proxmark3/armsrc/iso14443b.c

//-----------------------------------------------------------------------------
// Jonathan Westhues, split Nov 2006
//
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Routines to support ISO 14443B. This includes both the reader software and
// the `fake tag' modes.
//-----------------------------------------------------------------------------
#include "iso14443b.h"

#define RECEIVE_SAMPLES_TIMEOUT 50000
#define ISO14443B_DMA_BUFFER_SIZE 256

// Guard Time (per 14443-2)
#define TR0 0  
// Synchronization time (per 14443-2)
#define TR1 0
// Frame Delay Time PICC to PCD  (per 14443-3 Amendment 1)
#define TR2 0

// 4sample
//#define SEND4STUFFBIT(x) ToSendStuffBit(x);ToSendStuffBit(x);ToSendStuffBit(x);ToSendStuffBit(x);
#define SEND4STUFFBIT(x) ToSendStuffBit(x);

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 = 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
// a UART kind of thing that's implemented in software. When we get a
// frame (i.e., a group of bytes between SOF and EOF), we check the CRC.
// If it's good, then we can do something appropriate with it, and send
// a response.
//=============================================================================


//-----------------------------------------------------------------------------
// The software UART that receives commands from the reader, and its state variables.
//-----------------------------------------------------------------------------
static struct {
	enum {
		STATE_UNSYNCD,
		STATE_GOT_FALLING_EDGE_OF_SOF,
		STATE_AWAITING_START_BIT,
		STATE_RECEIVING_DATA
	}       state;
	uint16_t shiftReg;
	int      bitCnt;
	int      byteCnt;
	int      byteCntMax;
	int      posCnt;
	uint8_t  *output;
} Uart;

static void UartReset() {
	Uart.state = STATE_UNSYNCD;
	Uart.shiftReg = 0;
	Uart.bitCnt = 0;
	Uart.byteCnt = 0;
	Uart.byteCntMax = MAX_FRAME_SIZE;
	Uart.posCnt = 0;
}

static void UartInit(uint8_t *data) {
	Uart.output = data;
	UartReset();
//		memset(Uart.output, 0x00, MAX_FRAME_SIZE);
}

//-----------------------------------------------------------------------------
// The software Demod that receives commands from the tag, and its state variables.
//-----------------------------------------------------------------------------
static struct {
	enum {
		DEMOD_UNSYNCD,
		DEMOD_PHASE_REF_TRAINING,
		DEMOD_AWAITING_FALLING_EDGE_OF_SOF,
		DEMOD_GOT_FALLING_EDGE_OF_SOF,
		DEMOD_AWAITING_START_BIT,
		DEMOD_RECEIVING_DATA
	}       state;
	uint16_t bitCount;
	int      posCount;
	int      thisBit;
/* this had been used to add RSSI (Received Signal Strength Indication) to traces. Currently not implemented.
	int     metric;
	int     metricN;
*/
	uint16_t shiftReg;
	uint8_t  *output;
	uint16_t len;
	int      sumI;
	int      sumQ;
	uint32_t startTime, endTime;
} Demod;

// Clear out the state of the "UART" that receives from the tag.
static void DemodReset() {
	Demod.state = DEMOD_UNSYNCD;
	Demod.bitCount = 0;
	Demod.posCount = 0;
	Demod.thisBit = 0;
	Demod.shiftReg = 0;
	Demod.len = 0;
	Demod.sumI = 0;
	Demod.sumQ = 0;
	Demod.startTime = 0;
	Demod.endTime = 0;	
}

static void DemodInit(uint8_t *data) {
	Demod.output = data;
	DemodReset();
	//	memset(Demod.output, 0x00, MAX_FRAME_SIZE); 
}

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

//-----------------------------------------------------------------------------
// Code up a string of octets at layer 2 (including CRC, we don't generate
// that here) so that they can be transmitted to the reader. Doesn't transmit
// them yet, just leaves them ready to send in ToSend[].
//-----------------------------------------------------------------------------
static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
	/* ISO 14443 B
	*
	* Reader to card | ASK  - Amplitude Shift Keying Modulation (PCD to PICC for Type B) (NRZ-L encodig)
	* Card to reader | BPSK - Binary Phase Shift Keying Modulation, (PICC to PCD for Type B)
	*
	* fc - carrier frequency 13.56mHz
	* TR0 - Guard Time per 14443-2
	* TR1 - Synchronization Time per 14443-2
	* TR2 - PICC to PCD Frame Delay Time (per 14443-3 Amendment 1)
	*
	* Elementary Time Unit (ETU) is
	* - 128 Carrier Cycles (9.4395 µS) = 8 Subcarrier Units 
	* - 1 ETU = 1 bit
	* - 10 ETU = 1 startbit, 8 databits, 1 stopbit (10bits length)
	* - startbit is a 0
	* - stopbit is a 1
	*
	* Start of frame (SOF) is
	* - [10-11] ETU of ZEROS, unmodulated time
	* - [2-3] ETU of ONES,  
	*
	* End of frame (EOF) is
	* - [10-11] ETU of ZEROS, unmodulated time
	*
	*  -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
	*
	*
	* 
	* 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
	*
	*  Reader data transmission:
	*   - no modulation ONES
	*   - SOF
	*   - Command, data and CRC_B
	*   - EOF
	*   - no modulation ONES
	*
	*  Card data transmission
	*   - TR1
	*   - SOF
	*   - data  (each bytes is:  1startbit,8bits, 1stopbit)
	*   - CRC_B
	*   - EOF
	*
	* FPGA implementation :
	* At this point only Type A is implemented. This means that we are using a
	* bit rate of 106 kbit/s, or fc/128. Oversample by 4, which ought to make
	* things practical for the ARM (fc/32, 423.8 kbits/s, ~50 kbytes/s)
	*
	*/
	
	// ToSendStuffBit,  40 calls
	// 1 ETU = 1startbit, 1stopbit, 8databits == 10bits.
	// 1 ETU = 10 * 4 == 40 stuffbits ( ETU_TAG_BIT )
	int i,j;
	uint8_t b;
	
	ToSendReset();

