//-----------------------------------------------------------------------------
// Gerhard de Koning Gans - May 2008
// Hagen Fritsch - June 2010
// Gerhard de Koning Gans - May 2011
//
// 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 iClass.
//-----------------------------------------------------------------------------
// Based on ISO14443a implementation. Still in experimental phase.
// Contribution made during a security research at Radboud University Nijmegen
// 
// Please feel free to contribute and extend iClass support!!
//-----------------------------------------------------------------------------
//
// TODO:
// =====
// - iClass emulation
// - reader emulation
//
// FIX:
// ====
// We still have sometimes a demodulation error when snooping iClass communication.
// The resulting trace of a read-block-03 command may look something like this:
//
//  +  22279:    :     0c  03  e8  01    
//
//    ...with an incorrect answer...
//
//  +     85:   0: TAG ff! ff! ff! ff! ff! ff! ff! ff! bb  33  bb  00  01! 0e! 04! bb     !crc
//
// We still left the error signalling bytes in the traces like 0xbb
//
// A correct trace should look like this:
//
// +  21112:    :     0c  03  e8  01    
// +     85:   0: TAG ff  ff  ff  ff  ff  ff  ff  ff  ea  f5    
//
//-----------------------------------------------------------------------------

#include "proxmark3.h"
#include "apps.h"
#include "util.h"
#include "string.h"

#include "iclass.h"

static uint8_t *trace = (uint8_t *) BigBuf;
static int traceLen = 0;
static int rsamples = 0;

// CARD TO READER
// 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
// 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

static 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
};

//static const uint8_t MajorityNibble[16] = { 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1 };
//static const uint8_t MajorityNibble[16] =   { 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 };

// BIG CHANGE - UNDERSTAND THIS BEFORE WE COMMIT
#define RECV_CMD_OFFSET   3032
#define RECV_RES_OFFSET   3096
#define DMA_BUFFER_OFFSET 3160
#define DMA_BUFFER_SIZE   4096
#define TRACE_LENGTH      3000


//-----------------------------------------------------------------------------
// The software UART that receives commands from the reader, and its state
// variables.
//-----------------------------------------------------------------------------
static struct {
    enum {
        STATE_UNSYNCD,
        STATE_START_OF_COMMUNICATION,
	STATE_RECEIVING
    }       state;
    uint16_t    shiftReg;
    int     bitCnt;
    int     byteCnt;
    int     byteCntMax;
    int     posCnt;
    int     nOutOfCnt;
    int     OutOfCnt;
    int     syncBit;
	int     parityBits;
	int     samples;
    int     highCnt;
    int     swapper;
    int     counter;
    int     bitBuffer;
    int     dropPosition;
    uint8_t   *output;
} Uart;

static RAMFUNC int MillerDecoding(int bit)
{
	int error = 0;
	int bitright;

	if(!Uart.bitBuffer) {
		Uart.bitBuffer = bit ^ 0xFF0;
		return FALSE;
	}
	else {
		Uart.bitBuffer <<= 4;
		Uart.bitBuffer ^= bit;
	}
	
	/*if(Uart.swapper) {
		Uart.output[Uart.byteCnt] = Uart.bitBuffer & 0xFF;
		Uart.byteCnt++;
		Uart.swapper = 0;
		if(Uart.byteCnt > 15) { return TRUE; }
	}
	else {
		Uart.swapper = 1;
	}*/

	if(Uart.state != STATE_UNSYNCD) {
		Uart.posCnt++;

		if((Uart.bitBuffer & Uart.syncBit) ^ Uart.syncBit) {
			bit = 0x00;
		}
		else {
			bit = 0x01;
		}
		if(((Uart.bitBuffer << 1) & Uart.syncBit) ^ Uart.syncBit) {
			bitright = 0x00;
		}
		else {
			bitright = 0x01;
		}
		if(bit != bitright) { bit = bitright; }

		
		// So, now we only have to deal with *bit*, lets see...
		if(Uart.posCnt == 1) {
			// measurement first half bitperiod
			if(!bit) {
				// Drop in first half means that we are either seeing
				// an SOF or an EOF.

				if(Uart.nOutOfCnt == 1) {
					// End of Communication
					Uart.state = STATE_UNSYNCD;
					Uart.highCnt = 0;
					if(Uart.byteCnt == 0) {
						// Its not straightforward to show single EOFs
						// So just leave it and do not return TRUE
						Uart.output[Uart.byteCnt] = 0xf0;
						Uart.byteCnt++;

