X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/b86225188edcbcd6af6a545920115d67130882bc..4c543dbd3fbaf27f47b59f214fc8c96816a8769a:/armsrc/iso14443b.c

diff --git a/armsrc/iso14443b.c b/armsrc/iso14443b.c
index be43d47e..cc8cd65a 100644
--- a/armsrc/iso14443b.c
+++ b/armsrc/iso14443b.c
@@ -11,7 +11,8 @@
 #include "iso14443b.h"
 
 #ifndef FWT_TIMEOUT_14B
-# define FWT_TIMEOUT_14B 60000
+// defaults to 2000ms
+# define FWT_TIMEOUT_14B 35312
 #endif
 #ifndef ISO14443B_DMA_BUFFER_SIZE
 # define ISO14443B_DMA_BUFFER_SIZE 256
@@ -37,29 +38,19 @@
 // 4sample
 #define SEND4STUFFBIT(x) ToSendStuffBit(x);ToSendStuffBit(x);ToSendStuffBit(x);ToSendStuffBit(x);
 //#define SEND4STUFFBIT(x) ToSendStuffBit(x);
+ // iceman, this threshold value,  what makes 8 a good amplituted for this IQ values? 
+#ifndef SUBCARRIER_DETECT_THRESHOLD
+# define SUBCARRIER_DETECT_THRESHOLD	8
+#endif
 
+static void iso14b_set_timeout(uint32_t timeout);
+static void iso14b_set_maxframesize(uint16_t size);
 static void switch_off(void);
 
 // the block number for the ISO14443-4 PCB  (used with APDUs)
 static uint8_t pcb_blocknum = 0;
-
 static uint32_t iso14b_timeout = FWT_TIMEOUT_14B;
-// param timeout is in ftw_ 
-void iso14b_set_timeout(uint32_t timeout) {
-	// 9.4395us = 1etu.
-	// clock is about 1.5 us
-	iso14b_timeout = timeout;
-	if(MF_DBGLEVEL >= 2) Dbprintf("ISO14443B Timeout set to %ld fwt", iso14b_timeout);
-}
 
-static void switch_off(void){	
-	if (MF_DBGLEVEL > 3) Dbprintf("switch_off");
-	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-	SpinDelay(100);
-	FpgaDisableSscDma();
-	set_tracing(FALSE);
-	LEDsoff();	
-}
 
 //=============================================================================
 // An ISO 14443 Type B tag. We listen for commands from the reader, using
@@ -150,6 +141,44 @@ static void DemodInit(uint8_t *data) {
 	//	memset(Demod.output, 0x00, MAX_FRAME_SIZE); 
 }
 
+
+/*
+* 9.4395 us = 1 ETU  and clock is about 1.5 us
+* 13560000Hz 
+* 1000ms/s
+* timeout in ETUs (time to transfer 1 bit, 9.4395 us)
+*
+* Formula to calculate FWT (in ETUs) by timeout (in ms):
+* fwt = 13560000 * 1000 / (8*16) * timeout; 
+* Sample:  3sec == 3000ms
+*  13560000 * 1000 / (8*16) * 3000  == 
+*    13560000000 / 384000 = 35312 FWT
+* @param timeout is in frame wait time, fwt, measured in ETUs
+*/ 
+static void iso14b_set_timeout(uint32_t timeout) {
+	#define MAX_TIMEOUT 40542464 	// 13560000Hz * 1000ms / (2^32-1) * (8*16)
+	if(timeout > MAX_TIMEOUT)
+		timeout = MAX_TIMEOUT;
+
+	iso14b_timeout = timeout;
+	if(MF_DBGLEVEL >= 3) Dbprintf("ISO14443B Timeout set to %ld fwt", iso14b_timeout);
+}
+static void iso14b_set_maxframesize(uint16_t size) {
+	if (size > 256)
+		size = MAX_FRAME_SIZE;
+	
+	Uart.byteCntMax = size;
+	if(MF_DBGLEVEL >= 3) Dbprintf("ISO14443B Max frame size set to %d bytes", Uart.byteCntMax);
+}
+static void switch_off(void){	
+	if (MF_DBGLEVEL > 3) Dbprintf("switch_off");
+	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+	SpinDelay(100);
+	FpgaDisableSscDma();
+	set_tracing(FALSE);
+	LEDsoff();	
+}
+
 void AppendCrc14443b(uint8_t* data, int len) {
 	ComputeCrc14443(CRC_14443_B, data, len, data+len, data+len+1);
 }
@@ -208,7 +237,7 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
 	*  Card data transmission
 	*   - TR1
 	*   - SOF
-	*   - data  (each bytes is:  1startbit,8bits, 1stopbit)
+	*   - data  (each bytes is:  1startbit, 8bits, 1stopbit)
 	*   - CRC_B
 	*   - EOF
 	*
@@ -251,13 +280,14 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
 		// Data bits
 		b = cmd[i];
 		for(j = 0; j < 8; ++j) {
-			if(b & 1) { 
-				SEND4STUFFBIT(1); 
-				//ToSendStuffBit(1);
-			} else {
-				SEND4STUFFBIT(0);
-				//ToSendStuffBit(0);
-			}
+			// if(b & 1) { 
+				// SEND4STUFFBIT(1); 
+				// //ToSendStuffBit(1);
+			// } else {
+				// SEND4STUFFBIT(0);
+				// //ToSendStuffBit(0);
+			// }
+			SEND4STUFFBIT( b & 1 );
 			b >>= 1;
 		}
 
