/*
* MFRC522.cpp - Library to use ARDUINO RFID MODULE KIT 13.56 MHZ WITH TAGS SPI W AND R BY COOQROBOT.
* NOTE: Please also check the comments in MFRC522.h - they provide useful hints and background information.
* Released into the public domain.
*/

#include <Arduino.h>
#include <MFRC522.h>

/////////////////////////////////////////////////////////////////////////////////////
// Functions for setting up the Arduino
/////////////////////////////////////////////////////////////////////////////////////
/**
 * Constructor.
 */
MFRC522::MFRC522() {
} // End constructor

/**
 * Constructor.
 * Prepares the output pins.
 */
MFRC522::MFRC522(   byte chipSelectPin,     ///< Arduino pin connected to MFRC522's SPI slave select input (Pin 24, NSS, active low)
                    byte resetPowerDownPin  ///< Arduino pin connected to MFRC522's reset and power down input (Pin 6, NRSTPD, active low)
                ) {
    _chipSelectPin = chipSelectPin;
    _resetPowerDownPin = resetPowerDownPin;
} // End constructor

/////////////////////////////////////////////////////////////////////////////////////
// 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(    byte reg,       ///< The register to write to. One of the PCD_Register enums.
                                    byte value      ///< The value to write.
                                ) {
    SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV4, MSBFIRST, SPI_MODE0)); // Set the settings to work with SPI bus
    digitalWrite(_chipSelectPin, LOW);      // Select slave
    SPI.transfer(reg & 0x7E);               // MSB == 0 is for writing. LSB is not used in address. Datasheet section 8.1.2.3.
    SPI.transfer(value);
    digitalWrite(_chipSelectPin, HIGH);     // Release slave again
    SPI.endTransaction(); // Stop using the SPI bus
} // 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(    byte reg,       ///< The register to write to. One of the PCD_Register enums.
                                    byte count,     ///< The number of bytes to write to the register
                                    byte *values    ///< The values to write. Byte array.
                                ) {
    SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV4, MSBFIRST, SPI_MODE0)); // Set the settings to work with SPI bus
    digitalWrite(_chipSelectPin, LOW);      // Select slave
    SPI.transfer(reg & 0x7E);               // MSB == 0 is for writing. LSB is not used in address. Datasheet section 8.1.2.3.
    for (byte index = 0; index < count; index++) {
        SPI.transfer(values[index]);
    }
    digitalWrite(_chipSelectPin, HIGH);     // Release slave again
    SPI.endTransaction(); // Stop using the SPI bus
} // 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.
 */
byte MFRC522::PCD_ReadRegister( byte reg    ///< The register to read from. One of the PCD_Register enums.
                                ) {
    byte value;
    SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV4, MSBFIRST, SPI_MODE0)); // Set the settings to work with SPI bus
    digitalWrite(_chipSelectPin, LOW);          // Select slave
    SPI.transfer(0x80 | (reg & 0x7E));          // MSB == 1 is for reading. LSB is not used in address. Datasheet section 8.1.2.3.
    value = SPI.transfer(0);                    // Read the value back. Send 0 to stop reading.
    digitalWrite(_chipSelectPin, HIGH);         // Release slave again
    SPI.endTransaction(); // Stop using the SPI bus
    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( byte reg,       ///< The register to read from. One of the PCD_Register enums.
                                byte count,     ///< The number of bytes to read
                                byte *values,   ///< Byte array to store the values in.
                                byte rxAlign    ///< Only bit positions rxAlign..7 in values[0] are updated.
                                ) {
    if (count == 0) {
        return;
    }
    //Serial.print(F("Reading "));  Serial.print(count); Serial.println(F(" bytes from register."));
    byte address = 0x80 | (reg & 0x7E);     // MSB == 1 is for reading. LSB is not used in address. Datasheet section 8.1.2.3.
    byte index = 0;                         // Index in values array.
    SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV4, MSBFIRST, SPI_MODE0)); // Set the settings to work with SPI bus
    digitalWrite(_chipSelectPin, LOW);      // Select slave
    count--;                                // One read is performed outside of the loop
    SPI.transfer(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
            byte mask = 0;
            for (byte i = rxAlign; i <= 7; i++) {
                mask |= (1 << i);
            }
            // Read value and tell that we want to read the same address again.
            byte value = SPI.transfer(address);
            // Apply mask to both current value of values[0] and the new data in value.
            values[0] = (values[index] & ~mask) | (value & mask);
        }
        else { // Normal case
            values[index] = SPI.transfer(address);  // Read value and tell that we want to read the same address again.
        }
        index++;
    }
    values[index] = SPI.transfer(0);            // Read the final byte. Send 0 to stop reading.
    digitalWrite(_chipSelectPin, HIGH);         // Release slave again
    SPI.endTransaction(); // Stop using the SPI bus
} // End PCD_ReadRegister()

/**
 * Sets the bits given in mask in register reg.
 */
void MFRC522::PCD_SetRegisterBitMask(   byte reg,   ///< The register to update. One of the PCD_Register enums.
                                        byte mask   ///< The bits to set.
                                    ) {
    byte tmp;
    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_ClearRegisterBitMask( byte reg,   ///< The register to update. One of the PCD_Register enums.
                                        byte mask   ///< The bits to clear.
                                      ) {
    byte tmp;
    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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PCD_CalculateCRC(  byte *data,     ///< In: Pointer to the data to transfer to the FIFO for CRC calculation.
                                                byte length,    ///< In: The number of bytes to transfer.
                                                byte *result    ///< Out: Pointer to result buffer. Result is written to result[0..1], low byte first.
                     ) {
    PCD_WriteRegister(CommandReg, PCD_Idle);        // Stop any active command.
    PCD_WriteRegister(DivIrqReg, 0x04);             // Clear the CRCIRq interrupt request bit
    PCD_SetRegisterBitMask(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 17.73�s.
    word i = 5000;
    byte 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;
        }
    }
    PCD_WriteRegister(CommandReg, PCD_Idle);        // Stop calculating CRC for new content in the FIFO.

    // 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() {
    // Set the chipSelectPin as digital output, do not select the slave yet
    pinMode(_chipSelectPin, OUTPUT);
    digitalWrite(_chipSelectPin, HIGH);

    // Set the resetPowerDownPin as digital output, do not reset or power down.
    pinMode(_resetPowerDownPin, OUTPUT);

    if (digitalRead(_resetPowerDownPin) == LOW) {   //The MFRC522 chip is in power down mode.
        digitalWrite(_resetPowerDownPin, HIGH);     // Exit power down mode. This triggers a hard reset.
        // Section 8.8.2 in the datasheet says the oscillator start-up time is the start up time of the crystal + 37,74�s. Let us be generous: 50ms.
        delay(38);
    }
    else { // Perform a soft reset
        PCD_Reset();
    }

    // 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 25�s.
    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_AntennaOn();                        // Enable the antenna driver pins TX1 and TX2 (they were disabled by the reset)
} // End PCD_Init()

