scoutos / scout_avr / src / range.cpp @ ec9e417d
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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
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#if defined(__AVR_ATmega128RFA1__)
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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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unsigned int range; |
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static void on_edge(int which) |
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{ |
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unsigned int time = TCNT1; |
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if (read_INT0)
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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 = -1;
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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 0xFFFF; |
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} |