@@ -298,9 +328,9 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
  *          false if we are still waiting for some more
  */
 static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
-	switch(Uart.state) {
+	switch (Uart.state) {
 		case STATE_UNSYNCD:
-			if(!bit) {
+			if (!bit) {
 				// we went low, so this could be the beginning of an SOF
 				Uart.state = STATE_GOT_FALLING_EDGE_OF_SOF;
 				Uart.posCnt = 0;
@@ -310,9 +340,9 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 
 		case STATE_GOT_FALLING_EDGE_OF_SOF:
 			Uart.posCnt++;
-			if(Uart.posCnt == 2) {	// sample every 4 1/fs in the middle of a bit
-				if(bit) {
-					if(Uart.bitCnt > 9) {
+			if (Uart.posCnt == 2) {	// sample every 4 1/fs in the middle of a bit
+				if (bit) {
+					if (Uart.bitCnt > 9) {
 						// we've seen enough consecutive
 						// zeros that it's a valid SOF
 						Uart.posCnt = 0;
@@ -320,8 +350,7 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 						Uart.state = STATE_AWAITING_START_BIT;
 						LED_A_ON(); // Indicate we got a valid SOF
 					} else {
-						// didn't stay down long enough
-						// before going high, error
+						// didn't stay down long enough before going high, error
 						Uart.state = STATE_UNSYNCD;
 					}
 				} else {
@@ -329,10 +358,9 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 				}
 				Uart.bitCnt++;
 			}
-			if(Uart.posCnt >= 4) Uart.posCnt = 0;
-			if(Uart.bitCnt > 12) {
-				// Give up if we see too many zeros without
-				// a one, too.
+			if (Uart.posCnt >= 4) Uart.posCnt = 0;
+			if (Uart.bitCnt > 12) {
+				// Give up if we see too many zeros without a one, too.
 				LED_A_OFF();
 				Uart.state = STATE_UNSYNCD;
 			}
@@ -340,10 +368,9 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 
 		case STATE_AWAITING_START_BIT:
 			Uart.posCnt++;
-			if(bit) {
-				if(Uart.posCnt > 50/2) {	// max 57us between characters = 49 1/fs, max 3 etus after low phase of SOF = 24 1/fs
-					// stayed high for too long between
-					// characters, error
+			if (bit) {
+				if (Uart.posCnt > 50/2) {	// max 57us between characters = 49 1/fs, max 3 etus after low phase of SOF = 24 1/fs
+					// stayed high for too long between characters, error
 					Uart.state = STATE_UNSYNCD;
 				}
 			} else {
@@ -357,26 +384,26 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 
 		case STATE_RECEIVING_DATA:
 			Uart.posCnt++;
-			if(Uart.posCnt == 2) {
+			if (Uart.posCnt == 2) {
 				// time to sample a bit
 				Uart.shiftReg >>= 1;
-				if(bit) {
+				if (bit) {
 					Uart.shiftReg |= 0x200;
 				}
 				Uart.bitCnt++;
 			}
-			if(Uart.posCnt >= 4) {
+			if (Uart.posCnt >= 4) {
 				Uart.posCnt = 0;
 			}
-			if(Uart.bitCnt == 10) {
-				if((Uart.shiftReg & 0x200) && !(Uart.shiftReg & 0x001))
+			if (Uart.bitCnt == 10) {
+				if ((Uart.shiftReg & 0x200) && !(Uart.shiftReg & 0x001))
 				{
 					// this is a data byte, with correct
 					// start and stop bits
 					Uart.output[Uart.byteCnt] = (Uart.shiftReg >> 1) & 0xff;
 					Uart.byteCnt++;
 
