Emv scan via contact interface (#789)

[proxmark3-svn] / armsrc / iso14443b.c

//-----------------------------------------------------------------------------
// Jonathan Westhues, split Nov 2006
// piwi 2018
//
// 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"

#include "proxmark3.h"
#include "apps.h"
#include "util.h"
#include "string.h"
#include "iso14443crc.h"
#include "fpgaloader.h"

#define RECEIVE_SAMPLES_TIMEOUT 1000 // TR0 max is 256/fs = 256/(848kHz) = 302us or 64 samples from FPGA. 1000 seems to be much too high?
#define ISO14443B_DMA_BUFFER_SIZE 128

// PCB Block number for APDUs
static uint8_t pcb_blocknum = 0;

//=============================================================================
// 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.
//=============================================================================

//-----------------------------------------------------------------------------
// 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)
{
        int i;

        ToSendReset();

        // Transmit a burst of ones, as the initial thing that lets the
        // reader get phase sync. This (TR1) must be > 80/fs, per spec,
        // but tag that I've tried (a Paypass) exceeds that by a fair bit,
        // so I will too.
        for(i = 0; i < 20; i++) {
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
        }

        // Send SOF.
        for(i = 0; i < 10; i++) {
                ToSendStuffBit(0);
                ToSendStuffBit(0);
                ToSendStuffBit(0);
                ToSendStuffBit(0);
        }
        for(i = 0; i < 2; i++) {
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
        }

        for(i = 0; i < len; i++) {
                int j;
                uint8_t b = cmd[i];

                // Start bit
                ToSendStuffBit(0);
                ToSendStuffBit(0);
                ToSendStuffBit(0);
                ToSendStuffBit(0);

                // Data bits
                for(j = 0; j < 8; j++) {
                        if(b & 1) {
                                ToSendStuffBit(1);
                                ToSendStuffBit(1);
                                ToSendStuffBit(1);
                                ToSendStuffBit(1);
                        } else {
                                ToSendStuffBit(0);
                                ToSendStuffBit(0);
                                ToSendStuffBit(0);
                                ToSendStuffBit(0);
                        }
                        b >>= 1;
                }

                // Stop bit
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
        }

        // Send EOF.
        for(i = 0; i < 10; i++) {
                ToSendStuffBit(0);
                ToSendStuffBit(0);
                ToSendStuffBit(0);
                ToSendStuffBit(0);
        }
        for(i = 0; i < 2; i++) {
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
                ToSendStuffBit(1);
        }

        // Convert from last byte pos to length
        ToSendMax++;
}

//-----------------------------------------------------------------------------
// 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;

/* 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 Handle14443bUartBit(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;
}


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


static void UartInit(uint8_t *data)
{
        Uart.output = data;
        UartReset();
}


//-----------------------------------------------------------------------------
// 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);

        // Now run a `software UART' on the stream of incoming samples.
        UartInit(received);

        for(;;) {
                WDT_HIT();

                if(BUTTON_PRESS()) return false;

                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
                        uint8_t b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        for(uint8_t mask = 0x80; mask != 0x00; mask >>= 1) {
                                if(Handle14443bUartBit(b & mask)) {
                                        *len = Uart.byteCnt;
                                        return true;
                                }
                        }
                }
        }

        return false;
}

//-----------------------------------------------------------------------------
// Main loop of simulated tag: receive commands from reader, decide what
// response to send, and send it.
//-----------------------------------------------------------------------------
void SimulateIso14443bTag(void)
{
        // the only commands we understand is WUPB, AFI=0, Select All, N=1:
        static const uint8_t cmd1[] = { 0x05, 0x00, 0x08, 0x39, 0x73 }; // WUPB
        // ... and REQB, AFI=0, Normal Request, N=1:
        static const uint8_t cmd2[] = { 0x05, 0x00, 0x00, 0x71, 0xFF }; // REQB
        // ... and HLTB
        static const uint8_t cmd3[] = { 0x50, 0xff, 0xff, 0xff, 0xff }; // HLTB
        // ... and ATTRIB
        static const uint8_t cmd4[] = { 0x1D, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}; // ATTRIB

