Merge pull request #876 from pwpiwi/fix_iclass_reader

[proxmark3-svn] / armsrc / iso15693.c

diff --git a/armsrc/iso15693.c b/armsrc/iso15693.c
index c092b3834ccfbd112091edad498ea26383e116e7..3b39d576fbe8930091dbb3f232613c2a4631e925 100644 (file)
--- a/armsrc/iso15693.c
+++ b/armsrc/iso15693.c
@@ -2,546 +2,1088 @@
 // Jonathan Westhues, split Nov 2006
 // Modified by Greg Jones, Jan 2009
 // Modified by Adrian Dabrowski "atrox", Mar-Sept 2010,Oct 2011
 // Jonathan Westhues, split Nov 2006
 // Modified by Greg Jones, Jan 2009
 // Modified by Adrian Dabrowski "atrox", Mar-Sept 2010,Oct 2011

+// Modified by piwi, Oct 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 15693. This includes both the reader software and
 //
 // 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 15693. This includes both the reader software and

-// the `fake tag' modes, but at the moment I've implemented only the reader
-// stuff, and that barely.
-// Modified to perform modulation onboard in arm rather than on PC
-// Also added additional reader commands (SELECT, READ etc.)
+// the `fake tag' modes.

 //-----------------------------------------------------------------------------
 //-----------------------------------------------------------------------------

-// The ISO 15693 describes two transmission modes from reader to tag, and 4 
-// transmission modes from tag to reader. As of Mar 2010 this code only 
-// supports one of each: "1of4" mode from reader to tag, and the highspeed 
-// variant with one subcarrier from card to reader.
-// As long, as the card fully support ISO 15693 this is no problem, since the 
-// reader chooses both data rates, but some non-standard tags do not. Further for 
-// the simulation to work, we will need to support all data rates.
+
+// The ISO 15693 describes two transmission modes from reader to tag, and four
+// transmission modes from tag to reader. As of Oct 2018 this code supports
+// both reader modes and the high speed variant with one subcarrier from card to reader.
+// As long as the card fully support ISO 15693 this is no problem, since the
+// reader chooses both data rates, but some non-standard tags do not.
+// For card simulation, the code supports both high and low speed modes with one subcarrier.

 //
 // VCD (reader) -> VICC (tag)
 // 1 out of 256:
 //
 // VCD (reader) -> VICC (tag)
 // 1 out of 256:

-//     data rate: 1,66 kbit/s (fc/8192) 
-//     used for long range
+//  data rate: 1,66 kbit/s (fc/8192)
+//  used for long range

 // 1 out of 4:
 // 1 out of 4:

-//     data rate: 26,48 kbit/s (fc/512)
-//     used for short range, high speed
-// 
+//  data rate: 26,48 kbit/s (fc/512)
+//  used for short range, high speed
+//

 // VICC (tag) -> VCD (reader)
 // Modulation:
 // VICC (tag) -> VCD (reader)
 // Modulation:

-//             ASK / one subcarrier (423,75 khz)
-//             FSK / two subcarriers (423,75 khz && 484,28 khz)
+//      ASK / one subcarrier (423,75 khz)
+//      FSK / two subcarriers (423,75 khz && 484,28 khz)

 // Data Rates / Modes:
 // Data Rates / Modes:

-//     low ASK: 6,62 kbit/s
-//     low FSK: 6.67 kbit/s
-//     high ASK: 26,48 kbit/s
-//     high FSK: 26,69 kbit/s
+//  low ASK: 6,62 kbit/s
+//  low FSK: 6.67 kbit/s
+//  high ASK: 26,48 kbit/s
+//  high FSK: 26,69 kbit/s

 //-----------------------------------------------------------------------------
 //-----------------------------------------------------------------------------

-// added "1 out of 256" mode (for VCD->PICC) - atrox 20100911

 
 
 // Random Remarks:
 // *) UID is always used "transmission order" (LSB), which is reverse to display order
 
 // TODO / BUGS / ISSUES:
 
 
 // Random Remarks:
 // *) UID is always used "transmission order" (LSB), which is reverse to display order
 
 // TODO / BUGS / ISSUES:

-// *) writing to tags takes longer: we miss the answer from the tag in most cases
-//    -> tweak the read-timeout times
-// *) signal decoding from the card is still a bit shaky. 
-// *) signal decoding is unable to detect collissions.
-// *) add anti-collission support for inventory-commands 
+// *) signal decoding is unable to detect collisions.
+// *) add anti-collision support for inventory-commands

 // *) read security status of a block
 // *) read security status of a block

-// *) sniffing and simulation do only support one transmission mode. need to support 
-//             all 8 transmission combinations
-//     *) remove or refactor code under "depricated"
+// *) sniffing and simulation do not support two subcarrier modes.
+// *) remove or refactor code under "deprecated"

 // *) document all the functions
 
 // *) document all the functions
 

+#include "iso15693.h"

 
 #include "proxmark3.h"
 #include "util.h"
 #include "apps.h"
 #include "string.h"
 #include "iso15693tools.h"
 
 #include "proxmark3.h"
 #include "util.h"
 #include "apps.h"
 #include "string.h"
 #include "iso15693tools.h"

+#include "protocols.h"

 #include "cmd.h"
 #include "cmd.h"

+#include "BigBuf.h"
+#include "fpgaloader.h"

 
 #define arraylen(x) (sizeof(x)/sizeof((x)[0]))
 
 
 #define arraylen(x) (sizeof(x)/sizeof((x)[0]))
 

-///////////////////////////////////////////////////////////////////////
-// ISO 15693 Part 2 - Air Interface
-// This section basicly contains transmission and receiving of bits
-///////////////////////////////////////////////////////////////////////
+// Delays in SSP_CLK ticks.
+// SSP_CLK runs at 13,56MHz / 32 = 423.75kHz when simulating a tag
+#define DELAY_READER_TO_ARM               8
+#define DELAY_ARM_TO_READER               0
+//SSP_CLK runs at 13.56MHz / 4 = 3,39MHz when acting as reader. All values should be multiples of 16
+#define DELAY_TAG_TO_ARM                 32
+#define DELAY_ARM_TO_TAG                 16
+
+static int DEBUG = 0;

 
 

-#define FrameSOF              Iso15693FrameSOF
-#define Logic0                Iso15693Logic0
-#define Logic1                Iso15693Logic1
-#define FrameEOF              Iso15693FrameEOF

 
 

-#define Crc(data,datalen)     Iso15693Crc(data,datalen)
-#define AddCrc(data,datalen)  Iso15693AddCrc(data,datalen)
-#define sprintUID(target,uid)  Iso15693sprintUID(target,uid)
+// specific LogTrace function for ISO15693: the duration needs to be scaled because otherwise it won't fit into a uint16_t
+bool LogTrace_ISO15693(const uint8_t *btBytes, uint16_t iLen, uint32_t timestamp_start, uint32_t timestamp_end, uint8_t *parity, bool readerToTag) {
+       uint32_t duration = timestamp_end - timestamp_start;
+       duration /= 32;
+       timestamp_end = timestamp_start + duration;
+       return LogTrace(btBytes, iLen, timestamp_start, timestamp_end, parity, readerToTag);
+}

 
 

-// approximate amplitude=sqrt(ci^2+cq^2) 
-#define AMPLITUDE(ci, cq) (MAX(ABS(ci), ABS(cq)) + (MIN(ABS(ci), ABS(cq))>>1))

 
 

-static int DEBUG = 0;
+///////////////////////////////////////////////////////////////////////
+// ISO 15693 Part 2 - Air Interface
+// This section basically contains transmission and receiving of bits
+///////////////////////////////////////////////////////////////////////

 
 

+// buffers
+#define ISO15693_DMA_BUFFER_SIZE       2048 // must be a power of 2
+#define ISO15693_MAX_RESPONSE_LENGTH     36 // allows read single block with the maximum block size of 256bits. Read multiple blocks not supported yet
+#define ISO15693_MAX_COMMAND_LENGTH      45 // allows write single block with the maximum block size of 256bits. Write multiple blocks not supported yet

 
 // ---------------------------
 
 // ---------------------------

-// Signal Processing 
+// Signal Processing

 // ---------------------------
 
 // prepare data using "1 out of 4" code for later transmission
 // ---------------------------
 
 // prepare data using "1 out of 4" code for later transmission

-// resulting data rate is 26,48 kbit/s (fc/512)
+// resulting data rate is 26.48 kbit/s (fc/512)

 // cmd ... data
 // n ... length of data
 // cmd ... data
 // n ... length of data

-static void CodeIso15693AsReader(uint8_t *cmd, int n)
-{
-       int i, j;
+void CodeIso15693AsReader(uint8_t *cmd, int n) {

 
        ToSendReset();
 
 
        ToSendReset();
 

-       // Give it a bit of slack at the beginning
-       for(i = 0; i < 24; i++) {
-               ToSendStuffBit(1);
-       }
-

        // SOF for 1of4
        // SOF for 1of4

-       ToSendStuffBit(0);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(0);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       for(i = 0; i < n; i++) {
-               for(j = 0; j < 8; j += 2) {
-                       int these = (cmd[i] >> j) & 3;
+       ToSend[++ToSendMax] = 0x84; //10000100
+
+       // data
+       for (int i = 0; i < n; i++) {
+               for (int j = 0; j < 8; j += 2) {
+                       int these = (cmd[i] >> j) & 0x03;

                        switch(these) {
                                case 0:
                        switch(these) {
                                case 0:

-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(0);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
+                                       ToSend[++ToSendMax] = 0x40; //01000000

                                        break;
                                case 1:
                                        break;
                                case 1:

-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(0);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
+                                       ToSend[++ToSendMax] = 0x10; //00010000

                                        break;
                                case 2:
                                        break;
                                case 2:

-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(0);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
+                                       ToSend[++ToSendMax] = 0x04; //00000100

                                        break;
                                case 3:
                                        break;
                                case 3:

-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(1);
-                                       ToSendStuffBit(0);
+                                       ToSend[++ToSendMax] = 0x01; //00000001

                                        break;
                        }
                }
        }
                                        break;
                        }
                }
        }

+

        // EOF
        // EOF

-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(0);
-       ToSendStuffBit(1);
-
-       // And slack at the end, too.
-       for(i = 0; i < 24; i++) {
-               ToSendStuffBit(1);
-       }
+       ToSend[++ToSendMax] = 0x20; //0010 + 0000 padding
+
+       ToSendMax++;

 }
 
 }
 

-// encode data using "1 out of 256" sheme
-// data rate is 1,66 kbit/s (fc/8192) 
+// encode data using "1 out of 256" scheme
+// data rate is 1,66 kbit/s (fc/8192)

 // is designed for more robust communication over longer distances
 static void CodeIso15693AsReader256(uint8_t *cmd, int n)
 {
 // is designed for more robust communication over longer distances
 static void CodeIso15693AsReader256(uint8_t *cmd, int n)
 {

-       int i, j;
-

        ToSendReset();
 
        ToSendReset();
 

-       // Give it a bit of slack at the beginning
-       for(i = 0; i < 24; i++) {
-               ToSendStuffBit(1);
-       }
-

        // SOF for 1of256
        // SOF for 1of256

-       ToSendStuffBit(0);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(0);
-       
-       for(i = 0; i < n; i++) {
-               for (j = 0; j<=255; j++) {
-                       if (cmd[i]==j) {
-                               ToSendStuffBit(1);
+       ToSend[++ToSendMax] = 0x81; //10000001
+
+       // data
+       for(int i = 0; i < n; i++) {
+               for (int j = 0; j <= 255; j++) {
+                       if (cmd[i] == j) {

                                ToSendStuffBit(0);
                                ToSendStuffBit(0);

-                       } else {
-                               ToSendStuffBit(1);

                                ToSendStuffBit(1);
                                ToSendStuffBit(1);

-                       }                       
-               }       
+                       } else {
+                               ToSendStuffBit(0);
+                               ToSendStuffBit(0);
+                       }
+               }

