ADD: @pwpiwi 's latest code from his 'hardnested' branch.

[proxmark3-svn] / armsrc / iso14443a.c

 //-----------------------------------------------------------------------------
// Merlok - June 2011, 2012
// Gerhard de Koning Gans - May 2008
// Hagen Fritsch - June 2010
//
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Routines to support ISO 14443 type A.
//-----------------------------------------------------------------------------

#include "proxmark3.h"
#include "apps.h"
#include "util.h"
#include "string.h"
#include "cmd.h"
#include "iso14443crc.h"
#include "iso14443a.h"
#include "crapto1.h"
#include "mifareutil.h"
#include "BigBuf.h"
#include "parity.h"

static uint32_t iso14a_timeout;
int rsamples = 0;
uint8_t trigger = 0;
// the block number for the ISO14443-4 PCB
static uint8_t iso14_pcb_blocknum = 0;

//
// ISO14443 timing:
//
// minimum time between the start bits of consecutive transfers from reader to tag: 7000 carrier (13.56Mhz) cycles
#define REQUEST_GUARD_TIME (7000/16 + 1)
// minimum time between last modulation of tag and next start bit from reader to tag: 1172 carrier cycles 
#define FRAME_DELAY_TIME_PICC_TO_PCD (1172/16 + 1) 
// bool LastCommandWasRequest = FALSE;

//
// Total delays including SSC-Transfers between ARM and FPGA. These are in carrier clock cycles (1/13,56MHz)
//
// When the PM acts as reader and is receiving tag data, it takes
// 3 ticks delay in the AD converter
// 16 ticks until the modulation detector completes and sets curbit
// 8 ticks until bit_to_arm is assigned from curbit
// 8*16 ticks for the transfer from FPGA to ARM
// 4*16 ticks until we measure the time
// - 8*16 ticks because we measure the time of the previous transfer 
#define DELAY_AIR2ARM_AS_READER (3 + 16 + 8 + 8*16 + 4*16 - 8*16) 

// When the PM acts as a reader and is sending, it takes
// 4*16 ticks until we can write data to the sending hold register
// 8*16 ticks until the SHR is transferred to the Sending Shift Register
// 8 ticks until the first transfer starts
// 8 ticks later the FPGA samples the data
// 1 tick to assign mod_sig_coil
#define DELAY_ARM2AIR_AS_READER (4*16 + 8*16 + 8 + 8 + 1)

// When the PM acts as tag and is receiving it takes
// 2 ticks delay in the RF part (for the first falling edge),
// 3 ticks for the A/D conversion,
// 8 ticks on average until the start of the SSC transfer,
// 8 ticks until the SSC samples the first data
// 7*16 ticks to complete the transfer from FPGA to ARM
// 8 ticks until the next ssp_clk rising edge
// 4*16 ticks until we measure the time 
// - 8*16 ticks because we measure the time of the previous transfer 
#define DELAY_AIR2ARM_AS_TAG (2 + 3 + 8 + 8 + 7*16 + 8 + 4*16 - 8*16)
 
// The FPGA will report its internal sending delay in
uint16_t FpgaSendQueueDelay;
// the 5 first bits are the number of bits buffered in mod_sig_buf
// the last three bits are the remaining ticks/2 after the mod_sig_buf shift
#define DELAY_FPGA_QUEUE (FpgaSendQueueDelay<<1)

// When the PM acts as tag and is sending, it takes
// 4*16 ticks until we can write data to the sending hold register
// 8*16 ticks until the SHR is transferred to the Sending Shift Register
// 8 ticks until the first transfer starts
// 8 ticks later the FPGA samples the data
// + a varying number of ticks in the FPGA Delay Queue (mod_sig_buf)
// + 1 tick to assign mod_sig_coil
#define DELAY_ARM2AIR_AS_TAG (4*16 + 8*16 + 8 + 8 + DELAY_FPGA_QUEUE + 1)

// When the PM acts as sniffer and is receiving tag data, it takes
// 3 ticks A/D conversion
// 14 ticks to complete the modulation detection
// 8 ticks (on average) until the result is stored in to_arm
// + the delays in transferring data - which is the same for
// sniffing reader and tag data and therefore not relevant
#define DELAY_TAG_AIR2ARM_AS_SNIFFER (3 + 14 + 8) 
 
// When the PM acts as sniffer and is receiving reader data, it takes
// 2 ticks delay in analogue RF receiver (for the falling edge of the 
// start bit, which marks the start of the communication)
// 3 ticks A/D conversion
// 8 ticks on average until the data is stored in to_arm.
// + the delays in transferring data - which is the same for
// sniffing reader and tag data and therefore not relevant
#define DELAY_READER_AIR2ARM_AS_SNIFFER (2 + 3 + 8) 

//variables used for timing purposes:
//these are in ssp_clk cycles:
static uint32_t NextTransferTime;
static uint32_t LastTimeProxToAirStart;
static uint32_t LastProxToAirDuration;



// CARD TO READER - manchester
// Sequence D: 11110000 modulation with subcarrier during first half
// Sequence E: 00001111 modulation with subcarrier during second half
// Sequence F: 00000000 no modulation with subcarrier
// READER TO CARD - miller
// Sequence X: 00001100 drop after half a period
// Sequence Y: 00000000 no drop
// Sequence Z: 11000000 drop at start
#define SEC_D 0xf0
#define SEC_E 0x0f
#define SEC_F 0x00
#define SEC_X 0x0c
#define SEC_Y 0x00
#define SEC_Z 0xc0

void iso14a_set_trigger(bool enable) {
        trigger = enable;
}


void iso14a_set_timeout(uint32_t timeout) {
        iso14a_timeout = timeout;
        if(MF_DBGLEVEL >= 3) Dbprintf("ISO14443A Timeout set to %ld (%dms)", iso14a_timeout, iso14a_timeout / 106);
}


void iso14a_set_ATS_timeout(uint8_t *ats) {

        uint8_t tb1;
        uint8_t fwi; 
        uint32_t fwt;
        
        if (ats[0] > 1) {                                                       // there is a format byte T0
                if ((ats[1] & 0x20) == 0x20) {                  // there is an interface byte TB(1)
                        if ((ats[1] & 0x10) == 0x10) {          // there is an interface byte TA(1) preceding TB(1)
                                tb1 = ats[3];
                        } else {
                                tb1 = ats[2];
                        }
                        fwi = (tb1 & 0xf0) >> 4;                        // frame waiting indicator (FWI)
                        fwt = 256 * 16 * (1 << fwi);            // frame waiting time (FWT) in 1/fc
                        
                        iso14a_set_timeout(fwt/(8*16));
                }
        }
}


//-----------------------------------------------------------------------------
// Generate the parity value for a byte sequence
//
//-----------------------------------------------------------------------------
void GetParity(const uint8_t *pbtCmd, uint16_t iLen, uint8_t *par)
{
        uint16_t paritybit_cnt = 0;
        uint16_t paritybyte_cnt = 0;
        uint8_t parityBits = 0;

        for (uint16_t i = 0; i < iLen; i++) {
                // Generate the parity bits
                parityBits |= ((oddparity8(pbtCmd[i])) << (7-paritybit_cnt));
                if (paritybit_cnt == 7) {
                        par[paritybyte_cnt] = parityBits;       // save 8 Bits parity
                        parityBits = 0;                                         // and advance to next Parity Byte
                        paritybyte_cnt++;
                        paritybit_cnt = 0;
                } else {
                        paritybit_cnt++;
                }
        }

        // save remaining parity bits
        par[paritybyte_cnt] = parityBits;
        
}

void AppendCrc14443a(uint8_t* data, int len)
{
        ComputeCrc14443(CRC_14443_A,data,len,data+len,data+len+1);
}

void AppendCrc14443b(uint8_t* data, int len)
{
        ComputeCrc14443(CRC_14443_B,data,len,data+len,data+len+1);
}


//=============================================================================
// ISO 14443 Type A - Miller decoder
//=============================================================================
// Basics:
// This decoder is used when the PM3 acts as a tag.
// The reader will generate "pauses" by temporarily switching of the field. 
// At the PM3 antenna we will therefore measure a modulated antenna voltage. 
// The FPGA does a comparison with a threshold and would deliver e.g.:
// ........  1 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1  .......
// The Miller decoder needs to identify the following sequences:
// 2 (or 3) ticks pause followed by 6 (or 5) ticks unmodulated:         pause at beginning - Sequence Z ("start of communication" or a "0")
// 8 ticks without a modulation:                                                                        no pause - Sequence Y (a "0" or "end of communication" or "no information")
// 4 ticks unmodulated followed by 2 (or 3) ticks pause:                        pause in second half - Sequence X (a "1")
// Note 1: the bitstream may start at any time. We therefore need to sync.
// Note 2: the interpretation of Sequence Y and Z depends on the preceding sequence.
//-----------------------------------------------------------------------------
static tUart Uart;

// Lookup-Table to decide if 4 raw bits are a modulation.
// We accept the following:
// 0001  -   a 3 tick wide pause
// 0011  -   a 2 tick wide pause, or a three tick wide pause shifted left
// 0111  -   a 2 tick wide pause shifted left
// 1001  -   a 2 tick wide pause shifted right
const bool Mod_Miller_LUT[] = {
        FALSE,  TRUE, FALSE, TRUE,  FALSE, FALSE, FALSE, TRUE,
        FALSE,  TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE
};
#define IsMillerModulationNibble1(b) (Mod_Miller_LUT[(b & 0x000000F0) >> 4])
#define IsMillerModulationNibble2(b) (Mod_Miller_LUT[(b & 0x0000000F)])

void UartReset()
{
        Uart.state = STATE_UNSYNCD;
        Uart.bitCount = 0;
        Uart.len = 0;                                           // number of decoded data bytes
        Uart.parityLen = 0;                                     // number of decoded parity bytes
        Uart.shiftReg = 0;                                      // shiftreg to hold decoded data bits
        Uart.parityBits = 0;                            // holds 8 parity bits
        Uart.startTime = 0;
        Uart.endTime = 0;
        
        Uart.byteCntMax = 0;
        Uart.posCnt = 0;
        Uart.syncBit = 9999;
}

void UartInit(uint8_t *data, uint8_t *parity)
{
        Uart.output = data;
        Uart.parity = parity;
        Uart.fourBits = 0x00000000;                     // clear the buffer for 4 Bits
        UartReset();
}

// use parameter non_real_time to provide a timestamp. Set to 0 if the decoder should measure real time
static RAMFUNC bool MillerDecoding(uint8_t bit, uint32_t non_real_time)
{

        Uart.fourBits = (Uart.fourBits << 8) | bit;
        
        if (Uart.state == STATE_UNSYNCD) {                                                                                      // not yet synced
        
                Uart.syncBit = 9999;                                                                                                    // not set
                
                // 00x11111 2|3 ticks pause followed by 6|5 ticks unmodulated           Sequence Z (a "0" or "start of communication")
                // 11111111 8 ticks unmodulation                                                                        Sequence Y (a "0" or "end of communication" or "no information")
                // 111100x1 4 ticks unmodulated followed by 2|3 ticks pause                     Sequence X (a "1")

                // The start bit is one ore more Sequence Y followed by a Sequence Z (... 11111111 00x11111). We need to distinguish from
                // Sequence X followed by Sequence Y followed by Sequence Z     (111100x1 11111111 00x11111)
                // we therefore look for a ...xx1111 11111111 00x11111xxxxxx... pattern 
                // (12 '1's followed by 2 '0's, eventually followed by another '0', followed by 5 '1's)
                //
#define ISO14443A_STARTBIT_MASK         0x07FFEF80              // mask is    00001111 11111111 1110 1111 10000000
#define ISO14443A_STARTBIT_PATTERN      0x07FF8F80              // pattern is 00001111 11111111 1000 1111 10000000

                if              ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 0)) == ISO14443A_STARTBIT_PATTERN >> 0) Uart.syncBit = 7;
                else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 1)) == ISO14443A_STARTBIT_PATTERN >> 1) Uart.syncBit = 6;
                else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 2)) == ISO14443A_STARTBIT_PATTERN >> 2) Uart.syncBit = 5;
                else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 3)) == ISO14443A_STARTBIT_PATTERN >> 3) Uart.syncBit = 4;
                else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 4)) == ISO14443A_STARTBIT_PATTERN >> 4) Uart.syncBit = 3;
                else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 5)) == ISO14443A_STARTBIT_PATTERN >> 5) Uart.syncBit = 2;
                else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 6)) == ISO14443A_STARTBIT_PATTERN >> 6) Uart.syncBit = 1;
                else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 7)) == ISO14443A_STARTBIT_PATTERN >> 7) Uart.syncBit = 0;

                if (Uart.syncBit != 9999) {                                                                                             // found a sync bit
                                Uart.startTime = non_real_time?non_real_time:(GetCountSspClk() & 0xfffffff8);
                                Uart.startTime -= Uart.syncBit;
                                Uart.endTime = Uart.startTime;
                                Uart.state = STATE_START_OF_COMMUNICATION;
                        }

        } else {

                if (IsMillerModulationNibble1(Uart.fourBits >> Uart.syncBit)) {                 
                        if (IsMillerModulationNibble2(Uart.fourBits >> Uart.syncBit)) {         // Modulation in both halves - error
                                UartReset();
                        } else {                                                                                                                        // Modulation in first half = Sequence Z = logic "0"
                                if (Uart.state == STATE_MILLER_X) {                                                             // error - must not follow after X
                                        UartReset();
                                } else {
                                        Uart.bitCount++;
                                        Uart.shiftReg = (Uart.shiftReg >> 1);                                           // add a 0 to the shiftreg
                                        Uart.state = STATE_MILLER_Z;
                                        Uart.endTime = Uart.startTime + 8*(9*Uart.len + Uart.bitCount + 1) - 6;
                                        if(Uart.bitCount >= 9) {                                                                        // if we decoded a full byte (including parity)
                                                Uart.output[Uart.len++] = (Uart.shiftReg & 0xff);
                                                Uart.parityBits <<= 1;                                                                  // make room for the parity bit
                                                Uart.parityBits |= ((Uart.shiftReg >> 8) & 0x01);               // store parity bit
                                                Uart.bitCount = 0;
                                                Uart.shiftReg = 0;
                                                if((Uart.len&0x0007) == 0) {                                                    // every 8 data bytes
                                                        Uart.parity[Uart.parityLen++] = Uart.parityBits;        // store 8 parity bits
                                                        Uart.parityBits = 0;
                                                }
                                        }
                                }
                        }
                } else {
                        if (IsMillerModulationNibble2(Uart.fourBits >> Uart.syncBit)) {         // Modulation second half = Sequence X = logic "1"
                                Uart.bitCount++;
                                Uart.shiftReg = (Uart.shiftReg >> 1) | 0x100;                                   // add a 1 to the shiftreg
                                Uart.state = STATE_MILLER_X;
                                Uart.endTime = Uart.startTime + 8*(9*Uart.len + Uart.bitCount + 1) - 2;
                                if(Uart.bitCount >= 9) {                                                                                // if we decoded a full byte (including parity)
                                        Uart.output[Uart.len++] = (Uart.shiftReg & 0xff);
                                        Uart.parityBits <<= 1;                                                                          // make room for the new parity bit
                                        Uart.parityBits |= ((Uart.shiftReg >> 8) & 0x01);                       // store parity bit
                                        Uart.bitCount = 0;
                                        Uart.shiftReg = 0;
                                        if ((Uart.len&0x0007) == 0) {                                                           // every 8 data bytes
                                                Uart.parity[Uart.parityLen++] = Uart.parityBits;                // store 8 parity bits
                                                Uart.parityBits = 0;
                                        }
                                }
                        } else {                                                                                                                        // no modulation in both halves - Sequence Y
                                if (Uart.state == STATE_MILLER_Z || Uart.state == STATE_MILLER_Y) {     // Y after logic "0" - End of Communication
                                        Uart.state = STATE_UNSYNCD;
                                        Uart.bitCount--;                                                                                        // last "0" was part of EOC sequence
                                        Uart.shiftReg <<= 1;                                                                            // drop it
                                        if(Uart.bitCount > 0) {                                                                         // if we decoded some bits
                                                Uart.shiftReg >>= (9 - Uart.bitCount);                                  // right align them
                                                Uart.output[Uart.len++] = (Uart.shiftReg & 0xff);               // add last byte to the output
                                                Uart.parityBits <<= 1;                                                                  // add a (void) parity bit
                                                Uart.parityBits <<= (8 - (Uart.len&0x0007));                    // left align parity bits
                                                Uart.parity[Uart.parityLen++] = Uart.parityBits;                // and store it
                                                return TRUE;
                                        } else if (Uart.len & 0x0007) {                                                         // there are some parity bits to store
                                                Uart.parityBits <<= (8 - (Uart.len&0x0007));                    // left align remaining parity bits
                                                Uart.parity[Uart.parityLen++] = Uart.parityBits;                // and store them
                                        }
                                        if (Uart.len) {
                                                return TRUE;                                                                                    // we are finished with decoding the raw data sequence
                                        } else {
                                                UartReset();                                                                                    // Nothing received - start over
                                        }
                                }
                                if (Uart.state == STATE_START_OF_COMMUNICATION) {                               // error - must not follow directly after SOC
                                        UartReset();
                                } else {                                                                                                                // a logic "0"
                                        Uart.bitCount++;
                                        Uart.shiftReg = (Uart.shiftReg >> 1);                                           // add a 0 to the shiftreg
                                        Uart.state = STATE_MILLER_Y;
                                        if(Uart.bitCount >= 9) {                                                                        // if we decoded a full byte (including parity)
                                                Uart.output[Uart.len++] = (Uart.shiftReg & 0xff);
                                                Uart.parityBits <<= 1;                                                                  // make room for the parity bit
                                                Uart.parityBits |= ((Uart.shiftReg >> 8) & 0x01);               // store parity bit
                                                Uart.bitCount = 0;
                                                Uart.shiftReg = 0;
                                                if ((Uart.len&0x0007) == 0) {                                                   // every 8 data bytes
                                                        Uart.parity[Uart.parityLen++] = Uart.parityBits;        // store 8 parity bits
                                                        Uart.parityBits = 0;
                                                }
                                        }
                                }
                        }
                }
                        