/**
 * Initializes the MFRC522 chip.
 */
void MFRC522::PCD_Init( byte chipSelectPin,     ///< Arduino pin connected to MFRC522's SPI slave select input (Pin 24, NSS, active low)
                        byte resetPowerDownPin  ///< Arduino pin connected to MFRC522's reset and power down input (Pin 6, NRSTPD, active low)
                    ) {
    _chipSelectPin = chipSelectPin;
    _resetPowerDownPin = resetPowerDownPin;
    // Set the chipSelectPin as digital output, do not select the slave yet
    PCD_Init();
} // 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 + 37,74�s. Let us be generous: 50ms.
    delay(38);
    // 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 are disabled.
 */
void MFRC522::PCD_AntennaOn() {
    byte value = PCD_ReadRegister(TxControlReg);
    if ((value & 0x03) != 0x03) {
        PCD_WriteRegister(TxControlReg, value | 0x03);
    }
} // End PCD_AntennaOn()

/**
 * Turns the antenna off by disabling pins TX1 and TX2.
 */
void MFRC522::PCD_AntennaOff() {
    PCD_ClearRegisterBitMask(TxControlReg, 0x03);
} // End PCD_AntennaOff()

/**
 * Get the current MFRC522 Receiver Gain (RxGain[2:0]) value.
 * See 9.3.3.6 / table 98 in http://www.nxp.com/documents/data_sheet/MFRC522.pdf
 * NOTE: Return value scrubbed with (0x07<<4)=01110000b as RCFfgReg may use reserved bits.
 *
 * @return Value of the RxGain, scrubbed to the 3 bits used.
 */
byte MFRC522::PCD_GetAntennaGain() {
    return PCD_ReadRegister(RFCfgReg) & (0x07<<4);
} // End PCD_GetAntennaGain()

/**
 * Set the MFRC522 Receiver Gain (RxGain) to value specified by given mask.
 * See 9.3.3.6 / table 98 in http://www.nxp.com/documents/data_sheet/MFRC522.pdf
 * NOTE: Given mask is scrubbed with (0x07<<4)=01110000b as RCFfgReg may use reserved bits.
 */
void MFRC522::PCD_SetAntennaGain(byte mask) {
    if (PCD_GetAntennaGain() != mask) {                     // only bother if there is a change
        PCD_ClearRegisterBitMask(RFCfgReg, (0x07<<4));      // clear needed to allow 000 pattern
        PCD_SetRegisterBitMask(RFCfgReg, mask & (0x07<<4)); // only set RxGain[2:0] bits
    }
} // End PCD_SetAntennaGain()

/**
 * Performs a self-test of the MFRC522
 * See 16.1.1 in http://www.nxp.com/documents/data_sheet/MFRC522.pdf
 *
 * @return Whether or not the test passed. Or false if no firmware reference is available.
 */
bool MFRC522::PCD_PerformSelfTest() {
    // This follows directly the steps outlined in 16.1.1
    // 1. Perform a soft reset.
    PCD_Reset();

    // 2. Clear the internal buffer by writing 25 bytes of 00h
    byte ZEROES[25] = {0x00};
    PCD_SetRegisterBitMask(FIFOLevelReg, 0x80); // flush the FIFO buffer
    PCD_WriteRegister(FIFODataReg, 25, ZEROES); // write 25 bytes of 00h to FIFO
    PCD_WriteRegister(CommandReg, PCD_Mem);     // transfer to internal buffer

    // 3. Enable self-test
    PCD_WriteRegister(AutoTestReg, 0x09);

    // 4. Write 00h to FIFO buffer
    PCD_WriteRegister(FIFODataReg, 0x00);

    // 5. Start self-test by issuing the CalcCRC command
    PCD_WriteRegister(CommandReg, PCD_CalcCRC);

    // 6. Wait for self-test to complete
    word i;
    byte n;
    for (i = 0; i < 0xFF; i++) {
        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;
        }
    }
    PCD_WriteRegister(CommandReg, PCD_Idle);        // Stop calculating CRC for new content in the FIFO.

    // 7. Read out resulting 64 bytes from the FIFO buffer.
    byte result[64];
    PCD_ReadRegister(FIFODataReg, 64, result, 0);

    // Auto self-test done
    // Reset AutoTestReg register to be 0 again. Required for normal operation.
    PCD_WriteRegister(AutoTestReg, 0x00);

    // Determine firmware version (see section 9.3.4.8 in spec)
    byte version = PCD_ReadRegister(VersionReg);

    // Pick the appropriate reference values
    const byte *reference;
    switch (version) {
        case 0x88:  // Fudan Semiconductor FM17522 clone
            reference = FM17522_firmware_reference;
            break;
        case 0x90:  // Version 0.0
            reference = MFRC522_firmware_referenceV0_0;
            break;
        case 0x91:  // Version 1.0
            reference = MFRC522_firmware_referenceV1_0;
            break;
        case 0x92:  // Version 2.0
            reference = MFRC522_firmware_referenceV2_0;
            break;
        default:    // Unknown version
            return false; // abort test
    }

    // Verify that the results match up to our expectations
    for (i = 0; i < 64; i++) {
        if (result[i] != pgm_read_byte(&(reference[i]))) {
            return false;
        }
    }

    // Test passed; all is good.
    return true;
} // End PCD_PerformSelfTest()

/////////////////////////////////////////////////////////////////////////////////////
// Functions for communicating with PICCs
/////////////////////////////////////////////////////////////////////////////////////

/**
 * Executes the Transceive command.
 * CRC validation can only be done if backData and backLen are specified.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PCD_TransceiveData(    byte *sendData,     ///< Pointer to the data to transfer to the FIFO.
                                                    byte sendLen,       ///< Number of bytes to transfer to the FIFO.
                                                    byte *backData,     ///< NULL or pointer to buffer if data should be read back after executing the command.
                                                    byte *backLen,      ///< In: Max number of bytes to write to *backData. Out: The number of bytes returned.
                                                    byte *validBits,    ///< In/Out: The number of valid bits in the last byte. 0 for 8 valid bits. Default NULL.
                                                    byte rxAlign,       ///< In: Defines the bit position in backData[0] for the first bit received. Default 0.
                                                    bool checkCRC       ///< In: True => The last two bytes of the response is assumed to be a CRC_A that must be validated.
                                 ) {
    byte 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 command, waits for completion and transfers data back from the FIFO.
 * CRC validation can only be done if backData and backLen are specified.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PCD_CommunicateWithPICC(   byte command,       ///< The command to execute. One of the PCD_Command enums.
                                                        byte waitIRq,       ///< The bits in the ComIrqReg register that signals successful completion of the command.
                                                        byte *sendData,     ///< Pointer to the data to transfer to the FIFO.
                                                        byte sendLen,       ///< Number of bytes to transfer to the FIFO.
                                                        byte *backData,     ///< NULL or pointer to buffer if data should be read back after executing the command.
                                                        byte *backLen,      ///< In: Max number of bytes to write to *backData. Out: The number of bytes returned.
                                                        byte *validBits,    ///< In/Out: The number of valid bits in the last byte. 0 for 8 valid bits.
                                                        byte rxAlign,       ///< In: Defines the bit position in backData[0] for the first bit received. Default 0.
                                                        bool checkCRC       ///< In: True => The last two bytes of the response is assumed to be a CRC_A that must be validated.
                                     ) {
    byte n, _validBits;
    unsigned int i;