	// Transmit a burst of ones, as the initial thing that lets the
	// reader get phase sync. 
	// This loop is TR1, per specification
	// TR1 minimum must be > 80/fs
	// TR1 maximum 200/fs 
	// 80/fs < TR1 < 200/fs
	// 10 ETU < TR1 < 24 ETU

	// Send SOF.
	// 10-11 ETU * 4times samples ZEROS
	for(i = 0; i < 10; i++) { SEND4STUFFBIT(0); }
	
	// 2-3 ETU * 4times samples ONES
	for(i = 0; i < 3; i++)  { SEND4STUFFBIT(1); }
	
	// data
	for(i = 0; i < len; ++i) {
		
		// Start bit
		SEND4STUFFBIT(0);

		// Data bits
		b = cmd[i];
		for(j = 0; j < 8; ++j) {
			if(b & 1) { 
				SEND4STUFFBIT(1); 
			} else {
				SEND4STUFFBIT(0);
			}
			b >>= 1;
		}

		// Stop bit
		SEND4STUFFBIT(1);
		
		// Extra Guard bit
		// For PICC it ranges 0-18us (1etu = 9us)
		SEND4STUFFBIT(1);
	}

	// Send EOF.
	// 10-11 ETU * 4 sample rate = ZEROS
	for(i = 0; i < 10; i++) { SEND4STUFFBIT(0); }
	
	// why this?
	for(i = 0; i < 40; i++) { SEND4STUFFBIT(1); }
	
	// Convert from last byte pos to length
	++ToSendMax;
}


/* Receive & handle a bit coming from the reader.
 *
 * This function is called 4 times per bit (every 2 subcarrier cycles).
 * Subcarrier frequency fs is 848kHz, 1/fs = 1,18us, i.e. function is called every 2,36us
 *
 * LED handling:
 * LED A -> ON once we have received the SOF and are expecting the rest.
 * LED A -> OFF once we have received EOF or are in error state or unsynced
 *
 * Returns: true if we received a EOF
 *          false if we are still waiting for some more
 */
static RAMFUNC int Handle14443bReaderUartBit(uint8_t bit) {
	switch(Uart.state) {
		case STATE_UNSYNCD:
			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;
				Uart.bitCnt = 0;
			}
			break;

		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) {
						// we've seen enough consecutive
						// zeros that it's a valid SOF
						Uart.posCnt = 0;
						Uart.byteCnt = 0;
						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
						Uart.state = STATE_UNSYNCD;
					}
				} else {
					// do nothing, keep waiting
				}
				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.
				LED_A_OFF();
				Uart.state = STATE_UNSYNCD;
			}
			break;

		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
					Uart.state = STATE_UNSYNCD;
				}
			} else {
				// falling edge, this starts the data byte
				Uart.posCnt = 0;
				Uart.bitCnt = 0;
				Uart.shiftReg = 0;
				Uart.state = STATE_RECEIVING_DATA;
			}
			break;

		case STATE_RECEIVING_DATA:
			Uart.posCnt++;
			if(Uart.posCnt == 2) {
				// time to sample a bit
				Uart.shiftReg >>= 1;
				if(bit) {
					Uart.shiftReg |= 0x200;
				}
				Uart.bitCnt++;
			}
			if(Uart.posCnt >= 4) {
				Uart.posCnt = 0;
			}
			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) {
						// Buffer overflowed, give up
						LED_A_OFF();
						Uart.state = STATE_UNSYNCD;
					} else {
						// so get the next byte now
						Uart.posCnt = 0;
						Uart.state = STATE_AWAITING_START_BIT;
					}
				} else if (Uart.shiftReg == 0x000) {
					// this is an EOF byte
					LED_A_OFF(); // Finished receiving
					Uart.state = STATE_UNSYNCD;
					if (Uart.byteCnt != 0) {
					return TRUE;
					}
				} else {
					// this is an error
					LED_A_OFF();
					Uart.state = STATE_UNSYNCD;
				}
			}
			break;

		default:
			LED_A_OFF();
			Uart.state = STATE_UNSYNCD;
			break;
	}

	return FALSE;
}

//-----------------------------------------------------------------------------
// Receive a command (from the reader to us, where we are the simulated tag),
// and store it in the given buffer, up to the given maximum length. Keeps
// spinning, waiting for a well-framed command, until either we get one
// (returns TRUE) or someone presses the pushbutton on the board (FALSE).
//
// Assume that we're called with the SSC (to the FPGA) and ADC path set
// correctly.
//-----------------------------------------------------------------------------
static int GetIso14443bCommandFromReader(uint8_t *received, uint16_t *len) {
	// Set FPGA mode to "simulated ISO 14443B tag", no modulation (listen
	// only, since we are receiving, not transmitting).
	// Signal field is off with the appropriate LED
	LED_D_OFF();
	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_NO_MODULATION);
		
	StartCountSspClk();
	
	volatile uint8_t b;

	// clear receiving shift register and holding register
	// What does this loop do? Is it TR1?
   	for(uint8_t c = 0; c < 10;) {
		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
			AT91C_BASE_SSC->SSC_THR = 0xFF;
			++c;
		}
	}
	
	// Now run a `software UART' on the stream of incoming samples.
	UartInit(received);

	b = 0;
	uint8_t mask;
	while( !BUTTON_PRESS() ) {
		WDT_HIT();

		if ( AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY ) {
			b = (uint8_t) AT91C_BASE_SSC->SSC_RHR;
			for ( mask = 0x80; mask != 0; mask >>= 1) {
				if ( Handle14443bReaderUartBit(b & mask)) {
					*len = Uart.byteCnt;
					return TRUE;
				}
			}
		}
	}	
	return FALSE;
}

void ClearFpgaShiftingRegisters(void){

	volatile uint8_t b;

	// clear receiving shift register and holding register
	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));
	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));
		if (AT91C_BASE_SSC->SSC_RHR) break;
	}
	
