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[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 "iso14443a.h"

#include <stdio.h>
#include <string.h>
#include "proxmark3.h"
#include "apps.h"
#include "util.h"
#include "cmd.h"
#include "iso14443crc.h"
#include "crapto1/crapto1.h"
#include "mifareutil.h"
#include "mifaresniff.h"
#include "BigBuf.h"
#include "protocols.h"
#include "parity.h"
#include "fpgaloader.h"

typedef struct {
	enum {
		DEMOD_UNSYNCD,
		// DEMOD_HALF_SYNCD,
		// DEMOD_MOD_FIRST_HALF,
		// DEMOD_NOMOD_FIRST_HALF,
		DEMOD_MANCHESTER_DATA
	} state;
	uint16_t twoBits;
	uint16_t highCnt;
	uint16_t bitCount;
	uint16_t collisionPos;
	uint16_t syncBit;
	uint8_t  parityBits;
	uint8_t  parityLen;
	uint16_t shiftReg;
	uint16_t samples;
	uint16_t len;
	uint32_t startTime, endTime;
	uint8_t  *output;
	uint8_t  *parity;
} tDemod;

typedef enum {
	MOD_NOMOD = 0,
	MOD_SECOND_HALF,
	MOD_FIRST_HALF,
	MOD_BOTH_HALVES
	} Modulation_t;

typedef struct {
	enum {
		STATE_UNSYNCD,
		STATE_START_OF_COMMUNICATION,
		STATE_MILLER_X,
		STATE_MILLER_Y,
		STATE_MILLER_Z,
		// DROP_NONE,
		// DROP_FIRST_HALF,
		} state;
	uint16_t shiftReg;
	int16_t  bitCount;
	uint16_t len;
	uint16_t byteCntMax;
	uint16_t posCnt;
	uint16_t syncBit;
	uint8_t  parityBits;
	uint8_t  parityLen;
	uint32_t fourBits;
	uint32_t startTime, endTime;
	uint8_t *output;
	uint8_t *parity;
} tUart;

static uint32_t iso14a_timeout;
#define MAX_ISO14A_TIMEOUT 524288

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

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

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

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

// When the PM acts as tag and is receiving it takes
// 2 ticks delay in the RF part (for the first falling edge),
// 3 ticks for the A/D conversion,
// 8 ticks on average until the start of the SSC transfer,
// 8 ticks until the SSC samples the first data
// 7*16 ticks to complete the transfer from FPGA to ARM
// 8 ticks until the next ssp_clk rising edge
// 4*16 ticks until we measure the time
// - 8*16 ticks because we measure the time of the previous transfer
#define DELAY_AIR2ARM_AS_TAG (2 + 3 + 8 + 8 + 7*16 + 8 + 4*16 - 8*16)

// The FPGA will report its internal sending delay in
uint16_t FpgaSendQueueDelay;
// the 5 first bits are the number of bits buffered in mod_sig_buf
// the last three bits are the remaining ticks/2 after the mod_sig_buf shift
#define DELAY_FPGA_QUEUE (FpgaSendQueueDelay<<1)

// When the PM acts as tag and is sending, it takes
// 4*16 + 8 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 later the FPGA samples the first data
// + 16 ticks until assigned to mod_sig
// + 1 tick to assign mod_sig_coil
// + a varying number of ticks in the FPGA Delay Queue (mod_sig_buf)
#define DELAY_ARM2AIR_AS_TAG (4*16 + 8 + 8*16 + 8 + 16 + 1 + DELAY_FPGA_QUEUE)

// When the PM acts as sniffer and is receiving tag data, it takes
// 3 ticks A/D conversion
// 14 ticks to complete the modulation detection
// 8 ticks (on average) until the result is stored in to_arm
// + the delays in transferring data - which is the same for
// sniffing reader and tag data and therefore not relevant
#define DELAY_TAG_AIR2ARM_AS_SNIFFER (3 + 14 + 8)

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

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



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

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


void iso14a_set_timeout(uint32_t timeout) {
	// adjust timeout by FPGA delays and 2 additional ssp_frames to detect SOF
	iso14a_timeout = timeout + (DELAY_AIR2ARM_AS_READER + DELAY_ARM2AIR_AS_READER)/(16*8) + 2;
	if(MF_DBGLEVEL >= 3) Dbprintf("ISO14443A Timeout set to %ld (%dms)", timeout, timeout / 106);
}


uint32_t iso14a_get_timeout(void) {
	return iso14a_timeout - (DELAY_AIR2ARM_AS_READER + DELAY_ARM2AIR_AS_READER)/(16*8) - 2;
}

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

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

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

}

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

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


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

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

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

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

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

	Uart.fourBits = (Uart.fourBits << 8) | bit;

	if (Uart.state == STATE_UNSYNCD) {                                          // not yet synced