    // Prepare values for BitFramingReg
    byte txLastBits = validBits ? *validBits : 0;
    byte 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_SetRegisterBitMask(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_SetRegisterBitMask(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 17.86�s.
    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 conditions 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.
    byte 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.
        byte controlBuffer[2];
        MFRC522::StatusCode status = PCD_CalculateCRC(&backData[0], *backLen - 2, &controlBuffer[0]);
        if (status != STATUS_OK) {
            return status;
        }
        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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PICC_RequestA( byte *bufferATQA,   ///< The buffer to store the ATQA (Answer to request) in
                                            byte *bufferSize    ///< Buffer size, at least two bytes. Also number of bytes returned if STATUS_OK.
                                        ) {
    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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PICC_WakeupA(  byte *bufferATQA,   ///< The buffer to store the ATQA (Answer to request) in
                                            byte *bufferSize    ///< Buffer size, at least two bytes. Also number of bytes returned if STATUS_OK.
                                        ) {
    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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PICC_REQA_or_WUPA( byte command,       ///< The command to send - PICC_CMD_REQA or PICC_CMD_WUPA
                                                byte *bufferATQA,   ///< The buffer to store the ATQA (Answer to request) in
                                                byte *bufferSize    ///< Buffer size, at least two bytes. Also number of bytes returned if STATUS_OK.
                                            ) {
    byte validBits;
    MFRC522::StatusCode status;

    if (bufferATQA == NULL || *bufferSize < 2) {    // The ATQA response is 2 bytes long.
        return STATUS_NO_ROOM;
    }
    PCD_ClearRegisterBitMask(CollReg, 0x80);        // ValuesAfterColl=1 => Bits received after collision are cleared.
    validBits = 7;                                  // For REQA and WUPA we need the short frame format - transmit only 7 bits of the last (and only) byte. TxLastBits = BitFramingReg[2..0]
    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.
 * Before calling this function the PICCs must be placed in the READY(*) state by calling PICC_RequestA() or PICC_WakeupA().
 * On success:
 *      - The chosen PICC is in state ACTIVE(*) and all other PICCs have returned to state IDLE/HALT. (Figure 7 of the ISO/IEC 14443-3 draft.)
 *      - The UID size and value of the chosen PICC is returned in *uid along with the SAK.
 *
 * A PICC UID consists of 4, 7 or 10 bytes.
 * Only 4 bytes can be specified in a SELECT command, so for the longer UIDs two or three iterations are used:
 *      UID size    Number of UID bytes     Cascade levels      Example of PICC
 *      ========    ===================     ==============      ===============
 *      single               4                      1               MIFARE Classic
 *      double               7                      2               MIFARE Ultralight
 *      triple              10                      3               Not currently in use?
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PICC_Select(   Uid *uid,           ///< Pointer to Uid struct. Normally output, but can also be used to supply a known UID.
                                            byte validBits      ///< The number of known UID bits supplied in *uid. Normally 0. If set you must also supply uid->size.
                                         ) {
    bool uidComplete;
    bool selectDone;
    bool useCascadeTag;
    byte cascadeLevel = 1;
    MFRC522::StatusCode result;
    byte count;
    byte index;
    byte uidIndex;                  // The first index in uid->uidByte[] that is used in the current Cascade Level.
    int8_t currentLevelKnownBits;       // The number of known UID bits in the current Cascade Level.
    byte buffer[9];                 // The SELECT/ANTICOLLISION commands uses a 7 byte standard frame + 2 bytes CRC_A
    byte bufferUsed;                // The number of bytes used in the buffer, ie the number of bytes to transfer to the FIFO.
    byte rxAlign;                   // Used in BitFramingReg. Defines the bit position for the first bit received.
    byte txLastBits;                // Used in BitFramingReg. The number of valid bits in the last transmitted byte.
    byte *responseBuffer;
    byte 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 are 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
    PCD_ClearRegisterBitMask(CollReg, 0x80);        // ValuesAfterColl=1 => Bits received after collision are cleared.

    // 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?
        currentLevelKnownBits = validBits - (8 * uidIndex);
        if (currentLevelKnownBits < 0) {
            currentLevelKnownBits = 0;
        }
        // Copy the known bits from uid->uidByte[] to buffer[]
        index = 2; // destination index in buffer[]
        if (useCascadeTag) {
            buffer[index++] = PICC_CMD_CT;
        }
        byte bytesToCopy = currentLevelKnownBits / 8 + (currentLevelKnownBits % 8 ? 1 : 0); // The number of bytes needed to represent the known bits for this level.
        if (bytesToCopy) {
            byte maxBytes = useCascadeTag ? 3 : 4; // Max 4 bytes in each Cascade Level. Only 3 left if we use the Cascade Tag
            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(F("SELECT: currentLevelKnownBits=")); Serial.println(currentLevelKnownBits, DEC);
                buffer[1] = 0x70; // NVB - Number of Valid Bits: Seven whole bytes
                // Calculate 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(F("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 separate 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.
                byte valueOfCollReg = PCD_ReadRegister(CollReg); // CollReg[7..0] bits are: ValuesAfterColl reserved CollPosNotValid CollPos[4:0]
                if (valueOfCollReg & 0x20) { // CollPosNotValid
                    return STATUS_COLLISION; // Without a valid collision position we cannot continue
                }
                byte collisionPos = valueOfCollReg & 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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PICC_HaltA() {
    MFRC522::StatusCode result;
    byte 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) {
        return result;
    }

    // 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 a success.
    result = PCD_TransceiveData(buffer, sizeof(buffer), NULL, 0);
    if (result == STATUS_TIMEOUT) {
        return STATUS_OK;
    }
    if (result == STATUS_OK) { // That is ironically NOT ok in this case ;-)
        return STATUS_ERROR;
    }
    return result;
} // End PICC_HaltA()


/////////////////////////////////////////////////////////////////////////////////////
// Functions for communicating with MIFARE PICCs
/////////////////////////////////////////////////////////////////////////////////////

/**
 * Executes the MFRC522 MFAuthent command.
 * This command manages MIFARE authentication to enable a secure communication to any MIFARE Mini, MIFARE 1K and MIFARE 4K card.
 * The authentication is described in the MFRC522 datasheet section 10.3.1.9 and http://www.nxp.com/documents/data_sheet/MF1S503x.pdf section 10.1.
 * For use with MIFARE Classic PICCs.
 * The PICC must be selected - ie in state ACTIVE(*) - before calling this function.
 * Remember to call PCD_StopCrypto1() after communicating with the authenticated PICC - otherwise no new communications can start.
 *
 * All keys are set to FFFFFFFFFFFFh at chip delivery.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise. Probably STATUS_TIMEOUT if you supply the wrong key.
 */
MFRC522::StatusCode MFRC522::PCD_Authenticate(byte command,     ///< PICC_CMD_MF_AUTH_KEY_A or PICC_CMD_MF_AUTH_KEY_B
                                            byte blockAddr,     ///< The block number. See numbering in the comments in the .h file.
                                            MIFARE_Key *key,    ///< Pointer to the Crypteo1 key to use (6 bytes)
                                            Uid *uid            ///< Pointer to Uid struct. The first 4 bytes of the UID is used.
                                            ) {
    byte waitIRq = 0x10;        // IdleIRq