        }
        }

+

        // EOF
        // EOF

-       ToSendStuffBit(1);
-       ToSendStuffBit(1);
-       ToSendStuffBit(0);
-       ToSendStuffBit(1);
-
-       // And slack at the end, too.
-       for(i = 0; i < 24; i++) {
-               ToSendStuffBit(1);
+       ToSend[++ToSendMax] = 0x20; //0010 + 0000 padding
+
+       ToSendMax++;
+}
+
+
+// static uint8_t encode4Bits(const uint8_t b) {
+       // uint8_t c = b & 0xF;
+       // // OTA, the least significant bits first
+       // //         The columns are
+       // //               1 - Bit value to send
+       // //               2 - Reversed (big-endian)
+       // //               3 - Manchester Encoded
+       // //               4 - Hex values
+
+       // switch(c){
+       // //                          1       2         3         4
+         // case 15: return 0x55; // 1111 -> 1111 -> 01010101 -> 0x55
+         // case 14: return 0x95; // 1110 -> 0111 -> 10010101 -> 0x95
+         // case 13: return 0x65; // 1101 -> 1011 -> 01100101 -> 0x65
+         // case 12: return 0xa5; // 1100 -> 0011 -> 10100101 -> 0xa5
+         // case 11: return 0x59; // 1011 -> 1101 -> 01011001 -> 0x59
+         // case 10: return 0x99; // 1010 -> 0101 -> 10011001 -> 0x99
+         // case 9:  return 0x69; // 1001 -> 1001 -> 01101001 -> 0x69
+         // case 8:  return 0xa9; // 1000 -> 0001 -> 10101001 -> 0xa9
+         // case 7:  return 0x56; // 0111 -> 1110 -> 01010110 -> 0x56
+         // case 6:  return 0x96; // 0110 -> 0110 -> 10010110 -> 0x96
+         // case 5:  return 0x66; // 0101 -> 1010 -> 01100110 -> 0x66
+         // case 4:  return 0xa6; // 0100 -> 0010 -> 10100110 -> 0xa6
+         // case 3:  return 0x5a; // 0011 -> 1100 -> 01011010 -> 0x5a
+         // case 2:  return 0x9a; // 0010 -> 0100 -> 10011010 -> 0x9a
+         // case 1:  return 0x6a; // 0001 -> 1000 -> 01101010 -> 0x6a
+         // default: return 0xaa; // 0000 -> 0000 -> 10101010 -> 0xaa
+
+       // }
+// }
+
+static const uint8_t encode_4bits[16] = { 0xaa, 0x6a, 0x9a, 0x5a, 0xa6, 0x66, 0x96, 0x56, 0xa9, 0x69, 0x99, 0x59, 0xa5, 0x65, 0x95, 0x55 };
+
+void CodeIso15693AsTag(uint8_t *cmd, size_t len) {
+       /*
+        * SOF comprises 3 parts;
+        * * An unmodulated time of 56.64 us
+        * * 24 pulses of 423.75 kHz (fc/32)
+        * * A logic 1, which starts with an unmodulated time of 18.88us
+        *   followed by 8 pulses of 423.75kHz (fc/32)
+        *
+        * EOF comprises 3 parts:
+        * - A logic 0 (which starts with 8 pulses of fc/32 followed by an unmodulated
+        *   time of 18.88us.
+        * - 24 pulses of fc/32
+        * - An unmodulated time of 56.64 us
+        *
+        * A logic 0 starts with 8 pulses of fc/32
+        * followed by an unmodulated time of 256/fc (~18,88us).
+        *
+        * A logic 0 starts with unmodulated time of 256/fc (~18,88us) followed by
+        * 8 pulses of fc/32 (also 18.88us)
+        *
+        * A bit here becomes 8 pulses of fc/32. Therefore:
+        * The SOF can be written as 00011101 = 0x1D
+        * The EOF can be written as 10111000 = 0xb8
+        * A logic 1 is 01
+        * A logic 0 is 10
+        *
+        * */
+
+       ToSendReset();
+
+       // SOF
+       ToSend[++ToSendMax] = 0x1D;  // 00011101
+
+       // data
+       for (int i = 0; i < len; i++) {
+               ToSend[++ToSendMax] = encode_4bits[cmd[i] & 0xF];
+               ToSend[++ToSendMax] = encode_4bits[cmd[i] >> 4];

        }
        }

+
+       // EOF
+       ToSend[++ToSendMax] = 0xB8; // 10111000
+
+       ToSendMax++;

 }
 
 
 }
 
 

-// Transmit the command (to the tag) that was placed in ToSend[].
-static void TransmitTo15693Tag(const uint8_t *cmd, int len, int *samples, int *wait)
-{
-    int c;
-
-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_TX);
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
-       if(*wait < 10) { *wait = 10; }
-
-    c = 0;
-    for(;;) {
-        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-            AT91C_BASE_SSC->SSC_THR = ~cmd[c];
-            c++;
-            if(c >= len) {
-                break;
-            }
-        }
-        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
-            volatile uint32_t r = AT91C_BASE_SSC->SSC_RHR;
-            (void)r;
-        }
-        WDT_HIT();
-    }
-       *samples = (c + *wait) << 3;
+// Transmit the command (to the tag) that was placed in cmd[].
+void TransmitTo15693Tag(const uint8_t *cmd, int len, uint32_t *start_time) {
+
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_MODE_SEND_FULL_MOD);
+
+       if (*start_time < DELAY_ARM_TO_TAG) {
+               *start_time = DELAY_ARM_TO_TAG;
+       }
+
+       *start_time = (*start_time - DELAY_ARM_TO_TAG) & 0xfffffff0;
+
+       while (GetCountSspClk() > *start_time) { // we may miss the intended time
+               *start_time += 16; // next possible time
+       }
+
+
+       while (GetCountSspClk() < *start_time)
+               /* wait */ ;
+
+       LED_B_ON();
+       for (int c = 0; c < len; c++) {
+               uint8_t data = cmd[c];
+               for (int i = 0; i < 8; i++) {
+                       uint16_t send_word = (data & 0x80) ? 0xffff : 0x0000;
+                       while (!(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY))) ;
+                       AT91C_BASE_SSC->SSC_THR = send_word;
+                       while (!(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY))) ;
+                       AT91C_BASE_SSC->SSC_THR = send_word;
+
+                       data <<= 1;
+               }
+               WDT_HIT();
+       }
+       LED_B_OFF();
+
+       *start_time = *start_time + DELAY_ARM_TO_TAG;
+

 }
 
 }
 

+

 //-----------------------------------------------------------------------------
 //-----------------------------------------------------------------------------

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

 //-----------------------------------------------------------------------------
 //-----------------------------------------------------------------------------

-static void TransmitTo15693Reader(const uint8_t *cmd, int len, int *samples, int *wait)
-{
-    int c = 0;
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR|FPGA_HF_SIMULATOR_MODULATE_424K);
-       if(*wait < 10) { *wait = 10; }
-
-    for(;;) {
-        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-            AT91C_BASE_SSC->SSC_THR = cmd[c];
-            c++;
-            if(c >= len) {
-                break;
-            }
-        }
-        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
-            volatile uint32_t r = AT91C_BASE_SSC->SSC_RHR;
-            (void)r;
-        }
-        WDT_HIT();
-    }
-       *samples = (c + *wait) << 3;
-}
-
+void TransmitTo15693Reader(const uint8_t *cmd, size_t len, uint32_t *start_time, uint32_t slot_time, bool slow) {
+       // don't use the FPGA_HF_SIMULATOR_MODULATE_424K_8BIT minor mode. It would spoil GetCountSspClk()
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_MODULATE_424K);

 
 

-// Read from Tag
-// Parameters:
-//             receivedResponse
-//             maxLen
-//             samples
-//             elapsed
-// returns: 
-//             number of decoded bytes
-static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *samples, int *elapsed)
-{
-       int c = 0;
-       uint8_t *dest = BigBuf_get_addr();
+       uint32_t modulation_start_time = *start_time - DELAY_ARM_TO_READER + 3 * 8;  // no need to transfer the unmodulated start of SOF

 
 

-// NOW READ RESPONSE
-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
-       c = 0;
-       for(;;) {
-               if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
-                       uint16_t iq = AT91C_BASE_SSC->SSC_RHR;
-                       // The samples are correlations against I and Q versions of the
-                       // tone that the tag AM-modulates. We just want power. 
-                       int8_t i = iq >> 8;
-                       int8_t q = iq;
-                       uint8_t r = AMPLITUDE(i, q);
-
-                       dest[c++] = r;
-                       
-                       if(c >= 4000) {
-                               break;
-                       }
+       while (GetCountSspClk() > (modulation_start_time & 0xfffffff8) + 3) { // we will miss the intended time
+               if (slot_time) {
+                       modulation_start_time += slot_time; // use next available slot
+               } else {
+                       modulation_start_time = (modulation_start_time & 0xfffffff8) + 8; // next possible time

                }
        }
 
                }
        }
 

-       //////////////////////////////////////////
-       /////////// DEMODULATE ///////////////////
-       //////////////////////////////////////////
+       while (GetCountSspClk() < (modulation_start_time & 0xfffffff8))
+               /* wait */ ;

 
 

-       int i, j;
-       int max = 0, maxPos=0;
+       uint8_t shift_delay = modulation_start_time & 0x00000007;

 
 

-       int skip = 2;
+       *start_time = modulation_start_time + DELAY_ARM_TO_READER - 3 * 8;

 
 

-       // First, correlate for SOF
-       for(i = 0; i < 200; i++) {  // usually, SOF is found around i = 60
-               int corr = 0;
-               for(j = 0; j < arraylen(FrameSOF); j += skip) {
-                       corr += FrameSOF[j]*dest[i+(j/skip)];
+       LED_C_ON();
+       uint8_t bits_to_shift = 0x00;
+       uint8_t bits_to_send = 0x00;
+       for (size_t c = 0; c < len; c++) {
+               for (int i = (c==0?4:7); i >= 0; i--) {
+                       uint8_t cmd_bits = ((cmd[c] >> i) & 0x01) ? 0xff : 0x00;
+                       for (int j = 0; j < (slow?4:1); ) {
+                               if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
+                                       bits_to_send = bits_to_shift << (8 - shift_delay) | cmd_bits >> shift_delay;
+                                       AT91C_BASE_SSC->SSC_THR = bits_to_send;
+                                       bits_to_shift = cmd_bits;
+                                       j++;
+                               }
+                       }

                }
                }

-               if(corr > max) {
-                       max = corr;
-                       maxPos = i;
+               WDT_HIT();
+       }
+       // send the remaining bits, padded with 0:
+       bits_to_send = bits_to_shift << (8 - shift_delay);
+       for ( ; ; ) {
+               if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
+                       AT91C_BASE_SSC->SSC_THR = bits_to_send;
+                       break;

                }
        }
                }
        }

-       if (DEBUG) Dbprintf("SOF at %d, correlation %d", maxPos, max/(arraylen(FrameSOF)/skip));
+       LED_C_OFF();
+}

 
 

-       int k = 0; // this will be our return value

 
 

-       // greg - If correlation is less than 1 then there's little point in continuing
-       if ((max/(arraylen(FrameSOF)/skip)) >= 1)
-       {
+//=============================================================================
+// An ISO 15693 decoder for tag responses (one subcarrier only).
+// Uses cross correlation to identify each bit and EOF.
+// This function is called 8 times per bit (every 2 subcarrier cycles).
+// Subcarrier frequency fs is 424kHz, 1/fs = 2,36us,
+// 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
+//=============================================================================
+
+#define NOISE_THRESHOLD          160                   // don't try to correlate noise
+#define MAX_PREVIOUS_AMPLITUDE   (-1 - NOISE_THRESHOLD)
+
+typedef struct DecodeTag {
+       enum {
+               STATE_TAG_SOF_LOW,
+               STATE_TAG_SOF_RISING_EDGE,
+               STATE_TAG_SOF_HIGH,
+               STATE_TAG_SOF_HIGH_END,
+               STATE_TAG_RECEIVING_DATA,
+               STATE_TAG_EOF,
+               STATE_TAG_EOF_TAIL
+       }         state;
+       int       bitCount;
+       int       posCount;
+       enum {
+               LOGIC0,
+               LOGIC1,
+               SOF_PART1,
+               SOF_PART2
+       }         lastBit;
+       uint16_t  shiftReg;
+       uint16_t  max_len;
+       uint8_t   *output;
+       int       len;
+       int       sum1, sum2;
+       int       threshold_sof;
+       int       threshold_half;
+       uint16_t  previous_amplitude;
+} DecodeTag_t;
+
+
+static int inline __attribute__((always_inline)) Handle15693SamplesFromTag(uint16_t amplitude, DecodeTag_t *DecodeTag)
+{
+       switch(DecodeTag->state) {
+               case STATE_TAG_SOF_LOW:
+                       // waiting for a rising edge
+                       if (amplitude > NOISE_THRESHOLD + DecodeTag->previous_amplitude) {
+                               if (DecodeTag->posCount > 10) {
+                                       DecodeTag->threshold_sof = amplitude - DecodeTag->previous_amplitude;
+                                       DecodeTag->threshold_half = 0;
+                                       DecodeTag->state = STATE_TAG_SOF_RISING_EDGE;
+                               } else {
+                                       DecodeTag->posCount = 0;
+                               }
+                       } else {
+                               DecodeTag->posCount++;
+                               DecodeTag->previous_amplitude = amplitude;
+                       }
+                       break;
+
+               case STATE_TAG_SOF_RISING_EDGE:
+                       if (amplitude - DecodeTag->previous_amplitude > DecodeTag->threshold_sof) { // edge still rising
+                               if (amplitude - DecodeTag->threshold_sof > DecodeTag->threshold_sof) { // steeper edge, take this as time reference
+                                       DecodeTag->posCount = 1;
+                               } else {
+                                       DecodeTag->posCount = 2;
+                               }
+                               DecodeTag->threshold_sof = (amplitude - DecodeTag->previous_amplitude) / 2;
+                       } else {
+                               DecodeTag->posCount = 2;
+                               DecodeTag->threshold_sof = DecodeTag->threshold_sof/2;
+                       }
+                       // DecodeTag->posCount = 2;
+                       DecodeTag->state = STATE_TAG_SOF_HIGH;
+                       break;
+
+               case STATE_TAG_SOF_HIGH:
+                       // waiting for 10 times high. Take average over the last 8
+                       if (amplitude > DecodeTag->threshold_sof) {
+                               DecodeTag->posCount++;
+                               if (DecodeTag->posCount > 2) {
+                                       DecodeTag->threshold_half += amplitude; // keep track of average high value
+                               }
+                               if (DecodeTag->posCount == 10) {
+                                       DecodeTag->threshold_half >>= 2; // (4 times 1/2 average)
+                                       DecodeTag->state = STATE_TAG_SOF_HIGH_END;
+                               }
+                       } else { // high phase was too short
+                               DecodeTag->posCount = 1;
+                               DecodeTag->previous_amplitude = amplitude;
+                               DecodeTag->state = STATE_TAG_SOF_LOW;
+                       }
+                       break;
+
+               case STATE_TAG_SOF_HIGH_END:
+                       // check for falling edge
+                       if (DecodeTag->posCount == 13 && amplitude < DecodeTag->threshold_sof) {
+                               DecodeTag->lastBit = SOF_PART1;  // detected 1st part of SOF (12 samples low and 12 samples high)
+                               DecodeTag->shiftReg = 0;
+                               DecodeTag->bitCount = 0;
+                               DecodeTag->len = 0;
+                               DecodeTag->sum1 = amplitude;
+                               DecodeTag->sum2 = 0;
+                               DecodeTag->posCount = 2;
+                               DecodeTag->state = STATE_TAG_RECEIVING_DATA;
+                               FpgaDisableTracing(); // DEBUGGING
+                               Dbprintf("amplitude = %d, threshold_sof = %d, threshold_half/4 = %d, previous_amplitude = %d",
+                                       amplitude,
+                                       DecodeTag->threshold_sof,
+                                       DecodeTag->threshold_half/4,
+                                       DecodeTag->previous_amplitude); // DEBUGGING
+                               LED_C_ON();
+                       } else {
+                               DecodeTag->posCount++;
+                               if (DecodeTag->posCount > 13) { // high phase too long
+                                       DecodeTag->posCount = 0;
+                                       DecodeTag->previous_amplitude = amplitude;
+                                       DecodeTag->state = STATE_TAG_SOF_LOW;
+                                       LED_C_OFF();
+                               }
+                       }
+                       break;