	// Clear TXRDY:
	AT91C_BASE_SSC->SSC_THR = 0xFF;
}

void WaitForFpgaDelayQueueIsEmpty( uint16_t delay ){
	// Ensure that the FPGA Delay Queue is empty before we switch to TAGSIM_LISTEN again:
	uint8_t fpga_queued_bits = delay >> 3;  // twich /8 ??   >>3, 
	for (uint8_t i = 0; i <= fpga_queued_bits/8 + 1; ) {
		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
			AT91C_BASE_SSC->SSC_THR = 0xFF;
			i++;
		}
	}
}

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();

		// 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;
			}
		}
		
		WaitForFpgaDelayQueueIsEmpty(fpgasendQueueDelay);
}	
//-----------------------------------------------------------------------------
// Main loop of simulated tag: receive commands from reader, decide what
// response to send, and send it.
//-----------------------------------------------------------------------------
void SimulateIso14443bTag(uint32_t pupi) {

	///////////// setup device.
	FpgaDownloadAndGo(FPGA_BITSTREAM_HF);

	// allocate command receive buffer
	BigBuf_free();
	BigBuf_Clear_ext(false);
	clear_trace(); //sim
	set_tracing(TRUE);
	
	// connect Demodulated Signal to ADC:
	SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

	// Set up the synchronous serial port
	FpgaSetupSsc();
	/////////////

	uint16_t len, cmdsReceived = 0;
	int cardSTATE = SIM_NOFIELD;
	int vHf = 0;	// in mV
	// uint32_t time_0 = 0;
	// uint32_t t2r_time = 0;
	// uint32_t r2t_time = 0;
	uint8_t *receivedCmd = BigBuf_malloc(MAX_FRAME_SIZE);	
	
	// the only commands we understand is WUPB, AFI=0, Select All, N=1:
//	static const uint8_t cmdWUPB[] = { ISO14443B_REQB, 0x00, 0x08, 0x39, 0x73 }; // WUPB
	// ... and REQB, AFI=0, Normal Request, N=1:
//	static const uint8_t cmdREQB[] = { ISO14443B_REQB, 0x00, 0x00, 0x71, 0xFF }; // REQB
	// ... and ATTRIB
//	static const uint8_t cmdATTRIB[] = { ISO14443B_ATTRIB, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}; // ATTRIB

	// ... if not PUPI/UID is supplied we always respond with ATQB, PUPI = 820de174, Application Data = 0x20381922,
	// supports only 106kBit/s in both directions, max frame size = 32Bytes,
	// supports ISO14443-4, FWI=8 (77ms), NAD supported, CID not supported:
	uint8_t respATQB[] = { 	0x50, 0x82, 0x0d, 0xe1, 0x74, 0x20, 0x38, 0x19, 
							0x22, 0x00, 0x21, 0x85, 0x5e, 0xd7 };
							
	// response to HLTB and ATTRIB
	static const uint8_t respOK[] = {0x00, 0x78, 0xF0};

	// ...PUPI/UID supplied from user. Adjust ATQB response accordingly
	if ( pupi > 0 ) {
		num_to_bytes(pupi, 4, respATQB+1);
		ComputeCrc14443(CRC_14443_B, respATQB, 12, respATQB+13, respATQB+14);
	}

	// prepare "ATQB" tag answer (encoded):
	CodeIso14443bAsTag(respATQB, sizeof(respATQB));
	uint8_t *encodedATQB = BigBuf_malloc(ToSendMax);
	uint16_t encodedATQBLen = ToSendMax;
	memcpy(encodedATQB, ToSend, ToSendMax); 

	
	// prepare "OK" tag answer (encoded):
	CodeIso14443bAsTag(respOK, sizeof(respOK));
	uint8_t *encodedOK = BigBuf_malloc(ToSendMax);
	uint16_t encodedOKLen = ToSendMax;	
	memcpy(encodedOK, ToSend, ToSendMax); 
	
	// Simulation loop
	while (!BUTTON_PRESS() && !usb_poll_validate_length()) {
		WDT_HIT();

		// find reader field
		if (cardSTATE == SIM_NOFIELD) {
			vHf = (MAX_ADC_HF_VOLTAGE * AvgAdc(ADC_CHAN_HF)) >> 10;
			if ( vHf > MF_MINFIELDV ) {
				cardSTATE = SIM_IDLE; 
				LED_A_ON();
			}
		} 
		if (cardSTATE == SIM_NOFIELD) continue;

		// Get reader command
		if (!GetIso14443bCommandFromReader(receivedCmd, &len)) {
			Dbprintf("button pressed, received %d commands", cmdsReceived);
			break;
		}

		// ISO14443-B protocol states:
		// REQ or WUP request in ANY state 
		// WUP in HALTED state
		if (len == 5 ) {
				if ( (receivedCmd[0] == ISO14443B_REQB && (receivedCmd[2] & 0x8)== 0x8 && cardSTATE == SIM_HALTED) ||
            	      receivedCmd[0] == ISO14443B_REQB ){
				LogTrace(receivedCmd, len, 0, 0, NULL, TRUE);						  
				cardSTATE = SIM_SELECTING;
			}
		}
		
		/*
		* How should this flow go?
		*  REQB or WUPB
		*   send response  ( waiting for Attrib)
		*  ATTRIB
		*   send response  ( waiting for commands 7816) 
		*  HALT
		    send halt response ( waiting for wupb )
		*/
		
		switch(cardSTATE){
			case SIM_NOFIELD:
			case SIM_HALTED:
			case SIM_IDLE:{
				LogTrace(receivedCmd, len, 0, 0, NULL, TRUE);	
				break;
			}
			case SIM_SELECTING: {
				TransmitFor14443b_AsTag( encodedATQB, encodedATQBLen );
				LogTrace(respATQB, sizeof(respATQB), 0, 0, NULL, FALSE);
				cardSTATE = SIM_WORK;
				break;
			}
			case SIM_HALTING: {
				TransmitFor14443b_AsTag( encodedOK, encodedOKLen );
				LogTrace(respOK, sizeof(respOK), 0, 0, NULL, FALSE);
				cardSTATE = SIM_HALTED;
				break;
			}
			case SIM_ACKNOWLEDGE:{
				TransmitFor14443b_AsTag( encodedOK, encodedOKLen );
				LogTrace(respOK, sizeof(respOK), 0, 0, NULL, FALSE);
				cardSTATE = SIM_IDLE;			
				break;
			}
			case SIM_WORK:{
				if ( len == 7 && receivedCmd[0] == ISO14443B_HALT ) {
					cardSTATE = SIM_HALTED;
				} else if ( len == 11 && receivedCmd[0] == ISO14443B_ATTRIB ) {
					cardSTATE = SIM_ACKNOWLEDGE;
				} else {
					// Todo:
					// - SLOT MARKER
					// - ISO7816
					// - emulate with a memory dump
					Dbprintf("new cmd from reader: len=%d, cmdsRecvd=%d", len, cmdsReceived);

