X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/ffeb77fdc6c57449b6a5607b4468eb981a05dd4e..e1778858ddc53a6a82e8ee24f02e6b673687f69a:/armsrc/iso14443b.c

diff --git a/armsrc/iso14443b.c b/armsrc/iso14443b.c
index 0c887a25..8802623d 100644
--- a/armsrc/iso14443b.c
+++ b/armsrc/iso14443b.c
@@ -10,42 +10,47 @@
 //-----------------------------------------------------------------------------
 #include "iso14443b.h"
 
-#define RECEIVE_SAMPLES_TIMEOUT 50000
-#define ISO14443B_DMA_BUFFER_SIZE 256
+#ifndef FWT_TIMEOUT_14B
+// defaults to 2000ms
+# define FWT_TIMEOUT_14B 35312
+#endif
+#ifndef ISO14443B_DMA_BUFFER_SIZE
+# define ISO14443B_DMA_BUFFER_SIZE 256
+#endif
+#ifndef RECEIVE_MASK
+# define RECEIVE_MASK  (ISO14443B_DMA_BUFFER_SIZE-1)
+#endif
 
 // Guard Time (per 14443-2)
-#define TR0 0  
+#ifndef TR0
+# define TR0 0
+#endif
+
 // Synchronization time (per 14443-2)
-#define TR1 0
+#ifndef TR1
+# define TR1 0
+#endif
 // Frame Delay Time PICC to PCD  (per 14443-3 Amendment 1)
-#define TR2 0
+#ifndef TR2
+# define TR2 0
+#endif
 
 // 4sample
-//#define SEND4STUFFBIT(x) ToSendStuffBit(x);ToSendStuffBit(x);ToSendStuffBit(x);ToSendStuffBit(x);
-#define SEND4STUFFBIT(x) ToSendStuffBit(x);
+#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;
 
-static uint32_t iso14b_timeout = RECEIVE_SAMPLES_TIMEOUT;
-// 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
@@ -136,6 +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);
 }
@@ -173,16 +216,19 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
 	*  -TO VERIFY THIS BELOW-
 	* The mode FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_MODULATE_BPSK which we use to simulate tag
 	* works like this:  
-	* - A 1-bit input to the FPGA becomes 8 pulses at 847.5kHz (9.44µS)
-	* - A 0-bit input to the FPGA becomes an unmodulated time of 9.44µS
-	*
+	* - A 1-bit input to the FPGA becomes 8 pulses at 847.5kHz (1.18µS / pulse) == 9.44us
+	* - A 0-bit input to the FPGA becomes an unmodulated time of 1.18µS  or does it become 8 nonpulses for 9.44us
 	*
+	* FPGA doesn't seem to work with ETU.  It seems to work with pulse / duration instead.
 	* 
 	* Card sends data ub 847.e kHz subcarrier
-	* 848k = 9.44µS  = 128 fc
-	* 424k = 18.88µS = 256 fc
-	* 212k = 37.76µS = 512 fc
-	* 106k = 75.52µS = 1024 fc
+	* subcar |duration| FC division
+	* -------+--------+------------
+	* 106kHz | 9.44µS | FC/128
+	* 212kHz | 4.72µS | FC/64
+	* 424kHz | 2.36µS | FC/32
+	* 848kHz | 1.18µS | FC/16
+	* -------+--------+------------
 	*
 	*  Reader data transmission:
 	*   - no modulation ONES
@@ -194,7 +240,7 @@ 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
 	*
@@ -205,9 +251,6 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
 	*
 	*/
 	
-	// ToSendStuffBit,  40 calls
-	// 1 ETU = 1startbit, 1stopbit, 8databits == 10bits.
-	// 1 ETU = 10 * 4 == 40 stuffbits ( ETU_TAG_BIT )
 	int i,j;
 	uint8_t b;
 	
@@ -224,41 +267,51 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
 	// Send SOF.
 	// 10-11 ETU * 4times samples ZEROS
 	for(i = 0; i < 10; i++) { SEND4STUFFBIT(0); }
+	//for(i = 0; i < 10; i++) { ToSendStuffBit(0); }
 	
 	// 2-3 ETU * 4times samples ONES
 	for(i = 0; i < 3; i++)  { SEND4STUFFBIT(1); }
+	//for(i = 0; i < 3; i++)  { ToSendStuffBit(1); }
 	