 
 

-               i = maxPos + arraylen(FrameSOF)/skip;
-       
-               uint8_t outBuf[20];
-               memset(outBuf, 0, sizeof(outBuf));
-               uint8_t mask = 0x01;
-               for(;;) {
-                       int corr0 = 0, corr00 = 0, corr01 = 0, corr1 = 0, corrEOF = 0;
-                       for(j = 0; j < arraylen(Logic0); j += skip) {
-                               corr0 += Logic0[j]*dest[i+(j/skip)];
+               case STATE_TAG_RECEIVING_DATA:
+                       if (DecodeTag->posCount == 1) {
+                               DecodeTag->sum1 = 0;
+                               DecodeTag->sum2 = 0;

                        }
                        }

-                       corr01 = corr00 = corr0;
-                       for(j = 0; j < arraylen(Logic0); j += skip) {
-                               corr00 += Logic0[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
-                               corr01 += Logic1[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
+                       if (DecodeTag->posCount <= 4) {
+                               DecodeTag->sum1 += amplitude;
+                       } else {
+                               DecodeTag->sum2 += amplitude;

                        }
                        }

-                       for(j = 0; j < arraylen(Logic1); j += skip) {
-                               corr1 += Logic1[j]*dest[i+(j/skip)];
+                       if (DecodeTag->posCount == 8) {
+                               if (DecodeTag->sum1 > DecodeTag->threshold_half && DecodeTag->sum2 > DecodeTag->threshold_half) { // modulation in both halves
+                                       if (DecodeTag->lastBit == LOGIC0) {  // this was already part of EOF
+                                               DecodeTag->state = STATE_TAG_EOF;
+                                       } else {
+                                               DecodeTag->posCount = 0;
+                                               DecodeTag->previous_amplitude = amplitude;
+                                               DecodeTag->state = STATE_TAG_SOF_LOW;
+                                               LED_C_OFF();
+                                       }
+                               } else if (DecodeTag->sum1 < DecodeTag->threshold_half && DecodeTag->sum2 > DecodeTag->threshold_half) { // modulation in second half
+                                       // logic 1
+                                       if (DecodeTag->lastBit == SOF_PART1) { // still part of SOF
+                                               DecodeTag->lastBit = SOF_PART2;    // SOF completed
+                                       } else {
+                                               DecodeTag->lastBit = LOGIC1;
+                                               DecodeTag->shiftReg >>= 1;
+                                               DecodeTag->shiftReg |= 0x80;
+                                               DecodeTag->bitCount++;
+                                               if (DecodeTag->bitCount == 8) {
+                                                       DecodeTag->output[DecodeTag->len] = DecodeTag->shiftReg;
+                                                       DecodeTag->len++;
+                                                       // if (DecodeTag->shiftReg == 0x12 && DecodeTag->len == 1) FpgaDisableTracing(); // DEBUGGING
+                                                       if (DecodeTag->len > DecodeTag->max_len) {
+                                                               // buffer overflow, give up
+                                                               LED_C_OFF();
+                                                               return true;
+                                                       }
+                                                       DecodeTag->bitCount = 0;
+                                                       DecodeTag->shiftReg = 0;
+                                               }
+                                       }
+                               } else if (DecodeTag->sum1 > DecodeTag->threshold_half && DecodeTag->sum2 < DecodeTag->threshold_half) { // modulation in first half
+                                       // logic 0
+                                       if (DecodeTag->lastBit == SOF_PART1) { // incomplete SOF
+                                               DecodeTag->posCount = 0;
+                                               DecodeTag->previous_amplitude = amplitude;
+                                               DecodeTag->state = STATE_TAG_SOF_LOW;
+                                               LED_C_OFF();
+                                       } else {
+                                               DecodeTag->lastBit = LOGIC0;
+                                               DecodeTag->shiftReg >>= 1;
+                                               DecodeTag->bitCount++;
+                                               if (DecodeTag->bitCount == 8) {
+                                                       DecodeTag->output[DecodeTag->len] = DecodeTag->shiftReg;
+                                                       DecodeTag->len++;
+                                                       // if (DecodeTag->shiftReg == 0x12 && DecodeTag->len == 1) FpgaDisableTracing(); // DEBUGGING
+                                                       if (DecodeTag->len > DecodeTag->max_len) {
+                                                               // buffer overflow, give up
+                                                               DecodeTag->posCount = 0;
+                                                               DecodeTag->previous_amplitude = amplitude;
+                                                               DecodeTag->state = STATE_TAG_SOF_LOW;
+                                                               LED_C_OFF();
+                                                       }
+                                                       DecodeTag->bitCount = 0;
+                                                       DecodeTag->shiftReg = 0;
+                                               }
+                                       }
+                               } else { // no modulation
+                                       if (DecodeTag->lastBit == SOF_PART2) { // only SOF (this is OK for iClass)
+                                               LED_C_OFF();
+                                               return true;
+                                       } else {
+                                               DecodeTag->posCount = 0;
+                                               DecodeTag->state = STATE_TAG_SOF_LOW;
+                                               LED_C_OFF();
+                                       }
+                               }
+                               DecodeTag->posCount = 0;

                        }
                        }

-                       for(j = 0; j < arraylen(FrameEOF); j += skip) {
-                               corrEOF += FrameEOF[j]*dest[i+(j/skip)];
+                       DecodeTag->posCount++;
+                       break;
+
+               case STATE_TAG_EOF:
+                       if (DecodeTag->posCount == 1) {
+                               DecodeTag->sum1 = 0;
+                               DecodeTag->sum2 = 0;

                        }
                        }

-                       // Even things out by the length of the target waveform.
-                       corr00 *= 2;
-                       corr01 *= 2;
-                       corr0 *= 4;
-                       corr1 *= 4;
-       
-                       if(corrEOF > corr1 && corrEOF > corr00 && corrEOF > corr01) {
-                               if (DEBUG) Dbprintf("EOF at %d, correlation %d (corr01: %d, corr00: %d, corr1: %d, corr0: %d)", 
-                                       i, corrEOF, corr01, corr00, corr1, corr0);
-                               break;
-                       } else if(corr1 > corr0) {
-                               i += arraylen(Logic1)/skip;
-                               outBuf[k] |= mask;
+                       if (DecodeTag->posCount <= 4) {
+                               DecodeTag->sum1 += amplitude;

                        } else {
                        } else {

-                               i += arraylen(Logic0)/skip;
+                               DecodeTag->sum2 += amplitude;

                        }
                        }

-                       mask <<= 1;
-                       if(mask == 0) {
-                               k++;
-                               mask = 0x01;
+                       if (DecodeTag->posCount == 8) {
+                               if (DecodeTag->sum1 > DecodeTag->threshold_half && DecodeTag->sum2 < DecodeTag->threshold_half) { // modulation in first half
+                                       DecodeTag->posCount = 0;
+                                       DecodeTag->state = STATE_TAG_EOF_TAIL;
+                               } else {
+                                       DecodeTag->posCount = 0;
+                                       DecodeTag->previous_amplitude = amplitude;
+                                       DecodeTag->state = STATE_TAG_SOF_LOW;
+                                       LED_C_OFF();
+                               }

                        }
                        }

-                       if((i+(int)arraylen(FrameEOF)/skip) >= 4000) {
-                               DbpString("ran off end!");
-                               break;
+                       DecodeTag->posCount++;
+                       break;
+
+               case STATE_TAG_EOF_TAIL:
+                       if (DecodeTag->posCount == 1) {
+                               DecodeTag->sum1 = 0;
+                               DecodeTag->sum2 = 0;

                        }
                        }

-               }
-               if(mask != 0x01) { // this happens, when we miss the EOF
-                       // TODO: for some reason this happens quite often
-                       if (DEBUG) Dbprintf("error, uneven octet! (extra bits!) mask=%02x", mask);
-                       if (mask<0x08) k--; // discard the last uneven octet;
-                       // 0x08 is an assumption - but works quite often
-               }
-       //      uint8_t str1 [8];
-       //      itoa(k,str1);
-       //      strncat(str1," octets read",8);
-       
-       //      DbpString(  str1);    // DbpString("%d octets", k);
-       
-       //      for(i = 0; i < k; i+=3) {
-       //              //DbpString("# %2d: %02x ", i, outBuf[i]);
-       //              DbpIntegers(outBuf[i],outBuf[i+1],outBuf[i+2]);
-       //      }
-       
-               for(i = 0; i < k; i++) {
-                       receivedResponse[i] = outBuf[i];
-               }
-       } // "end if correlation > 0"   (max/(arraylen(FrameSOF)/skip))
-       return k; // return the number of bytes demodulated
+                       if (DecodeTag->posCount <= 4) {
+                               DecodeTag->sum1 += amplitude;
+                       } else {
+                               DecodeTag->sum2 += amplitude;
+                       }
+                       if (DecodeTag->posCount == 8) {
+                               if (DecodeTag->sum1 < DecodeTag->threshold_half && DecodeTag->sum2 < DecodeTag->threshold_half) { // no modulation in both halves
+                                       LED_C_OFF();
+                                       return true;
+                               } else {
+                                       DecodeTag->posCount = 0;
+                                       DecodeTag->previous_amplitude = amplitude;
+                                       DecodeTag->state = STATE_TAG_SOF_LOW;
+                                       LED_C_OFF();
+                               }
+                       }
+                       DecodeTag->posCount++;
+                       break;
+       }
+
+       return false;
+}

 
 

-///    DbpString("CRC=%04x", Iso15693Crc(outBuf, k-2));

 
 

+static void DecodeTagInit(DecodeTag_t *DecodeTag, uint8_t *data, uint16_t max_len) {
+       DecodeTag->previous_amplitude = MAX_PREVIOUS_AMPLITUDE;
+       DecodeTag->posCount = 0;
+       DecodeTag->state = STATE_TAG_SOF_LOW;
+       DecodeTag->output = data;
+       DecodeTag->max_len = max_len;

 }
 
 
 }
 
 

-// Now the GetISO15693 message from sniffing command
-static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int *samples, int *elapsed)
-{
-       int c = 0;
-       uint8_t *dest = BigBuf_get_addr();
+static void DecodeTagReset(DecodeTag_t *DecodeTag) {
+       DecodeTag->posCount = 0;
+       DecodeTag->state = STATE_TAG_SOF_LOW;
+       DecodeTag->previous_amplitude = MAX_PREVIOUS_AMPLITUDE;
+}
+
+
+/*
+ *  Receive and decode the tag response, also log to tracebuffer
+ */
+int GetIso15693AnswerFromTag(uint8_t* response, uint16_t max_len, uint16_t timeout, uint32_t *eof_time) {
+
+       int samples = 0;
+       int ret = 0;
+
+       uint16_t dmaBuf[ISO15693_DMA_BUFFER_SIZE];
+
+       // the Decoder data structure
+       DecodeTag_t DecodeTag = { 0 };
+       DecodeTagInit(&DecodeTag, response, max_len);
+
+       // wait for last transfer to complete
+       while (!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXEMPTY));
+
+       // And put the FPGA in the appropriate mode
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_424_KHZ | FPGA_HF_READER_MODE_RECEIVE_AMPLITUDE);
+
+       // Setup and start DMA.
+       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER);
+       FpgaSetupSscDma((uint8_t*) dmaBuf, ISO15693_DMA_BUFFER_SIZE);
+       uint32_t dma_start_time = 0;
+       uint16_t *upTo = dmaBuf;

 
 

-// NOW READ RESPONSE
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
-       //spindelay(60);        // greg - experiment to get rid of some of the 0 byte/failed reads
-       c = 0;

        for(;;) {
        for(;;) {

-               if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
-                       uint16_t iq = AT91C_BASE_SSC->SSC_RHR;
-                       // The samples are correlations against I and Q versions of the
-                       // tone that the tag AM-modulates. We just want power, 
-                       // so abs(I) + abs(Q) is close to what we want.
-                       int8_t i = iq >> 8;
-                       int8_t q = iq;
-                       uint8_t r = AMPLITUDE(i, q);
+               uint16_t behindBy = ((uint16_t*)AT91C_BASE_PDC_SSC->PDC_RPR - upTo) & (ISO15693_DMA_BUFFER_SIZE-1);

 
 

-                       dest[c++] = r;
+               if (behindBy == 0) continue;

 
 

-                       if(c >= BIGBUF_SIZE) {
+               samples++;
+               if (samples == 1) {
+                       // DMA has transferred the very first data
+                       dma_start_time = GetCountSspClk() & 0xfffffff0;
+               }
+
+               uint16_t tagdata = *upTo++;
+
+               if(upTo >= dmaBuf + ISO15693_DMA_BUFFER_SIZE) {                // we have read all of the DMA buffer content.
+                       upTo = dmaBuf;                                             // start reading the circular buffer from the beginning
+                       if(behindBy > (9*ISO15693_DMA_BUFFER_SIZE/10)) {
+                               Dbprintf("About to blow circular buffer - aborted! behindBy=%d", behindBy);
+                               ret = -1;

                                break;
                        }
                }
                                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 = ISO15693_DMA_BUFFER_SIZE;   // DMA Next Counter registers
+               }

 
 

-       //////////////////////////////////////////
-       /////////// DEMODULATE ///////////////////
-       //////////////////////////////////////////
+               if (Handle15693SamplesFromTag(tagdata, &DecodeTag)) {
+                       *eof_time = dma_start_time + samples*16 - DELAY_TAG_TO_ARM; // end of EOF
+                       if (DecodeTag.lastBit == SOF_PART2) {
+                               *eof_time -= 8*16; // needed 8 additional samples to confirm single SOF (iCLASS)
+                       }
+                       if (DecodeTag.len > DecodeTag.max_len) {
+                               ret = -2; // buffer overflow
+                       }
+                       break;
+               }

