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Viewing changes to src/rc-interface/receiver.cc

  • Committer: Tim Marston
  • Date: 2014-01-22 23:54:34 UTC
  • Revision ID: tim@ed.am-20140122235434-lgc7n5xdoljkiwco
completed (hopefully) the RC interface software

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src/rc-interface/receiver.cc
 
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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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bool Receiver::read_channels( int channel_values[] )
 
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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;
 
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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 );
 
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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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}