SUM_PPM.cpp

/* 
 To use this software, you must adhere to the license terms described below, and assume all responsibility for the use
 of the software.  The user is responsible for all consequences or damage that may result from using this software.
 The user is responsible for ensuring that the hardware used to run this software complies with local regulations and that 
 any radio signal generated from use of this software is legal for that user to generate.  The author(s) of this software 
 assume no liability whatsoever.  The author(s) of this software is not responsible for legal or civil consequences of 
 using this software, including, but not limited to, any damages cause by lost control of a vehicle using this software.  
 If this software is copied or modified, this disclaimer must accompany all copies.
 
 This PPM algorithm originated from:
             https://code.google.com/archive/p/generate-ppm-signal/
 under GNU GPL 2.  Second version dated Mar 14, 2013.
 Modifications and additions released here under GPL.
 */

/*
 This project is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.

 RC_RX_CABELL_V3_FHSS is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with RC_RX_CABELL_V3_FHSS.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#include "RX.h"
#include "Arduino.h"
#include "SUM_PPM.h"

uint8_t ppmPin = 0xFF;  // initialized to invalid pin
volatile int16_t ppmValueArray [CABELL_NUM_CHANNELS]; 
uint8_t ppmChannelCount; 
bool ppmEnabled = false;


//------------------------------------------------------------------------------------------------------------------------
void ppmSetup(uint8_t pin, uint8_t channelCount){  
  
  ppmPin = pin;
  ppmChannelCount = min(PPM_MaxChannels,channelCount);
  
  pinMode(ppmPin, OUTPUT);
  digitalWrite(ppmPin, !onState);  //set the PPM signal pin to the default state (off)

  noInterrupts();
  TCCR1A = 0; // set entire TCCR1 register to 0
  TCCR1B = 0;
  
  OCR1A = 100;  // compare match register, change this
  TCCR1B |= (1 << WGM12);  // turn on CTC mode
  TCCR1B |= (1 << CS11);  // 8 pre-scaler: 0,5 microseconds at 16mhz
  TIMSK1 |= (1 << OCIE1A); // enable timer compare interrupt
  interrupts();
  ppmEnabled = true;

}

bool PPMEnabled() {
  return ppmEnabled;
}

//------------------------------------------------------------------------------------------------------------------------
void ppmDisable(){  
  
  noInterrupts();
  TCCR1A = 0; // set entire TCCR1 register to 0
  TCCR1B = 0;
  TIMSK1 &= ~(1<<OCIE1A);   // Disable Interrupt Counter 1, output compare A (TIMER1_CMPA_vect)
  interrupts();
  ppmEnabled = false;

}

//------------------------------------------------------------------------------------------------------------------------
void setPPMOutputChannelValue(uint8_t channel, uint16_t value) {
  uint16_t correction = MICROSECOND_RANGE_OFFSET + (uint16_t)((float)value * MICROSECOND_RANGE_EXPANSION) ;
  value = (constrain(value,CHANNEL_MIN_VALUE,CHANNEL_MAX_VALUE) + correction - PPM_PulseLen_us) * TICKS_PER_US;
  if (ppmValueArray[channel] != value) {
    noInterrupts();
    ppmValueArray[channel] = value;
    interrupts();
  }
}

//------------------------------------------------------------------------------------------------------------------------
void SUM_PPM_ISR() {  
  static boolean state = true;
  static byte cur_chan_numb = 0;
  static unsigned int calc_rest = 0;
  
  if(state) {  //start pulse
    PPM_PIN_ON;
    //digitalWrite(ppmPin, onState);
    OCR1A = PPM_PulseLen_ticks;
    state = false;
  }
  else{  //end pulse and calculate when to start the next pulse
    PPM_PIN_OFF;
    //digitalWrite(ppmPin, !onState);

    if(cur_chan_numb >= ppmChannelCount){
      calc_rest = calc_rest + PPM_PulseLen_ticks;
      OCR1A = (PPM_FrLen_ticks - calc_rest);
      cur_chan_numb = 0;
      calc_rest = 0;
    } else {
      int16_t ppmValue = ppmValueArray[cur_chan_numb];          //Copy out of volatile storage since it is used more than once
      OCR1A = ppmValue;
      calc_rest = calc_rest + ppmValue + PPM_PulseLen_ticks;
      cur_chan_numb++;
    }     
    state = true;
  }
}