					// CRC Check
					uint8_t b1, b2;
					if (len >= 3){ // if crc exists
						ComputeCrc14443(CRC_14443_B, receivedCmd, len-2, &b1, &b2);
						if(b1 != receivedCmd[len-2] || b2 != receivedCmd[len-1])
							DbpString("+++CRC fail");
						else
							DbpString("CRC passes");
					}
					cardSTATE = SIM_IDLE; 
				}
				break;
			}
			default: break;
		}
			
		++cmdsReceived;
		if(cmdsReceived > 1000) {
			DbpString("14B Simulate, 1000 commands later...");
			break;
		}
	}
	if (MF_DBGLEVEL >= 1) Dbprintf("Emulator stopped. Tracing: %d  trace length: %d ", tracing, BigBuf_get_traceLen());
	switch_off(); //simulate
}

//=============================================================================
// An ISO 14443 Type B reader. We take layer two commands, code them
// appropriately, and then send them to the tag. We then listen for the
// tag's response, which we leave in the buffer to be demodulated on the
// PC side.
//=============================================================================

/*
 * Handles reception of a bit from the tag
 *
 * This function is called 2 times per bit (every 4 subcarrier cycles).
 * Subcarrier frequency fs is 848kHz, 1/fs = 1,18us, i.e. function is called every 4,72us
 *
 * LED handling:
 * LED C -> ON once we have received the SOF and are expecting the rest.
 * LED C -> OFF once we have received EOF or are unsynced
 *
 * Returns: true if we received a EOF
 *          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;
// 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() { \
		if(Demod.sumI > 0) { \
			v = ci; \
		} else { \
			v = -ci; \
		} \
		if(Demod.sumQ > 0) { \
			v += cq; \
		} else { \
			v -= 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() { \
		if(ci < 0) { \
			if(cq < 0) { /* ci < 0, cq < 0 */ \
				if (cq < ci) { \
					v = -cq - (ci >> 1); \
				} else { \
					v = -ci - (cq >> 1); \
				} \
			} else {	/* ci < 0, cq >= 0 */ \
				if (cq < -ci) { \
					v = -ci + (cq >> 1); \
				} else { \
					v = cq - (ci >> 1); \
				} \
			} \
		} else { \
			if(cq < 0) { /* ci >= 0, cq < 0 */ \
				if (-cq < ci) { \
					v = ci - (cq >> 1); \
				} else { \
					v = -cq + (ci >> 1); \
				} \
			} else {	/* ci >= 0, cq >= 0 */ \
				if (cq < ci) { \
					v = ci + (cq >> 1); \
				} else { \
					v = cq + (ci >> 1); \
				} \
			} \
		} \
	}

//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); \
 	}

	switch(Demod.state) {
		case DEMOD_UNSYNCD:

			CHECK_FOR_SUBCARRIER();

			// subcarrier detected
			if(v > SUBCARRIER_DETECT_THRESHOLD) {
				Demod.state = DEMOD_PHASE_REF_TRAINING;
				Demod.sumI = ci;
				Demod.sumQ = cq;
				Demod.posCount = 1;
			}
			break;

		case DEMOD_PHASE_REF_TRAINING:
			if(Demod.posCount < 8) {

				CHECK_FOR_SUBCARRIER();
				
				if (v > SUBCARRIER_DETECT_THRESHOLD) {
					// set the reference phase (will code a logic '1') by averaging over 32 1/fs.
					// note: synchronization time > 80 1/fs
					Demod.sumI += ci;
					Demod.sumQ += cq;
					++Demod.posCount;
				} else {	
					// subcarrier lost
					Demod.state = DEMOD_UNSYNCD;
				}
			} else {
				Demod.state = DEMOD_AWAITING_FALLING_EDGE_OF_SOF;
			}
			break;

		case DEMOD_AWAITING_FALLING_EDGE_OF_SOF:
			
			MAKE_SOFT_DECISION();
			
			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;
			}
			++Demod.posCount;
			break;

		case DEMOD_GOT_FALLING_EDGE_OF_SOF:
			++Demod.posCount;
			
			MAKE_SOFT_DECISION();
			
			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) { 
					Demod.state = DEMOD_UNSYNCD;
				} else {
					LED_C_ON(); // Got SOF
					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) { 
					Demod.state = DEMOD_UNSYNCD;
					LED_C_OFF();
				}
			}
			break;

		case DEMOD_AWAITING_START_BIT:
			++Demod.posCount;
			
			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
					Demod.state = DEMOD_UNSYNCD;
					LED_C_OFF();
				}
			} else {							// start bit detected
				Demod.bitCount = 0;
				Demod.posCount = 1;				// this was the first half
				Demod.thisBit = v;
				Demod.shiftReg = 0;
				Demod.state = DEMOD_RECEIVING_DATA;
			}
			break;

		case DEMOD_RECEIVING_DATA:
			
			MAKE_SOFT_DECISION();

			if (Demod.posCount == 0) { 
				// first half of bit
				Demod.thisBit = v;
				Demod.posCount = 1;
			} else {
				// second half of bit
				Demod.thisBit += v;
				Demod.shiftReg >>= 1;

				// logic '1'
				if(Demod.thisBit > 0)  Demod.shiftReg |= 0x200;

				++Demod.bitCount;
				
				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;
						++Demod.len;
						Demod.state = DEMOD_AWAITING_START_BIT;
					} else {
						Demod.state = DEMOD_UNSYNCD;
						Demod.endTime = GetCountSspClk();
						LED_C_OFF();
						