        } 

    return FALSE;       // not finished yet, need more data
}



//=============================================================================
// ISO 14443 Type A - Manchester decoder
//=============================================================================
// Basics:
// This decoder is used when the PM3 acts as a reader.
// The tag will modulate the reader field by asserting different loads to it. As a consequence, the voltage
// at the reader antenna will be modulated as well. The FPGA detects the modulation for us and would deliver e.g. the following:
// ........ 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .......
// The Manchester decoder needs to identify the following sequences:
// 4 ticks modulated followed by 4 ticks unmodulated:   Sequence D = 1 (also used as "start of communication")
// 4 ticks unmodulated followed by 4 ticks modulated:   Sequence E = 0
// 8 ticks unmodulated:                                                                 Sequence F = end of communication
// 8 ticks modulated:                                                                   A collision. Save the collision position and treat as Sequence D
// Note 1: the bitstream may start at any time. We therefore need to sync.
// Note 2: parameter offset is used to determine the position of the parity bits (required for the anticollision command only)
static tDemod Demod;

// Lookup-Table to decide if 4 raw bits are a modulation.
// We accept three or four "1" in any position
const bool Mod_Manchester_LUT[] = {
        FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, TRUE,
        FALSE, FALSE, FALSE, TRUE,  FALSE, TRUE,  TRUE,  TRUE
};

#define IsManchesterModulationNibble1(b) (Mod_Manchester_LUT[(b & 0x00F0) >> 4])
#define IsManchesterModulationNibble2(b) (Mod_Manchester_LUT[(b & 0x000F)])


void DemodReset()
{
        Demod.state = DEMOD_UNSYNCD;
        Demod.len = 0;                                          // number of decoded data bytes
        Demod.parityLen = 0;
        Demod.shiftReg = 0;                                     // shiftreg to hold decoded data bits
        Demod.parityBits = 0;                           // 
        Demod.collisionPos = 0;                         // Position of collision bit
        Demod.twoBits = 0xffff;                         // buffer for 2 Bits
        Demod.highCnt = 0;
        Demod.startTime = 0;
        Demod.endTime = 0;
        
        //
        Demod.bitCount = 0;
        Demod.syncBit = 0xFFFF;
        Demod.samples = 0;
}

void DemodInit(uint8_t *data, uint8_t *parity)
{
        Demod.output = data;
        Demod.parity = parity;
        DemodReset();
}

// use parameter non_real_time to provide a timestamp. Set to 0 if the decoder should measure real time
static RAMFUNC int ManchesterDecoding(uint8_t bit, uint16_t offset, uint32_t non_real_time)
{

        Demod.twoBits = (Demod.twoBits << 8) | bit;
        
        if (Demod.state == DEMOD_UNSYNCD) {

                if (Demod.highCnt < 2) {                                                                                        // wait for a stable unmodulated signal
                        if (Demod.twoBits == 0x0000) {
                                Demod.highCnt++;
                        } else {
                                Demod.highCnt = 0;
                        }
                } else {
                        Demod.syncBit = 0xFFFF;                 // not set
                        if              ((Demod.twoBits & 0x7700) == 0x7000) Demod.syncBit = 7; 
                        else if ((Demod.twoBits & 0x3B80) == 0x3800) Demod.syncBit = 6;
                        else if ((Demod.twoBits & 0x1DC0) == 0x1C00) Demod.syncBit = 5;
                        else if ((Demod.twoBits & 0x0EE0) == 0x0E00) Demod.syncBit = 4;
                        else if ((Demod.twoBits & 0x0770) == 0x0700) Demod.syncBit = 3;
                        else if ((Demod.twoBits & 0x03B8) == 0x0380) Demod.syncBit = 2;
                        else if ((Demod.twoBits & 0x01DC) == 0x01C0) Demod.syncBit = 1;
                        else if ((Demod.twoBits & 0x00EE) == 0x00E0) Demod.syncBit = 0;
                        if (Demod.syncBit != 0xFFFF) {
                                Demod.startTime = non_real_time?non_real_time:(GetCountSspClk() & 0xfffffff8);
                                Demod.startTime -= Demod.syncBit;
                                Demod.bitCount = offset;                        // number of decoded data bits
                                Demod.state = DEMOD_MANCHESTER_DATA;
                        }
                }

        } else {

                if (IsManchesterModulationNibble1(Demod.twoBits >> Demod.syncBit)) {            // modulation in first half
                        if (IsManchesterModulationNibble2(Demod.twoBits >> Demod.syncBit)) {    // ... and in second half = collision
                                if (!Demod.collisionPos) {
                                        Demod.collisionPos = (Demod.len << 3) + Demod.bitCount;
                                }
                        }                                                                                                                       // modulation in first half only - Sequence D = 1
                        Demod.bitCount++;
                        Demod.shiftReg = (Demod.shiftReg >> 1) | 0x100;                         // in both cases, add a 1 to the shiftreg
                        if(Demod.bitCount == 9) {                                                                       // if we decoded a full byte (including parity)
                                Demod.output[Demod.len++] = (Demod.shiftReg & 0xff);
                                Demod.parityBits <<= 1;                                                                 // make room for the parity bit
                                Demod.parityBits |= ((Demod.shiftReg >> 8) & 0x01);     // store parity bit
                                Demod.bitCount = 0;
                                Demod.shiftReg = 0;
                                if((Demod.len&0x0007) == 0) {                                                   // every 8 data bytes
                                        Demod.parity[Demod.parityLen++] = Demod.parityBits;     // store 8 parity bits
                                        Demod.parityBits = 0;
                                }
                        }
                        Demod.endTime = Demod.startTime + 8*(9*Demod.len + Demod.bitCount + 1) - 4;
                } else {                                                                                                                // no modulation in first half
                        if (IsManchesterModulationNibble2(Demod.twoBits >> Demod.syncBit)) {    // and modulation in second half = Sequence E = 0
                                Demod.bitCount++;
                                Demod.shiftReg = (Demod.shiftReg >> 1);                                 // add a 0 to the shiftreg
                                if(Demod.bitCount >= 9) {                                                               // if we decoded a full byte (including parity)
                                        Demod.output[Demod.len++] = (Demod.shiftReg & 0xff);
                                        Demod.parityBits <<= 1;                                                         // make room for the new parity bit
                                        Demod.parityBits |= ((Demod.shiftReg >> 8) & 0x01); // store parity bit
                                        Demod.bitCount = 0;
                                        Demod.shiftReg = 0;
                                        if ((Demod.len&0x0007) == 0) {                                          // every 8 data bytes
                                                Demod.parity[Demod.parityLen++] = Demod.parityBits;     // store 8 parity bits1
                                                Demod.parityBits = 0;
                                        }
                                }
                                Demod.endTime = Demod.startTime + 8*(9*Demod.len + Demod.bitCount + 1);
                        } else {                                                                                                        // no modulation in both halves - End of communication
                                if(Demod.bitCount > 0) {                                                                // there are some remaining data bits
                                        Demod.shiftReg >>= (9 - Demod.bitCount);                        // right align the decoded bits
                                        Demod.output[Demod.len++] = Demod.shiftReg & 0xff;      // and add them to the output
                                        Demod.parityBits <<= 1;                                                         // add a (void) parity bit
                                        Demod.parityBits <<= (8 - (Demod.len&0x0007));          // left align remaining parity bits
                                        Demod.parity[Demod.parityLen++] = Demod.parityBits;     // and store them
                                        return TRUE;
                                } else if (Demod.len & 0x0007) {                                                // there are some parity bits to store
                                        Demod.parityBits <<= (8 - (Demod.len&0x0007));          // left align remaining parity bits
                                        Demod.parity[Demod.parityLen++] = Demod.parityBits;     // and store them
                                }
                                if (Demod.len) {
                                        return TRUE;                                                                            // we are finished with decoding the raw data sequence
                                } else {                                                                                                // nothing received. Start over
                                        DemodReset();
                                }
                        }
                }
        } 
    return FALSE;       // not finished yet, need more data
}

//=============================================================================
// Finally, a `sniffer' for ISO 14443 Type A
// Both sides of communication!
//=============================================================================

//-----------------------------------------------------------------------------
// Record the sequence of commands sent by the reader to the tag, with
// triggering so that we start recording at the point that the tag is moved
// near the reader.
//-----------------------------------------------------------------------------
void RAMFUNC SniffIso14443a(uint8_t param) {
        // param:
        // bit 0 - trigger from first card answer
        // bit 1 - trigger from first reader 7-bit request
        LEDsoff();

        iso14443a_setup(FPGA_HF_ISO14443A_SNIFFER);
        
        // Allocate memory from BigBuf for some buffers
        // free all previous allocations first
        BigBuf_free();
        
        // init trace buffer
        clear_trace();
        set_tracing(TRUE);
        
        // The command (reader -> tag) that we're receiving.
        uint8_t *receivedCmd = BigBuf_malloc(MAX_FRAME_SIZE);
        uint8_t *receivedCmdPar = BigBuf_malloc(MAX_PARITY_SIZE);
        
        // The response (tag -> reader) that we're receiving.
        uint8_t *receivedResponse = BigBuf_malloc(MAX_FRAME_SIZE);
        uint8_t *receivedResponsePar = BigBuf_malloc(MAX_PARITY_SIZE);
        
        // The DMA buffer, used to stream samples from the FPGA
        uint8_t *dmaBuf = BigBuf_malloc(DMA_BUFFER_SIZE);

        uint8_t *data = dmaBuf;
        uint8_t previous_data = 0;
        int maxDataLen = 0;
        int dataLen = 0;
        bool TagIsActive = FALSE;
        bool ReaderIsActive = FALSE;
        
        // Set up the demodulator for tag -> reader responses.
        DemodInit(receivedResponse, receivedResponsePar);
        
        // Set up the demodulator for the reader -> tag commands
        UartInit(receivedCmd, receivedCmdPar);
        
        // Setup and start DMA.
        FpgaSetupSscDma((uint8_t *)dmaBuf, DMA_BUFFER_SIZE);
        
        // We won't start recording the frames that we acquire until we trigger;
        // a good trigger condition to get started is probably when we see a
        // response from the tag.
        // triggered == FALSE -- to wait first for card
        bool triggered = !(param & 0x03); 
        
        // And now we loop, receiving samples.
        for(uint32_t rsamples = 0; TRUE; ) {

                if(BUTTON_PRESS()) {
                        DbpString("cancelled by button");
                        break;
                }

                LED_A_ON();
                WDT_HIT();

                int register readBufDataP = data - dmaBuf;
                int register dmaBufDataP = DMA_BUFFER_SIZE - AT91C_BASE_PDC_SSC->PDC_RCR;
                if (readBufDataP <= dmaBufDataP){
                        dataLen = dmaBufDataP - readBufDataP;
                } else {
                        dataLen = DMA_BUFFER_SIZE - readBufDataP + dmaBufDataP;
                }
                // test for length of buffer
                if(dataLen > maxDataLen) {
                        maxDataLen = dataLen;
                        if(dataLen > (9 * DMA_BUFFER_SIZE / 10)) {
                                Dbprintf("blew circular buffer! dataLen=%d", dataLen);
                                break;
                        }
                }
                if(dataLen < 1) continue;

                // primary buffer was stopped( <-- we lost data!
                if (!AT91C_BASE_PDC_SSC->PDC_RCR) {
                        AT91C_BASE_PDC_SSC->PDC_RPR = (uint32_t) dmaBuf;
                        AT91C_BASE_PDC_SSC->PDC_RCR = DMA_BUFFER_SIZE;
                        Dbprintf("RxEmpty ERROR!!! data length:%d", dataLen); // temporary
                }
                // secondary buffer sets as primary, secondary buffer was stopped
                if (!AT91C_BASE_PDC_SSC->PDC_RNCR) {
                        AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) dmaBuf;
                        AT91C_BASE_PDC_SSC->PDC_RNCR = DMA_BUFFER_SIZE;
                }

                LED_A_OFF();
                
                if (rsamples & 0x01) {                          // Need two samples to feed Miller and Manchester-Decoder

                        if(!TagIsActive) {              // no need to try decoding reader data if the tag is sending
                                uint8_t readerdata = (previous_data & 0xF0) | (*data >> 4);
                                if (MillerDecoding(readerdata, (rsamples-1)*4)) {
                                        LED_C_ON();

                                        // check - if there is a short 7bit request from reader
                                        if ((!triggered) && (param & 0x02) && (Uart.len == 1) && (Uart.bitCount == 7)) triggered = TRUE;

                                        if(triggered) {
                                                if (!LogTrace(receivedCmd, 
                                                                                Uart.len, 
                                                                                Uart.startTime*16 - DELAY_READER_AIR2ARM_AS_SNIFFER,
                                                                                Uart.endTime*16 - DELAY_READER_AIR2ARM_AS_SNIFFER,
                                                                                Uart.parity, 
                                                                                TRUE)) break;
                                        }
                                        /* And ready to receive another command. */
                                        UartReset();
                                        /* And also reset the demod code, which might have been */
                                        /* false-triggered by the commands from the reader. */
                                        DemodReset();
                                        LED_B_OFF();
                                }
                                ReaderIsActive = (Uart.state != STATE_UNSYNCD);
                        }

                        if(!ReaderIsActive) {           // no need to try decoding tag data if the reader is sending - and we cannot afford the time
                                uint8_t tagdata = (previous_data << 4) | (*data & 0x0F);
                                if(ManchesterDecoding(tagdata, 0, (rsamples-1)*4)) {
                                        LED_B_ON();

                                        if (!LogTrace(receivedResponse, 
                                                                        Demod.len, 
                                                                        Demod.startTime*16 - DELAY_TAG_AIR2ARM_AS_SNIFFER, 
                                                                        Demod.endTime*16 - DELAY_TAG_AIR2ARM_AS_SNIFFER,
                                                                        Demod.parity,
                                                                        FALSE)) break;

                                        if ((!triggered) && (param & 0x01)) triggered = TRUE;

                                        // And ready to receive another response.
                                        DemodReset();
                                        // And reset the Miller decoder including itS (now outdated) input buffer
                                        UartInit(receivedCmd, receivedCmdPar);

                                        LED_C_OFF();
                                } 
                                TagIsActive = (Demod.state != DEMOD_UNSYNCD);
                        }
                }

                previous_data = *data;
                rsamples++;
                data++;
                if(data == dmaBuf + DMA_BUFFER_SIZE) {
                        data = dmaBuf;
                }
        } // main cycle

        FpgaDisableSscDma();
        LEDsoff();

        Dbprintf("maxDataLen=%d, Uart.state=%x, Uart.len=%d", maxDataLen, Uart.state, Uart.len);
        Dbprintf("traceLen=%d, Uart.output[0]=%08x", BigBuf_get_traceLen(), (uint32_t)Uart.output[0]);
        
        set_tracing(FALSE);     
}

//-----------------------------------------------------------------------------
// Prepare tag messages
//-----------------------------------------------------------------------------
static void CodeIso14443aAsTagPar(const uint8_t *cmd, uint16_t len, uint8_t *parity)
{
        ToSendReset();

        // Correction bit, might be removed when not needed
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(1);  // 1
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        
        // Send startbit
        ToSend[++ToSendMax] = SEC_D;
        LastProxToAirDuration = 8 * ToSendMax - 4;

        for(uint16_t i = 0; i < len; i++) {
                uint8_t b = cmd[i];

                // Data bits
                for(uint16_t j = 0; j < 8; j++) {
                        if(b & 1) {
                                ToSend[++ToSendMax] = SEC_D;
                        } else {
                                ToSend[++ToSendMax] = SEC_E;
                        }
                        b >>= 1;
                }