						// Calculate the parity bit for the client...
						Uart.parityBits = 1;
					}
					else {
						return TRUE;
					}
				}
				else if(Uart.state != STATE_START_OF_COMMUNICATION) {
					// When not part of SOF or EOF, it is an error
					Uart.state = STATE_UNSYNCD;
					Uart.highCnt = 0;
					error = 4;
				}
			}
		}
		else {
			// measurement second half bitperiod
			// Count the bitslot we are in... (ISO 15693)
			Uart.nOutOfCnt++;
			
			if(!bit) {
				if(Uart.dropPosition) {
					if(Uart.state == STATE_START_OF_COMMUNICATION) {
						error = 1;
					}
					else {
						error = 7;
					}
					// It is an error if we already have seen a drop in current frame
					Uart.state = STATE_UNSYNCD;
					Uart.highCnt = 0;
				}
				else {
					Uart.dropPosition = Uart.nOutOfCnt;
				}
			}

			Uart.posCnt = 0;

			
			if(Uart.nOutOfCnt == Uart.OutOfCnt && Uart.OutOfCnt == 4) {
				Uart.nOutOfCnt = 0;
				
				if(Uart.state == STATE_START_OF_COMMUNICATION) {
					if(Uart.dropPosition == 4) {
						Uart.state = STATE_RECEIVING;
						Uart.OutOfCnt = 256;
					}
					else if(Uart.dropPosition == 3) {
						Uart.state = STATE_RECEIVING;
						Uart.OutOfCnt = 4;
						//Uart.output[Uart.byteCnt] = 0xdd;
						//Uart.byteCnt++;
					}
					else {
						Uart.state = STATE_UNSYNCD;
						Uart.highCnt = 0;
					}
					Uart.dropPosition = 0;
				}
				else {
					// RECEIVING DATA
					// 1 out of 4
					if(!Uart.dropPosition) {
						Uart.state = STATE_UNSYNCD;
						Uart.highCnt = 0;
						error = 9;
					}
					else {
						Uart.shiftReg >>= 2;
						
						// Swap bit order
						Uart.dropPosition--;
						//if(Uart.dropPosition == 1) { Uart.dropPosition = 2; }
						//else if(Uart.dropPosition == 2) { Uart.dropPosition = 1; }
						
						Uart.shiftReg ^= ((Uart.dropPosition & 0x03) << 6);
						Uart.bitCnt += 2;
						Uart.dropPosition = 0;

						if(Uart.bitCnt == 8) {
							Uart.output[Uart.byteCnt] = (Uart.shiftReg & 0xff);
							Uart.byteCnt++;

							// Calculate the parity bit for the client...
							Uart.parityBits <<= 1;
							Uart.parityBits ^= OddByteParity[(Uart.shiftReg & 0xff)];

							Uart.bitCnt = 0;
							Uart.shiftReg = 0;
						}
					}
				}
			}
			else if(Uart.nOutOfCnt == Uart.OutOfCnt) {
				// RECEIVING DATA
				// 1 out of 256
				if(!Uart.dropPosition) {
					Uart.state = STATE_UNSYNCD;
					Uart.highCnt = 0;
					error = 3;
				}
				else {
					Uart.dropPosition--;
					Uart.output[Uart.byteCnt] = (Uart.dropPosition & 0xff);
					Uart.byteCnt++;

					// Calculate the parity bit for the client...
					Uart.parityBits <<= 1;
					Uart.parityBits ^= OddByteParity[(Uart.dropPosition & 0xff)];

					Uart.bitCnt = 0;
					Uart.shiftReg = 0;
					Uart.nOutOfCnt = 0;
					Uart.dropPosition = 0;
				}
			}

			/*if(error) {
				Uart.output[Uart.byteCnt] = 0xAA;
				Uart.byteCnt++;
				Uart.output[Uart.byteCnt] = error & 0xFF;
				Uart.byteCnt++;
				Uart.output[Uart.byteCnt] = 0xAA;
				Uart.byteCnt++;
				Uart.output[Uart.byteCnt] = (Uart.bitBuffer >> 8) & 0xFF;
				Uart.byteCnt++;
				Uart.output[Uart.byteCnt] = Uart.bitBuffer & 0xFF;
				Uart.byteCnt++;
				Uart.output[Uart.byteCnt] = (Uart.syncBit >> 3) & 0xFF;
				Uart.byteCnt++;
				Uart.output[Uart.byteCnt] = 0xAA;
				Uart.byteCnt++;
				return TRUE;
			}*/
		}