 
 

-       int i, j;
-       int max = 0, maxPos=0;
+               if (samples > timeout && DecodeTag.state < STATE_TAG_RECEIVING_DATA) {
+                       ret = -1;   // timeout
+                       break;
+               }

 
 

-       int skip = 2;
+       }

 
 

-       // First, correlate for SOF
-       for(i = 0; i < 38000; i++) {
-               int corr = 0;
-               for(j = 0; j < arraylen(FrameSOF); j += skip) {
-                       corr += FrameSOF[j]*dest[i+(j/skip)];
-               }
-               if(corr > max) {
-                       max = corr;
-                       maxPos = i;
-               }
+       FpgaDisableSscDma();
+
+       if (DEBUG) Dbprintf("samples = %d, ret = %d, Decoder: state = %d, lastBit = %d, len = %d, bitCount = %d, posCount = %d",
+                                               samples, ret, DecodeTag.state, DecodeTag.lastBit, DecodeTag.len, DecodeTag.bitCount, DecodeTag.posCount);
+
+       if (ret < 0) {
+               return ret;

        }
        }

-       if (DEBUG) Dbprintf("SOF at %d, correlation %d", maxPos,max/(arraylen(FrameSOF)/skip));

 
 

-       int k = 0; // this will be our return value
+       uint32_t sof_time = *eof_time
+                                               - DecodeTag.len * 8 * 8 * 16 // time for byte transfers
+                                               - 32 * 16  // time for SOF transfer
+                                               - (DecodeTag.lastBit != SOF_PART2?32*16:0); // time for EOF transfer

 
 

-       // greg - If correlation is less than 1 then there's little point in continuing
-       if ((max/(arraylen(FrameSOF)/skip)) >= 1)       // THIS SHOULD BE 1
-       {
-       
-               i = maxPos + arraylen(FrameSOF)/skip;
-       
-               uint8_t outBuf[20];
-               memset(outBuf, 0, sizeof(outBuf));
-               uint8_t mask = 0x01;
-               for(;;) {
-                       int corr0 = 0, corr00 = 0, corr01 = 0, corr1 = 0, corrEOF = 0;
-                       for(j = 0; j < arraylen(Logic0); j += skip) {
-                               corr0 += Logic0[j]*dest[i+(j/skip)];
+       if (DEBUG) Dbprintf("timing: sof_time = %d, eof_time = %d", sof_time, *eof_time);
+
+       LogTrace_ISO15693(DecodeTag.output, DecodeTag.len, sof_time*4, *eof_time*4, NULL, false);
+
+       return DecodeTag.len;
+}
+
+
+//=============================================================================
+// An ISO15693 decoder for reader commands.
+//
+// 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 B -> ON once we have received the SOF and are expecting the rest.
+//    LED B -> 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
+//=============================================================================
+
+typedef struct DecodeReader {
+       enum {
+               STATE_READER_UNSYNCD,
+               STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF,
+               STATE_READER_AWAIT_1ST_RISING_EDGE_OF_SOF,
+               STATE_READER_AWAIT_2ND_FALLING_EDGE_OF_SOF,
+               STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF,
+               STATE_READER_AWAIT_END_OF_SOF_1_OUT_OF_4,
+               STATE_READER_RECEIVE_DATA_1_OUT_OF_4,
+               STATE_READER_RECEIVE_DATA_1_OUT_OF_256
+       }           state;
+       enum {
+               CODING_1_OUT_OF_4,
+               CODING_1_OUT_OF_256
+       }           Coding;
+       uint8_t     shiftReg;
+       uint8_t     bitCount;
+       int         byteCount;
+       int         byteCountMax;
+       int         posCount;
+       int         sum1, sum2;
+       uint8_t     *output;
+} DecodeReader_t;
+
+
+static void DecodeReaderInit(DecodeReader_t* DecodeReader, uint8_t *data, uint16_t max_len)
+{
+       DecodeReader->output = data;
+       DecodeReader->byteCountMax = max_len;
+       DecodeReader->state = STATE_READER_UNSYNCD;
+       DecodeReader->byteCount = 0;
+       DecodeReader->bitCount = 0;
+       DecodeReader->posCount = 1;
+       DecodeReader->shiftReg = 0;
+}
+
+
+static void DecodeReaderReset(DecodeReader_t* DecodeReader)
+{
+       DecodeReader->state = STATE_READER_UNSYNCD;
+}
+
+
+static int inline __attribute__((always_inline)) Handle15693SampleFromReader(uint8_t bit, DecodeReader_t *restrict DecodeReader)
+{
+       switch (DecodeReader->state) {
+               case STATE_READER_UNSYNCD:
+                       // wait for unmodulated carrier
+                       if (bit) {
+                               DecodeReader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;

                        }
                        }

-                       corr01 = corr00 = corr0;
-                       for(j = 0; j < arraylen(Logic0); j += skip) {
-                               corr00 += Logic0[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
-                               corr01 += Logic1[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
+                       break;
+
+               case STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF:
+                       if (!bit) {
+                               // we went low, so this could be the beginning of a SOF
+                               DecodeReader->posCount = 1;
+                               DecodeReader->state = STATE_READER_AWAIT_1ST_RISING_EDGE_OF_SOF;

                        }
                        }

-                       for(j = 0; j < arraylen(Logic1); j += skip) {
-                               corr1 += Logic1[j]*dest[i+(j/skip)];
+                       break;
+
+               case STATE_READER_AWAIT_1ST_RISING_EDGE_OF_SOF:
+                       DecodeReader->posCount++;
+                       if (bit) { // detected rising edge
+                               if (DecodeReader->posCount < 4) { // rising edge too early (nominally expected at 5)
+                                       DecodeReader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
+                               } else { // SOF
+                                       DecodeReader->state = STATE_READER_AWAIT_2ND_FALLING_EDGE_OF_SOF;
+                               }
+                       } else {
+                               if (DecodeReader->posCount > 5) { // stayed low for too long
+                                       DecodeReaderReset(DecodeReader);
+                               } else {
+                                       // do nothing, keep waiting
+                               }

                        }
                        }

-                       for(j = 0; j < arraylen(FrameEOF); j += skip) {
-                               corrEOF += FrameEOF[j]*dest[i+(j/skip)];
+                       break;
+
+               case STATE_READER_AWAIT_2ND_FALLING_EDGE_OF_SOF:
+                       DecodeReader->posCount++;
+                       if (!bit) { // detected a falling edge
+                               if (DecodeReader->posCount < 20) {         // falling edge too early (nominally expected at 21 earliest)
+                                       DecodeReaderReset(DecodeReader);
+                               } else if (DecodeReader->posCount < 23) {  // SOF for 1 out of 4 coding
+                                       DecodeReader->Coding = CODING_1_OUT_OF_4;
+                                       DecodeReader->state = STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF;
+                               } else if (DecodeReader->posCount < 28) {  // falling edge too early (nominally expected at 29 latest)
+                                       DecodeReaderReset(DecodeReader);
+                               } else {                                   // SOF for 1 out of 256 coding
+                                       DecodeReader->Coding = CODING_1_OUT_OF_256;
+                                       DecodeReader->state = STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF;
+                               }
+                       } else {
+                               if (DecodeReader->posCount > 29) { // stayed high for too long
+                                       DecodeReader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
+                               } else {
+                                       // do nothing, keep waiting
+                               }

                        }
                        }

-                       // Even things out by the length of the target waveform.
-                       corr00 *= 2;
-                       corr01 *= 2;
-                       corr0 *= 4;
-                       corr1 *= 4;
-       
-                       if(corrEOF > corr1 && corrEOF > corr00 && corrEOF > corr01) {
-                               if (DEBUG) Dbprintf("EOF at %d, correlation %d (corr01: %d, corr00: %d, corr1: %d, corr0: %d)", 
-                                       i, corrEOF, corr01, corr00, corr1, corr0);
-                               break;
-                       } else if(corr1 > corr0) {
-                               i += arraylen(Logic1)/skip;
-                               outBuf[k] |= mask;
+                       break;
+
+               case STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF:
+                       DecodeReader->posCount++;
+                       if (bit) { // detected rising edge
+                               if (DecodeReader->Coding == CODING_1_OUT_OF_256) {
+                                       if (DecodeReader->posCount < 32) { // rising edge too early (nominally expected at 33)
+                                               DecodeReader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
+                                       } else {
+                                               DecodeReader->posCount = 1;
+                                               DecodeReader->bitCount = 0;
+                                               DecodeReader->byteCount = 0;
+                                               DecodeReader->sum1 = 1;
+                                               DecodeReader->state = STATE_READER_RECEIVE_DATA_1_OUT_OF_256;
+                                               LED_B_ON();
+                                       }
+                               } else { // CODING_1_OUT_OF_4
+                                       if (DecodeReader->posCount < 24) { // rising edge too early (nominally expected at 25)
+                                               DecodeReader->state = STATE_READER_AWAIT_1ST_FALLING_EDGE_OF_SOF;
+                                       } else {
+                                               DecodeReader->posCount = 1;
+                                               DecodeReader->state = STATE_READER_AWAIT_END_OF_SOF_1_OUT_OF_4;
+                                       }
+                               }

                        } else {
                        } else {

-                               i += arraylen(Logic0)/skip;
+                               if (DecodeReader->Coding == CODING_1_OUT_OF_256) {
+                                       if (DecodeReader->posCount > 34) { // signal stayed low for too long
+                                               DecodeReaderReset(DecodeReader);
+                                       } else {
+                                               // do nothing, keep waiting
+                                       }
+                               } else { // CODING_1_OUT_OF_4
+                                       if (DecodeReader->posCount > 26) { // signal stayed low for too long
+                                               DecodeReaderReset(DecodeReader);
+                                       } else {
+                                               // do nothing, keep waiting
+                                       }
+                               }
+                       }
+                       break;
+
+               case STATE_READER_AWAIT_END_OF_SOF_1_OUT_OF_4:
+                       DecodeReader->posCount++;
+                       if (bit) {
+                               if (DecodeReader->posCount == 9) {
+                                       DecodeReader->posCount = 1;
+                                       DecodeReader->bitCount = 0;
+                                       DecodeReader->byteCount = 0;
+                                       DecodeReader->sum1 = 1;
+                                       DecodeReader->state = STATE_READER_RECEIVE_DATA_1_OUT_OF_4;
+                                       LED_B_ON();
+                               } else {
+                                       // do nothing, keep waiting
+                               }
+                       } else { // unexpected falling edge
+                                       DecodeReaderReset(DecodeReader);
+                       }
+                       break;
+
+               case STATE_READER_RECEIVE_DATA_1_OUT_OF_4:
+                       bit = !!bit;
+                       DecodeReader->posCount++;
+                       if (DecodeReader->posCount == 1) {
+                               DecodeReader->sum1 = bit;
+                       } else if (DecodeReader->posCount <= 4) {
+                               DecodeReader->sum1 += bit;
+                       } else if (DecodeReader->posCount == 5) {
+                               DecodeReader->sum2 = bit;
+                       } else {
+                               DecodeReader->sum2 += bit;
+                       }
+                       if (DecodeReader->posCount == 8) {
+                               DecodeReader->posCount = 0;
+                               if (DecodeReader->sum1 <= 1 && DecodeReader->sum2 >= 3) { // EOF
+                                       LED_B_OFF(); // Finished receiving
+                                       DecodeReaderReset(DecodeReader);
+                                       if (DecodeReader->byteCount != 0) {
+                                               return true;
+                                       }
+                               }
+                               if (DecodeReader->sum1 >= 3 && DecodeReader->sum2 <= 1) { // detected a 2bit position
+                                       DecodeReader->shiftReg >>= 2;
+                                       DecodeReader->shiftReg |= (DecodeReader->bitCount << 6);
+                               }
+                               if (DecodeReader->bitCount == 15) { // we have a full byte
+                                       DecodeReader->output[DecodeReader->byteCount++] = DecodeReader->shiftReg;
+                                       if (DecodeReader->byteCount > DecodeReader->byteCountMax) {
+                                               // buffer overflow, give up
+                                               LED_B_OFF();
+                                               DecodeReaderReset(DecodeReader);
+                                       }
+                                       DecodeReader->bitCount = 0;
+                                       DecodeReader->shiftReg = 0;
+                               } else {
+                                       DecodeReader->bitCount++;
+                               }
+                       }
+                       break;
+
+               case STATE_READER_RECEIVE_DATA_1_OUT_OF_256:
+                       bit = !!bit;
+                       DecodeReader->posCount++;
+                       if (DecodeReader->posCount == 1) {
+                               DecodeReader->sum1 = bit;
+                       } else if (DecodeReader->posCount <= 4) {
+                               DecodeReader->sum1 += bit;
+                       } else if (DecodeReader->posCount == 5) {
+                               DecodeReader->sum2 = bit;
+                       } else {
+                               DecodeReader->sum2 += bit;
+                       }
+                       if (DecodeReader->posCount == 8) {
+                               DecodeReader->posCount = 0;
+                               if (DecodeReader->sum1 <= 1 && DecodeReader->sum2 >= 3) { // EOF
+                                       LED_B_OFF(); // Finished receiving
+                                       DecodeReaderReset(DecodeReader);
+                                       if (DecodeReader->byteCount != 0) {
+                                               return true;
+                                       }
+                               }
+                               if (DecodeReader->sum1 >= 3 && DecodeReader->sum2 <= 1) { // detected the bit position
+                                       DecodeReader->shiftReg = DecodeReader->bitCount;
+                               }
+                               if (DecodeReader->bitCount == 255) { // we have a full byte
+                                       DecodeReader->output[DecodeReader->byteCount++] = DecodeReader->shiftReg;
+                                       if (DecodeReader->byteCount > DecodeReader->byteCountMax) {
+                                               // buffer overflow, give up
+                                               LED_B_OFF();
+                                               DecodeReaderReset(DecodeReader);
+                                       }
+                               }
+                               DecodeReader->bitCount++;

