rcservo.ino

/* Sample RC servo input for 4 channels using Input Capture hardware perihperal and interrupts
 *  Written for Rick Anderson by Brian Schmalz
 *  11/11/2017
 *  This software is put in the public domain. 
 *  This sketch is means for a chipKIT Fubarino SD board, but can be easily adpated to any PIC32 based Arduino compatible board.
 */

/* Fubarino SD can only use pins 0, 1, 2, 3, and 10 as Input Capture.
 * On any chipKIT board with PPS (like Fubarino Mini) additional setup is necessary to map the Input Capture
 * peripherals to speciffic I/O pins, but you have much more flexibility in pin assignments.
 */
// Which pins correspond to which RC input channel?
#define RC_INPUT_1 0
#define RC_INPUT_2 1
#define RC_INPUT_3 2
#define RC_INPUT_4 3
// How many RC input channels are there?
#define RC_INPUT_COUNT 4

// These two arrays hold the latest pulse measurements for each RC input channel
volatile uint16_t pulseHighTime[RC_INPUT_COUNT];
volatile uint16_t pulseLowTime[RC_INPUT_COUNT];

/* Four Input Capture Interrupt Service Routines
 *  These functions get called on each rising and falling edge. They check to see
 *  if a rising edge or falling edge just happened, then read out the Timer2 value that
 *  got latched on the edge, and calculate the high and low pulse times, then stick those
 *  times in the proper array.
 */
void __USER_ISR InputCatpure1_ISR(void) {
  static uint16_t risingEdgeTime = 0;
  static uint16_t fallingEdgeTime = 0;
  
  clearIntFlag(_INPUT_CAPTURE_1_IRQ);
  if (IC1CONbits.ICBNE == 1)
  {
    if (digitalRead(RC_INPUT_1) == HIGH)
    {
      risingEdgeTime = IC1BUF;
      pulseLowTime[0] = risingEdgeTime - fallingEdgeTime;
    }
    else
    {
      fallingEdgeTime = IC1BUF;
      pulseHighTime[0] = fallingEdgeTime - risingEdgeTime;
    }
  }
}

void __USER_ISR InputCatpure2_ISR(void) {
  static uint16_t risingEdgeTime = 0;
  static uint16_t fallingEdgeTime = 0;
  
  clearIntFlag(_INPUT_CAPTURE_2_IRQ);
  if (IC2CONbits.ICBNE == 1)
  {
    if (digitalRead(RC_INPUT_2) == HIGH)
    {
      risingEdgeTime = IC2BUF;
      pulseLowTime[1] = risingEdgeTime - fallingEdgeTime;
    }
    else
    {
      fallingEdgeTime = IC2BUF;
      pulseHighTime[1] = fallingEdgeTime - risingEdgeTime;
    }
  }
}

void __USER_ISR InputCatpure3_ISR(void) {
  static uint16_t risingEdgeTime = 0;
  static uint16_t fallingEdgeTime = 0;
  
  clearIntFlag(_INPUT_CAPTURE_3_IRQ);
  if (IC3CONbits.ICBNE == 1)
  {
    if (digitalRead(RC_INPUT_3) == HIGH)
    {
      risingEdgeTime = IC3BUF;
      pulseLowTime[2] = risingEdgeTime - fallingEdgeTime;
    }
    else
    {
      fallingEdgeTime = IC3BUF;
      pulseHighTime[2] = fallingEdgeTime - risingEdgeTime;
    }
  }
}

void __USER_ISR InputCatpure4_ISR(void) {
  static uint16_t risingEdgeTime = 0;
  static uint16_t fallingEdgeTime = 0;
  
  clearIntFlag(_INPUT_CAPTURE_4_IRQ);
  if (IC4CONbits.ICBNE == 1)
  {
    if (digitalRead(RC_INPUT_4) == HIGH)
    {
      risingEdgeTime = IC4BUF;
      pulseLowTime[3] = risingEdgeTime - fallingEdgeTime;
    }
    else
    {
      fallingEdgeTime = IC4BUF;
      pulseHighTime[3] = fallingEdgeTime - risingEdgeTime;
    }
  }
}

void setup() {
  Serial.begin(9600);
  delay(3000);
  Serial.println("OK we are starting now");

  /* Set up each of the four Input Capture modules 
   * We want them to generate an interrupt on each rising and falling edge of the input
   * We also want them all to use Timer2 as their timebase timer
   */
  IC1CON = 0;
  IC1CONbits.ICM = 1;   // Captured and interrupt on every rising and falling edge
  IC1CONbits.ICTMR = 1; // Set to user Timer2
  IC1CONbits.ON = 1;    // Turn IC1 on

