chg: LF t55xx trace

[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 "../include/proxmark3.h"
#include "apps.h"
#include "util.h"
#include "string.h"
#include "../common/cmd.h"
#include "../common/iso14443crc.h"
#include "iso14443a.h"
#include "crapto1.h"
#include "mifareutil.h"

static uint32_t iso14a_timeout;
uint8_t *trace = (uint8_t *) BigBuf+TRACE_OFFSET;
int rsamples = 0;
int traceLen = 0;
int tracing = TRUE;
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:
uint32_t NextTransferTime;
uint32_t LastTimeProxToAirStart;
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

const uint8_t OddByteParity[256] = {
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1
};


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

void iso14a_clear_trace() {
	memset(trace, 0x44, TRACE_SIZE);
	traceLen = 0;
}

void iso14a_set_tracing(bool enable) {
	tracing = enable;
}

void iso14a_set_timeout(uint32_t timeout) {
	iso14a_timeout = timeout;
}

//-----------------------------------------------------------------------------
// Generate the parity value for a byte sequence
//
//-----------------------------------------------------------------------------
byte_t oddparity (const byte_t bt)
{
	return OddByteParity[bt];
}

uint32_t GetParity(const uint8_t * pbtCmd, int iLen)
{
	int i;
	uint32_t dwPar = 0;

	// Generate the parity bits
	for (i = 0; i < iLen; i++) {
		// and save them to a 32Bit word
		dwPar |= ((OddByteParity[pbtCmd[i]]) << i);
	}
	return dwPar;
}

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

// The function LogTrace() is also used by the iClass implementation in iClass.c
bool RAMFUNC LogTrace(const uint8_t * btBytes, uint8_t iLen, uint32_t timestamp, uint32_t dwParity, bool readerToTag)
{
	if (!tracing) return FALSE;
	// Return when trace is full
	if (traceLen + sizeof(timestamp) + sizeof(dwParity) + iLen >= TRACE_SIZE) {
		tracing = FALSE;	// don't trace any more
		return FALSE;
	}
	
	// Trace the random, i'm curious
	trace[traceLen++] = ((timestamp >> 0) & 0xff);
	trace[traceLen++] = ((timestamp >> 8) & 0xff);
	trace[traceLen++] = ((timestamp >> 16) & 0xff);
	trace[traceLen++] = ((timestamp >> 24) & 0xff);

	if (!readerToTag) {
		trace[traceLen - 1] |= 0x80;
	}
	trace[traceLen++] = ((dwParity >> 0) & 0xff);
	trace[traceLen++] = ((dwParity >> 8) & 0xff);
	trace[traceLen++] = ((dwParity >> 16) & 0xff);
	trace[traceLen++] = ((dwParity >> 24) & 0xff);
	trace[traceLen++] = iLen;
	if (btBytes != NULL && iLen != 0) {
		memcpy(trace + traceLen, btBytes, iLen);
	}
	traceLen += iLen;
	return TRUE;
}

//=============================================================================
// 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 two or three consecutive "0" in any position with the rest "1"
const bool Mod_Miller_LUT[] = {
	TRUE,  TRUE,  FALSE, TRUE,  FALSE, FALSE, FALSE, FALSE,
	TRUE,  TRUE,  FALSE, FALSE, TRUE,  FALSE, FALSE, FALSE
};
#define IsMillerModulationNibble1(b) (Mod_Miller_LUT[(b & 0x00F0) >> 4])
#define IsMillerModulationNibble2(b) (Mod_Miller_LUT[(b & 0x000F)])

void UartReset()
{
	Uart.state = STATE_UNSYNCD;
	Uart.bitCount = 0;
	Uart.len = 0;						// number of decoded data bytes
	Uart.shiftReg = 0;					// shiftreg to hold decoded data bits
	Uart.parityBits = 0;				// 
	Uart.twoBits = 0x0000;	 			// buffer for 2 Bits
	Uart.highCnt = 0;
	Uart.startTime = 0;
	Uart.endTime = 0;
}