						// This is EOF (start, stop and all data bits == '0'
						if(s == 0) return TRUE;
					}
				}
				Demod.posCount = 0;
			}
			break;

		default:
			Demod.state = DEMOD_UNSYNCD;
			LED_C_OFF();
			break;
	}
	return FALSE;
}


/*
 *  Demodulate the samples we received from the tag, also log to tracebuffer
 *  quiet: set to 'TRUE' to disable debug output
 */
static void GetTagSamplesFor14443bDemod() {
	bool gotFrame = FALSE;
	int lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;
	int max = 0, ci = 0, cq = 0, samples = 0;
	uint32_t time_0 = 0, time_stop = 0;

	BigBuf_free();
	
	// Set up the demodulator for tag -> reader responses.
	DemodInit(BigBuf_malloc(MAX_FRAME_SIZE));
	
	// The DMA buffer, used to stream samples from the FPGA
	int8_t *dmaBuf = (int8_t*) BigBuf_malloc(ISO14443B_DMA_BUFFER_SIZE);
	int8_t *upTo = dmaBuf;
	
	// Setup and start DMA.
	if ( !FpgaSetupSscDma((uint8_t*) dmaBuf, ISO14443B_DMA_BUFFER_SIZE) ){
		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;

		// 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) {

			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;

			// 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();
		}

		time_stop = GetCountSspClk() - time_0;
	
		if(time_stop > iso14b_timeout || gotFrame)	break;
	}
	
	FpgaDisableSscDma();

	if (MF_DBGLEVEL >= 3) {
		Dbprintf("max behindby = %d, samples = %d, gotFrame = %s, Demod.state = %d, Demod.len = %u",
			max,
			samples, 
			(gotFrame) ? "true" : "false", 
			Demod.state,
			Demod.len
		);
	}
	if ( Demod.len > 0 )
		LogTrace(Demod.output, Demod.len, Demod.startTime, Demod.endTime, NULL, FALSE);
}


//-----------------------------------------------------------------------------
// Transmit the command (to the tag) that was placed in ToSend[].
//-----------------------------------------------------------------------------
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

	// What does this loop do? Is it TR1?
   	for(c = 0; c < 10;) {
		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
			AT91C_BASE_SSC->SSC_THR = 0xFF;
			++c;
		}
	}
	
	// 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;
		}
	}
	WDT_HIT();
}

//-----------------------------------------------------------------------------
// 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)
{
	/*
	*  Reader data transmission:
	*   - no modulation ONES
	*   - SOF
	*   - Command, data and CRC_B
	*   - EOF
	*   - no modulation ONES
	*
	* 	1 ETU == 1 BIT!
	*   TR0 - 8 ETUS minimum.
	*/
	int i;
	uint8_t b;
	
	ToSendReset();

	// Send SOF
	// 10-11 ETUs of ZERO 
	for(i = 0; i < 10; ++i) ToSendStuffBit(0);
	
	// 2-3 ETUs of ONE
	ToSendStuffBit(1);
	ToSendStuffBit(1);
	ToSendStuffBit(1);
	
	// Sending cmd, LSB
	// from here we add BITS
	for(i = 0; i < len; ++i) {
	    // Start bit
		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);		
		// Stop bit
		ToSendStuffBit(1);
		// EGT extra guard time
		// For PCD it ranges 0-57us (1etu = 9us)
		ToSendStuffBit(1);
		ToSendStuffBit(1);
		ToSendStuffBit(1);
	}
	
	// Send EOF
	// 10-11 ETUs of ZERO
	for(i = 0; i < 10; ++i) ToSendStuffBit(0);

	// 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);
	
	// TR1 - Synchronization time
	// Convert from last character reference to length
	++ToSendMax;
}


/**
  Convenience function to encode, transmit and trace iso 14443b comms
  **/
static void CodeAndTransmit14443bAsReader(const uint8_t *cmd, int len) {
	
	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);
}

/* Sends an APDU to the tag
 * TODO: check CRC and preamble
 */
uint8_t iso14443b_apdu(uint8_t const *message, size_t message_length, uint8_t *response)
{
	uint8_t crc[2] = {0x00, 0x00};
	uint8_t message_frame[message_length + 4];
	// PCB
	message_frame[0] = 0x0A | pcb_blocknum;
	pcb_blocknum ^= 1;
	// CID
	message_frame[1] = 0;
	// INF
	memcpy(message_frame + 2, message, message_length);
	// EDC (CRC)
	ComputeCrc14443(CRC_14443_B, message_frame, message_length + 2, &message_frame[message_length + 2], &message_frame[message_length + 3]);
	// send
	CodeAndTransmit14443bAsReader(message_frame, message_length + 4); //no
	// get response
	GetTagSamplesFor14443bDemod(); //no
	if(Demod.len < 3)
		return 0;
	
	// VALIDATE CRC
    ComputeCrc14443(CRC_14443_B, Demod.output, Demod.len-2, &crc[0], &crc[1]);
	if ( crc[0] != Demod.output[Demod.len-2] || crc[1] != Demod.output[Demod.len-1] )
		return 0;
	
	// copy response contents
	if(response != NULL)
		memcpy(response, Demod.output, Demod.len);

	return Demod.len;
}

/**
* SRx Initialise.
*/
uint8_t iso14443b_select_srx_card(iso14b_card_select_t *card )
{
	// INITIATE command: wake up the tag using the INITIATE
	static const uint8_t init_srx[] = { ISO14443B_INITIATE, 0x00, 0x97, 0x5b };
	// SELECT command (with space for CRC)
	uint8_t select_srx[] = { ISO14443B_SELECT, 0x00, 0x00, 0x00};
	// temp to calc crc.
	uint8_t crc[2] = {0x00, 0x00};
	
	CodeAndTransmit14443bAsReader(init_srx, sizeof(init_srx));
	GetTagSamplesFor14443bDemod(); //no

	if (Demod.len == 0) return 2;

	// Randomly generated Chip ID	
	if (card) card->chipid = Demod.output[0];
	
	select_srx[1] = Demod.output[0];
	