        // ... and 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:
        static const uint8_t response1[] = {
                0x50, 0x82, 0x0d, 0xe1, 0x74, 0x20, 0x38, 0x19, 0x22,
                0x00, 0x21, 0x85, 0x5e, 0xd7
        };
        // response to HLTB and ATTRIB
        static const uint8_t response2[] = {0x00, 0x78, 0xF0};


        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);

        clear_trace();
        set_tracing(true);

        const uint8_t *resp;
        uint8_t *respCode;
        uint16_t respLen, respCodeLen;

        // allocate command receive buffer
        BigBuf_free();
        uint8_t *receivedCmd = BigBuf_malloc(MAX_FRAME_SIZE);

        uint16_t len;
        uint16_t cmdsRecvd = 0;

        // prepare the (only one) tag answer:
        CodeIso14443bAsTag(response1, sizeof(response1));
        uint8_t *resp1Code = BigBuf_malloc(ToSendMax);
        memcpy(resp1Code, ToSend, ToSendMax);
        uint16_t resp1CodeLen = ToSendMax;

        // prepare the (other) tag answer:
        CodeIso14443bAsTag(response2, sizeof(response2));
        uint8_t *resp2Code = BigBuf_malloc(ToSendMax);
        memcpy(resp2Code, ToSend, ToSendMax);
        uint16_t resp2CodeLen = ToSendMax;

        // We need to listen to the high-frequency, peak-detected path.
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
        FpgaSetupSsc(FPGA_MAJOR_MODE_HF_SIMULATOR);

        cmdsRecvd = 0;

        for(;;) {

                if(!GetIso14443bCommandFromReader(receivedCmd, &len)) {
                        Dbprintf("button pressed, received %d commands", cmdsRecvd);
                        break;
                }

                LogTrace(receivedCmd, len, 0, 0, NULL, true);

                // Good, look at the command now.
                if ( (len == sizeof(cmd1) && memcmp(receivedCmd, cmd1, len) == 0)
                        || (len == sizeof(cmd2) && memcmp(receivedCmd, cmd2, len) == 0) ) {
                        resp = response1;
                        respLen = sizeof(response1);
                        respCode = resp1Code;
                        respCodeLen = resp1CodeLen;
                } else if ( (len == sizeof(cmd3) && receivedCmd[0] == cmd3[0])
                        || (len == sizeof(cmd4) && receivedCmd[0] == cmd4[0]) ) {
                        resp = response2;
                        respLen = sizeof(response2);
                        respCode = resp2Code;
                        respCodeLen = resp2CodeLen;
                } else {
                        Dbprintf("new cmd from reader: len=%d, cmdsRecvd=%d", len, cmdsRecvd);
                        // And print whether the CRC fails, just for good measure
                        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]) {
                                        // Not so good, try again.
                                        DbpString("+++CRC fail");
                
                                } else {
                                        DbpString("CRC passes");
                                }
                        }
                        //get rid of compiler warning
                        respCodeLen = 0;
                        resp = response1;
                        respLen = 0;
                        respCode = resp1Code;
                        //don't crash at new command just wait and see if reader will send other new cmds.
                        //break;
                }

                cmdsRecvd++;

                if(cmdsRecvd > 0x30) {
                        DbpString("many commands later...");
                        break;
                }

                if(respCodeLen <= 0) continue;

                // Modulate BPSK
                // Signal field is off with the appropriate LED
                LED_D_OFF();
                FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_MODULATE_BPSK);
                AT91C_BASE_SSC->SSC_THR = 0xff;
                FpgaSetupSsc(FPGA_MAJOR_MODE_HF_SIMULATOR);

                // Transmit the response.
                uint16_t i = 0;
                for(;;) {
                        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
                                uint8_t b = respCode[i];

                                AT91C_BASE_SSC->SSC_THR = b;

                                i++;
                                if(i > respCodeLen) {
                                        break;
                                }
                        }
                        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
                                volatile uint8_t b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                                (void)b;
                        }
                }

                // trace the response:
                LogTrace(resp, respLen, 0, 0, NULL, false);

        }
}

//=============================================================================
// 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.
//=============================================================================

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;
        int     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;
        int     len;
        int     sumI;
        int     sumQ;
} Demod;

/*
 * 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
 *
 */
static RAMFUNC int Handle14443bSamplesDemod(int ci, int cq)
{
        int v;

