)
{
        unsigned int sleeptime = 0, dist = 0;

        InitUltrasonics();

        // chripen:
        count40kHz = 0;

        while(count40kHz != 20) {
                OCR2 = 100 + 20 / 2 - count40kHz;
        }

        TCCR2   = (1 << WGM21) | (1 << CS20);
        OCR2    = 100;

        // analyse echoes:
        while(TRUE) {
                _delay_us(1);
                sleeptime++;

                if((ACSR & (1 << ACI))) {
                        dist = (unsigned int) ((long) ((344L * ((sleeptime * 1000L) / 72L) / 10000L) / 2L));
                        ACSR |= (1 << ACI);
                        break;
                }
                
                ACSR |= (1 << ACI);
                
                if(sleeptime > 3500) {
                        return -1;
                }
        }
        
        RestoreAsuro();
        return dist;
}

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