	ComputeCrc14443(CRC_14443_B, select_srx, 2, &select_srx[2], &select_srx[3]);
	CodeAndTransmit14443bAsReader(select_srx, sizeof(select_srx));
	GetTagSamplesFor14443bDemod(); //no
	
	if (Demod.len != 3)	return 2;
	
	// Check the CRC of the answer:
	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;
	
	// Check response from the tag: should be the same UID as the command we just sent:
	if (select_srx[1] != Demod.output[0]) return 1;

	// First get the tag's UID:
	select_srx[0] = ISO14443B_GET_UID;

	ComputeCrc14443(CRC_14443_B, select_srx, 1 , &select_srx[1], &select_srx[2]);
	CodeAndTransmit14443bAsReader(select_srx, 3); // Only first three bytes for this one
	GetTagSamplesFor14443bDemod(); //no

	if (Demod.len != 10) return 2;
	
	// The check the CRC of the answer
	ComputeCrc14443(CRC_14443_B, Demod.output, Demod.len-2, &crc[0], &crc[1]);
	if(crc[0] != Demod.output[8] || crc[1] != Demod.output[9]) return 3;

	if (card) {
		card->uidlen = 8;
		memcpy(card->uid, Demod.output, 8);
	}

	return 0;
}
/* Perform the ISO 14443 B Card Selection procedure
 * Currently does NOT do any collision handling.
 * It expects 0-1 cards in the device's range.
 * TODO: Support multiple cards (perform anticollision)
 * TODO: Verify CRC checksums
 */
uint8_t iso14443b_select_card(iso14b_card_select_t *card )
{
	// WUPB command (including CRC)
	// Note: WUPB wakes up all tags, REQB doesn't wake up tags in HALT state
	static const uint8_t wupb[] = { ISO14443B_REQB, 0x00, 0x08, 0x39, 0x73 };
	// ATTRIB command (with space for CRC)
	uint8_t attrib[] = { ISO14443B_ATTRIB, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, 0x00};

	// temp to calc crc.
	uint8_t crc[2] = {0x00, 0x00};
	
	// first, wake up the tag
	CodeAndTransmit14443bAsReader(wupb, sizeof(wupb));
	GetTagSamplesFor14443bDemod(); //select_card
	
	// ATQB too short?
	if (Demod.len < 14) return 2;
	
	// VALIDATE CRC
    ComputeCrc14443(CRC_14443_B, Demod.output, Demod.len-2, &crc[0], &crc[1]);
	if ( crc[0] != Demod.output[12] || crc[1] != Demod.output[13] )
		return 3;
	
	if (card) {
		card->uidlen = 4;
		memcpy(card->uid, Demod.output+1, 4);
		memcpy(card->atqb, Demod.output+5, 7);
	}

    // copy the PUPI to ATTRIB  ( PUPI == UID )
    memcpy(attrib + 1, Demod.output + 1, 4);
	
    // copy the protocol info from ATQB (Protocol Info -> Protocol_Type) into ATTRIB (Param 3)
    attrib[7] = Demod.output[10] & 0x0F;
    ComputeCrc14443(CRC_14443_B, attrib, 9, attrib + 9, attrib + 10);

    CodeAndTransmit14443bAsReader(attrib, sizeof(attrib));
    GetTagSamplesFor14443bDemod();//select_card

    // Answer to ATTRIB too short?
    if(Demod.len < 3) return 2;

	// VALIDATE CRC
    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) 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);
	}
	// reset PCB block number
	pcb_blocknum = 0;
	return 0;
}

// Set up ISO 14443 Type B communication (similar to iso14443a_setup)
// field is setup for "Sending as Reader"
void iso14443b_setup() {
	if (MF_DBGLEVEL > 3) Dbprintf("iso1443b_setup Enter");
	LEDsoff();
	FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
	//BigBuf_free();
	//BigBuf_Clear_ext(false);
	
	// Initialize Demod and Uart structs
	DemodInit(BigBuf_malloc(MAX_FRAME_SIZE));
	UartInit(BigBuf_malloc(MAX_FRAME_SIZE));

	// connect Demodulated Signal to ADC:
	SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

	// Set up the synchronous serial port
	FpgaSetupSsc();
	
	// Signal field is on with the appropriate LED
	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);
	SpinDelay(100);

	// Start the timer
	StartCountSspClk();
	
	LED_D_ON();
	if (MF_DBGLEVEL > 3) Dbprintf("iso1443b_setup Exit");
}

//-----------------------------------------------------------------------------
// Read a SRI512 ISO 14443B tag.
//
// SRI512 tags are just simple memory tags, here we're looking at making a dump
// of the contents of the memory. No anticollision algorithm is done, we assume
// we have a single tag in the field.
//
// I tried to be systematic and check every answer of the tag, every CRC, etc...
//-----------------------------------------------------------------------------
void ReadSTMemoryIso14443b(uint8_t numofblocks)
{
	FpgaDownloadAndGo(FPGA_BITSTREAM_HF);

	// Make sure that we start from off, since the tags are stateful;
	// confusing things will happen if we don't reset them between reads.
	switch_off();  // before ReadStMemory

	set_tracing(TRUE);

	uint8_t i = 0x00;

	SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
	FpgaSetupSsc();

	// Now give it time to spin up.
	// Signal field is on with the appropriate LED
	LED_D_ON();
	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR | FPGA_HF_READER_RX_XCORR_848_KHZ);
	SpinDelay(20);

	// First command: wake up the tag using the INITIATE command
	uint8_t cmd1[] = {ISO14443B_INITIATE, 0x00, 0x97, 0x5b};
	CodeAndTransmit14443bAsReader(cmd1, sizeof(cmd1)); //no
	GetTagSamplesFor14443bDemod(); // no

	if (Demod.len == 0) {
		DbpString("No response from tag");
		set_tracing(FALSE);	
		return;
	} else {
		Dbprintf("Randomly generated Chip ID (+ 2 byte CRC): %02x %02x %02x",
				Demod.output[0], Demod.output[1], Demod.output[2]);
	}

