Diff: MFRC522.cpp

Revision:

0:b416214256cd

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MFRC522.cpp	Tue Nov 07 16:35:14 2017 +0000
@@ -0,0 +1,1154 @@
+/*
+* MFRC522.cpp - Library to use ARDUINO RFID MODULE KIT 13.56 MHZ WITH TAGS SPI W AND R BY COOQROBOT.
+* _Please_ see the comments in MFRC522.h - they give useful hints and background.
+* Released into the public domain.
+*/
+
+#include "MFRC522.h"
+
+static const char* const _TypeNamePICC[] =
+{
+  "Unknown type",
+  "PICC compliant with ISO/IEC 14443-4",
+  "PICC compliant with ISO/IEC 18092 (NFC)",
+  "MIFARE Mini, 320 bytes",
+  "MIFARE 1KB",
+  "MIFARE 4KB",
+  "MIFARE Ultralight or Ultralight C",
+  "MIFARE Plus",
+  "MIFARE TNP3XXX",
+
+  /* not complete UID */
+  "SAK indicates UID is not complete"
+};
+
+static const char* const _ErrorMessage[] =
+{
+  "Unknown error",
+  "Success",
+  "Error in communication",
+  "Collision detected",
+  "Timeout in communication",
+  "A buffer is not big enough",
+  "Internal error in the code, should not happen",
+  "Invalid argument",
+  "The CRC_A does not match",
+  "A MIFARE PICC responded with NAK"
+};
+
+#define MFRC522_MaxPICCs (sizeof(_TypeNamePICC)/sizeof(_TypeNamePICC[0]))
+#define MFRC522_MaxError (sizeof(_ErrorMessage)/sizeof(_ErrorMessage[0]))
+
+/////////////////////////////////////////////////////////////////////////////////////
+// Functions for setting up the driver
+/////////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Constructor.
+ * Prepares the output pins.
+ */
+MFRC522::MFRC522(PinName mosi,
+                 PinName miso,
+                 PinName sclk,
+                 PinName cs,
+                 PinName reset) : m_SPI(mosi, miso, sclk), m_CS(cs), m_RESET(reset)
+{
+  /* Configure SPI bus */
+  m_SPI.format(8, 0);
+  m_SPI.frequency(8000000);
+
+  /* Release SPI-CS pin */
+  m_CS       = 1;
+
+  /* Release RESET pin */
+  m_RESET    = 1;
+} // End constructor
+
+
+/**
+ * Destructor.
+ */
+MFRC522::~MFRC522()
+{
+
+}
+
+
+/////////////////////////////////////////////////////////////////////////////////////
+// Basic interface functions for communicating with the MFRC522
+/////////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Writes a byte to the specified register in the MFRC522 chip.
+ * The interface is described in the datasheet section 8.1.2.
+ */
+void MFRC522::PCD_WriteRegister(uint8_t reg, uint8_t value)
+{
+  m_CS = 0; /* Select SPI Chip MFRC522 */
+
+  // MSB == 0 is for writing. LSB is not used in address. Datasheet section 8.1.2.3.
+  (void) m_SPI.write(reg & 0x7E);
+  (void) m_SPI.write(value);
+
+  m_CS = 1; /* Release SPI Chip MFRC522 */
+} // End PCD_WriteRegister()
+
+/**
+ * Writes a number of bytes to the specified register in the MFRC522 chip.
+ * The interface is described in the datasheet section 8.1.2.
+ */
+void MFRC522::PCD_WriteRegister(uint8_t reg, uint8_t count, uint8_t *values)
+{
+  m_CS = 0; /* Select SPI Chip MFRC522 */
+
+  // MSB == 0 is for writing. LSB is not used in address. Datasheet section 8.1.2.3.
+  (void) m_SPI.write(reg & 0x7E);
+  for (uint8_t index = 0; index < count; index++)
+  {
+    (void) m_SPI.write(values[index]);
+  }
+
+  m_CS = 1; /* Release SPI Chip MFRC522 */
+} // End PCD_WriteRegister()
+
+/**
+ * Reads a byte from the specified register in the MFRC522 chip.
+ * The interface is described in the datasheet section 8.1.2.
+ */
+uint8_t MFRC522::PCD_ReadRegister(uint8_t reg)
+{
+  uint8_t value;
+  m_CS = 0; /* Select SPI Chip MFRC522 */
+
+  // MSB == 1 is for reading. LSB is not used in address. Datasheet section 8.1.2.3.
+  (void) m_SPI.write(0x80 | reg);
+
+  // Read the value back. Send 0 to stop reading.
+  value = m_SPI.write(0);
+
+  m_CS = 1; /* Release SPI Chip MFRC522 */
+
+  return value;
+} // End PCD_ReadRegister()
+
+/**
+ * Reads a number of bytes from the specified register in the MFRC522 chip.
+ * The interface is described in the datasheet section 8.1.2.
+ */
+void MFRC522::PCD_ReadRegister(uint8_t reg, uint8_t count, uint8_t *values, uint8_t rxAlign)
+{
+  if (count == 0) { return; }
+
+  uint8_t address = 0x80 | reg;  // MSB == 1 is for reading. LSB is not used in address. Datasheet section 8.1.2.3.
+  uint8_t index = 0;             // Index in values array.
+
+  m_CS = 0;                      /* Select SPI Chip MFRC522 */
+  count--;                       // One read is performed outside of the loop
+  (void) m_SPI.write(address);   // Tell MFRC522 which address we want to read
+
+  while (index < count)
+  {
+    if ((index == 0) && rxAlign) // Only update bit positions rxAlign..7 in values[0]
+    {
+      // Create bit mask for bit positions rxAlign..7
+      uint8_t mask = 0;
+      for (uint8_t i = rxAlign; i <= 7; i++)
+      {
+        mask |= (1 << i);
+      }
+
+      // Read value and tell that we want to read the same address again.