    // Build command buffer
    byte sendData[12];
    sendData[0] = command;
    sendData[1] = blockAddr;
    for (byte i = 0; i < MF_KEY_SIZE; i++) {    // 6 key bytes
        sendData[2+i] = key->keyByte[i];
    }
    for (byte 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_ClearRegisterBitMask(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.
 *
 * For MIFARE Classic the sector containing the block must be authenticated before calling this function.
 *
 * For MIFARE Ultralight only addresses 00h to 0Fh are decoded.
 * The MF0ICU1 returns a NAK for higher addresses.
 * The MF0ICU1 responds to the READ command by sending 16 bytes starting from the page address defined by the command argument.
 * For example; if blockAddr is 03h then pages 03h, 04h, 05h, 06h are returned.
 * A roll-back is implemented: If blockAddr is 0Eh, then the contents of pages 0Eh, 0Fh, 00h and 01h are returned.
 *
 * The buffer must be at least 18 bytes because a CRC_A is also returned.
 * Checks the CRC_A before returning STATUS_OK.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_Read(   byte blockAddr,     ///< MIFARE Classic: The block (0-0xff) number. MIFARE Ultralight: The first page to return data from.
                                            byte *buffer,       ///< The buffer to store the data in
                                            byte *bufferSize    ///< Buffer size, at least 18 bytes. Also number of bytes returned if STATUS_OK.
                                        ) {
    MFRC522::StatusCode result;

    // Sanity check
    if (buffer == NULL || *bufferSize < 18) {
        return STATUS_NO_ROOM;
    }

    // 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.
 *
 * For MIFARE Classic the sector containing the block must be authenticated before calling this function.
 *
 * For MIFARE Ultralight the operation is called "COMPATIBILITY WRITE".
 * Even though 16 bytes are transferred to the Ultralight PICC, only the least significant 4 bytes (bytes 0 to 3)
 * are written to the specified address. It is recommended to set the remaining bytes 04h to 0Fh to all logic 0.
 * *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_Write(  byte blockAddr, ///< MIFARE Classic: The block (0-0xff) number. MIFARE Ultralight: The page (2-15) to write to.
                                            byte *buffer,   ///< The 16 bytes to write to the PICC
                                            byte bufferSize ///< Buffer size, must be at least 16 bytes. Exactly 16 bytes are written.
                                        ) {
    MFRC522::StatusCode 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.
    byte cmdBuffer[2];
    cmdBuffer[0] = PICC_CMD_MF_WRITE;
    cmdBuffer[1] = blockAddr;
    result = PCD_MIFARE_Transceive(cmdBuffer, 2); // Adds CRC_A and checks that the response is MF_ACK.
    if (result != STATUS_OK) {
        return result;
    }

    // Step 2: Transfer the data
    result = PCD_MIFARE_Transceive(buffer, bufferSize); // Adds CRC_A and checks that the response is MF_ACK.
    if (result != STATUS_OK) {
        return result;
    }

    return STATUS_OK;
} // End MIFARE_Write()

/**
 * Writes a 4 byte page to the active MIFARE Ultralight PICC.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_Ultralight_Write(   byte page,      ///< The page (2-15) to write to.
                                                        byte *buffer,   ///< The 4 bytes to write to the PICC
                                                        byte bufferSize ///< Buffer size, must be at least 4 bytes. Exactly 4 bytes are written.
                                                    ) {
    MFRC522::StatusCode result;

    // Sanity check
    if (buffer == NULL || bufferSize < 4) {
        return STATUS_INVALID;
    }

    // Build commmand buffer
    byte 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.
 * For MIFARE Classic only. The sector containing the block must be authenticated before calling this function.
 * Only for blocks in "value block" mode, ie with access bits [C1 C2 C3] = [110] or [001].
 * Use MIFARE_Transfer() to store the result in a block.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_Decrement(  byte blockAddr, ///< The block (0-0xff) number.
                                                long delta      ///< This number is subtracted from the value of block blockAddr.
                                            ) {
    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.
 * For MIFARE Classic only. The sector containing the block must be authenticated before calling this function.
 * Only for blocks in "value block" mode, ie with access bits [C1 C2 C3] = [110] or [001].
 * Use MIFARE_Transfer() to store the result in a block.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_Increment(  byte blockAddr, ///< The block (0-0xff) number.
                                                long delta      ///< This number is added to the value of block blockAddr.
                                            ) {
    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.
 * For MIFARE Classic only. The sector containing the block must be authenticated before calling this function.
 * Only for blocks in "value block" mode, ie with access bits [C1 C2 C3] = [110] or [001].
 * Use MIFARE_Transfer() to store the result in a block.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_Restore(    byte blockAddr ///< The block (0-0xff) number.
                                            ) {
    // 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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_TwoStepHelper(  byte command,   ///< The command to use
                                                    byte blockAddr, ///< The block (0-0xff) number.
                                                    long data       ///< The data to transfer in step 2
                                                    ) {
    MFRC522::StatusCode result;
    byte 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;
    result = PCD_MIFARE_Transceive( cmdBuffer, 2); // Adds CRC_A and checks that the response is MF_ACK.
    if (result != STATUS_OK) {
        return result;
    }

    // Step 2: Transfer the data
    result = PCD_MIFARE_Transceive( (byte *)&data, 4, true); // Adds CRC_A and accept timeout as success.
    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.
 * For MIFARE Classic only. The sector containing the block must be authenticated before calling this function.
 * Only for blocks in "value block" mode, ie with access bits [C1 C2 C3] = [110] or [001].
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_Transfer(   byte blockAddr ///< The block (0-0xff) number.
                                            ) {
    MFRC522::StatusCode result;
    byte 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;
    result = PCD_MIFARE_Transceive( cmdBuffer, 2); // Adds CRC_A and checks that the response is MF_ACK.
    if (result != STATUS_OK) {
        return result;
    }
    return STATUS_OK;
} // End MIFARE_Transfer()

/**
 * Helper routine to read the current value from a Value Block.
 *
 * Only for MIFARE Classic and only for blocks in "value block" mode, that
 * is: with access bits [C1 C2 C3] = [110] or [001]. The sector containing
 * the block must be authenticated before calling this function.
 *
 * @param[in]   blockAddr   The block (0x00-0xff) number.
 * @param[out]  value       Current value of the Value Block.
 * @return STATUS_OK on success, STATUS_??? otherwise.
  */
MFRC522::StatusCode MFRC522::MIFARE_GetValue(byte blockAddr, long *value) {
    MFRC522::StatusCode status;
    byte buffer[18];
    byte size = sizeof(buffer);

    // Read the block
    status = MIFARE_Read(blockAddr, buffer, &size);
    if (status == STATUS_OK) {
        // Extract the value
        *value = (long(buffer[3])<<24) | (long(buffer[2])<<16) | (long(buffer[1])<<8) | long(buffer[0]);
    }
    return status;
} // End MIFARE_GetValue()

/**
 * Helper routine to write a specific value into a Value Block.
 *
 * Only for MIFARE Classic and only for blocks in "value block" mode, that
 * is: with access bits [C1 C2 C3] = [110] or [001]. The sector containing
 * the block must be authenticated before calling this function.
 *
 * @param[in]   blockAddr   The block (0x00-0xff) number.
 * @param[in]   value       New value of the Value Block.
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::MIFARE_SetValue(byte blockAddr, long value) {
    byte buffer[18];