                // Get the parity bit
                if (parity[i>>3] & (0x80>>(i&0x0007))) {
                        ToSend[++ToSendMax] = SEC_D;
                        LastProxToAirDuration = 8 * ToSendMax - 4;
                } else {
                        ToSend[++ToSendMax] = SEC_E;
                        LastProxToAirDuration = 8 * ToSendMax;
                }
        }

        // Send stopbit
        ToSend[++ToSendMax] = SEC_F;

        // Convert from last byte pos to length
        ToSendMax++;
}

static void CodeIso14443aAsTag(const uint8_t *cmd, uint16_t len)
{
        uint8_t par[MAX_PARITY_SIZE];
        
        GetParity(cmd, len, par);
        CodeIso14443aAsTagPar(cmd, len, par);
}


static void Code4bitAnswerAsTag(uint8_t cmd)
{
        int i;

        ToSendReset();

        // Correction bit, might be removed when not needed
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(1);  // 1
        ToSendStuffBit(0);
        ToSendStuffBit(0);
        ToSendStuffBit(0);

        // Send startbit
        ToSend[++ToSendMax] = SEC_D;

        uint8_t b = cmd;
        for(i = 0; i < 4; i++) {
                if(b & 1) {
                        ToSend[++ToSendMax] = SEC_D;
                        LastProxToAirDuration = 8 * ToSendMax - 4;
                } else {
                        ToSend[++ToSendMax] = SEC_E;
                        LastProxToAirDuration = 8 * ToSendMax;
                }
                b >>= 1;
        }

        // Send stopbit
        ToSend[++ToSendMax] = SEC_F;

        // Convert from last byte pos to length
        ToSendMax++;
}

//-----------------------------------------------------------------------------
// Wait for commands from reader
// Stop when button is pressed
// Or return TRUE when command is captured
//-----------------------------------------------------------------------------
static int GetIso14443aCommandFromReader(uint8_t *received, uint8_t *parity, int *len)
{
    // Set FPGA mode to "simulated ISO 14443 tag", no modulation (listen
    // only, since we are receiving, not transmitting).
    // Signal field is off with the appropriate LED
    LED_D_OFF();
    FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_TAGSIM_LISTEN);

    // Now run a `software UART' on the stream of incoming samples.
        UartInit(received, parity);

        // clear RXRDY:
    uint8_t b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;

    for(;;) {
        WDT_HIT();

        if(BUTTON_PRESS()) return FALSE;
                
        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
            b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        if(MillerDecoding(b, 0)) {
                                *len = Uart.len;
                                return TRUE;
                        }
                }
    }
}

static int EmSendCmd14443aRaw(uint8_t *resp, uint16_t respLen, bool correctionNeeded);
int EmSend4bitEx(uint8_t resp, bool correctionNeeded);
int EmSend4bit(uint8_t resp);
int EmSendCmdExPar(uint8_t *resp, uint16_t respLen, bool correctionNeeded, uint8_t *par);
int EmSendCmdEx(uint8_t *resp, uint16_t respLen, bool correctionNeeded);
int EmSendCmd(uint8_t *resp, uint16_t respLen);
int EmSendCmdPar(uint8_t *resp, uint16_t respLen, uint8_t *par);
bool EmLogTrace(uint8_t *reader_data, uint16_t reader_len, uint32_t reader_StartTime, uint32_t reader_EndTime, uint8_t *reader_Parity,
                                 uint8_t *tag_data, uint16_t tag_len, uint32_t tag_StartTime, uint32_t tag_EndTime, uint8_t *tag_Parity);

static uint8_t* free_buffer_pointer;

typedef struct {
  uint8_t* response;
  size_t   response_n;
  uint8_t* modulation;
  size_t   modulation_n;
  uint32_t ProxToAirDuration;
} tag_response_info_t;

bool prepare_tag_modulation(tag_response_info_t* response_info, size_t max_buffer_size) {
        // Example response, answer to MIFARE Classic read block will be 16 bytes + 2 CRC = 18 bytes
        // This will need the following byte array for a modulation sequence
        //    144        data bits (18 * 8)
        //     18        parity bits
        //      2        Start and stop
        //      1        Correction bit (Answer in 1172 or 1236 periods, see FPGA)
        //      1        just for the case
        // ----------- +
        //    166 bytes, since every bit that needs to be send costs us a byte
        //
 
 
  // Prepare the tag modulation bits from the message
  CodeIso14443aAsTag(response_info->response,response_info->response_n);
  
  // Make sure we do not exceed the free buffer space
  if (ToSendMax > max_buffer_size) {
    Dbprintf("Out of memory, when modulating bits for tag answer:");
    Dbhexdump(response_info->response_n,response_info->response,false);
    return false;
  }
  
  // Copy the byte array, used for this modulation to the buffer position
  memcpy(response_info->modulation,ToSend,ToSendMax);
  
  // Store the number of bytes that were used for encoding/modulation and the time needed to transfer them
  response_info->modulation_n = ToSendMax;
  response_info->ProxToAirDuration = LastProxToAirDuration;
  
  return true;
}


// "precompile" responses. There are 7 predefined responses with a total of 28 bytes data to transmit.
// Coded responses need one byte per bit to transfer (data, parity, start, stop, correction) 
// 28 * 8 data bits, 28 * 1 parity bits, 7 start bits, 7 stop bits, 7 correction bits
// -> need 273 bytes buffer
// 44 * 8 data bits, 44 * 1 parity bits, 9 start bits, 9 stop bits, 9 correction bits --370
// 47 * 8 data bits, 47 * 1 parity bits, 10 start bits, 10 stop bits, 10 correction bits 
#define ALLOCATED_TAG_MODULATION_BUFFER_SIZE 453 

bool prepare_allocated_tag_modulation(tag_response_info_t* response_info) {
  // Retrieve and store the current buffer index
  response_info->modulation = free_buffer_pointer;
  
  // Determine the maximum size we can use from our buffer
  size_t max_buffer_size = ALLOCATED_TAG_MODULATION_BUFFER_SIZE;
  
  // Forward the prepare tag modulation function to the inner function
  if (prepare_tag_modulation(response_info, max_buffer_size)) {
    // Update the free buffer offset
    free_buffer_pointer += ToSendMax;
    return true;
  } else {
    return false;
  }
}

//-----------------------------------------------------------------------------
// Main loop of simulated tag: receive commands from reader, decide what
// response to send, and send it.
//-----------------------------------------------------------------------------
void SimulateIso14443aTag(int tagType, int flags, byte_t* data)
{
        uint32_t counters[] = {0,0,0};
        //Here, we collect UID,NT,AR,NR,UID2,NT2,AR2,NR2
        // This can be used in a reader-only attack.
        // (it can also be retrieved via 'hf 14a list', but hey...
        uint32_t ar_nr_responses[] = {0,0,0,0,0,0,0,0,0,0};
        uint8_t ar_nr_collected = 0;
        
        uint8_t sak;
                                        
        // PACK response to PWD AUTH for EV1/NTAG
        uint8_t response8[4] =  {0,0,0,0};
        
        // The first response contains the ATQA (note: bytes are transmitted in reverse order).
        uint8_t response1[2] =  {0,0};
        
        switch (tagType) {
                case 1: { // MIFARE Classic
                        // Says: I am Mifare 1k - original line
                        response1[0] = 0x04;
                        response1[1] = 0x00;
                        sak = 0x08;
                } break;
                case 2: { // MIFARE Ultralight
                        // Says: I am a stupid memory tag, no crypto
                        response1[0] = 0x44;
                        response1[1] = 0x00;
                        sak = 0x00;
                } break;
                case 3: { // MIFARE DESFire
                        // Says: I am a DESFire tag, ph33r me
                        response1[0] = 0x04;
                        response1[1] = 0x03;
                        sak = 0x20;
                } break;
                case 4: { // ISO/IEC 14443-4
                        // Says: I am a javacard (JCOP)
                        response1[0] = 0x04;
                        response1[1] = 0x00;
                        sak = 0x28;
                } break;
                case 5: { // MIFARE TNP3XXX
                        // Says: I am a toy
                        response1[0] = 0x01;
                        response1[1] = 0x0f;
                        sak = 0x01;
                } break;
                case 6: { // MIFARE Mini
                        // Says: I am a Mifare Mini, 320b
                        response1[0] = 0x44;
                        response1[1] = 0x00;
                        sak = 0x09;
                } break;
                case 7: { // NTAG?
                        // Says: I am a NTAG, 
                        response1[0] = 0x44;
                        response1[1] = 0x00;
                        sak = 0x00;
                        // PACK
                        response8[0] = 0x80;
                        response8[1] = 0x80;
                        ComputeCrc14443(CRC_14443_A, response8, 2, &response8[2], &response8[3]);
                } break;                
                default: {
                        Dbprintf("Error: unkown tagtype (%d)",tagType);
                        return;
                } break;
        }
        
        // The second response contains the (mandatory) first 24 bits of the UID
        uint8_t response2[5] = {0x00};

        // Check if the uid uses the (optional) part
        uint8_t response2a[5] = {0x00};
        
        if (flags & FLAG_7B_UID_IN_DATA) {
                response2[0] = 0x88;
                response2[1] = data[0];
                response2[2] = data[1];
                response2[3] = data[2];

                response2a[0] = data[3];
                response2a[1] = data[4];
                response2a[2] = data[5];
                response2a[3] = data[6]; //??
                response2a[4] = response2a[0] ^ response2a[1] ^ response2a[2] ^ response2a[3];

                // Configure the ATQA and SAK accordingly
                response1[0] |= 0x40;
                sak |= 0x04;
        } else {
                memcpy(response2, data, 4);
                //num_to_bytes(uid_1st,4,response2);
                // Configure the ATQA and SAK accordingly
                response1[0] &= 0xBF;
                sak &= 0xFB;
        }

        // Calculate the BitCountCheck (BCC) for the first 4 bytes of the UID.
        response2[4] = response2[0] ^ response2[1] ^ response2[2] ^ response2[3];

        // Prepare the mandatory SAK (for 4 and 7 byte UID)
        uint8_t response3[3]  = {0x00};
        response3[0] = sak;
        ComputeCrc14443(CRC_14443_A, response3, 1, &response3[1], &response3[2]);

        // Prepare the optional second SAK (for 7 byte UID), drop the cascade bit
        uint8_t response3a[3]  = {0x00};
        response3a[0] = sak & 0xFB;
        ComputeCrc14443(CRC_14443_A, response3a, 1, &response3a[1], &response3a[2]);

        uint8_t response5[] = { 0x00, 0x00, 0x00, 0x00 }; // Very random tag nonce
        uint8_t response6[] = { 0x04, 0x58, 0x80, 0x02, 0x00, 0x00 }; // dummy ATS (pseudo-ATR), answer to RATS: 
        // Format byte = 0x58: FSCI=0x08 (FSC=256), TA(1) and TC(1) present, 
        // TA(1) = 0x80: different divisors not supported, DR = 1, DS = 1
        // TB(1) = not present. Defaults: FWI = 4 (FWT = 256 * 16 * 2^4 * 1/fc = 4833us), SFGI = 0 (SFG = 256 * 16 * 2^0 * 1/fc = 302us)
        // TC(1) = 0x02: CID supported, NAD not supported
        ComputeCrc14443(CRC_14443_A, response6, 4, &response6[4], &response6[5]);

        // Prepare GET_VERSION (different for EV-1 / NTAG)
        //uint8_t response7_EV1[] = {0x00, 0x04, 0x03, 0x01, 0x01, 0x00, 0x0b, 0x03, 0xfd, 0xf7};  //EV1 48bytes VERSION.
        uint8_t response7_NTAG[] = {0x00, 0x04, 0x04, 0x02, 0x01, 0x00, 0x11, 0x03, 0x01, 0x9e}; //NTAG 215
        
        // Prepare CHK_TEARING
        uint8_t response9[] =  {0xBD,0x90,0x3f};
        
        #define TAG_RESPONSE_COUNT 10
        tag_response_info_t responses[TAG_RESPONSE_COUNT] = {
                { .response = response1,  .response_n = sizeof(response1)  },  // Answer to request - respond with card type
                { .response = response2,  .response_n = sizeof(response2)  },  // Anticollision cascade1 - respond with uid
                { .response = response2a, .response_n = sizeof(response2a) },  // Anticollision cascade2 - respond with 2nd half of uid if asked
                { .response = response3,  .response_n = sizeof(response3)  },  // Acknowledge select - cascade 1
                { .response = response3a, .response_n = sizeof(response3a) },  // Acknowledge select - cascade 2
                { .response = response5,  .response_n = sizeof(response5)  },  // Authentication answer (random nonce)
                { .response = response6,  .response_n = sizeof(response6)  },  // dummy ATS (pseudo-ATR), answer to RATS
                { .response = response7_NTAG,  .response_n = sizeof(response7_NTAG)  },  // EV1/NTAG GET_VERSION response
                { .response = response8,   .response_n = sizeof(response8) },  // EV1/NTAG PACK response
                { .response = response9,   .response_n = sizeof(response9) }  // EV1/NTAG CHK_TEAR response
        };

        // Allocate 512 bytes for the dynamic modulation, created when the reader queries for it
        // Such a response is less time critical, so we can prepare them on the fly
        #define DYNAMIC_RESPONSE_BUFFER_SIZE 64
        #define DYNAMIC_MODULATION_BUFFER_SIZE 512
        uint8_t dynamic_response_buffer[DYNAMIC_RESPONSE_BUFFER_SIZE];
        uint8_t dynamic_modulation_buffer[DYNAMIC_MODULATION_BUFFER_SIZE];
        tag_response_info_t dynamic_response_info = {
                .response = dynamic_response_buffer,
                .response_n = 0,
                .modulation = dynamic_modulation_buffer,
                .modulation_n = 0
        };
  
        // We need to listen to the high-frequency, peak-detected path.
        iso14443a_setup(FPGA_HF_ISO14443A_TAGSIM_LISTEN);

        BigBuf_free_keep_EM();

        // allocate buffers:
        uint8_t *receivedCmd = BigBuf_malloc(MAX_FRAME_SIZE);
        uint8_t *receivedCmdPar = BigBuf_malloc(MAX_PARITY_SIZE);
        free_buffer_pointer = BigBuf_malloc(ALLOCATED_TAG_MODULATION_BUFFER_SIZE);

        // clear trace
        clear_trace();
        set_tracing(TRUE);

        // Prepare the responses of the anticollision phase
        // there will be not enough time to do this at the moment the reader sends it REQA
        for (size_t i=0; i<TAG_RESPONSE_COUNT; i++) {
                prepare_allocated_tag_modulation(&responses[i]);
        }

        int len = 0;

        // To control where we are in the protocol
        int order = 0;
        int lastorder;

        // Just to allow some checks
        int happened = 0;
        int happened2 = 0;
        int cmdsRecvd = 0;

        cmdsRecvd = 0;
        tag_response_info_t* p_response;

        LED_A_ON();
        for(;;) {
                // Clean receive command buffer
                
                if(!GetIso14443aCommandFromReader(receivedCmd, receivedCmdPar, &len)) {
                        DbpString("Button press");
                        break;
                }

                p_response = NULL;
                
                // Okay, look at the command now.
                lastorder = order;
                if(receivedCmd[0] == 0x26) { // Received a REQUEST
                        p_response = &responses[0]; order = 1;
                } else if(receivedCmd[0] == 0x52) { // Received a WAKEUP
                        p_response = &responses[0]; order = 6;
                } else if(receivedCmd[1] == 0x20 && receivedCmd[0] == 0x93) {   // Received request for UID (cascade 1)
                        p_response = &responses[1]; order = 2;
                } else if(receivedCmd[1] == 0x20 && receivedCmd[0] == 0x95) {   // Received request for UID (cascade 2)
                        p_response = &responses[2]; order = 20;
                } else if(receivedCmd[1] == 0x70 && receivedCmd[0] == 0x93) {   // Received a SELECT (cascade 1)
                        p_response = &responses[3]; order = 3;
                } else if(receivedCmd[1] == 0x70 && receivedCmd[0] == 0x95) {   // Received a SELECT (cascade 2)
                        p_response = &responses[4]; order = 30;
                } else if(receivedCmd[0] == 0x30) {     // Received a (plain) READ
                        uint8_t block = receivedCmd[1];
                        if ( tagType == 7 ) {
                                uint16_t start = 4 * block;
                                
                                /*if ( block < 4 ) {
                                    //NTAG 215
                                        uint8_t blockdata[50] = {
                                        data[0],data[1],data[2], 0x88 ^ data[0] ^ data[1] ^ data[2],
                                        data[3],data[4],data[5],data[6],
                                        data[3] ^ data[4] ^ data[5] ^ data[6],0x48,0x0f,0xe0,
                                        0xe1,0x10,0x12,0x00,
                                        0x03,0x00,0xfe,0x00, 
                                        0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                                        0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                                        0x00,0x00,0x00,0x00,
                                        0x00,0x00};
                                        AppendCrc14443a(blockdata+start, 16);
                                        EmSendCmdEx( blockdata+start, MAX_MIFARE_FRAME_SIZE, false);
                                } else {*/      
                                        uint8_t emdata[MAX_MIFARE_FRAME_SIZE];
                                        emlGetMemBt( emdata, start, 16);
                                        AppendCrc14443a(emdata, 16);
                                        EmSendCmdEx(emdata, sizeof(emdata), false);                             
                                //}
                                p_response = NULL;
                                
