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root / scout_avr / src / range.cpp @ 807483bf

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#include "range.h"
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extern "C"
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{
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#include <avr/io.h>
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#include <avr/interrupt.h>
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}
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/* Ultrasonic Sensor:
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 * -if RX pin is left open, it will continuously take readings
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 * -PW output is 147us/in.
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 * -PW will be high for a maximum of 37.5ms if no target is detected
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 * 
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 * 37.5ms * 8 MHz / 8 prescaler = 37500 max wait
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 */
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// so that we can test on a 328 or the stk600
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#if defined(__AVR_ATmega128RFA1__) || defined(__AVR_ATmega2560__)
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#  define read_INT0 (PIND & _BV(PD0))
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#  define read_INT1 (PIND & _BV(PD1))
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#elif defined(__AVR_ATmega328P__) || defined(__AVR_ATmega328__)
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#  define read_INT0 (PIND & _BV(PD2))
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#  define read_INT1 (PIND & _BV(PD3))
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#else
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#  error "Please define read_INTx for this device"
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#endif
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struct range_t {
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  unsigned int start; // timer value on rising edge
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  unsigned int value; // last measured range
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} range[2];
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static void on_edge(int which)
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{
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  unsigned char int_high;
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  unsigned int time = TCNT1;
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  if (which)
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  {
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    int_high = read_INT1;
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  }
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  else
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  {
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    int_high = read_INT0;
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  }
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  if (int_high)
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  {
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    range[which].start = time;
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  }
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  else
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  {
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    // if timer overflowed since start, this arithmetic should still work out
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    range[which].value = time - range[which].start;
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  }
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}
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ISR(INT0_vect)
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{
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  on_edge(0);
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}
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ISR(INT1_vect)
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{
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  on_edge(1);
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}
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void range_init()
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{
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  // ISCx = 1, edge triggered
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  EICRA |= _BV(ISC10) | _BV(ISC00);
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  // enable INT0 and INT1
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  EIMSK |= _BV(INT1) | _BV(INT0);
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  // CS1 = 2, 1/8 prescaler
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  TCCR1B = _BV(CS11);
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  range[0].value = RANGE_ERR;
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  range[1].value = RANGE_ERR;
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}
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unsigned int range_get(int which)
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{
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  unsigned int ret;
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  if (0 <= which && which <= 1)
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  {
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    cli();
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    ret = range[which].value;
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    sei();
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    return ret;
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  }
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  else return RANGE_ERR;
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}