Arduino NANO PPM to Hoverboard.ino

/*
 * Test Code For Hoverboard with this firmware:
 * https://github.com/p-h-a-i-l/hoverboard-firmware-hack
 * 
 * Connect the PPM Receiver Data Pin to Arduino Pin 3
 * And set the Amount of channels of the PPM Receiver.
 * this code uses the Arduino Hardware serial.
 * 
 */

byte interruptPin = 3; // Arduino PPM Pin
byte channelAmount = 10; // PPM Channel count
#define SteerChannel 1
#define SpeedChannel 2



unsigned long minChannelValue = 1000;
unsigned long maxChannelValue = 2000;
unsigned long channelValueMaxError = 10;
unsigned long blankTime = 2100;
volatile unsigned long *rawValues = NULL;
volatile unsigned long *validValues = NULL;
volatile byte pulseCounter = 0;
volatile unsigned long microsAtLastPulse = 0;

typedef struct MsgToHoverboard_t {
  unsigned char SOM;
  unsigned char len;
  unsigned char cmd;
  unsigned char code;
  int16_t base_pwm;
  int16_t steer;
  unsigned char CS;
};

typedef union UART_Packet_t {
  MsgToHoverboard_t msgToHover;
  byte UART_Packet[sizeof(MsgToHoverboard_t)];
};

void setHoverboardPWM( int16_t base_pwm, int16_t steer )
{
  UART_Packet_t ups;
  ups.msgToHover.SOM = 2 ;  // PROTOCOL_SOM; //Start of Message;
  ups.msgToHover.len = 7;   // payload + SC only
  ups.msgToHover.cmd  = 'W'; // PROTOCOL_CMD_WRITEVAL;  // Write value
  ups.msgToHover.code = 0x07; // speed data from params array
  ups.msgToHover.base_pwm = base_pwm;
  ups.msgToHover.steer = steer;
  ups.msgToHover.CS = 0;
  for (int i = 0; i < ups.msgToHover.len; i++) {
    ups.msgToHover.CS -= ups.UART_Packet[i + 1];
  }
  Serial.write(ups.UART_Packet, sizeof(UART_Packet_t));
}

void setup() {
  PPMReader(interruptPin, channelAmount);
  Serial.begin(115200);
}

void loop() {
  int steer = map(latestValidChannelValue(SteerChannel, 0), 1100, 1900, -1000, 1000); // PPM CHANNEL 1 for Steering
  int speed = map(latestValidChannelValue(SpeedChannel, 0), 1100, 1900, -1000, 1000); // PPM CHANNEL 2 for Speed
  setHoverboardPWM(speed, steer);
  delay(5);
}

void PPMReader(byte interruptPin, byte channelAmount) {
  if (interruptPin > 0 && channelAmount > 0) {
    rawValues = new unsigned long[channelAmount];
    validValues = new unsigned long[channelAmount];
    for (int i = 0; i < channelAmount; ++i) {
      rawValues[i] = 1500;
      validValues[i] = 1500;
    }
    pinMode(interruptPin, INPUT);
    attachInterrupt(digitalPinToInterrupt(interruptPin), interruptfrompin, RISING);
  }
}

void interruptfrompin() {
  unsigned long previousMicros = microsAtLastPulse;
  microsAtLastPulse = micros();
  unsigned long time = microsAtLastPulse - previousMicros;

  if (time > blankTime) {
    pulseCounter = 0;
  }
  else {
    if (pulseCounter < channelAmount) {
      rawValues[pulseCounter] = time;
      if (time >= minChannelValue - channelValueMaxError && time <= maxChannelValue + channelValueMaxError) {
        validValues[pulseCounter] = constrain(time, minChannelValue, maxChannelValue);
      }
    }
    ++pulseCounter;
  }
}

unsigned long rawChannelValue(byte channel) {
  unsigned long value = 0;
  if (channel >= 1 && channel <= channelAmount) {
    noInterrupts();
    value = rawValues[channel - 1];
    interrupts();
  }
  return value;
}

unsigned long latestValidChannelValue(byte channel, unsigned long defaultValue) {
  unsigned long value = defaultValue;
  if (channel >= 1 && channel <= channelAmount) {
    noInterrupts();
    value = validValues[channel - 1];
    interrupts();
  }
  return value;
}