                        }
                        }

-                       mask <<= 1;
-                       if(mask == 0) {
-                               k++;
-                               mask = 0x01;
+                       break;
+
+               default:
+                       LED_B_OFF();
+                       DecodeReaderReset(DecodeReader);
+                       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 len) or someone presses the pushbutton on the board (returns -1).
+//
+// Assume that we're called with the SSC (to the FPGA) and ADC path set
+// correctly.
+//-----------------------------------------------------------------------------
+
+int GetIso15693CommandFromReader(uint8_t *received, size_t max_len, uint32_t *eof_time) {
+       int samples = 0;
+       bool gotFrame = false;
+       uint8_t b;
+
+       uint8_t dmaBuf[ISO15693_DMA_BUFFER_SIZE];
+
+       // the decoder data structure
+       DecodeReader_t DecodeReader = {0};
+       DecodeReaderInit(&DecodeReader, received, max_len);
+
+       // wait for last transfer to complete
+       while (!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXEMPTY));
+
+       LED_D_OFF();
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_NO_MODULATION);
+
+       // clear receive register and wait for next transfer
+       uint32_t temp = AT91C_BASE_SSC->SSC_RHR;
+       (void) temp;
+       while (!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY)) ;
+
+       uint32_t dma_start_time = GetCountSspClk() & 0xfffffff8;
+
+       // Setup and start DMA.
+       FpgaSetupSscDma(dmaBuf, ISO15693_DMA_BUFFER_SIZE);
+       uint8_t *upTo = dmaBuf;
+
+       for (;;) {
+               uint16_t behindBy = ((uint8_t*)AT91C_BASE_PDC_SSC->PDC_RPR - upTo) & (ISO15693_DMA_BUFFER_SIZE-1);
+
+               if (behindBy == 0) continue;
+
+               b = *upTo++;
+               if (upTo >= dmaBuf + ISO15693_DMA_BUFFER_SIZE) {               // we have read all of the DMA buffer content.
+                       upTo = dmaBuf;                                             // start reading the circular buffer from the beginning
+                       if (behindBy > (9*ISO15693_DMA_BUFFER_SIZE/10)) {
+                               Dbprintf("About to blow circular buffer - aborted! behindBy=%d", behindBy);
+                               break;

                        }
                        }

-                       if((i+(int)arraylen(FrameEOF)/skip) >= BIGBUF_SIZE) {
-                               DbpString("ran off end!");
+               }
+               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 = ISO15693_DMA_BUFFER_SIZE;   // DMA Next Counter registers
+               }
+
+               for (int i = 7; i >= 0; i--) {
+                       if (Handle15693SampleFromReader((b >> i) & 0x01, &DecodeReader)) {
+                               *eof_time = dma_start_time + samples - DELAY_READER_TO_ARM; // end of EOF
+                               gotFrame = true;

                                break;
                        }
                                break;
                        }

+                       samples++;

                }
                }

-               if(mask != 0x01) {
-                       DbpString("sniff: error, uneven octet! (discard extra bits!)");
-       ///             DbpString("   mask=%02x", mask);
+
+               if (gotFrame) {
+                       break;

                }
                }

-       //      uint8_t str1 [8];
-       //      itoa(k,str1);
-       //      strncat(str1," octets read",8);
-       
-       //      DbpString(  str1);    // DbpString("%d octets", k);
-       
-       //      for(i = 0; i < k; i+=3) {
-       //              //DbpString("# %2d: %02x ", i, outBuf[i]);
-       //              DbpIntegers(outBuf[i],outBuf[i+1],outBuf[i+2]);
-       //      }
-       
-               for(i = 0; i < k; i++) {
-                       receivedResponse[i] = outBuf[i];
+
+               if (BUTTON_PRESS()) {
+                       DecodeReader.byteCount = -1;
+                       break;

                }
                }

-       } // "end if correlation > 0"   (max/(arraylen(FrameSOF)/skip))
-       return k; // return the number of bytes demodulated

 
 

-///    DbpString("CRC=%04x", Iso15693Crc(outBuf, k-2));
+               WDT_HIT();
+       }
+
+       FpgaDisableSscDma();
+
+       if (DEBUG) Dbprintf("samples = %d, gotFrame = %d, Decoder: state = %d, len = %d, bitCount = %d, posCount = %d",
+                                               samples, gotFrame, DecodeReader.state, DecodeReader.byteCount, DecodeReader.bitCount, DecodeReader.posCount);
+
+       if (DecodeReader.byteCount > 0) {
+               uint32_t sof_time = *eof_time
+                                               - DecodeReader.byteCount * (DecodeReader.Coding==CODING_1_OUT_OF_4?128:2048) // time for byte transfers
+                                               - 32  // time for SOF transfer
+                                               - 16; // time for EOF transfer
+               LogTrace_ISO15693(DecodeReader.output, DecodeReader.byteCount, sof_time*32, *eof_time*32, NULL, true);
+       }
+
+       return DecodeReader.byteCount;
+}
+
+
+// Encode (into the ToSend buffers) an identify request, which is the first
+// thing that you must send to a tag to get a response.
+static void BuildIdentifyRequest(void)
+{
+       uint8_t cmd[5];
+
+       uint16_t crc;
+       // one sub-carrier, inventory, 1 slot, fast rate
+       // AFI is at bit 5 (1<<4) when doing an INVENTORY
+       cmd[0] = (1 << 2) | (1 << 5) | (1 << 1);
+       // inventory command code
+       cmd[1] = 0x01;
+       // no mask
+       cmd[2] = 0x00;
+       //Now the CRC
+       crc = Iso15693Crc(cmd, 3);
+       cmd[3] = crc & 0xff;
+       cmd[4] = crc >> 8;
+
+       CodeIso15693AsReader(cmd, sizeof(cmd));

 }
 
 
 }
 
 

-static void BuildIdentifyRequest(void);

 //-----------------------------------------------------------------------------
 // Start to read an ISO 15693 tag. We send an identify request, then wait
 // for the response. The response is not demodulated, just left in the buffer
 //-----------------------------------------------------------------------------
 // Start to read an ISO 15693 tag. We send an identify request, then wait
 // for the response. The response is not demodulated, just left in the buffer


@@ -549,156 +1091,199 @@ static void BuildIdentifyRequest(void);
 //-----------------------------------------------------------------------------
 void AcquireRawAdcSamplesIso15693(void)
 {
 //-----------------------------------------------------------------------------
 void AcquireRawAdcSamplesIso15693(void)
 {

-       uint8_t *dest = BigBuf_get_addr();
+       LED_A_ON();

 
 

-       int c = 0;
+       uint8_t *dest = BigBuf_get_addr();

 
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
 
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);

-       BuildIdentifyRequest();
-
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER);
+       LED_D_ON();
+       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER);

        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 

+       BuildIdentifyRequest();
+

        // Give the tags time to energize
        // Give the tags time to energize

-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);

        SpinDelay(100);
 
        // Now send the command
        SpinDelay(100);
 
        // Now send the command

-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_TX);
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
+       uint32_t start_time = 0;
+       TransmitTo15693Tag(ToSend, ToSendMax, &start_time);

 
 

-       c = 0;
-       for(;;) {
-               if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-                       AT91C_BASE_SSC->SSC_THR = ~ToSend[c];
-                       c++;
-                       if(c == ToSendMax+3) {
-                               break;
-                       }
-               }
-               WDT_HIT();
-       }
+       // wait for last transfer to complete
+       while (!(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXEMPTY)) ;

 
 

-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_424_KHZ | FPGA_HF_READER_MODE_RECEIVE_AMPLITUDE);

 
 

-       c = 0;
-       for(;;) {
+       for(int c = 0; c < 4000; ) {

                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
                if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {

-                       uint16_t iq = AT91C_BASE_SSC->SSC_RHR;
-                       // The samples are correlations against I and Q versions of the
-                       // tone that the tag AM-modulates. We just want power, 
-                       // so abs(I) + abs(Q) is close to what we want.
-                       int8_t i = iq >> 8;
-                       int8_t q = iq;
-                       uint8_t r = AMPLITUDE(i, q);
-
-                       dest[c++] = r;
-
-                       if(c >= 4000) {
-                               break;
-                       }
+                       uint16_t r = AT91C_BASE_SSC->SSC_RHR;
+                       dest[c++] = r >> 5;

                }
        }
                }
        }

+
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+       LEDsoff();

 }
 
 
 }
 
 

-void RecordRawAdcSamplesIso15693(void)
+void SnoopIso15693(void)

 {
 {

-       uint8_t *dest = BigBuf_get_addr();
+       LED_A_ON();
+       
+       FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
+       BigBuf_free();

 
 

-       int c = 0;
+       clear_trace();
+       set_tracing(true);

 
 

-       FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
-       // Setup SSC
-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       // The DMA buffer, used to stream samples from the FPGA
+       uint16_t* dmaBuf = (uint16_t*)BigBuf_malloc(ISO15693_DMA_BUFFER_SIZE*sizeof(uint16_t));
+       uint16_t *upTo;

 
 

-       // Start from off (no field generated)
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-       SpinDelay(200);
+       // Count of samples received so far, so that we can include timing
+       // information in the trace buffer.
+       int samples = 0;
+
+       DecodeTag_t DecodeTag = {0};
+       uint8_t response[ISO15693_MAX_RESPONSE_LENGTH];
+       DecodeTagInit(&DecodeTag, response, sizeof(response));
+
+       DecodeReader_t DecodeReader = {0};;
+       uint8_t cmd[ISO15693_MAX_COMMAND_LENGTH];
+       DecodeReaderInit(&DecodeReader, cmd, sizeof(cmd));

 
 

+       // Print some debug information about the buffer sizes
+       if (DEBUG) {
+               Dbprintf("Snooping buffers initialized:");
+               Dbprintf("  Trace:         %i bytes", BigBuf_max_traceLen());
+               Dbprintf("  Reader -> tag: %i bytes", ISO15693_MAX_COMMAND_LENGTH);
+               Dbprintf("  tag -> Reader: %i bytes", ISO15693_MAX_RESPONSE_LENGTH);
+               Dbprintf("  DMA:           %i bytes", ISO15693_DMA_BUFFER_SIZE * sizeof(uint16_t));
+       }
+       Dbprintf("Snoop started. Press PM3 Button to stop.");
+
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_MODE_SNOOP_AMPLITUDE);

        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 

-       SpinDelay(100);
+       // Setup for the DMA.
+       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER);
+       upTo = dmaBuf;
+       FpgaSetupSscDma((uint8_t*) dmaBuf, ISO15693_DMA_BUFFER_SIZE);

 
 

-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       bool TagIsActive = false;
+       bool ReaderIsActive = false;
+       bool ExpectTagAnswer = false;

 
 

-       c = 0;
+       // And now we loop, receiving samples.

        for(;;) {
        for(;;) {

-               if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
-                       uint16_t iq = AT91C_BASE_SSC->SSC_RHR;
-                       // The samples are correlations against I and Q versions of the
-                       // tone that the tag AM-modulates. We just want power, 
-                       // so abs(I) + abs(Q) is close to what we want.
-                       int8_t i = iq >> 8;
-                       int8_t q = iq;
-                       uint8_t r = AMPLITUDE(i, q);
+               uint16_t behindBy = ((uint16_t*)AT91C_BASE_PDC_SSC->PDC_RPR - upTo) & (ISO15693_DMA_BUFFER_SIZE-1);
+
+               if (behindBy == 0) continue;

 
 

-                       dest[c++] = r;
+               uint16_t snoopdata = *upTo++;

 
 

-                       if(c >= 14000) {
+               if(upTo >= dmaBuf + ISO15693_DMA_BUFFER_SIZE) {                    // we have read all of the DMA buffer content.
+                       upTo = dmaBuf;                                                 // start reading the circular buffer from the beginning
+                       if(behindBy > (9*ISO15693_DMA_BUFFER_SIZE/10)) {
+                               Dbprintf("About to blow circular buffer - aborted! behindBy=%d, samples=%d", behindBy, samples);

                                break;
                        }
                                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 = ISO15693_DMA_BUFFER_SIZE;   // DMA Next Counter registers
+                               WDT_HIT();
+                               if(BUTTON_PRESS()) {
+                                       DbpString("Snoop stopped.");
+                                       break;
+                               }
+                       }
+               }
+               samples++;
+
+               if (!TagIsActive) {                                            // no need to try decoding reader data if the tag is sending
+                       if (Handle15693SampleFromReader(snoopdata & 0x02, &DecodeReader)) {
+                               FpgaDisableSscDma();
+                               ExpectTagAnswer = true;
+                               LogTrace_ISO15693(DecodeReader.output, DecodeReader.byteCount, samples*64, samples*64, NULL, true);
+                               /* And ready to receive another command. */
+                               DecodeReaderReset(&DecodeReader);
+                               /* And also reset the demod code, which might have been */
+                               /* false-triggered by the commands from the reader. */
+                               DecodeTagReset(&DecodeTag);
+                               upTo = dmaBuf;
+                               FpgaSetupSscDma((uint8_t*) dmaBuf, ISO15693_DMA_BUFFER_SIZE);
+                       }
+                       if (Handle15693SampleFromReader(snoopdata & 0x01, &DecodeReader)) {
+                               FpgaDisableSscDma();
+                               ExpectTagAnswer = true;
+                               LogTrace_ISO15693(DecodeReader.output, DecodeReader.byteCount, samples*64, samples*64, NULL, true);
+                               /* And ready to receive another command. */
+                               DecodeReaderReset(&DecodeReader);
+                               /* And also reset the demod code, which might have been */
+                               /* false-triggered by the commands from the reader. */
+                               DecodeTagReset(&DecodeTag);
+                               upTo = dmaBuf;
+                               FpgaSetupSscDma((uint8_t*) dmaBuf, ISO15693_DMA_BUFFER_SIZE);
+                       }
+                       ReaderIsActive = (DecodeReader.state >= STATE_READER_AWAIT_2ND_RISING_EDGE_OF_SOF);
+               }
+
+               if (!ReaderIsActive && ExpectTagAnswer) {                       // no need to try decoding tag data if the reader is currently sending or no answer expected yet
+                       if (Handle15693SamplesFromTag(snoopdata >> 2, &DecodeTag)) {
+                               FpgaDisableSscDma();
+                               //Use samples as a time measurement
+                               LogTrace_ISO15693(DecodeTag.output, DecodeTag.len, samples*64, samples*64, NULL, false);
+                               // And ready to receive another response.
+                               DecodeTagReset(&DecodeTag);
+                               DecodeReaderReset(&DecodeReader);
+                               ExpectTagAnswer = false;
+                               upTo = dmaBuf;
+                               FpgaSetupSscDma((uint8_t*) dmaBuf, ISO15693_DMA_BUFFER_SIZE);
+                       }
+                       TagIsActive = (DecodeTag.state >= STATE_TAG_RECEIVING_DATA);