-					if(Uart.byteCnt >= Uart.byteCntMax) {
+					if (Uart.byteCnt >= Uart.byteCntMax) {
 						// Buffer overflowed, give up
 						LED_A_OFF();
 						Uart.state = STATE_UNSYNCD;
@@ -389,9 +416,9 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 					// this is an EOF byte
 					LED_A_OFF(); // Finished receiving
 					Uart.state = STATE_UNSYNCD;
-					if (Uart.byteCnt != 0) {
-					return TRUE;
-					}
+					if (Uart.byteCnt != 0)
+						return TRUE;
+					
 				} else {
 					// this is an error
 					LED_A_OFF();
@@ -405,7 +432,6 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 			Uart.state = STATE_UNSYNCD;
 			break;
 	}
-
 	return FALSE;
 }
 
@@ -716,13 +742,9 @@ void SimulateIso14443bTag(uint32_t pupi) {
  *          false if we are still waiting for some more
  *
  */
- // iceman, this threshold value,  what makes 8 a good amplituted for this IQ values? 
-#ifndef SUBCARRIER_DETECT_THRESHOLD
-# define SUBCARRIER_DETECT_THRESHOLD	6
-#endif
-
 static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
-	int v = 0, myI = 0, myQ = 0;
+	int v = 0, myI = ABS(ci), myQ = ABS(cq);
+
 // The soft decision on the bit uses an estimate of just the
 // quadrant of the reference angle, not the exact angle.
 #define MAKE_SOFT_DECISION() { \
@@ -774,8 +796,6 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 
 //note: couldn't we just use MAX(ABS(ci),ABS(cq)) + (MIN(ABS(ci),ABS(cq))/2) from common.h - marshmellow
 #define CHECK_FOR_SUBCARRIER() { \
-		myI = ABS(ci); \
-		myQ = ABS(cq); \
 		v = MAX(myI, myQ) + (MIN(myI, myQ) >> 1); \
  	}
 
@@ -783,9 +803,9 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 		case DEMOD_UNSYNCD:
 
 			CHECK_FOR_SUBCARRIER();
-
+		
 			// subcarrier detected
-			if(v > SUBCARRIER_DETECT_THRESHOLD) {
+			if (v > SUBCARRIER_DETECT_THRESHOLD) {
 				Demod.state = DEMOD_PHASE_REF_TRAINING;
 				Demod.sumI = ci;
 				Demod.sumQ = cq;
@@ -794,7 +814,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 			break;
 
 		case DEMOD_PHASE_REF_TRAINING:
-			if(Demod.posCount < 8) {
+			if (Demod.posCount < 8) {
 
 				CHECK_FOR_SUBCARRIER();
 				
@@ -817,7 +837,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 			
 			MAKE_SOFT_DECISION();
 			
-			if(v < 0) {	// logic '0' detected
+			if (v < 0) {	// logic '0' detected
 				Demod.state = DEMOD_GOT_FALLING_EDGE_OF_SOF;
 				Demod.posCount = 0;	// start of SOF sequence
 			} else {
@@ -832,13 +852,13 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 			
 			MAKE_SOFT_DECISION();
 			