// 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; \
                } \
        }

#define SUBCARRIER_DETECT_THRESHOLD     8

// Subcarrier amplitude v = sqrt(ci^2 + cq^2), approximated here by max(abs(ci),abs(cq)) + 1/2*min(abs(ci),abs(cq)))
#define AMPLITUDE(ci,cq) (MAX(ABS(ci),ABS(cq)) + (MIN(ABS(ci),ABS(cq))/2))
        switch(Demod.state) {
                case DEMOD_UNSYNCD:
                        if(AMPLITUDE(ci,cq) > SUBCARRIER_DETECT_THRESHOLD) {    // subcarrier detected
                                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) {
                                if (AMPLITUDE(ci,cq) > 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 {
                                if(Demod.posCount > 200/4) {    // maximum length of TR1 = 200 1/fs
                                        Demod.state = DEMOD_UNSYNCD;
                                }
                        }
                        Demod.posCount++;
                        break;

                case DEMOD_GOT_FALLING_EDGE_OF_SOF:
                        Demod.posCount++;
                        MAKE_SOFT_DECISION();
                        if(v > 0) {
                                if(Demod.posCount < 9*2) { // low phase of SOF too short (< 9 etu). Note: spec is >= 10, but FPGA tends to "smear" edges
                                        Demod.state = DEMOD_UNSYNCD;
                                } else {
                                        LED_C_ON(); // Got SOF
                                        Demod.state = DEMOD_AWAITING_START_BIT;
                                        Demod.posCount = 0;
                                        Demod.len = 0;
/* this had been used to add RSSI (Received Signal Strength Indication) to traces. Currently not implemented.
                                        Demod.metricN = 0;
                                        Demod.metric = 0;
*/
                                }
                        } else {
                                if(Demod.posCount > 12*2) { // low phase of SOF too long (> 12 etu)
                                        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;

/* this had been used to add RSSI (Received Signal Strength Indication) to traces. Currently not implemented.
                                if(Demod.thisBit > 0) {
                                        Demod.metric += Demod.thisBit;
                                } else {
                                        Demod.metric -= Demod.thisBit;
                                }
                                (Demod.metricN)++;
*/

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

                                Demod.bitCount++;
                                if(Demod.bitCount == 10) {
                                        uint16_t s = Demod.shiftReg;
                                        if((s & 0x200) && !(s & 0x001)) { // stop bit == '1', start bit == '0'
                                                uint8_t b = (s >> 1);
                                                Demod.output[Demod.len] = b;
                                                Demod.len++;
                                                Demod.state = DEMOD_AWAITING_START_BIT;
                                        } else {
                                                Demod.state = DEMOD_UNSYNCD;
                                                LED_C_OFF();
                                                if(s == 0x000) {
                                                        // This is EOF (start, stop and all data bits == '0'
                                                        return true;
                                                }
                                        }
                                }
                                Demod.posCount = 0;
                        }
                        break;

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

        return false;
}


static void DemodReset()
{
        // Clear out the state of the "UART" that receives from the tag.
        Demod.len = 0;
        Demod.state = DEMOD_UNSYNCD;
        Demod.posCount = 0;
        memset(Demod.output, 0x00, MAX_FRAME_SIZE);
}


static void DemodInit(uint8_t *data)
{
        Demod.output = data;
        DemodReset();
}


/*
 *  Demodulate the samples we received from the tag, also log to tracebuffer
 *  quiet: set to 'true' to disable debug output
 */
static void GetSamplesFor14443bDemod(int n, bool quiet)
{
        int maxBehindBy = 0;
        bool gotFrame = false;
        int lastRxCounter, samples = 0;
        int8_t ci, cq;
        
        // Allocate memory from BigBuf for some buffers
        // free all previous allocations first
        BigBuf_free();

        // The response (tag -> reader) that we're receiving.
        uint8_t *receivedResponse = BigBuf_malloc(MAX_FRAME_SIZE);

        // The DMA buffer, used to stream samples from the FPGA
        uint16_t *dmaBuf = (uint16_t*) BigBuf_malloc(ISO14443B_DMA_BUFFER_SIZE * sizeof(uint16_t));