// 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.twoBits = (Uart.twoBits << 8) | bit;
	
	if (Uart.state == STATE_UNSYNCD) {												// not yet synced
		if (Uart.highCnt < 7) {													// wait for a stable unmodulated signal
			if (Uart.twoBits == 0xffff) {
				Uart.highCnt++;
			} else {
				Uart.highCnt = 0;
			}
		} else {	
			Uart.syncBit = 0xFFFF; // not set
			// look for 00xx1111 (the start bit)
			if 		((Uart.twoBits & 0x6780) == 0x0780) Uart.syncBit = 7; 
			else if ((Uart.twoBits & 0x33C0) == 0x03C0) Uart.syncBit = 6;
			else if ((Uart.twoBits & 0x19E0) == 0x01E0) Uart.syncBit = 5;
			else if ((Uart.twoBits & 0x0CF0) == 0x00F0) Uart.syncBit = 4;
			else if ((Uart.twoBits & 0x0678) == 0x0078) Uart.syncBit = 3;
			else if ((Uart.twoBits & 0x033C) == 0x003C) Uart.syncBit = 2;
			else if ((Uart.twoBits & 0x019E) == 0x001E) Uart.syncBit = 1;
			else if ((Uart.twoBits & 0x00CF) == 0x000F) Uart.syncBit = 0;
			if (Uart.syncBit != 0xFFFF) {
				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.twoBits >> Uart.syncBit)) {			
			if (IsMillerModulationNibble2(Uart.twoBits >> Uart.syncBit)) {		// Modulation in both halves - error
				UartReset();
				Uart.highCnt = 6;
			} else {															// Modulation in first half = Sequence Z = logic "0"
				if (Uart.state == STATE_MILLER_X) {								// error - must not follow after X
					UartReset();
					Uart.highCnt = 6;
				} 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;
					}
				}
			}
		} else {
			if (IsMillerModulationNibble2(Uart.twoBits >> 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;
				}
			} 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;
					if(Uart.len == 0 && Uart.bitCount > 0) {										// if we decoded some bits
						Uart.shiftReg >>= (9 - Uart.bitCount);					// add them to the output
						Uart.output[Uart.len++] = (Uart.shiftReg & 0xff);
						Uart.parityBits <<= 1;									// no parity bit - add "0"
						Uart.bitCount--;										// last "0" was part of the EOC sequence
					}
					return TRUE;
				}
				if (Uart.state == STATE_START_OF_COMMUNICATION) {				// error - must not follow directly after SOC
					UartReset();
					Uart.highCnt = 6;
				} 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;
					}
				}
			}
		}
			
	} 

    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.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;
}

// 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;
			}
			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;
				}
				Demod.endTime = Demod.startTime + 8*(9*Demod.len + Demod.bitCount + 1);
			} else {													// no modulation in both halves - End of communication
				if (Demod.len > 0 || Demod.bitCount > 0) {				// received something
					if(Demod.bitCount > 0) {							// if we decoded bits
						Demod.shiftReg >>= (9 - Demod.bitCount);		// add the remaining decoded bits to the output
						Demod.output[Demod.len++] = Demod.shiftReg & 0xff;
						// No parity bit, so just shift a 0
						Demod.parityBits <<= 1;
					}
					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 SnoopIso14443a(uint8_t param) {
	// param:
	// bit 0 - trigger from first card answer
	// bit 1 - trigger from first reader 7-bit request
	
	LEDsoff();
	// init trace buffer
	iso14a_clear_trace();
	iso14a_set_tracing(TRUE);

	// 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); 
	
	// 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 = (((uint8_t *)BigBuf) + RECV_CMD_OFFSET);
	// The response (tag -> reader) that we're receiving.
	uint8_t *receivedResponse = (((uint8_t *)BigBuf) + RECV_RES_OFFSET);

	// As we receive stuff, we copy it from receivedCmd or receivedResponse
	// into trace, along with its length and other annotations.
	//uint8_t *trace = (uint8_t *)BigBuf;
	
