/elec/quadcopter

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16 by Tim Marston
added (unfinished) rc-interface module to src; added arduino.mk
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//
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// receiver.cc
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//
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#include "receiver.h"
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#include "config.h"
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#include <Arduino.h>
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#include <limits.h>
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// channel sequence order
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static const int channel_order_[] = { CHANNEL_ORDER };
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// set to the time of the last pulse edges
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static unsigned long new_pulse_up_[2] = { 0, 0 };
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static unsigned long new_pulse_down_ = 0;
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static char new_pulse_interrupt_;
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// ISR to handle the PPM signals
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inline void signal_handler( int interrupt, int pin )
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{
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	// record rising/falling edge
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	if( digitalRead( pin ) )
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		new_pulse_up_[ interrupt ] = micros();
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	else {
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		new_pulse_down_ = micros();
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		// record which interrupt just had a falling edge
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		new_pulse_interrupt_ = interrupt;
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	}
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}
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static void signal_handler_0()
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{
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	signal_handler( 0, 2 );
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}
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static void signal_handler_1()
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{
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	signal_handler( 1, 3 );
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}
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void Receiver::setup()
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{
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	// set up an interrupts
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	attachInterrupt( 0, signal_handler_0, CHANGE );
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	attachInterrupt( 1, signal_handler_1, CHANGE );
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	digitalWrite( 2, LOW );
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	digitalWrite( 3, LOW );
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}
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static unsigned long calculate_duration( unsigned long then, unsigned long now )
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{
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	return now - then;
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	if( now < then )
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		return now + ( ULONG_MAX - then );
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	else
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		return now - then;
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}
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18 by Tim Marston
completed (hopefully) the RC interface software
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bool Receiver::read_channels( int channel_values[] )
16 by Tim Marston
added (unfinished) rc-interface module to src; added arduino.mk
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{
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	static unsigned long last_pulse_down = 0;
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	static int next_channel = 0;
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	// capture pulse values atomically
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	noInterrupts();
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	unsigned long pulse_up = new_pulse_up_[ (int)new_pulse_interrupt_ ];
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	unsigned long pulse_down = new_pulse_down_;
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	char new_pulse_interrupt = new_pulse_interrupt_;
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	interrupts();
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	// if the amount of time that has passed since the last falling edge is
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	// greater than the frame gap, reset the next channel so that we can start
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	// reading them again
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	if( next_channel &&
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		new_pulse_interrupt == 1 &&
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		calculate_duration( pulse_down, micros() ) > MIN_FRAME_GAP_WIDTH )
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	{
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		// reset the next channel (which restarts reading them)
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		next_channel = 0;
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	}
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	// check for a new complete pulse
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	if( pulse_down != last_pulse_down )
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	{
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		// are there still pulses to read?
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		if( next_channel < NUM_CHANNELS )
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		{
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			unsigned long duration =
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				calculate_duration( pulse_up, pulse_down );
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			// does this pulse look ok?
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			if( duration >= MIN_PULSE_WIDTH &&
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				duration <= MAX_PULSE_WIDTH )
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			{
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				// store channel value
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				int channel = channel_order_[ next_channel ] - 1;
17 by Tim Marston
rc-interface: mostly completed it (untested, but rx and tx code should work)
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				channel_values[ channel ] = MAX_CHANNEL_VALUE *
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					( duration - MIN_PULSE_WIDTH ) /
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					( MAX_PULSE_WIDTH - MIN_PULSE_WIDTH );
16 by Tim Marston
added (unfinished) rc-interface module to src; added arduino.mk
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				// we got a channel
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				next_channel++;
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			}
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			else {
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				// set invalid channel number (to indicate error)
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				next_channel = NUM_CHANNELS + 1;
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			}
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		}
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		last_pulse_down = pulse_down;
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	}
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	// if we've read a frame, invalidate the frame (so we don't report it a
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	// second time) and return true
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	if( next_channel == NUM_CHANNELS ) {
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		next_channel++;
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		return true;
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	}
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	return false;
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}