 	// data
 	for(i = 0; i < len; ++i) {
 		
 		// Start bit
 		SEND4STUFFBIT(0);
+		//ToSendStuffBit(0);
 
 		// Data bits
 		b = cmd[i];
 		for(j = 0; j < 8; ++j) {
-			if(b & 1) { 
-				SEND4STUFFBIT(1); 
-			} else {
-				SEND4STUFFBIT(0);
-			}
+			// if(b & 1) { 
+				// SEND4STUFFBIT(1); 
+				// //ToSendStuffBit(1);
+			// } else {
+				// SEND4STUFFBIT(0);
+				// //ToSendStuffBit(0);
+			// }
+			SEND4STUFFBIT( b & 1 );
 			b >>= 1;
 		}
 
 		// Stop bit
 		SEND4STUFFBIT(1);
+		//ToSendStuffBit(1);
 		
 		// Extra Guard bit
 		// For PICC it ranges 0-18us (1etu = 9us)
 		SEND4STUFFBIT(1);
+		//ToSendStuffBit(1);
 	}
 
 	// Send EOF.
 	// 10-11 ETU * 4 sample rate = ZEROS
 	for(i = 0; i < 10; i++) { SEND4STUFFBIT(0); }
+	//for(i = 0; i < 10; i++) { ToSendStuffBit(0); }
 	
 	// why this?
 	for(i = 0; i < 40; i++) { SEND4STUFFBIT(1); }
+	//for(i = 0; i < 40; i++) { ToSendStuffBit(1); }
 	
 	// Convert from last byte pos to length
 	++ToSendMax;
@@ -278,9 +331,9 @@ 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;
@@ -290,9 +343,9 @@ 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;
@@ -300,8 +353,7 @@ 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 {
@@ -309,10 +361,9 @@ 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;
 			}
@@ -320,10 +371,9 @@ 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 {
@@ -337,26 +387,26 @@ 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;
@@ -369,9 +419,9 @@ 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();
@@ -385,7 +435,6 @@ static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
 			Uart.state = STATE_UNSYNCD;
 			break;
 	}
-
 	return FALSE;
 }
 
@@ -407,7 +456,7 @@ static int GetIso14443bCommandFromReader(uint8_t *received, uint16_t *len) {
 		
 	StartCountSspClk();
 	
-	volatile uint8_t b;
+	volatile uint8_t b = 0;
 
 	// clear receiving shift register and holding register
 	// What does this loop do? Is it TR1?
@@ -421,7 +470,6 @@ static int GetIso14443bCommandFromReader(uint8_t *received, uint16_t *len) {
 	// Now run a `software UART' on the stream of incoming samples.
 	UartInit(received);
 
-	b = 0;
 	uint8_t mask;
 	while( !BUTTON_PRESS() ) {
 		WDT_HIT();
@@ -444,13 +492,14 @@ void ClearFpgaShiftingRegisters(void){
 	volatile uint8_t b;
 
 	// clear receiving shift register and holding register
-	while(!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY));
+	while(!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY)) {};
+
 	b = AT91C_BASE_SSC->SSC_RHR; (void) b;
 
-	while(!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY));
+	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 (uint8_t j = 0; j < 5; j++) {	// allow timeout - better late than never
 		while(!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY));
@@ -458,7 +507,7 @@ void ClearFpgaShiftingRegisters(void){
 	}
 	
 	// Clear TXRDY:
-	AT91C_BASE_SSC->SSC_THR = 0xFF;
+	//AT91C_BASE_SSC->SSC_THR = 0xFF;
 }
 
 void WaitForFpgaDelayQueueIsEmpty( uint16_t delay ){
@@ -474,26 +523,33 @@ void WaitForFpgaDelayQueueIsEmpty( uint16_t delay ){
 
 static void TransmitFor14443b_AsTag( uint8_t *response, uint16_t len) {
 
-		// Signal field is off with the appropriate LED
-		LED_D_OFF();
-		uint16_t fpgasendQueueDelay = 0;
-		
-		// Modulate BPSK
-		FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_MODULATE_BPSK);
-		
-		ClearFpgaShiftingRegisters();
-		
-		FpgaSetupSsc();
+	volatile uint32_t b;
+	
+	// Signal field is off with the appropriate LED
+	LED_D_OFF();
+	//uint16_t fpgasendQueueDelay = 0;
+	
+	// Modulate BPSK
+	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_MODULATE_BPSK);
+	SpinDelay(40);
+	
+	ClearFpgaShiftingRegisters();
+	
+	FpgaSetupSsc();
 
