CHG: used @marshmellow42 's version to fix lf continuous demod problems.

[proxmark3-svn] / armsrc / hitag2.c

//-----------------------------------------------------------------------------
// 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.
//-----------------------------------------------------------------------------
// Hitag2 emulation (preliminary test version)
//
// (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
//-----------------------------------------------------------------------------
// Hitag2 complete rewrite of the code
// - Fixed modulation/encoding issues
// - Rewrote code for transponder emulation
// - Added snooping of transponder communication
// - Added reader functionality
//
// (c) 2012 Roel Verdult
//-----------------------------------------------------------------------------

#include "proxmark3.h"
#include "apps.h"
#include "util.h"
#include "hitag2.h"
#include "string.h"
#include "BigBuf.h"

static bool bQuiet;
static bool bCrypto;
static bool bAuthenticating;
static bool bPwd;
static bool bSuccessful;

struct hitag2_tag {
	uint32_t uid;
	enum {
		TAG_STATE_RESET      = 0x01,       // Just powered up, awaiting GetSnr
		TAG_STATE_ACTIVATING = 0x02 ,      // In activation phase (password mode), sent UID, awaiting reader password
		TAG_STATE_ACTIVATED  = 0x03,       // Activation complete, awaiting read/write commands
		TAG_STATE_WRITING    = 0x04,       // In write command, awaiting sector contents to be written
	} state;
	unsigned int active_sector;
	byte_t crypto_active;
	uint64_t cs;
	byte_t sectors[12][4];
};

static struct hitag2_tag tag = {
    .state = TAG_STATE_RESET,
    .sectors = {                         // Password mode:               | Crypto mode:
        [0]  = { 0x02, 0x4e, 0x02, 0x20}, // UID                          | UID
        [1]  = { 0x4d, 0x49, 0x4b, 0x52}, // Password RWD                 | 32 bit LSB key
        [2]  = { 0x20, 0xf0, 0x4f, 0x4e}, // Reserved                     | 16 bit MSB key, 16 bit reserved
        [3]  = { 0x0e, 0xaa, 0x48, 0x54}, // Configuration, password TAG  | Configuration, password TAG
        [4]  = { 0x46, 0x5f, 0x4f, 0x4b}, // Data: F_OK
        [5]  = { 0x55, 0x55, 0x55, 0x55}, // Data: UUUU
        [6]  = { 0xaa, 0xaa, 0xaa, 0xaa}, // Data: ....
        [7]  = { 0x55, 0x55, 0x55, 0x55}, // Data: UUUU
        [8]  = { 0x00, 0x00, 0x00, 0x00}, // RSK Low
        [9]  = { 0x00, 0x00, 0x00, 0x00}, // RSK High
        [10] = { 0x00, 0x00, 0x00, 0x00}, // RCF
        [11] = { 0x00, 0x00, 0x00, 0x00}, // SYNC
    },
};

// ToDo: define a meaningful maximum size for auth_table. The bigger this is, the lower will be the available memory for traces. 
// Historically it used to be FREE_BUFFER_SIZE, which was 2744.
#define AUTH_TABLE_LENGTH 2744
static byte_t* auth_table;
static size_t auth_table_pos = 0;
static size_t auth_table_len = AUTH_TABLE_LENGTH;

static byte_t password[4];
static byte_t NrAr[8];
static byte_t key[8];
static uint64_t cipher_state;

/* Following is a modified version of cryptolib.com/ciphers/hitag2/ */
// Software optimized 48-bit Philips/NXP Mifare Hitag2 PCF7936/46/47/52 stream cipher algorithm by I.C. Wiener 2006-2007.
// For educational purposes only.
// No warranties or guarantees of any kind.
// This code is released into the public domain by its author.

// Basic macros:

#define u8				uint8_t
#define u32				uint32_t
#define u64				uint64_t
#define rev8(x)			((((x)>>7)&1)+((((x)>>6)&1)<<1)+((((x)>>5)&1)<<2)+((((x)>>4)&1)<<3)+((((x)>>3)&1)<<4)+((((x)>>2)&1)<<5)+((((x)>>1)&1)<<6)+(((x)&1)<<7))
#define rev16(x)		(rev8 (x)+(rev8 (x>> 8)<< 8))
#define rev32(x)		(rev16(x)+(rev16(x>>16)<<16))
#define rev64(x)		(rev32(x)+(rev32(x>>32)<<32))
#define bit(x,n)		(((x)>>(n))&1)
#define bit32(x,n)		((((x)[(n)>>5])>>((n)))&1)
#define inv32(x,i,n)	((x)[(i)>>5]^=((u32)(n))<<((i)&31))
#define rotl64(x, n)	((((u64)(x))<<((n)&63))+(((u64)(x))>>((0-(n))&63)))

// Single bit Hitag2 functions:
#define i4(x,a,b,c,d)	((u32)((((x)>>(a))&1)+(((x)>>(b))&1)*2+(((x)>>(c))&1)*4+(((x)>>(d))&1)*8))

static const u32 ht2_f4a = 0x2C79;		// 0010 1100 0111 1001
static const u32 ht2_f4b = 0x6671;		// 0110 0110 0111 0001
static const u32 ht2_f5c = 0x7907287B;	// 0111 1001 0000 0111 0010 1000 0111 1011

static u32 _f20 (const u64 x)
{
	u32	i5;

	i5 = ((ht2_f4a >> i4 (x, 1, 2, 4, 5)) & 1)* 1
	   + ((ht2_f4b >> i4 (x, 7,11,13,14)) & 1)* 2
	   + ((ht2_f4b >> i4 (x,16,20,22,25)) & 1)* 4
	   + ((ht2_f4b >> i4 (x,27,28,30,32)) & 1)* 8
	   + ((ht2_f4a >> i4 (x,33,42,43,45)) & 1)*16;

	return (ht2_f5c >> i5) & 1;
}

static u64 _hitag2_init (const u64 key, const u32 serial, const u32 IV)
{
	u32	i;
	u64	x = ((key & 0xFFFF) << 32) + serial;

	for (i = 0; i < 32; i++)
	{
		x >>= 1;
		x += (u64) (_f20 (x) ^ (((IV >> i) ^ (key >> (i+16))) & 1)) << 47;
	}
	return x;
}

static u64 _hitag2_round (u64 *state)
{
	u64 x = *state;

	x = (x >>  1) +
	 ((((x >>  0) ^ (x >>  2) ^ (x >>  3) ^ (x >>  6)
	  ^ (x >>  7) ^ (x >>  8) ^ (x >> 16) ^ (x >> 22)
	  ^ (x >> 23) ^ (x >> 26) ^ (x >> 30) ^ (x >> 41)
	  ^ (x >> 42) ^ (x >> 43) ^ (x >> 46) ^ (x >> 47)) & 1) << 47);