                }
                }

+

        }
        }

-       Dbprintf("finished recording");
+
+       FpgaDisableSscDma();
+       BigBuf_free();
+
+       LEDsoff();
+
+       DbpString("Snoop statistics:");
+       Dbprintf("  ExpectTagAnswer: %d", ExpectTagAnswer);
+       Dbprintf("  DecodeTag State: %d", DecodeTag.state);
+       Dbprintf("  DecodeTag byteCnt: %d", DecodeTag.len);
+       Dbprintf("  DecodeReader State: %d", DecodeReader.state);
+       Dbprintf("  DecodeReader byteCnt: %d", DecodeReader.byteCount);
+       Dbprintf("  Trace length: %d", BigBuf_get_traceLen());

 }
 
 
 }
 
 

-// Initialize the proxmark as iso15k reader 
-// (this might produces glitches that confuse some tags
+// Initialize the proxmark as iso15k reader

 void Iso15693InitReader() {
 void Iso15693InitReader() {

-       LED_A_ON();
-       LED_B_ON();
-       LED_C_OFF();
-       LED_D_OFF();
-       

        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);

-       // Setup SSC
-       // FpgaSetupSsc();

 
        // Start from off (no field generated)
 
        // Start from off (no field generated)

+       LED_D_OFF();

        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelay(10);
 
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelay(10);
 
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER);

 
        // Give the tags time to energize
 
        // Give the tags time to energize

-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       LED_D_ON();
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER);

        SpinDelay(250);
        SpinDelay(250);

-
-       LED_A_ON();
-       LED_B_OFF();
-       LED_C_OFF();
-       LED_D_OFF();

 }
 
 ///////////////////////////////////////////////////////////////////////
 // ISO 15693 Part 3 - Air Interface
 }
 
 ///////////////////////////////////////////////////////////////////////
 // ISO 15693 Part 3 - Air Interface

-// This section basicly contains transmission and receiving of bits
+// This section basically contains transmission and receiving of bits

 ///////////////////////////////////////////////////////////////////////
 
 ///////////////////////////////////////////////////////////////////////
 

-// Encode (into the ToSend buffers) an identify request, which is the first
-// thing that you must send to a tag to get a response.
-static void BuildIdentifyRequest(void)
-{
-       uint8_t cmd[5];
-
-       uint16_t crc;
-       // one sub-carrier, inventory, 1 slot, fast rate
-       // AFI is at bit 5 (1<<4) when doing an INVENTORY
-       cmd[0] = (1 << 2) | (1 << 5) | (1 << 1);
-       // inventory command code
-       cmd[1] = 0x01;
-       // no mask
-       cmd[2] = 0x00;
-       //Now the CRC
-       crc = Crc(cmd, 3);
-       cmd[3] = crc & 0xff;
-       cmd[4] = crc >> 8;
-
-       CodeIso15693AsReader(cmd, sizeof(cmd));
-}

 
 // uid is in transmission order (which is reverse of display order)
 static void BuildReadBlockRequest(uint8_t *uid, uint8_t blockNumber )
 
 // uid is in transmission order (which is reverse of display order)
 static void BuildReadBlockRequest(uint8_t *uid, uint8_t blockNumber )


@@ -706,12 +1291,11 @@ static void BuildReadBlockRequest(uint8_t *uid, uint8_t blockNumber )
        uint8_t cmd[13];
 
        uint16_t crc;
        uint8_t cmd[13];
 
        uint16_t crc;

-       // If we set the Option_Flag in this request, the VICC will respond with the secuirty status of the block
-       // followed by teh block data
-       // one sub-carrier, inventory, 1 slot, fast rate
-       cmd[0] = (1 << 6)| (1 << 5) | (1 << 1); // no SELECT bit, ADDR bit, OPTION bit
+       // If we set the Option_Flag in this request, the VICC will respond with the security status of the block
+       // followed by the block data
+       cmd[0] = ISO15693_REQ_OPTION | ISO15693_REQ_ADDRESS | ISO15693_REQ_DATARATE_HIGH;

        // READ BLOCK command code
        // READ BLOCK command code

-       cmd[1] = 0x20;
+       cmd[1] = ISO15693_READBLOCK;

        // UID may be optionally specified here
        // 64-bit UID
        cmd[2] = uid[0];
        // UID may be optionally specified here
        // 64-bit UID
        cmd[2] = uid[0];


@@ -723,25 +1307,24 @@ static void BuildReadBlockRequest(uint8_t *uid, uint8_t blockNumber )
        cmd[8] = uid[6];
        cmd[9] = uid[7]; // 0xe0; // always e0 (not exactly unique)
        // Block number to read
        cmd[8] = uid[6];
        cmd[9] = uid[7]; // 0xe0; // always e0 (not exactly unique)
        // Block number to read

-       cmd[10] = blockNumber;//0x00;
+       cmd[10] = blockNumber;

        //Now the CRC
        //Now the CRC

-       crc = Crc(cmd, 11); // the crc needs to be calculated over 12 bytes
+       crc = Iso15693Crc(cmd, 11); // the crc needs to be calculated over 11 bytes

        cmd[11] = crc & 0xff;
        cmd[12] = crc >> 8;
 
        CodeIso15693AsReader(cmd, sizeof(cmd));
 }
 
        cmd[11] = crc & 0xff;
        cmd[12] = crc >> 8;
 
        CodeIso15693AsReader(cmd, sizeof(cmd));
 }
 

+

 // Now the VICC>VCD responses when we are simulating a tag
 // Now the VICC>VCD responses when we are simulating a tag

- static void BuildInventoryResponse( uint8_t *uid)
+static void BuildInventoryResponse(uint8_t *uid)

 {
        uint8_t cmd[12];
 
        uint16_t crc;
 {
        uint8_t cmd[12];
 
        uint16_t crc;

-       // one sub-carrier, inventory, 1 slot, fast rate
-       // AFI is at bit 5 (1<<4) when doing an INVENTORY
-    //(1 << 2) | (1 << 5) | (1 << 1);
-       cmd[0] = 0; // 
+
+       cmd[0] = 0; // No error, no protocol format extension

        cmd[1] = 0; // DSFID (data storage format identifier).  0x00 = not supported
        // 64-bit UID
        cmd[2] = uid[7]; //0x32;
        cmd[1] = 0; // DSFID (data storage format identifier).  0x00 = not supported
        // 64-bit UID
        cmd[2] = uid[7]; //0x32;


@@ -753,36 +1336,26 @@ static void BuildReadBlockRequest(uint8_t *uid, uint8_t blockNumber )
        cmd[8] = uid[1]; //0x05;
        cmd[9] = uid[0]; //0xe0;
        //Now the CRC
        cmd[8] = uid[1]; //0x05;
        cmd[9] = uid[0]; //0xe0;
        //Now the CRC

-       crc = Crc(cmd, 10);
+       crc = Iso15693Crc(cmd, 10);

        cmd[10] = crc & 0xff;
        cmd[11] = crc >> 8;
 
        cmd[10] = crc & 0xff;
        cmd[11] = crc >> 8;
 

-       CodeIso15693AsReader(cmd, sizeof(cmd));
+       CodeIso15693AsTag(cmd, sizeof(cmd));

 }
 
 // Universal Method for sending to and recv bytes from a tag
 }
 
 // Universal Method for sending to and recv bytes from a tag

-//     init ... should we initialize the reader?
-//     speed ... 0 low speed, 1 hi speed 
-//     **recv will return you a pointer to the received data
-//     If you do not need the answer use NULL for *recv[] 
-//     return: lenght of received data
-int SendDataTag(uint8_t *send, int sendlen, int init, int speed, uint8_t **recv) {
-
-       int samples = 0;
-       int tsamples = 0;
-       int wait = 0;
-       int elapsed = 0;
-       
-       LED_A_ON();
-       LED_B_ON();
-       LED_C_OFF();
-       LED_D_OFF();
-       
-       if (init) Iso15693InitReader();
+//  init ... should we initialize the reader?
+//  speed ... 0 low speed, 1 hi speed
+//  *recv will contain the tag's answer
+//  return: length of received data, or -1 for timeout
+int SendDataTag(uint8_t *send, int sendlen, bool init, int speed, uint8_t *recv, uint16_t max_recv_len, uint32_t start_time, uint32_t *eof_time) {
+
+       if (init) {
+               Iso15693InitReader();
+               StartCountSspClk();
+       }

 
 

-       int answerLen=0;
-       uint8_t *answer = BigBuf_get_addr() + 4000;
-       if (recv != NULL) memset(answer, 0, 100);
+       int answerLen = 0;

 
        if (!speed) {
                // low speed (1 out of 256)
 
        if (!speed) {
                // low speed (1 out of 256)


@@ -791,30 +1364,20 @@ int SendDataTag(uint8_t *send, int sendlen, int init, int speed, uint8_t **recv)
                // high speed (1 out of 4)
                CodeIso15693AsReader(send, sendlen);
        }
                // high speed (1 out of 4)
                CodeIso15693AsReader(send, sendlen);
        }

-       
-       LED_A_ON();
-       LED_B_OFF();
-       
-       TransmitTo15693Tag(ToSend,ToSendMax,&tsamples, &wait);  
+
+       TransmitTo15693Tag(ToSend, ToSendMax, &start_time);
+

        // Now wait for a response
        // Now wait for a response

-       if (recv!=NULL) {
-               LED_A_OFF();
-               LED_B_ON();
-               answerLen = GetIso15693AnswerFromTag(answer, 100, &samples, &elapsed) ; 
-               *recv=answer;
+       if (recv != NULL) {
+               answerLen = GetIso15693AnswerFromTag(recv, max_recv_len, ISO15693_READER_TIMEOUT, eof_time);

        }
 
        }
 

-       LED_A_OFF();
-       LED_B_OFF();
-       LED_C_OFF();
-       LED_D_OFF();
-       

        return answerLen;
 }
 
 
 // --------------------------------------------------------------------
        return answerLen;
 }
 
 
 // --------------------------------------------------------------------

-// Debug Functions 
+// Debug Functions

 // --------------------------------------------------------------------
 
 // Decodes a message from a tag and displays its metadata and content
 // --------------------------------------------------------------------
 
 // Decodes a message from a tag and displays its metadata and content


@@ -823,53 +1386,53 @@ void DbdecodeIso15693Answer(int len, uint8_t *d) {
        char status[DBD15STATLEN+1]={0};
        uint16_t crc;
 
        char status[DBD15STATLEN+1]={0};
        uint16_t crc;
 

-       if (len>3) {
-               if (d[0]&(1<<3)) 
-                       strncat(status,"ProtExt ",DBD15STATLEN);
-               if (d[0]&1) { 
+       if (len > 3) {
+               if (d[0] & ISO15693_RES_EXT)
+                       strncat(status,"ProtExt ", DBD15STATLEN);
+               if (d[0] & ISO15693_RES_ERROR) {

                        // error
                        // error

-                       strncat(status,"Error ",DBD15STATLEN);
+                       strncat(status,"Error ", DBD15STATLEN);

                        switch (d[1]) {
                        switch (d[1]) {

-                               case 0x01: 
-                                       strncat(status,"01:notSupp",DBD15STATLEN);
+                               case 0x01:
+                                       strncat(status,"01:notSupp", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x02: 
-                                       strncat(status,"02:notRecog",DBD15STATLEN);
+                               case 0x02:
+                                       strncat(status,"02:notRecog", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x03: 
-                                       strncat(status,"03:optNotSupp",DBD15STATLEN);
+                               case 0x03:
+                                       strncat(status,"03:optNotSupp", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x0f: 
-                                       strncat(status,"0f:noInfo",DBD15STATLEN);
+                               case 0x0f:
+                                       strncat(status,"0f:noInfo", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x10: 
-                                       strncat(status,"10:dontExist",DBD15STATLEN);
+                               case 0x10:
+                                       strncat(status,"10:doesn'tExist", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x11: 
-                                       strncat(status,"11:lockAgain",DBD15STATLEN);
+                               case 0x11:
+                                       strncat(status,"11:lockAgain", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x12: 
-                                       strncat(status,"12:locked",DBD15STATLEN);
+                               case 0x12:
+                                       strncat(status,"12:locked", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x13: 
-                                       strncat(status,"13:progErr",DBD15STATLEN);
+                               case 0x13:
+                                       strncat(status,"13:progErr", DBD15STATLEN);

                                        break;
                                        break;

-                               case 0x14: 
-                                       strncat(status,"14:lockErr",DBD15STATLEN);
+                               case 0x14:
+                                       strncat(status,"14:lockErr", DBD15STATLEN);

                                        break;
                                default:
                                        break;
                                default:

-                                       strncat(status,"unknownErr",DBD15STATLEN);
+                                       strncat(status,"unknownErr", DBD15STATLEN);

                        }
                        }

-                       strncat(status," ",DBD15STATLEN);
+                       strncat(status," ", DBD15STATLEN);

                } else {
                } else {

-                       strncat(status,"NoErr ",DBD15STATLEN);
+                       strncat(status,"NoErr ", DBD15STATLEN);

                }
                }

-                       
-               crc=Crc(d,len-2);
-               if ( (( crc & 0xff ) == d[len-2]) && (( crc >> 8 ) == d[len-1]) ) 
+
+               crc=Iso15693Crc(d,len-2);
+               if ( (( crc & 0xff ) == d[len-2]) && (( crc >> 8 ) == d[len-1]) )

                        strncat(status,"CrcOK",DBD15STATLEN);
                else
                        strncat(status,"CrcOK",DBD15STATLEN);
                else

-                       strncat(status,"CrcFail!",DBD15STATLEN); 
+                       strncat(status,"CrcFail!",DBD15STATLEN);

 
                Dbprintf("%s",status);
        }
 
                Dbprintf("%s",status);
        }


@@ -888,83 +1451,70 @@ void SetDebugIso15693(uint32_t debug) {
 }
 
 
 }
 
 

-
-//-----------------------------------------------------------------------------
-// Simulate an ISO15693 reader, perform anti-collision and then attempt to read a sector
+//---------------------------------------------------------------------------------------
+// Simulate an ISO15693 reader, perform anti-collision and then attempt to read a sector.

