]> git.zerfleddert.de Git - proxmark3-svn/blobdiff - armsrc/iso14443b.c
Coverity Scan 133850, need to ask @jason about this one.
[proxmark3-svn] / armsrc / iso14443b.c
index e1eae3b0370d6136b3366e1527d9bcc07ffb935b..e89c3becdd8a8777c91c1dce13dded2003e0775f 100644 (file)
 #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)
@@ -200,9 +205,6 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
        *
        */
        
-       // ToSendStuffBit,  40 calls
-       // 1 ETU = 1startbit, 1stopbit, 8databits == 10bits.
-       // 1 ETU = 10 * 4 == 40 stuffbits ( ETU_TAG_BIT )
        int i,j;
        uint8_t b;
        
@@ -218,77 +220,51 @@ static void CodeIso14443bAsTag(const uint8_t *cmd, int len) {
 
        // Send SOF.
        // 10-11 ETU * 4times samples ZEROS
-       for(i = 0; i < 10; i++) {
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-       }
+       for(i = 0; i < 10; i++) { SEND4STUFFBIT(0); }
+       //for(i = 0; i < 10; i++) { ToSendStuffBit(0); }
        
        // 2-3 ETU * 4times samples ONES
-       for(i = 0; i < 3; i++) {
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-       }
+       for(i = 0; i < 3; i++)  { SEND4STUFFBIT(1); }
+       //for(i = 0; i < 3; i++)  { ToSendStuffBit(1); }
        
        // data
        for(i = 0; i < len; ++i) {
                
                // Start bit
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
+               SEND4STUFFBIT(0);
+               //ToSendStuffBit(0);
 
                // Data bits
                b = cmd[i];
                for(j = 0; j < 8; ++j) {
-                       if(b & 1) {
-                               ToSendStuffBit(1);
-                               ToSendStuffBit(1);
-                               ToSendStuffBit(1);
-                               ToSendStuffBit(1);
+                       if(b & 1) { 
+                               SEND4STUFFBIT(1); 
+                               //ToSendStuffBit(1);
                        } else {
-                               ToSendStuffBit(0);
-                               ToSendStuffBit(0);
-                               ToSendStuffBit(0);
-                               ToSendStuffBit(0);
+                               SEND4STUFFBIT(0);
+                               //ToSendStuffBit(0);
                        }
                        b >>= 1;
                }
 
                // Stop bit
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
+               SEND4STUFFBIT(1);
+               //ToSendStuffBit(1);
                
                // Extra Guard bit
                // For PICC it ranges 0-18us (1etu = 9us)
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
+               SEND4STUFFBIT(1);
+               //ToSendStuffBit(1);
        }
 
        // Send EOF.
        // 10-11 ETU * 4 sample rate = ZEROS
-       for(i = 0; i < 10; i++) {
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-               ToSendStuffBit(0);
-       }
+       for(i = 0; i < 10; i++) { SEND4STUFFBIT(0); }
+       //for(i = 0; i < 10; i++) { ToSendStuffBit(0); }
        
        // why this?
-       for(i = 0; i < 40; i++) {
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-               ToSendStuffBit(1);
-       }
+       for(i = 0; i < 40; i++) { SEND4STUFFBIT(1); }
+       //for(i = 0; i < 40; i++) { ToSendStuffBit(1); }
        
        // Convert from last byte pos to length
        ++ToSendMax;
@@ -434,13 +410,25 @@ static int GetIso14443bCommandFromReader(uint8_t *received, uint16_t *len) {
        // 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);
-       
-       uint8_t mask, b = 0;
+
+       b = 0;
+       uint8_t mask;
        while( !BUTTON_PRESS() ) {
                WDT_HIT();
 
@@ -457,72 +445,76 @@ static int GetIso14443bCommandFromReader(uint8_t *received, uint16_t *len) {
        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);
                
-               // 8 ETU / 8bits. 8/4= 2 etus.
-               AT91C_BASE_SSC->SSC_THR = 0XFF;
-
+               ClearFpgaShiftingRegisters();
+               
                FpgaSetupSsc();
+               volatile uint32_t b;
 