	// The DMA buffer, used to stream samples from the FPGA
	uint8_t *dmaBuf = ((uint8_t *)BigBuf) + DMA_BUFFER_OFFSET;
	uint8_t *data = dmaBuf;
	uint8_t previous_data = 0;
	int maxDataLen = 0;
	int dataLen = 0;
	bool TagIsActive = FALSE;
	bool ReaderIsActive = FALSE;
	
	iso14443a_setup(FPGA_HF_ISO14443A_SNIFFER);

	// Set up the demodulator for tag -> reader responses.
	Demod.output = receivedResponse;

	// Set up the demodulator for the reader -> tag commands
	Uart.output = receivedCmd;

	// Setup and start DMA.
	FpgaSetupSscDma((uint8_t *)dmaBuf, DMA_BUFFER_SIZE);
	
	// 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 > 400) {
				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.parityBits, TRUE)) break;
						if (!LogTrace(NULL, 0, Uart.endTime*16 - DELAY_READER_AIR2ARM_AS_SNIFFER, 0, 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.parityBits, FALSE)) break;
					if (!LogTrace(NULL, 0, Demod.endTime*16 - DELAY_TAG_AIR2ARM_AS_SNIFFER, 0, FALSE)) break;

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

					// And ready to receive another response.
					DemodReset();
					LED_C_OFF();
				} 
				TagIsActive = (Demod.state != DEMOD_UNSYNCD);
			}
		}

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

	DbpString("COMMAND FINISHED");

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

//-----------------------------------------------------------------------------
// Prepare tag messages
//-----------------------------------------------------------------------------
static void CodeIso14443aAsTagPar(const uint8_t *cmd, int len, uint32_t dwParity)
{
	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;
	LastProxToAirDuration = 8 * ToSendMax - 4;

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

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

		// Get the parity bit
		if ((dwParity >> i) & 0x01) {
			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, int len){
	CodeIso14443aAsTagPar(cmd, len, GetParity(cmd, len));
}


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, int *len, int maxLen)
{
    // 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.
	UartReset();
    Uart.output = received;

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

static uint8_t* free_buffer_pointer = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);

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

void reset_free_buffer() {
  free_buffer_pointer = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);
}

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;
}

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 = (((uint8_t *)BigBuf)+FREE_BUFFER_OFFSET+FREE_BUFFER_SIZE)-free_buffer_pointer;
  
  // 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 uid_1st, int uid_2nd, byte_t* data)
{
	// Enable and clear the trace
	iso14a_clear_trace();
	iso14a_set_tracing(TRUE);

	uint8_t sak;

	// The first response contains the ATQA (note: bytes are transmitted in reverse order).
	uint8_t response1[2];
	
	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] = 0x04;
			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;
		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];

	// Check if the uid uses the (optional) part
	uint8_t response2a[5];
	if (uid_2nd) {
		response2[0] = 0x88;
		num_to_bytes(uid_1st,3,response2+1);
		num_to_bytes(uid_2nd,4,response2a);
		response2a[4] = response2a[0] ^ response2a[1] ^ response2a[2] ^ response2a[3];

		// Configure the ATQA and SAK accordingly
		response1[0] |= 0x40;
		sak |= 0x04;
	} else {
		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];
	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];
	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, 0x00, 0x02, 0x00, 0x00 }; // dummy ATS (pseudo-ATR), answer to RATS
	ComputeCrc14443(CRC_14443_A, response6, 4, &response6[4], &response6[5]);

	#define TAG_RESPONSE_COUNT 7
	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
	};

	// 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
	};
  
	// Reset the offset pointer of the free buffer
	reset_free_buffer();
  
	// 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]);
	}

	uint8_t *receivedCmd = (((uint8_t *)BigBuf) + RECV_CMD_OFFSET);
	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;

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

	cmdsRecvd = 0;
	tag_response_info_t* p_response;

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

		p_response = NULL;
		