-			if(v > 0) {
+			if (v > 0) {
 				// low phase of SOF too short (< 9 etu). Note: spec is >= 10, but FPGA tends to "smear" edges
-				if(Demod.posCount < 8*2) { 
+				if (Demod.posCount < 8*2) { 
 					Demod.state = DEMOD_UNSYNCD;
 				} else {
 					LED_C_ON(); // Got SOF
-					Demod.startTime = GetCountSspClk();
+					//Demod.startTime = GetCountSspClk();
 					Demod.state = DEMOD_AWAITING_START_BIT;
 					Demod.posCount = 0;
 					Demod.len = 0;
@@ -884,7 +904,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 				Demod.thisBit += v;
 				Demod.shiftReg >>= 1;
 
-				// logic '1'
+				// OR in a logic '1'
 				if (Demod.thisBit > 0)  Demod.shiftReg |= 0x200;
 
 				++Demod.bitCount;
@@ -895,18 +915,19 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 					uint16_t s = Demod.shiftReg;
 					
 					// stop bit == '1', start bit == '0'
-					if((s & 0x200) && !(s & 0x001)) { 
-						uint8_t b = (s >> 1);
-						Demod.output[Demod.len] = b;
+					if ((s & 0x200) && (s & 0x001) == 0 ) { 
+						// left shift to drop the startbit
+						Demod.output[Demod.len] =  (s >> 1) & 0xFF;
 						++Demod.len;
 						Demod.state = DEMOD_AWAITING_START_BIT;
 					} else {
+						// this one is a bit hard,  either its a correc byte or its unsynced.
 						Demod.state = DEMOD_UNSYNCD;
-						Demod.endTime = GetCountSspClk();
+						//Demod.endTime = GetCountSspClk();
 						LED_C_OFF();
 						
 						// This is EOF (start, stop and all data bits == '0'
-						if(s == 0) return TRUE;
+						if (s == 0) return TRUE;
 					}
 				}
 				Demod.posCount = 0;
@@ -929,7 +950,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 static void GetTagSamplesFor14443bDemod() {
 	bool gotFrame = FALSE, finished = FALSE;
 	int lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;
-	int ci = 0, cq = 0, samples = 0;
+	int ci = 0, cq = 0;
 	uint32_t time_0 = 0, time_stop = 0;
 
 	BigBuf_free();
@@ -963,8 +984,6 @@ static void GetTagSamplesFor14443bDemod() {
 		ci = upTo[0] >> 1;
 		cq = upTo[1] >> 1;
 		upTo += 2;
-		samples += 2;
-
 		lastRxCounter -= 2;
 
 		// restart DMA buffer to receive again.
@@ -976,7 +995,6 @@ static void GetTagSamplesFor14443bDemod() {
 		}
 
 		// https://github.com/Proxmark/proxmark3/issues/103
-		//gotFrame =  Handle14443bTagSamplesDemod(ci & 0xfe, cq & 0xfe);
 		gotFrame =  Handle14443bTagSamplesDemod(ci, cq);
 		time_stop = GetCountSspClk() - time_0;
 
@@ -984,21 +1002,23 @@ static void GetTagSamplesFor14443bDemod() {
 	}
 	
 	FpgaDisableSscDma();
-
+	
+	if ( upTo ) upTo = NULL;
+	
 	if (MF_DBGLEVEL >= 3) {
-		Dbprintf("time_stop = %u PDC_RCR = %u", time_stop,  AT91C_BASE_PDC_SSC->PDC_RCR);
-		Dbprintf("#Samples = %d, Demod.state = %d, Demod.len = %u",
-			samples, 			
+		Dbprintf("Demod.state = %d, Demod.len = %u,  PDC_RCR = %u",	
 			Demod.state,
-			Demod.len
+			Demod.len,
+			AT91C_BASE_PDC_SSC->PDC_RCR
 		);
 	}
 	
+	// print the last batch of IQ values from FPGA
 	if (MF_DBGLEVEL == 4)
 		Dbhexdump(ISO14443B_DMA_BUFFER_SIZE, (uint8_t *)dmaBuf, FALSE);	
 	
 	if ( Demod.len > 0 )
-		LogTrace(Demod.output, Demod.len, Demod.startTime, Demod.endTime, NULL, FALSE);
+		LogTrace(Demod.output, Demod.len, time_0, time_stop, NULL, FALSE);
 }
 
