diff --git a/.gitignore b/.gitignore
new file mode 100644
index 00000000..0a85cd68
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+
+Resources/Source_code/Workspace/stm32f4xx_drivers/Debug/
\ No newline at end of file
diff --git a/Resources/Arduino/i2c/002I2CSlaveTxString.ino/002I2CSlaveTxString.ino.ino b/Resources/Arduino/i2c/002I2CSlaveTxString.ino/002I2CSlaveTxString/002I2CSlaveTxString.ino
similarity index 100%
rename from Resources/Arduino/i2c/002I2CSlaveTxString.ino/002I2CSlaveTxString.ino.ino
rename to Resources/Arduino/i2c/002I2CSlaveTxString.ino/002I2CSlaveTxString/002I2CSlaveTxString.ino
diff --git a/Resources/Arduino/spi/001SPISlaveRxString/001SPISlaveRxString.ino b/Resources/Arduino/spi/001SPISlaveRxString/001SPISlaveRxString.ino
index fc8c4ac0..cc6064e8 100644
--- a/Resources/Arduino/spi/001SPISlaveRxString/001SPISlaveRxString.ino
+++ b/Resources/Arduino/spi/001SPISlaveRxString/001SPISlaveRxString.ino
@@ -16,27 +16,18 @@
 #define SPI_MOSI 11
 #define SPI_SS 10
 
-char dataBuff[500];
+#define MAX_I2C_PAYLOAD_LENGTH  500
+
+char dataBuff[MAX_I2C_PAYLOAD_LENGTH];
 //Initialize SPI slave.
 void SPI_SlaveInit(void) 
 { 
- #if 0 
   // Initialize SPI pins.
-  pinMode(SPI_SCK, INPUT);
-  pinMode(SPI_MOSI, INPUT);
-  pinMode(SPI_MISO, OUTPUT);
-  pinMode(SPI_SS, INPUT);
-  
-  // Enable SPI as slave.
-  SPCR = (1 << SPE);
- #endif 
-   // Initialize SPI pins.
   pinMode(SCK, INPUT);
   pinMode(MOSI, INPUT);
   pinMode(MISO, OUTPUT);
   pinMode(SS, INPUT);
-  //make SPI as slave
-  
+
   // Enable SPI as slave.
   SPCR = (1 << SPE);
 }
@@ -45,71 +36,67 @@ void SPI_SlaveInit(void)
 uint8_t SPI_SlaveReceive(void)
 {
   /* Wait for reception complete */
+  //Serial.println("in SPI_SlaveReceive - waiting for reception complete");
   while(!(SPSR & (1<<SPIF)));
+  //Serial.println("reception complete !!!");
   /* Return Data Register */
   return SPDR;
 }
 
-
-//sends one byte of data 
+//send one byte of data 
 void SPI_SlaveTransmit(char data)
 {
   /* Start transmission */
   SPDR = data;
-  
   /* Wait for transmission complete */
   while(!(SPSR & (1<<SPIF)));
 }
-  
+
 
 // The setup() function runs right after reset.
 void setup() 
 {
   // Initialize serial communication 
   Serial.begin(9600);
-  
+
   // Initialize SPI Slave.
   SPI_SlaveInit();
   
   Serial.println("Slave Initialized");
 }
- uint16_t dataLen = 0;
-  uint32_t i = 0;
+
+
 // The loop function runs continuously after setup().
 void loop() 
 {
+  uint32_t i;
+  uint8_t dataLen8;
+  //uint16_t dataLen16; // To support more than 255 bytes payload transfer in a single chunk. currently not in use.
+  Serial.println("\nSlave waiting for SS to go low");
 
- 
-  
-  Serial.println("Slave waiting for ss to go low");
-  while(digitalRead(SS) );
+  while(digitalRead(SS));
+  // Important !!! Avoid prints here! Enabling the print in the next line delays the slave Arduino and this cause it to miss data bytes sent from the master unless the master will add some delay between sending the length and the payload.
+  //Serial.println("SS is now Low"); 
 
- //  Serial.println("start");
-   
   //1. read the length  
-//  dataLen = (uint16_t)( SPI_SlaveReceive() | (SPI_SlaveReceive() << 8) );
+  //dataLen16 = (uint16_t)( SPI_SlaveReceive() | (SPI_SlaveReceive() << 8) );
   //Serial.println(String(dataLen,HEX));
- i = 0;
-  dataLen = SPI_SlaveReceive();
-  for(i = 0 ; i < dataLen ; i++ )
-  {
-    dataBuff[i] =  SPI_SlaveReceive();
-  }
-
+  dataLen8 = SPI_SlaveReceive();
+  //Serial.print("Received Data Len: ");
+  //Serial.println(String(dataLen8, DEC));
+  //Serial.println("Following will be the Received Data: ");
 