    // Translate the long into 4 bytes; repeated 2x in value block
    buffer[0] = buffer[ 8] = (value & 0xFF);
    buffer[1] = buffer[ 9] = (value & 0xFF00) >> 8;
    buffer[2] = buffer[10] = (value & 0xFF0000) >> 16;
    buffer[3] = buffer[11] = (value & 0xFF000000) >> 24;
    // Inverse 4 bytes also found in value block
    buffer[4] = ~buffer[0];
    buffer[5] = ~buffer[1];
    buffer[6] = ~buffer[2];
    buffer[7] = ~buffer[3];
    // Address 2x with inverse address 2x
    buffer[12] = buffer[14] = blockAddr;
    buffer[13] = buffer[15] = ~blockAddr;

    // Write the whole data block
    return MIFARE_Write(blockAddr, buffer, 16);
} // End MIFARE_SetValue()

/**
 * Authenticate with a NTAG216.
 *
 * Only for NTAG216. First implemented by Gargantuanman.
 *
 * @param[in]   passWord   password.
 * @param[in]   pACK       result success???.
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PCD_NTAG216_AUTH(byte* passWord, byte pACK[]) //Authenticate with 32bit password
{
    MFRC522::StatusCode result;
    byte                cmdBuffer[18]; // We need room for 16 bytes data and 2 bytes CRC_A.

    cmdBuffer[0] = 0x1B; //Comando de autentificacion

    for (byte i = 0; i<4; i++)
        cmdBuffer[i+1] = passWord[i];

    result = PCD_CalculateCRC(cmdBuffer, 5, &cmdBuffer[5]);

    if (result!=STATUS_OK) {
        return result;
    }

    // Transceive the data, store the reply in cmdBuffer[]
    byte waitIRq        = 0x30; // RxIRq and IdleIRq
    byte cmdBufferSize  = sizeof(cmdBuffer);
    byte validBits      = 0;
    byte rxlength       = 5;
    result = PCD_CommunicateWithPICC(PCD_Transceive, waitIRq, cmdBuffer, 7, cmdBuffer, &rxlength, &validBits);

    pACK[0] = cmdBuffer[0];
    pACK[1] = cmdBuffer[1];

    if (result!=STATUS_OK) {
        return result;
    }

    return STATUS_OK;
} // End PCD_NTAG216_AUTH()


/////////////////////////////////////////////////////////////////////////////////////
// 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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
MFRC522::StatusCode MFRC522::PCD_MIFARE_Transceive( byte *sendData,     ///< Pointer to the data to transfer to the FIFO. Do NOT include the CRC_A.
                                                    byte sendLen,       ///< Number of bytes in sendData.
                                                    bool acceptTimeout  ///< True => A timeout is also success
                                                ) {
    MFRC522::StatusCode result;
    byte 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[]
    byte waitIRq = 0x30;        // RxIRq and IdleIRq
    byte cmdBufferSize = sizeof(cmdBuffer);
    byte 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()

/**
 * Returns a __FlashStringHelper pointer to a status code name.
 *
 * @return const __FlashStringHelper *
 */
const __FlashStringHelper *MFRC522::GetStatusCodeName(MFRC522::StatusCode code  ///< One of the StatusCode enums.
                                        ) {
    switch (code) {
        case STATUS_OK:             return F("Success.");
        case STATUS_ERROR:          return F("Error in communication.");
        case STATUS_COLLISION:      return F("Collission detected.");
        case STATUS_TIMEOUT:        return F("Timeout in communication.");
        case STATUS_NO_ROOM:        return F("A buffer is not big enough.");
        case STATUS_INTERNAL_ERROR: return F("Internal error in the code. Should not happen.");
        case STATUS_INVALID:        return F("Invalid argument.");
        case STATUS_CRC_WRONG:      return F("The CRC_A does not match.");
        case STATUS_MIFARE_NACK:    return F("A MIFARE PICC responded with NAK.");
        default:                    return F("Unknown error");
    }
} // End GetStatusCodeName()

/**
 * Translates the SAK (Select Acknowledge) to a PICC type.
 *
 * @return PICC_Type
 */
MFRC522::PICC_Type MFRC522::PICC_GetType(byte sak       ///< The SAK byte returned from PICC_Select().
                                        ) {
    // http://www.nxp.com/documents/application_note/AN10833.pdf
    // 3.2 Coding of Select Acknowledge (SAK)
    // ignore 8-bit (iso14443 starts with LSBit = bit 1)
    // fixes wrong type for manufacturer Infineon (http://nfc-tools.org/index.php?title=ISO14443A)
    sak &= 0x7F;
    switch (sak) {
        case 0x04:  return PICC_TYPE_NOT_COMPLETE;  // UID not complete
        case 0x09:  return PICC_TYPE_MIFARE_MINI;
        case 0x08:  return PICC_TYPE_MIFARE_1K;
        case 0x18:  return PICC_TYPE_MIFARE_4K;
        case 0x00:  return PICC_TYPE_MIFARE_UL;
        case 0x10:
        case 0x11:  return PICC_TYPE_MIFARE_PLUS;
        case 0x01:  return PICC_TYPE_TNP3XXX;
        case 0x20:  return PICC_TYPE_ISO_14443_4;
        case 0x40:  return PICC_TYPE_ISO_18092;
        default:    return PICC_TYPE_UNKNOWN;
    }
} // End PICC_GetType()

/**
 * Returns a __FlashStringHelper pointer to the PICC type name.
 *
 * @return const __FlashStringHelper *
 */
const __FlashStringHelper *MFRC522::PICC_GetTypeName(PICC_Type piccType ///< One of the PICC_Type enums.
                                                    ) {
    switch (piccType) {
        case PICC_TYPE_ISO_14443_4:     return F("PICC compliant with ISO/IEC 14443-4");
        case PICC_TYPE_ISO_18092:       return F("PICC compliant with ISO/IEC 18092 (NFC)");
        case PICC_TYPE_MIFARE_MINI:     return F("MIFARE Mini, 320 bytes");
        case PICC_TYPE_MIFARE_1K:       return F("MIFARE 1KB");
        case PICC_TYPE_MIFARE_4K:       return F("MIFARE 4KB");
        case PICC_TYPE_MIFARE_UL:       return F("MIFARE Ultralight or Ultralight C");
        case PICC_TYPE_MIFARE_PLUS:     return F("MIFARE Plus");
        case PICC_TYPE_TNP3XXX:         return F("MIFARE TNP3XXX");
        case PICC_TYPE_NOT_COMPLETE:    return F("SAK indicates UID is not complete.");
        case PICC_TYPE_UNKNOWN:
        default:                        return F("Unknown type");
    }
} // End PICC_GetTypeName()

/**
 * Dumps debug info about the connected PCD to Serial.
 * Shows all known firmware versions
 */
void MFRC522::PCD_DumpVersionToSerial() {
    // Get the MFRC522 firmware version
    byte v = PCD_ReadRegister(VersionReg);
    Serial.print(F("Firmware Version: 0x"));
    Serial.print(v, HEX);
    // Lookup which version
    switch(v) {
        case 0x88: Serial.println(F(" = (clone)"));  break;
        case 0x90: Serial.println(F(" = v0.0"));     break;
        case 0x91: Serial.println(F(" = v1.0"));     break;
        case 0x92: Serial.println(F(" = v2.0"));     break;
        default:   Serial.println(F(" = (unknown)"));
    }
    // When 0x00 or 0xFF is returned, communication probably failed
    if ((v == 0x00) || (v == 0xFF))
        Serial.println(F("WARNING: Communication failure, is the MFRC522 properly connected?"));
} // End PCD_DumpVersionToSerial()