-		// Transmit the response.
-		for(uint16_t i = 0; i < len;) {
-			if(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
-				AT91C_BASE_SSC->SSC_THR = response[++i];
-				fpgasendQueueDelay = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
-			}
+	// Transmit the response.
+	for(uint16_t i = 0; i < len;) {
+		if(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
+			AT91C_BASE_SSC->SSC_THR = response[++i];
 		}
-		
-		WaitForFpgaDelayQueueIsEmpty(fpgasendQueueDelay);
+		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+			b = AT91C_BASE_SSC->SSC_RHR;
+			(void)b;
+		}			
+	}
+	
+	//WaitForFpgaDelayQueueIsEmpty(fpgasendQueueDelay);
+	AT91C_BASE_SSC->SSC_THR = 0xFF;		
 }	
 //-----------------------------------------------------------------------------
 // Main loop of simulated tag: receive commands from reader, decide what
@@ -543,8 +599,9 @@ void SimulateIso14443bTag(uint32_t pupi) {
 
 	// ...PUPI/UID supplied from user. Adjust ATQB response accordingly
 	if ( pupi > 0 ) {
+		uint8_t len = sizeof(respATQB);
 		num_to_bytes(pupi, 4, respATQB+1);
-		ComputeCrc14443(CRC_14443_B, respATQB, 12, respATQB+13, respATQB+14);
+		ComputeCrc14443(CRC_14443_B, respATQB, 12, &respATQB[len-2], &respATQB[len-1]);
 	}
 
 	// prepare "ATQB" tag answer (encoded):
@@ -601,10 +658,10 @@ void SimulateIso14443bTag(uint32_t pupi) {
 		    send halt response ( waiting for wupb )
 		*/
 		
-		switch(cardSTATE){
-			case SIM_NOFIELD:
+		switch (cardSTATE) {
+			//case SIM_NOFIELD:
 			case SIM_HALTED:
-			case SIM_IDLE:{
+			case SIM_IDLE: {
 				LogTrace(receivedCmd, len, 0, 0, NULL, TRUE);	
 				break;
 			}
@@ -620,13 +677,13 @@ void SimulateIso14443bTag(uint32_t pupi) {
 				cardSTATE = SIM_HALTED;
 				break;
 			}
-			case SIM_ACKNOWLEDGE:{
+			case SIM_ACKNOWLEDGE: {
 				TransmitFor14443b_AsTag( encodedOK, encodedOKLen );
 				LogTrace(respOK, sizeof(respOK), 0, 0, NULL, FALSE);
 				cardSTATE = SIM_IDLE;			
 				break;
 			}
-			case SIM_WORK:{
+			case SIM_WORK: {
 				if ( len == 7 && receivedCmd[0] == ISO14443B_HALT ) {
 					cardSTATE = SIM_HALTED;
 				} else if ( len == 11 && receivedCmd[0] == ISO14443B_ATTRIB ) {
@@ -655,6 +712,7 @@ void SimulateIso14443bTag(uint32_t pupi) {
 		}
 			
 		++cmdsReceived;
+		// iceman, could add a switch to turn this on/off (if off, no logging?)
 		if(cmdsReceived > 1000) {
 			DbpString("14B Simulate, 1000 commands later...");
 			break;
@@ -685,12 +743,9 @@ void SimulateIso14443bTag(uint32_t pupi) {
  *          false if we are still waiting for some more
  *
  */
-#ifndef SUBCARRIER_DETECT_THRESHOLD
-# define SUBCARRIER_DETECT_THRESHOLD	8
-#endif
-
 static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
-	int v=0;// , myI, 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() { \
@@ -708,7 +763,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 
 // Subcarrier amplitude v = sqrt(ci^2 + cq^2), approximated here by abs(ci) + abs(cq)
 // Subcarrier amplitude v = sqrt(ci^2 + cq^2), approximated here by max(abs(ci),abs(cq)) + 1/2*min(abs(ci),abs(cq)))
-#define CHECK_FOR_SUBCARRIER() { \
+#define CHECK_FOR_SUBCARRIER_old() { \
 		if(ci < 0) { \
 			if(cq < 0) { /* ci < 0, cq < 0 */ \
 				if (cq < ci) { \
@@ -741,19 +796,17 @@ 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_un() { \
-		myI = ABS(ci); \
-		myQ = ABS(cq); \
-		v = MAX(myI,myQ) + (MIN(myI,myQ) >> 1); \
+#define CHECK_FOR_SUBCARRIER() { \
+		v = MAX(myI, myQ) + (MIN(myI, myQ) >> 1); \
  	}
 
 	switch(Demod.state) {
 		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;
@@ -762,7 +815,7 @@ 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();
 				