		Uart.syncBit = 9999;                                                    // not set
		// The start bit is one ore more Sequence Y followed by a Sequence Z (... 11111111 00x11111). We need to distinguish from
		// Sequence X followed by Sequence Y followed by Sequence Z (111100x1 11111111 00x11111)
		// we therefore look for a ...xx11111111111100x11111xxxxxx... pattern
		// (12 '1's followed by 2 '0's, eventually followed by another '0', followed by 5 '1's)
		#define ISO14443A_STARTBIT_MASK     0x07FFEF80                          // mask is    00000111 11111111 11101111 10000000
		#define ISO14443A_STARTBIT_PATTERN  0x07FF8F80                          // pattern is 00000111 11111111 10001111 10000000
		if      ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 0)) == ISO14443A_STARTBIT_PATTERN >> 0) Uart.syncBit = 7;
		else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 1)) == ISO14443A_STARTBIT_PATTERN >> 1) Uart.syncBit = 6;
		else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 2)) == ISO14443A_STARTBIT_PATTERN >> 2) Uart.syncBit = 5;
		else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 3)) == ISO14443A_STARTBIT_PATTERN >> 3) Uart.syncBit = 4;
		else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 4)) == ISO14443A_STARTBIT_PATTERN >> 4) Uart.syncBit = 3;
		else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 5)) == ISO14443A_STARTBIT_PATTERN >> 5) Uart.syncBit = 2;
		else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 6)) == ISO14443A_STARTBIT_PATTERN >> 6) Uart.syncBit = 1;
		else if ((Uart.fourBits & (ISO14443A_STARTBIT_MASK >> 7)) == ISO14443A_STARTBIT_PATTERN >> 7) Uart.syncBit = 0;

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

	} else {

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

	}

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



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

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

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


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

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

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

	Demod.twoBits = (Demod.twoBits << 8) | bit;

	if (Demod.state == DEMOD_UNSYNCD) {

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

	} else {

		if (IsManchesterModulationNibble1(Demod.twoBits >> Demod.syncBit)) {        // modulation in first half
			if (IsManchesterModulationNibble2(Demod.twoBits >> Demod.syncBit)) {    // ... and in second half = collision
				if (!Demod.collisionPos) {
					Demod.collisionPos = (Demod.len << 3) + Demod.bitCount;
				}
			}                                                           // modulation in first half only - Sequence D = 1
			Demod.bitCount++;
			Demod.shiftReg = (Demod.shiftReg >> 1) | 0x100;             // in both cases, add a 1 to the shiftreg
			if(Demod.bitCount == 9) {                                   // if we decoded a full byte (including parity)
				Demod.output[Demod.len++] = (Demod.shiftReg & 0xff);
				Demod.parityBits <<= 1;                                 // make room for the parity bit
				Demod.parityBits |= ((Demod.shiftReg >> 8) & 0x01);     // store parity bit
				Demod.bitCount = 0;
				Demod.shiftReg = 0;
				if((Demod.len&0x0007) == 0) {                           // every 8 data bytes
					Demod.parity[Demod.parityLen++] = Demod.parityBits; // store 8 parity bits
					Demod.parityBits = 0;
				}
			}
			Demod.endTime = Demod.startTime + 8*(9*Demod.len + Demod.bitCount + 1) - 4;
		} else {                                                        // no modulation in first half
			if (IsManchesterModulationNibble2(Demod.twoBits >> Demod.syncBit)) {    // and modulation in second half = Sequence E = 0
				Demod.bitCount++;
				Demod.shiftReg = (Demod.shiftReg >> 1);                 // add a 0 to the shiftreg
				if(Demod.bitCount >= 9) {                               // if we decoded a full byte (including parity)
					Demod.output[Demod.len++] = (Demod.shiftReg & 0xff);
					Demod.parityBits <<= 1;                             // make room for the new parity bit
					Demod.parityBits |= ((Demod.shiftReg >> 8) & 0x01); // store parity bit
					Demod.bitCount = 0;
					Demod.shiftReg = 0;
					if ((Demod.len&0x0007) == 0) {                      // every 8 data bytes
						Demod.parity[Demod.parityLen++] = Demod.parityBits; // store 8 parity bits1
						Demod.parityBits = 0;
					}
				}
				Demod.endTime = Demod.startTime + 8*(9*Demod.len + Demod.bitCount + 1);
			} else {                                                    // no modulation in both halves - End of communication
				LED_C_OFF();
				if(Demod.bitCount > 0) {                                // there are some remaining data bits
					Demod.shiftReg >>= (9 - Demod.bitCount);            // right align the decoded bits
					Demod.output[Demod.len++] = Demod.shiftReg & 0xff;  // and add them to the output
					Demod.parityBits <<= 1;                             // add a (void) parity bit
					Demod.parityBits <<= (8 - (Demod.len&0x0007));      // left align remaining parity bits
					Demod.parity[Demod.parityLen++] = Demod.parityBits; // and store them
					return true;
				} else if (Demod.len & 0x0007) {                        // there are some parity bits to store
					Demod.parityBits <<= (8 - (Demod.len&0x0007));      // left align remaining parity bits
					Demod.parity[Demod.parityLen++] = Demod.parityBits; // and store them
				}
				if (Demod.len) {
					return true;                                        // we are finished with decoding the raw data sequence
				} else {                                                // nothing received. Start over
					DemodReset();
				}
			}
		}

	}

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

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

//-----------------------------------------------------------------------------
// Record the sequence of commands sent by the reader to the tag, with
// triggering so that we start recording at the point that the tag is moved
// near the reader.
//-----------------------------------------------------------------------------
void RAMFUNC SnoopIso14443a(uint8_t param) {
	// param:
	// bit 0 - trigger from first card answer
	// bit 1 - trigger from first reader 7-bit request

	LEDsoff();
	LED_A_ON();

	iso14443a_setup(FPGA_HF_ISO14443A_SNIFFER);

	// Allocate memory from BigBuf for some buffers
	// free all previous allocations first
	BigBuf_free();

	// The command (reader -> tag) that we're receiving.
	uint8_t *receivedCmd = BigBuf_malloc(MAX_FRAME_SIZE);
	uint8_t *receivedCmdPar = BigBuf_malloc(MAX_PARITY_SIZE);

	// The response (tag -> reader) that we're receiving.
	uint8_t *receivedResponse = BigBuf_malloc(MAX_FRAME_SIZE);
	uint8_t *receivedResponsePar = BigBuf_malloc(MAX_PARITY_SIZE);