        // Set up the demodulator for tag -> reader responses.
        DemodInit(receivedResponse);

        // wait for last transfer to complete
        while (!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXEMPTY))

        // Setup and start DMA.
        FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
        FpgaSetupSscDma((uint8_t*) dmaBuf, ISO14443B_DMA_BUFFER_SIZE);

        uint16_t *upTo = dmaBuf;
        lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;

        // Signal field is ON with the appropriate LED:
        LED_D_ON();
        // And put the FPGA in the appropriate mode
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR | FPGA_HF_READER_RX_XCORR_848_KHZ);

        for(;;) {
                int behindBy = (lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR) & (ISO14443B_DMA_BUFFER_SIZE-1);
                if(behindBy > maxBehindBy) {
                        maxBehindBy = behindBy;
                }

                if(behindBy < 1) continue;

                ci = *upTo >> 8;
                cq = *upTo;
                upTo++;
                lastRxCounter--;
                if(upTo >= dmaBuf + ISO14443B_DMA_BUFFER_SIZE) {               // we have read all of the DMA buffer content.
                        upTo = dmaBuf;                                             // start reading the circular buffer from the beginning
                        lastRxCounter += ISO14443B_DMA_BUFFER_SIZE;
                }
                if (AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_ENDRX)) {              // DMA Counter Register had reached 0, already rotated.
                        AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) dmaBuf;          // refresh the DMA Next Buffer and
                        AT91C_BASE_PDC_SSC->PDC_RNCR = ISO14443B_DMA_BUFFER_SIZE;  // DMA Next Counter registers
                }
                samples++;

                if(Handle14443bSamplesDemod(ci, cq)) {
                        gotFrame = true;
                        break;
                }

                if(samples > n) {
                        break;
                }
        }

        FpgaDisableSscDma();

        if (!quiet) Dbprintf("max behindby = %d, samples = %d, gotFrame = %d, Demod.len = %d, Demod.sumI = %d, Demod.sumQ = %d", maxBehindBy, samples, gotFrame, Demod.len, Demod.sumI, Demod.sumQ);
        //Tracing
        if (Demod.len > 0) {
                LogTrace(Demod.output, Demod.len, 0, 0, NULL, false);
        }
}


//-----------------------------------------------------------------------------
// Transmit the command (to the tag) that was placed in ToSend[].
//-----------------------------------------------------------------------------
static void TransmitFor14443b(void)
{
        int c;

        FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_TX);

        // Signal field is ON with the appropriate Red LED
        LED_D_ON();
        // Signal we are transmitting with the Green LED
        LED_B_ON();
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);

        c = 0;
        for(;;) {
                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
                        AT91C_BASE_SSC->SSC_THR = ~ToSend[c];
                        c++;
                        if(c >= ToSendMax) {
                                break;
                        }
                }
                WDT_HIT();
        }
        LED_B_OFF(); // Finished sending
}


//-----------------------------------------------------------------------------
// 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)
{
        int i, j;
        uint8_t b;

        ToSendReset();

        // Send SOF
        for(i = 0; i < 10; i++) {
                ToSendStuffBit(0);
        }
        ToSendStuffBit(1);
        ToSendStuffBit(1);

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

        // Send EOF
        for(i = 0; i < 10; i++) {
                ToSendStuffBit(0);
        }
        ToSendStuffBit(1);

        // ensure that last byte is filled up
        for(i = 0; i < 8; i++) {
                ToSendStuffBit(1);
        }

        // 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);
        TransmitFor14443b();
        LogTrace(cmd,len, 0, 0, NULL, true);
}

/* Sends an APDU to the tag
 * TODO: check CRC and preamble
 */
int iso14443b_apdu(uint8_t const *message, size_t message_length, uint8_t *response)
{
        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);
        // get response
        GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);
        if(Demod.len < 3)
        {
                return 0;
        }
        // TODO: Check CRC
        // copy response contents
        if(response != NULL)
        {
                memcpy(response, Demod.output, Demod.len);
        }
        return Demod.len;
}

/* 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
 */
int iso14443b_select_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[] = { 0x05, 0x00, 0x08, 0x39, 0x73 };
        // ATTRIB command (with space for CRC)
        uint8_t attrib[] = { 0x1D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, 0x00};