@@ -785,12 +838,12 @@ 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 {
 				// maximum length of TR1 = 200 1/fs
-				if(Demod.posCount > 25*2) Demod.state = DEMOD_UNSYNCD;
+				if(Demod.posCount > 26*2) Demod.state = DEMOD_UNSYNCD;
 			}
 			++Demod.posCount;
 			break;
@@ -800,20 +853,20 @@ 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 < 9*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;
 				}
 			} else {
 				// low phase of SOF too long (> 12 etu)
-				if (Demod.posCount > 12*2) { 
+				if (Demod.posCount > 14*2) { 
 					Demod.state = DEMOD_UNSYNCD;
 					LED_C_OFF();
 				}
@@ -826,7 +879,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 			MAKE_SOFT_DECISION();
 			
 			if (v > 0) {
-				if(Demod.posCount > 3*2) { 		// max 19us between characters = 16 1/fs, max 3 etu after low phase of SOF = 24 1/fs
+				if(Demod.posCount > 2*2) { 		// max 19us between characters = 16 1/fs, max 3 etu after low phase of SOF = 24 1/fs
 					Demod.state = DEMOD_UNSYNCD;
 					LED_C_OFF();
 				}
@@ -852,28 +905,30 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
 				Demod.thisBit += v;
 				Demod.shiftReg >>= 1;
 
-				// logic '1'
-				if(Demod.thisBit > 0)  Demod.shiftReg |= 0x200;
+				// OR in a logic '1'
+				if (Demod.thisBit > 0)  Demod.shiftReg |= 0x200;
 
 				++Demod.bitCount;
 				
-				if(Demod.bitCount == 10) {
+				// 1 start 8 data 1 stop = 10
+				if (Demod.bitCount == 10) {
 					
 					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;
@@ -894,9 +949,9 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
  *  quiet: set to 'TRUE' to disable debug output
  */
 static void GetTagSamplesFor14443bDemod() {
-	bool gotFrame = FALSE;
+	bool gotFrame = FALSE, finished = FALSE;
 	int lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;
-	int max = 0, ci = 0, cq = 0, samples = 0;
+	int ci = 0, cq = 0;
 	uint32_t time_0 = 0, time_stop = 0;
 
 	BigBuf_free();
@@ -913,62 +968,58 @@ static void GetTagSamplesFor14443bDemod() {
 		if (MF_DBGLEVEL > 1) Dbprintf("FpgaSetupSscDma failed. Exiting"); 
 		return;
 	}
-	
-	time_0 = GetCountSspClk();
-	
+
 	// And put the FPGA in the appropriate mode
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR | FPGA_HF_READER_RX_XCORR_848_KHZ);
-	
-	while( !BUTTON_PRESS() ) {
-		WDT_HIT();
 
-		int behindBy = lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR;
-		if(behindBy > max) max = behindBy;
+	// get current clock
+	time_0 = GetCountSspClk();
+	
+	// rx counter - dma counter? (how much?) & (mod) mask > 2. (since 2bytes at the time is read)
+	while ( !finished ) {
 
-		// rx counter - dma counter? (how much?) & (mod) dma buff / 2.  (since 2bytes at the time is read)
-		while(((lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR) & (ISO14443B_DMA_BUFFER_SIZE-1)) > 2) {
+		LED_A_INV();
+		WDT_HIT();
 
-			ci = upTo[0];
-			cq = upTo[1];
-			upTo += 2;
-			samples += 2;
-			
-			// restart DMA buffer to receive again.
-			if(upTo >= dmaBuf + ISO14443B_DMA_BUFFER_SIZE) {
-				upTo = dmaBuf;
-				AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) upTo;
-				AT91C_BASE_PDC_SSC->PDC_RNCR = ISO14443B_DMA_BUFFER_SIZE;
-			}
-			
-			lastRxCounter -= 2;
-			if(lastRxCounter <= 0)
-				lastRxCounter += ISO14443B_DMA_BUFFER_SIZE;
+		// LSB is a fpga signal bit.
+		ci = upTo[0] >> 1;
+		cq = upTo[1] >> 1;
+		upTo += 2;
+		lastRxCounter -= 2;
 