	// The DMA buffer, used to stream samples from the FPGA
	uint8_t *dmaBuf = BigBuf_malloc(DMA_BUFFER_SIZE);

	// init trace buffer
	clear_trace();
	set_tracing(true);

	uint8_t *data = dmaBuf;
	uint8_t previous_data = 0;
	int maxDataLen = 0;
	int dataLen = 0;
	bool TagIsActive = false;
	bool ReaderIsActive = false;

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

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

	// Setup and start DMA.
	FpgaSetupSscDma((uint8_t *)dmaBuf, DMA_BUFFER_SIZE);

	// We won't start recording the frames that we acquire until we trigger;
	// a good trigger condition to get started is probably when we see a
	// response from the tag.
	// triggered == false -- to wait first for card
	bool triggered = !(param & 0x03);

	// And now we loop, receiving samples.
	for (uint32_t rsamples = 0; true; ) {

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

		WDT_HIT();

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

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

		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)) {
					// check - if there is a short 7bit request from reader
					if ((!triggered) && (param & 0x02) && (Uart.len == 1) && (Uart.bitCount == 7)) {
						triggered = true;
					}
					if(triggered) {
						if (!LogTrace(receivedCmd,
										Uart.len,
										Uart.startTime*16 - DELAY_READER_AIR2ARM_AS_SNIFFER,
										Uart.endTime*16 - DELAY_READER_AIR2ARM_AS_SNIFFER,
										Uart.parity,
										true)) break;
					}
					/* And ready to receive another command. */
					UartReset();
					/* And also reset the demod code, which might have been */
					/* false-triggered by the commands from the reader. */
					DemodReset();
				}
				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)) {
					if (!LogTrace(receivedResponse,
									Demod.len,
									Demod.startTime*16 - DELAY_TAG_AIR2ARM_AS_SNIFFER,
									Demod.endTime*16 - DELAY_TAG_AIR2ARM_AS_SNIFFER,
									Demod.parity,
									false)) break;
					if ((!triggered) && (param & 0x01)) triggered = true;
					// And ready to receive another response.
					DemodReset();
					// And reset the Miller decoder including itS (now outdated) input buffer
					UartInit(receivedCmd, receivedCmdPar);
				}
				TagIsActive = (Demod.state != DEMOD_UNSYNCD);
			}
		}

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

	FpgaDisableSscDma();
	LEDsoff();

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

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

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

	// Send startbit
	ToSend[++ToSendMax] = SEC_D;
	LastProxToAirDuration = 8 * ToSendMax - 4;

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

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

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

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

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


static void 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++;
}


static uint8_t *LastReaderTraceTime = NULL;

static void EmLogTraceReader(void) {
	// remember last reader trace start to fix timing info later
	LastReaderTraceTime = BigBuf_get_addr() + BigBuf_get_traceLen();
	LogTrace(Uart.output, Uart.len, Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG, Uart.parity, true);
}


static void FixLastReaderTraceTime(uint32_t tag_StartTime) {
	uint32_t reader_EndTime = Uart.endTime*16 - DELAY_AIR2ARM_AS_TAG;
	uint32_t reader_StartTime = Uart.startTime*16 - DELAY_AIR2ARM_AS_TAG;
	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_StartTime = tag_StartTime - exact_fdt - reader_modlen;
	LastReaderTraceTime[0] = (reader_StartTime >> 0) & 0xff;
	LastReaderTraceTime[1] = (reader_StartTime >> 8) & 0xff;
	LastReaderTraceTime[2] = (reader_StartTime >> 16) & 0xff;
	LastReaderTraceTime[3] = (reader_StartTime >> 24) & 0xff;
}


static void EmLogTraceTag(uint8_t *tag_data, uint16_t tag_len, uint8_t *tag_Parity, uint32_t ProxToAirDuration) {
	uint32_t tag_StartTime = LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_TAG;
	uint32_t tag_EndTime = (LastTimeProxToAirStart + ProxToAirDuration)*16 + DELAY_ARM2AIR_AS_TAG;
	LogTrace(tag_data, tag_len, tag_StartTime, tag_EndTime, tag_Parity, false);
	FixLastReaderTraceTime(tag_StartTime);
}


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

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

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

	for (;;) {
		WDT_HIT();

		if(BUTTON_PRESS()) return false;

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


int EmSend4bit(uint8_t resp);
static int EmSendCmdExPar(uint8_t *resp, uint16_t respLen, uint8_t *par);
int EmSendCmd(uint8_t *resp, uint16_t respLen);
int EmSendPrecompiledCmd(tag_response_info_t *response_info);


static 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
  GetParity(response_info->response, response_info->response_n, &(response_info->par));
  CodeIso14443aAsTagPar(response_info->response,response_info->response_n, &(response_info->par));

  // Make sure we do not exceed the free buffer space
  if (ToSendMax > max_buffer_size) {
	Dbprintf("Out of memory, when modulating bits for tag answer:");
	Dbhexdump(response_info->response_n, response_info->response, false);
	return false;
  }

  // Copy the byte array, used for this modulation to the buffer position
  memcpy(response_info->modulation, ToSend, ToSendMax);

  // Store the number of bytes that were used for encoding/modulation and the time needed to transfer them
  response_info->modulation_n = ToSendMax;
  response_info->ProxToAirDuration = LastProxToAirDuration;

  return true;
}


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

bool prepare_allocated_tag_modulation(tag_response_info_t* response_info, uint8_t **buffer, size_t *max_buffer_size) {

  // Retrieve and store the current buffer index
  response_info->modulation = *buffer;

