//
// Program name: i2Cslave04
//    from http://www.instructables.com/id/I2C-between-Arduinos/
//    By Cornel Amariei for Packt Publishing
//
// Purpose: 
//   Program two Arduinos to communicate via i2C 
//   this is slave node
//
// Edit History:
//   rev. 01: orig 
//   rev. 02: added serial print to monitor status
//   rev. 03: '#' turns on LED, '*' turns it off
//   rev. 04: when requestFrom is rcvd from master, single char is sent back to master 
//           
//
// Program operation/flow:
//   intended for receiving 3x4 membrane keypad keypresses
//   '#' turns on LED, '*' turns it off
//   when request for data rcvd from master, last valid numeric char sent from master is returned,
//   when chars are received from master, if valid numeric, z (char to be returned on request) is set 
//   
//
// Hardware configuration:
//   13 is LED on protoboard
//   A4 is SDA (data)
//   A5 is SCL (clock)
//   both i2C lines need a pullup, however the internal pullups in Unos are sufficient
//
// ------------------------------------------------------

// **************   INCLUDES   *******************

   #include <Wire.h>
// ----------   END   includes   ------------

// **************   GLOBALS   *******************

   int LEDonboard = 13;
   char x = 'x'; // dummy initial value for incoming char
   char z = 'z'; // dummy initial value for char to be sent back to master upon request
// ----------------   END   globals   -----------------

// **************   SETUP   *******************

void setup() {

   Serial.begin (9600);
   
   pinMode (LEDonboard, OUTPUT);
   
   Wire.begin(9);  // Start the I2C Bus as Slave on address 9
   Wire.onReceive(receiveEvent);  // Attach a function to trigger when something is received.
   Wire.onRequest(answerRequest); // used in slave to specify function to run when request is received from master 

   // at end of setup: blink LEDonboard
   // blinkOnboard (prePause, numBlinks, blinkOnTime, betweenBlinks, postPause);
   blinkOnboard (500, 1, 150, 160, 500); // some# slow
   blinkOnboard (500, 3, 90, 160, 500); // some# fast
}
// --------------   END   setup   --------------

// **************   LOOP   *******************

void loop() { 

   // this section toggles onboard LED with '#' and '*'
   if (x == '#') { //If value received is '#', 
      digitalWrite(LEDonboard, HIGH);
   } // endif '#'
   if (x == '*') { //If value received is '#', 
      digitalWrite(LEDonboard, LOW);
   } // endif '*'
}
// ---------------   END   loop   ---------------

// ****************   FUNCTION DEFS   *****************

void answerRequest() {
      // sends data back to master 
      Wire.write(z);
      Serial.print("sending: ");
      Serial.println(z);
      Serial.println(" ");
} // -----------------   END answerRequest   ----------------------

void receiveEvent(int bytes) {
  x = Wire.read();    // read one character from the I2C
  // if it's valid numeric, set z = x
  if ( (x == '0') || (x == '1') || (x == '2') || (x == '3') || (x == '4') || (x == '5') || (x == '6') || (x == '7') || (x == '8') || (x == '9') ) {
    z = x;
  }
  
  Serial.print("char rcvd: ");
  Serial.println(x);
  Serial.println(" ");
} // -----------------   END receiveEvent   ----------------------

void blinkOnboard (int prePause, int numBlinks, int blinkOn, int betweenBlinks, int postPause) {
      // blinks onboard LED-13
      // takes parameters: pre-pause; # blinks; blinkOn duration; betweenBlink pause duration; post-pause
      delay(prePause);
      for (int n = 0; n < numBlinks; n++) { 
          digitalWrite(LEDonboard, HIGH);
          delay(blinkOn);
          digitalWrite(LEDonboard, LOW);
          delay(betweenBlinks);
      } // endfor
      delay(postPause);
} // -----------------   END blinkOnboard   ----------------------

// ---------------   END   function defs   ------------



// ---------------   END   program   ------------------