-  //  Serial.println(String(i,HEX));
+  for(i = 0 ; i < dataLen8 ; i++ ) {
+    dataBuff[i] = SPI_SlaveReceive();
+  }
   dataBuff[i] = '\0';
-  
-  Serial.println("Rcvd:");
-  Serial.println(dataBuff);
-  Serial.print("Length:");
-  Serial.println(dataLen);
-  
- 
-    
- 
-}
 
+  Serial.print("Rcvd: '");
+  Serial.print(dataBuff);
+  Serial.print("'. Length: ");
+  Serial.println(dataLen8);
 
-   
-   
+//  Serial.println("Slave waiting for ss to go high");
+//  while(!digitalRead(SS));
+//  Serial.println("SS HIGH\n\n");
+}
diff --git a/Resources/Arduino/spi/002SPISlaveCmdHandling/002SPISlaveCmdHandling.ino b/Resources/Arduino/spi/002SPISlaveCmdHandling/002SPISlaveCmdHandling.ino
index 16d44b70..697a4312 100644
--- a/Resources/Arduino/spi/002SPISlaveCmdHandling/002SPISlaveCmdHandling.ino
+++ b/Resources/Arduino/spi/002SPISlaveCmdHandling/002SPISlaveCmdHandling.ino
@@ -1,12 +1,9 @@
 /*
-
  * SPI pin numbers:
  * SCK   13  // Serial Clock.
  * MISO  12  // Master In Slave Out.
  * MOSI  11  // Master Out Slave In.
  * SS    10  // Slave Select
- *
-
  */
 
 #include <SPI.h>
@@ -17,18 +14,17 @@ boolean ledState = HIGH;      // LED state flag.
 
 uint8_t dataBuff[255];
 
-uint8_t board_id[10] = "ARDUINOUNO";
-
-#define NACK 0xA5
-#define ACK 0xF5
+char board_id[10] = "ARDUINOUNO";
 
+#define NACK  0xA5
+#define ACK   0xF5
 
 //command codes
 #define COMMAND_LED_CTRL          0x50
 #define COMMAND_SENSOR_READ       0x51
 #define COMMAND_LED_READ          0x52
-#define COMMAND_PRINT           0x53
-#define COMMAND_ID_READ         0x54
+#define COMMAND_PRINT             0x53
+#define COMMAND_ID_READ           0x54
 
 #define LED_ON     1
 #define LED_OFF    0
@@ -44,12 +40,12 @@ uint8_t board_id[10] = "ARDUINOUNO";
 void SPI_SlaveInit(void) 
 { 
   // Initialize SPI pins.
-  pinMode(SCK, INPUT);
+  pinMode(SCK,  INPUT);
   pinMode(MOSI, INPUT);
   pinMode(MISO, OUTPUT);
-  pinMode(SS, INPUT);
+  pinMode(SS,   INPUT);
+
   //make SPI as slave
-  
   // Enable SPI as slave.
   SPCR = (1 << SPE);
 }
@@ -72,6 +68,8 @@ void SPI_SlaveTransmit(uint8_t data)
   
   /* Wait for transmission complete */
   while(!(SPSR & (1<<SPIF)));
+//  Serial.print("SPISlave sent byte: 0x");
+//  Serial.println(data, HEX);
 }
   
 
@@ -80,102 +78,113 @@ void setup()
 {
   // Initialize serial for troubleshooting.
   Serial.begin(9600);
-  
   // Initialize slave LED pin.
   pinMode(led, OUTPUT);
-  
   digitalWrite(led,LOW);
-  
   // Initialize SPI Slave.
   SPI_SlaveInit();
-  
   Serial.println("Slave Initialized");
 }
 
 
-byte checkData(byte commnad)
+byte checkCmdOpcode(byte cmdOpcode)
 {
-  //todo
-  return ACK;
+  Serial.print("command received: 0x");
+  Serial.println(cmdOpcode, HEX);
+  if ((cmdOpcode == COMMAND_LED_CTRL) ||
+      (cmdOpcode == COMMAND_SENSOR_READ) ||
+      (cmdOpcode == COMMAND_LED_READ) ||
+      (cmdOpcode == COMMAND_PRINT) ||
+      (cmdOpcode == COMMAND_ID_READ)) {
+    return ACK;
+  }
+  // Illegal opcode received.
+  return NACK;
 }
 
 // The loop function runs continuously after setup().
 void loop() 
 {
-  byte data,command,len,ackornack=NACK;
+  byte data, cmdOpcode, len, ackOrNack = NACK;
   
-  //1. fist make sure that ss is low . so lets wait until ss is low 
-  Serial.println("Slave waiting for ss to go low");
+  //1. wait until ss is low
+  Serial.println("Slave waiting for SS to go low");
   while(digitalRead(SS) );
+  // Avoid prints here !!! It slows the slave and as a result received bytes will not be read.
+  //Serial.println("Slave's SS is now low (Slave was selected for communication)");
   