	}
	else {
		bit = Uart.bitBuffer & 0xf0;
		bit >>= 4;
		bit ^= 0x0F; // drops become 1s ;-)
		if(bit) {
			// should have been high or at least (4 * 128) / fc
			// according to ISO this should be at least (9 * 128 + 20) / fc
			if(Uart.highCnt == 8) {
				// we went low, so this could be start of communication
				// it turns out to be safer to choose a less significant
				// syncbit... so we check whether the neighbour also represents the drop
				Uart.posCnt = 1;   // apparently we are busy with our first half bit period
				Uart.syncBit = bit & 8;
				Uart.samples = 3;
				if(!Uart.syncBit)	{ Uart.syncBit = bit & 4; Uart.samples = 2; }
				else if(bit & 4)	{ Uart.syncBit = bit & 4; Uart.samples = 2; bit <<= 2; }
				if(!Uart.syncBit)	{ Uart.syncBit = bit & 2; Uart.samples = 1; }
				else if(bit & 2)	{ Uart.syncBit = bit & 2; Uart.samples = 1; bit <<= 1; }
				if(!Uart.syncBit)	{ Uart.syncBit = bit & 1; Uart.samples = 0;
					if(Uart.syncBit && (Uart.bitBuffer & 8)) {
						Uart.syncBit = 8;

						// the first half bit period is expected in next sample
						Uart.posCnt = 0;
						Uart.samples = 3;
					}
				}
				else if(bit & 1)	{ Uart.syncBit = bit & 1; Uart.samples = 0; }

				Uart.syncBit <<= 4;
				Uart.state = STATE_START_OF_COMMUNICATION;
				Uart.bitCnt = 0;
				Uart.byteCnt = 0;
				Uart.parityBits = 0;
				Uart.nOutOfCnt = 0;
				Uart.OutOfCnt = 4; // Start at 1/4, could switch to 1/256
				Uart.dropPosition = 0;
				Uart.shiftReg = 0;
				error = 0;
			}
			else {
				Uart.highCnt = 0;
			}
		}
		else {
			if(Uart.highCnt < 8) {
				Uart.highCnt++;
			}
		}
	}

    return FALSE;
}

//=============================================================================
// ISO 14443 Type A - Manchester
//=============================================================================

static struct {
    enum {
        DEMOD_UNSYNCD,
		DEMOD_START_OF_COMMUNICATION,
		DEMOD_START_OF_COMMUNICATION2,
		DEMOD_START_OF_COMMUNICATION3,
		DEMOD_SOF_COMPLETE,
		DEMOD_MANCHESTER_D,
		DEMOD_MANCHESTER_E,
		DEMOD_END_OF_COMMUNICATION,
		DEMOD_END_OF_COMMUNICATION2,
		DEMOD_MANCHESTER_F,
        DEMOD_ERROR_WAIT
    }       state;
    int     bitCount;
    int     posCount;
	int     syncBit;
	int     parityBits;
    uint16_t    shiftReg;
	int     buffer;
	int     buffer2;
	int	buffer3;
	int     buff;
	int     samples;
    int     len;
	enum {
		SUB_NONE,
		SUB_FIRST_HALF,
		SUB_SECOND_HALF,
		SUB_BOTH
	}		sub;
    uint8_t   *output;
} Demod;

static RAMFUNC int ManchesterDecoding(int v)
{
	int bit;
	int modulation;
	int error = 0;

	bit = Demod.buffer;
	Demod.buffer = Demod.buffer2;
	Demod.buffer2 = Demod.buffer3;
	Demod.buffer3 = v;

	if(Demod.buff < 3) {
		Demod.buff++;
		return FALSE;
	}

	if(Demod.state==DEMOD_UNSYNCD) {
		Demod.output[Demod.len] = 0xfa;
		Demod.syncBit = 0;
		//Demod.samples = 0;
		Demod.posCount = 1;		// This is the first half bit period, so after syncing handle the second part
	/*	if(bit & 0x08) { Demod.syncBit = 0x08; }
		if(!Demod.syncBit)	{
			if(bit & 0x04) { Demod.syncBit = 0x04; }
		}
		else if(bit & 0x04) { Demod.syncBit = 0x04; bit <<= 4; }
		if(!Demod.syncBit)	{
			if(bit & 0x02) { Demod.syncBit = 0x02; }
		}
		else if(bit & 0x02) { Demod.syncBit = 0x02; bit <<= 4; }
		if(!Demod.syncBit)	{
			if(bit & 0x01) { Demod.syncBit = 0x01; }

			if(Demod.syncBit && (Demod.buffer & 0x08)) {
				Demod.syncBit = 0x08;