+      uint8_t value = m_SPI.write(address);
+
+      // Apply mask to both current value of values[0] and the new data in value.
+      values[0] = (values[index] & ~mask) | (value & mask);
+    }
+    else
+    {
+      // Read value and tell that we want to read the same address again.
+      values[index] = m_SPI.write(address);
+    }
+
+    index++;
+  }
+
+  values[index] = m_SPI.write(0); // Read the final byte. Send 0 to stop reading.
+
+  m_CS = 1;                       /* Release SPI Chip MFRC522 */
+} // End PCD_ReadRegister()
+
+/**
+ * Sets the bits given in mask in register reg.
+ */
+void MFRC522::PCD_SetRegisterBits(uint8_t reg, uint8_t mask)
+{
+  uint8_t tmp = PCD_ReadRegister(reg);
+  PCD_WriteRegister(reg, tmp | mask);     // set bit mask
+} // End PCD_SetRegisterBitMask()
+
+/**
+ * Clears the bits given in mask from register reg.
+ */
+void MFRC522::PCD_ClrRegisterBits(uint8_t reg, uint8_t mask)
+{
+  uint8_t tmp = PCD_ReadRegister(reg);
+  PCD_WriteRegister(reg, tmp & (~mask));    // clear bit mask
+} // End PCD_ClearRegisterBitMask()
+
+
+/**
+ * Use the CRC coprocessor in the MFRC522 to calculate a CRC_A.
+ */
+uint8_t MFRC522::PCD_CalculateCRC(uint8_t *data, uint8_t length, uint8_t *result)
+{
+  PCD_WriteRegister(CommandReg, PCD_Idle);      // Stop any active command.
+  PCD_WriteRegister(DivIrqReg, 0x04);           // Clear the CRCIRq interrupt request bit
+  PCD_SetRegisterBits(FIFOLevelReg, 0x80);      // FlushBuffer = 1, FIFO initialization
+  PCD_WriteRegister(FIFODataReg, length, data); // Write data to the FIFO
+  PCD_WriteRegister(CommandReg, PCD_CalcCRC);   // Start the calculation
+
+  // Wait for the CRC calculation to complete. Each iteration of the while-loop takes 17.73us.
+  uint16_t i = 5000;
+  uint8_t n;
+  while (1)
+  {
+    n = PCD_ReadRegister(DivIrqReg);  // DivIrqReg[7..0] bits are: Set2 reserved reserved MfinActIRq   reserved CRCIRq reserved reserved
+    if (n & 0x04)
+    {
+      // CRCIRq bit set - calculation done
+      break;
+    }
+    
+    if (--i == 0)
+    {
+      // The emergency break. We will eventually terminate on this one after 89ms.
+      // Communication with the MFRC522 might be down.
+      return STATUS_TIMEOUT;
+    }
+  }
+
+  // Stop calculating CRC for new content in the FIFO.
+  PCD_WriteRegister(CommandReg, PCD_Idle);
+
+  // Transfer the result from the registers to the result buffer
+  result[0] = PCD_ReadRegister(CRCResultRegL);
+  result[1] = PCD_ReadRegister(CRCResultRegH);
+  return STATUS_OK;
+} // End PCD_CalculateCRC()
+
+
+/////////////////////////////////////////////////////////////////////////////////////
+// Functions for manipulating the MFRC522
+/////////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Initializes the MFRC522 chip.
+ */
+void MFRC522::PCD_Init()
+{
+  /* Reset MFRC522 */
+  m_RESET = 0;
+  wait_ms(10);
+  m_RESET = 1;
+  
+  // Section 8.8.2 in the datasheet says the oscillator start-up time is the start up time of the crystal + 37,74us. Let us be generous: 50ms.
+  wait_ms(50);
+
+  // When communicating with a PICC we need a timeout if something goes wrong.
+  // f_timer = 13.56 MHz / (2*TPreScaler+1) where TPreScaler = [TPrescaler_Hi:TPrescaler_Lo].
+  // TPrescaler_Hi are the four low bits in TModeReg. TPrescaler_Lo is TPrescalerReg.
+  PCD_WriteRegister(TModeReg, 0x80);      // TAuto=1; timer starts automatically at the end of the transmission in all communication modes at all speeds
+  PCD_WriteRegister(TPrescalerReg, 0xA9); // TPreScaler = TModeReg[3..0]:TPrescalerReg, ie 0x0A9 = 169 => f_timer=40kHz, ie a timer period of 25us.
+  PCD_WriteRegister(TReloadRegH, 0x03);   // Reload timer with 0x3E8 = 1000, ie 25ms before timeout.
+  PCD_WriteRegister(TReloadRegL, 0xE8);
+
+  PCD_WriteRegister(TxASKReg, 0x40);      // Default 0x00. Force a 100 % ASK modulation independent of the ModGsPReg register setting
+  PCD_WriteRegister(ModeReg, 0x3D);       // Default 0x3F. Set the preset value for the CRC coprocessor for the CalcCRC command to 0x6363 (ISO 14443-3 part 6.2.4)
+
+  PCD_WriteRegister(RFCfgReg, (0x07<<4)); // Set Rx Gain to max
+
+  PCD_AntennaOn();                        // Enable the antenna driver pins TX1 and TX2 (they were disabled by the reset)
+} // End PCD_Init()
+
+/**
+ * Performs a soft reset on the MFRC522 chip and waits for it to be ready again.
+ */
+void MFRC522::PCD_Reset()
+{
+  PCD_WriteRegister(CommandReg, PCD_SoftReset); // Issue the SoftReset command.
+  // The datasheet does not mention how long the SoftRest command takes to complete.
+  // But the MFRC522 might have been in soft power-down mode (triggered by bit 4 of CommandReg)
+  // Section 8.8.2 in the datasheet says the oscillator start-up time is the start up time of the crystal + 37,74us. Let us be generous: 50ms.