                        } else {                        
                                EmSendCmdEx(data+(4*block),16,false);
                                // Dbprintf("Read request from reader: %x %x",receivedCmd[0],receivedCmd[1]);
                                // We already responded, do not send anything with the EmSendCmd14443aRaw() that is called below
                                p_response = NULL;
                        }
                } else if(receivedCmd[0] == 0x3A) {     // Received a FAST READ (ranged read)
                                
                                uint8_t emdata[MAX_FRAME_SIZE];
                                int start =  receivedCmd[1] * 4;
                                int len   = (receivedCmd[2] - receivedCmd[1] + 1) * 4;
                                emlGetMemBt( emdata, start, len);
                                AppendCrc14443a(emdata, len);
                                EmSendCmdEx(emdata, len+2, false);                              
                                p_response = NULL;
                                
                } else if(receivedCmd[0] == 0x3C && tagType == 7) {     // Received a READ SIGNATURE -- 
                                // ECC data,  taken from a NTAG215 amiibo token. might work. LEN: 32, + 2 crc
                                uint8_t data[] = {0x56,0x06,0xa6,0x4f,0x43,0x32,0x53,0x6f,
                                                                  0x43,0xda,0x45,0xd6,0x61,0x38,0xaa,0x1e,
                                                                  0xcf,0xd3,0x61,0x36,0xca,0x5f,0xbb,0x05,
                                                                  0xce,0x21,0x24,0x5b,0xa6,0x7a,0x79,0x07,
                                                                  0x00,0x00};
                                AppendCrc14443a(data, sizeof(data)-2);
                                EmSendCmdEx(data,sizeof(data),false);
                                p_response = NULL;                                      
                } else if (receivedCmd[0] == 0x39 && tagType == 7) {    // Received a READ COUNTER -- 
                        uint8_t index = receivedCmd[1];
                        uint8_t data[] =  {0x00,0x00,0x00,0x14,0xa5};
                        if ( counters[index] > 0) {
                                num_to_bytes(counters[index], 3, data);
                                AppendCrc14443a(data, sizeof(data)-2);
                        }
                        EmSendCmdEx(data,sizeof(data),false);                           
                        p_response = NULL;
                } else if (receivedCmd[0] == 0xA5 && tagType == 7) {    // Received a INC COUNTER -- 
                        // number of counter
                        uint8_t counter = receivedCmd[1];
                        uint32_t val = bytes_to_num(receivedCmd+2,4);
                        counters[counter] = val;
                
                        // send ACK
                        uint8_t ack[] = {0x0a};
                        EmSendCmdEx(ack,sizeof(ack),false);
                        p_response = NULL;
                        
                } else if(receivedCmd[0] == 0x3E && tagType == 7) {     // Received a CHECK_TEARING_EVENT -- 
                                p_response = &responses[9];                             
                } else if(receivedCmd[0] == 0x50) {     // Received a HALT

                        if (tracing) {
                                LogTrace(receivedCmd, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                        }
                        p_response = NULL;
                } else if(receivedCmd[0] == 0x60 || receivedCmd[0] == 0x61) {   // Received an authentication request
                                        
                        if ( tagType == 7 ) {   // IF NTAG /EV1  0x60 == GET_VERSION, not a authentication request.
                                p_response = &responses[7];
                        } else {
                                p_response = &responses[5]; order = 7;
                        }
                } else if(receivedCmd[0] == 0xE0) {     // Received a RATS request
                        if (tagType == 1 || tagType == 2) {     // RATS not supported
                                EmSend4bit(CARD_NACK_NA);
                                p_response = NULL;
                        } else {
                                p_response = &responses[6]; order = 70;
                        }
                } else if (order == 7 && len == 8) { // Received {nr] and {ar} (part of authentication)
                        if (tracing) {
                                LogTrace(receivedCmd, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                        }
                        uint32_t nonce = bytes_to_num(response5,4);
                        uint32_t nr = bytes_to_num(receivedCmd,4);
                        uint32_t ar = bytes_to_num(receivedCmd+4,4);
                        //Dbprintf("Auth attempt {nonce}{nr}{ar}: %08x %08x %08x", nonce, nr, ar);

                        if(flags & FLAG_NR_AR_ATTACK )
                        {
                                if(ar_nr_collected < 2){
                                        // Avoid duplicates... probably not necessary, nr should vary. 
                                        //if(ar_nr_responses[3] != nr){                                         
                                                ar_nr_responses[ar_nr_collected*5]   = 0;
                                                ar_nr_responses[ar_nr_collected*5+1] = 0;
                                                ar_nr_responses[ar_nr_collected*5+2] = nonce;
                                                ar_nr_responses[ar_nr_collected*5+3] = nr;
                                                ar_nr_responses[ar_nr_collected*5+4] = ar;
                                                ar_nr_collected++;
                                        //}
                                }                       

                                if(ar_nr_collected > 1 ) {
                                
                                        if (MF_DBGLEVEL >= 2) {
                                                        Dbprintf("Collected two pairs of AR/NR which can be used to extract keys from reader:");
                                                        Dbprintf("../tools/mfkey/mfkey32 %07x%08x %08x %08x %08x %08x %08x",
                                                                ar_nr_responses[0], // UID1
                                                                ar_nr_responses[1], // UID2
                                                                ar_nr_responses[2], // NT
                                                                ar_nr_responses[3], // AR1
                                                                ar_nr_responses[4], // NR1
                                                                ar_nr_responses[8], // AR2
                                                                ar_nr_responses[9]  // NR2
                                                        );
                                                        Dbprintf("../tools/mfkey/mfkey32v2 %06x%08x %08x %08x %08x %08x %08x %08x",
                                                                ar_nr_responses[0], // UID1
                                                                ar_nr_responses[1], // UID2
                                                                ar_nr_responses[2], // NT1
                                                                ar_nr_responses[3], // AR1
                                                                ar_nr_responses[4], // NR1
                                                                ar_nr_responses[7], // NT2
                                                                ar_nr_responses[8], // AR2
                                                                ar_nr_responses[9]  // NR2
                                                                );
                                        }
                                        uint8_t len = ar_nr_collected*5*4;
                                        cmd_send(CMD_ACK,CMD_SIMULATE_MIFARE_CARD,len,0,&ar_nr_responses,len);
                                        ar_nr_collected = 0;
                                        memset(ar_nr_responses, 0x00, len);
                                }
                        }
                } else if (receivedCmd[0] == 0x1a ) // ULC authentication
                {
                        
                }
                else if (receivedCmd[0] == 0x1b) // NTAG / EV-1 authentication
                {
                        if ( tagType == 7 ) {
                                p_response =  &responses[8]; // PACK response
                                uint32_t pwd = bytes_to_num(receivedCmd+1,4);
                                
                                if ( MF_DBGLEVEL >= 3)  Dbprintf("Auth attempt: %08x", pwd);    
                        }
                }
                else {
                        // Check for ISO 14443A-4 compliant commands, look at left nibble
                        switch (receivedCmd[0]) {
                                case 0x02:
                                case 0x03: {  // IBlock (command no CID)
                                        dynamic_response_info.response[0] = receivedCmd[0];
                                        dynamic_response_info.response[1] = 0x90;
                                        dynamic_response_info.response[2] = 0x00;
                                        dynamic_response_info.response_n = 3;
                                } break;
                                case 0x0B:
                                case 0x0A: { // IBlock (command CID)
                                  dynamic_response_info.response[0] = receivedCmd[0];
                                  dynamic_response_info.response[1] = 0x00;
                                  dynamic_response_info.response[2] = 0x90;
                                  dynamic_response_info.response[3] = 0x00;
                                  dynamic_response_info.response_n = 4;
                                } break;

                                case 0x1A:
                                case 0x1B: { // Chaining command
                                  dynamic_response_info.response[0] = 0xaa | ((receivedCmd[0]) & 1);
                                  dynamic_response_info.response_n = 2;
                                } break;

                                case 0xaa:
                                case 0xbb: {
                                  dynamic_response_info.response[0] = receivedCmd[0] ^ 0x11;
                                  dynamic_response_info.response_n = 2;
                                } break;
                                  
                                case 0xBA: { // ping / pong
                                        dynamic_response_info.response[0] = 0xAB;
                                        dynamic_response_info.response[1] = 0x00;
                                        dynamic_response_info.response_n = 2;
                                } break;

                                case 0xCA:
                                case 0xC2: { // Readers sends deselect command
                                        dynamic_response_info.response[0] = 0xCA;
                                        dynamic_response_info.response[1] = 0x00;
                                        dynamic_response_info.response_n = 2;
                                } break;

                                default: {
                                        // Never seen this command before
                                        if (tracing) {
                                                LogTrace(receivedCmd, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        }
                                        Dbprintf("Received unknown command (len=%d):",len);
                                        Dbhexdump(len,receivedCmd,false);
                                        // Do not respond
                                        dynamic_response_info.response_n = 0;
                                } break;
                        }
      
                        if (dynamic_response_info.response_n > 0) {
                                // Copy the CID from the reader query
                                dynamic_response_info.response[1] = receivedCmd[1];

                                // Add CRC bytes, always used in ISO 14443A-4 compliant cards
                                AppendCrc14443a(dynamic_response_info.response,dynamic_response_info.response_n);
                                dynamic_response_info.response_n += 2;
        
                                if (prepare_tag_modulation(&dynamic_response_info,DYNAMIC_MODULATION_BUFFER_SIZE) == false) {
                                        Dbprintf("Error preparing tag response");
                                        if (tracing) {
                                                LogTrace(receivedCmd, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        }
                                        break;
                                }
                                p_response = &dynamic_response_info;
                        }
                }

                // Count number of wakeups received after a halt
                if(order == 6 && lastorder == 5) { happened++; }

                // Count number of other messages after a halt
                if(order != 6 && lastorder == 5) { happened2++; }

                if(cmdsRecvd > 999) {
                        DbpString("1000 commands later...");
                        break;
                }
                cmdsRecvd++;

                if (p_response != NULL) {
                        EmSendCmd14443aRaw(p_response->modulation, p_response->modulation_n, receivedCmd[0] == 0x52);
                        // do the tracing for the previous reader request and this tag answer:
                        uint8_t par[MAX_PARITY_SIZE];
                        GetParity(p_response->response, p_response->response_n, par);
        
                        EmLogTrace(Uart.output, 
                                                Uart.len, 
                                                Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, 
                                                Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 
                                                Uart.parity,
                                                p_response->response, 
                                                p_response->response_n,
                                                LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_TAG,
                                                (LastTimeProxToAirStart + p_response->ProxToAirDuration)*16 + DELAY_ARM2AIR_AS_TAG, 
                                                par);
                }
                
                if (!tracing) {
                        Dbprintf("Trace Full. Simulation stopped.");
                        break;
                }
        }

        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        set_tracing(FALSE);
        BigBuf_free_keep_EM();
        LED_A_OFF();
        
        if (MF_DBGLEVEL >= 4){
                Dbprintf("-[ Wake ups after halt [%d]", happened);
                Dbprintf("-[ Messages after halt [%d]", happened2);
                Dbprintf("-[ Num of received cmd [%d]", cmdsRecvd);
        }
}


// prepare a delayed transfer. This simply shifts ToSend[] by a number
// of bits specified in the delay parameter.
void PrepareDelayedTransfer(uint16_t delay)
{
        uint8_t bitmask = 0;
        uint8_t bits_to_shift = 0;
        uint8_t bits_shifted = 0;

        delay &= 0x07;
        if (delay) {
                for (uint16_t i = 0; i < delay; i++) {
                        bitmask |= (0x01 << i);
                }
                ToSend[ToSendMax++] = 0x00;
                for (uint16_t i = 0; i < ToSendMax; i++) {
                        bits_to_shift = ToSend[i] & bitmask;
                        ToSend[i] = ToSend[i] >> delay;
                        ToSend[i] = ToSend[i] | (bits_shifted << (8 - delay));
                        bits_shifted = bits_to_shift;
                }
        }
}


//-------------------------------------------------------------------------------------
// Transmit the command (to the tag) that was placed in ToSend[].
// Parameter timing:
// if NULL: transfer at next possible time, taking into account
//                      request guard time and frame delay time
// if == 0:     transfer immediately and return time of transfer
// if != 0: delay transfer until time specified
//-------------------------------------------------------------------------------------
static void TransmitFor14443a(const uint8_t *cmd, uint16_t len, uint32_t *timing)
{
        
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_MOD);

        uint32_t ThisTransferTime = 0;

        if (timing) {
                if(*timing == 0) {                                                                              // Measure time
                        *timing = (GetCountSspClk() + 8) & 0xfffffff8;
                } else {
                        PrepareDelayedTransfer(*timing & 0x00000007);           // Delay transfer (fine tuning - up to 7 MF clock ticks)
                }
                if(MF_DBGLEVEL >= 4 && GetCountSspClk() >= (*timing & 0xfffffff8)) Dbprintf("TransmitFor14443a: Missed timing");
                while(GetCountSspClk() < (*timing & 0xfffffff8));               // Delay transfer (multiple of 8 MF clock ticks)
                LastTimeProxToAirStart = *timing;
        } else {
                ThisTransferTime = ((MAX(NextTransferTime, GetCountSspClk()) & 0xfffffff8) + 8);
                while(GetCountSspClk() < ThisTransferTime);
                LastTimeProxToAirStart = ThisTransferTime;
        }
        
        // clear TXRDY
        AT91C_BASE_SSC->SSC_THR = SEC_Y;

        uint16_t c = 0;
        for(;;) {
                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
                        AT91C_BASE_SSC->SSC_THR = cmd[c];
                        c++;
                        if(c >= len) {
                                break;
                        }
                }
        }
        
        NextTransferTime = MAX(NextTransferTime, LastTimeProxToAirStart + REQUEST_GUARD_TIME);
}


//-----------------------------------------------------------------------------
// Prepare reader command (in bits, support short frames) to send to FPGA
//-----------------------------------------------------------------------------
void CodeIso14443aBitsAsReaderPar(const uint8_t *cmd, uint16_t bits, const uint8_t *parity)
{
        int i, j;
        int last;
        uint8_t b;

        ToSendReset();

        // Start of Communication (Seq. Z)
        ToSend[++ToSendMax] = SEC_Z;
        LastProxToAirDuration = 8 * (ToSendMax+1) - 6;
        last = 0;

        size_t bytecount = nbytes(bits);
        // Generate send structure for the data bits
        for (i = 0; i < bytecount; i++) {
                // Get the current byte to send
                b = cmd[i];
                size_t bitsleft = MIN((bits-(i*8)),8);

                for (j = 0; j < bitsleft; j++) {
                        if (b & 1) {
                                // Sequence X
                                ToSend[++ToSendMax] = SEC_X;
                                LastProxToAirDuration = 8 * (ToSendMax+1) - 2;
                                last = 1;
                        } else {
                                if (last == 0) {
                                // Sequence Z
                                ToSend[++ToSendMax] = SEC_Z;
                                LastProxToAirDuration = 8 * (ToSendMax+1) - 6;
                                } else {
                                        // Sequence Y
                                        ToSend[++ToSendMax] = SEC_Y;
                                        last = 0;
                                }
                        }
                        b >>= 1;
                }

                // Only transmit parity bit if we transmitted a complete byte
                if (j == 8 && parity != NULL) {
                        // Get the parity bit
                        if (parity[i>>3] & (0x80 >> (i&0x0007))) {
                                // Sequence X
                                ToSend[++ToSendMax] = SEC_X;
                                LastProxToAirDuration = 8 * (ToSendMax+1) - 2;
                                last = 1;
                        } else {
                                if (last == 0) {
                                        // Sequence Z
                                        ToSend[++ToSendMax] = SEC_Z;
                                        LastProxToAirDuration = 8 * (ToSendMax+1) - 6;
                                } else {
                                        // Sequence Y
                                        ToSend[++ToSendMax] = SEC_Y;
                                        last = 0;
                                }
                        }
                }
        }

        // End of Communication: Logic 0 followed by Sequence Y
        if (last == 0) {
                // Sequence Z
                ToSend[++ToSendMax] = SEC_Z;
                LastProxToAirDuration = 8 * (ToSendMax+1) - 6;
        } else {
                // Sequence Y
                ToSend[++ToSendMax] = SEC_Y;
                last = 0;
        }
        ToSend[++ToSendMax] = SEC_Y;

        // Convert to length of command:
        ToSendMax++;
}

//-----------------------------------------------------------------------------
// Prepare reader command to send to FPGA
//-----------------------------------------------------------------------------
void CodeIso14443aAsReaderPar(const uint8_t *cmd, uint16_t len, const uint8_t *parity)
{
  CodeIso14443aBitsAsReaderPar(cmd, len*8, parity);
}