	*state = x;
	return _f20 (x);
}

// "MIKRON"             =  O  N  M  I  K  R
// Key                  = 4F 4E 4D 49 4B 52             - Secret 48-bit key
// Serial               = 49 43 57 69                   - Serial number of the tag, transmitted in clear
// Random               = 65 6E 45 72                   - Random IV, transmitted in clear
//~28~DC~80~31  = D7 23 7F CE                   - Authenticator value = inverted first 4 bytes of the keystream

// The code below must print out "D7 23 7F CE 8C D0 37 A9 57 49 C1 E6 48 00 8A B6".
// The inverse of the first 4 bytes is sent to the tag to authenticate.
// The rest is encrypted by XORing it with the subsequent keystream.

static u32 _hitag2_byte (u64 * x)
{
	u32	i, c;

	for (i = 0, c = 0; i < 8; i++) c += (u32) _hitag2_round (x) << (i^7);
	return c;
}

static int hitag2_reset(void) {
	tag.state = TAG_STATE_RESET;
	tag.crypto_active = 0;
	return 0;
}

static int hitag2_init(void) {
	hitag2_reset();
	return 0;
}

static void hitag2_cipher_reset(struct hitag2_tag *tag, const byte_t *iv)
{
	uint64_t key =  ((uint64_t)tag->sectors[2][2]) |
                  ((uint64_t)tag->sectors[2][3] << 8) |
                  ((uint64_t)tag->sectors[1][0] << 16) |
                  ((uint64_t)tag->sectors[1][1] << 24) |
                  ((uint64_t)tag->sectors[1][2] << 32) |
                  ((uint64_t)tag->sectors[1][3] << 40);
	uint32_t uid =  ((uint32_t)tag->sectors[0][0]) |
                  ((uint32_t)tag->sectors[0][1] << 8) |
                  ((uint32_t)tag->sectors[0][2] << 16) |
                  ((uint32_t)tag->sectors[0][3] << 24);
	uint32_t iv_ = (((uint32_t)(iv[0]))) |
			(((uint32_t)(iv[1])) << 8) |
			(((uint32_t)(iv[2])) << 16) |
			(((uint32_t)(iv[3])) << 24);
	tag->cs = _hitag2_init(rev64(key), rev32(uid), rev32(iv_));
}

static int hitag2_cipher_authenticate(uint64_t* cs, const byte_t *authenticator_is)
{
	byte_t authenticator_should[4];
	authenticator_should[0] = ~_hitag2_byte(cs);
	authenticator_should[1] = ~_hitag2_byte(cs);
	authenticator_should[2] = ~_hitag2_byte(cs);
	authenticator_should[3] = ~_hitag2_byte(cs);
	return (memcmp(authenticator_should, authenticator_is, 4) == 0);
}

static int hitag2_cipher_transcrypt(uint64_t* cs, byte_t *data, unsigned int bytes, unsigned int bits)
{
	int i;
	for(i=0; i<bytes; i++) data[i] ^= _hitag2_byte(cs);
	for(i=0; i<bits; i++) data[bytes] ^= _hitag2_round(cs) << (7-i);
	return 0;
}

// Sam7s has several timers, we will use the source TIMER_CLOCK1 (aka AT91C_TC_CLKS_TIMER_DIV1_CLOCK)
// TIMER_CLOCK1 = MCK/2, MCK is running at 48 MHz, Timer is running at 48/2 = 24 MHz
// Hitag units (T0) have duration of 8 microseconds (us), which is 1/125000 per second (carrier)
// T0 = TIMER_CLOCK1 / 125000 = 192
#define T0 192

#define SHORT_COIL()	LOW(GPIO_SSC_DOUT)
#define OPEN_COIL()		HIGH(GPIO_SSC_DOUT)

#define HITAG_FRAME_LEN 20
#define HITAG_T_STOP  36 /* T_EOF should be > 36 */
#define HITAG_T_LOW		8  /* T_LOW should be 4..10 */
#define HITAG_T_0_MIN 15 /* T[0] should be 18..22 */
#define HITAG_T_1_MIN 25 /* T[1] should be 26..30 */
//#define HITAG_T_EOF   40 /* T_EOF should be > 36 */
#define HITAG_T_EOF   80	 /* T_EOF should be > 36 */
#define HITAG_T_WAIT_1 200 /* T_wresp should be 199..206 */
#define HITAG_T_WAIT_2 90 /* T_wresp should be 199..206 */
#define HITAG_T_WAIT_MAX 300 /* bit more than HITAG_T_WAIT_1 + HITAG_T_WAIT_2 */

#define HITAG_T_TAG_ONE_HALF_PERIOD		10
#define HITAG_T_TAG_TWO_HALF_PERIOD		25
#define HITAG_T_TAG_THREE_HALF_PERIOD	41 
#define HITAG_T_TAG_FOUR_HALF_PERIOD	57 

#define HITAG_T_TAG_HALF_PERIOD			16
#define HITAG_T_TAG_FULL_PERIOD			32

#define HITAG_T_TAG_CAPTURE_ONE_HALF	13
#define HITAG_T_TAG_CAPTURE_TWO_HALF	25
#define HITAG_T_TAG_CAPTURE_THREE_HALF	41 
#define HITAG_T_TAG_CAPTURE_FOUR_HALF   57 


static void hitag_send_bit(int bit) {
	LED_A_ON();
	// Reset clock for the next bit 
	AT91C_BASE_TC0->TC_CCR = AT91C_TC_SWTRG;
	
	// Fixed modulation, earlier proxmark version used inverted signal
	if(bit == 0) {
		// Manchester: Unloaded, then loaded |__--|
		LOW(GPIO_SSC_DOUT);
		while(AT91C_BASE_TC0->TC_CV < T0*HITAG_T_TAG_HALF_PERIOD);
		HIGH(GPIO_SSC_DOUT);
		while(AT91C_BASE_TC0->TC_CV < T0*HITAG_T_TAG_FULL_PERIOD);
	} else {
		// Manchester: Loaded, then unloaded |--__|
		HIGH(GPIO_SSC_DOUT);
		while(AT91C_BASE_TC0->TC_CV < T0*HITAG_T_TAG_HALF_PERIOD);
		LOW(GPIO_SSC_DOUT);
		while(AT91C_BASE_TC0->TC_CV < T0*HITAG_T_TAG_FULL_PERIOD);
	}
	LED_A_OFF();
}

static void hitag_send_frame(const byte_t* frame, size_t frame_len)
{
	// Send start of frame
	for(size_t i=0; i<5; i++) {
		hitag_send_bit(1);
	}