  // Forward the prepare tag modulation function to the inner function
  if (prepare_tag_modulation(response_info, *max_buffer_size)) {
	// Update the free buffer offset and the remaining buffer size
	*buffer += ToSendMax;
	*max_buffer_size -= 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)
{
	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;
		case 5: { // MIFARE TNP3XXX
			// Says: I am a toy
			response1[0] = 0x01;
			response1[1] = 0x0f;
			sak = 0x01;
		} break;
		default: {
			Dbprintf("Error: unkown tagtype (%d)",tagType);
			return;
		} break;
	}

	// The second response contains the (mandatory) first 24 bits of the UID
	uint8_t response2[5] = {0x00};

	// Check if the uid uses the (optional) part
	uint8_t response2a[5] = {0x00};

	if (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]  = {0x00};
	response3[0] = sak;
	ComputeCrc14443(CRC_14443_A, response3, 1, &response3[1], &response3[2]);

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

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

	#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
	};

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

	BigBuf_free_keep_EM();

	// allocate buffers:
	uint8_t *receivedCmd = BigBuf_malloc(MAX_FRAME_SIZE);
	uint8_t *receivedCmdPar = BigBuf_malloc(MAX_PARITY_SIZE);
	uint8_t *free_buffer_pointer = BigBuf_malloc(ALLOCATED_TAG_MODULATION_BUFFER_SIZE);
	size_t free_buffer_size = ALLOCATED_TAG_MODULATION_BUFFER_SIZE;
	// clear trace
	clear_trace();
	set_tracing(true);

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

	int len = 0;

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

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

	cmdsRecvd = 0;
	tag_response_info_t* p_response;

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

		p_response = NULL;

		// Okay, look at the command now.
		lastorder = order;
		if(receivedCmd[0] == 0x26) { // Received a REQUEST
			p_response = &responses[0]; order = 1;
		} else if(receivedCmd[0] == 0x52) { // Received a WAKEUP
			p_response = &responses[0]; order = 6;
		} else if(receivedCmd[1] == 0x20 && receivedCmd[0] == 0x93) {   // Received request for UID (cascade 1)
			p_response = &responses[1]; order = 2;
		} else if(receivedCmd[1] == 0x20 && receivedCmd[0] == 0x95) {   // Received request for UID (cascade 2)
			p_response = &responses[2]; order = 20;
		} else if(receivedCmd[1] == 0x70 && receivedCmd[0] == 0x93) {   // Received a SELECT (cascade 1)
			p_response = &responses[3]; order = 3;
		} else if(receivedCmd[1] == 0x70 && receivedCmd[0] == 0x95) {   // Received a SELECT (cascade 2)
			p_response = &responses[4]; order = 30;
		} else if(receivedCmd[0] == 0x30) { // Received a (plain) READ
			EmSendCmd(data+(4*receivedCmd[1]),16);
			// 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
			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 {nr] and {ar} (part of authentication)
			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
					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");
					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) {
			EmSendPrecompiledCmd(p_response);
		}

		if (!get_tracing()) {
			Dbprintf("Trace Full. Simulation stopped.");
			break;
		}
	}

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


// prepare a delayed transfer. This simply shifts ToSend[] by a number
// of bits specified in the delay parameter.
static 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, startup frame guard time and frame delay time
// if == 0: transfer immediately and return time of transfer
// if != 0: delay transfer until time specified
//-------------------------------------------------------------------------------------
static void TransmitFor14443a(const uint8_t *cmd, uint16_t len, uint32_t *timing)
{
	LED_B_ON();
	LED_D_ON();
	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);
	LED_B_OFF();
}


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

	ToSendReset();

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

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

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

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

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

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


//-----------------------------------------------------------------------------
// 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
//-----------------------------------------------------------------------------
int EmGetCmd(uint8_t *received, uint16_t *len, uint8_t *parity)
{
	uint32_t field_off_time = -1;
	uint32_t samples = 0;
	int ret = 0;
	uint8_t b = 0;;
	uint8_t dmaBuf[DMA_BUFFER_SIZE];
	uint8_t *upTo = dmaBuf;

	*len = 0;

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

	// start ADC
	AT91C_BASE_ADC->ADC_CR = AT91C_ADC_START;

	// Ensure that the FPGA Delay Queue is empty before we switch to TAGSIM_LISTEN
	while (GetCountSspClk() < LastTimeProxToAirStart + LastProxToAirDuration + (FpgaSendQueueDelay>>3) - 8 - 3) /* wait */ ;

	// Set FPGA mode to "simulated ISO 14443 tag", no modulation (listen
	// only, since we are receiving, not transmitting).
	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_TAGSIM_LISTEN);

	// clear receive register, measure time of next transfer
	uint32_t temp = AT91C_BASE_SSC->SSC_RHR; (void) temp;
	while (!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY)) ;
	uint32_t start_time = GetCountSspClk() & 0xfffffff8;