				// The first half bitperiod is expected in next sample
				Demod.posCount = 0;
				Demod.output[Demod.len] = 0xfb;
			}
		}
		else if(bit & 0x01) { Demod.syncBit = 0x01; }
	*/

		if(bit & 0x08) {
			Demod.syncBit = 0x08;
		}

		if(bit & 0x04) {
			if(Demod.syncBit) {
				bit <<= 4;
			}
			Demod.syncBit = 0x04;
		}

		if(bit & 0x02) {
			if(Demod.syncBit) {
				bit <<= 2;
			}
			Demod.syncBit = 0x02;
		}

		if(bit & 0x01 && Demod.syncBit) {
			Demod.syncBit = 0x01;
		}
		
		if(Demod.syncBit) {
			Demod.len = 0;
			Demod.state = DEMOD_START_OF_COMMUNICATION;
			Demod.sub = SUB_FIRST_HALF;
			Demod.bitCount = 0;
			Demod.shiftReg = 0;
			Demod.parityBits = 0;
			Demod.samples = 0;
			if(Demod.posCount) {
				//if(trigger) LED_A_OFF();  // Not useful in this case...
				switch(Demod.syncBit) {
					case 0x08: Demod.samples = 3; break;
					case 0x04: Demod.samples = 2; break;
					case 0x02: Demod.samples = 1; break;
					case 0x01: Demod.samples = 0; break;
				}
				// SOF must be long burst... otherwise stay unsynced!!!
				if(!(Demod.buffer & Demod.syncBit) || !(Demod.buffer2 & Demod.syncBit)) {
					Demod.state = DEMOD_UNSYNCD;
				}
			}
			else {
				// SOF must be long burst... otherwise stay unsynced!!!
				if(!(Demod.buffer2 & Demod.syncBit) || !(Demod.buffer3 & Demod.syncBit)) {
					Demod.state = DEMOD_UNSYNCD;
					error = 0x88;
				}

			}
			error = 0;

		}
	}
	else {
		modulation = bit & Demod.syncBit;
		modulation |= ((bit << 1) ^ ((Demod.buffer & 0x08) >> 3)) & Demod.syncBit;
		//modulation = ((bit << 1) ^ ((Demod.buffer & 0x08) >> 3)) & Demod.syncBit;

		Demod.samples += 4;

		if(Demod.posCount==0) {
			Demod.posCount = 1;
			if(modulation) {
				Demod.sub = SUB_FIRST_HALF;
			}
			else {
				Demod.sub = SUB_NONE;
			}
		}
		else {
			Demod.posCount = 0;
			/*(modulation && (Demod.sub == SUB_FIRST_HALF)) {
				if(Demod.state!=DEMOD_ERROR_WAIT) {
					Demod.state = DEMOD_ERROR_WAIT;
					Demod.output[Demod.len] = 0xaa;
					error = 0x01;
				}
			}*/
			//else if(modulation) {
			if(modulation) {
				if(Demod.sub == SUB_FIRST_HALF) {
					Demod.sub = SUB_BOTH;
				}
				else {
					Demod.sub = SUB_SECOND_HALF;
				}
			}
			else if(Demod.sub == SUB_NONE) {
				if(Demod.state == DEMOD_SOF_COMPLETE) {
					Demod.output[Demod.len] = 0x0f;
					Demod.len++;
					Demod.parityBits <<= 1;
					Demod.parityBits ^= OddByteParity[0x0f];
					Demod.state = DEMOD_UNSYNCD;
//					error = 0x0f;
					return TRUE;
				}
				else {
					Demod.state = DEMOD_ERROR_WAIT;
					error = 0x33;
				}
				/*if(Demod.state!=DEMOD_ERROR_WAIT) {
					Demod.state = DEMOD_ERROR_WAIT;
					Demod.output[Demod.len] = 0xaa;
					error = 0x01;
				}*/
			}