+  wait_ms(50);
+
+  // Wait for the PowerDown bit in CommandReg to be cleared
+  while (PCD_ReadRegister(CommandReg) & (1<<4))
+  {
+    // PCD still restarting - unlikely after waiting 50ms, but better safe than sorry.
+  }
+} // End PCD_Reset()
+
+/**
+ * Turns the antenna on by enabling pins TX1 and TX2.
+ * After a reset these pins disabled.
+ */
+void MFRC522::PCD_AntennaOn()
+{
+  uint8_t value = PCD_ReadRegister(TxControlReg);
+  if ((value & 0x03) != 0x03)
+  {
+    PCD_WriteRegister(TxControlReg, value | 0x03);
+  }
+} // End PCD_AntennaOn()
+
+/////////////////////////////////////////////////////////////////////////////////////
+// Functions for communicating with PICCs
+/////////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Executes the Transceive command.
+ * CRC validation can only be done if backData and backLen are specified.
+ */
+uint8_t MFRC522::PCD_TransceiveData(uint8_t *sendData,
+                                    uint8_t sendLen,
+                                    uint8_t *backData,
+                                    uint8_t *backLen,
+                                    uint8_t *validBits,
+                                    uint8_t rxAlign,
+                                    bool    checkCRC)
+{
+  uint8_t waitIRq = 0x30;    // RxIRq and IdleIRq
+  return PCD_CommunicateWithPICC(PCD_Transceive, waitIRq, sendData, sendLen, backData, backLen, validBits, rxAlign, checkCRC);
+} // End PCD_TransceiveData()
+
+/**
+ * Transfers data to the MFRC522 FIFO, executes a commend, waits for completion and transfers data back from the FIFO.
+ * CRC validation can only be done if backData and backLen are specified.
+ */
+uint8_t MFRC522::PCD_CommunicateWithPICC(uint8_t command,
+                                         uint8_t waitIRq,
+                                         uint8_t *sendData,
+                                         uint8_t sendLen,
+                                         uint8_t *backData,
+                                         uint8_t *backLen,
+                                         uint8_t *validBits,
+                                         uint8_t rxAlign,
+                                         bool    checkCRC)
+{
+  uint8_t n, _validBits = 0;
+  uint32_t i;
+
+  // Prepare values for BitFramingReg
+  uint8_t txLastBits = validBits ? *validBits : 0;
+  uint8_t bitFraming = (rxAlign << 4) + txLastBits;   // RxAlign = BitFramingReg[6..4]. TxLastBits = BitFramingReg[2..0]
+
+  PCD_WriteRegister(CommandReg, PCD_Idle);            // Stop any active command.
+  PCD_WriteRegister(ComIrqReg, 0x7F);                 // Clear all seven interrupt request bits
+  PCD_SetRegisterBits(FIFOLevelReg, 0x80);            // FlushBuffer = 1, FIFO initialization
+  PCD_WriteRegister(FIFODataReg, sendLen, sendData);  // Write sendData to the FIFO
+  PCD_WriteRegister(BitFramingReg, bitFraming);       // Bit adjustments
+  PCD_WriteRegister(CommandReg, command);             // Execute the command
+  if (command == PCD_Transceive)
+  {
+    PCD_SetRegisterBits(BitFramingReg, 0x80);      // StartSend=1, transmission of data starts
+  }
+
+  // Wait for the command to complete.
+  // In PCD_Init() we set the TAuto flag in TModeReg. This means the timer automatically starts when the PCD stops transmitting.
+  // Each iteration of the do-while-loop takes 17.86us.
+  i = 2000;
+  while (1)
+  {
+    n = PCD_ReadRegister(ComIrqReg);  // ComIrqReg[7..0] bits are: Set1 TxIRq RxIRq IdleIRq   HiAlertIRq LoAlertIRq ErrIRq TimerIRq
+    if (n & waitIRq)
+    {          // One of the interrupts that signal success has been set.
+      break;
+    }
+
+    if (n & 0x01)
+    {           // Timer interrupt - nothing received in 25ms
+      return STATUS_TIMEOUT;
+    }
+
+    if (--i == 0)
+    {           // The emergency break. If all other condions fail we will eventually terminate on this one after 35.7ms. Communication with the MFRC522 might be down.
+      return STATUS_TIMEOUT;
+    }
+  }
+
+  // Stop now if any errors except collisions were detected.
+  uint8_t errorRegValue = PCD_ReadRegister(ErrorReg); // ErrorReg[7..0] bits are: WrErr TempErr reserved BufferOvfl   CollErr CRCErr ParityErr ProtocolErr
+  if (errorRegValue & 0x13)
+  {  // BufferOvfl ParityErr ProtocolErr
+    return STATUS_ERROR;
+  }
+
+  // If the caller wants data back, get it from the MFRC522.
+  if (backData && backLen)
+  {
+    n = PCD_ReadRegister(FIFOLevelReg);           // Number of bytes in the FIFO
+    if (n > *backLen)
+    {
+      return STATUS_NO_ROOM;
+    }
+
+    *backLen = n;                       // Number of bytes returned
+    PCD_ReadRegister(FIFODataReg, n, backData, rxAlign);    // Get received data from FIFO
+    _validBits = PCD_ReadRegister(ControlReg) & 0x07; // RxLastBits[2:0] indicates the number of valid bits in the last received byte. If this value is 000b, the whole byte is valid.
+    if (validBits)
+    {
+      *validBits = _validBits;
+    }
+  }
+
+  // Tell about collisions
+  if (errorRegValue & 0x08)
+  { // CollErr
+    return STATUS_COLLISION;
+  }
+
+  // Perform CRC_A validation if requested.
+  if (backData && backLen && checkCRC)
+  {
+    // In this case a MIFARE Classic NAK is not OK.