	// Send the content of the frame
	for(size_t i=0; i<frame_len; i++) {
		hitag_send_bit((frame[i/8] >> (7-(i%8)))&1);
	}

	// Drop the modulation
	LOW(GPIO_SSC_DOUT);
}


static void hitag2_handle_reader_command(byte_t* rx, const size_t rxlen, byte_t* tx, size_t* txlen)
{
	byte_t rx_air[HITAG_FRAME_LEN];
	
	// Copy the (original) received frame how it is send over the air
	memcpy(rx_air,rx,nbytes(rxlen));

	if(tag.crypto_active) {
		hitag2_cipher_transcrypt(&(tag.cs),rx,rxlen/8,rxlen%8);
	}
	
	// Reset the transmission frame length 
	*txlen = 0;
	
	// Try to find out which command was send by selecting on length (in bits)
	switch (rxlen) {
		// Received 11000 from the reader, request for UID, send UID 
		case 05: {
			// Always send over the air in the clear plaintext mode
			if(rx_air[0] != 0xC0) {
				// Unknown frame ?
				return;
			}
			*txlen = 32;
			memcpy(tx,tag.sectors[0],4);
			tag.crypto_active = 0;
		}
		break;

		// Read/Write command: ..xx x..y  yy with yyy == ~xxx, xxx is sector number 
		case 10: {
			unsigned int sector = (~( ((rx[0]<<2)&0x04) | ((rx[1]>>6)&0x03) ) & 0x07);
			// Verify complement of sector index
			if(sector != ((rx[0]>>3)&0x07)) {
				//DbpString("Transmission error (read/write)");
				return;
			}

			switch (rx[0] & 0xC6) {
				// Read command: 11xx x00y
				case 0xC0:
					memcpy(tx,tag.sectors[sector],4);
					*txlen = 32;
				break;
					
				 // Inverted Read command: 01xx x10y
				case 0x44:
					for (size_t i=0; i<4; i++) {
						tx[i] = tag.sectors[sector][i] ^ 0xff;
					}
					*txlen = 32;
				break;

				// Write command: 10xx x01y
				case 0x82:
					// Prepare write, acknowledge by repeating command
					memcpy(tx,rx,nbytes(rxlen));
					*txlen = rxlen;
					tag.active_sector = sector;
					tag.state=TAG_STATE_WRITING;
				break;
				
				// Unknown command
				default:
					Dbprintf("Uknown command: %02x %02x",rx[0],rx[1]);
					return;
				break;
			}
		}
		break;

		// Writing data or Reader password
		case 32: {
			if(tag.state == TAG_STATE_WRITING) {
				// These are the sector contents to be written. We don't have to do anything else.
				memcpy(tag.sectors[tag.active_sector],rx,nbytes(rxlen));
				tag.state=TAG_STATE_RESET;
				return;
			} else {
				// Received RWD password, respond with configuration and our password
				if(memcmp(rx,tag.sectors[1],4) != 0) {
					DbpString("Reader password is wrong");
					return;
				}
				*txlen = 32;
				memcpy(tx,tag.sectors[3],4);
			}
		}
		break;

		// Received RWD authentication challenge and respnse
		case 64: {
			// Store the authentication attempt
			if (auth_table_len < (AUTH_TABLE_LENGTH-8)) {
				memcpy(auth_table+auth_table_len,rx,8);
				auth_table_len += 8;
			}

			// Reset the cipher state
			hitag2_cipher_reset(&tag,rx);
			// Check if the authentication was correct
			if(!hitag2_cipher_authenticate(&(tag.cs),rx+4)) {
				// The reader failed to authenticate, do nothing
				Dbprintf("auth: %02x%02x%02x%02x%02x%02x%02x%02x Failed!",rx[0],rx[1],rx[2],rx[3],rx[4],rx[5],rx[6],rx[7]);
				return;
			}
			// Succesful, but commented out reporting back to the Host, this may delay to much.
			// Dbprintf("auth: %02x%02x%02x%02x%02x%02x%02x%02x OK!",rx[0],rx[1],rx[2],rx[3],rx[4],rx[5],rx[6],rx[7]);

			// Activate encryption algorithm for all further communication
			tag.crypto_active = 1;

			// Use the tag password as response
			memcpy(tx,tag.sectors[3],4);
			*txlen = 32;
		}
		break;
	}

//	LogTraceHitag(rx,rxlen,0,0,false);
//	LogTraceHitag(tx,*txlen,0,0,true);
	
	if(tag.crypto_active) {
		hitag2_cipher_transcrypt(&(tag.cs), tx, *txlen/8, *txlen%8);
	}
}

static void hitag_reader_send_bit(int bit) {
	LED_A_ON();
	// Reset clock for the next bit 
	AT91C_BASE_TC0->TC_CCR = AT91C_TC_SWTRG;
	
	// Binary puls length modulation (BPLM) is used to encode the data stream
	// This means that a transmission of a one takes longer than that of a zero
	
	// Enable modulation, which means, drop the field
	HIGH(GPIO_SSC_DOUT);
	
	// Wait for 4-10 times the carrier period
	while(AT91C_BASE_TC0->TC_CV < T0*6);
	//	SpinDelayUs(8*8);
	
	// Disable modulation, just activates the field again
	LOW(GPIO_SSC_DOUT);
	
	if(bit == 0) {
		// Zero bit: |_-|
		while(AT91C_BASE_TC0->TC_CV < T0*22);

	} else {
		// One bit: |_--|
		while(AT91C_BASE_TC0->TC_CV < T0*28);
	}
	LED_A_OFF();
}


static void hitag_reader_send_frame(const byte_t* frame, size_t frame_len)
{
	// Send the content of the frame
	for(size_t i=0; i<frame_len; i++) {
		hitag_reader_send_bit((frame[i/8] >> (7-(i%8)))&1);
	}
	// Send EOF 
	AT91C_BASE_TC0->TC_CCR = AT91C_TC_SWTRG;
	// Enable modulation, which means, drop the field
	HIGH(GPIO_SSC_DOUT);
	// Wait for 4-10 times the carrier period
	while(AT91C_BASE_TC0->TC_CV < T0*6);
	// Disable modulation, just activates the field again
	LOW(GPIO_SSC_DOUT);
}

size_t blocknr;

static bool hitag2_password(byte_t* rx, const size_t rxlen, byte_t* tx, size_t* txlen) {
	// Reset the transmission frame length
	*txlen = 0;
	