        // first, wake up the tag
        CodeAndTransmit14443bAsReader(wupb, sizeof(wupb));
        GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);
        // ATQB too short?
        if (Demod.len < 14)
        {
                return 2;
        }

    // select the tag
    // copy the PUPI to ATTRIB
    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));
    GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);
    // Answer to ATTRIB too short?
    if(Demod.len < 3)
        {
                return 2;
        }
        // reset PCB block number
        pcb_blocknum = 0;
        return 1;
}

// Set up ISO 14443 Type B communication (similar to iso14443a_setup)
void iso14443b_setup() {
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
        // Set up the synchronous serial port
        FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_TX);
        // connect Demodulated Signal to ADC:
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

        // Signal field is on with the appropriate LED
    LED_D_ON();
        FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);

        DemodReset();
        UartReset();
}

//-----------------------------------------------------------------------------
// 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(uint32_t dwLast)
{
        uint8_t i = 0x00;

        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.
        LED_D_OFF();
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelay(200);

        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
        FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);

        // 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(200);

        clear_trace();
        set_tracing(true);

        // First command: wake up the tag using the INITIATE command
        uint8_t cmd1[] = {0x06, 0x00, 0x97, 0x5b};
        CodeAndTransmit14443bAsReader(cmd1, sizeof(cmd1));
        GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);

        if (Demod.len == 0) {
                DbpString("No response from tag");
                LED_D_OFF();
                FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                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] = 0x0E; // 0x0E is SELECT
        cmd1[1] = Demod.output[0];
        ComputeCrc14443(CRC_14443_B, cmd1, 2, &cmd1[2], &cmd1[3]);
        CodeAndTransmit14443bAsReader(cmd1, sizeof(cmd1));
        GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);
        if (Demod.len != 3) {
                Dbprintf("Expected 3 bytes from tag, got %d", Demod.len);
                LED_D_OFF();
                FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                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.");
                LED_D_OFF();
                FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                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]);
                LED_D_OFF();
                FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                return;
        }

        // Tag is now selected,
        // First get the tag's UID:
        cmd1[0] = 0x0B;
        ComputeCrc14443(CRC_14443_B, cmd1, 1 , &cmd1[1], &cmd1[2]);
        CodeAndTransmit14443bAsReader(cmd1, 3); // Only first three bytes for this one
        GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);
        if (Demod.len != 10) {
                Dbprintf("Expected 10 bytes from tag, got %d", Demod.len);
                LED_D_OFF();
                FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                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", dwLast);
        cmd1[0] = 0x08;
        i = 0x00;
        dwLast++;
        for (;;) {
                if (i == dwLast) {
                        DbpString("System area block (0xff):");
                        i = 0xff;
                }
                cmd1[1] = i;
                ComputeCrc14443(CRC_14443_B, cmd1, 2, &cmd1[2], &cmd1[3]);
                CodeAndTransmit14443bAsReader(cmd1, sizeof(cmd1));
                GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);
                if (Demod.len != 6) { // Check if we got an answer from the tag
                        DbpString("Expected 6 bytes from tag, got less...");
                        LED_D_OFF();
                        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                        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++;
        }
        
        LED_D_OFF();
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
}


//=============================================================================
// 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)
{
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
        BigBuf_free();

        clear_trace();
        set_tracing(true);

        // The DMA buffer, used to stream samples from the FPGA
        uint16_t *dmaBuf = (uint16_t*) BigBuf_malloc(ISO14443B_DMA_BUFFER_SIZE * sizeof(uint16_t));
        int lastRxCounter;
        uint16_t *upTo;
        int8_t ci, cq;
        int maxBehindBy = 0;

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

        DemodInit(BigBuf_malloc(MAX_FRAME_SIZE));
        UartInit(BigBuf_malloc(MAX_FRAME_SIZE));

        // Print some 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);

        // Signal field is off, no reader signal, no tag signal
        LEDsoff();

        // And put the 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);
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

        // Setup for the DMA.
        FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
        upTo = dmaBuf;
        lastRxCounter = ISO14443B_DMA_BUFFER_SIZE;
        FpgaSetupSscDma((uint8_t*) dmaBuf, ISO14443B_DMA_BUFFER_SIZE);

        bool TagIsActive = false;
        bool ReaderIsActive = false;
        // 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
        // reader command
        bool triggered = false;