 // all demodulation performed in arm rather than host. - greg
 // all demodulation performed in arm rather than host. - greg

-//-----------------------------------------------------------------------------
-void ReaderIso15693(uint32_t parameter)
-{
+//---------------------------------------------------------------------------------------
+void ReaderIso15693(uint32_t parameter) {
+

        LED_A_ON();
        LED_A_ON();

-       LED_B_ON();
-       LED_C_OFF();
-       LED_D_OFF();

 
 

-       int answerLen1 = 0;
-       int answerLen2 = 0;
-       // int answerLen3 = 0;
-       int i = 0;
-       int samples = 0;
-       int tsamples = 0;
-       int wait = 0;
-       int elapsed = 0;
+       set_tracing(true);
+
+       int answerLen = 0;

        uint8_t TagUID[8] = {0x00};
 
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
 
        uint8_t TagUID[8] = {0x00};
 
        FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
 

-       uint8_t *answer1 = BigBuf_get_addr() + 4000;
-       uint8_t *answer2 = BigBuf_get_addr() + 4100;
-       // uint8_t *answer3 = BigBuf_get_addr() + 4200;
-       // Blank arrays
-       memset(answer1, 0x00, 200);
+       uint8_t answer[ISO15693_MAX_RESPONSE_LENGTH];

 
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
        // Setup SSC
 
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
        // Setup SSC

-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER);

 
        // Start from off (no field generated)
 
        // Start from off (no field generated)

-       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-       SpinDelay(200);
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+       SpinDelay(200);

 
        // Give the tags time to energize
 
        // Give the tags time to energize

-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       LED_D_ON();
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER);

        SpinDelay(200);
        SpinDelay(200);

+       StartCountSspClk();

 
 

-       LED_A_ON();
-       LED_B_OFF();
-       LED_C_OFF();
-       LED_D_OFF();

 
        // FIRST WE RUN AN INVENTORY TO GET THE TAG UID
        // THIS MEANS WE CAN PRE-BUILD REQUESTS TO SAVE CPU TIME
 
        // Now send the IDENTIFY command
        BuildIdentifyRequest();
 
        // FIRST WE RUN AN INVENTORY TO GET THE TAG UID
        // THIS MEANS WE CAN PRE-BUILD REQUESTS TO SAVE CPU TIME
 
        // Now send the IDENTIFY command
        BuildIdentifyRequest();

-       
-       TransmitTo15693Tag(ToSend,ToSendMax,&tsamples, &wait);
-       
+       uint32_t start_time = 0;
+       TransmitTo15693Tag(ToSend, ToSendMax, &start_time);
+

        // Now wait for a response
        // Now wait for a response

-       answerLen1 = GetIso15693AnswerFromTag(answer1, 100, &samples, &elapsed) ;
+       uint32_t eof_time;
+       answerLen = GetIso15693AnswerFromTag(answer, sizeof(answer), DELAY_ISO15693_VCD_TO_VICC_READER * 2, &eof_time) ;
+       start_time = eof_time + DELAY_ISO15693_VICC_TO_VCD_READER;

 
 

-       if (answerLen1 >=12) // we should do a better check than this
+       if (answerLen >=12) // we should do a better check than this

        {
        {

-               TagUID[0] = answer1[2];
-               TagUID[1] = answer1[3];
-               TagUID[2] = answer1[4];
-               TagUID[3] = answer1[5];
-               TagUID[4] = answer1[6];
-               TagUID[5] = answer1[7];
-               TagUID[6] = answer1[8]; // IC Manufacturer code
-               TagUID[7] = answer1[9]; // always E0
+               TagUID[0] = answer[2];
+               TagUID[1] = answer[3];
+               TagUID[2] = answer[4];
+               TagUID[3] = answer[5];
+               TagUID[4] = answer[6];
+               TagUID[5] = answer[7];
+               TagUID[6] = answer[8]; // IC Manufacturer code
+               TagUID[7] = answer[9]; // always E0

 
        }
 
 
        }
 

-       Dbprintf("%d octets read from IDENTIFY request:", answerLen1);
-       DbdecodeIso15693Answer(answerLen1,answer1);
-       Dbhexdump(answerLen1,answer1,true);
+       Dbprintf("%d octets read from IDENTIFY request:", answerLen);
+       DbdecodeIso15693Answer(answerLen, answer);
+       Dbhexdump(answerLen, answer, false);

 
        // UID is reverse
 
        // UID is reverse

-       if (answerLen1>=12) 
+       if (answerLen >= 12)

                Dbprintf("UID = %02hX%02hX%02hX%02hX%02hX%02hX%02hX%02hX",
                        TagUID[7],TagUID[6],TagUID[5],TagUID[4],
                        TagUID[3],TagUID[2],TagUID[1],TagUID[0]);
                Dbprintf("UID = %02hX%02hX%02hX%02hX%02hX%02hX%02hX%02hX",
                        TagUID[7],TagUID[6],TagUID[5],TagUID[4],
                        TagUID[3],TagUID[2],TagUID[1],TagUID[0]);


@@ -979,161 +1529,238 @@ void ReaderIso15693(uint32_t parameter)
        // Dbhexdump(answerLen3,answer3,true);
 
        // read all pages
        // Dbhexdump(answerLen3,answer3,true);
 
        // read all pages

-       if (answerLen1>=12 && DEBUG) {
-               i=0;                    
-               while (i<32) {  // sanity check, assume max 32 pages
-                       BuildReadBlockRequest(TagUID,i);
-                       TransmitTo15693Tag(ToSend,ToSendMax,&tsamples, &wait);  
-                       answerLen2 = GetIso15693AnswerFromTag(answer2, 100, &samples, &elapsed);
-                       if (answerLen2>0) {
-                               Dbprintf("READ SINGLE BLOCK %d returned %d octets:",i,answerLen2);
-                               DbdecodeIso15693Answer(answerLen2,answer2);
-                               Dbhexdump(answerLen2,answer2,true);
-                               if ( *((uint32_t*) answer2) == 0x07160101 ) break; // exit on NoPageErr 
-                       } 
-                       i++;
-               } 
+       if (answerLen >= 12 && DEBUG) {
+               for (int i = 0; i < 32; i++) {  // sanity check, assume max 32 pages
+                       BuildReadBlockRequest(TagUID, i);
+                       TransmitTo15693Tag(ToSend, ToSendMax, &start_time);
+                       int answerLen = GetIso15693AnswerFromTag(answer, sizeof(answer), DELAY_ISO15693_VCD_TO_VICC_READER * 2, &eof_time);
+                       start_time = eof_time + DELAY_ISO15693_VICC_TO_VCD_READER;
+                       if (answerLen > 0) {
+                               Dbprintf("READ SINGLE BLOCK %d returned %d octets:", i, answerLen);
+                               DbdecodeIso15693Answer(answerLen, answer);
+                               Dbhexdump(answerLen, answer, false);
+                               if ( *((uint32_t*) answer) == 0x07160101 ) break; // exit on NoPageErr
+                       }
+               }

        }
 
        }
 

-       LED_A_OFF();
-       LED_B_OFF();
-       LED_C_OFF();
+       // for the time being, switch field off to protect rdv4.0
+       // note: this prevents using hf 15 cmd with s option - which isn't implemented yet anyway
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);

        LED_D_OFF();
        LED_D_OFF();

+
+       LED_A_OFF();

 }
 
 }
 

-// Simulate an ISO15693 TAG, perform anti-collision and then print any reader commands
-// all demodulation performed in arm rather than host. - greg
-void SimTagIso15693(uint32_t parameter, uint8_t *uid)
-{
-       LED_A_ON();
-       LED_B_ON();
-       LED_C_OFF();
-       LED_D_OFF();

 
 

-       int answerLen1 = 0;
-       int samples = 0;
-       int tsamples = 0;
-       int wait = 0;
-       int elapsed = 0;
+// Simulate an ISO15693 TAG.
+// For Inventory command: print command and send Inventory Response with given UID
+// TODO: interpret other reader commands and send appropriate response
+void SimTagIso15693(uint32_t parameter, uint8_t *uid) {

 
 

-       FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
+       LED_A_ON();

 
 

-       uint8_t *buf = BigBuf_get_addr() + 4000;
-       memset(buf, 0x00, 100);
-       
+       FpgaDownloadAndGo(FPGA_BITSTREAM_HF);

        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
        SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

-       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_NO_MODULATION);
+       FpgaSetupSsc(FPGA_MAJOR_MODE_HF_SIMULATOR);

 
 

-       // Start from off (no field generated)
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-       SpinDelay(200);
+       StartCountSspClk();

 
 

-       LED_A_OFF();
-       LED_B_OFF();
-       LED_C_ON();
-       LED_D_OFF();
+       uint8_t cmd[ISO15693_MAX_COMMAND_LENGTH];
+
+       // Build a suitable response to the reader INVENTORY command
+       BuildInventoryResponse(uid);

 
        // Listen to reader
 
        // Listen to reader

-       answerLen1 = GetIso15693AnswerFromSniff(buf, 100, &samples, &elapsed) ;
+       while (!BUTTON_PRESS()) {
+               uint32_t eof_time = 0, start_time = 0;
+               int cmd_len = GetIso15693CommandFromReader(cmd, sizeof(cmd), &eof_time);
+
+               if ((cmd_len >= 5) && (cmd[0] & ISO15693_REQ_INVENTORY) && (cmd[1] == ISO15693_INVENTORY)) { // TODO: check more flags
+                       bool slow = !(cmd[0] & ISO15693_REQ_DATARATE_HIGH);
+                       start_time = eof_time + DELAY_ISO15693_VCD_TO_VICC_SIM;
+                       TransmitTo15693Reader(ToSend, ToSendMax, &start_time, 0, slow);
+               }

 
 

-       if (answerLen1 >=1) // we should do a better check than this
-       {
-               // Build a suitable reponse to the reader INVENTORY cocmmand
-               // not so obsvious, but in the call to BuildInventoryResponse,  the command is copied to the global ToSend buffer used below.
-               
-               BuildInventoryResponse(uid);
-       
-               TransmitTo15693Reader(ToSend,ToSendMax, &tsamples, &wait);
+               Dbprintf("%d bytes read from reader:", cmd_len);
+               Dbhexdump(cmd_len, cmd, false);

        }
 
        }
 

-       Dbprintf("%d octets read from reader command: %x %x %x %x %x %x %x %x %x", answerLen1,
-               buf[0], buf[1], buf[2], buf[3],
-               buf[4], buf[5], buf[6], buf[7], buf[8]);
-
-       Dbprintf("Simulationg uid: %x %x %x %x %x %x %x %x",
-               uid[0], uid[1], uid[2], uid[3],
-               uid[4], uid[5], uid[6], uid[7]);
-
-       LED_A_OFF();
-       LED_B_OFF();
-       LED_C_OFF();
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);

        LED_D_OFF();
        LED_D_OFF();

+       LED_A_OFF();

 }
 
 
 // Since there is no standardized way of reading the AFI out of a tag, we will brute force it
 // (some manufactures offer a way to read the AFI, though)
 }
 
 
 // Since there is no standardized way of reading the AFI out of a tag, we will brute force it
 // (some manufactures offer a way to read the AFI, though)

-void BruteforceIso15693Afi(uint32_t speed) 
-{      
-       uint8_t data[20];
-       uint8_t *recv=data;
-       int datalen=0, recvlen=0;
-               
-       Iso15693InitReader();
-       
+void BruteforceIso15693Afi(uint32_t speed)
+{
+       LED_A_ON();
+
+       uint8_t data[6];
+       uint8_t recv[ISO15693_MAX_RESPONSE_LENGTH];
+       int datalen = 0, recvlen = 0;
+       uint32_t eof_time;
+

        // first without AFI
        // first without AFI

-       // Tags should respond wihtout AFI and with AFI=0 even when AFI is active
-       
-       data[0]=ISO15_REQ_SUBCARRIER_SINGLE | ISO15_REQ_DATARATE_HIGH | 
-               ISO15_REQ_INVENTORY | ISO15_REQINV_SLOT1;
-       data[1]=ISO15_CMD_INVENTORY;
-       data[2]=0; // mask length
-       datalen=AddCrc(data,3);
-       recvlen=SendDataTag(data,datalen,0,speed,&recv);
+       // Tags should respond without AFI and with AFI=0 even when AFI is active
+
+       data[0] = ISO15693_REQ_DATARATE_HIGH | ISO15693_REQ_INVENTORY | ISO15693_REQINV_SLOT1;
+       data[1] = ISO15693_INVENTORY;
+       data[2] = 0; // mask length
+       datalen = Iso15693AddCrc(data,3);
+       uint32_t start_time = GetCountSspClk();
+       recvlen = SendDataTag(data, datalen, true, speed, recv, sizeof(recv), 0, &eof_time);
+       start_time = eof_time + DELAY_ISO15693_VICC_TO_VCD_READER;