			switch(Demod.state) {
				case DEMOD_START_OF_COMMUNICATION:
					if(Demod.sub == SUB_BOTH) {
						//Demod.state = DEMOD_MANCHESTER_D;
						Demod.state = DEMOD_START_OF_COMMUNICATION2;
						Demod.posCount = 1;
						Demod.sub = SUB_NONE;
					}
					else {
						Demod.output[Demod.len] = 0xab;
						Demod.state = DEMOD_ERROR_WAIT;
						error = 0xd2;
					}
					break;
				case DEMOD_START_OF_COMMUNICATION2:
					if(Demod.sub == SUB_SECOND_HALF) {
						Demod.state = DEMOD_START_OF_COMMUNICATION3;
					}
					else {
						Demod.output[Demod.len] = 0xab;
						Demod.state = DEMOD_ERROR_WAIT;
						error = 0xd3;
					}
					break;
				case DEMOD_START_OF_COMMUNICATION3:
					if(Demod.sub == SUB_SECOND_HALF) {
//						Demod.state = DEMOD_MANCHESTER_D;
						Demod.state = DEMOD_SOF_COMPLETE;
						//Demod.output[Demod.len] = Demod.syncBit & 0xFF;
						//Demod.len++;
					}
					else {
						Demod.output[Demod.len] = 0xab;
						Demod.state = DEMOD_ERROR_WAIT;
						error = 0xd4;
					}
					break;
				case DEMOD_SOF_COMPLETE:
				case DEMOD_MANCHESTER_D:
				case DEMOD_MANCHESTER_E:
					// OPPOSITE FROM ISO14443 - 11110000 = 0 (1 in 14443)
					//                          00001111 = 1 (0 in 14443)
					if(Demod.sub == SUB_SECOND_HALF) { // SUB_FIRST_HALF
						Demod.bitCount++;
						Demod.shiftReg = (Demod.shiftReg >> 1) ^ 0x100;
						Demod.state = DEMOD_MANCHESTER_D;
					}
					else if(Demod.sub == SUB_FIRST_HALF) { // SUB_SECOND_HALF
						Demod.bitCount++;
						Demod.shiftReg >>= 1;
						Demod.state = DEMOD_MANCHESTER_E;
					}
					else if(Demod.sub == SUB_BOTH) {
						Demod.state = DEMOD_MANCHESTER_F;
					}
					else {
						Demod.state = DEMOD_ERROR_WAIT;
						error = 0x55;
					}
					break;

				case DEMOD_MANCHESTER_F:
					// Tag response does not need to be a complete byte!
					if(Demod.len > 0 || Demod.bitCount > 0) {
						if(Demod.bitCount > 1) {  // was > 0, do not interpret last closing bit, is part of EOF
							Demod.shiftReg >>= (9 - Demod.bitCount);
							Demod.output[Demod.len] = Demod.shiftReg & 0xff;
							Demod.len++;
							// No parity bit, so just shift a 0
							Demod.parityBits <<= 1;
						}

						Demod.state = DEMOD_UNSYNCD;
						return TRUE;
					}
					else {
						Demod.output[Demod.len] = 0xad;
						Demod.state = DEMOD_ERROR_WAIT;
						error = 0x03;
					}
					break;

				case DEMOD_ERROR_WAIT:
					Demod.state = DEMOD_UNSYNCD;
					break;

				default:
					Demod.output[Demod.len] = 0xdd;
					Demod.state = DEMOD_UNSYNCD;
					break;
			}

			/*if(Demod.bitCount>=9) {
				Demod.output[Demod.len] = Demod.shiftReg & 0xff;
				Demod.len++;

				Demod.parityBits <<= 1;
				Demod.parityBits ^= ((Demod.shiftReg >> 8) & 0x01);

				Demod.bitCount = 0;
				Demod.shiftReg = 0;
			}*/
			if(Demod.bitCount>=8) {
				Demod.shiftReg >>= 1;
				Demod.output[Demod.len] = (Demod.shiftReg & 0xff);
				Demod.len++;

				// FOR ISO15639 PARITY NOT SEND OTA, JUST CALCULATE IT FOR THE CLIENT
				Demod.parityBits <<= 1;
				Demod.parityBits ^= OddByteParity[(Demod.shiftReg & 0xff)];