/**
 * Dumps debug info about the selected PICC to Serial.
 * On success the PICC is halted after dumping the data.
 * For MIFARE Classic the factory default key of 0xFFFFFFFFFFFF is tried.
 */
void MFRC522::PICC_DumpToSerial(Uid *uid    ///< Pointer to Uid struct returned from a successful PICC_Select().
                                ) {
    MIFARE_Key key;

    // Dump UID, SAK and Type
    PICC_DumpDetailsToSerial(uid);

    // Dump contents
    PICC_Type piccType = PICC_GetType(uid->sak);
    switch (piccType) {
        case PICC_TYPE_MIFARE_MINI:
        case PICC_TYPE_MIFARE_1K:
        case PICC_TYPE_MIFARE_4K:
            // All keys are set to FFFFFFFFFFFFh at chip delivery from the factory.
            for (byte i = 0; i < 6; i++) {
                key.keyByte[i] = 0xFF;
            }
            PICC_DumpMifareClassicToSerial(uid, piccType, &key);
            break;

        case PICC_TYPE_MIFARE_UL:
            PICC_DumpMifareUltralightToSerial();
            break;

        case PICC_TYPE_ISO_14443_4:
        case PICC_TYPE_ISO_18092:
        case PICC_TYPE_MIFARE_PLUS:
        case PICC_TYPE_TNP3XXX:
            Serial.println(F("Dumping memory contents not implemented for that PICC type."));
            break;

        case PICC_TYPE_UNKNOWN:
        case PICC_TYPE_NOT_COMPLETE:
        default:
            break; // No memory dump here
    }

    Serial.println();
    PICC_HaltA(); // Already done if it was a MIFARE Classic PICC.
} // End PICC_DumpToSerial()

/**
 * Dumps card info (UID,SAK,Type) about the selected PICC to Serial.
 */
void MFRC522::PICC_DumpDetailsToSerial(Uid *uid ///< Pointer to Uid struct returned from a successful PICC_Select().
                                    ) {
    // UID
    Serial.print(F("Card UID:"));
    for (byte i = 0; i < uid->size; i++) {
        if(uid->uidByte[i] < 0x10)
            Serial.print(F(" 0"));
        else
            Serial.print(F(" "));
        Serial.print(uid->uidByte[i], HEX);
    }
    Serial.println();

    // SAK
    Serial.print(F("Card SAK: "));
    if(uid->sak < 0x10)
        Serial.print(F("0"));
    Serial.println(uid->sak, HEX);

    // (suggested) PICC type
    PICC_Type piccType = PICC_GetType(uid->sak);
    Serial.print(F("PICC type: "));
    Serial.println(PICC_GetTypeName(piccType));
} // End PICC_DumpDetailsToSerial()

/**
 * Dumps memory contents of a MIFARE Classic PICC.
 * On success the PICC is halted after dumping the data.
 */
void MFRC522::PICC_DumpMifareClassicToSerial(   Uid *uid,           ///< Pointer to Uid struct returned from a successful PICC_Select().
                                                PICC_Type piccType, ///< One of the PICC_Type enums.
                                                MIFARE_Key *key     ///< Key A used for all sectors.
                                            ) {
    byte no_of_sectors = 0;
    switch (piccType) {
        case PICC_TYPE_MIFARE_MINI:
            // Has 5 sectors * 4 blocks/sector * 16 bytes/block = 320 bytes.
            no_of_sectors = 5;
            break;

        case PICC_TYPE_MIFARE_1K:
            // Has 16 sectors * 4 blocks/sector * 16 bytes/block = 1024 bytes.
            no_of_sectors = 16;
            break;

        case PICC_TYPE_MIFARE_4K:
            // Has (32 sectors * 4 blocks/sector + 8 sectors * 16 blocks/sector) * 16 bytes/block = 4096 bytes.
            no_of_sectors = 40;
            break;

        default: // Should not happen. Ignore.
            break;
    }

    // Dump sectors, highest address first.
    if (no_of_sectors) {
        Serial.println(F("Sector Block   0  1  2  3   4  5  6  7   8  9 10 11  12 13 14 15  AccessBits"));
        for (int8_t i = no_of_sectors - 1; i >= 0; i--) {
            PICC_DumpMifareClassicSectorToSerial(uid, key, i);
        }
    }
    PICC_HaltA(); // Halt the PICC before stopping the encrypted session.
    PCD_StopCrypto1();
} // End PICC_DumpMifareClassicToSerial()

/**
 * Dumps memory contents of a sector of a MIFARE Classic PICC.
 * Uses PCD_Authenticate(), MIFARE_Read() and PCD_StopCrypto1.
 * Always uses PICC_CMD_MF_AUTH_KEY_A because only Key A can always read the sector trailer access bits.
 */
void MFRC522::PICC_DumpMifareClassicSectorToSerial(Uid *uid,            ///< Pointer to Uid struct returned from a successful PICC_Select().
                                                    MIFARE_Key *key,    ///< Key A for the sector.
                                                    byte sector         ///< The sector to dump, 0..39.
                                                    ) {
    MFRC522::StatusCode status;
    byte firstBlock;        // Address of lowest address to dump actually last block dumped)
    byte no_of_blocks;      // Number of blocks in sector
    bool isSectorTrailer;   // Set to true while handling the "last" (ie highest address) in the sector.

    // The access bits are stored in a peculiar fashion.
    // There are four groups:
    //      g[3]    Access bits for the sector trailer, block 3 (for sectors 0-31) or block 15 (for sectors 32-39)
    //      g[2]    Access bits for block 2 (for sectors 0-31) or blocks 10-14 (for sectors 32-39)
    //      g[1]    Access bits for block 1 (for sectors 0-31) or blocks 5-9 (for sectors 32-39)
    //      g[0]    Access bits for block 0 (for sectors 0-31) or blocks 0-4 (for sectors 32-39)
    // Each group has access bits [C1 C2 C3]. In this code C1 is MSB and C3 is LSB.
    // The four CX bits are stored together in a nible cx and an inverted nible cx_.
    byte c1, c2, c3;        // Nibbles
    byte c1_, c2_, c3_;     // Inverted nibbles
    bool invertedError;     // True if one of the inverted nibbles did not match
    byte g[4];              // Access bits for each of the four groups.
    byte group;             // 0-3 - active group for access bits
    bool firstInGroup;      // True for the first block dumped in the group

    // Determine position and size of sector.
    if (sector < 32) { // Sectors 0..31 has 4 blocks each
        no_of_blocks = 4;
        firstBlock = sector * no_of_blocks;
    }
    else if (sector < 40) { // Sectors 32-39 has 16 blocks each
        no_of_blocks = 16;
        firstBlock = 128 + (sector - 32) * no_of_blocks;
    }
    else { // Illegal input, no MIFARE Classic PICC has more than 40 sectors.
        return;
    }