-			// is this | 0x01 the error?   & 0xfe  in https://github.com/Proxmark/proxmark3/issues/103
-			//gotFrame =  Handle14443bTagSamplesDemod(ci & 0xfe, cq & 0xfe);
-			gotFrame =  Handle14443bTagSamplesDemod(ci, cq);
-			if ( gotFrame )	break;
-			LED_A_INV();
+		// restart DMA buffer to receive again.
+		if(upTo >= dmaBuf + ISO14443B_DMA_BUFFER_SIZE) {
+			upTo = dmaBuf;
+			lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;
+			AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) upTo;
+			AT91C_BASE_PDC_SSC->PDC_RNCR = ISO14443B_DMA_BUFFER_SIZE;
 		}
 
+		// https://github.com/Proxmark/proxmark3/issues/103
+		gotFrame =  Handle14443bTagSamplesDemod(ci, cq);
 		time_stop = GetCountSspClk() - time_0;
-	
-		if(time_stop > iso14b_timeout || gotFrame)	break;
+
+		finished = (time_stop > iso14b_timeout || gotFrame);
 	}
 	
 	FpgaDisableSscDma();
-
+	
+	if ( upTo ) upTo = NULL;
+	
 	if (MF_DBGLEVEL >= 3) {
-		Dbprintf("max behindby = %d, samples = %d, gotFrame = %s, Demod.state = %d, Demod.len = %u",
-			max,
-			samples, 
-			(gotFrame) ? "true" : "false", 
+		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);
 }
 
 
@@ -977,29 +1028,47 @@ static void GetTagSamplesFor14443bDemod() {
 //-----------------------------------------------------------------------------
 static void TransmitFor14443b_AsReader(void) {
 
-	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);
-	SpinDelay(20);
-	
-	int c;	
 	// we could been in following mode:
 	// FPGA_MAJOR_MODE_HF_READER_RX_XCORR | FPGA_HF_READER_RX_XCORR_848_KHZ
 	// if its second call or more
+	
+	// while(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
+		// AT91C_BASE_SSC->SSC_THR = 0XFF;
+	// }
+	
+	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);
+	SpinDelay(40);
 
+	int c;	
+	volatile uint32_t b;
+										 
 	// What does this loop do? Is it TR1?
-   	for(c = 0; c < 10;) {
+	// 0xFF = 8 bits of 1.    1 bit == 1Etu,..  
+	// loop 10 * 8 = 80 ETU of delay, with a non modulated signal.  why?
+	// 80*9 = 720us.
+   	for(c = 0; c < 50;) {
 		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
 			AT91C_BASE_SSC->SSC_THR = 0xFF;
 			++c;
 		}
+		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+			b = AT91C_BASE_SSC->SSC_RHR;
+			(void)b;
+		}
 	}
-	
+
 	// Send frame loop
 	for(c = 0; c < ToSendMax;) {
 		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-			AT91C_BASE_SSC->SSC_THR = ToSend[c];
-			++c;
+			AT91C_BASE_SSC->SSC_THR = ToSend[c++];
 		}
+		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+			b = AT91C_BASE_SSC->SSC_RHR;
+			(void)b;
+		}					
 	}
+	//WaitForFpgaDelayQueueIsEmpty(delay);
+	// We should wait here for the FPGA to send all bits.
 	WDT_HIT();
 }
 
@@ -1007,8 +1076,7 @@ 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
@@ -1019,6 +1087,9 @@ static void CodeIso14443bAsReader(const uint8_t *cmd, int len)
 	*
 	* 	1 ETU == 1 BIT!
 	*   TR0 - 8 ETUS minimum.
+	*
+	*   QUESTION:  how long is a 1 or 0 in pulses in the xcorr_848 mode?
+	*              1 "stuffbit" = 1ETU (9us)
 	*/
 	int i;
 	uint8_t b;
@@ -1041,14 +1112,24 @@ 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
@@ -1065,7 +1146,8 @@ static void CodeIso14443bAsReader(const uint8_t *cmd, int len)
 	// Transition time. TR0 - guard time
 	// 8ETUS minum?
 	// Per specification, Subcarrier must be stopped no later than 2 ETUs after EOF.	
-	for(i = 0; i < 40 ; ++i) ToSendStuffBit(1);
+	// I'm guessing this is for the FPGA to be able to send all bits before we switch to listening mode
+	for(i = 0; i < 32 ; ++i) ToSendStuffBit(1);
 	