	// Setup and start DMA.
	FpgaSetupSscDma(dmaBuf, DMA_BUFFER_SIZE);

	for(;;) {
		uint16_t behindBy = ((uint8_t*)AT91C_BASE_PDC_SSC->PDC_RPR - upTo) & (DMA_BUFFER_SIZE-1);

		if (behindBy == 0) continue;

		b = *upTo++;

		if(upTo >= dmaBuf + DMA_BUFFER_SIZE) {                   // we have read all of the DMA buffer content.
			upTo = dmaBuf;                                       // start reading the circular buffer from the beginning
			if(behindBy > (9*DMA_BUFFER_SIZE/10)) {
				Dbprintf("About to blow circular buffer - aborted! behindBy=%d", behindBy);
				ret = 1;
				break;
			}
		}
		if (AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_ENDRX)) {        // DMA Counter Register had reached 0, already rotated.
			AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) dmaBuf;    // refresh the DMA Next Buffer and
			AT91C_BASE_PDC_SSC->PDC_RNCR = DMA_BUFFER_SIZE;      // DMA Next Counter registers
		}

		if (BUTTON_PRESS()) {
			ret = 1;
			break;
		}

		// check reader's HF field
		if (AT91C_BASE_ADC->ADC_SR & ADC_END_OF_CONVERSION(ADC_CHAN_HF_LOW)) {
			if ((MAX_ADC_HF_VOLTAGE_LOW * AT91C_BASE_ADC->ADC_CDR[ADC_CHAN_HF_LOW]) >> 10 < MF_MINFIELDV) {
				if (GetTickCount() - field_off_time > 50) {
					ret = 2; // reader has switched off HF field for more than 50ms. Timeout
					break;
				}
			} else {
				field_off_time = GetTickCount(); // HF field is still there. Reset timer
			}
			AT91C_BASE_ADC->ADC_CR = AT91C_ADC_START; // restart ADC
		}

		if (MillerDecoding(b, start_time + samples*8)) {
			*len = Uart.len;
			EmLogTraceReader();
			ret = 0;
			break;
		}

		samples++;
	}

	FpgaDisableSscDma();
	return ret;
}


static int EmSendCmd14443aRaw(uint8_t *resp, uint16_t respLen)
{
	LED_C_ON();

	uint8_t b;
	uint16_t i = 0;
	bool correctionNeeded;

	// Modulate Manchester
	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_TAGSIM_MOD);

	// include correction bit if necessary
	if (Uart.bitCount == 7)
	{
		// Short tags (7 bits) don't have parity, determine the correct value from MSB
		correctionNeeded = Uart.output[0] & 0x40;
	}
	else
	{
		// Look at the last parity bit
		correctionNeeded = Uart.parity[(Uart.len-1)/8] & (0x80 >> ((Uart.len-1) & 7));
	}

	if (correctionNeeded) {
		// 1236, so correction bit needed
		i = 0;
	} else {
		i = 1;
	}

	// clear receiving shift register and holding register
	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;
	}

	LastTimeProxToAirStart = (GetCountSspClk() & 0xfffffff8) + (correctionNeeded?8:0);

	// 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;
		}
	}

	LED_C_OFF();
	return 0;
}


int EmSend4bit(uint8_t resp){
	Code4bitAnswerAsTag(resp);
	int res = EmSendCmd14443aRaw(ToSend, ToSendMax);
	// Log this tag answer and fix timing of previous reader command:
	EmLogTraceTag(&resp, 1, NULL, LastProxToAirDuration);
	return res;
}


static int EmSendCmdExPar(uint8_t *resp, uint16_t respLen, uint8_t *par){
	CodeIso14443aAsTagPar(resp, respLen, par);
	int res = EmSendCmd14443aRaw(ToSend, ToSendMax);
	// Log this tag answer and fix timing of previous reader command:
	EmLogTraceTag(resp, respLen, par, LastProxToAirDuration);
	return res;
}


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


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


int EmSendPrecompiledCmd(tag_response_info_t *response_info) {
	int ret = EmSendCmd14443aRaw(response_info->modulation, response_info->modulation_n);
	// Log this tag answer and fix timing of previous reader command:
	EmLogTraceTag(response_info->response, response_info->response_n, &(response_info->par), response_info->ProxToAirDuration);
	return ret;
}


//-----------------------------------------------------------------------------
// Wait a certain time for tag response
//  If a response is captured return true
//  If it takes too long return false
//-----------------------------------------------------------------------------
static int GetIso14443aAnswerFromTag(uint8_t *receivedResponse, uint8_t *receivedResponsePar, uint16_t offset)
{
	uint32_t c;

	// Set FPGA mode to "reader listen mode", no modulation (listen
	// only, since we are receiving, not transmitting).
	// Signal field is on with the appropriate LED
	LED_D_ON();
	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_LISTEN);

	// Now get the answer from the card
	DemodInit(receivedResponse, receivedResponsePar);

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

	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 && Demod.state == DEMOD_UNSYNCD) {
				return false;
			}
		}
	}
}


void ReaderTransmitBitsPar(uint8_t* frame, uint16_t bits, uint8_t *par, uint32_t *timing)
{
	CodeIso14443aBitsAsReaderPar(frame, bits, par);

	// Send command to tag
	TransmitFor14443a(ToSend, ToSendMax, timing);
	if(trigger)
		LED_A_ON();

	// Log reader command in trace buffer
	LogTrace(frame, nbytes(bits), LastTimeProxToAirStart*16 + DELAY_ARM2AIR_AS_READER, (LastTimeProxToAirStart + LastProxToAirDuration)*16 + DELAY_ARM2AIR_AS_READER, par, true);
}