				Demod.bitCount = 0;
				Demod.shiftReg = 0;
			}

			if(error) {
				Demod.output[Demod.len] = 0xBB;
				Demod.len++;
				Demod.output[Demod.len] = error & 0xFF;
				Demod.len++;
				Demod.output[Demod.len] = 0xBB;
				Demod.len++;
				Demod.output[Demod.len] = bit & 0xFF;
				Demod.len++;
				Demod.output[Demod.len] = Demod.buffer & 0xFF;
				Demod.len++;
				// Look harder ;-)
				Demod.output[Demod.len] = Demod.buffer2 & 0xFF;
				Demod.len++;
				Demod.output[Demod.len] = Demod.syncBit & 0xFF;
				Demod.len++;
				Demod.output[Demod.len] = 0xBB;
				Demod.len++;
				return TRUE;
			}

		}

	} // end (state != UNSYNCED)

    return FALSE;
}

//=============================================================================
// 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 SnoopIClass(void)
{
//	#define RECV_CMD_OFFSET 	2032	// original (working as of 21/2/09) values
//	#define RECV_RES_OFFSET		2096	// original (working as of 21/2/09) values
//	#define DMA_BUFFER_OFFSET	2160	// original (working as of 21/2/09) values
//	#define DMA_BUFFER_SIZE 	4096	// original (working as of 21/2/09) values
//	#define TRACE_LENGTH	 	2000	// original (working as of 21/2/09) values

    // 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.
    int triggered = FALSE; // FALSE to wait first for card

    // 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;
    
    traceLen = 0; // uncommented to fix ISSUE 15 - gerhard - jan2011

    // The DMA buffer, used to stream samples from the FPGA
    int8_t *dmaBuf = ((int8_t *)BigBuf) + DMA_BUFFER_OFFSET;
    int lastRxCounter;
    int8_t *upTo;
    int smpl;
    int maxBehindBy = 0;

    // Count of samples received so far, so that we can include timing
    // information in the trace buffer.
    int samples = 0;
    rsamples = 0;

    memset(trace, 0x44, RECV_CMD_OFFSET);

    // Set up the demodulator for tag -> reader responses.
    Demod.output = receivedResponse;
    Demod.len = 0;
    Demod.state = DEMOD_UNSYNCD;

    // Setup for the DMA.
    FpgaSetupSsc();
    upTo = dmaBuf;
    lastRxCounter = DMA_BUFFER_SIZE;
    FpgaSetupSscDma((uint8_t *)dmaBuf, DMA_BUFFER_SIZE);

    // And the reader -> tag commands
    memset(&Uart, 0, sizeof(Uart));
    Uart.output = receivedCmd;
    Uart.byteCntMax = 32; // was 100 (greg)////////////////////////////////////////////////////////////////////////
    Uart.state = STATE_UNSYNCD;

    // And put the FPGA in the appropriate mode
    // Signal field is off with the appropriate LED
    LED_D_OFF();
    FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_SNIFFER);
    SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

    int div = 0;
    //int div2 = 0;
    int decbyte = 0;
    int decbyter = 0;

    // And now we loop, receiving samples.
    for(;;) {
        LED_A_ON();
        WDT_HIT();
        int behindBy = (lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR) &
                                (DMA_BUFFER_SIZE-1);
        if(behindBy > maxBehindBy) {
            maxBehindBy = behindBy;
            if(behindBy > 400) {
                Dbprintf("blew circular buffer! behindBy=0x%x", behindBy);
                goto done;
            }
        }
        if(behindBy < 1) continue;

	LED_A_OFF();
        smpl = upTo[0];
        upTo++;
        lastRxCounter -= 1;
        if(upTo - dmaBuf > DMA_BUFFER_SIZE) {
            upTo -= DMA_BUFFER_SIZE;
            lastRxCounter += DMA_BUFFER_SIZE;
            AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) upTo;
            AT91C_BASE_PDC_SSC->PDC_RNCR = DMA_BUFFER_SIZE;
        }

        //samples += 4;
	samples += 1;
	//div2++;	