+    if ((*backLen == 1) && (_validBits == 4))
+    {
+      return STATUS_MIFARE_NACK;
+    }
+
+    // We need at least the CRC_A value and all 8 bits of the last byte must be received.
+    if ((*backLen < 2) || (_validBits != 0))
+    {
+      return STATUS_CRC_WRONG;
+    }
+
+    // Verify CRC_A - do our own calculation and store the control in controlBuffer.
+    uint8_t controlBuffer[2];
+    n = PCD_CalculateCRC(&backData[0], *backLen - 2, &controlBuffer[0]);
+    if (n != STATUS_OK)
+    {
+      return n;
+    }
+
+    if ((backData[*backLen - 2] != controlBuffer[0]) || (backData[*backLen - 1] != controlBuffer[1]))
+    {
+      return STATUS_CRC_WRONG;
+    }
+  }
+
+  return STATUS_OK;
+} // End PCD_CommunicateWithPICC()
+
+/*
+ * Transmits a REQuest command, Type A. Invites PICCs in state IDLE to go to READY and prepare for anticollision or selection. 7 bit frame.
+ * Beware: When two PICCs are in the field at the same time I often get STATUS_TIMEOUT - probably due do bad antenna design.
+ */
+uint8_t MFRC522::PICC_RequestA(uint8_t *bufferATQA, uint8_t *bufferSize)
+{
+  return PICC_REQA_or_WUPA(PICC_CMD_REQA, bufferATQA, bufferSize);
+} // End PICC_RequestA()
+
+/**
+ * Transmits a Wake-UP command, Type A. Invites PICCs in state IDLE and HALT to go to READY(*) and prepare for anticollision or selection. 7 bit frame.
+ * Beware: When two PICCs are in the field at the same time I often get STATUS_TIMEOUT - probably due do bad antenna design.
+ */
+uint8_t MFRC522::PICC_WakeupA(uint8_t *bufferATQA, uint8_t *bufferSize)
+{
+  return PICC_REQA_or_WUPA(PICC_CMD_WUPA, bufferATQA, bufferSize);
+} // End PICC_WakeupA()
+
+/*
+ * Transmits REQA or WUPA commands.
+ * Beware: When two PICCs are in the field at the same time I often get STATUS_TIMEOUT - probably due do bad antenna design.
+ */
+uint8_t MFRC522::PICC_REQA_or_WUPA(uint8_t command, uint8_t *bufferATQA, uint8_t *bufferSize)
+{
+  uint8_t validBits;
+  uint8_t status;
+
+  if (bufferATQA == NULL || *bufferSize < 2)
+  {  // The ATQA response is 2 bytes long.
+    return STATUS_NO_ROOM;
+  }
+
+  // ValuesAfterColl=1 => Bits received after collision are cleared.
+  PCD_ClrRegisterBits(CollReg, 0x80);
+
+  // For REQA and WUPA we need the short frame format
+  // - transmit only 7 bits of the last (and only) byte. TxLastBits = BitFramingReg[2..0]
+  validBits = 7;
+
+  status = PCD_TransceiveData(&command, 1, bufferATQA, bufferSize, &validBits);
+  if (status != STATUS_OK)
+  {
+    return status;
+  }
+
+  if ((*bufferSize != 2) || (validBits != 0))
+  {   // ATQA must be exactly 16 bits.
+    return STATUS_ERROR;
+  }
+
+  return STATUS_OK;
+} // End PICC_REQA_or_WUPA()
+
+/*
+ * Transmits SELECT/ANTICOLLISION commands to select a single PICC.
+ */
+uint8_t MFRC522::PICC_Select(Uid *uid, uint8_t validBits)
+{
+  bool uidComplete;
+  bool selectDone;
+  bool useCascadeTag;
+  uint8_t cascadeLevel = 1;
+  uint8_t result;
+  uint8_t count;
+  uint8_t index;
+  uint8_t uidIndex;          // The first index in uid->uidByte[] that is used in the current Cascade Level.
+  uint8_t currentLevelKnownBits;   // The number of known UID bits in the current Cascade Level.
+  uint8_t buffer[9];         // The SELECT/ANTICOLLISION commands uses a 7 byte standard frame + 2 bytes CRC_A
+  uint8_t bufferUsed;        // The number of bytes used in the buffer, ie the number of bytes to transfer to the FIFO.
+  uint8_t rxAlign;           // Used in BitFramingReg. Defines the bit position for the first bit received.
+  uint8_t txLastBits;        // Used in BitFramingReg. The number of valid bits in the last transmitted byte.
+  uint8_t *responseBuffer;
+  uint8_t responseLength;
+
+  // Description of buffer structure:
+  //    Byte 0: SEL         Indicates the Cascade Level: PICC_CMD_SEL_CL1, PICC_CMD_SEL_CL2 or PICC_CMD_SEL_CL3
+  //    Byte 1: NVB         Number of Valid Bits (in complete command, not just the UID): High nibble: complete bytes, Low nibble: Extra bits.
+  //    Byte 2: UID-data or CT    See explanation below. CT means Cascade Tag.
+  //    Byte 3: UID-data
+  //    Byte 4: UID-data
+  //    Byte 5: UID-data
+  //    Byte 6: BCC         Block Check Character - XOR of bytes 2-5
+  //    Byte 7: CRC_A
+  //    Byte 8: CRC_A
+  // The BCC and CRC_A is only transmitted if we know all the UID bits of the current Cascade Level.
+  //
+  // Description of bytes 2-5: (Section 6.5.4 of the ISO/IEC 14443-3 draft: UID contents and cascade levels)
+  //    UID size  Cascade level Byte2 Byte3 Byte4 Byte5
+  //    ========  ============= ===== ===== ===== =====
+  //     4 bytes    1     uid0  uid1  uid2  uid3
+  //     7 bytes    1     CT    uid0  uid1  uid2
+  //                2     uid3  uid4  uid5  uid6
+  //    10 bytes    1     CT    uid0  uid1  uid2
+  //                2     CT    uid3  uid4  uid5
+  //                3     uid6  uid7  uid8  uid9
+
+  // Sanity checks
+  if (validBits > 80)
+  {
+    return STATUS_INVALID;
+  }
+
+  // Prepare MFRC522
+  // ValuesAfterColl=1 => Bits received after collision are cleared.