    // Dump blocks, highest address first.
    byte byteCount;
    byte buffer[18];
    byte blockAddr;
    isSectorTrailer = true;
    for (int8_t blockOffset = no_of_blocks - 1; blockOffset >= 0; blockOffset--) {
        blockAddr = firstBlock + blockOffset;
        // Sector number - only on first line
        if (isSectorTrailer) {
            if(sector < 10)
                Serial.print(F("   ")); // Pad with spaces
            else
                Serial.print(F("  ")); // Pad with spaces
            Serial.print(sector);
            Serial.print(F("   "));
        }
        else {
            Serial.print(F("       "));
        }
        // Block number
        if(blockAddr < 10)
            Serial.print(F("   ")); // Pad with spaces
        else {
            if(blockAddr < 100)
                Serial.print(F("  ")); // Pad with spaces
            else
                Serial.print(F(" ")); // Pad with spaces
        }
        Serial.print(blockAddr);
        Serial.print(F("  "));
        // Establish encrypted communications before reading the first block
        if (isSectorTrailer) {
            status = PCD_Authenticate(PICC_CMD_MF_AUTH_KEY_A, firstBlock, key, uid);
            if (status != STATUS_OK) {
                Serial.print(F("PCD_Authenticate() failed: "));
                Serial.println(GetStatusCodeName(status));
                return;
            }
        }
        // Read block
        byteCount = sizeof(buffer);
        status = MIFARE_Read(blockAddr, buffer, &byteCount);
        if (status != STATUS_OK) {
            Serial.print(F("MIFARE_Read() failed: "));
            Serial.println(GetStatusCodeName(status));
            continue;
        }
        // Dump data
        for (byte index = 0; index < 16; index++) {
            if(buffer[index] < 0x10)
                Serial.print(F(" 0"));
            else
                Serial.print(F(" "));
            Serial.print(buffer[index], HEX);
            if ((index % 4) == 3) {
                Serial.print(F(" "));
            }
        }
        // Parse sector trailer data
        if (isSectorTrailer) {
            c1  = buffer[7] >> 4;
            c2  = buffer[8] & 0xF;
            c3  = buffer[8] >> 4;
            c1_ = buffer[6] & 0xF;
            c2_ = buffer[6] >> 4;
            c3_ = buffer[7] & 0xF;
            invertedError = (c1 != (~c1_ & 0xF)) || (c2 != (~c2_ & 0xF)) || (c3 != (~c3_ & 0xF));
            g[0] = ((c1 & 1) << 2) | ((c2 & 1) << 1) | ((c3 & 1) << 0);
            g[1] = ((c1 & 2) << 1) | ((c2 & 2) << 0) | ((c3 & 2) >> 1);
            g[2] = ((c1 & 4) << 0) | ((c2 & 4) >> 1) | ((c3 & 4) >> 2);
            g[3] = ((c1 & 8) >> 1) | ((c2 & 8) >> 2) | ((c3 & 8) >> 3);
            isSectorTrailer = false;
        }

        // Which access group is this block in?
        if (no_of_blocks == 4) {
            group = blockOffset;
            firstInGroup = true;
        }
        else {
            group = blockOffset / 5;
            firstInGroup = (group == 3) || (group != (blockOffset + 1) / 5);
        }

        if (firstInGroup) {
            // Print access bits
            Serial.print(F(" [ "));
            Serial.print((g[group] >> 2) & 1, DEC); Serial.print(F(" "));
            Serial.print((g[group] >> 1) & 1, DEC); Serial.print(F(" "));
            Serial.print((g[group] >> 0) & 1, DEC);
            Serial.print(F(" ] "));
            if (invertedError) {
                Serial.print(F(" Inverted access bits did not match! "));
            }
        }

        if (group != 3 && (g[group] == 1 || g[group] == 6)) { // Not a sector trailer, a value block
            long value = (long(buffer[3])<<24) | (long(buffer[2])<<16) | (long(buffer[1])<<8) | long(buffer[0]);
            Serial.print(F(" Value=0x")); Serial.print(value, HEX);
            Serial.print(F(" Adr=0x")); Serial.print(buffer[12], HEX);
        }
        Serial.println();
    }

    return;
} // End PICC_DumpMifareClassicSectorToSerial()

/**
 * Dumps memory contents of a MIFARE Ultralight PICC.
 */
void MFRC522::PICC_DumpMifareUltralightToSerial() {
    MFRC522::StatusCode status;
    byte byteCount;
    byte buffer[18];
    byte i;

    Serial.println(F("Page  0  1  2  3"));
    // Try the mpages of the original Ultralight. Ultralight C has more pages.
    for (byte page = 0; page < 16; page +=4) { // Read returns data for 4 pages at a time.
        // Read pages
        byteCount = sizeof(buffer);
        status = MIFARE_Read(page, buffer, &byteCount);
        if (status != STATUS_OK) {
            Serial.print(F("MIFARE_Read() failed: "));
            Serial.println(GetStatusCodeName(status));
            break;
        }
        // Dump data
        for (byte offset = 0; offset < 4; offset++) {
            i = page + offset;
            if(i < 10)
                Serial.print(F("  ")); // Pad with spaces
            else
                Serial.print(F(" ")); // Pad with spaces
            Serial.print(i);
            Serial.print(F("  "));
            for (byte index = 0; index < 4; index++) {
                i = 4 * offset + index;
                if(buffer[i] < 0x10)
                    Serial.print(F(" 0"));
                else
                    Serial.print(F(" "));
                Serial.print(buffer[i], HEX);
            }
            Serial.println();
        }
    }
} // End PICC_DumpMifareUltralightToSerial()

/**
 * Calculates the bit pattern needed for the specified access bits. In the [C1 C2 C3] tuples C1 is MSB (=4) and C3 is LSB (=1).
 */
void MFRC522::MIFARE_SetAccessBits( byte *accessBitBuffer,  ///< Pointer to byte 6, 7 and 8 in the sector trailer. Bytes [0..2] will be set.
                                    byte g0,                ///< Access bits [C1 C2 C3] for block 0 (for sectors 0-31) or blocks 0-4 (for sectors 32-39)
                                    byte g1,                ///< Access bits C1 C2 C3] for block 1 (for sectors 0-31) or blocks 5-9 (for sectors 32-39)
                                    byte g2,                ///< Access bits C1 C2 C3] for block 2 (for sectors 0-31) or blocks 10-14 (for sectors 32-39)
                                    byte g3                 ///< Access bits C1 C2 C3] for the sector trailer, block 3 (for sectors 0-31) or block 15 (for sectors 32-39)
                                ) {
    byte c1 = ((g3 & 4) << 1) | ((g2 & 4) << 0) | ((g1 & 4) >> 1) | ((g0 & 4) >> 2);
    byte c2 = ((g3 & 2) << 2) | ((g2 & 2) << 1) | ((g1 & 2) << 0) | ((g0 & 2) >> 1);
    byte 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()


/**
 * Performs the "magic sequence" needed to get Chinese UID changeable
 * Mifare cards to allow writing to sector 0, where the card UID is stored.
 *
 * Note that you do not need to have selected the card through REQA or WUPA,
 * this sequence works immediately when the card is in the reader vicinity.
 * This means you can use this method even on "bricked" cards that your reader does
 * not recognise anymore (see MFRC522::MIFARE_UnbrickUidSector).
 *
 * Of course with non-bricked devices, you're free to select them before calling this function.
 */
bool MFRC522::MIFARE_OpenUidBackdoor(bool logErrors) {
    // Magic sequence:
    // > 50 00 57 CD (HALT + CRC)
    // > 40 (7 bits only)
    // < A (4 bits only)
    // > 43
    // < A (4 bits only)
    // Then you can write to sector 0 without authenticating