 
@@ -1055,8 +1075,7 @@ static void TransmitFor14443b_AsReader(void) {
 // Code a layer 2 command (string of octets, including CRC) into ToSend[],
 // so that it is ready to transmit to the tag using TransmitFor14443b().
 //-----------------------------------------------------------------------------
-static void CodeIso14443bAsReader(const uint8_t *cmd, int len)
-{
+static void CodeIso14443bAsReader(const uint8_t *cmd, int len) {
 	/*
 	*  Reader data transmission:
 	*   - no modulation ONES
@@ -1092,14 +1111,24 @@ static void CodeIso14443bAsReader(const uint8_t *cmd, int len)
 		ToSendStuffBit(0);
 		// Data bits
 		b = cmd[i];		
-		if (  b & 1 )    ToSendStuffBit(1); else ToSendStuffBit(0);
-		if ( (b>>1) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
-		if ( (b>>2) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
-		if ( (b>>3) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
-		if ( (b>>4) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
-		if ( (b>>5) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
-		if ( (b>>6) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
-		if ( (b>>7) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);		
+		// if (  b & 1 )    ToSendStuffBit(1); else ToSendStuffBit(0);
+		// if ( (b>>1) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
+		// if ( (b>>2) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
+		// if ( (b>>3) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
+		// if ( (b>>4) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
+		// if ( (b>>5) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
+		// if ( (b>>6) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);
+		// if ( (b>>7) & 1) ToSendStuffBit(1); else ToSendStuffBit(0);	
+
+		ToSendStuffBit(  b & 1); 
+		ToSendStuffBit( (b>>1) & 1); 		
+		ToSendStuffBit( (b>>2) & 1); 
+		ToSendStuffBit( (b>>3) & 1); 
+		ToSendStuffBit( (b>>4) & 1); 
+		ToSendStuffBit( (b>>5) & 1); 
+		ToSendStuffBit( (b>>6) & 1); 		
+		ToSendStuffBit( (b>>7) & 1); 
+		
 		// Stop bit
 		ToSendStuffBit(1);
 		// EGT extra guard time
@@ -1125,19 +1154,19 @@ static void CodeIso14443bAsReader(const uint8_t *cmd, int len)
 }
 
 
-/**
-  Convenience function to encode, transmit and trace iso 14443b comms
-  **/
+/*
+*  Convenience function to encode, transmit and trace iso 14443b comms
+*/
 static void CodeAndTransmit14443bAsReader(const uint8_t *cmd, int len) {
+
+	uint32_t time_start = GetCountSspClk();
 	
 	CodeIso14443bAsReader(cmd, len);
-	
-	uint32_t time_start = GetCountSspClk();
 
 	TransmitFor14443b_AsReader();
-	
+
 	if(trigger) LED_A_ON();
-	
+
 	LogTrace(cmd, len, time_start, GetCountSspClk()-time_start, NULL, TRUE);
 }
 
@@ -1283,10 +1312,23 @@ uint8_t iso14443b_select_card(iso14b_card_select_t *card )
     ComputeCrc14443(CRC_14443_B, Demod.output, Demod.len-2, &crc[0], &crc[1]);
 	if ( crc[0] != Demod.output[1] || crc[1] != Demod.output[2] ) 
 		return 3;
-	
-	// CID
+
 	if (card) { 
+	
+		// CID
 		card->cid = Demod.output[0];
+
+		// MAX FRAME
+		uint16_t maxFrame = card->atqb[5] >> 4;
+		if (maxFrame < 5) 		maxFrame = 8 * maxFrame + 16;
+		else if (maxFrame == 5)	maxFrame = 64;
+		else if (maxFrame == 6)	maxFrame = 96;
+		else if (maxFrame == 7)	maxFrame = 128;
+		else if (maxFrame == 8)	maxFrame = 256;
+		else maxFrame = 257;
+		iso14b_set_maxframesize(maxFrame);
+		
+		// FWT 
 		uint8_t fwt = card->atqb[6] >> 4;
 		if ( fwt < 16 ){
 			uint32_t fwt_time = (302 << fwt);
@@ -1517,16 +1559,13 @@ static void iso1444b_setup_snoop(void){
 void RAMFUNC SnoopIso14443b(void) {
 