+  PCD_ClrRegisterBits(CollReg, 0x80);
+
+  // Repeat Cascade Level loop until we have a complete UID.
+  uidComplete = false;
+  while ( ! uidComplete)
+  {
+    // Set the Cascade Level in the SEL byte, find out if we need to use the Cascade Tag in byte 2.
+    switch (cascadeLevel)
+    {
+      case 1:
+        buffer[0] = PICC_CMD_SEL_CL1;
+        uidIndex = 0;
+        useCascadeTag = validBits && (uid->size > 4); // When we know that the UID has more than 4 bytes
+        break;
+
+      case 2:
+        buffer[0] = PICC_CMD_SEL_CL2;
+        uidIndex = 3;
+        useCascadeTag = validBits && (uid->size > 7); // When we know that the UID has more than 7 bytes
+        break;
+
+      case 3:
+        buffer[0] = PICC_CMD_SEL_CL3;
+        uidIndex = 6;
+        useCascadeTag = false;            // Never used in CL3.
+        break;
+
+      default:
+        return STATUS_INTERNAL_ERROR;
+        //break;
+    }
+
+    // How many UID bits are known in this Cascade Level?
+    if(validBits > (8 * uidIndex))
+    {
+      currentLevelKnownBits = validBits - (8 * uidIndex);
+    }
+    else
+    {
+      currentLevelKnownBits = 0;
+    }
+
+    // Copy the known bits from uid->uidByte[] to buffer[]
+    index = 2; // destination index in buffer[]
+    if (useCascadeTag)
+    {
+      buffer[index++] = PICC_CMD_CT;
+    }
+
+    uint8_t bytesToCopy = currentLevelKnownBits / 8 + (currentLevelKnownBits % 8 ? 1 : 0); // The number of bytes needed to represent the known bits for this level.
+    if (bytesToCopy)
+    {
+      // Max 4 bytes in each Cascade Level. Only 3 left if we use the Cascade Tag
+      uint8_t maxBytes = useCascadeTag ? 3 : 4;
+      if (bytesToCopy > maxBytes)
+      {
+        bytesToCopy = maxBytes;
+      }
+
+      for (count = 0; count < bytesToCopy; count++)
+      {
+        buffer[index++] = uid->uidByte[uidIndex + count];
+      }
+    }
+
+    // Now that the data has been copied we need to include the 8 bits in CT in currentLevelKnownBits
+    if (useCascadeTag)
+    {
+      currentLevelKnownBits += 8;
+    }
+
+    // Repeat anti collision loop until we can transmit all UID bits + BCC and receive a SAK - max 32 iterations.
+    selectDone = false;
+    while ( ! selectDone)
+    {
+      // Find out how many bits and bytes to send and receive.
+      if (currentLevelKnownBits >= 32)
+      { // All UID bits in this Cascade Level are known. This is a SELECT.
+        //Serial.print("SELECT: currentLevelKnownBits="); Serial.println(currentLevelKnownBits, DEC);
+        buffer[1] = 0x70; // NVB - Number of Valid Bits: Seven whole bytes
+
+        // Calulate BCC - Block Check Character
+        buffer[6] = buffer[2] ^ buffer[3] ^ buffer[4] ^ buffer[5];
+
+        // Calculate CRC_A
+        result = PCD_CalculateCRC(buffer, 7, &buffer[7]);
+        if (result != STATUS_OK)
+        {
+          return result;
+        }
+
+        txLastBits      = 0; // 0 => All 8 bits are valid.
+        bufferUsed      = 9;
+
+        // Store response in the last 3 bytes of buffer (BCC and CRC_A - not needed after tx)
+        responseBuffer  = &buffer[6];
+        responseLength  = 3;
+      }
+      else
+      { // This is an ANTICOLLISION.
+        //Serial.print("ANTICOLLISION: currentLevelKnownBits="); Serial.println(currentLevelKnownBits, DEC);
+        txLastBits     = currentLevelKnownBits % 8;
+        count          = currentLevelKnownBits / 8;  // Number of whole bytes in the UID part.
+        index          = 2 + count;                  // Number of whole bytes: SEL + NVB + UIDs
+        buffer[1]      = (index << 4) + txLastBits;  // NVB - Number of Valid Bits
+        bufferUsed     = index + (txLastBits ? 1 : 0);
+
+        // Store response in the unused part of buffer
+        responseBuffer = &buffer[index];
+        responseLength = sizeof(buffer) - index;
+      }
+
+      // Set bit adjustments
+      rxAlign = txLastBits;                     // Having a seperate variable is overkill. But it makes the next line easier to read.
+      PCD_WriteRegister(BitFramingReg, (rxAlign << 4) + txLastBits);  // RxAlign = BitFramingReg[6..4]. TxLastBits = BitFramingReg[2..0]
+
+      // Transmit the buffer and receive the response.
+      result = PCD_TransceiveData(buffer, bufferUsed, responseBuffer, &responseLength, &txLastBits, rxAlign);
+      if (result == STATUS_COLLISION)
+      { // More than one PICC in the field => collision.
+        result = PCD_ReadRegister(CollReg);     // CollReg[7..0] bits are: ValuesAfterColl reserved CollPosNotValid CollPos[4:0]
+        if (result & 0x20)
+        { // CollPosNotValid
+          return STATUS_COLLISION; // Without a valid collision position we cannot continue
+        }
+
+        uint8_t collisionPos = result & 0x1F; // Values 0-31, 0 means bit 32.