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


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


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


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


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


static void iso14a_set_ATS_times(uint8_t *ats) {

	uint8_t tb1;
	uint8_t fwi, sfgi;
	uint32_t fwt, sfgt;

	if (ats[0] > 1) {                           // there is a format byte T0
		if ((ats[1] & 0x20) == 0x20) {          // there is an interface byte TB(1)
			if ((ats[1] & 0x10) == 0x10) {      // there is an interface byte TA(1) preceding TB(1)
				tb1 = ats[3];
			} else {
				tb1 = ats[2];
			}
			fwi = (tb1 & 0xf0) >> 4;            // frame waiting time integer (FWI)
			if (fwi != 15) {
				fwt = 256 * 16 * (1 << fwi);    // frame waiting time (FWT) in 1/fc
				iso14a_set_timeout(fwt/(8*16));
			}
			sfgi = tb1 & 0x0f;                  // startup frame guard time integer (SFGI)
			if (sfgi != 0 && sfgi != 15) {
				sfgt = 256 * 16 * (1 << sfgi);  // startup frame guard time (SFGT) in 1/fc
				NextTransferTime = MAX(NextTransferTime, Demod.endTime + (sfgt - DELAY_AIR2ARM_AS_READER - DELAY_ARM2AIR_AS_READER)/16);
			}
		}
	}
}


static int GetATQA(uint8_t *resp, uint8_t *resp_par) {

#define WUPA_RETRY_TIMEOUT  10  // 10ms
	uint8_t wupa[]       = { 0x52 };  // 0x26 - REQA  0x52 - WAKE-UP

	uint32_t save_iso14a_timeout = iso14a_get_timeout();
	iso14a_set_timeout(1236/(16*8)+1);      // response to WUPA is expected at exactly 1236/fc. No need to wait longer.

	uint32_t start_time = GetTickCount();
	int len;

	// we may need several tries if we did send an unknown command or a wrong authentication before...
	do {
		// Broadcast for a card, WUPA (0x52) will force response from all cards in the field
		ReaderTransmitBitsPar(wupa, 7, NULL, NULL);
		// Receive the ATQA
		len = ReaderReceive(resp, resp_par);
	} while (len == 0 && GetTickCount() <= start_time + WUPA_RETRY_TIMEOUT);

	iso14a_set_timeout(save_iso14a_timeout);
	return len;
}


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

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

	// init card struct
	if(p_hi14a_card) {
		p_hi14a_card->uidlen = 0;
		memset(p_hi14a_card->uid, 0, 10);
		p_hi14a_card->ats_len = 0;
	}

	if (!GetATQA(resp, resp_par)) {
		return 0;
	}

	if(p_hi14a_card) {
		memcpy(p_hi14a_card->atqa, resp, 2);
	}

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

	// check for proprietary anticollision:
	if ((resp[0] & 0x1F) == 0) {
		return 3;
	}

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

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

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

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

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

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

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

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

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

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

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

	// PICC compilant with iso14443a-4 ---> (SAK & 0x20 != 0)
	if( (sak & 0x20) == 0) return 2;

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

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

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

		// reset the PCB block number
		iso14_pcb_blocknum = 0;

		// set default timeout and delay next transfer based on ATS
		iso14a_set_ATS_times(resp);

	}
	return 1;
}


void iso14443a_setup(uint8_t fpga_minor_mode) {
	FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
	// Set up the synchronous serial port
	FpgaSetupSsc(FPGA_MAJOR_MODE_HF_ISO14443A);
	// 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);

	// Set ADC to read field strength
	AT91C_BASE_ADC->ADC_CR = AT91C_ADC_SWRST;
	AT91C_BASE_ADC->ADC_MR =
				ADC_MODE_PRESCALE(63) |
				ADC_MODE_STARTUP_TIME(1) |
				ADC_MODE_SAMPLE_HOLD_TIME(15);
	AT91C_BASE_ADC->ADC_CHER = ADC_CHANNEL(ADC_CHAN_HF_LOW);

	// Start the timer
	StartCountSspClk();

	DemodReset();
	UartReset();
	LastTimeProxToAirStart = 0;
	FpgaSendQueueDelay = 0;
	LastProxToAirDuration = 20; // arbitrary small value. Avoid lock in EmGetCmd()
	NextTransferTime = 2*DELAY_ARM2AIR_AS_READER;
	iso14a_set_timeout(1060); // 10ms default
}

/* Peter Fillmore 2015
Added card id field to the function
 info from ISO14443A standard
b1 = Block Number
b2 = RFU (always 1)
b3 = depends on block
b4 = Card ID following if set to 1
b5 = depends on block type
b6 = depends on block type
b7,b8 = block type.
Coding of I-BLOCK:
b8 b7 b6 b5 b4 b3 b2 b1
0  0  0  x  x  x  1  x
b5 = chaining bit
Coding of R-block:
b8 b7 b6 b5 b4 b3 b2 b1
1  0  1  x  x  0  1  x
b5 = ACK/NACK
Coding of S-block:
b8 b7 b6 b5 b4 b3 b2 b1
1  1  x  x  x  0  1  0
b5,b6 = 00 - DESELECT
		11 - WTX
*/
int iso14_apdu(uint8_t *cmd, uint16_t cmd_len, bool send_chaining, void *data, uint8_t *res) {
	uint8_t parity[MAX_PARITY_SIZE];
	uint8_t real_cmd[cmd_len + 4];

	if (cmd_len) {
		// ISO 14443 APDU frame: PCB [CID] [NAD] APDU CRC PCB=0x02
		real_cmd[0] = 0x02; // bnr,nad,cid,chn=0; i-block(0x00)
		if (send_chaining) {
			real_cmd[0] |= 0x10;
		}
		// put block number into the PCB
		real_cmd[0] |= iso14_pcb_blocknum;
		memcpy(real_cmd + 1, cmd, cmd_len);
	} else {
		// R-block. ACK
		real_cmd[0] = 0xA2; // r-block + ACK
		real_cmd[0] |= iso14_pcb_blocknum;
	}
	AppendCrc14443a(real_cmd, cmd_len + 1);