	// Try to find out which command was send by selecting on length (in bits)
	switch (rxlen) {
		// No answer, try to resurrect
		case 0: {
			// Stop if there is no answer (after sending password)
			if (bPwd) {
				DbpString("Password failed!");
				return false;
			}
			*txlen = 5;
			memcpy(tx,"\xc0",nbytes(*txlen));
		} break;
			
		// Received UID, tag password
		case 32: {
			if (!bPwd) {
				*txlen = 32;
				memcpy(tx,password,4);
				bPwd = true;
				memcpy(tag.sectors[blocknr],rx,4);
				blocknr++;
			} else {
				
				if(blocknr == 1){
					//store password in block1, the TAG answers with Block3, but we need the password in memory
					memcpy(tag.sectors[blocknr],tx,4);
				} else {
					memcpy(tag.sectors[blocknr],rx,4);
				}
				
				blocknr++;
				if (blocknr > 7) {
					DbpString("Read succesful!");
					bSuccessful = true;
					return false;
				}
				*txlen = 10;
				tx[0] = 0xc0 | (blocknr << 3) | ((blocknr^7) >> 2);
				tx[1] = ((blocknr^7) << 6);
			}
		} break;
			
		// Unexpected response
    default: {
			Dbprintf("Uknown frame length: %d",rxlen);
			return false;
		} break;
	}
	return true;
}

static bool hitag2_crypto(byte_t* rx, const size_t rxlen, byte_t* tx, size_t* txlen) {
	// Reset the transmission frame length
	*txlen = 0;
	
  if(bCrypto) {
		hitag2_cipher_transcrypt(&cipher_state,rx,rxlen/8,rxlen%8);
	}

	// Try to find out which command was send by selecting on length (in bits)
	switch (rxlen) {
      // No answer, try to resurrect
		case 0: {
			// Stop if there is no answer while we are in crypto mode (after sending NrAr)
			if (bCrypto) {
        // Failed during authentication
        if (bAuthenticating) {
          DbpString("Authentication failed!");
          return false;
        } else {
          // Failed reading a block, could be (read/write) locked, skip block and re-authenticate
          if (blocknr == 1) {
            // Write the low part of the key in memory
            memcpy(tag.sectors[1],key+2,4);
          } else if (blocknr == 2) {
            // Write the high part of the key in memory
            tag.sectors[2][0] = 0x00;
            tag.sectors[2][1] = 0x00;
            tag.sectors[2][2] = key[0];
            tag.sectors[2][3] = key[1];
          } else {
            // Just put zero's in the memory (of the unreadable block)
            memset(tag.sectors[blocknr],0x00,4);
          }
          blocknr++;
          bCrypto = false;
        }
			} else {
				*txlen = 5;
				memcpy(tx,"\xc0",nbytes(*txlen));
			}
		} break;
			
      // Received UID, crypto tag answer
		case 32: {
			if (!bCrypto) {
        uint64_t ui64key = key[0] | ((uint64_t)key[1]) << 8 | ((uint64_t)key[2]) << 16 | ((uint64_t)key[3]) << 24 | ((uint64_t)key[4]) << 32 | ((uint64_t)key[5]) << 40;
        uint32_t ui32uid = rx[0] | ((uint32_t)rx[1]) << 8 | ((uint32_t)rx[2]) << 16 | ((uint32_t)rx[3]) << 24;
        cipher_state = _hitag2_init(rev64(ui64key), rev32(ui32uid), 0);
        memset(tx,0x00,4);
        memset(tx+4,0xff,4);
        hitag2_cipher_transcrypt(&cipher_state,tx+4,4,0);
				*txlen = 64;
				bCrypto = true;
				bAuthenticating = true;
			} else {
        // Check if we received answer tag (at)
        if (bAuthenticating) {
			bAuthenticating = false;
        } else {
			// Store the received block
			memcpy(tag.sectors[blocknr],rx,4);
			blocknr++;
        }
        if (blocknr > 7) {
			DbpString("Read succesful!");
			bSuccessful = true;
			return false;
        }
        *txlen = 10;
        tx[0] = 0xc0 | (blocknr << 3) | ((blocknr^7) >> 2);
        tx[1] = ((blocknr^7) << 6);
			}
		} break;
			
      // Unexpected response
		default: {
			Dbprintf("Uknown frame length: %d",rxlen);
			return false;
		} break;
	}
	
  
	if(bCrypto) {
		// We have to return now to avoid double encryption
		if (!bAuthenticating) {
		  hitag2_cipher_transcrypt(&cipher_state, tx, *txlen/8, *txlen%8);
		}
	}

	return true;
}


static bool hitag2_authenticate(byte_t* rx, const size_t rxlen, byte_t* tx, size_t* txlen) {
	// Reset the transmission frame length 
	*txlen = 0;
	
	// Try to find out which command was send by selecting on length (in bits)
	switch (rxlen) {
		// No answer, try to resurrect
		case 0: {
			// Stop if there is no answer while we are in crypto mode (after sending NrAr)
			if (bCrypto) {
				DbpString("Authentication failed!");
				return false;
			}
			*txlen = 5;
			memcpy(tx,"\xc0",nbytes(*txlen));
		} break;
			
		// Received UID, crypto tag answer
		case 32: {
			if (!bCrypto) {
				*txlen = 64;
				memcpy(tx,NrAr,8);
				bCrypto = true;
			} else {
				DbpString("Authentication succesful!");
				return true;
			}
		} break;
			
		// Unexpected response
		default: {
			Dbprintf("Uknown frame length: %d",rxlen);
			return false;
		} break;
	}
	
	return true;
}


static bool hitag2_test_auth_attempts(byte_t* rx, const size_t rxlen, byte_t* tx, size_t* txlen) {

	// Reset the transmission frame length 
	*txlen = 0;
	
