//This is a demo code example for using SPI without a
//predefined library on the chipKIT uC32

//globals
int chipSelect = 3;
int masterOutSlaveIn = 5;
int masterInSlaveOut = 7;
int serialClock = 9;
int dataInput [8];
int arrayLocation;
int receivedValue;

//This code operates under the presumption that SPI is operating
//on the popular style of having the data be transmitted MSB 
//first and to be "picked up" by the other device on the 
//falling edge of the clock 
void setup(){
  pinMode(chipSelect, OUTPUT);
  pinMode(masterOutSlaveIn, OUTPUT);
  pinMode(masterInSlaveOut, INPUT);
  pinMode(serialClock, OUTPUT);
}

void loop(){
  digitalWrite(chipSelect, LOW);
  sendLargeValue();
  digitalWrite(chipSelect, HIGH);
  
  delay(1);
  
  digitalWrite(chipSelect, LOW);
  sendSmallValue();
  digitalWrite(chipSelect, HIGH);
  
  delay(1);
}

void sendLargeValue(){
  arrayLocation = 0;
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1); 
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, HIGH); //1
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  receiveValue();
}

void sendSmallValue(){
  arrayLocation = 0;
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  digitalWrite(serialClock, HIGH);
  digitalWrite(masterOutSlaveIn, LOW); //0
  collectBit();
  digitalWrite(serialClock, LOW); //transfer
  delay(1);
  receiveValue();
}

void collectBit(){
  dataInput[arrayLocation] = digitalRead(masterInSlaveOut);
  arrayLocation++;
}

void receiveValue(){ //presuming the MSB was received first
  receivedValue = 0;
  for(int i=0; i<8; i++){
    receivedValue = receivedValue + dataInput[i]<<(7-i);
    }
}