  IC2CON = 0;
  IC2CONbits.ICM = 1;   // Captured and interrupt on every rising and falling edge
  IC2CONbits.ICTMR = 1; // Set to user Timer2
  IC2CONbits.ON = 1;    // Turn IC2 on

  IC3CON = 0;
  IC3CONbits.ICM = 1;   // Captured and interrupt on every rising and falling edge
  IC3CONbits.ICTMR = 1; // Set to user Timer2
  IC3CONbits.ON = 1;    // Turn IC3 on

  IC4CON = 0;
  IC4CONbits.ICM = 1;   // Captured and interrupt on every rising and falling edge
  IC4CONbits.ICTMR = 1; // Set to user Timer2
  IC4CONbits.ON = 1;    // Turn IC4 on

  /* Set up Timer2: We want it to simply count up. We set the prescaler to 1:64
   *  so that the 40MHz PCLK gets divided down to 1.25Mhz. This is nice because
   *  then it gives us both high and low periods under 65535 for normal RC servo
   *  times (0-3 ms high time and 17-20ms low time)
   */
  PR2 = 0xFFFF;         // Run from 0 to 0xFFFF
  T2CONbits.TCKPS = 5;  // 1:32 prescale, which means 40MHz/64 or 1.25MHz clock rate
  T2CONbits.TON = 1;    // Turn on Timer2

  // Set all input captures as inputs
  pinMode(RC_INPUT_1, INPUT);
  pinMode(RC_INPUT_2, INPUT);
  pinMode(RC_INPUT_3, INPUT);
  pinMode(RC_INPUT_4, INPUT);
  Serial.println("ready");

  // Set each Input Capture up to use its ISR routine
  setIntVector(_INPUT_CAPTURE_1_VECTOR, InputCatpure1_ISR);
  setIntPriority(_INPUT_CAPTURE_1_VECTOR, 4, 0);
  clearIntFlag(_INPUT_CAPTURE_1_IRQ);
  setIntEnable(_INPUT_CAPTURE_1_IRQ);

  setIntVector(_INPUT_CAPTURE_2_VECTOR, InputCatpure2_ISR);
  setIntPriority(_INPUT_CAPTURE_2_VECTOR, 4, 0);
  clearIntFlag(_INPUT_CAPTURE_2_IRQ);
  setIntEnable(_INPUT_CAPTURE_2_IRQ);

  setIntVector(_INPUT_CAPTURE_3_VECTOR, InputCatpure3_ISR);
  setIntPriority(_INPUT_CAPTURE_3_VECTOR, 4, 0);
  clearIntFlag(_INPUT_CAPTURE_3_IRQ);
  setIntEnable(_INPUT_CAPTURE_3_IRQ);

  setIntVector(_INPUT_CAPTURE_4_VECTOR, InputCatpure4_ISR);
  setIntPriority(_INPUT_CAPTURE_4_VECTOR, 4, 0);
  clearIntFlag(_INPUT_CAPTURE_4_IRQ);
  setIntEnable(_INPUT_CAPTURE_4_IRQ);
}

void loop() {
  static uint32_t lastPrintTime = 0;
  float uSscale = 0.4;
  
  /* So the way things work, the ISRs will get called and they will constantly update
   *  the pulseHighTime and pulseLowTime arrays "in the background". In other words the
   *  mainline code here doesn't ever have to do anything other than simply read out
   *  the values in the arrays, and those values will always be the most recent pulse
   *  measurements. If you care about converting the values to real time (like in 
   *  microsconds), the units for these values are in 1.25MHz 'counts'. So 1ms = 1250
   *  'counts'.
   */
  // To demo things, simply print out all 4 high and low pulse times every half second
  if ((millis() - lastPrintTime) > 500)
  {
    lastPrintTime = millis();
    char pulses[100];
    char micros[100];
    sprintf(pulses, "high1: %05u low1: %05u high2: %05u low2: %05u high3: %05u low3: %05u high4: %05u low4: %05u\n",
      pulseHighTime[0],
      pulseLowTime[0],
      pulseHighTime[1],
      pulseLowTime[1],
      pulseHighTime[2],
      pulseLowTime[2],
      pulseHighTime[3],
      pulseLowTime[3]
    );
    Serial.print(pulses);
    sprintf(micros, "ch1: %05u ch2: %05u ch3: %05u ch4: %05u\n",    
      (int) (pulseHighTime[0] * uSscale),
      (int) (pulseHighTime[1] * uSscale),
      (int) (pulseHighTime[2] * uSscale),
      (int) (pulseHighTime[3] * uSscale)
    );

    Serial.print(micros); 
  }
}