	// Try to find out which command was send by selecting on length (in bits)
	switch (rxlen) {
			// No answer, try to resurrect
		case 0: {
			// Stop if there is no answer while we are in crypto mode (after sending NrAr)
			if (bCrypto) {
				Dbprintf("auth: %02x%02x%02x%02x%02x%02x%02x%02x Failed, removed entry!",NrAr[0],NrAr[1],NrAr[2],NrAr[3],NrAr[4],NrAr[5],NrAr[6],NrAr[7]);

				// Removing failed entry from authentiations table
				memcpy(auth_table+auth_table_pos,auth_table+auth_table_pos+8,8);
				auth_table_len -= 8;

				// Return if we reached the end of the authentications table
				bCrypto = false;
				if (auth_table_pos == auth_table_len) {
					return false;
				}

				// Copy the next authentication attempt in row (at the same position, b/c we removed last failed entry)
				memcpy(NrAr,auth_table+auth_table_pos,8);
			}
			*txlen = 5;
			memcpy(tx,"\xc0",nbytes(*txlen));
		}	break;
			
			// Received UID, crypto tag answer, or read block response
		case 32: {
			if (!bCrypto) {
				*txlen = 64;
				memcpy(tx,NrAr,8);
				bCrypto = true;
			} else {
				Dbprintf("auth: %02x%02x%02x%02x%02x%02x%02x%02x OK",NrAr[0],NrAr[1],NrAr[2],NrAr[3],NrAr[4],NrAr[5],NrAr[6],NrAr[7]);
				bCrypto = false;
				if ((auth_table_pos+8) == auth_table_len) {
					return false;
				}
				auth_table_pos += 8;
				memcpy(NrAr,auth_table+auth_table_pos,8);
			}
		} break;
			
		default: {
			Dbprintf("Uknown frame length: %d",rxlen);
			return false;
		} break;
	}
	
	return true;
}


void SnoopHitag(uint32_t type) {
	int frame_count;
	int response;
	int overflow;
	bool rising_edge;
	bool reader_frame;
	int lastbit;
	bool bSkip;
	int tag_sof;
	byte_t rx[HITAG_FRAME_LEN];
	size_t rxlen=0;
	
	FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
	
	// free eventually allocated BigBuf memory
	BigBuf_free(); BigBuf_Clear_ext(false);
	
	// Clean up trace and prepare it for storing frames
	clear_trace();
	set_tracing(TRUE);
	
	auth_table_len = 0;
	auth_table_pos = 0;

    auth_table = (byte_t *)BigBuf_malloc(AUTH_TABLE_LENGTH);
	memset(auth_table, 0x00, AUTH_TABLE_LENGTH);
	
	DbpString("Starting Hitag2 snoop");
	LED_D_ON();
	
	// Set up eavesdropping mode, frequency divisor which will drive the FPGA
	// and analog mux selection.
	FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_EDGE_DETECT  | FPGA_LF_EDGE_DETECT_TOGGLE_MODE);
	FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
	SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
	RELAY_OFF();
	
	// Configure output pin that is connected to the FPGA (for modulating)
	AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
	AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;

	// Disable modulation, we are going to eavesdrop, not modulate ;)
	LOW(GPIO_SSC_DOUT);
	
	// Enable Peripheral Clock for TIMER_CLOCK1, used to capture edges of the reader frames
	AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC1);
	AT91C_BASE_PIOA->PIO_BSR = GPIO_SSC_FRAME;
	
	// Disable timer during configuration	
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
	
	// Capture mode, defaul timer source = MCK/2 (TIMER_CLOCK1), TIOA is external trigger,
	// external trigger rising edge, load RA on rising edge of TIOA.
	uint32_t t1_channel_mode = AT91C_TC_CLKS_TIMER_DIV1_CLOCK | AT91C_TC_ETRGEDG_BOTH | AT91C_TC_ABETRG | AT91C_TC_LDRA_BOTH;
	AT91C_BASE_TC1->TC_CMR = t1_channel_mode;
	
	// Enable and reset counter
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
	
	// Reset the received frame, frame count and timing info
	memset(rx,0x00,sizeof(rx));
	frame_count = 0;
	response = 0;
	overflow = 0;
	reader_frame = false;
	lastbit = 1;
	bSkip = true;
	tag_sof = 4;
	
	while(!BUTTON_PRESS() && !usb_poll_validate_length()) {
		// Watchdog hit
		WDT_HIT();
		
		// Receive frame, watch for at most T0*EOF periods
		while (AT91C_BASE_TC1->TC_CV < T0*HITAG_T_EOF) {
			// Check if rising edge in modulation is detected
			if(AT91C_BASE_TC1->TC_SR & AT91C_TC_LDRAS) {
				// Retrieve the new timing values 
				int ra = (AT91C_BASE_TC1->TC_RA/T0);
				
				// Find out if we are dealing with a rising or falling edge
				rising_edge = (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_FRAME) > 0;

				// Shorter periods will only happen with reader frames
				if (!reader_frame && rising_edge && ra < HITAG_T_TAG_CAPTURE_ONE_HALF) {
					// Switch from tag to reader capture
					LED_C_OFF();
					reader_frame = true;
					memset(rx,0x00,sizeof(rx));
					rxlen = 0;
				}
				
				// Only handle if reader frame and rising edge, or tag frame and falling edge
				if (reader_frame != rising_edge) {
				  overflow += ra;
					continue;
				}
				
				// Add the buffered timing values of earlier captured edges which were skipped
				ra += overflow;
				overflow = 0;
				