 	// TR1 - Synchronization time
 	// Convert from last character reference to length
@@ -1073,19 +1155,19 @@ 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);
 }
 
@@ -1231,14 +1313,28 @@ 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;
+
+	if (card) { 
 	
-	// CID
-	if (card) card->cid = Demod.output[0];
-	
-	uint8_t fwt = card->atqb[6]>>4;
-	if ( fwt < 16 ){
-		uint32_t fwt_time = (302 << fwt);
-		iso14b_set_timeout( fwt_time);
+		// 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);
+			iso14b_set_timeout( fwt_time);
+		}
 	}
 	// reset PCB block number
 	pcb_blocknum = 0;
@@ -1464,16 +1560,13 @@ 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;
 
@@ -1496,40 +1589,25 @@ void RAMFUNC SnoopIso14443b(void) {
 	for(;;) {
 
 		WDT_HIT();
-		
-		int behindBy = (lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR) & (ISO14443B_DMA_BUFFER_SIZE-1);
 
-		if ( behindBy > maxBehindBy )
-			maxBehindBy = behindBy;
-		
-		if ( behindBy < 2 ) continue;
-		
 		ci = upTo[0];
 		cq = upTo[1];
-		upTo += 2;
-		
+		upTo += 2;		
 		lastRxCounter -= 2;
 		
 		if (upTo >= dmaBuf + ISO14443B_DMA_BUFFER_SIZE) {
 			upTo = dmaBuf;
-			lastRxCounter += ISO14443B_DMA_BUFFER_SIZE;
+			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;
 			}
 		}
@@ -1541,7 +1619,7 @@ void RAMFUNC SnoopIso14443b(void) {
 			// no need to try decoding reader data if the tag is sending
 			if (Handle14443bReaderUartBit(ci & 0x01)) {
 
-				time_stop = (GetCountSspClk()-time_0);
+				time_stop = GetCountSspClk() - time_0;
 				
 				if (triggered)
 					LogTrace(Uart.output, Uart.byteCnt, time_start, time_stop, NULL, TRUE);
@@ -1552,34 +1630,35 @@ void RAMFUNC SnoopIso14443b(void) {
 				/* false-triggered by the commands from the reader. */
 				DemodReset();
 			} else {
-				time_start = (GetCountSspClk()-time_0);
+				time_start = GetCountSspClk() - time_0;
 			}
 			
 			if (Handle14443bReaderUartBit(cq & 0x01)) {
 				
-				time_stop = (GetCountSspClk()-time_0);
+				time_stop = GetCountSspClk() - time_0;
 				
 				if (triggered)
 					LogTrace(Uart.output, Uart.byteCnt, time_start, time_stop, NULL, TRUE);
 
-					/* 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();
+				/* 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();
 			} else {
-				time_start = (GetCountSspClk()-time_0);
+				time_start = GetCountSspClk() - time_0;
 			}
 			ReaderIsActive = (Uart.state > STATE_GOT_FALLING_EDGE_OF_SOF);
 			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);
+				time_stop = GetCountSspClk() - time_0;
 				
 				LogTrace(Demod.output, Demod.len, time_start, time_stop, NULL, FALSE);
 
@@ -1588,7 +1667,7 @@ void RAMFUNC SnoopIso14443b(void) {
 				// And ready to receive another response.
 				DemodReset();
 			} else {
-				time_start = (GetCountSspClk()-time_0);
+				time_start = GetCountSspClk() - time_0;
 			}
 			TagIsActive = (Demod.state > DEMOD_GOT_FALLING_EDGE_OF_SOF);
 		}
@@ -1597,13 +1676,12 @@ 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 ( dmaBuf ) dmaBuf = NULL;
-	if ( upTo )   upTo = NULL;
+	if ( upTo ) upTo = NULL;
+	
 	// Uart.byteCntMax  should be set with ATQB value..
 }