		// doob - added loads of debug strings so we can see what the reader is saying to us during the sim as hi14alist is not populated
		// 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
			EmSendCmdEx(data+(4*receivedCmd[0]),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] == 0x50) {	// Received a HALT
//			DbpString("Reader requested we HALT!:");
			if (tracing) {
				LogTrace(receivedCmd, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parityBits, TRUE);
				LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, TRUE);
			}
			p_response = NULL;
		} else if(receivedCmd[0] == 0x60 || receivedCmd[0] == 0x61) {	// Received an authentication request
			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 authentication request
			if (tracing) {
				LogTrace(receivedCmd, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parityBits, TRUE);
				LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, TRUE);
			}
			uint32_t nr = bytes_to_num(receivedCmd,4);
			uint32_t ar = bytes_to_num(receivedCmd+4,4);
			Dbprintf("Auth attempt {nr}{ar}: %08x %08x",nr,ar);
		} else {
			// Check for ISO 14443A-4 compliant commands, look at left nibble
			switch (receivedCmd[0]) {

				case 0x0B:
				case 0x0A: { // IBlock (command)
				  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: { //
				  memcpy(dynamic_response_info.response,"\xAB\x00",2);
				  dynamic_response_info.response_n = 2;
				} break;

				case 0xCA:
				case 0xC2: { // Readers sends deselect command
				  memcpy(dynamic_response_info.response,"\xCA\x00",2);
				  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.parityBits, TRUE);
						LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
						LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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:
			EmLogTrace(Uart.output, 
						Uart.len, 
						Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, 
						Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 
						Uart.parityBits,
						p_response->response, 
						p_response->response_n,
						LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_TAG,
						(LastTimeProxToAirStart + p_response->ProxToAirDuration)*16 + DELAY_ARM2AIR_AS_TAG, 
						SwapBits(GetParity(p_response->response, p_response->response_n), p_response->response_n));
		}
		
		if (!tracing) {
			Dbprintf("Trace Full. Simulation stopped.");
			break;
		}
	}

	Dbprintf("%x %x %x", happened, happened2, cmdsRecvd);
	LED_A_OFF();
}


// 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, int 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, int bits, uint32_t dwParity)
{
	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 (last) parity bit if we transmitted a complete byte
		if (j == 8) {
			// Get the parity bit
			if ((dwParity >> i) & 0x01) {
				// 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, int len, uint32_t dwParity)
{
  CodeIso14443aBitsAsReaderPar(cmd,len*8,dwParity);
}

//-----------------------------------------------------------------------------
// 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, int *len)
{
	*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(32) |
				ADC_MODE_STARTUP_TIME(16) |
				ADC_MODE_SAMPLE_HOLD_TIME(8);
	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.
	UartReset();
	Uart.output = received;

	// 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 ((33000 * (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, int 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:
	for (i = 0; i < 2 ; ) {
		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:
	EmLogTrace(Uart.output, 
				Uart.len, 
				Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, 
				Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 
				Uart.parityBits,
				&resp, 
				1, 
				LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_TAG,
				(LastTimeProxToAirStart + LastProxToAirDuration)*16 + DELAY_ARM2AIR_AS_TAG, 
				SwapBits(GetParity(&resp, 1), 1));
	return res;
}

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

int EmSendCmdExPar(uint8_t *resp, int respLen, bool correctionNeeded, uint32_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.parityBits,
				resp, 
				respLen, 
				LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_TAG,
				(LastTimeProxToAirStart + LastProxToAirDuration)*16 + DELAY_ARM2AIR_AS_TAG, 
				SwapBits(GetParity(resp, respLen), respLen));
	return res;
}

int EmSendCmdEx(uint8_t *resp, int respLen, bool correctionNeeded){
	return EmSendCmdExPar(resp, respLen, correctionNeeded, GetParity(resp, respLen));
}

int EmSendCmd(uint8_t *resp, int respLen){
	return EmSendCmdExPar(resp, respLen, false, GetParity(resp, respLen));
}

int EmSendCmdPar(uint8_t *resp, int respLen, uint32_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, uint32_t reader_Parity,
				 uint8_t *tag_data, uint16_t tag_len, uint32_t tag_StartTime, uint32_t tag_EndTime, uint32_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_Parity, TRUE)) {
			return FALSE;
		} else if (!LogTrace(NULL, 0, reader_EndTime, 0, TRUE)) {
			return FALSE;
		} else if (!LogTrace(tag_data, tag_len, tag_StartTime, tag_Parity, FALSE)) {
			return FALSE;
		} else {
			return (!LogTrace(NULL, 0, tag_EndTime, 0, 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, uint16_t offset, int maxLen)
{
	uint16_t c;
	