                // 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];
-                               ++i;
+                               AT91C_BASE_SSC->SSC_THR = response[++i];
                        }
+                       if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+                               b = AT91C_BASE_SSC->SSC_RHR;
+                               (void)b;
+                       }                       
                }
+               
+               //WaitForFpgaDelayQueueIsEmpty(fpgasendQueueDelay);
+               AT91C_BASE_SSC->SSC_THR = 0xFF;         
 }      
 //-----------------------------------------------------------------------------
 // Main loop of simulated tag: receive commands from reader, decide what
 // response to send, and send it.
 //-----------------------------------------------------------------------------
 void SimulateIso14443bTag(uint32_t pupi) {
-       // the only commands we understand is WUPB, AFI=0, Select All, N=1:
-       static const uint8_t cmd1[] = { ISO14443B_REQB, 0x00, 0x08, 0x39, 0x73 }; // WUPB
-       // ... and REQB, AFI=0, Normal Request, N=1:
-       static const uint8_t cmd2[] = { ISO14443B_REQB, 0x00, 0x00, 0x71, 0xFF }; // REQB
-       // ... and ATTRIB
-       static const uint8_t cmd4[] = { 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 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};
-
-       // PUPI/UID supplied
-       if ( pupi > 0 ) {
-               uint8_t len = sizeof(response1);
-               num_to_bytes(pupi, 4, response1+1);
-               ComputeCrc14443(CRC_14443_B, response1, len-2, response1+len-2, response1+len-1);
-               //print it..
-       }
-       
-       uint16_t len, cmdsRecvd = 0;
-       uint8_t *receivedCmd = BigBuf_malloc(MAX_FRAME_SIZE);
-       
-       uint8_t *resp1Code;
-       uint8_t *resp2Code;
-       uint16_t resp1CodeLen, resp2CodeLen;
-       
-       // uint32_t time_0 = 0;
-       // uint32_t t2r_time = 0;
-       // uint32_t r2t_time = 0;
-       
-       int cardSTATE = MFEMUL_NOFIELD;
-       int vHf = 0;    // in mV
-       
+       ///////////// setup device.
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
 
        // allocate command receive buffer
@@ -536,104 +528,153 @@ void SimulateIso14443bTag(uint32_t pupi) {
 
        // Set up the synchronous serial port
        FpgaSetupSsc();
+       /////////////
 
-       // prepare the (only one) tag answer:
-       CodeIso14443bAsTag(response1, sizeof(response1));
-       resp1Code = BigBuf_malloc(ToSendMax);
-       resp1CodeLen = ToSendMax;
-       memcpy(resp1Code, ToSend, ToSendMax); 
+       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 ) {
+               uint8_t len = sizeof(respATQB);
+               num_to_bytes(pupi, 4, respATQB+1);
+               ComputeCrc14443(CRC_14443_B, respATQB, 12, &respATQB[len-2], &respATQB[len-1]);
+       }
+
+       // prepare "ATQB" tag answer (encoded):
+       CodeIso14443bAsTag(respATQB, sizeof(respATQB));
+       uint8_t *encodedATQB = BigBuf_malloc(ToSendMax);
+       uint16_t encodedATQBLen = ToSendMax;
+       memcpy(encodedATQB, ToSend, ToSendMax); 
+
        
-       // prepare the (other) tag answer:
-       CodeIso14443bAsTag(response2, sizeof(response2));
-       resp2Code = BigBuf_malloc(ToSendMax);
-       resp2CodeLen = ToSendMax;       
-       memcpy(resp2Code, 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 == MFEMUL_NOFIELD) {
+               if (cardSTATE == SIM_NOFIELD) {
                        vHf = (MAX_ADC_HF_VOLTAGE * AvgAdc(ADC_CHAN_HF)) >> 10;
-                       if ( vHf > MF_MINFIELDV )
-                               cardSTATE = MFEMUL_IDLE; 
+                       if ( vHf > MF_MINFIELDV ) {
+                               cardSTATE = SIM_IDLE; 
+                               LED_A_ON();
+                       }
                } 
-               if (cardSTATE == MFEMUL_NOFIELD) continue;
+               if (cardSTATE == SIM_NOFIELD) continue;
 
-               
+               // Get reader command
                if (!GetIso14443bCommandFromReader(receivedCmd, &len)) {
-                       Dbprintf("button pressed, received %d commands", cmdsRecvd);
+                       Dbprintf("button pressed, received %d commands", cmdsReceived);
                        break;
                }
 