	ReaderTransmit(real_cmd, cmd_len + 3, NULL);

	size_t len = ReaderReceive(data, parity);
	uint8_t *data_bytes = (uint8_t *) data;

	if (!len) {
		return 0; //DATA LINK ERROR
	} else {
		// S-Block WTX
		while (len && ((data_bytes[0] & 0xF2) == 0xF2)) {
			uint32_t save_iso14a_timeout = iso14a_get_timeout();
			// temporarily increase timeout
			iso14a_set_timeout(MAX((data_bytes[1] & 0x3f) * save_iso14a_timeout, MAX_ISO14A_TIMEOUT));
			// Transmit WTX back
			// byte1 - WTXM [1..59]. command FWT=FWT*WTXM
			data_bytes[1] = data_bytes[1] & 0x3f; // 2 high bits mandatory set to 0b
			// now need to fix CRC.
			AppendCrc14443a(data_bytes, len - 2);
			// transmit S-Block
			ReaderTransmit(data_bytes, len, NULL);
			// retrieve the result again (with increased timeout)
			len = ReaderReceive(data, parity);
			data_bytes = data;
			// restore timeout
			iso14a_set_timeout(save_iso14a_timeout);
		}

		// if we received an I- or R(ACK)-Block with a block number equal to the
		// current block number, toggle the current block number
		if (len >= 3 // PCB+CRC = 3 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;
		}

		// if we received I-block with chaining we need to send ACK and receive another block of data
		if (res)
			*res = data_bytes[0];

		// crc check
		if (len >= 3 && !CheckCrc14443(CRC_14443_A, data_bytes, len)) {
			return -1;
		}

	}

	if (len) {
		// cut frame byte
		len -= 1;
		// memmove(data_bytes, data_bytes + 1, len);
		for (int i = 0; i < len; i++)
			data_bytes[i] = data_bytes[i + 1];
	}

	return len;
}


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

	set_tracing(true);

	if(param & ISO14A_CLEAR_TRACE) {
		clear_trace();
	}

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

	if(param & ISO14A_CONNECT) {
		LED_A_ON();
		iso14443a_setup(FPGA_HF_ISO14443A_READER_LISTEN);
		if(!(param & ISO14A_NO_SELECT)) {
			iso14a_card_select_t *card = (iso14a_card_select_t*)buf;
			arg0 = iso14443a_select_card(NULL, card, NULL, true, 0, param & ISO14A_NO_RATS);

			// if we cant select then we cant send data
			if (arg0 != 1 && arg0 != 2) {
				// 1 - all is OK with ATS, 2 - without ATS
				cantSELECT = true;
			}
			FpgaDisableTracing();
			LED_B_ON();
			cmd_send(CMD_ACK,arg0,card->uidlen,0,buf,sizeof(iso14a_card_select_t));
			LED_B_OFF();
		}
	}

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

	if(param & ISO14A_APDU && !cantSELECT) {
		uint8_t res;
		arg0 = iso14_apdu(cmd, len, (param & ISO14A_SEND_CHAINING), buf, &res);
		FpgaDisableTracing();
		LED_B_ON();
		cmd_send(CMD_ACK, arg0, res, 0, buf, sizeof(buf));
		LED_B_OFF();
	}

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

		LED_B_ON();
		cmd_send(CMD_ACK,arg0,0,0,buf,sizeof(buf));
		LED_B_OFF();
	}

	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.
static 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[MAX_MIFARE_FRAME_SIZE];
	uint8_t receivedAnswerPar[MAX_MIFARE_PARITY_SIZE];

	iso14443a_setup(FPGA_HF_ISO14443A_READER_MOD);

	// free eventually allocated BigBuf memory. We want all for tracing.
	BigBuf_free();

	clear_trace();
	set_tracing(true);

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

	uint32_t nt = 0;
	uint32_t previous_nt = 0;
	static uint32_t nt_attacked = 0;
	uint8_t par_list[8] = {0x00};
	uint8_t ks_list[8] = {0x00};

	#define PRNG_SEQUENCE_LENGTH  (1 << 16);
	uint32_t sync_time = GetCountSspClk() & 0xfffffff8;
	static int32_t sync_cycles;
	int catch_up_cycles = 0;
	int last_catch_up = 0;
	uint16_t elapsed_prng_sequences;
	uint16_t consecutive_resyncs = 0;
	int isOK = 0;

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

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


	#define MAX_UNEXPECTED_RANDOM   4       // maximum number of unexpected (i.e. real) random numbers when trying to sync. Then give up.
	#define MAX_SYNC_TRIES          32
	#define SYNC_TIME_BUFFER        16      // if there is only SYNC_TIME_BUFFER left before next planned sync, wait for next PRNG cycle
	#define NUM_DEBUG_INFOS         8       // per strategy
	#define MAX_STRATEGY            3
	uint16_t unexpected_random = 0;
	uint16_t sync_tries = 0;
	int16_t debug_info_nr = -1;
	uint16_t strategy = 0;
	int32_t debug_info[MAX_STRATEGY][NUM_DEBUG_INFOS];
	uint32_t select_time;
	uint32_t halt_time;

	for (uint16_t i = 0; true; i++) {

		LED_C_ON();
		WDT_HIT();

		// Test if the action was cancelled
		if(BUTTON_PRESS()) {
			isOK = -1;
			break;
		}

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

		if (strategy == 3) {
			// test with FPGA power off/on
			FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
			SpinDelay(200);
			iso14443a_setup(FPGA_HF_ISO14443A_READER_MOD);
			SpinDelay(100);
		}

		if(!iso14443a_select_card(uid, NULL, &cuid, true, 0, true)) {
			if (MF_DBGLEVEL >= 1)   Dbprintf("Mifare: Can't select card");
			continue;
		}
		select_time = GetCountSspClk();

