MFRC522_I2C.cpp

/*
 * MFRC522.cpp - Library to use ARDUINO RFID MODULE KIT 13.56 MHZ WITH TAGS I2C
 * BY AROZCAN MFRC522.cpp - Based on ARDUINO RFID MODULE KIT 13.56 MHZ WITH TAGS
 * SPI Library BY COOQROBOT. NOTE: Please also check the comments in MFRC522.h -
 * they provide useful hints and background information. Released into the
 * public domain. Author: arozcan @
 * https://github.com/arozcan/MFRC522-I2C-Library
 */

#include "MFRC522_I2C.h"
#include <Arduino.h>
#include <Wire.h>

/////////////////////////////////////////////////////////////////////////////////////
// Functions for setting up the Arduino
/////////////////////////////////////////////////////////////////////////////////////

/**
 * Constructor.
 * Prepares the output pins.
 */
MFRC522::MFRC522(byte chipAddress
                 // byte resetPowerDownPin	///< Arduino pin connected to MFRC522's reset
                 // and power down input (Pin 6, NRSTPD, active low)
)
{
    _chipAddress = chipAddress;
    // _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.
)
{
    Wire.beginTransmission(_chipAddress);
    Wire.write(reg);
    Wire.write(value);
    Wire.endTransmission();
}  // 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.
)
{
    Wire.beginTransmission(_chipAddress);
    Wire.write(reg);
    for (byte index = 0; index < count; index++) {
        Wire.write(values[index]);
    }
    Wire.endTransmission();
}  // 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;
    // digitalWrite(_chipSelectPin, LOW);			// Select slave
    Wire.beginTransmission(_chipAddress);
    Wire.write(reg);
    Wire.endTransmission();
    const uint8_t sz = 1;
    Wire.requestFrom(_chipAddress, sz);
    value = Wire.read();
    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;
    }
    byte address = reg;
    byte index   = 0;  // Index in values array.
    Wire.beginTransmission(_chipAddress);
    Wire.write(address);
    Wire.endTransmission();
    Wire.requestFrom(_chipAddress, count);
    while (Wire.available()) {
        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 = Wire.read();
            // 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] = Wire.read();
        }
        index++;
    }
}  // 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.
 */
byte 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

    // 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(50);
    // }
    // 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()

/**
 * 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(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 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.
 */
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;
    }

    // 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.
 */
byte 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.
 */
byte 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 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.
    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];
        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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
byte 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.
 */
byte 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.
 */
byte 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;
    byte 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.
 */
byte 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;
    byte 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 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
    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 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
                }
                byte 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.
 *
 * @return STATUS_OK on success, STATUS_??? otherwise.
 */
byte MFRC522::PICC_HaltA()
{
    byte 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 an 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.
 */
byte 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.
 */
byte 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.
)
{
    byte 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.
 */
byte 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.
)
{
    byte 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.
 */
byte 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.
)
{
    byte 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.
 */
byte 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.
 */
byte 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.
 */
byte 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.
 */
byte 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
)
{
    byte 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.
 */
byte MFRC522::MIFARE_Transfer(byte blockAddr  ///< The block (0-0xff) number.
)
{
    byte 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.
 */
byte MFRC522::MIFARE_GetValue(byte blockAddr, long *value)
{
    byte 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.
 */
byte 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()

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

/**
 * Translates the SAK (Select Acknowledge) to a PICC type.
 *
 * @return PICC_Type
 */
byte MFRC522::PICC_GetType(byte sak  ///< The SAK byte returned from PICC_Select().
)
{
    if (sak & 0x04) {  // UID not complete
        return PICC_TYPE_NOT_COMPLETE;
    }

    switch (sak) {
        case 0x09:
            return PICC_TYPE_MIFARE_MINI;
            break;
        case 0x08:
            return PICC_TYPE_MIFARE_1K;
            break;
        case 0x18:
            return PICC_TYPE_MIFARE_4K;
            break;
        case 0x00:
            return PICC_TYPE_MIFARE_UL;
            break;
        case 0x10:
        case 0x11:
            return PICC_TYPE_MIFARE_PLUS;
            break;
        case 0x01:
            return PICC_TYPE_TNP3XXX;
            break;
        default:
            break;
    }

    if (sak & 0x20) {
        return PICC_TYPE_ISO_14443_4;
    }

    if (sak & 0x40) {
        return PICC_TYPE_ISO_18092;
    }

    return PICC_TYPE_UNKNOWN;
}  // End PICC_GetType()

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

/**
 * 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;

    // 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();

    // PICC type
    byte piccType = PICC_GetType(uid->sak);
    Serial.print(F("PICC type: "));
    Serial.println(PICC_GetTypeName(piccType));

    // Dump contents
    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 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().
                                             byte 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.
)
{
    byte 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()
{
    byte 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] tupples 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;
    byte 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};
    byte 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
    byte 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);
    byte 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()
{
    byte result = PICC_Select(&uid);
    return (result == STATUS_OK);
}  // End PICC_ReadCardSerial()