				if (reader_frame) {
					LED_B_ON();
					// Capture reader frame
					if(ra >= HITAG_T_STOP) {
						if (rxlen != 0) {
							//DbpString("wierd0?");
						}
						// Capture the T0 periods that have passed since last communication or field drop (reset)
						response = (ra - HITAG_T_LOW);
					} else if(ra >= HITAG_T_1_MIN ) {
						// '1' bit 
						rx[rxlen / 8] |= 1 << (7-(rxlen%8));
						rxlen++;
					} else if(ra >= HITAG_T_0_MIN) {
						// '0' bit 
						rx[rxlen / 8] |= 0 << (7-(rxlen%8));
						rxlen++;
					} else {
						// Ignore wierd value, is to small to mean anything
					}
				} else {
					LED_C_ON();
					// Capture tag frame (manchester decoding using only falling edges)
					if(ra >= HITAG_T_EOF) {
						if (rxlen != 0) {
							//DbpString("wierd1?");
						}
						// Capture the T0 periods that have passed since last communication or field drop (reset)
						// We always recieve a 'one' first, which has the falling edge after a half period |-_|
						response = ra-HITAG_T_TAG_HALF_PERIOD;
					} else if(ra >= HITAG_T_TAG_CAPTURE_FOUR_HALF) {
						// Manchester coding example |-_|_-|-_| (101)
						rx[rxlen / 8] |= 0 << (7-(rxlen%8));
						rxlen++;
						rx[rxlen / 8] |= 1 << (7-(rxlen%8));
						rxlen++;
					} else if(ra >= HITAG_T_TAG_CAPTURE_THREE_HALF) {
						// Manchester coding example |_-|...|_-|-_| (0...01)
						rx[rxlen / 8] |= 0 << (7-(rxlen%8));
						rxlen++;
						// We have to skip this half period at start and add the 'one' the second time 
						if (!bSkip) {
							rx[rxlen / 8] |= 1 << (7-(rxlen%8));
							rxlen++;
						}
						lastbit = !lastbit;
						bSkip = !bSkip;
					} else if(ra >= HITAG_T_TAG_CAPTURE_TWO_HALF) {
						// Manchester coding example |_-|_-| (00) or |-_|-_| (11)
						if (tag_sof) {
							// Ignore bits that are transmitted during SOF
							tag_sof--;
						} else {
							// bit is same as last bit
							rx[rxlen / 8] |= lastbit << (7-(rxlen%8));
							rxlen++;
						}
					} else {
						// Ignore wierd value, is to small to mean anything
					}
				}
			}
		}
		
		// Check if frame was captured
		if(rxlen > 0) {
			frame_count++;
			if (!LogTraceHitag(rx,rxlen,response,0,reader_frame)) {
				DbpString("Trace full");
				break;
			}

			// Check if we recognize a valid authentication attempt
			if (nbytes(rxlen) == 8) {
				// Store the authentication attempt
				if (auth_table_len < (AUTH_TABLE_LENGTH-8)) {
					memcpy(auth_table+auth_table_len,rx,8);
					auth_table_len += 8;
				}
			}
			
			// Reset the received frame and response timing info
			memset(rx,0x00,sizeof(rx));
			response = 0;
			reader_frame = false;
			lastbit = 1;
			bSkip = true;
			tag_sof = 4;
			overflow = 0;
			
			LED_B_OFF();
			LED_C_OFF();
		} else {
			// Save the timer overflow, will be 0 when frame was received
			overflow += (AT91C_BASE_TC1->TC_CV/T0);
		}
		// Reset the frame length
		rxlen = 0;
		// Reset the timer to restart while-loop that receives frames
		AT91C_BASE_TC1->TC_CCR = AT91C_TC_SWTRG;
	}
    LED_A_ON();
	LED_B_OFF();
	LED_C_OFF();
	LED_D_OFF();
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
    AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS;
	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
    LED_A_OFF();
	set_tracing(TRUE);
//	Dbprintf("frame received: %d",frame_count);
//	Dbprintf("Authentication Attempts: %d",(auth_table_len/8));
//	DbpString("All done");
}

void SimulateHitagTag(bool tag_mem_supplied, byte_t* data) {
	int frame_count;
	int response;
	int overflow;
	byte_t rx[HITAG_FRAME_LEN];
	size_t rxlen=0;
	byte_t tx[HITAG_FRAME_LEN];
	size_t txlen=0;
	bool bQuitTraceFull = false;
	bQuiet = false;
	
	FpgaDownloadAndGo(FPGA_BITSTREAM_LF);

	// free eventually allocated BigBuf memory
	BigBuf_free(); BigBuf_Clear_ext(false);

	// Clean up trace and prepare it for storing frames
	clear_trace();
	set_tracing(TRUE);
	
	auth_table_len = 0;
	auth_table_pos = 0;
    byte_t* auth_table;

    auth_table = (byte_t *)BigBuf_malloc(AUTH_TABLE_LENGTH);
	memset(auth_table, 0x00, AUTH_TABLE_LENGTH);

	DbpString("Starting Hitag2 simulation");
	LED_D_ON();
	hitag2_init();
	
	if (tag_mem_supplied) {
		DbpString("Loading hitag2 memory...");
		memcpy((byte_t*)tag.sectors,data,48);
	}

	uint32_t block = 0;
	for (size_t i=0; i<12; i++) {
		for (size_t j=0; j<4; j++) {
			block <<= 8;
			block |= tag.sectors[i][j];
		}
		Dbprintf("| %d | %08x |",i,block);
	}
	
	// Set up simulator mode, frequency divisor which will drive the FPGA
	// and analog mux selection.
	FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_EDGE_DETECT | FPGA_LF_EDGE_DETECT_READER_FIELD);
	FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
	SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
	RELAY_OFF();

	// Configure output pin that is connected to the FPGA (for modulating)
	AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
	AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;

	// Disable modulation at default, which means release resistance
	LOW(GPIO_SSC_DOUT);
	
	// Enable Peripheral Clock for TIMER_CLOCK0, used to measure exact timing before answering
	AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC0);
	
	// Enable Peripheral Clock for TIMER_CLOCK1, used to capture edges of the reader frames
	AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC1);
	AT91C_BASE_PIOA->PIO_BSR = GPIO_SSC_FRAME;
	
    // Disable timer during configuration	
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;

	// Capture mode, default timer source = MCK/2 (TIMER_CLOCK1), TIOA is external trigger,
	// external trigger rising edge, load RA on rising edge of TIOA.
	AT91C_BASE_TC1->TC_CMR = AT91C_TC_CLKS_TIMER_DIV1_CLOCK | AT91C_TC_ETRGEDG_RISING | AT91C_TC_ABETRG | AT91C_TC_LDRA_RISING;
	
	// Reset the received frame, frame count and timing info
	memset(rx,0x00,sizeof(rx));
	frame_count = 0;
	response = 0;
	overflow = 0;

	// Enable and reset counter
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
	
	while(!BUTTON_PRESS() && !usb_poll_validate_length()) {
		// Watchdog hit
		WDT_HIT();
		
		// Receive frame, watch for at most T0*EOF periods
		while (AT91C_BASE_TC1->TC_CV < T0*HITAG_T_EOF) {
			// Check if rising edge in modulation is detected
			if(AT91C_BASE_TC1->TC_SR & AT91C_TC_LDRAS) {
				// Retrieve the new timing values 
				int ra = (AT91C_BASE_TC1->TC_RA/T0) + overflow;
				overflow = 0;

				// Reset timer every frame, we have to capture the last edge for timing
				AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
				