-               // REQ or WUP request in ANY state and WUP in HALTED state
-               if (len == 5 && ( 
-                                (receivedCmd[0] == ISO14443B_REQB && cardSTATE != MFEMUL_HALTED) ||
-                 receivedCmd[0] == ISO14443A_CMD_WUPA
-                                )
-                       ) {
-                       TransmitFor14443b_AsTag( resp1Code, resp1CodeLen );
-                       LogTrace(response1, sizeof(response1), 0, 0, NULL, FALSE);
-                       cardSTATE = MFEMUL_SELECT1;
-                       continue;
-               }               
-                       
-               if ( (len == 5 && memcmp(receivedCmd, cmd1, len) == 0) || 
-                    (len == 5 && memcmp(receivedCmd, cmd2, len) == 0) ) {
-                               //WUPB && REQB
-                               cardSTATE = MFEMUL_SELECT1;
-               } else if ( len == 7 && receivedCmd[0] == ISO14443B_HALT ) {
-                               cardSTATE = MFEMUL_HALTED;
-               } else if ( len == sizeof(cmd4) && receivedCmd[0] == ISO14443B_ATTRIB ) {
-                               cardSTATE = MFEMUL_SELECT2;
-               } else {
-                       // SLOT MARKER command?!?
-                       // ISO7816?!?
-                       Dbprintf("new cmd from reader: len=%d, cmdsRecvd=%d", len, cmdsRecvd);
-
-                       // 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");
+               // 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;
                        }
-                       cardSTATE = MFEMUL_IDLE;                        
                }
-
+               
+               /*
+               * 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 MFEMUL_NOFIELD:
-                       case MFEMUL_HALTED:
-                       case MFEMUL_IDLE:{
+                       case SIM_NOFIELD:
+                       case SIM_HALTED:
+                       case SIM_IDLE:{
                                LogTrace(receivedCmd, len, 0, 0, NULL, TRUE);   
                                break;
                        }
-                       case MFEMUL_SELECT1: 
-                               TransmitFor14443b_AsTag( resp1Code, resp1CodeLen );
-                               LogTrace(response1, sizeof(response1), 0, 0, NULL, FALSE);
-                               cardSTATE = MFEMUL_WORK;
+                       case SIM_SELECTING: {
+                               TransmitFor14443b_AsTag( encodedATQB, encodedATQBLen );
+                               LogTrace(respATQB, sizeof(respATQB), 0, 0, NULL, FALSE);
+                               cardSTATE = SIM_WORK;
                                break;
-                       case MFEMUL_SELECT2:
-                               TransmitFor14443b_AsTag( resp2Code, resp2CodeLen );
-                               LogTrace(response2, sizeof(response2), 0, 0, NULL, FALSE);
-                               cardSTATE = MFEMUL_HALTED;
+                       }
+                       case SIM_HALTING: {
+                               TransmitFor14443b_AsTag( encodedOK, encodedOKLen );
+                               LogTrace(respOK, sizeof(respOK), 0, 0, NULL, FALSE);
+                               cardSTATE = SIM_HALTED;
                                break;
-                       case MFEMUL_WORK:
+                       }
+                       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;
                }
                        
-               ++cmdsRecvd;
-               if(cmdsRecvd > 1000) {
+               ++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
 }
 
@@ -763,7 +804,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
                                Demod.posCount = 0;     // start of SOF sequence
                        } else {
                                // maximum length of TR1 = 200 1/fs
-                               if(Demod.posCount > 25*2) Demod.state = DEMOD_UNSYNCD;
+                               if(Demod.posCount > 26*2) Demod.state = DEMOD_UNSYNCD;
                        }
                        ++Demod.posCount;
                        break;
@@ -775,7 +816,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
                        