	// There is a response, SELECT the uid
	DbpString("Now SELECT tag:");
	cmd1[0] = ISO14443B_SELECT; // 0x0E is SELECT
	cmd1[1] = Demod.output[0];
	ComputeCrc14443(CRC_14443_B, cmd1, 2, &cmd1[2], &cmd1[3]);
	CodeAndTransmit14443bAsReader(cmd1, sizeof(cmd1)); //no
	GetTagSamplesFor14443bDemod(); //no
	if (Demod.len != 3) {
		Dbprintf("Expected 3 bytes from tag, got %d", Demod.len);
		set_tracing(FALSE);	
		return;
	}
	// Check the CRC of the answer:
	ComputeCrc14443(CRC_14443_B, Demod.output, 1 , &cmd1[2], &cmd1[3]);
	if(cmd1[2] != Demod.output[1] || cmd1[3] != Demod.output[2]) {
		DbpString("CRC Error reading select response.");
		set_tracing(FALSE);	
		return;
	}
	// Check response from the tag: should be the same UID as the command we just sent:
	if (cmd1[1] != Demod.output[0]) {
		Dbprintf("Bad response to SELECT from Tag, aborting: %02x %02x", cmd1[1], Demod.output[0]);
		set_tracing(FALSE);	
		return;
	}

	// Tag is now selected,
	// First get the tag's UID:
	cmd1[0] = ISO14443B_GET_UID;
	ComputeCrc14443(CRC_14443_B, cmd1, 1 , &cmd1[1], &cmd1[2]);
	CodeAndTransmit14443bAsReader(cmd1, 3); // no --  Only first three bytes for this one
	GetTagSamplesFor14443bDemod(); //no
	if (Demod.len != 10) {
		Dbprintf("Expected 10 bytes from tag, got %d", Demod.len);
		set_tracing(FALSE);	
		return;
	}
	// The check the CRC of the answer (use cmd1 as temporary variable):
	ComputeCrc14443(CRC_14443_B, Demod.output, 8, &cmd1[2], &cmd1[3]);
	if(cmd1[2] != Demod.output[8] || cmd1[3] != Demod.output[9]) {
		Dbprintf("CRC Error reading block! Expected: %04x got: %04x",
				(cmd1[2]<<8)+cmd1[3], (Demod.output[8]<<8)+Demod.output[9]);
	// Do not return;, let's go on... (we should retry, maybe ?)
	}
	Dbprintf("Tag UID (64 bits): %08x %08x",
			(Demod.output[7]<<24) + (Demod.output[6]<<16) + (Demod.output[5]<<8) + Demod.output[4],
			(Demod.output[3]<<24) + (Demod.output[2]<<16) + (Demod.output[1]<<8) + Demod.output[0]);

	// Now loop to read all 16 blocks, address from 0 to last block
	Dbprintf("Tag memory dump, block 0 to %d", numofblocks);
	cmd1[0] = 0x08;
	i = 0x00;
	++numofblocks;
	
	for (;;) {
		if (i == numofblocks) {
			DbpString("System area block (0xff):");
			i = 0xff;
		}
		cmd1[1] = i;
		ComputeCrc14443(CRC_14443_B, cmd1, 2, &cmd1[2], &cmd1[3]);
		CodeAndTransmit14443bAsReader(cmd1, sizeof(cmd1)); //no
		GetTagSamplesFor14443bDemod(); //no
		
		if (Demod.len != 6) { // Check if we got an answer from the tag
			DbpString("Expected 6 bytes from tag, got less...");
			return;
		}
		// The check the CRC of the answer (use cmd1 as temporary variable):
		ComputeCrc14443(CRC_14443_B, Demod.output, 4, &cmd1[2], &cmd1[3]);
			if(cmd1[2] != Demod.output[4] || cmd1[3] != Demod.output[5]) {
			Dbprintf("CRC Error reading block! Expected: %04x got: %04x",
					(cmd1[2]<<8)+cmd1[3], (Demod.output[4]<<8)+Demod.output[5]);
		// Do not return;, let's go on... (we should retry, maybe ?)
		}
		// Now print out the memory location:
		Dbprintf("Address=%02x, Contents=%08x, CRC=%04x", i,
				(Demod.output[3]<<24) + (Demod.output[2]<<16) + (Demod.output[1]<<8) + Demod.output[0],
				(Demod.output[4]<<8)+Demod.output[5]);

		if (i == 0xff) break;
		++i;
	}
	
	set_tracing(FALSE);
}


static void iso1444b_setup_snoop(void){
	if (MF_DBGLEVEL > 3) Dbprintf("iso1443b_setup_snoop Enter");
	LEDsoff();
	FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
	BigBuf_free();
	BigBuf_Clear_ext(false); 
	clear_trace();//setup snoop
	set_tracing(TRUE);

	// Initialize Demod and Uart structs
	DemodInit(BigBuf_malloc(MAX_FRAME_SIZE));
	UartInit(BigBuf_malloc(MAX_FRAME_SIZE));

	if (MF_DBGLEVEL > 1) {
		// Print debug information about the buffer sizes
		Dbprintf("Snooping buffers initialized:");
		Dbprintf("  Trace: %i bytes", BigBuf_max_traceLen());
		Dbprintf("  Reader -> tag: %i bytes", MAX_FRAME_SIZE);
		Dbprintf("  tag -> Reader: %i bytes", MAX_FRAME_SIZE);
		Dbprintf("  DMA: %i bytes", ISO14443B_DMA_BUFFER_SIZE);
	}

	// connect Demodulated Signal to ADC:
	SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

	// Setup for the DMA.
	FpgaSetupSsc();

	// Set FPGA in the appropriate mode
	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR | FPGA_HF_READER_RX_XCORR_848_KHZ | FPGA_HF_READER_RX_XCORR_SNOOP);
	SpinDelay(20);	

	// Start the SSP timer
	StartCountSspClk();
	if (MF_DBGLEVEL > 3) Dbprintf("iso1443b_setup_snoop Exit");
}

//=============================================================================
// Finally, the `sniffer' combines elements from both the reader and
// simulated tag, to show both sides of the conversation.
//=============================================================================