//-----------------------------------------------------------------------------
// Wait for commands from reader
// Stop when button is pressed (return 1) or field was gone (return 2)
// Or return 0 when command is captured
//-----------------------------------------------------------------------------
static int EmGetCmd(uint8_t *received, uint16_t *len, uint8_t *parity)
{
        *len = 0;

        uint32_t timer = 0, vtime = 0;
        int analogCnt = 0;
        int analogAVG = 0;

        // Set FPGA mode to "simulated ISO 14443 tag", no modulation (listen
        // only, since we are receiving, not transmitting).
        // Signal field is off with the appropriate LED
        LED_D_OFF();
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_TAGSIM_LISTEN);

        // Set ADC to read field strength
        AT91C_BASE_ADC->ADC_CR = AT91C_ADC_SWRST;
        AT91C_BASE_ADC->ADC_MR =
                                ADC_MODE_PRESCALE(63) |
                                ADC_MODE_STARTUP_TIME(1) |
                                ADC_MODE_SAMPLE_HOLD_TIME(15);
        AT91C_BASE_ADC->ADC_CHER = ADC_CHANNEL(ADC_CHAN_HF);
        // start ADC
        AT91C_BASE_ADC->ADC_CR = AT91C_ADC_START;
        
        // Now run a 'software UART' on the stream of incoming samples.
        UartInit(received, parity);

        // Clear RXRDY:
    uint8_t b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
        
        for(;;) {
                WDT_HIT();

                if (BUTTON_PRESS()) return 1;

                // test if the field exists
                if (AT91C_BASE_ADC->ADC_SR & ADC_END_OF_CONVERSION(ADC_CHAN_HF)) {
                        analogCnt++;
                        analogAVG += AT91C_BASE_ADC->ADC_CDR[ADC_CHAN_HF];
                        AT91C_BASE_ADC->ADC_CR = AT91C_ADC_START;
                        if (analogCnt >= 32) {
                                if ((MAX_ADC_HF_VOLTAGE * (analogAVG / analogCnt) >> 10) < MF_MINFIELDV) {
                                        vtime = GetTickCount();
                                        if (!timer) timer = vtime;
                                        // 50ms no field --> card to idle state
                                        if (vtime - timer > 50) return 2;
                                } else
                                        if (timer) timer = 0;
                                analogCnt = 0;
                                analogAVG = 0;
                        }
                }

                // receive and test the miller decoding
        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
            b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        if(MillerDecoding(b, 0)) {
                                *len = Uart.len;
                                return 0;
                        }
        }

        }
}


static int EmSendCmd14443aRaw(uint8_t *resp, uint16_t respLen, bool correctionNeeded)
{
        uint8_t b;
        uint16_t i = 0;
        uint32_t ThisTransferTime;
        
        // Modulate Manchester
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_TAGSIM_MOD);

        // include correction bit if necessary
        if (Uart.parityBits & 0x01) {
                correctionNeeded = TRUE;
        }
        if(correctionNeeded) {
                // 1236, so correction bit needed
                i = 0;
        } else {
                i = 1;
        }

        // clear receiving shift register and holding register
        while(!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY));
        b = AT91C_BASE_SSC->SSC_RHR; (void) b;
        while(!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY));
        b = AT91C_BASE_SSC->SSC_RHR; (void) b;
        
        // wait for the FPGA to signal fdt_indicator == 1 (the FPGA is ready to queue new data in its delay line)
        for (uint16_t j = 0; j < 5; j++) {      // allow timeout - better late than never
                while(!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY));
                if (AT91C_BASE_SSC->SSC_RHR) break;
        }

        while ((ThisTransferTime = GetCountSspClk()) & 0x00000007);

        // Clear TXRDY:
        AT91C_BASE_SSC->SSC_THR = SEC_F;

        // send cycle
        for(; i < respLen; ) {
                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
                        AT91C_BASE_SSC->SSC_THR = resp[i++];
                        FpgaSendQueueDelay = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                }
        
                if(BUTTON_PRESS()) break;
        }

        // Ensure that the FPGA Delay Queue is empty before we switch to TAGSIM_LISTEN again:
        uint8_t fpga_queued_bits = FpgaSendQueueDelay >> 3;
        for (i = 0; i <= fpga_queued_bits/8 + 1; ) {
                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
                        AT91C_BASE_SSC->SSC_THR = SEC_F;
                        FpgaSendQueueDelay = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        i++;
                }
        }

        LastTimeProxToAirStart = ThisTransferTime + (correctionNeeded?8:0);

        return 0;
}

int EmSend4bitEx(uint8_t resp, bool correctionNeeded){
        Code4bitAnswerAsTag(resp);
        int res = EmSendCmd14443aRaw(ToSend, ToSendMax, correctionNeeded);
        // do the tracing for the previous reader request and this tag answer:
        uint8_t par[1];
        GetParity(&resp, 1, par);
        EmLogTrace(Uart.output, 
                                Uart.len, 
                                Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, 
                                Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 
                                Uart.parity,
                                &resp, 
                                1, 
                                LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_TAG,
                                (LastTimeProxToAirStart + LastProxToAirDuration)*16 + DELAY_ARM2AIR_AS_TAG, 
                                par);
        return res;
}

int EmSend4bit(uint8_t resp){
        return EmSend4bitEx(resp, false);
}

int EmSendCmdExPar(uint8_t *resp, uint16_t respLen, bool correctionNeeded, uint8_t *par){
        CodeIso14443aAsTagPar(resp, respLen, par);
        int res = EmSendCmd14443aRaw(ToSend, ToSendMax, correctionNeeded);
        // do the tracing for the previous reader request and this tag answer:
        EmLogTrace(Uart.output, 
                                Uart.len, 
                                Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, 
                                Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 
                                Uart.parity,
                                resp, 
                                respLen, 
                                LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_TAG,
                                (LastTimeProxToAirStart + LastProxToAirDuration)*16 + DELAY_ARM2AIR_AS_TAG, 
                                par);
        return res;
}

int EmSendCmdEx(uint8_t *resp, uint16_t respLen, bool correctionNeeded){
        uint8_t par[MAX_PARITY_SIZE];
        GetParity(resp, respLen, par);
        return EmSendCmdExPar(resp, respLen, correctionNeeded, par);
}

int EmSendCmd(uint8_t *resp, uint16_t respLen){
        uint8_t par[MAX_PARITY_SIZE];
        GetParity(resp, respLen, par);
        return EmSendCmdExPar(resp, respLen, false, par);
}

int EmSendCmdPar(uint8_t *resp, uint16_t respLen, uint8_t *par){
        return EmSendCmdExPar(resp, respLen, false, par);
}

bool EmLogTrace(uint8_t *reader_data, uint16_t reader_len, uint32_t reader_StartTime, uint32_t reader_EndTime, uint8_t *reader_Parity,
                                 uint8_t *tag_data, uint16_t tag_len, uint32_t tag_StartTime, uint32_t tag_EndTime, uint8_t *tag_Parity)
{
        if (tracing) {
                // we cannot exactly measure the end and start of a received command from reader. However we know that the delay from
                // end of the received command to start of the tag's (simulated by us) answer is n*128+20 or n*128+84 resp.
                // with n >= 9. The start of the tags answer can be measured and therefore the end of the received command be calculated:
                uint16_t reader_modlen = reader_EndTime - reader_StartTime;
                uint16_t approx_fdt = tag_StartTime - reader_EndTime;
                uint16_t exact_fdt = (approx_fdt - 20 + 32)/64 * 64 + 20;
                reader_EndTime = tag_StartTime - exact_fdt;
                reader_StartTime = reader_EndTime - reader_modlen;
                if (!LogTrace(reader_data, reader_len, reader_StartTime, reader_EndTime, reader_Parity, TRUE)) {
                        return FALSE;
                } else return(!LogTrace(tag_data, tag_len, tag_StartTime, tag_EndTime, tag_Parity, FALSE));
        } else {
                return TRUE;
        }
}

//-----------------------------------------------------------------------------
// Wait a certain time for tag response
//  If a response is captured return TRUE
//  If it takes too long return FALSE
//-----------------------------------------------------------------------------
static int GetIso14443aAnswerFromTag(uint8_t *receivedResponse, uint8_t *receivedResponsePar, uint16_t offset)
{
        uint32_t c = 0x00;
        
        // Set FPGA mode to "reader listen mode", no modulation (listen
        // only, since we are receiving, not transmitting).
        // Signal field is on with the appropriate LED
        LED_D_ON();
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_LISTEN);
        
        // Now get the answer from the card
        DemodInit(receivedResponse, receivedResponsePar);

        // clear RXRDY:
    uint8_t b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;

        for(;;) {
                WDT_HIT();

                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
                        b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        if(ManchesterDecoding(b, offset, 0)) {
                                NextTransferTime = MAX(NextTransferTime, Demod.endTime - (DELAY_AIR2ARM_AS_READER + DELAY_ARM2AIR_AS_READER)/16 + FRAME_DELAY_TIME_PICC_TO_PCD);
                                return TRUE;
                        } else if (c++ > iso14a_timeout && Demod.state == DEMOD_UNSYNCD) {
                                return FALSE; 
                        }
                }
        }
}

void ReaderTransmitBitsPar(uint8_t* frame, uint16_t bits, uint8_t *par, uint32_t *timing)
{
        CodeIso14443aBitsAsReaderPar(frame, bits, par);
  
        // Send command to tag
        TransmitFor14443a(ToSend, ToSendMax, timing);
        if(trigger)
                LED_A_ON();
  
        // Log reader command in trace buffer
        if (tracing) {
                LogTrace(frame, nbytes(bits), LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_READER, (LastTimeProxToAirStart + LastProxToAirDuration)*16 + DELAY_ARM2AIR_AS_READER, par, TRUE);
        }
}

void ReaderTransmitPar(uint8_t* frame, uint16_t len, uint8_t *par, uint32_t *timing)
{
  ReaderTransmitBitsPar(frame, len*8, par, timing);
}

void ReaderTransmitBits(uint8_t* frame, uint16_t len, uint32_t *timing)
{
  // Generate parity and redirect
  uint8_t par[MAX_PARITY_SIZE];
  GetParity(frame, len/8, par);
  ReaderTransmitBitsPar(frame, len, par, timing);
}

void ReaderTransmit(uint8_t* frame, uint16_t len, uint32_t *timing)
{
  // Generate parity and redirect
  uint8_t par[MAX_PARITY_SIZE];
  GetParity(frame, len, par);
  ReaderTransmitBitsPar(frame, len*8, par, timing);
}

int ReaderReceiveOffset(uint8_t* receivedAnswer, uint16_t offset, uint8_t *parity)
{
        if (!GetIso14443aAnswerFromTag(receivedAnswer, parity, offset)) return FALSE;
        if (tracing) {
                LogTrace(receivedAnswer, Demod.len, Demod.startTime*16 - DELAY_AIR2ARM_AS_READER, Demod.endTime*16 - DELAY_AIR2ARM_AS_READER, parity, FALSE);
        }
        return Demod.len;
}

int ReaderReceive(uint8_t *receivedAnswer, uint8_t *parity)
{
        if (!GetIso14443aAnswerFromTag(receivedAnswer, parity, 0)) return FALSE;
        if (tracing) {
                LogTrace(receivedAnswer, Demod.len, Demod.startTime*16 - DELAY_AIR2ARM_AS_READER, Demod.endTime*16 - DELAY_AIR2ARM_AS_READER, parity, FALSE);
        }
        return Demod.len;
}

// performs iso14443a anticollision (optional) and card select procedure
// fills the uid and cuid pointer unless NULL
// fills the card info record unless NULL
// if anticollision is false, then the UID must be provided in uid_ptr[] 
// and num_cascades must be set (1: 4 Byte UID, 2: 7 Byte UID, 3: 10 Byte UID)
int iso14443a_select_card(byte_t *uid_ptr, iso14a_card_select_t *p_hi14a_card, uint32_t *cuid_ptr, bool anticollision, uint8_t num_cascades) {
        uint8_t wupa[]       = { 0x52 };  // 0x26 - REQA  0x52 - WAKE-UP
        uint8_t sel_all[]    = { 0x93,0x20 };
        uint8_t sel_uid[]    = { 0x93,0x70,0x00,0x00,0x00,0x00,0x00,0x00,0x00};
        uint8_t rats[]       = { 0xE0,0x80,0x00,0x00 }; // FSD=256, FSDI=8, CID=0
        uint8_t resp[MAX_FRAME_SIZE]; // theoretically. A usual RATS will be much smaller
        uint8_t resp_par[MAX_PARITY_SIZE];
        byte_t uid_resp[4];
        size_t uid_resp_len;

        uint8_t sak = 0x04; // cascade uid
        int cascade_level = 0;
        int len;

        // Broadcast for a card, WUPA (0x52) will force response from all cards in the field
    ReaderTransmitBitsPar(wupa, 7, NULL, NULL);
        
        // Receive the ATQA
        if(!ReaderReceive(resp, resp_par)) return 0;

        if(p_hi14a_card) {
                memcpy(p_hi14a_card->atqa, resp, 2);
                p_hi14a_card->uidlen = 0;
                memset(p_hi14a_card->uid,0,10);
        }

        if (anticollision) {
        // clear uid
        if (uid_ptr) {
                memset(uid_ptr,0,10);
        }
        }

        // check for proprietary anticollision:
        if ((resp[0] & 0x1F) == 0) {
                return 3;
        }
        
        // OK we will select at least at cascade 1, lets see if first byte of UID was 0x88 in
        // which case we need to make a cascade 2 request and select - this is a long UID
        // While the UID is not complete, the 3nd bit (from the right) is set in the SAK.
        for(; sak & 0x04; cascade_level++) {
                // SELECT_* (L1: 0x93, L2: 0x95, L3: 0x97)
                sel_uid[0] = sel_all[0] = 0x93 + cascade_level * 2;

                if (anticollision) {
                // SELECT_ALL
                ReaderTransmit(sel_all, sizeof(sel_all), NULL);
                if (!ReaderReceive(resp, resp_par)) return 0;

                if (Demod.collisionPos) {                       // we had a collision and need to construct the UID bit by bit
                        memset(uid_resp, 0, 4);
                        uint16_t uid_resp_bits = 0;
                        uint16_t collision_answer_offset = 0;
                        // anti-collision-loop:
                        while (Demod.collisionPos) {
                                Dbprintf("Multiple tags detected. Collision after Bit %d", Demod.collisionPos);
                                for (uint16_t i = collision_answer_offset; i < Demod.collisionPos; i++, uid_resp_bits++) {      // add valid UID bits before collision point
                                        uint16_t UIDbit = (resp[i/8] >> (i % 8)) & 0x01;
                                        uid_resp[uid_resp_bits / 8] |= UIDbit << (uid_resp_bits % 8);
                                }
                                uid_resp[uid_resp_bits/8] |= 1 << (uid_resp_bits % 8);                                  // next time select the card(s) with a 1 in the collision position
                                uid_resp_bits++;
                                // construct anticollosion command:
                                sel_uid[1] = ((2 + uid_resp_bits/8) << 4) | (uid_resp_bits & 0x07);     // length of data in bytes and bits
                                for (uint16_t i = 0; i <= uid_resp_bits/8; i++) {
                                        sel_uid[2+i] = uid_resp[i];
                                }
                                collision_answer_offset = uid_resp_bits%8;
                                ReaderTransmitBits(sel_uid, 16 + uid_resp_bits, NULL);
                                if (!ReaderReceiveOffset(resp, collision_answer_offset, resp_par)) return 0;
                        }
                        // finally, add the last bits and BCC of the UID
                        for (uint16_t i = collision_answer_offset; i < (Demod.len-1)*8; i++, uid_resp_bits++) {
                                uint16_t UIDbit = (resp[i/8] >> (i%8)) & 0x01;
                                uid_resp[uid_resp_bits/8] |= UIDbit << (uid_resp_bits % 8);
                        }

                } else {                // no collision, use the response to SELECT_ALL as current uid
                        memcpy(uid_resp, resp, 4);
                }
                } else {
                        if (cascade_level < num_cascades - 1) {
                                uid_resp[0] = 0x88;
                                memcpy(uid_resp+1, uid_ptr+cascade_level*3, 3);
                        } else {
                                memcpy(uid_resp, uid_ptr+cascade_level*3, 4);
                        }
                }
                uid_resp_len = 4;

                // calculate crypto UID. Always use last 4 Bytes.
                if(cuid_ptr) {
                        *cuid_ptr = bytes_to_num(uid_resp, 4);
                }

                // Construct SELECT UID command
                sel_uid[1] = 0x70;                                                                                                      // transmitting a full UID (1 Byte cmd, 1 Byte NVB, 4 Byte UID, 1 Byte BCC, 2 Bytes CRC)
                memcpy(sel_uid+2, uid_resp, 4);                                                                         // the UID received during anticollision, or the provided UID
                sel_uid[6] = sel_uid[2] ^ sel_uid[3] ^ sel_uid[4] ^ sel_uid[5];         // calculate and add BCC
                AppendCrc14443a(sel_uid, 7);                                                                            // calculate and add CRC
                ReaderTransmit(sel_uid, sizeof(sel_uid), NULL);

