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

  • Committer: Tim Marston
  • Date: 2013-10-23 19:58:45 UTC
  • Revision ID: tim@ed.am-20131023195845-6coin3ndwkkc52np
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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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}