//-----------------------------------------------------------------------------
// Record the sequence of commands sent by the reader to the tag, with
// triggering so that we start recording at the point that the tag is moved
// near the reader.
//-----------------------------------------------------------------------------
/*
 * Memory usage for this function, (within BigBuf)
 * Last Received command (reader->tag) - MAX_FRAME_SIZE
 * Last Received command (tag->reader) - MAX_FRAME_SIZE
 * DMA Buffer - ISO14443B_DMA_BUFFER_SIZE
 * Demodulated samples received - all the rest
 */
void RAMFUNC SnoopIso14443b(void) {

	uint32_t time_0 = 0, time_start = 0, time_stop = 0;
	
	// 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 TagIsActive = FALSE;
	bool ReaderIsActive = FALSE;

	iso1444b_setup_snoop();
	
	// The DMA buffer, used to stream samples from the FPGA
	int8_t *dmaBuf = (int8_t*) BigBuf_malloc(ISO14443B_DMA_BUFFER_SIZE);
	int8_t *upTo = dmaBuf;

	// Setup and start DMA.
	if ( !FpgaSetupSscDma((uint8_t*) dmaBuf, ISO14443B_DMA_BUFFER_SIZE) ){
		if (MF_DBGLEVEL > 1) Dbprintf("FpgaSetupSscDma failed. Exiting"); 
		BigBuf_free();
		return;
	}
	
	time_0 = GetCountSspClk();
		
	// And now we loop, receiving samples.
	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;
		
		lastRxCounter -= 2;
		
		if (upTo >= dmaBuf + ISO14443B_DMA_BUFFER_SIZE) {
			upTo = dmaBuf;
			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");
				break;
			}
				
			if(BUTTON_PRESS()) {
				DbpString("cancelled");
				break;
			}
		}
		
		if (!TagIsActive) {		
		
			LED_A_ON();
			
			// no need to try decoding reader data if the tag is sending
			if (Handle14443bReaderUartBit(ci & 0x01)) {

				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();
			} else {
				time_start = (GetCountSspClk()-time_0);
			}
			
			if (Handle14443bReaderUartBit(cq & 0x01)) {
				
				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();
			} else {
				time_start = (GetCountSspClk()-time_0);
			}
			ReaderIsActive = (Uart.state > STATE_GOT_FALLING_EDGE_OF_SOF);
			LED_A_OFF();
		}
		
		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)) {
				
				time_stop = (GetCountSspClk()-time_0);
				
				LogTrace(Demod.output, Demod.len, time_start, time_stop, NULL, FALSE);

				triggered = TRUE;

				// And ready to receive another response.
				DemodReset();
			} else {
				time_start = (GetCountSspClk()-time_0);
			}
			TagIsActive = (Demod.state > DEMOD_GOT_FALLING_EDGE_OF_SOF);
		}
	}

	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;
	// Uart.byteCntMax  should be set with ATQB value..
}

void iso14b_set_trigger(bool enable) {
	trigger = enable;
}

/*
 * Send raw command to tag ISO14443B
 * @Input
 * param   flags enum ISO14B_COMMAND.  (mifare.h)
 * len     len of buffer data
 * data    buffer with bytes to send
 *
 * @Output
 * none
 *
 */
void SendRawCommand14443B_Ex(UsbCommand *c)
{
	iso14b_command_t param = c->arg[0];
	size_t len = c->arg[1] & 0xffff;
	uint8_t *cmd = c->d.asBytes;
	uint8_t status = 0;
	uint32_t sendlen = sizeof(iso14b_card_select_t);
	uint8_t buf[USB_CMD_DATA_SIZE] = {0x00};

	if (MF_DBGLEVEL > 3) Dbprintf("14b raw: param, %04x", param );
	
	// turn on trigger (LED_A)
	if ((param & ISO14B_REQUEST_TRIGGER) == ISO14B_REQUEST_TRIGGER)
		iso14b_set_trigger(TRUE);
	
	if ((param & ISO14B_CONNECT) == ISO14B_CONNECT) {
		// Make sure that we start from off, since the tags are stateful;
		// confusing things will happen if we don't reset them between reads.
		//switch_off();  // before connect in raw
		iso14443b_setup();
	}
	
	set_tracing(TRUE);

	if ((param & ISO14B_SELECT_STD) == ISO14B_SELECT_STD) {
		iso14b_card_select_t *card = (iso14b_card_select_t*)buf;
		status = iso14443b_select_card(card);	
		cmd_send(CMD_ACK, status, sendlen, 0, buf, sendlen);
		// 0: OK 2: attrib fail, 3:crc fail,
		if ( status > 0 ) return;
	} 
	
	if ((param & ISO14B_SELECT_SR) == ISO14B_SELECT_SR) {
		iso14b_card_select_t *card = (iso14b_card_select_t*)buf;
		status = iso14443b_select_srx_card(card);
		cmd_send(CMD_ACK, status, sendlen, 0, buf, sendlen);
		// 0: OK 2: attrib fail, 3:crc fail,
		if ( status > 0 ) return;
	} 
	
	if ((param & ISO14B_APDU) == ISO14B_APDU) {
		status = iso14443b_apdu(cmd, len, buf);
		cmd_send(CMD_ACK, status, status, 0, buf, status);
	}
	
	if ((param & ISO14B_RAW) == ISO14B_RAW) {
		if((param & ISO14B_APPEND_CRC) == ISO14B_APPEND_CRC) {
			AppendCrc14443b(cmd, len);
			len += 2;
		}
	
		CodeAndTransmit14443bAsReader(cmd, len); // raw		
		GetTagSamplesFor14443bDemod(); // raw
		
		sendlen = MIN(Demod.len, USB_CMD_DATA_SIZE);
		status =  (Demod.len > 0) ? 0 : 1;
		cmd_send(CMD_ACK, status, sendlen, 0, Demod.output, sendlen);
	}
	
	// turn off trigger (LED_A)
	if ((param & ISO14B_REQUEST_TRIGGER) == ISO14B_REQUEST_TRIGGER)
		iso14b_set_trigger(FALSE);

	// turn off antenna et al
	// we don't send a HALT command.
	if ((param & ISO14B_DISCONNECT) == ISO14B_DISCONNECT) {
		if (MF_DBGLEVEL > 3) Dbprintf("disconnect");
		switch_off(); // disconnect raw
	} else {
		//FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);		
	}
	
}