                        if(v > 0) {
                                // low phase of SOF too short (< 9 etu). Note: spec is >= 10, but FPGA tends to "smear" edges
-                               if(Demod.posCount < 9*2) { 
+                               if(Demod.posCount < 8*2) { 
                                        Demod.state = DEMOD_UNSYNCD;
                                } else {
                                        LED_C_ON(); // Got SOF
@@ -786,7 +827,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
                                }
                        } else {
                                // low phase of SOF too long (> 12 etu)
-                               if (Demod.posCount > 12*2) { 
+                               if (Demod.posCount > 14*2) { 
                                        Demod.state = DEMOD_UNSYNCD;
                                        LED_C_OFF();
                                }
@@ -799,7 +840,7 @@ static RAMFUNC int Handle14443bTagSamplesDemod(int ci, int cq) {
                        MAKE_SOFT_DECISION();
                        
                        if (v > 0) {
-                               if(Demod.posCount > 3*2) {              // max 19us between characters = 16 1/fs, max 3 etu after low phase of SOF = 24 1/fs
+                               if(Demod.posCount > 2*2) {              // max 19us between characters = 16 1/fs, max 3 etu after low phase of SOF = 24 1/fs
                                        Demod.state = DEMOD_UNSYNCD;
                                        LED_C_OFF();
                                }
@@ -891,7 +932,7 @@ static void GetTagSamplesFor14443bDemod() {
        
        // 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();
 
@@ -950,29 +991,47 @@ static void GetTagSamplesFor14443bDemod() {
 //-----------------------------------------------------------------------------
 static void TransmitFor14443b_AsReader(void) {
 
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);
-       SpinDelay(20);
-       
-       int c;  
        // we could been in following mode:
        // FPGA_MAJOR_MODE_HF_READER_RX_XCORR | FPGA_HF_READER_RX_XCORR_848_KHZ
        // if its second call or more
+       
+       // while(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
+               // AT91C_BASE_SSC->SSC_THR = 0XFF;
+       // }
+       
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX | FPGA_HF_READER_TX_SHALLOW_MOD);
+       SpinDelay(40);
 
+       int c;  
+       volatile uint32_t b;
+                                                                                
        // What does this loop do? Is it TR1?
-       for(c = 0; c < 10;) {
+       // 0xFF = 8 bits of 1.    1 bit == 1Etu,..  
+       // loop 10 * 8 = 80 ETU of delay, with a non modulated signal.  why?
+       // 80*9 = 720us.
+       for(c = 0; c < 50;) {
                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
                        AT91C_BASE_SSC->SSC_THR = 0xFF;
                        ++c;
                }
+               if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+                       b = AT91C_BASE_SSC->SSC_RHR;
+                       (void)b;
+               }
        }
-       
+
        // Send frame loop
        for(c = 0; c < ToSendMax;) {
                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-                       AT91C_BASE_SSC->SSC_THR = ToSend[c];
-                       ++c;
+                       AT91C_BASE_SSC->SSC_THR = ToSend[c++];
                }
+               if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+                       b = AT91C_BASE_SSC->SSC_RHR;
+                       (void)b;
+               }                                       
        }
+       //WaitForFpgaDelayQueueIsEmpty(delay);
+       // We should wait here for the FPGA to send all bits.
        WDT_HIT();
 }
 
@@ -992,6 +1051,9 @@ static void CodeIso14443bAsReader(const uint8_t *cmd, int len)
        *
        *       1 ETU == 1 BIT!
        *   TR0 - 8 ETUS minimum.
+       *
+       *   QUESTION:  how long is a 1 or 0 in pulses in the xcorr_848 mode?
+       *              1 "stuffbit" = 1ETU (9us)
        */
        int i;
        uint8_t b;
@@ -1038,7 +1100,8 @@ static void CodeIso14443bAsReader(const uint8_t *cmd, int len)
        // Transition time. TR0 - guard time
        // 8ETUS minum?
        // Per specification, Subcarrier must be stopped no later than 2 ETUs after EOF.        
-       for(i = 0; i < 40 ; ++i) ToSendStuffBit(1);
+       // I'm guessing this is for the FPGA to be able to send all bits before we switch to listening mode
+       for(i = 0; i < 32 ; ++i) ToSendStuffBit(1);
        
        // TR1 - Synchronization time
        // Convert from last character reference to length
@@ -1206,12 +1269,13 @@ uint8_t iso14443b_select_card(iso14b_card_select_t *card )
                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);
+       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;
@@ -1575,8 +1639,8 @@ void RAMFUNC SnoopIso14443b(void) {
        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..
 }
 
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