	// 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
	DemodReset();
	Demod.output = receivedResponse;

	// clear RXRDY:
    uint8_t b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
	
	c = 0;
	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) {
				return FALSE; 
			}
		}
	}
}

void ReaderTransmitBitsPar(uint8_t* frame, int bits, uint32_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, par, TRUE);
		LogTrace(NULL, 0, (LastTimeProxToAirStart + LastProxToAirDuration)*16 + DELAY_ARM2AIR_AS_READER, 0, TRUE);
	}
}

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

void ReaderTransmitBits(uint8_t* frame, int len, uint32_t *timing)
{
  // Generate parity and redirect
  ReaderTransmitBitsPar(frame,len,GetParity(frame,len/8), timing);
}

void ReaderTransmit(uint8_t* frame, int len, uint32_t *timing)
{
  // Generate parity and redirect
  ReaderTransmitBitsPar(frame,len*8,GetParity(frame,len), timing);
}

int ReaderReceiveOffset(uint8_t* receivedAnswer, uint16_t offset)
{
	if (!GetIso14443aAnswerFromTag(receivedAnswer,offset,160)) return FALSE;
	if (tracing) {
		LogTrace(receivedAnswer, Demod.len, Demod.startTime*16 - DELAY_AIR2ARM_AS_READER, Demod.parityBits, FALSE);
		LogTrace(NULL, 0, Demod.endTime*16 - DELAY_AIR2ARM_AS_READER, 0, FALSE);
	}
	return Demod.len;
}

int ReaderReceive(uint8_t* receivedAnswer)
{
	return ReaderReceiveOffset(receivedAnswer, 0);
}

int ReaderReceivePar(uint8_t *receivedAnswer, uint32_t *parptr)
{
	if (!GetIso14443aAnswerFromTag(receivedAnswer,0,160)) return FALSE;
	if (tracing) {
		LogTrace(receivedAnswer, Demod.len, Demod.startTime*16 - DELAY_AIR2ARM_AS_READER, Demod.parityBits, FALSE);
		LogTrace(NULL, 0, Demod.endTime*16 - DELAY_AIR2ARM_AS_READER, 0, FALSE);
	}
	*parptr = Demod.parityBits;
	return Demod.len;
}

/* performs iso14443a anticollision procedure
 * fills the uid pointer unless NULL
 * fills resp_data unless NULL */
int iso14443a_select_card(byte_t* uid_ptr, iso14a_card_select_t* p_hi14a_card, uint32_t* cuid_ptr) {
  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 = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);	// was 3560 - tied to other size changes
  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,7,0, NULL);
	
  // Receive the ATQA
  if(!ReaderReceive(resp)) return 0;
  // Dbprintf("atqa: %02x %02x",resp[0],resp[1]);

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

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

  // 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;

    // SELECT_ALL
    ReaderTransmit(sel_all,sizeof(sel_all), NULL);
    if (!ReaderReceive(resp)) 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 & 0xf8] |= 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)) 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);
	}
	uid_resp_len = 4;
       // Dbprintf("uid: %02x %02x %02x %02x",uid_resp[0],uid_resp[1],uid_resp[2],uid_resp[3]);

    // 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
	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)) return 0;
    sak = resp[0];