+        if (collisionPos == 0)
+        {
+          collisionPos = 32;
+        }
+
+        if (collisionPos <= currentLevelKnownBits)
+        { // No progress - should not happen
+          return STATUS_INTERNAL_ERROR;
+        }
+
+        // Choose the PICC with the bit set.
+        currentLevelKnownBits = collisionPos;
+        count          = (currentLevelKnownBits - 1) % 8; // The bit to modify
+        index          = 1 + (currentLevelKnownBits / 8) + (count ? 1 : 0); // First byte is index 0.
+        buffer[index] |= (1 << count);
+      }
+      else if (result != STATUS_OK)
+      {
+        return result;
+      }
+      else
+      { // STATUS_OK
+        if (currentLevelKnownBits >= 32)
+        { // This was a SELECT.
+          selectDone = true; // No more anticollision
+          // We continue below outside the while.
+        }
+        else
+        { // This was an ANTICOLLISION.
+          // We now have all 32 bits of the UID in this Cascade Level
+          currentLevelKnownBits = 32;
+          // Run loop again to do the SELECT.
+        }
+      }
+    } // End of while ( ! selectDone)
+
+    // We do not check the CBB - it was constructed by us above.
+
+    // Copy the found UID bytes from buffer[] to uid->uidByte[]
+    index       = (buffer[2] == PICC_CMD_CT) ? 3 : 2; // source index in buffer[]
+    bytesToCopy = (buffer[2] == PICC_CMD_CT) ? 3 : 4;
+    for (count = 0; count < bytesToCopy; count++)
+    {
+      uid->uidByte[uidIndex + count] = buffer[index++];
+    }
+
+    // Check response SAK (Select Acknowledge)
+    if (responseLength != 3 || txLastBits != 0)
+    {   // SAK must be exactly 24 bits (1 byte + CRC_A).
+      return STATUS_ERROR;
+    }
+
+    // Verify CRC_A - do our own calculation and store the control in buffer[2..3] - those bytes are not needed anymore.
+    result = PCD_CalculateCRC(responseBuffer, 1, &buffer[2]);
+    if (result != STATUS_OK)
+    {
+      return result;
+    }
+
+    if ((buffer[2] != responseBuffer[1]) || (buffer[3] != responseBuffer[2]))
+    {
+      return STATUS_CRC_WRONG;
+    }
+
+    if (responseBuffer[0] & 0x04)
+    { // Cascade bit set - UID not complete yes
+      cascadeLevel++;
+    }
+    else
+    {
+      uidComplete = true;
+      uid->sak = responseBuffer[0];
+    }
+  } // End of while ( ! uidComplete)
+
+  // Set correct uid->size
+  uid->size = 3 * cascadeLevel + 1;
+
+  return STATUS_OK;
+} // End PICC_Select()
+
+/*
+ * Instructs a PICC in state ACTIVE(*) to go to state HALT.
+ */
+uint8_t MFRC522::PICC_HaltA()
+{
+  uint8_t result;
+  uint8_t buffer[4];
+
+  // Build command buffer
+  buffer[0] = PICC_CMD_HLTA;
+  buffer[1] = 0;
+
+  // Calculate CRC_A
+  result = PCD_CalculateCRC(buffer, 2, &buffer[2]);
+  if (result == STATUS_OK)
+  {
+    // Send the command.
+    // The standard says:
+    //    If the PICC responds with any modulation during a period of 1 ms after the end of the frame containing the
+    //    HLTA command, this response shall be interpreted as 'not acknowledge'.
+    // We interpret that this way: Only STATUS_TIMEOUT is an success.
+    result = PCD_TransceiveData(buffer, sizeof(buffer), NULL, 0);
+    if (result == STATUS_TIMEOUT)
+    {
+      result = STATUS_OK;
+    }
+    else if (result == STATUS_OK)
+    { // That is ironically NOT ok in this case ;-)
+      result = STATUS_ERROR;
+    }
+  }
+
+  return result;
+} // End PICC_HaltA()
+
+
+/////////////////////////////////////////////////////////////////////////////////////
+// Functions for communicating with MIFARE PICCs
+/////////////////////////////////////////////////////////////////////////////////////
+
+/*
+ * Executes the MFRC522 MFAuthent command.
+ */
+uint8_t MFRC522::PCD_Authenticate(uint8_t command, uint8_t blockAddr, MIFARE_Key *key, Uid *uid)
+{
+  uint8_t i, waitIRq = 0x10;    // IdleIRq
+
+  // Build command buffer
+  uint8_t sendData[12];
+  sendData[0] = command;
+  sendData[1] = blockAddr;
+
+  for (i = 0; i < MF_KEY_SIZE; i++)
+  {  // 6 key bytes
+    sendData[2+i] = key->keyByte[i];
+  }
+
+  for (i = 0; i < 4; i++)
+  { // The first 4 bytes of the UID
+    sendData[8+i] = uid->uidByte[i];
+  }
+
+  // Start the authentication.
+  return PCD_CommunicateWithPICC(PCD_MFAuthent, waitIRq, &sendData[0], sizeof(sendData));
+} // End PCD_Authenticate()
+
+/*
+ * Used to exit the PCD from its authenticated state.
+ * Remember to call this function after communicating with an authenticated PICC - otherwise no new communications can start.
+ */
+void MFRC522::PCD_StopCrypto1()
+{
+  // Clear MFCrypto1On bit
+  PCD_ClrRegisterBits(Status2Reg, 0x08); // Status2Reg[7..0] bits are: TempSensClear I2CForceHS reserved reserved   MFCrypto1On ModemState[2:0]
+} // End PCD_StopCrypto1()
+
+/*
+ * Reads 16 bytes (+ 2 bytes CRC_A) from the active PICC.