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

			// if we missed the sync time already or are about to miss it, advance to the next nonce repeat
			while(sync_time < GetCountSspClk() + SYNC_TIME_BUFFER) {
				elapsed_prng_sequences++;
				sync_time = (sync_time & 0xfffffff8) + sync_cycles;
			}

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

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

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

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

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

		if ((nt != nt_attacked) && nt_attacked) {   // we somehow lost sync. Try to catch up again...
			catch_up_cycles = -dist_nt(nt_attacked, nt);
			if (catch_up_cycles == 99999) {         // invalid nonce received. Don't resync on that one.
				catch_up_cycles = 0;
				continue;
			}
			catch_up_cycles /= elapsed_prng_sequences;
			if (catch_up_cycles == last_catch_up) {
				consecutive_resyncs++;
			}
			else {
				last_catch_up = catch_up_cycles;
				consecutive_resyncs = 0;
			}
			if (consecutive_resyncs < 3) {
				if (MF_DBGLEVEL >= 3) Dbprintf("Lost sync in cycle %d. nt_distance=%d. Consecutive Resyncs = %d. Trying one time catch up...\n", i, -catch_up_cycles, consecutive_resyncs);
			}
			else {
				sync_cycles = sync_cycles + catch_up_cycles;
				if (MF_DBGLEVEL >= 3) Dbprintf("Lost sync in cycle %d for the fourth time consecutively (nt_distance = %d). Adjusting sync_cycles to %d.\n", i, -catch_up_cycles, sync_cycles);
				last_catch_up = 0;
				catch_up_cycles = 0;
				consecutive_resyncs = 0;
			}
			continue;
		}

		consecutive_resyncs = 0;

		// Receive answer. This will be a 4 Bit NACK when the 8 parity bits are OK after decoding
		if (ReaderReceive(receivedAnswer, receivedAnswerPar)) {
			catch_up_cycles = 8;    // the PRNG is delayed by 8 cycles due to the NAC (4Bits = 0x05 encrypted) transfer

			if (nt_diff == 0) {
				par_low = par[0] & 0xE0; // there is no need to check all parities for other nt_diff. Parity Bits for mf_nr_ar[0..2] won't change
			}

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

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

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

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


	mf_nr_ar[3] &= 0x1F;

	if (isOK == -4) {
		if (MF_DBGLEVEL >= 3) {
			for (uint16_t i = 0; i <= MAX_STRATEGY; i++) {
				for (uint16_t j = 0; j < NUM_DEBUG_INFOS; j++) {
					Dbprintf("collected debug info[%d][%d] = %d", i, j, debug_info[i][j]);
				}
			}
		}
	}

	FpgaDisableTracing();

	uint8_t buf[32];
	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, 8);

	cmd_send(CMD_ACK, isOK, 0, 0, buf, 32);

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

	set_tracing(false);
}


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

	// C(red) A(yellow) B(green)
	LEDsoff();
	LED_A_ON();

	// init trace buffer
	clear_trace();
	set_tracing(true);

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

	iso14443a_setup(FPGA_HF_ISO14443A_SNIFFER);

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

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

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

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

	// init sniffer
	MfSniffInit();

	// And now we loop, receiving samples.
	for (uint32_t sniffCounter = 0; true; ) {

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

		WDT_HIT();

		if ((sniffCounter & 0x0000FFFF) == 0) { // from time to time
			// check if a transaction is completed (timeout after 2000ms).
			// if yes, stop the DMA transfer and send what we have so far to the client
			if (MfSniffSend(2000)) {
				// Reset everything - we missed some sniffed data anyway while the DMA was stopped
				sniffCounter = 0;
				data = dmaBuf;
				maxDataLen = 0;
				ReaderIsActive = false;
				TagIsActive = false;
				FpgaSetupSscDma((uint8_t *)dmaBuf, DMA_BUFFER_SIZE); // set transfer address and number of bytes. Start transfer.
			}
		}

		int register readBufDataP = data - dmaBuf;  // number of bytes we have processed so far
		int register dmaBufDataP = DMA_BUFFER_SIZE - AT91C_BASE_PDC_SSC->PDC_RCR; // number of bytes already transferred
		if (readBufDataP <= dmaBufDataP){           // we are processing the same block of data which is currently being transferred
			dataLen = dmaBufDataP - readBufDataP;   // number of bytes still to be processed
		} else {
			dataLen = DMA_BUFFER_SIZE - readBufDataP + dmaBufDataP; // number of bytes still to be processed
		}
		// test for length of buffer
		if(dataLen > maxDataLen) {                  // we are more behind than ever...
			maxDataLen = dataLen;
			if(dataLen > (9 * DMA_BUFFER_SIZE / 10)) {
				Dbprintf("blew circular buffer! dataLen=0x%x", dataLen);
				break;
			}
		}
		if(dataLen < 1) continue;

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

		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)) {

					if (MfSniffLogic(receivedCmd, Uart.len, Uart.parity, Uart.bitCount, true)) break;

					/* And ready to receive another command. */
					UartInit(receivedCmd, receivedCmdPar);

					/* And also reset the demod code */
					DemodReset();
				}
				ReaderIsActive = (Uart.state != STATE_UNSYNCD);
			}

			if(!ReaderIsActive) {       // no need to try decoding tag data if the reader is sending
				uint8_t tagdata = (previous_data << 4) | (*data & 0x0F);
				if(ManchesterDecoding(tagdata, 0, (sniffCounter-1)*4)) {

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

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

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

	} // main cycle

	FpgaDisableTracing();
	FpgaDisableSscDma();
	LEDsoff();

	DbpString("COMMAND FINISHED.");

	MfSniffEnd();

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