    // Test if more parts of the uid are comming
    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
      memcpy(uid_resp, uid_resp + 1, 3);
      uid_resp_len = 3;
    }

    if(uid_ptr) {
      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;
  }

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

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

  if (!(len = ReaderReceive(resp))) 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;
  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(1050); // 10ms default  10*105 = 
}

int iso14_apdu(uint8_t * cmd, size_t cmd_len, void * data) {
	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);
	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 arg0 = 0;
	byte_t buf[USB_CMD_DATA_SIZE];
  
	if(param & ISO14A_CONNECT) {
		iso14a_clear_trace();
	}

	iso14a_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);
			cmd_send(CMD_ACK,arg0,card->uidlen,0,buf,sizeof(iso14a_card_select_t));
		}
	}

	if(param & ISO14A_SET_TIMEOUT) {
		iso14a_set_timeout(c->arg[2]);
	}

	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) {
			AppendCrc14443a(cmd,len);
			len += 2;
			lenbits += 16; 
		}
		if(lenbits>0) {

			ReaderTransmitBitsPar(cmd,lenbits,GetParity(cmd,lenbits/8), NULL);
		} else {
			ReaderTransmit(cmd,len, NULL);
		}
		arg0 = ReaderReceive(buf);
		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);
	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 < 32768; 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 = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);

	iso14a_clear_trace();
	iso14a_set_tracing(TRUE);

	byte_t nt_diff = 0;
	byte_t par = 0;
	//byte_t par_mask = 0xff;
	static byte_t par_low = 0;
	bool led_on = TRUE;
	uint8_t uid[10];
	uint32_t cuid;

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

	static uint32_t sync_time;
	static uint32_t sync_cycles;
	int catch_up_cycles = 0;
	int last_catch_up = 0;
	uint16_t consecutive_resyncs = 0;
	int isOK = 0;



	if (first_try) { 
		mf_nr_ar3 = 0;
		iso14443a_setup(FPGA_HF_ISO14443A_READER_MOD);
		sync_time = GetCountSspClk() & 0xfffffff8;
		sync_cycles = 65536;									// theory: Mifare Classic's random generator repeats every 2^16 cycles (and so do the nonces).
		nt_attacked = 0;
		nt = 0;
		par = 0;
	}
	else {
		// we were unsuccessful on a previous call. Try another READER nonce (first 3 parity bits remain the same)
		// nt_attacked = prng_successor(nt_attacked, 1);
		mf_nr_ar3++;
		mf_nr_ar[3] = mf_nr_ar3;
		par = par_low;
	}

	LED_A_ON();
	LED_B_OFF();
	LED_C_OFF();
	
  
	for(uint16_t i = 0; TRUE; i++) {
		
		WDT_HIT();

		// Test if the action was cancelled
		if(BUTTON_PRESS()) {
			break;
		}
		
		LED_C_ON();

		if(!iso14443a_select_card(uid, NULL, &cuid)) {
			if (MF_DBGLEVEL >= 1)	Dbprintf("Mifare: Can't select card");
			continue;
		}

		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) {
			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);

		// Receive the (4 Byte) "random" nonce
		if (!ReaderReceive(receivedAnswer)) {
			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, try again
					continue;
				}
				sync_cycles = (sync_cycles - nt_distance);
				if (MF_DBGLEVEL >= 3) Dbprintf("calibrating in cycle %d. nt_distance=%d, Sync_cycles: %d\n", i, nt_distance, 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;
			}
			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);
			}
			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))
		{
			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 & 0x07; // 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] = par;
			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 = par_low;
		} else {
			if (nt_diff == 0 && first_try)
			{
				par++;
			} else {
				par = (((par >> 3) + 1) << 3) | par_low;
			}
		}
	}


	mf_nr_ar[3] &= 0x1F;
	
	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();

	iso14a_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;
	uint32_t par = 0;
	int 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 = eml_get_bigbufptr_recbuf();
	uint8_t *response = eml_get_bigbufptr_sendbuf();
	
	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};
	uint8_t rSAK1[] = {0x04, 0xda, 0x17};

	uint8_t rAUTH_NT[] = {0x01, 0x02, 0x03, 0x04};
	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};
	uint8_t ar_nr_collected = 0;

	// clear trace
    iso14a_clear_trace();
	iso14a_set_tracing(TRUE);