        WDT_HIT();
        if (recvlen>=12) {
        WDT_HIT();
        if (recvlen>=12) {

-               Dbprintf("NoAFI UID=%s",sprintUID(NULL,&recv[2]));
+               Dbprintf("NoAFI UID=%s", Iso15693sprintUID(NULL, &recv[2]));

        }
        }

-       
+

        // now with AFI
        // now with AFI

-       
-       data[0]=ISO15_REQ_SUBCARRIER_SINGLE | ISO15_REQ_DATARATE_HIGH | 
-               ISO15_REQ_INVENTORY | ISO15_REQINV_AFI | ISO15_REQINV_SLOT1;
-       data[1]=ISO15_CMD_INVENTORY;
-       data[2]=0; // AFI
-       data[3]=0; // mask length
-       
-       for (int i=0;i<256;i++) {
-               data[2]=i & 0xFF;
-               datalen=AddCrc(data,4);
-               recvlen=SendDataTag(data,datalen,0,speed,&recv);
+
+       data[0] = ISO15693_REQ_DATARATE_HIGH | ISO15693_REQ_INVENTORY | ISO15693_REQINV_AFI | ISO15693_REQINV_SLOT1;
+       data[1] = ISO15693_INVENTORY;
+       data[2] = 0; // AFI
+       data[3] = 0; // mask length
+
+       for (int i = 0; i < 256; i++) {
+               data[2] = i & 0xFF;
+               datalen = Iso15693AddCrc(data,4);
+               recvlen = SendDataTag(data, datalen, false, speed, recv, sizeof(recv), start_time, &eof_time);
+               start_time = eof_time + DELAY_ISO15693_VICC_TO_VCD_READER;

                WDT_HIT();
                WDT_HIT();

-               if (recvlen>=12) {
-                       Dbprintf("AFI=%i UID=%s",i,sprintUID(NULL,&recv[2]));
+               if (recvlen >= 12) {
+                       Dbprintf("AFI=%i UID=%s", i, Iso15693sprintUID(NULL, &recv[2]));

                }
                }

-       }       
+       }

        Dbprintf("AFI Bruteforcing done.");
        Dbprintf("AFI Bruteforcing done.");

-       
+
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+       LED_D_OFF();
+       LED_A_OFF();
+

 }
 
 // Allows to directly send commands to the tag via the client
 }
 
 // Allows to directly send commands to the tag via the client

-void DirectTag15693Command(uint32_t datalen,uint32_t speed, uint32_t recv, uint8_t data[]) {
+void DirectTag15693Command(uint32_t datalen, uint32_t speed, uint32_t recv, uint8_t data[]) {
+
+       LED_A_ON();
+
+       int recvlen = 0;
+       uint8_t recvbuf[ISO15693_MAX_RESPONSE_LENGTH];
+       uint32_t eof_time;

 
 

-       int recvlen=0;
-       uint8_t *recvbuf = BigBuf_get_addr();
-//     UsbCommand n;
-       

        if (DEBUG) {
        if (DEBUG) {

-               Dbprintf("SEND");
-               Dbhexdump(datalen,data,true);
+               Dbprintf("SEND:");
+               Dbhexdump(datalen, data, false);

        }
        }

-       
-       recvlen=SendDataTag(data,datalen,1,speed,(recv?&recvbuf:NULL));

 
 

-       if (recv) { 
-               LED_B_ON();
-               cmd_send(CMD_ACK,recvlen>48?48:recvlen,0,0,recvbuf,48);
-               LED_B_OFF();    
-               
+       recvlen = SendDataTag(data, datalen, true, speed, (recv?recvbuf:NULL), sizeof(recvbuf), 0, &eof_time);
+
+       // for the time being, switch field off to protect rdv4.0
+       // note: this prevents using hf 15 cmd with s option - which isn't implemented yet anyway
+       FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+       LED_D_OFF();
+
+       if (recv) {

                if (DEBUG) {
                if (DEBUG) {

-                       Dbprintf("RECV");
-                       DbdecodeIso15693Answer(recvlen,recvbuf); 
-                       Dbhexdump(recvlen,recvbuf,true);
+                       Dbprintf("RECV:");
+                       if (recvlen > 0) {
+                               Dbhexdump(recvlen, recvbuf, false);
+                               DbdecodeIso15693Answer(recvlen, recvbuf);
+                       }
+               }
+               if (recvlen > ISO15693_MAX_RESPONSE_LENGTH) {
+                       recvlen = ISO15693_MAX_RESPONSE_LENGTH;

                }
                }

+               cmd_send(CMD_ACK, recvlen, 0, 0, recvbuf, ISO15693_MAX_RESPONSE_LENGTH);

        }
 
        }
 

+       LED_A_OFF();

 }
 
 }
 

+//-----------------------------------------------------------------------------
+// Work with "magic Chinese" card.
+//
+//-----------------------------------------------------------------------------
+
+// Set the UID to the tag (based on Iceman work).
+void SetTag15693Uid(uint8_t *uid) {
+
+       LED_A_ON();
+
+       uint8_t cmd[4][9] = {0x00};
+       uint16_t crc;
+
+       int recvlen = 0;
+       uint8_t recvbuf[ISO15693_MAX_RESPONSE_LENGTH];
+       uint32_t eof_time;
+
+       // Command 1 : 02213E00000000
+       cmd[0][0] = 0x02;
+       cmd[0][1] = 0x21;
+       cmd[0][2] = 0x3e;
+       cmd[0][3] = 0x00;
+       cmd[0][4] = 0x00;
+       cmd[0][5] = 0x00;
+       cmd[0][6] = 0x00;
+
+       // Command 2 : 02213F69960000
+       cmd[1][0] = 0x02;
+       cmd[1][1] = 0x21;
+       cmd[1][2] = 0x3f;
+       cmd[1][3] = 0x69;
+       cmd[1][4] = 0x96;
+       cmd[1][5] = 0x00;
+       cmd[1][6] = 0x00;
+
+       // Command 3 : 022138u8u7u6u5 (where uX = uid byte X)
+       cmd[2][0] = 0x02;
+       cmd[2][1] = 0x21;
+       cmd[2][2] = 0x38;
+       cmd[2][3] = uid[7];
+       cmd[2][4] = uid[6];
+       cmd[2][5] = uid[5];
+       cmd[2][6] = uid[4];
+
+       // Command 4 : 022139u4u3u2u1 (where uX = uid byte X)
+       cmd[3][0] = 0x02;
+       cmd[3][1] = 0x21;
+       cmd[3][2] = 0x39;
+       cmd[3][3] = uid[3];
+       cmd[3][4] = uid[2];
+       cmd[3][5] = uid[1];
+       cmd[3][6] = uid[0];
+
+       for (int i = 0; i < 4; i++) {
+               // Add the CRC
+               crc = Iso15693Crc(cmd[i], 7);
+               cmd[i][7] = crc & 0xff;
+               cmd[i][8] = crc >> 8;
+
+               if (DEBUG) {
+                       Dbprintf("SEND:");
+                       Dbhexdump(sizeof(cmd[i]), cmd[i], false);
+               }
+
+               recvlen = SendDataTag(cmd[i], sizeof(cmd[i]), true, 1, recvbuf, sizeof(recvbuf), 0, &eof_time);
+
+               if (DEBUG) {
+                       Dbprintf("RECV:");
+                       if (recvlen > 0) {
+                               Dbhexdump(recvlen, recvbuf, false);
+                               DbdecodeIso15693Answer(recvlen, recvbuf);
+                       }
+               }
+
+               cmd_send(CMD_ACK, recvlen>ISO15693_MAX_RESPONSE_LENGTH?ISO15693_MAX_RESPONSE_LENGTH:recvlen, 0, 0, recvbuf, ISO15693_MAX_RESPONSE_LENGTH);
+       }
+
+       LED_A_OFF();
+}

 
 
 
 
 
 


@@ -1149,8 +1776,8 @@ static void __attribute__((unused)) BuildSysInfoRequest(uint8_t *uid)
        uint8_t cmd[12];
 
        uint16_t crc;
        uint8_t cmd[12];
 
        uint16_t crc;

-       // If we set the Option_Flag in this request, the VICC will respond with the secuirty status of the block
-       // followed by teh block data
+       // If we set the Option_Flag in this request, the VICC will respond with the security status of the block
+       // followed by the block data

        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =  (1 << 5) | (1 << 1); // no SELECT bit
        // System Information command code
        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =  (1 << 5) | (1 << 1); // no SELECT bit
        // System Information command code


@@ -1166,7 +1793,7 @@ static void __attribute__((unused)) BuildSysInfoRequest(uint8_t *uid)
        cmd[8] = 0x05;
        cmd[9]= 0xe0; // always e0 (not exactly unique)
        //Now the CRC
        cmd[8] = 0x05;
        cmd[9]= 0xe0; // always e0 (not exactly unique)
        //Now the CRC

-       crc = Crc(cmd, 10); // the crc needs to be calculated over 2 bytes
+       crc = Iso15693Crc(cmd, 10); // the crc needs to be calculated over 2 bytes

        cmd[10] = crc & 0xff;
        cmd[11] = crc >> 8;
 
        cmd[10] = crc & 0xff;
        cmd[11] = crc >> 8;
 


@@ -1180,8 +1807,8 @@ static void __attribute__((unused)) BuildReadMultiBlockRequest(uint8_t *uid)
        uint8_t cmd[14];
 
        uint16_t crc;
        uint8_t cmd[14];
 
        uint16_t crc;

-       // If we set the Option_Flag in this request, the VICC will respond with the secuirty status of the block
-       // followed by teh block data
+       // If we set the Option_Flag in this request, the VICC will respond with the security status of the block
+       // followed by the block data

        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =  (1 << 5) | (1 << 1); // no SELECT bit
        // READ Multi BLOCK command code
        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =  (1 << 5) | (1 << 1); // no SELECT bit
        // READ Multi BLOCK command code


@@ -1201,7 +1828,7 @@ static void __attribute__((unused)) BuildReadMultiBlockRequest(uint8_t *uid)
        // Number of Blocks to read
        cmd[11] = 0x2f; // read quite a few
        //Now the CRC
        // Number of Blocks to read
        cmd[11] = 0x2f; // read quite a few
        //Now the CRC

-       crc = Crc(cmd, 12); // the crc needs to be calculated over 2 bytes
+       crc = Iso15693Crc(cmd, 12); // the crc needs to be calculated over 2 bytes

        cmd[12] = crc & 0xff;
        cmd[13] = crc >> 8;
 
        cmd[12] = crc & 0xff;
        cmd[13] = crc >> 8;
 


@@ -1214,8 +1841,8 @@ static void __attribute__((unused)) BuildArbitraryRequest(uint8_t *uid,uint8_t C
        uint8_t cmd[14];
 
        uint16_t crc;
        uint8_t cmd[14];
 
        uint16_t crc;

-       // If we set the Option_Flag in this request, the VICC will respond with the secuirty status of the block
-       // followed by teh block data
+       // If we set the Option_Flag in this request, the VICC will respond with the security status of the block
+       // followed by the block data

        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =   (1 << 5) | (1 << 1); // no SELECT bit
        // READ BLOCK command code
        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =   (1 << 5) | (1 << 1); // no SELECT bit
        // READ BLOCK command code


@@ -1234,9 +1861,9 @@ static void __attribute__((unused)) BuildArbitraryRequest(uint8_t *uid,uint8_t C
        cmd[10] = 0x00;
        cmd[11] = 0x0a;
 
        cmd[10] = 0x00;
        cmd[11] = 0x0a;
 

-//     cmd[12] = 0x00;
-//     cmd[13] = 0x00; //Now the CRC
-       crc = Crc(cmd, 12); // the crc needs to be calculated over 2 bytes
+//  cmd[12] = 0x00;
+//  cmd[13] = 0x00; //Now the CRC
+       crc = Iso15693Crc(cmd, 12); // the crc needs to be calculated over 2 bytes

        cmd[12] = crc & 0xff;
        cmd[13] = crc >> 8;
 
        cmd[12] = crc & 0xff;
        cmd[13] = crc >> 8;
 


@@ -1249,8 +1876,8 @@ static void __attribute__((unused)) BuildArbitraryCustomRequest(uint8_t uid[], u
        uint8_t cmd[14];
 
        uint16_t crc;
        uint8_t cmd[14];
 
        uint16_t crc;

-       // If we set the Option_Flag in this request, the VICC will respond with the secuirty status of the block
-       // followed by teh block data
+       // If we set the Option_Flag in this request, the VICC will respond with the security status of the block
+       // followed by the block data

        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =   (1 << 5) | (1 << 1); // no SELECT bit
        // READ BLOCK command code
        // one sub-carrier, inventory, 1 slot, fast rate
        cmd[0] =   (1 << 5) | (1 << 1); // no SELECT bit
        // READ BLOCK command code


@@ -1266,12 +1893,12 @@ static void __attribute__((unused)) BuildArbitraryCustomRequest(uint8_t uid[], u
        cmd[8] = 0x05;
        cmd[9]= 0xe0; // always e0 (not exactly unique)
        // Parameter
        cmd[8] = 0x05;
        cmd[9]= 0xe0; // always e0 (not exactly unique)
        // Parameter

-       cmd[10] = 0x05; // for custom codes this must be manufcturer code
+       cmd[10] = 0x05; // for custom codes this must be manufacturer code

        cmd[11] = 0x00;
 
        cmd[11] = 0x00;
 

-//     cmd[12] = 0x00;
-//     cmd[13] = 0x00; //Now the CRC
-       crc = Crc(cmd, 12); // the crc needs to be calculated over 2 bytes
+//  cmd[12] = 0x00;
+//  cmd[13] = 0x00; //Now the CRC
+       crc = Iso15693Crc(cmd, 12); // the crc needs to be calculated over 2 bytes

        cmd[12] = crc & 0xff;
        cmd[13] = crc >> 8;
 
        cmd[12] = crc & 0xff;
        cmd[13] = crc >> 8;