+ */
+uint8_t MFRC522::MIFARE_Read(uint8_t blockAddr, uint8_t *buffer, uint8_t *bufferSize)
+{
+  uint8_t result = STATUS_NO_ROOM;
+
+  // Sanity check
+  if ((buffer == NULL) || (*bufferSize < 18))
+  {
+    return result;
+  }
+
+  // Build command buffer
+  buffer[0] = PICC_CMD_MF_READ;
+  buffer[1] = blockAddr;
+
+  // Calculate CRC_A
+  result = PCD_CalculateCRC(buffer, 2, &buffer[2]);
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  // Transmit the buffer and receive the response, validate CRC_A.
+  return PCD_TransceiveData(buffer, 4, buffer, bufferSize, NULL, 0, true);
+} // End MIFARE_Read()
+
+/*
+ * Writes 16 bytes to the active PICC.
+ */
+uint8_t MFRC522::MIFARE_Write(uint8_t blockAddr, uint8_t *buffer, uint8_t bufferSize)
+{
+  uint8_t result;
+
+  // Sanity check
+  if (buffer == NULL || bufferSize < 16)
+  {
+    return STATUS_INVALID;
+  }
+
+  // Mifare Classic protocol requires two communications to perform a write.
+  // Step 1: Tell the PICC we want to write to block blockAddr.
+  uint8_t cmdBuffer[2];
+  cmdBuffer[0] = PICC_CMD_MF_WRITE;
+  cmdBuffer[1] = blockAddr;
+  // Adds CRC_A and checks that the response is MF_ACK.
+  result = PCD_MIFARE_Transceive(cmdBuffer, 2);
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  // Step 2: Transfer the data
+  // Adds CRC_A and checks that the response is MF_ACK.
+  result = PCD_MIFARE_Transceive(buffer, bufferSize);
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  return STATUS_OK;
+} // End MIFARE_Write()
+
+/*
+ * Writes a 4 byte page to the active MIFARE Ultralight PICC.
+ */
+uint8_t MFRC522::MIFARE_UltralightWrite(uint8_t page, uint8_t *buffer, uint8_t bufferSize)
+{
+  uint8_t result;
+
+  // Sanity check
+  if (buffer == NULL || bufferSize < 4)
+  {
+    return STATUS_INVALID;
+  }
+
+  // Build commmand buffer
+  uint8_t cmdBuffer[6];
+  cmdBuffer[0] = PICC_CMD_UL_WRITE;
+  cmdBuffer[1] = page;
+  memcpy(&cmdBuffer[2], buffer, 4);
+
+  // Perform the write
+  result = PCD_MIFARE_Transceive(cmdBuffer, 6); // Adds CRC_A and checks that the response is MF_ACK.
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  return STATUS_OK;
+} // End MIFARE_Ultralight_Write()
+
+/*
+ * MIFARE Decrement subtracts the delta from the value of the addressed block, and stores the result in a volatile memory.
+ */
+uint8_t MFRC522::MIFARE_Decrement(uint8_t blockAddr, uint32_t delta)
+{
+  return MIFARE_TwoStepHelper(PICC_CMD_MF_DECREMENT, blockAddr, delta);
+} // End MIFARE_Decrement()
+
+/*
+ * MIFARE Increment adds the delta to the value of the addressed block, and stores the result in a volatile memory.
+ */
+uint8_t MFRC522::MIFARE_Increment(uint8_t blockAddr, uint32_t delta)
+{
+  return MIFARE_TwoStepHelper(PICC_CMD_MF_INCREMENT, blockAddr, delta);
+} // End MIFARE_Increment()
+
+/**
+ * MIFARE Restore copies the value of the addressed block into a volatile memory.
+ */
+uint8_t MFRC522::MIFARE_Restore(uint8_t blockAddr)
+{
+  // The datasheet describes Restore as a two step operation, but does not explain what data to transfer in step 2.
+  // Doing only a single step does not work, so I chose to transfer 0L in step two.
+  return MIFARE_TwoStepHelper(PICC_CMD_MF_RESTORE, blockAddr, 0L);
+} // End MIFARE_Restore()
+
+/*
+ * Helper function for the two-step MIFARE Classic protocol operations Decrement, Increment and Restore.
+ */
+uint8_t MFRC522::MIFARE_TwoStepHelper(uint8_t command, uint8_t blockAddr, uint32_t data)
+{
+  uint8_t result;
+  uint8_t cmdBuffer[2]; // We only need room for 2 bytes.
+
+  // Step 1: Tell the PICC the command and block address
+  cmdBuffer[0] = command;
+  cmdBuffer[1] = blockAddr;
+
+  // Adds CRC_A and checks that the response is MF_ACK.
+  result = PCD_MIFARE_Transceive(cmdBuffer, 2);
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  // Step 2: Transfer the data
+  // Adds CRC_A and accept timeout as success.
+  result = PCD_MIFARE_Transceive((uint8_t *) &data, 4, true);
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  return STATUS_OK;
+} // End MIFARE_TwoStepHelper()
+
+/*
+ * MIFARE Transfer writes the value stored in the volatile memory into one MIFARE Classic block.
+ */
+uint8_t MFRC522::MIFARE_Transfer(uint8_t blockAddr)
+{
+  uint8_t cmdBuffer[2]; // We only need room for 2 bytes.
+
+  // Tell the PICC we want to transfer the result into block blockAddr.
+  cmdBuffer[0] = PICC_CMD_MF_TRANSFER;
+  cmdBuffer[1] = blockAddr;
+
+  // Adds CRC_A and checks that the response is MF_ACK.
+  return PCD_MIFARE_Transceive(cmdBuffer, 2);
+} // End MIFARE_Transfer()
+
+
+/////////////////////////////////////////////////////////////////////////////////////
+// Support functions
+/////////////////////////////////////////////////////////////////////////////////////
+
+/*
+ * Wrapper for MIFARE protocol communication.
+ * Adds CRC_A, executes the Transceive command and checks that the response is MF_ACK or a timeout.