        // And now we loop, receiving samples.
        for(;;) {
                int behindBy = (lastRxCounter - AT91C_BASE_PDC_SSC->PDC_RCR) & (ISO14443B_DMA_BUFFER_SIZE-1);
                if(behindBy > maxBehindBy) {
                        maxBehindBy = behindBy;
                }

                if(behindBy < 1) continue;

                ci = *upTo>>8;
                cq = *upTo;
                upTo++;
                lastRxCounter--;
                if(upTo >= dmaBuf + ISO14443B_DMA_BUFFER_SIZE) {               // we have read all of the DMA buffer content.
                        upTo = dmaBuf;                                             // start reading the circular buffer from the beginning again
                        lastRxCounter += ISO14443B_DMA_BUFFER_SIZE;
                        if(behindBy > (9*ISO14443B_DMA_BUFFER_SIZE/10)) { 
                                Dbprintf("About to blow circular buffer - aborted! behindBy=%d", behindBy);
                                break;
                        }
                }
                if (AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_ENDRX)) {              // DMA Counter Register had reached 0, already rotated.
                        AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) dmaBuf;          // refresh the DMA Next Buffer and
                        AT91C_BASE_PDC_SSC->PDC_RNCR = ISO14443B_DMA_BUFFER_SIZE;  // DMA Next Counter registers
                        WDT_HIT();
                        if(BUTTON_PRESS()) {
                                DbpString("cancelled");
                                break;
                        }
                }

                samples++;

                if (!TagIsActive) {                                                     // no need to try decoding reader data if the tag is sending
                        if(Handle14443bUartBit(ci & 0x01)) {
                                triggered = true;
                                LogTrace(Uart.output, Uart.byteCnt, samples, samples, 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();
                        }
                        if(Handle14443bUartBit(cq & 0x01)) {
                                triggered = true;
                                LogTrace(Uart.output, Uart.byteCnt, samples, samples, 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();
                        }
                        ReaderIsActive = (Uart.state > STATE_GOT_FALLING_EDGE_OF_SOF);
                }

                if(!ReaderIsActive && triggered) {                                              // no need to try decoding tag data if the reader is sending or not yet triggered
                        if(Handle14443bSamplesDemod(ci/2, cq/2)) {
                                //Use samples as a time measurement
                                LogTrace(Demod.output, Demod.len, samples, samples, NULL, false);
                                // And ready to receive another response.
                                DemodReset();
                        }
                        TagIsActive = (Demod.state > DEMOD_GOT_FALLING_EDGE_OF_SOF);
                }

        }

        FpgaDisableSscDma();
        LEDsoff();
        DbpString("Snoop statistics:");
        Dbprintf("  Max behind by: %i", maxBehindBy);
        Dbprintf("  Uart State: %x", Uart.state);
        Dbprintf("  Uart ByteCnt: %i", Uart.byteCnt);
        Dbprintf("  Uart ByteCntMax: %i", Uart.byteCntMax);
        Dbprintf("  Trace length: %i", BigBuf_get_traceLen());
}


/*
 * Send raw command to tag ISO14443B
 * @Input
 * datalen     len of buffer data
 * recv        bool when true wait for data from tag and send to client
 * powerfield  bool leave the field on when true
 * data        buffer with byte to send
 *
 * @Output
 * none
 *
 */
void SendRawCommand14443B(uint32_t datalen, uint32_t recv, uint8_t powerfield, uint8_t data[])
{
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

        // switch field on and give tag some time to power up
        LED_D_ON();
        FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_TX);
        SpinDelay(10);

        if (datalen){
                set_tracing(true);
                
                CodeAndTransmit14443bAsReader(data, datalen);

                if(recv) {
                        GetSamplesFor14443bDemod(RECEIVE_SAMPLES_TIMEOUT, true);
                        uint16_t iLen = MIN(Demod.len, USB_CMD_DATA_SIZE);
                        cmd_send(CMD_ACK, iLen, 0, 0, Demod.output, iLen);
                }
        }

        if(!powerfield) {
                FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                LED_D_OFF();
        }
}