				LED_B_ON();
				
				// Capture reader frame
				if(ra >= HITAG_T_STOP) {
					if (rxlen != 0) {
						//DbpString("wierd0?");
					}
					// Capture the T0 periods that have passed since last communication or field drop (reset)
					response = (ra - HITAG_T_LOW);
				} else if(ra >= HITAG_T_1_MIN ) {
					// '1' bit 
					rx[rxlen / 8] |= 1 << (7-(rxlen%8));
					rxlen++;
				} else if(ra >= HITAG_T_0_MIN) {
					// '0' bit 
					rx[rxlen / 8] |= 0 << (7-(rxlen%8));
					rxlen++;
				} else {
					// Ignore wierd value, is to small to mean anything
				}
			}
		}
		
		// Check if frame was captured
		if(rxlen > 4) {
			frame_count++;
			if (!bQuiet) {
				if (!LogTraceHitag(rx,rxlen,response,0,true)) {
					DbpString("Trace full");
					if (bQuitTraceFull) {
						break;
					} else {
						bQuiet = true;
					}
				}
			}
			
			// Disable timer 1 with external trigger to avoid triggers during our own modulation
			AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;

			// Process the incoming frame (rx) and prepare the outgoing frame (tx)
			hitag2_handle_reader_command(rx,rxlen,tx,&txlen);
			
			// Wait for HITAG_T_WAIT_1 carrier periods after the last reader bit,
			// not that since the clock counts since the rising edge, but T_Wait1 is
			// with respect to the falling edge, we need to wait actually (T_Wait1 - T_Low)
			// periods. The gap time T_Low varies (4..10). All timer values are in 
			// terms of T0 units
			while(AT91C_BASE_TC0->TC_CV < T0*(HITAG_T_WAIT_1-HITAG_T_LOW));

			// Send and store the tag answer (if there is any)
			if (txlen) {
				// Transmit the tag frame
				hitag_send_frame(tx,txlen);
				// Store the frame in the trace
				if (!bQuiet) {
					if (!LogTraceHitag(tx,txlen,0,0,false)) {
						DbpString("Trace full");
						if (bQuitTraceFull) {
							break;
						} else {
							bQuiet = true;
						}
					}
				}
			}
			
			// Reset the received frame and response timing info
			memset(rx,0x00,sizeof(rx));
			response = 0;
			
			// Enable and reset external trigger in timer for capturing future frames
			AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
			LED_B_OFF();
		}
		// Reset the frame length
		rxlen = 0;
		// Save the timer overflow, will be 0 when frame was received
		overflow += (AT91C_BASE_TC1->TC_CV/T0);
		// Reset the timer to restart while-loop that receives frames
		AT91C_BASE_TC1->TC_CCR = AT91C_TC_SWTRG;
	}
	LED_B_OFF();
	LED_D_OFF();
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
	AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS;
	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
	
	DbpString("Sim Stopped");
	set_tracing(TRUE);
}

void ReaderHitag(hitag_function htf, hitag_data* htd) {
	int frame_count;
	int response;
	byte_t rx[HITAG_FRAME_LEN];
	size_t rxlen=0;
	byte_t txbuf[HITAG_FRAME_LEN];
	byte_t* tx = txbuf;
	size_t txlen=0;
	int lastbit;
	bool bSkip;
	int reset_sof; 
	int tag_sof;
	int t_wait = HITAG_T_WAIT_MAX;
	bool bStop;
	bool bQuitTraceFull = false;
  
	FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
	// Reset the return status
	bSuccessful = false;
  
	// Clean up trace and prepare it for storing frames
	clear_trace();
	set_tracing(TRUE);
	
	DbpString("Starting Hitag reader family");

	// Check configuration
	switch(htf) {
		case RHT2F_PASSWORD: {
			Dbprintf("List identifier in password mode");
			memcpy(password,htd->pwd.password,4);
      		blocknr = 0;
			bQuitTraceFull = false;
			bQuiet = false;
			bPwd = false;
		} break;
      
		case RHT2F_AUTHENTICATE: {
			DbpString("Authenticating using nr,ar pair:");
			memcpy(NrAr,htd->auth.NrAr,8);
			Dbhexdump(8,NrAr,false);
			bQuiet = false;
			bCrypto = false;
			bAuthenticating = false;
			bQuitTraceFull = true;
		} break;
      
		case RHT2F_CRYPTO: {
			DbpString("Authenticating using key:");
			memcpy(key,htd->crypto.key,6);	  //HACK; 4 or 6??  I read both in the code.
			Dbhexdump(6,key,false);
			blocknr = 0;
			bQuiet = false;
			bCrypto = false;
			bAuthenticating = false;
			bQuitTraceFull = true;
		} break;

		case RHT2F_TEST_AUTH_ATTEMPTS: {
			Dbprintf("Testing %d authentication attempts",(auth_table_len/8));
			auth_table_pos = 0;
			memcpy(NrAr, auth_table, 8);
			bQuitTraceFull = false;
			bQuiet = false;
			bCrypto = false;
		} break;
			
		default: {
			Dbprintf("Error, unknown function: %d",htf);
			set_tracing(FALSE);
			return;
		} break;
	}
	
	LED_D_ON();
	hitag2_init();
	
	// Configure output and enable pin that is connected to the FPGA (for modulating)
	AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
	AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
	
	// Set fpga in edge detect with reader field, we can modulate as reader now
	FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_EDGE_DETECT | FPGA_LF_EDGE_DETECT_READER_FIELD);

	// Set Frequency divisor which will drive the FPGA and analog mux selection
	FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
	SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
	RELAY_OFF();

	// Disable modulation at default, which means enable the field
	LOW(GPIO_SSC_DOUT);

	// Give it a bit of time for the resonant antenna to settle.
	SpinDelay(30);
	
	// Enable Peripheral Clock for TIMER_CLOCK0, used to measure exact timing before answering
	AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC0);

	// Enable Peripheral Clock for TIMER_CLOCK1, used to capture edges of the tag frames
	AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC1);
	AT91C_BASE_PIOA->PIO_BSR = GPIO_SSC_FRAME;
	
    // Disable timer during configuration	
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
	
	// Capture mode, defaul timer source = MCK/2 (TIMER_CLOCK1), TIOA is external trigger,
	// external trigger rising edge, load RA on falling edge of TIOA.
	AT91C_BASE_TC1->TC_CMR = AT91C_TC_CLKS_TIMER_DIV1_CLOCK | AT91C_TC_ETRGEDG_FALLING | AT91C_TC_ABETRG | AT91C_TC_LDRA_FALLING;
	