+ */
+uint8_t MFRC522::PCD_MIFARE_Transceive(uint8_t *sendData, uint8_t sendLen, bool acceptTimeout)
+{
+  uint8_t result;
+  uint8_t cmdBuffer[18]; // We need room for 16 bytes data and 2 bytes CRC_A.
+
+  // Sanity check
+  if (sendData == NULL || sendLen > 16)
+  {
+    return STATUS_INVALID;
+  }
+
+  // Copy sendData[] to cmdBuffer[] and add CRC_A
+  memcpy(cmdBuffer, sendData, sendLen);
+  result = PCD_CalculateCRC(cmdBuffer, sendLen, &cmdBuffer[sendLen]);
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  sendLen += 2;
+
+  // Transceive the data, store the reply in cmdBuffer[]
+  uint8_t waitIRq = 0x30;    // RxIRq and IdleIRq
+  uint8_t cmdBufferSize = sizeof(cmdBuffer);
+  uint8_t validBits = 0;
+  result = PCD_CommunicateWithPICC(PCD_Transceive, waitIRq, cmdBuffer, sendLen, cmdBuffer, &cmdBufferSize, &validBits);
+  if (acceptTimeout && result == STATUS_TIMEOUT)
+  {
+    return STATUS_OK;
+  }
+
+  if (result != STATUS_OK)
+  {
+    return result;
+  }
+
+  // The PICC must reply with a 4 bit ACK
+  if (cmdBufferSize != 1 || validBits != 4)
+  {
+    return STATUS_ERROR;
+  }
+
+  if (cmdBuffer[0] != MF_ACK)
+  {
+    return STATUS_MIFARE_NACK;
+  }
+
+  return STATUS_OK;
+} // End PCD_MIFARE_Transceive()
+
+
+/*
+ * Translates the SAK (Select Acknowledge) to a PICC type.
+ */
+uint8_t MFRC522::PICC_GetType(uint8_t sak)
+{
+  uint8_t retType = PICC_TYPE_UNKNOWN;
+
+  if (sak & 0x04)
+  { // UID not complete
+    retType = PICC_TYPE_NOT_COMPLETE;
+  }
+  else
+  {
+    switch (sak)
+    {
+      case 0x09: retType = PICC_TYPE_MIFARE_MINI; break;
+      case 0x08: retType = PICC_TYPE_MIFARE_1K;   break;
+      case 0x18: retType = PICC_TYPE_MIFARE_4K;   break;
+      case 0x00: retType = PICC_TYPE_MIFARE_UL;   break;
+      case 0x10:
+      case 0x11: retType = PICC_TYPE_MIFARE_PLUS; break;
+      case 0x01: retType = PICC_TYPE_TNP3XXX;     break;
+      default:
+        if (sak & 0x20)
+        {
+          retType = PICC_TYPE_ISO_14443_4;
+        }
+        else if (sak & 0x40)
+        {
+          retType = PICC_TYPE_ISO_18092;
+        }
+        break;
+    }
+  }
+
+  return (retType);
+} // End PICC_GetType()
+
+/*
+ * Returns a string pointer to the PICC type name.
+ */
+char* MFRC522::PICC_GetTypeName(uint8_t piccType)
+{
+  if(piccType == PICC_TYPE_NOT_COMPLETE)
+  {
+    piccType = MFRC522_MaxPICCs - 1;
+  }
+
+  return((char *) _TypeNamePICC[piccType]);
+} // End PICC_GetTypeName()
+
+/*
+ * Returns a string pointer to a status code name.
+ */
+char* MFRC522::GetStatusCodeName(uint8_t code)
+{
+  return((char *) _ErrorMessage[code]);
+} // End GetStatusCodeName()
+
+/*
+ * Calculates the bit pattern needed for the specified access bits. In the [C1 C2 C3] tupples C1 is MSB (=4) and C3 is LSB (=1).
+ */
+void MFRC522::MIFARE_SetAccessBits(uint8_t *accessBitBuffer,  
+                                   uint8_t g0,                
+                                   uint8_t g1,                
+                                   uint8_t g2,                
+                                   uint8_t g3)
+{
+  uint8_t c1 = ((g3 & 4) << 1) | ((g2 & 4) << 0) | ((g1 & 4) >> 1) | ((g0 & 4) >> 2);
+  uint8_t c2 = ((g3 & 2) << 2) | ((g2 & 2) << 1) | ((g1 & 2) << 0) | ((g0 & 2) >> 1);
+  uint8_t c3 = ((g3 & 1) << 3) | ((g2 & 1) << 2) | ((g1 & 1) << 1) | ((g0 & 1) << 0);
+
+  accessBitBuffer[0] = (~c2 & 0xF) << 4 | (~c1 & 0xF);
+  accessBitBuffer[1] =          c1 << 4 | (~c3 & 0xF);
+  accessBitBuffer[2] =          c3 << 4 | c2;
+} // End MIFARE_SetAccessBits()
+
+/////////////////////////////////////////////////////////////////////////////////////
+// Convenience functions - does not add extra functionality
+/////////////////////////////////////////////////////////////////////////////////////
+
+/*
+ * Returns true if a PICC responds to PICC_CMD_REQA.
+ * Only "new" cards in state IDLE are invited. Sleeping cards in state HALT are ignored.
+ */
+bool MFRC522::PICC_IsNewCardPresent(void)
+{
+  uint8_t bufferATQA[2];
+  uint8_t bufferSize = sizeof(bufferATQA);
+  uint8_t result = PICC_RequestA(bufferATQA, &bufferSize);
+  return ((result == STATUS_OK) || (result == STATUS_COLLISION));
+} // End PICC_IsNewCardPresent()
+
+/*
+ * Simple wrapper around PICC_Select.
+ */
+bool MFRC522::PICC_ReadCardSerial(void)
+{
+  uint8_t result = PICC_Select(&uid);
+  return (result == STATUS_OK);
+} // End PICC_ReadCardSerial()