	//if(div2 > 3) {
		//div2 = 0;
	//decbyte ^= ((smpl & 0x01) << (3 - div));
	//decbyte ^= (((smpl & 0x01) | ((smpl & 0x02) >> 1)) << (3 - div)); // better already...
	//decbyte ^= (((smpl & 0x01) | ((smpl & 0x02) >> 1) | ((smpl & 0x04) >> 2)) << (3 - div)); // even better...
	if(smpl & 0xF) {
		decbyte ^= (1 << (3 - div));
	}
	//decbyte ^= (MajorityNibble[(smpl & 0x0F)] << (3 - div));
	
	// FOR READER SIDE COMMUMICATION...
	//decbyte ^=  ((smpl & 0x10) << (3 - div));
	decbyter <<= 2;
	decbyter ^= (smpl & 0x30);

	div++;
	
	if((div + 1) % 2 == 0) {
		smpl = decbyter;	
		if(MillerDecoding((smpl & 0xF0) >> 4)) {
		    rsamples = samples - Uart.samples;
		    LED_C_ON();
		    //if(triggered) {
			trace[traceLen++] = ((rsamples >>  0) & 0xff);
			trace[traceLen++] = ((rsamples >>  8) & 0xff);
			trace[traceLen++] = ((rsamples >> 16) & 0xff);
			trace[traceLen++] = ((rsamples >> 24) & 0xff);
			trace[traceLen++] = ((Uart.parityBits >>  0) & 0xff);
			trace[traceLen++] = ((Uart.parityBits >>  8) & 0xff);
			trace[traceLen++] = ((Uart.parityBits >> 16) & 0xff);
			trace[traceLen++] = ((Uart.parityBits >> 24) & 0xff);
			trace[traceLen++] = Uart.byteCnt;
			memcpy(trace+traceLen, receivedCmd, Uart.byteCnt);
			traceLen += Uart.byteCnt;
			if(traceLen > TRACE_LENGTH) break;
		    //}
		    /* And ready to receive another command. */
		    Uart.state = STATE_UNSYNCD;
		    /* And also reset the demod code, which might have been */
		    /* false-triggered by the commands from the reader. */
		    Demod.state = DEMOD_UNSYNCD;
		    LED_B_OFF();
		    Uart.byteCnt = 0;
		}
		decbyter = 0;
	}

	if(div > 3) {
		smpl = decbyte;
		if(ManchesterDecoding(smpl & 0x0F)) {
		    rsamples = samples - Demod.samples;
		    LED_B_ON();

		    // timestamp, as a count of samples
		    trace[traceLen++] = ((rsamples >>  0) & 0xff);
		    trace[traceLen++] = ((rsamples >>  8) & 0xff);
		    trace[traceLen++] = ((rsamples >> 16) & 0xff);
		    trace[traceLen++] = 0x80 | ((rsamples >> 24) & 0xff);
		    trace[traceLen++] = ((Demod.parityBits >>  0) & 0xff);
		    trace[traceLen++] = ((Demod.parityBits >>  8) & 0xff);
		    trace[traceLen++] = ((Demod.parityBits >> 16) & 0xff);
		    trace[traceLen++] = ((Demod.parityBits >> 24) & 0xff);
		    // length
		    trace[traceLen++] = Demod.len;
		    memcpy(trace+traceLen, receivedResponse, Demod.len);
		    traceLen += Demod.len;
		    if(traceLen > TRACE_LENGTH) break;

		    triggered = TRUE;

		    // And ready to receive another response.
		    memset(&Demod, 0, sizeof(Demod));
		    Demod.output = receivedResponse;
		    Demod.state = DEMOD_UNSYNCD;
		    LED_C_OFF();
		}
		
		div = 0;
		decbyte = 0x00;
	}
	//}

        if(BUTTON_PRESS()) {
            DbpString("cancelled_a");
            goto done;
        }
    }

    DbpString("COMMAND FINISHED");

    Dbprintf("%x %x %x", maxBehindBy, Uart.state, Uart.byteCnt);
    Dbprintf("%x %x %x", Uart.byteCntMax, traceLen, (int)Uart.output[0]);

done:
    AT91C_BASE_PDC_SSC->PDC_PTCR = AT91C_PDC_RXTDIS;
    Dbprintf("%x %x %x", maxBehindBy, Uart.state, Uart.byteCnt);
    Dbprintf("%x %x %x", Uart.byteCntMax, traceLen, (int)Uart.output[0]);
    LED_A_OFF();
    LED_B_OFF();
	LED_C_OFF();
	LED_D_OFF();
}