                // Receive the SAK
                if (!ReaderReceive(resp, resp_par)) return 0;
                sak = resp[0];

    // Test if more parts of the uid are coming
                if ((sak & 0x04) /* && uid_resp[0] == 0x88 */) {
                        // Remove first byte, 0x88 is not an UID byte, it CT, see page 3 of:
                        // http://www.nxp.com/documents/application_note/AN10927.pdf
                        uid_resp[0] = uid_resp[1];
                        uid_resp[1] = uid_resp[2];
                        uid_resp[2] = uid_resp[3]; 
                        uid_resp_len = 3;
                }

                if(uid_ptr && anticollision) {
                        memcpy(uid_ptr + (cascade_level*3), uid_resp, uid_resp_len);
                }

                if(p_hi14a_card) {
                        memcpy(p_hi14a_card->uid + (cascade_level*3), uid_resp, uid_resp_len);
                        p_hi14a_card->uidlen += uid_resp_len;
                }
        }

        if(p_hi14a_card) {
                p_hi14a_card->sak = sak;
                p_hi14a_card->ats_len = 0;
        }

        // non iso14443a compliant tag
        if( (sak & 0x20) == 0) return 2; 

        // Request for answer to select
        AppendCrc14443a(rats, 2);
        ReaderTransmit(rats, sizeof(rats), NULL);

        if (!(len = ReaderReceive(resp, resp_par))) return 0;

        
        if(p_hi14a_card) {
                memcpy(p_hi14a_card->ats, resp, sizeof(p_hi14a_card->ats));
                p_hi14a_card->ats_len = len;
        }

        // reset the PCB block number
        iso14_pcb_blocknum = 0;

        // set default timeout based on ATS
        iso14a_set_ATS_timeout(resp);

        return 1;       
}

void iso14443a_setup(uint8_t fpga_minor_mode) {
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
        // Set up the synchronous serial port
        FpgaSetupSsc();
        // connect Demodulated Signal to ADC:
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

        // Signal field is on with the appropriate LED
        if (fpga_minor_mode == FPGA_HF_ISO14443A_READER_MOD
                || fpga_minor_mode == FPGA_HF_ISO14443A_READER_LISTEN) {
                LED_D_ON();
        } else {
                LED_D_OFF();
        }
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | fpga_minor_mode);

        // Start the timer
        StartCountSspClk();
        
        DemodReset();
        UartReset();
        NextTransferTime = 2*DELAY_ARM2AIR_AS_READER;
        iso14a_set_timeout(10*106); // 10ms default
}

int iso14_apdu(uint8_t *cmd, uint16_t cmd_len, void *data) {
        uint8_t parity[MAX_PARITY_SIZE];
        uint8_t real_cmd[cmd_len+4];
        real_cmd[0] = 0x0a; //I-Block
        // put block number into the PCB
        real_cmd[0] |= iso14_pcb_blocknum;
        real_cmd[1] = 0x00; //CID: 0 //FIXME: allow multiple selected cards
        memcpy(real_cmd+2, cmd, cmd_len);
        AppendCrc14443a(real_cmd,cmd_len+2);
 
        ReaderTransmit(real_cmd, cmd_len+4, NULL);
        size_t len = ReaderReceive(data, parity);
        uint8_t *data_bytes = (uint8_t *) data;
        if (!len)
                return 0; //DATA LINK ERROR
        // if we received an I- or R(ACK)-Block with a block number equal to the
        // current block number, toggle the current block number
        else if (len >= 4 // PCB+CID+CRC = 4 bytes
                 && ((data_bytes[0] & 0xC0) == 0 // I-Block
                     || (data_bytes[0] & 0xD0) == 0x80) // R-Block with ACK bit set to 0
                 && (data_bytes[0] & 0x01) == iso14_pcb_blocknum) // equal block numbers
        {
                iso14_pcb_blocknum ^= 1;
        }

        return len;
}

//-----------------------------------------------------------------------------
// Read an ISO 14443a tag. Send out commands and store answers.
//
//-----------------------------------------------------------------------------
void ReaderIso14443a(UsbCommand *c)
{
        iso14a_command_t param = c->arg[0];
        uint8_t *cmd = c->d.asBytes;
        size_t len = c->arg[1] & 0xffff;
        size_t lenbits = c->arg[1] >> 16;
        uint32_t timeout = c->arg[2];
        uint32_t arg0 = 0;
        byte_t buf[USB_CMD_DATA_SIZE];
        uint8_t par[MAX_PARITY_SIZE];
  
        if(param & ISO14A_CONNECT) {
                clear_trace();
        }

        set_tracing(TRUE);

        if(param & ISO14A_REQUEST_TRIGGER) {
                iso14a_set_trigger(TRUE);
        }

        if(param & ISO14A_CONNECT) {
                iso14443a_setup(FPGA_HF_ISO14443A_READER_LISTEN);
                if(!(param & ISO14A_NO_SELECT)) {
                        iso14a_card_select_t *card = (iso14a_card_select_t*)buf;
                        arg0 = iso14443a_select_card(NULL,card,NULL, true, 0);
                        cmd_send(CMD_ACK,arg0,card->uidlen,0,buf,sizeof(iso14a_card_select_t));
                }
        }

        if(param & ISO14A_SET_TIMEOUT) {
                iso14a_set_timeout(timeout);
        }

        if(param & ISO14A_APDU) {
                arg0 = iso14_apdu(cmd, len, buf);
                cmd_send(CMD_ACK,arg0,0,0,buf,sizeof(buf));
        }

        if(param & ISO14A_RAW) {
                if(param & ISO14A_APPEND_CRC) {
                        if(param & ISO14A_TOPAZMODE) {
                                AppendCrc14443b(cmd,len);
                        } else {
                                AppendCrc14443a(cmd,len);
                        }
                        len += 2;
                        if (lenbits) lenbits += 16;
                }
                if(lenbits>0) {                         // want to send a specific number of bits (e.g. short commands)
                        if(param & ISO14A_TOPAZMODE) {
                                int bits_to_send = lenbits;
                                uint16_t i = 0;
                                ReaderTransmitBitsPar(&cmd[i++], MIN(bits_to_send, 7), NULL, NULL);             // first byte is always short (7bits) and no parity
                                bits_to_send -= 7;
                                while (bits_to_send > 0) {
                                        ReaderTransmitBitsPar(&cmd[i++], MIN(bits_to_send, 8), NULL, NULL);     // following bytes are 8 bit and no parity
                                        bits_to_send -= 8;
                                }
                        } else {
                        GetParity(cmd, lenbits/8, par);
                                ReaderTransmitBitsPar(cmd, lenbits, par, NULL);                                                 // bytes are 8 bit with odd parity
                        }
                } else {                                        // want to send complete bytes only
                        if(param & ISO14A_TOPAZMODE) {
                                uint16_t i = 0;
                                ReaderTransmitBitsPar(&cmd[i++], 7, NULL, NULL);                                                // first byte: 7 bits, no paritiy
                                while (i < len) {
                                        ReaderTransmitBitsPar(&cmd[i++], 8, NULL, NULL);                                        // following bytes: 8 bits, no paritiy
                                }
                } else {
                                ReaderTransmit(cmd,len, NULL);                                                                                  // 8 bits, odd parity
                        }
                }
                arg0 = ReaderReceive(buf, par);
                cmd_send(CMD_ACK,arg0,0,0,buf,sizeof(buf));
        }

        if(param & ISO14A_REQUEST_TRIGGER) {
                iso14a_set_trigger(FALSE);
        }

        if(param & ISO14A_NO_DISCONNECT) {
                return;
        }

        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        set_tracing(FALSE);
        LEDsoff();
}


// Determine the distance between two nonces.
// Assume that the difference is small, but we don't know which is first.
// Therefore try in alternating directions.
int32_t dist_nt(uint32_t nt1, uint32_t nt2) {

        uint16_t i;
        uint32_t nttmp1, nttmp2;

        if (nt1 == nt2) return 0;

        nttmp1 = nt1;
        nttmp2 = nt2;
        
        for (i = 1; i < 0xFFFF; i++) {
                nttmp1 = prng_successor(nttmp1, 1);
                if (nttmp1 == nt2) return i;
                nttmp2 = prng_successor(nttmp2, 1);
                        if (nttmp2 == nt1) return -i;
                }
        
        return(-99999); // either nt1 or nt2 are invalid nonces
}


//-----------------------------------------------------------------------------
// Recover several bits of the cypher stream. This implements (first stages of)
// the algorithm described in "The Dark Side of Security by Obscurity and
// Cloning MiFare Classic Rail and Building Passes, Anywhere, Anytime"
// (article by Nicolas T. Courtois, 2009)
//-----------------------------------------------------------------------------
void ReaderMifare(bool first_try)
{
        // Mifare AUTH
        uint8_t mf_auth[]    = { 0x60,0x00,0xf5,0x7b };
        uint8_t mf_nr_ar[]   = { 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 };
        static uint8_t mf_nr_ar3;

        uint8_t receivedAnswer[MAX_MIFARE_FRAME_SIZE];
        uint8_t receivedAnswerPar[MAX_MIFARE_PARITY_SIZE];

        if (first_try) { 
                iso14443a_setup(FPGA_HF_ISO14443A_READER_MOD);
        }
        
        // free eventually allocated BigBuf memory. We want all for tracing.
        BigBuf_free();
        
        clear_trace();
        set_tracing(TRUE);

        byte_t nt_diff = 0;
        uint8_t par[1] = {0};   // maximum 8 Bytes to be sent here, 1 byte parity is therefore enough
        static byte_t par_low = 0;
        bool led_on = TRUE;
        uint8_t uid[10]  ={0};
        uint32_t cuid;

        uint32_t nt = 0;
        uint32_t previous_nt = 0;
        static uint32_t nt_attacked = 0;
        byte_t par_list[8] = {0x00};
        byte_t ks_list[8] = {0x00};

   #define PRNG_SEQUENCE_LENGTH  (1 << 16);
        static uint32_t sync_time = 0;
        static int32_t sync_cycles = 0;
        int catch_up_cycles = 0;
        int last_catch_up = 0;
        uint16_t elapsed_prng_sequences;
        uint16_t consecutive_resyncs = 0;
        int isOK = 0;

        if (first_try) { 
                mf_nr_ar3 = 0;
                sync_time = GetCountSspClk() & 0xfffffff8;
                sync_cycles = PRNG_SEQUENCE_LENGTH; //65536;    //0x10000                       // theory: Mifare Classic's random generator repeats every 2^16 cycles (and so do the nonces).
                nt_attacked = 0;
                par[0] = 0;
        }
        else {
                // we were unsuccessful on a previous call. Try another READER nonce (first 3 parity bits remain the same)
                mf_nr_ar3++;
                mf_nr_ar[3] = mf_nr_ar3;
                par[0] = par_low;
        }

        LED_A_ON();
        LED_B_OFF();
        LED_C_OFF();
        

        #define MAX_UNEXPECTED_RANDOM   4               // maximum number of unexpected (i.e. real) random numbers when trying to sync. Then give up.
        #define MAX_SYNC_TRIES                  32
        #define NUM_DEBUG_INFOS                 8               // per strategy
        #define MAX_STRATEGY                    3
        uint16_t unexpected_random = 0;
        uint16_t sync_tries = 0;
        int16_t debug_info_nr = -1;
        uint16_t strategy = 0;
        int32_t debug_info[MAX_STRATEGY][NUM_DEBUG_INFOS];
        uint32_t select_time;
        uint32_t halt_time;
  
        for(uint16_t i = 0; TRUE; i++) {
                
                LED_C_ON();
                WDT_HIT();

                // Test if the action was cancelled
                if(BUTTON_PRESS()) {
                        isOK = -1;
                        break;
                }
                
                if (strategy == 2) {
                        // test with additional hlt command
                        halt_time = 0;
                        int len = mifare_sendcmd_short(NULL, false, 0x50, 0x00, receivedAnswer, receivedAnswerPar, &halt_time);
                        if (len && MF_DBGLEVEL >= 3) {
                                Dbprintf("Unexpected response of %d bytes to hlt command (additional debugging).", len);
                        }
                }

                if (strategy == 3) {
                        // test with FPGA power off/on
                        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                        SpinDelay(200);
                        iso14443a_setup(FPGA_HF_ISO14443A_READER_MOD);
                        SpinDelay(100);
                }
                
                if(!iso14443a_select_card(uid, NULL, &cuid, true, 0)) {
                        if (MF_DBGLEVEL >= 1)   Dbprintf("Mifare: Can't select card");
                        continue;
                }
                select_time = GetCountSspClk();

                elapsed_prng_sequences = 1;
                if (debug_info_nr == -1) {
                        sync_time = (sync_time & 0xfffffff8) + sync_cycles + catch_up_cycles;
                        catch_up_cycles = 0;

                        // if we missed the sync time already, advance to the next nonce repeat
                        while(GetCountSspClk() > sync_time) {
                                elapsed_prng_sequences++;
                                sync_time = (sync_time & 0xfffffff8) + sync_cycles;
                        }

                        // Transmit MIFARE_CLASSIC_AUTH at synctime. Should result in returning the same tag nonce (== nt_attacked) 
                        ReaderTransmit(mf_auth, sizeof(mf_auth), &sync_time);
                } else {
                        // collect some information on tag nonces for debugging:
                        #define DEBUG_FIXED_SYNC_CYCLES PRNG_SEQUENCE_LENGTH
                        if (strategy == 0) {
                                // nonce distances at fixed time after card select:
                                sync_time = select_time + DEBUG_FIXED_SYNC_CYCLES;
                        } else if (strategy == 1) {
                                // nonce distances at fixed time between authentications:
                                sync_time = sync_time + DEBUG_FIXED_SYNC_CYCLES;
                        } else if (strategy == 2) {
                                // nonce distances at fixed time after halt:
                                sync_time = halt_time + DEBUG_FIXED_SYNC_CYCLES;
                        } else {
                                // nonce_distances at fixed time after power on
                                sync_time = DEBUG_FIXED_SYNC_CYCLES;
                        }
                        ReaderTransmit(mf_auth, sizeof(mf_auth), &sync_time);
                }                       

                // Receive the (4 Byte) "random" nonce
                if (!ReaderReceive(receivedAnswer, receivedAnswerPar)) {
                        if (MF_DBGLEVEL >= 1)   Dbprintf("Mifare: Couldn't receive tag nonce");
                        continue;
                  }

                previous_nt = nt;
                nt = bytes_to_num(receivedAnswer, 4);

                // Transmit reader nonce with fake par
                ReaderTransmitPar(mf_nr_ar, sizeof(mf_nr_ar), par, NULL);

                if (first_try && previous_nt && !nt_attacked) { // we didn't calibrate our clock yet
                        int nt_distance = dist_nt(previous_nt, nt);
                        if (nt_distance == 0) {
                                nt_attacked = nt;
                        } else {
                                if (nt_distance == -99999) { // invalid nonce received
                                        unexpected_random++;
                                        if (unexpected_random > MAX_UNEXPECTED_RANDOM) {
                                                isOK = -3;              // Card has an unpredictable PRNG. Give up      
                                                break;
                                        } else {
                                                continue;               // continue trying...
                                        }
                                }
                                if (++sync_tries > MAX_SYNC_TRIES) {
                                        if (strategy > MAX_STRATEGY || MF_DBGLEVEL < 3) {
                                                isOK = -4;                      // Card's PRNG runs at an unexpected frequency or resets unexpectedly
                                                break;
                                        } else {                                // continue for a while, just to collect some debug info
                                                debug_info[strategy][debug_info_nr] = nt_distance;
                                                debug_info_nr++;
                                                if (debug_info_nr == NUM_DEBUG_INFOS) {
                                                        strategy++;
                                                        debug_info_nr = 0;
                                                }
                                                continue;
                                        }
                                }
                                sync_cycles = (sync_cycles - nt_distance/elapsed_prng_sequences);
                                if (sync_cycles <= 0) {
                                        sync_cycles += PRNG_SEQUENCE_LENGTH;
                                }
                                if (MF_DBGLEVEL >= 3) {
                                        Dbprintf("calibrating in cycle %d. nt_distance=%d, elapsed_prng_sequences=%d, new sync_cycles: %d\n", i, nt_distance, elapsed_prng_sequences, sync_cycles);
                                }
                                continue;
                        }
                }

                if ((nt != nt_attacked) && nt_attacked) {       // we somehow lost sync. Try to catch up again...
                        catch_up_cycles = -dist_nt(nt_attacked, nt);
                        if (catch_up_cycles == 99999) {                 // invalid nonce received. Don't resync on that one.
                                catch_up_cycles = 0;
                                continue;
                        }
                        catch_up_cycles /= elapsed_prng_sequences;
                        if (catch_up_cycles == last_catch_up) {
                                consecutive_resyncs++;
                        }
                        else {
                                last_catch_up = catch_up_cycles;
                            consecutive_resyncs = 0;
                        }
                        if (consecutive_resyncs < 3) {
                                if (MF_DBGLEVEL >= 3) Dbprintf("Lost sync in cycle %d. nt_distance=%d. Consecutive Resyncs = %d. Trying one time catch up...\n", i, -catch_up_cycles, consecutive_resyncs);
                        }
                        else {  
                                sync_cycles = sync_cycles + catch_up_cycles;
                                if (MF_DBGLEVEL >= 3) Dbprintf("Lost sync in cycle %d for the fourth time consecutively (nt_distance = %d). Adjusting sync_cycles to %d.\n", i, -catch_up_cycles, sync_cycles);
                                last_catch_up = 0;
                                catch_up_cycles = 0;
                                consecutive_resyncs = 0;
                        }
                        continue;
                }
 
                consecutive_resyncs = 0;
                