 	uint32_t time_0 = 0, time_start = 0, time_stop = 0;
-	
+	int ci = 0, cq = 0;
+	int lastRxCounter = ISO14443B_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.
-	int triggered = TRUE;			// TODO: set and evaluate trigger condition	
-	int ci, cq;
-	int maxBehindBy = 0;
-	//int behindBy  = 0;
-	int lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;
-	
+	bool triggered = TRUE;			// TODO: set and evaluate trigger condition		
 	bool TagIsActive = FALSE;
 	bool ReaderIsActive = FALSE;
 
@@ -1549,26 +1588,10 @@ void RAMFUNC SnoopIso14443b(void) {
 	for(;;) {
 
 		WDT_HIT();
-		
-		/* iceman: the & (and) should do what?
-			ISO14443B_DMA_BUFFER_SIZE = 256
-			Should it be a "mod 255" ?
-			
-		 (lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR) & (ISO14443B_DMA_BUFFER_SIZE-1);
-		 
-		*/
-		int behindBy = (lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR) & RECEIVE_MASK;
 
-		if ( behindBy > maxBehindBy )
-			maxBehindBy = behindBy;
-		
-		// this one needs the inner loop from tr
-		if ( behindBy < 2 ) continue;
-		
 		ci = upTo[0];
 		cq = upTo[1];
-		upTo += 2;
-		
+		upTo += 2;		
 		lastRxCounter -= 2;
 		
 		if (upTo >= dmaBuf + ISO14443B_DMA_BUFFER_SIZE) {
@@ -1576,21 +1599,14 @@ void RAMFUNC SnoopIso14443b(void) {
 			lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;
 			AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) dmaBuf;
 			AT91C_BASE_PDC_SSC->PDC_RNCR = ISO14443B_DMA_BUFFER_SIZE;
-			WDT_HIT();
-			
-			// TODO: understand whether we can increase/decrease as we want or not?
-			if ( behindBy > ( 9 * ISO14443B_DMA_BUFFER_SIZE/10) ) { 
-				Dbprintf("blew circular buffer! behindBy = %d", behindBy);
-				break;
-			}
-			
-			if(!tracing) {
-				DbpString("Trace full");
+		
+			if (!tracing) {
+				if (MF_DBGLEVEL >= 2) DbpString("Trace full");
 				break;
 			}
 				
-			if(BUTTON_PRESS()) {
-				DbpString("cancelled");
+			if (BUTTON_PRESS()) {
+				if (MF_DBGLEVEL >= 2) DbpString("cancelled");
 				break;
 			}
 		}
@@ -1635,10 +1651,11 @@ void RAMFUNC SnoopIso14443b(void) {
 			LED_A_OFF();
 		}
 		
-		if(!ReaderIsActive) {
+		if (!ReaderIsActive) {
 			// no need to try decoding tag data if the reader is sending - and we cannot afford the time
 			// is this | 0x01 the error?   & 0xfe  in https://github.com/Proxmark/proxmark3/issues/103
-			if(Handle14443bTagSamplesDemod(ci & 0xFE, cq & 0xFE)) {
+			// LSB is a fpga signal bit.
+			if (Handle14443bTagSamplesDemod(ci >> 1, cq >> 1)) {
 				
 				time_stop = GetCountSspClk() - time_0;
 				
@@ -1658,12 +1675,11 @@ void RAMFUNC SnoopIso14443b(void) {
 	switch_off(); // Snoop
 	
 	DbpString("Snoop statistics:");
-	Dbprintf("  Max behind by: %i", maxBehindBy);
 	Dbprintf("  Uart State: %x  ByteCount: %i  ByteCountMax: %i", Uart.state,  Uart.byteCnt,  Uart.byteCntMax);
 	Dbprintf("  Trace length: %i", BigBuf_get_traceLen());
 
 	// free mem refs.
-	if ( upTo )   upTo = NULL;
+	if ( upTo ) upTo = NULL;
 	
 	// Uart.byteCntMax  should be set with ATQB value..
 }