RoboBuggy

/**

 * @file receiver.c

 * @brief Contains Code for dealing with RC Receiver

 * NOTE: AIL and THR are flipped.

 * AIL is on pin 2

 * THR is on pin 3

 *

 * @author Matt Sebek (msebek)

 * @author Zach Dawson (zsd)

 */

#include <Arduino.h>

#include "receiver.h"

#define AIL_LEFTMOST 2000

#define AIL_RIGHTMOST 980

#define AIL_CENTERMOST 1480

#define THR_LEFTMOST -1

#define THR_RIGHTMOST -1

#define THR_CENTERMOST -1

#define AIL_RECEIVER_PIN 2

#define AIL_RECEIVER_INT 0

#define THR_RECEIVER_PIN 3

#define THR_RECEIVER_INT 1

//For 72 MHz RC reciever

//#define PWM_TIME 21800

//#define PWM_THRESH 130

//#define BIG_PULSE 10

//High pulse lasts over 1/10 of period

//#define SHORT_PULSE 21

//High pulse lasts under 1/21 of period

//For 2.4 GHz racecar reciever

#define PWM_TIME 18370

#define PWM_THRESH 130

#define BIG_PULSE 8

//High pulse lasts over 1/8 of period

#define SHORT_PULSE 19

//High pulse lasts under 1/19 of period

// Defined in receiver.h

// #define THR_INDEX 0

// #define AIL_INDEX 1

// Note: arr[0] is thr, arr[1] is ail

static volatile unsigned long up_switch_time[2];

static volatile unsigned long down_switch_time[2];

static volatile unsigned long rc_value[2];

// NOTE THAT WE ARE ASSUMING:

//  Main Loop-length is shorter than PWM pulse length. 

//    Otherwise, you could recieve stale values in your main loop.

// Loop reading rc_values must set rc_available false after reading

// When our code gets really busy this will become inaccurate,

// (i believe since micros gets shifted a bit) but for

// the current application its easy to understand and works very well

// TODO if things start twitching, move to using registers directly.

// TODO if this starts twitching, also micros has a resolution of 4us.

static void receiver_on_ail_interrupt() {

  if(digitalRead(AIL_RECEIVER_PIN) == HIGH) {

    // High Received

    if((micros() - up_switch_time[AIL_INDEX] > PWM_TIME - PWM_THRESH) &&

       (micros() - up_switch_time[AIL_INDEX] < PWM_TIME + PWM_THRESH)) {

      // TODO this prevent an instantaneous start-up error, where the

      // above condition is true, and up_switch_time 

      if((down_switch_time[AIL_INDEX] > up_switch_time[AIL_INDEX]) &&        

         (rc_available[AIL_INDEX] == 0)) {

          rc_value[AIL_INDEX] = (down_switch_time[AIL_INDEX] - 

                                 up_switch_time[AIL_INDEX]);

          rc_available[AIL_INDEX] = 1;

          if(rc_value[AIL_INDEX]/(PWM_TIME/BIG_PULSE) >= 1 || rc_value[AIL_INDEX]/(PWM_TIME/SHORT_PULSE) == 0)

            rc_available[AIL_INDEX] == 0;

      }

    }

    up_switch_time[AIL_INDEX] = micros();

  } else {

    // Low received

    if(up_switch_time[AIL_INDEX]) {

      down_switch_time[AIL_INDEX] = micros();

    }

  }

}

static void receiver_on_thr_interrupt() {

  if(digitalRead(THR_RECEIVER_PIN) == HIGH) {

    // High Received

    if((micros() - up_switch_time[THR_INDEX] > PWM_TIME - PWM_THRESH) &&

       (micros() - up_switch_time[THR_INDEX] < PWM_TIME + PWM_THRESH)) {

      // TODO this prevent an instantaneous start-up error, where the

      // above condition is true, and up_switch_time 

      if((down_switch_time[THR_INDEX] > up_switch_time[THR_INDEX]) &&        

         (rc_available[THR_INDEX] == 0)) {

          rc_value[THR_INDEX] = (down_switch_time[THR_INDEX] - 

                                 up_switch_time[THR_INDEX]);

          rc_available[THR_INDEX] = 1;

          if(rc_value[THR_INDEX]/(PWM_TIME/10) >= 1 || rc_value[THR_INDEX]/(PWM_TIME/21) == 0)

            rc_available[THR_INDEX] == 0;

      }

    }

    up_switch_time[THR_INDEX] = micros();

  } else {

    // Low received

    if(up_switch_time[THR_INDEX]) {

      down_switch_time[THR_INDEX] = micros();

    }

  }

}

// Returns error code

int receiver_init() {

  up_switch_time[0] = 0;

  up_switch_time[1] = 0;

  down_switch_time[0] = 0;

  down_switch_time[1] = 0;

  attachInterrupt(THR_RECEIVER_INT, receiver_on_thr_interrupt, CHANGE);

  attachInterrupt(AIL_RECEIVER_INT, receiver_on_ail_interrupt, CHANGE);

}

// Index = 0 to check thr, index = 1 to check

// Returns 0 to 180, with 90 being center.

// TODO measure throttle positions.

int receiver_get_angle(int index) {

  // Math to convert nThrottleIn to 0-180.

  int ret_val = (int)(rc_value[index]-AIL_RIGHTMOST)*3/17;

  rc_available[index] = 0;

  return ret_val;

}