                // Receive answer. This will be a 4 Bit NACK when the 8 parity bits are OK after decoding
                if (ReaderReceive(receivedAnswer, receivedAnswerPar)) {
                        catch_up_cycles = 8;    // the PRNG is delayed by 8 cycles due to the NAC (4Bits = 0x05 encrypted) transfer
        
                        if (nt_diff == 0) {
                                par_low = par[0] & 0xE0; // there is no need to check all parities for other nt_diff. Parity Bits for mf_nr_ar[0..2] won't change
                        }

                        led_on = !led_on;
                        if(led_on) LED_B_ON(); else LED_B_OFF();

                        par_list[nt_diff] = SwapBits(par[0], 8);
                        ks_list[nt_diff] = receivedAnswer[0] ^ 0x05;

                        // Test if the information is complete
                        if (nt_diff == 0x07) {
                                isOK = 1;
                                break;
                        }

                        nt_diff = (nt_diff + 1) & 0x07;
                        mf_nr_ar[3] = (mf_nr_ar[3] & 0x1F) | (nt_diff << 5);
                        par[0] = par_low;
                } else {
                        if (nt_diff == 0 && first_try)
                        {
                                par[0]++;
                                if (par[0] == 0x00) {           // tried all 256 possible parities without success. Card doesn't send NACK.
                                        isOK = -2;
                                        break;
                                }
                        } else {
                                par[0] = ((par[0] & 0x1F) + 1) | par_low;
                        }
                }
        }


        mf_nr_ar[3] &= 0x1F;
        
        if (isOK == -4) {
                if (MF_DBGLEVEL >= 3) {
                        for (uint16_t i = 0; i <= MAX_STRATEGY; i++) {
                                for(uint16_t j = 0; j < NUM_DEBUG_INFOS; j++) {
                                        Dbprintf("collected debug info[%d][%d] = %d", i, j, debug_info[i][j]);
                                }
                        }
                }
        }
        
        byte_t buf[28];
        memcpy(buf + 0,  uid, 4);
        num_to_bytes(nt, 4, buf + 4);
        memcpy(buf + 8,  par_list, 8);
        memcpy(buf + 16, ks_list, 8);
        memcpy(buf + 24, mf_nr_ar, 4);
                
        cmd_send(CMD_ACK,isOK,0,0,buf,28);

        // Thats it...
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        LEDsoff();

        set_tracing(FALSE);
}

/**
  *MIFARE 1K simulate.
  *
  *@param flags :
  *     FLAG_INTERACTIVE - In interactive mode, we are expected to finish the operation with an ACK
  * 4B_FLAG_UID_IN_DATA - means that there is a 4-byte UID in the data-section, we're expected to use that
  * 7B_FLAG_UID_IN_DATA - means that there is a 7-byte UID in the data-section, we're expected to use that
  *     FLAG_NR_AR_ATTACK  - means we should collect NR_AR responses for bruteforcing later
  *@param exitAfterNReads, exit simulation after n blocks have been read, 0 is inifite
  */
void Mifare1ksim(uint8_t flags, uint8_t exitAfterNReads, uint8_t arg2, uint8_t *datain)
{
        int cardSTATE = MFEMUL_NOFIELD;
        int _7BUID = 0;
        int vHf = 0;    // in mV
        int res;
        uint32_t selTimer = 0;
        uint32_t authTimer = 0;
        uint16_t len = 0;
        uint8_t cardWRBL = 0;
        uint8_t cardAUTHSC = 0;
        uint8_t cardAUTHKEY = 0xff;  // no authentication
//      uint32_t cardRr = 0;
        uint32_t cuid = 0;
        //uint32_t rn_enc = 0;
        uint32_t ans = 0;
        uint32_t cardINTREG = 0;
        uint8_t cardINTBLOCK = 0;
        struct Crypto1State mpcs = {0, 0};
        struct Crypto1State *pcs;
        pcs = &mpcs;
        uint32_t numReads = 0;//Counts numer of times reader read a block
        uint8_t receivedCmd[MAX_MIFARE_FRAME_SIZE];
        uint8_t receivedCmd_par[MAX_MIFARE_PARITY_SIZE];
        uint8_t response[MAX_MIFARE_FRAME_SIZE];
        uint8_t response_par[MAX_MIFARE_PARITY_SIZE];
        
        uint8_t rATQA[] = {0x04, 0x00}; // Mifare classic 1k 4BUID
        uint8_t rUIDBCC1[] = {0xde, 0xad, 0xbe, 0xaf, 0x62};
        uint8_t rUIDBCC2[] = {0xde, 0xad, 0xbe, 0xaf, 0x62}; // !!!
        uint8_t rSAK[] = {0x08, 0xb6, 0xdd}; // Mifare Classic
        //uint8_t rSAK[] = {0x09, 0x3f, 0xcc };  // Mifare Mini 
        uint8_t rSAK1[] = {0x04, 0xda, 0x17};

        uint8_t rAUTH_NT[] = {0x01, 0x01, 0x01, 0x01};
        uint8_t rAUTH_AT[] = {0x00, 0x00, 0x00, 0x00};
                
        //Here, we collect UID,NT,AR,NR,UID2,NT2,AR2,NR2
        // This can be used in a reader-only attack.
        // (it can also be retrieved via 'hf 14a list', but hey...
        uint32_t ar_nr_responses[] = {0,0,0,0,0,0,0,0,0,0};
        uint8_t ar_nr_collected = 0;

        // Authenticate response - nonce
        uint32_t nonce = bytes_to_num(rAUTH_NT, 4);
        
        //-- Determine the UID
        // Can be set from emulator memory, incoming data
        // and can be 7 or 4 bytes long
        if (flags & FLAG_4B_UID_IN_DATA)
        {
                // 4B uid comes from data-portion of packet
                memcpy(rUIDBCC1,datain,4);
                rUIDBCC1[4] = rUIDBCC1[0] ^ rUIDBCC1[1] ^ rUIDBCC1[2] ^ rUIDBCC1[3];

        } else if (flags & FLAG_7B_UID_IN_DATA) {
                // 7B uid comes from data-portion of packet
                memcpy(&rUIDBCC1[1],datain,3);
                memcpy(rUIDBCC2, datain+3, 4);
                _7BUID = true;
        } else {
                // get UID from emul memory
                emlGetMemBt(receivedCmd, 7, 1);
                _7BUID = !(receivedCmd[0] == 0x00);
                if (!_7BUID) {                     // ---------- 4BUID
                        emlGetMemBt(rUIDBCC1, 0, 4);
                } else {                           // ---------- 7BUID
                        emlGetMemBt(&rUIDBCC1[1], 0, 3);
                        emlGetMemBt(rUIDBCC2, 3, 4);
                }
        }

        // save uid.
        ar_nr_responses[0*5]   = bytes_to_num(rUIDBCC1+1, 3);
        if ( _7BUID )
                ar_nr_responses[0*5+1] = bytes_to_num(rUIDBCC2, 4);

        /*
         * Regardless of what method was used to set the UID, set fifth byte and modify
         * the ATQA for 4 or 7-byte UID
         */
        rUIDBCC1[4] = rUIDBCC1[0] ^ rUIDBCC1[1] ^ rUIDBCC1[2] ^ rUIDBCC1[3];
        if (_7BUID) {
                rATQA[0] = 0x44;
                rUIDBCC1[0] = 0x88;
                rUIDBCC1[4] = rUIDBCC1[0] ^ rUIDBCC1[1] ^ rUIDBCC1[2] ^ rUIDBCC1[3];
                rUIDBCC2[4] = rUIDBCC2[0] ^ rUIDBCC2[1] ^ rUIDBCC2[2] ^ rUIDBCC2[3];
        }

        if (MF_DBGLEVEL >= 1)   {
                if (!_7BUID) {
                        Dbprintf("4B UID: %02x%02x%02x%02x", 
                                rUIDBCC1[0], rUIDBCC1[1], rUIDBCC1[2], rUIDBCC1[3]);
                } else {
                        Dbprintf("7B UID: (%02x)%02x%02x%02x%02x%02x%02x%02x",
                                rUIDBCC1[0], rUIDBCC1[1], rUIDBCC1[2], rUIDBCC1[3],
                                rUIDBCC2[0], rUIDBCC2[1] ,rUIDBCC2[2], rUIDBCC2[3]);
                }
        }

        // We need to listen to the high-frequency, peak-detected path.
        iso14443a_setup(FPGA_HF_ISO14443A_TAGSIM_LISTEN);

        // free eventually allocated BigBuf memory but keep Emulator Memory
        BigBuf_free_keep_EM();

        // clear trace
        clear_trace();
        set_tracing(TRUE);


        bool finished = FALSE;
        while (!BUTTON_PRESS() && !finished) {
                WDT_HIT();

                // find reader field
                if (cardSTATE == MFEMUL_NOFIELD) {
                        vHf = (MAX_ADC_HF_VOLTAGE * AvgAdc(ADC_CHAN_HF)) >> 10;
                        if (vHf > MF_MINFIELDV) {
                                cardSTATE_TO_IDLE();
                                LED_A_ON();
                        }
                } 
                if(cardSTATE == MFEMUL_NOFIELD) continue;

                //Now, get data
                res = EmGetCmd(receivedCmd, &len, receivedCmd_par);
                if (res == 2) { //Field is off!
                        cardSTATE = MFEMUL_NOFIELD;
                        LEDsoff();
                        continue;
                } else if (res == 1) {
                        break;  //return value 1 means button press
                }
                        
                // REQ or WUP request in ANY state and WUP in HALTED state
                if (len == 1 && ((receivedCmd[0] == 0x26 && cardSTATE != MFEMUL_HALTED) || receivedCmd[0] == 0x52)) {
                        selTimer = GetTickCount();
                        EmSendCmdEx(rATQA, sizeof(rATQA), (receivedCmd[0] == 0x52));
                        cardSTATE = MFEMUL_SELECT1;

                        // init crypto block
                        LED_B_OFF();
                        LED_C_OFF();
                        crypto1_destroy(pcs);
                        cardAUTHKEY = 0xff;
                        continue;
                }
                
                switch (cardSTATE) {
                        case MFEMUL_NOFIELD:
                        case MFEMUL_HALTED:
                        case MFEMUL_IDLE:{
                                LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                break;
                        }
                        case MFEMUL_SELECT1:{
                                // select all
                                if (len == 2 && (receivedCmd[0] == 0x93 && receivedCmd[1] == 0x20)) {
                                        if (MF_DBGLEVEL >= 4)   Dbprintf("SELECT ALL received");
                                        EmSendCmd(rUIDBCC1, sizeof(rUIDBCC1));
                                        break;
                                }

                                if (MF_DBGLEVEL >= 4 && len == 9 && receivedCmd[0] == 0x93 && receivedCmd[1] == 0x70 )
                                {
                                        Dbprintf("SELECT %02x%02x%02x%02x received",receivedCmd[2],receivedCmd[3],receivedCmd[4],receivedCmd[5]);
                                }
                                // select card
                                if (len == 9 && 
                                                (receivedCmd[0] == 0x93 && receivedCmd[1] == 0x70 && memcmp(&receivedCmd[2], rUIDBCC1, 4) == 0)) {
                                        EmSendCmd(_7BUID?rSAK1:rSAK, _7BUID?sizeof(rSAK1):sizeof(rSAK));
                                        cuid = bytes_to_num(rUIDBCC1, 4);
                                        if (!_7BUID) {
                                                cardSTATE = MFEMUL_WORK;
                                                LED_B_ON();
                                                if (MF_DBGLEVEL >= 4)   Dbprintf("--> WORK. anticol1 time: %d", GetTickCount() - selTimer);
                                                break;
                                        } else {
                                                cardSTATE = MFEMUL_SELECT2;
                                        }
                                }
                                break;
                        }
                        case MFEMUL_AUTH1:{
                                if( len != 8)
                                {
                                        cardSTATE_TO_IDLE();
                                        LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        break;
                                }

                                uint32_t ar = bytes_to_num(receivedCmd, 4);
                                uint32_t nr = bytes_to_num(&receivedCmd[4], 4);

                                //Collect AR/NR
                                //if(ar_nr_collected < 2 && cardAUTHSC == 2){
                                if(ar_nr_collected < 2){
                                        if(ar_nr_responses[2] != ar)
                                        {// Avoid duplicates... probably not necessary, ar should vary. 
                                                //ar_nr_responses[ar_nr_collected*5]   = 0;
                                                //ar_nr_responses[ar_nr_collected*5+1] = 0;
                                                ar_nr_responses[ar_nr_collected*5+2] = nonce;
                                                ar_nr_responses[ar_nr_collected*5+3] = nr;
                                                ar_nr_responses[ar_nr_collected*5+4] = ar;
                                                ar_nr_collected++;
                                        }                                               
                                        // Interactive mode flag, means we need to send ACK
                                        if(flags & FLAG_INTERACTIVE && ar_nr_collected == 2)
                                        {
                                                finished = true;
                                        }
                                }

                                // --- crypto
                                //crypto1_word(pcs, ar , 1);
                                //cardRr = nr ^ crypto1_word(pcs, 0, 0);

                                //test if auth OK
                                //if (cardRr != prng_successor(nonce, 64)){
                                        
                                        //if (MF_DBGLEVEL >= 4) Dbprintf("AUTH FAILED for sector %d with key %c. cardRr=%08x, succ=%08x",
                                        //      cardAUTHSC, cardAUTHKEY == 0 ? 'A' : 'B',
                                        //              cardRr, prng_successor(nonce, 64));
                                        // Shouldn't we respond anything here?
                                        // Right now, we don't nack or anything, which causes the
                                        // reader to do a WUPA after a while. /Martin
                                        // -- which is the correct response. /piwi
                                        //cardSTATE_TO_IDLE();
                                        //LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        //break;
                                //}

                                ans = prng_successor(nonce, 96) ^ crypto1_word(pcs, 0, 0);

                                num_to_bytes(ans, 4, rAUTH_AT);
                                // --- crypto
                                EmSendCmd(rAUTH_AT, sizeof(rAUTH_AT));
                                LED_C_ON();
                                cardSTATE = MFEMUL_WORK;
                                if (MF_DBGLEVEL >= 4)   Dbprintf("AUTH COMPLETED for sector %d with key %c. time=%d", 
                                        cardAUTHSC, cardAUTHKEY == 0 ? 'A' : 'B',
                                        GetTickCount() - authTimer);
                                break;
                        }
                        case MFEMUL_SELECT2:{
                                if (!len) { 
                                        LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        break;
                                }
                                if (len == 2 && (receivedCmd[0] == 0x95 && receivedCmd[1] == 0x20)) {
                                        EmSendCmd(rUIDBCC2, sizeof(rUIDBCC2));
                                        break;
                                }

                                // select 2 card
                                if (len == 9 && 
                                                (receivedCmd[0] == 0x95 && receivedCmd[1] == 0x70 && memcmp(&receivedCmd[2], rUIDBCC2, 4) == 0)) {
                                        EmSendCmd(rSAK, sizeof(rSAK));
                                        cuid = bytes_to_num(rUIDBCC2, 4);
                                        cardSTATE = MFEMUL_WORK;
                                        LED_B_ON();
                                        if (MF_DBGLEVEL >= 4)   Dbprintf("--> WORK. anticol2 time: %d", GetTickCount() - selTimer);
                                        break;
                                }
                                
                                // i guess there is a command). go into the work state.
                                if (len != 4) {
                                        LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        break;
                                }
                                cardSTATE = MFEMUL_WORK;
                                //goto lbWORK;
                                //intentional fall-through to the next case-stmt
                        }

                        case MFEMUL_WORK:{
                                if (len == 0) {
                                        LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        break;
                                }
                                
                                bool encrypted_data = (cardAUTHKEY != 0xFF) ;

                                if(encrypted_data) {
                                        // decrypt seqence
                                        mf_crypto1_decrypt(pcs, receivedCmd, len);
                                }
                                