-  //2. now lets wait until rx buffer has a byte
-  command = SPI_SlaveReceive();
-  ackornack = checkData(command);
-  
-  SPI_SlaveTransmit(ackornack);
-  
+  //2. wait until rx buffer has a byte
+  cmdOpcode = SPI_SlaveReceive();
+  ackOrNack = checkCmdOpcode(cmdOpcode);
+  SPI_SlaveTransmit(ackOrNack);
   len = SPI_SlaveReceive(); //dummy byte
   
-  if(command == COMMAND_LED_CTRL)
-  {
+  if (cmdOpcode == COMMAND_LED_CTRL) {
     //read 2 more bytes pin number and value 
     uint8_t pin = SPI_SlaveReceive(); 
     uint8_t value = SPI_SlaveReceive(); 
-    Serial.println("RCVD:COMMAND_LED_CTRL");
-    if(value == (uint8_t)LED_ON)
-    {
+    Serial.print("RCVD:COMMAND_LED_CTRL Set pin ");
+    Serial.print(pin);
+    if (value == (uint8_t)LED_ON) {
+      Serial.println(" ON (1).");
       digitalWrite(pin,HIGH);
-    }else if (value == (uint8_t) LED_OFF)
-    {
+    } else if (value == (uint8_t)LED_OFF) {
+      Serial.println(" OFF (0).");
       digitalWrite(pin,LOW);
+    } else {
+      Serial.print(" -- ERROR: value unexpected: 0x");
+      Serial.println(value, HEX);
     }
-  
-  }else if ( command == COMMAND_SENSOR_READ)
-  {
+    
+  } else if (cmdOpcode == COMMAND_SENSOR_READ) {
     //read analog pin number 
     uint16_t aread;
     uint8_t pin = SPI_SlaveReceive(); 
     //pinMode(pin+14, INPUT_PULLUP);
     uint8_t val;
+    uint8_t dummyByte;
     aread = analogRead(pin+14);
     val = map(aread, 0, 1023, 0, 255);
-    
     SPI_SlaveTransmit(val);
-  
-    val = SPI_SlaveReceive(); //dummy read
-    
-    Serial.println("RCVD:COMMAND_SENSOR_READ");
-  
+    dummyByte = SPI_SlaveReceive(); //dummy read
+    Serial.print("RCVD:COMMAND_SENSOR_READ from pin");
+    Serial.print(pin);
+    Serial.print(" Analog port value: ");
+    Serial.print(aread);
+    Serial.print(", ");
+    Serial.println(val);
     
-  
-  }else if ( command == COMMAND_LED_READ)
-  {
+  } else if (cmdOpcode == COMMAND_LED_READ) {
     uint8_t pin = SPI_SlaveReceive(); 
     uint8_t val = digitalRead(pin);
     SPI_SlaveTransmit(val);
+    Serial.print("RCVD:COMMAND_LED_READ. LED pin val: "); // prints are defered in order not to hold the SPI communication
+    Serial.println(val);
     val = SPI_SlaveReceive(); //dummy read
-    Serial.println("RCVD:COMMAND_LED_READ");
-  
-  }else if ( command == COMMAND_PRINT)
-  {
+    
+  } else if (cmdOpcode == COMMAND_PRINT) {
     uint8_t len = SPI_SlaveReceive(); 
-    for(int i=0 ; i < len ; i++)
+    for (int i = 0; i < len; i++)
     {
       dataBuff[i] = SPI_SlaveReceive();
     }
-    Serial.println((char*)dataBuff);
-    
-    Serial.println("RCVD:COMMAND_PRINT");
-  
-  }else if ( command == COMMAND_ID_READ)
-  {
-    for(int i=0 ; i < strlen(board_id) ; i++)
+    dataBuff[len] = 0; // null termination at the end of the received string.
+    Serial.println("RCVD:COMMAND_PRINT"); // This print is defered to the end of the handle in order not to miss any SPI RXed byte
+    Serial.print("printed string len: ");
+    Serial.println(len);
+    Serial.println((char*)&dataBuff);
+  
+  } else if (cmdOpcode == COMMAND_ID_READ) {
+    // send the length of the responding ID string.
+    SPI_SlaveTransmit(strlen(board_id));
+    // send the ID string.
+    for(int i = 0; i < strlen(board_id); i++)
     {
       SPI_SlaveTransmit(board_id[i]);
+      SPI_SlaveReceive(); //dummy read
     }
-      SPI_SlaveReceive();
-    Serial.println("RCVD:COMMAND_ID_READ");
+    Serial.print("RCVD:COMMAND_ID_READ. Board string sent: ");
+    Serial.println(board_id);
   }
- 
-
+  Serial.println("");
 }