    PICC_HaltA(); // 50 00 57 CD

    byte cmd = 0x40;
    byte validBits = 7; /* Our command is only 7 bits. After receiving card response,
                          this will contain amount of valid response bits. */
    byte response[32]; // Card's response is written here
    byte received;
    MFRC522::StatusCode status = PCD_TransceiveData(&cmd, (byte)1, response, &received, &validBits, (byte)0, false); // 40
    if(status != STATUS_OK) {
        if(logErrors) {
            Serial.println(F("Card did not respond to 0x40 after HALT command. Are you sure it is a UID changeable one?"));
            Serial.print(F("Error name: "));
            Serial.println(GetStatusCodeName(status));
        }
        return false;
    }
    if (received != 1 || response[0] != 0x0A) {
        if (logErrors) {
            Serial.print(F("Got bad response on backdoor 0x40 command: "));
            Serial.print(response[0], HEX);
            Serial.print(F(" ("));
            Serial.print(validBits);
            Serial.print(F(" valid bits)\r\n"));
        }
        return false;
    }

    cmd = 0x43;
    validBits = 8;
    status = PCD_TransceiveData(&cmd, (byte)1, response, &received, &validBits, (byte)0, false); // 43
    if(status != STATUS_OK) {
        if(logErrors) {
            Serial.println(F("Error in communication at command 0x43, after successfully executing 0x40"));
            Serial.print(F("Error name: "));
            Serial.println(GetStatusCodeName(status));
        }
        return false;
    }
    if (received != 1 || response[0] != 0x0A) {
        if (logErrors) {
            Serial.print(F("Got bad response on backdoor 0x43 command: "));
            Serial.print(response[0], HEX);
            Serial.print(F(" ("));
            Serial.print(validBits);
            Serial.print(F(" valid bits)\r\n"));
        }
        return false;
    }

    // You can now write to sector 0 without authenticating!
    return true;
} // End MIFARE_OpenUidBackdoor()

/**
 * Reads entire block 0, including all manufacturer data, and overwrites
 * that block with the new UID, a freshly calculated BCC, and the original
 * manufacturer data.
 *
 * It assumes a default KEY A of 0xFFFFFFFFFFFF.
 * Make sure to have selected the card before this function is called.
 */
bool MFRC522::MIFARE_SetUid(byte *newUid, byte uidSize, bool logErrors) {

    // UID + BCC byte can not be larger than 16 together
    if (!newUid || !uidSize || uidSize > 15) {
        if (logErrors) {
            Serial.println(F("New UID buffer empty, size 0, or size > 15 given"));
        }
        return false;
    }

    // Authenticate for reading
    MIFARE_Key key = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
    MFRC522::StatusCode status = PCD_Authenticate(MFRC522::PICC_CMD_MF_AUTH_KEY_A, (byte)1, &key, &uid);
    if (status != STATUS_OK) {

        if (status == STATUS_TIMEOUT) {
            // We get a read timeout if no card is selected yet, so let's select one

            // Wake the card up again if sleeping
//            byte atqa_answer[2];
//            byte atqa_size = 2;
//            PICC_WakeupA(atqa_answer, &atqa_size);

            if (!PICC_IsNewCardPresent() || !PICC_ReadCardSerial()) {
                Serial.println(F("No card was previously selected, and none are available. Failed to set UID."));
                return false;
            }

            status = PCD_Authenticate(MFRC522::PICC_CMD_MF_AUTH_KEY_A, (byte)1, &key, &uid);
            if (status != STATUS_OK) {
                // We tried, time to give up
                if (logErrors) {
                    Serial.println(F("Failed to authenticate to card for reading, could not set UID: "));
                    Serial.println(GetStatusCodeName(status));
                }
                return false;
            }
        }
        else {
            if (logErrors) {
                Serial.print(F("PCD_Authenticate() failed: "));
                Serial.println(GetStatusCodeName(status));
            }
            return false;
        }
    }

    // Read block 0
    byte block0_buffer[18];
    byte byteCount = sizeof(block0_buffer);
    status = MIFARE_Read((byte)0, block0_buffer, &byteCount);
    if (status != STATUS_OK) {
        if (logErrors) {
            Serial.print(F("MIFARE_Read() failed: "));
            Serial.println(GetStatusCodeName(status));
            Serial.println(F("Are you sure your KEY A for sector 0 is 0xFFFFFFFFFFFF?"));
        }
        return false;
    }

    // Write new UID to the data we just read, and calculate BCC byte
    byte bcc = 0;
    for (int i = 0; i < uidSize; i++) {
        block0_buffer[i] = newUid[i];
        bcc ^= newUid[i];
    }

    // Write BCC byte to buffer
    block0_buffer[uidSize] = bcc;

    // Stop encrypted traffic so we can send raw bytes
    PCD_StopCrypto1();

    // Activate UID backdoor
    if (!MIFARE_OpenUidBackdoor(logErrors)) {
        if (logErrors) {
            Serial.println(F("Activating the UID backdoor failed."));
        }
        return false;
    }

    // Write modified block 0 back to card
    status = MIFARE_Write((byte)0, block0_buffer, (byte)16);
    if (status != STATUS_OK) {
        if (logErrors) {
            Serial.print(F("MIFARE_Write() failed: "));
            Serial.println(GetStatusCodeName(status));
        }
        return false;
    }

    // Wake the card up again
    byte atqa_answer[2];
    byte atqa_size = 2;
    PICC_WakeupA(atqa_answer, &atqa_size);

    return true;
}

/**
 * Resets entire sector 0 to zeroes, so the card can be read again by readers.
 */
bool MFRC522::MIFARE_UnbrickUidSector(bool logErrors) {
    MIFARE_OpenUidBackdoor(logErrors);

    byte block0_buffer[] = {0x01, 0x02, 0x03, 0x04, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

    // Write modified block 0 back to card
    MFRC522::StatusCode status = MIFARE_Write((byte)0, block0_buffer, (byte)16);
    if (status != STATUS_OK) {
        if (logErrors) {
            Serial.print(F("MIFARE_Write() failed: "));
            Serial.println(GetStatusCodeName(status));
        }
        return false;
    }
    return true;
}

/////////////////////////////////////////////////////////////////////////////////////
// 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.
 *
 * @return bool
 */
bool MFRC522::PICC_IsNewCardPresent() {
    byte bufferATQA[2];
    byte bufferSize = sizeof(bufferATQA);
    MFRC522::StatusCode result = PICC_RequestA(bufferATQA, &bufferSize);
    return (result == STATUS_OK || result == STATUS_COLLISION);
} // End PICC_IsNewCardPresent()

/**
 * Simple wrapper around PICC_Select.
 * Returns true if a UID could be read.
 * Remember to call PICC_IsNewCardPresent(), PICC_RequestA() or PICC_WakeupA() first.
 * The read UID is available in the class variable uid.
 *
 * @return bool
 */
bool MFRC522::PICC_ReadCardSerial() {
    MFRC522::StatusCode result = PICC_Select(&uid);
    return (result == STATUS_OK);
} // End