	// Enable and reset counters
	AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;

	// Reset the received frame, frame count and timing info
	frame_count = 0;
	response = 0;
	lastbit = 1;
	bStop = false;

	// Tag specific configuration settings (sof, timings, etc.)
	if (htf < 10){
		// hitagS settings
		reset_sof = 1;
		t_wait = 200;
		DbpString("Configured for hitagS reader");
	} else if (htf < 20) {
		// hitag1 settings
		reset_sof = 1;
		t_wait = 200;
		DbpString("Configured for hitag1 reader");
	} else if (htf < 30) {
		// hitag2 settings
		reset_sof = 4;
		t_wait = HITAG_T_WAIT_2;
		DbpString("Configured for hitag2 reader");
	} else {
		Dbprintf("Error, unknown hitag reader type: %d",htf);
		set_tracing(FALSE);	
		return;
	}
		
	while(!bStop && !BUTTON_PRESS()) {
		// Watchdog hit
		WDT_HIT();
		
		// Check if frame was captured and store it
		if(rxlen > 0) {
			frame_count++;
			if (!bQuiet) {
				if (!LogTraceHitag(rx,rxlen,response,0,false)) {
					DbpString("Trace full");
					if (bQuitTraceFull) {
						break;
					} else {
						bQuiet = true;
					}
				}
			}
		}
		
		// By default reset the transmission buffer
		tx = txbuf;
		switch(htf) {
			case RHT2F_PASSWORD: {
				bStop = !hitag2_password(rx,rxlen,tx,&txlen);
			} break;
			case RHT2F_AUTHENTICATE: {
				bStop = !hitag2_authenticate(rx,rxlen,tx,&txlen);
			} break;
			case RHT2F_CRYPTO: {
				bStop = !hitag2_crypto(rx,rxlen,tx,&txlen);
			} break;
			case RHT2F_TEST_AUTH_ATTEMPTS: {
				bStop = !hitag2_test_auth_attempts(rx,rxlen,tx,&txlen);
			} break;
			default: {
				Dbprintf("Error, unknown function: %d",htf);
				set_tracing(FALSE);
				return;
			} break;
		}
		
		// Send and store the reader command
		// Disable timer 1 with external trigger to avoid triggers during our own modulation
		AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
			
		// Wait for HITAG_T_WAIT_2 carrier periods after the last tag bit before transmitting,
		// Since the clock counts since the last falling edge, a 'one' means that the
		// falling edge occured halfway the period. with respect to this falling edge,
		// we need to wait (T_Wait2 + half_tag_period) when the last was a 'one'.
		// All timer values are in terms of T0 units
		while(AT91C_BASE_TC0->TC_CV < T0*(t_wait+(HITAG_T_TAG_HALF_PERIOD*lastbit)));
		
		// Transmit the reader frame
		hitag_reader_send_frame(tx,txlen);

		// Enable and reset external trigger in timer for capturing future frames
		AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;

		// Add transmitted frame to total count
		if(txlen > 0) {
			frame_count++;
			if (!bQuiet) {
				// Store the frame in the trace
				if (!LogTraceHitag(tx,txlen,HITAG_T_WAIT_2,0,true)) {
					if (bQuitTraceFull) {
						break;
					} else {
						bQuiet = true;
					}
				}
			}
		}
				
		// Reset values for receiving frames
		memset(rx,0x00,sizeof(rx));
		rxlen = 0;
		lastbit = 1;
		bSkip = true;
		tag_sof = reset_sof;
		response = 0;
		
		// Receive frame, watch for at most T0*EOF periods
		while (AT91C_BASE_TC1->TC_CV < T0*HITAG_T_WAIT_MAX) {
			// Check if falling edge in tag modulation is detected
			if(AT91C_BASE_TC1->TC_SR & AT91C_TC_LDRAS) {
				// Retrieve the new timing values 
				int ra = (AT91C_BASE_TC1->TC_RA/T0);
				
				// Reset timer every frame, we have to capture the last edge for timing
				AT91C_BASE_TC0->TC_CCR = AT91C_TC_SWTRG;
				
				LED_B_ON();
				
				// Capture tag frame (manchester decoding using only falling edges)
				if(ra >= HITAG_T_EOF) {
					if (rxlen != 0) {
						//DbpString("wierd1?");
					}
					// Capture the T0 periods that have passed since last communication or field drop (reset)
					// We always recieve a 'one' first, which has the falling edge after a half period |-_|
					response = ra-HITAG_T_TAG_HALF_PERIOD;
				} else if(ra >= HITAG_T_TAG_CAPTURE_FOUR_HALF) {
					// Manchester coding example |-_|_-|-_| (101)
					rx[rxlen / 8] |= 0 << (7-(rxlen%8));
					rxlen++;
					rx[rxlen / 8] |= 1 << (7-(rxlen%8));
					rxlen++;
				} else if(ra >= HITAG_T_TAG_CAPTURE_THREE_HALF) {
					// Manchester coding example |_-|...|_-|-_| (0...01)
					rx[rxlen / 8] |= 0 << (7-(rxlen%8));
					rxlen++;
					// We have to skip this half period at start and add the 'one' the second time 
					if (!bSkip) {
						rx[rxlen / 8] |= 1 << (7-(rxlen%8));
						rxlen++;
					}
					lastbit = !lastbit;
					bSkip = !bSkip;
				} else if(ra >= HITAG_T_TAG_CAPTURE_TWO_HALF) {
					// Manchester coding example |_-|_-| (00) or |-_|-_| (11)
					if (tag_sof) {
						// Ignore bits that are transmitted during SOF
						tag_sof--;
					} else {
						// bit is same as last bit
						rx[rxlen / 8] |= lastbit << (7-(rxlen%8));
						rxlen++;
					}
				} else {
					// Ignore wierd value, is to small to mean anything
				}
			}

			// We can break this loop if we received the last bit from a frame
			if (AT91C_BASE_TC1->TC_CV > T0*HITAG_T_EOF) {
				if (rxlen>0) break;
			}
		}
	}
	LED_B_OFF();
	LED_D_OFF();
	AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
	AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS;
	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
	Dbprintf("DONE: frame received: %d",frame_count);
	cmd_send(CMD_ACK,bSuccessful,0,0,(byte_t*)tag.sectors,48);
  	set_tracing(FALSE);
}