	// 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);
		}
	}

	/*
	 * 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;
		rUIDBCC2[4] = 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);


	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]);
		}
	}

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

		// find reader field
		// Vref = 3300mV, and an 10:1 voltage divider on the input
		// can measure voltages up to 33000 mV
		if (cardSTATE == MFEMUL_NOFIELD) {
			vHf = (33000 * 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);
		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.parityBits, TRUE);
				LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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){
					if(ar_nr_responses[2] != ar)
					{// Avoid duplicates... probably not necessary, ar should vary. 
						ar_nr_responses[ar_nr_collected*4] = cuid;
						ar_nr_responses[ar_nr_collected*4+1] = nonce;
						ar_nr_responses[ar_nr_collected*4+2] = ar;
						ar_nr_responses[ar_nr_collected*4+3] = nr;
						ar_nr_collected++;
					}
				}

				// --- 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 >= 2)	Dbprintf("AUTH FAILED. cardRr=%08x, succ=%08x",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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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 >= 2) 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 >= 2) 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, &par);
					EmSendCmdPar(response, 18, 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 >= 2) 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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
					LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
				LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
				LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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.parityBits, TRUE);
				LogTrace(NULL, 0, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, 0, 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
		cmd_send(CMD_ACK,CMD_SIMULATE_MIFARE_CARD,0,0,&ar_nr_responses,ar_nr_collected*4*4);
	}

	if(flags & FLAG_NR_AR_ATTACK)
	{
		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 %08x %08x %08x %08x %08x %08x",
					 ar_nr_responses[0], // UID
					ar_nr_responses[1], //NT
					ar_nr_responses[2], //AR1
					ar_nr_responses[3], //NR1
					ar_nr_responses[6], //AR2
					ar_nr_responses[7] //NR2
					);
		} else {
			Dbprintf("Failed to obtain two AR/NR pairs!");
			if(ar_nr_collected >0) {
				Dbprintf("Only got these: UID=%08x, nonce=%08x, AR1=%08x, NR1=%08x",
						ar_nr_responses[0], // UID
						ar_nr_responses[1], //NT
						ar_nr_responses[2], //AR1
						ar_nr_responses[3] //NR1
						);
			}
		}
	}
	if (MF_DBGLEVEL >= 1)	Dbprintf("Emulator stopped. Tracing: %d  trace length: %d ",	tracing, traceLen);
}



//-----------------------------------------------------------------------------
// 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
	iso14a_clear_trace();
	iso14a_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 = (((uint8_t *)BigBuf) + RECV_CMD_OFFSET);
	// The response (tag -> reader) that we're receiving.
	uint8_t *receivedResponse = (((uint8_t *)BigBuf) + RECV_RES_OFFSET);

	// As we receive stuff, we copy it from receivedCmd or receivedResponse
	// into trace, along with its length and other annotations.
	//uint8_t *trace = (uint8_t *)BigBuf;
	
	// The DMA buffer, used to stream samples from the FPGA
	uint8_t *dmaBuf = ((uint8_t *)BigBuf) + DMA_BUFFER_OFFSET;
	uint8_t *data = dmaBuf;
	uint8_t previous_data = 0;
	int maxDataLen = 0;
	int dataLen = 0;
	bool ReaderIsActive = FALSE;
	bool TagIsActive = FALSE;

	iso14443a_setup(FPGA_HF_ISO14443A_SNIFFER);

	// Set up the demodulator for tag -> reader responses.
	Demod.output = receivedResponse;

	// Set up the demodulator for the reader -> tag commands
	Uart.output = receivedCmd;

	// 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 > 400) {
				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.parityBits, Uart.bitCount, TRUE)) break;

					/* And ready to receive another command. */
					UartReset();
					
					/* 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.parityBits, Demod.bitCount, FALSE)) break;

					// And ready to receive another response.
					DemodReset();
				}
				TagIsActive = (Demod.state != DEMOD_UNSYNCD);
			}
		}

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

	} // main cycle

	DbpString("COMMAND FINISHED");

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