                                if (len == 4 && (receivedCmd[0] == 0x60 || receivedCmd[0] == 0x61)) {
                                        authTimer = GetTickCount();
                                        cardAUTHSC = receivedCmd[1] / 4;  // received block num
                                        cardAUTHKEY = receivedCmd[0] - 0x60;
                                        crypto1_destroy(pcs);//Added by martin
                                        crypto1_create(pcs, emlGetKey(cardAUTHSC, cardAUTHKEY));

                                        if (!encrypted_data) { // first authentication
                                                if (MF_DBGLEVEL >= 4) Dbprintf("Reader authenticating for block %d (0x%02x) with key %d",receivedCmd[1] ,receivedCmd[1],cardAUTHKEY  );

                                                crypto1_word(pcs, cuid ^ nonce, 0);//Update crypto state
                                                num_to_bytes(nonce, 4, rAUTH_AT); // Send nonce
                                        } else { // nested authentication
                                                if (MF_DBGLEVEL >= 4) Dbprintf("Reader doing nested authentication for block %d (0x%02x) with key %d",receivedCmd[1] ,receivedCmd[1],cardAUTHKEY );
                                                ans = nonce ^ crypto1_word(pcs, cuid ^ nonce, 0); 
                                                num_to_bytes(ans, 4, rAUTH_AT);
                                        }

                                        EmSendCmd(rAUTH_AT, sizeof(rAUTH_AT));
                                        //Dbprintf("Sending rAUTH %02x%02x%02x%02x", rAUTH_AT[0],rAUTH_AT[1],rAUTH_AT[2],rAUTH_AT[3]);
                                        cardSTATE = MFEMUL_AUTH1;
                                        break;
                                }
                                
                                // rule 13 of 7.5.3. in ISO 14443-4. chaining shall be continued
                                // BUT... ACK --> NACK
                                if (len == 1 && receivedCmd[0] == CARD_ACK) {
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                        break;
                                }
                                
                                // rule 12 of 7.5.3. in ISO 14443-4. R(NAK) --> R(ACK)
                                if (len == 1 && receivedCmd[0] == CARD_NACK_NA) {
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_ACK));
                                        break;
                                }
                                
                                if(len != 4) {
                                        LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        break;
                                }

                                if(receivedCmd[0] == 0x30 // read block
                                                || receivedCmd[0] == 0xA0 // write block
                                                || receivedCmd[0] == 0xC0 // inc
                                                || receivedCmd[0] == 0xC1 // dec
                                                || receivedCmd[0] == 0xC2 // restore
                                                || receivedCmd[0] == 0xB0) { // transfer
                                        if (receivedCmd[1] >= 16 * 4) {
                                                EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                                if (MF_DBGLEVEL >= 4) Dbprintf("Reader tried to operate (0x%02) on out of range block: %d (0x%02x), nacking",receivedCmd[0],receivedCmd[1],receivedCmd[1]);
                                                break;
                                        }

                                        if (receivedCmd[1] / 4 != cardAUTHSC) {
                                                EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                                if (MF_DBGLEVEL >= 4) Dbprintf("Reader tried to operate (0x%02) on block (0x%02x) not authenticated for (0x%02x), nacking",receivedCmd[0],receivedCmd[1],cardAUTHSC);
                                                break;
                                        }
                                }
                                // read block
                                if (receivedCmd[0] == 0x30) {
                                        if (MF_DBGLEVEL >= 4) {
                                                Dbprintf("Reader reading block %d (0x%02x)",receivedCmd[1],receivedCmd[1]);
                                        }
                                        emlGetMem(response, receivedCmd[1], 1);
                                        AppendCrc14443a(response, 16);
                                        mf_crypto1_encrypt(pcs, response, 18, response_par);
                                        EmSendCmdPar(response, 18, response_par);
                                        numReads++;
                                        if(exitAfterNReads > 0 && numReads >= exitAfterNReads) {
                                                Dbprintf("%d reads done, exiting", numReads);
                                                finished = true;
                                        }
                                        break;
                                }
                                // write block
                                if (receivedCmd[0] == 0xA0) {
                                        if (MF_DBGLEVEL >= 4) Dbprintf("RECV 0xA0 write block %d (%02x)",receivedCmd[1],receivedCmd[1]);
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_ACK));
                                        cardSTATE = MFEMUL_WRITEBL2;
                                        cardWRBL = receivedCmd[1];
                                        break;
                                }
                                // increment, decrement, restore
                                if (receivedCmd[0] == 0xC0 || receivedCmd[0] == 0xC1 || receivedCmd[0] == 0xC2) {
                                        if (MF_DBGLEVEL >= 4) Dbprintf("RECV 0x%02x inc(0xC1)/dec(0xC0)/restore(0xC2) block %d (%02x)",receivedCmd[0],receivedCmd[1],receivedCmd[1]);
                                        if (emlCheckValBl(receivedCmd[1])) {
                                                if (MF_DBGLEVEL >= 4) Dbprintf("Reader tried to operate on block, but emlCheckValBl failed, nacking");
                                                EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                                break;
                                        }
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_ACK));
                                        if (receivedCmd[0] == 0xC1)
                                                cardSTATE = MFEMUL_INTREG_INC;
                                        if (receivedCmd[0] == 0xC0)
                                                cardSTATE = MFEMUL_INTREG_DEC;
                                        if (receivedCmd[0] == 0xC2)
                                                cardSTATE = MFEMUL_INTREG_REST;
                                        cardWRBL = receivedCmd[1];
                                        break;
                                }
                                // transfer
                                if (receivedCmd[0] == 0xB0) {
                                        if (MF_DBGLEVEL >= 4) Dbprintf("RECV 0x%02x transfer block %d (%02x)",receivedCmd[0],receivedCmd[1],receivedCmd[1]);
                                        if (emlSetValBl(cardINTREG, cardINTBLOCK, receivedCmd[1]))
                                                EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                        else
                                                EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_ACK));
                                        break;
                                }
                                // halt
                                if (receivedCmd[0] == 0x50 && receivedCmd[1] == 0x00) {
                                        LED_B_OFF();
                                        LED_C_OFF();
                                        cardSTATE = MFEMUL_HALTED;
                                        if (MF_DBGLEVEL >= 4)   Dbprintf("--> HALTED. Selected time: %d ms",  GetTickCount() - selTimer);
                                        LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                        break;
                                }
                                // RATS
                                if (receivedCmd[0] == 0xe0) {//RATS
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                        break;
                                }
                                // command not allowed
                                if (MF_DBGLEVEL >= 4)   Dbprintf("Received command not allowed, nacking");
                                EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                break;
                        }
                        case MFEMUL_WRITEBL2:{
                                if (len == 18){
                                        mf_crypto1_decrypt(pcs, receivedCmd, len);
                                        emlSetMem(receivedCmd, cardWRBL, 1);
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_ACK));
                                        cardSTATE = MFEMUL_WORK;
                                } else {
                                        cardSTATE_TO_IDLE();
                                        LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                }
                                break;
                        }
                        
                        case MFEMUL_INTREG_INC:{
                                mf_crypto1_decrypt(pcs, receivedCmd, len);
                                memcpy(&ans, receivedCmd, 4);
                                if (emlGetValBl(&cardINTREG, &cardINTBLOCK, cardWRBL)) {
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                        cardSTATE_TO_IDLE();
                                        break;
                                } 
                                LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                cardINTREG = cardINTREG + ans;
                                cardSTATE = MFEMUL_WORK;
                                break;
                        }
                        case MFEMUL_INTREG_DEC:{
                                mf_crypto1_decrypt(pcs, receivedCmd, len);
                                memcpy(&ans, receivedCmd, 4);
                                if (emlGetValBl(&cardINTREG, &cardINTBLOCK, cardWRBL)) {
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                        cardSTATE_TO_IDLE();
                                        break;
                                }
                                LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                cardINTREG = cardINTREG - ans;
                                cardSTATE = MFEMUL_WORK;
                                break;
                        }
                        case MFEMUL_INTREG_REST:{
                                mf_crypto1_decrypt(pcs, receivedCmd, len);
                                memcpy(&ans, receivedCmd, 4);
                                if (emlGetValBl(&cardINTREG, &cardINTBLOCK, cardWRBL)) {
                                        EmSend4bit(mf_crypto1_encrypt4bit(pcs, CARD_NACK_NA));
                                        cardSTATE_TO_IDLE();
                                        break;
                                }
                                LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, TRUE);
                                cardSTATE = MFEMUL_WORK;
                                break;
                        }
                }
        }

        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        LEDsoff();

        if(flags & FLAG_INTERACTIVE)// Interactive mode flag, means we need to send ACK
        {
                //May just aswell send the collected ar_nr in the response aswell
                uint8_t len = ar_nr_collected*5*4;
                cmd_send(CMD_ACK, CMD_SIMULATE_MIFARE_CARD, len, 0, &ar_nr_responses, len);
        }

        if(flags & FLAG_NR_AR_ATTACK && MF_DBGLEVEL >= 1 )
        {
                if(ar_nr_collected > 1 ) {
                        Dbprintf("Collected two pairs of AR/NR which can be used to extract keys from reader:");
                        Dbprintf("../tools/mfkey/mfkey32 %06x%08x %08x %08x %08x %08x %08x",
                                        ar_nr_responses[0], // UID1
                                        ar_nr_responses[1], // UID2
                                        ar_nr_responses[2], // NT
                                        ar_nr_responses[3], // AR1
                                        ar_nr_responses[4], // NR1
                                        ar_nr_responses[8], // AR2
                                        ar_nr_responses[9]  // NR2
                                        );
                        Dbprintf("../tools/mfkey/mfkey32v2 %06x%08x %08x %08x %08x %08x %08x %08x",
                                        ar_nr_responses[0], // UID1
                                        ar_nr_responses[1], // UID2
                                        ar_nr_responses[2], // NT1
                                        ar_nr_responses[3], // AR1
                                        ar_nr_responses[4], // NR1
                                        ar_nr_responses[7], // NT2
                                        ar_nr_responses[8], // AR2
                                        ar_nr_responses[9]  // NR2
                                        );
                } else {
                        Dbprintf("Failed to obtain two AR/NR pairs!");
                        if(ar_nr_collected > 0 ) {
                                Dbprintf("Only got these: UID=%07x%08x, nonce=%08x, AR1=%08x, NR1=%08x",
                                                ar_nr_responses[0], // UID1
                                                ar_nr_responses[1], // UID2
                                                ar_nr_responses[2], // NT
                                                ar_nr_responses[3], // AR1
                                                ar_nr_responses[4]  // NR1
                                                );
                        }
                }
        }
        if (MF_DBGLEVEL >= 1)   Dbprintf("Emulator stopped. Tracing: %d  trace length: %d ", tracing, BigBuf_get_traceLen());
        
        set_tracing(FALSE);
}


//-----------------------------------------------------------------------------
// MIFARE sniffer. 
// 
//-----------------------------------------------------------------------------
void RAMFUNC SniffMifare(uint8_t param) {
        // param:
        // bit 0 - trigger from first card answer
        // bit 1 - trigger from first reader 7-bit request

        // C(red) A(yellow) B(green)
        LEDsoff();
        // init trace buffer
        clear_trace();
        set_tracing(TRUE);

        // The command (reader -> tag) that we're receiving.
        // The length of a received command will in most cases be no more than 18 bytes.
        // So 32 should be enough!
        uint8_t receivedCmd[MAX_MIFARE_FRAME_SIZE];
        uint8_t receivedCmdPar[MAX_MIFARE_PARITY_SIZE];
        // The response (tag -> reader) that we're receiving.
        uint8_t receivedResponse[MAX_MIFARE_FRAME_SIZE];
        uint8_t receivedResponsePar[MAX_MIFARE_PARITY_SIZE];

        iso14443a_setup(FPGA_HF_ISO14443A_SNIFFER);

        // free eventually allocated BigBuf memory
        BigBuf_free();
        // allocate the DMA buffer, used to stream samples from the FPGA
        uint8_t *dmaBuf = BigBuf_malloc(DMA_BUFFER_SIZE);
        uint8_t *data = dmaBuf;
        uint8_t previous_data = 0;
        int maxDataLen = 0;
        int dataLen = 0;
        bool ReaderIsActive = FALSE;
        bool TagIsActive = FALSE;

        // Set up the demodulator for tag -> reader responses.
        DemodInit(receivedResponse, receivedResponsePar);

        // Set up the demodulator for the reader -> tag commands
        UartInit(receivedCmd, receivedCmdPar);

        // Setup for the DMA.
        FpgaSetupSscDma((uint8_t *)dmaBuf, DMA_BUFFER_SIZE); // set transfer address and number of bytes. Start transfer.

        LED_D_OFF();
        
        // init sniffer
        MfSniffInit();

        // And now we loop, receiving samples.
        for(uint32_t sniffCounter = 0; TRUE; ) {
        
                if(BUTTON_PRESS()) {
                        DbpString("cancelled by button");
                        break;
                }

                LED_A_ON();
                WDT_HIT();
                
                if ((sniffCounter & 0x0000FFFF) == 0) { // from time to time
                        // check if a transaction is completed (timeout after 2000ms).
                        // if yes, stop the DMA transfer and send what we have so far to the client
                        if (MfSniffSend(2000)) {                        
                                // Reset everything - we missed some sniffed data anyway while the DMA was stopped
                                sniffCounter = 0;
                                data = dmaBuf;
                                maxDataLen = 0;
                                ReaderIsActive = FALSE;
                                TagIsActive = FALSE;
                                FpgaSetupSscDma((uint8_t *)dmaBuf, DMA_BUFFER_SIZE); // set transfer address and number of bytes. Start transfer.
                        }
                }
                
                int register readBufDataP = data - dmaBuf;      // number of bytes we have processed so far
                int register dmaBufDataP = DMA_BUFFER_SIZE - AT91C_BASE_PDC_SSC->PDC_RCR; // number of bytes already transferred
                if (readBufDataP <= dmaBufDataP){                       // we are processing the same block of data which is currently being transferred
                        dataLen = dmaBufDataP - readBufDataP;   // number of bytes still to be processed
                } else {                                                                        
                        dataLen = DMA_BUFFER_SIZE - readBufDataP + dmaBufDataP; // number of bytes still to be processed
                }
                // test for length of buffer
                if(dataLen > maxDataLen) {                                      // we are more behind than ever...
                        maxDataLen = dataLen;                                   
                        if(dataLen > (9 * DMA_BUFFER_SIZE / 10)) {
                                Dbprintf("blew circular buffer! dataLen=0x%x", dataLen);
                                break;
                        }
                }
                if(dataLen < 1) continue;

                // primary buffer was stopped ( <-- we lost data!
                if (!AT91C_BASE_PDC_SSC->PDC_RCR) {
                        AT91C_BASE_PDC_SSC->PDC_RPR = (uint32_t) dmaBuf;
                        AT91C_BASE_PDC_SSC->PDC_RCR = DMA_BUFFER_SIZE;
                        Dbprintf("RxEmpty ERROR!!! data length:%d", dataLen); // temporary
                }
                // secondary buffer sets as primary, secondary buffer was stopped
                if (!AT91C_BASE_PDC_SSC->PDC_RNCR) {
                        AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) dmaBuf;
                        AT91C_BASE_PDC_SSC->PDC_RNCR = DMA_BUFFER_SIZE;
                }

                LED_A_OFF();
                
                if (sniffCounter & 0x01) {

                        if(!TagIsActive) {              // no need to try decoding tag data if the reader is sending
                                uint8_t readerdata = (previous_data & 0xF0) | (*data >> 4);
                                if(MillerDecoding(readerdata, (sniffCounter-1)*4)) {
                                        LED_C_INV();
                                        if (MfSniffLogic(receivedCmd, Uart.len, Uart.parity, Uart.bitCount, TRUE)) break;

                                        /* And ready to receive another command. */
                                        UartInit(receivedCmd, receivedCmdPar);
                                        
                                        /* And also reset the demod code */
                                        DemodReset();
                                }
                                ReaderIsActive = (Uart.state != STATE_UNSYNCD);
                        }
                        
                        if(!ReaderIsActive) {           // no need to try decoding tag data if the reader is sending
                                uint8_t tagdata = (previous_data << 4) | (*data & 0x0F);
                                if(ManchesterDecoding(tagdata, 0, (sniffCounter-1)*4)) {
                                        LED_C_INV();

                                        if (MfSniffLogic(receivedResponse, Demod.len, Demod.parity, Demod.bitCount, FALSE)) break;

                                        // And ready to receive another response.
                                        DemodReset();
                                        // And reset the Miller decoder including its (now outdated) input buffer
                                        UartInit(receivedCmd, receivedCmdPar);
                                }
                                TagIsActive = (Demod.state != DEMOD_UNSYNCD);
                        }
                }

                previous_data = *data;
                sniffCounter++;
                data++;
                if(data == dmaBuf + DMA_BUFFER_SIZE) {
                        data = dmaBuf;
                }

        } // main cycle

        FpgaDisableSscDma();
        MfSniffEnd();
        LEDsoff();
        Dbprintf("maxDataLen=%x, Uart.state=%x, Uart.len=%x", maxDataLen, Uart.state, Uart.len);
        set_tracing(FALSE);
}