usb communication (device side) housekeeping

[proxmark3-svn] / armsrc / legicrf.c

diff --git a/armsrc/legicrf.c b/armsrc/legicrf.c
index f2eb680b4adc66a185f12f81f0b7a9eb7444fd6e..3bc09732d1a231b4de22456a5af02bc7b7de1c27 100644 (file)
--- a/armsrc/legicrf.c
+++ b/armsrc/legicrf.c
@@ -1,5 +1,7 @@
 //-----------------------------------------------------------------------------
 // (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
 //-----------------------------------------------------------------------------
 // (c) 2009 Henryk Plötz <henryk@ploetzli.ch>

+//     2016 Iceman
+//     2018 AntiCat

 //
 // 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
 //
 // 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


@@ -8,745 +10,449 @@
 // LEGIC RF simulation code
 //-----------------------------------------------------------------------------
 
 // LEGIC RF simulation code
 //-----------------------------------------------------------------------------
 

+#include "legicrf.h"
+

 #include "proxmark3.h"
 #include "apps.h"
 #include "proxmark3.h"
 #include "apps.h"

+#include "cmd.h"

 #include "util.h"
 #include "string.h"
 #include "util.h"
 #include "string.h"

-
-#include "legicrf.h"

 #include "legic_prng.h"
 #include "legic_prng.h"

+#include "legic.h"

 #include "crc.h"
 #include "crc.h"

+#include "fpgaloader.h"
+
+static legic_card_select_t card;/* metadata of currently selected card */
+static crc_t legic_crc;
+
+//-----------------------------------------------------------------------------
+// Frame timing and pseudorandom number generator
+//
+// The Prng is forwarded every 100us (TAG_BIT_PERIOD), except when the reader is
+// transmitting. In that case the prng has to be forwarded every bit transmitted:
+//  - 60us for a 0 (RWD_TIME_0)
+//  - 100us for a 1 (RWD_TIME_1)
+//
+// The data dependent timing makes writing comprehensible code significantly
+// harder. The current aproach forwards the prng data based if there is data on
+// air and time based, using GET_TICKS, during computational and wait periodes.
+//
+// To not have the necessity to calculate/guess exection time dependend timeouts
+// tx_frame and rx_frame use a shared timestamp to coordinate tx and rx timeslots.
+//-----------------------------------------------------------------------------
+
+static uint32_t last_frame_end; /* ts of last bit of previews rx or tx frame */

 
 

-static struct legic_frame {
-       int bits;
-       uint32_t data;
-} current_frame;
-
-static enum {
-  STATE_DISCON,
-  STATE_IV,
-  STATE_CON,
-} legic_state;
-
-static crc_t    legic_crc;
-static int      legic_read_count;
-static uint32_t legic_prng_bc;
-static uint32_t legic_prng_iv;
-
-static int      legic_phase_drift;
-static int      legic_frame_drift;
-static int      legic_reqresp_drift;
-
-AT91PS_TC timer;
-AT91PS_TC prng_timer;
-
-static void setup_timer(void)
-{
-       /* Set up Timer 1 to use for measuring time between pulses. Since we're bit-banging
-        * this it won't be terribly accurate but should be good enough.
-        */
-       AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC1);
-       timer = AT91C_BASE_TC1;
-       timer->TC_CCR = AT91C_TC_CLKDIS;
-       timer->TC_CMR = AT91C_TC_CLKS_TIMER_DIV3_CLOCK;
-       timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
-
-       /* 
-     * Set up Timer 2 to use for measuring time between frames in 
-     * tag simulation mode. Runs 4x faster as Timer 1
-        */
-    AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC2);
-    prng_timer = AT91C_BASE_TC2;
-    prng_timer->TC_CCR = AT91C_TC_CLKDIS;
-       prng_timer->TC_CMR = AT91C_TC_CLKS_TIMER_DIV2_CLOCK;
-    prng_timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
+#define RWD_TIME_PAUSE       30 /* 20us */
+#define RWD_TIME_1          150 /* READER_TIME_PAUSE 20us off + 80us on = 100us */
+#define RWD_TIME_0           90 /* READER_TIME_PAUSE 20us off + 40us on = 60us */
+#define RWD_FRAME_WAIT      330 /* 220us from TAG frame end to READER frame start */
+#define TAG_FRAME_WAIT      495 /* 330us from READER frame end to TAG frame start */
+#define TAG_BIT_PERIOD      150 /* 100us */
+#define TAG_WRITE_TIMEOUT    60 /* 40 * 100us (write should take at most 3.6ms) */
+
+#define LEGIC_READ         0x01 /* Read Command */
+#define LEGIC_WRITE        0x00 /* Write Command */
+
+#define SESSION_IV         0x55 /* An arbitrary chose session IV, all shoud work */
+#define OFFSET_LOG         1024 /* The largest Legic Prime card is 1k */
+#define WRITE_LOWERLIMIT      4 /* UID and MCC are not writable */
+
+#define INPUT_THRESHOLD       8 /* heuristically determined, lower values */
+                                /* lead to detecting false ack during write */
+
+//-----------------------------------------------------------------------------
+// I/O interface abstraction (FPGA -> ARM)
+//-----------------------------------------------------------------------------
+
+static inline uint16_t rx_frame_from_fpga() {
+  for(;;) {
+    WDT_HIT();
+
+    // wait for frame be become available in rx holding register
+    if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+      return AT91C_BASE_SSC->SSC_RHR;
+    }
+  }

 }
 
 }
 

-/* At TIMER_CLOCK3 (MCK/32) */
-#define        RWD_TIME_1 150     /* RWD_TIME_PAUSE off, 80us on = 100us */
-#define RWD_TIME_0 90      /* RWD_TIME_PAUSE off, 40us on = 60us */
-#define RWD_TIME_PAUSE 30  /* 20us */
-#define RWD_TIME_FUZZ 20   /* rather generous 13us, since the peak detector + hysteresis fuzz quite a bit */
-#define TAG_TIME_BIT 150   /* 100us for every bit */
-#define TAG_TIME_WAIT 490  /* time from RWD frame end to tag frame start, experimentally determined */
-
-#define SIM_DIVISOR  586   /* prng_time/SIM_DIVISOR count prng needs to be forwared */
-#define SIM_SHIFT    900   /* prng_time+SIM_SHIFT shift of delayed start */
-
-#define SESSION_IV 0x55
-#define OFFSET_LOG 1024
-
-#define FUZZ_EQUAL(value, target, fuzz) ((value) > ((target)-(fuzz)) && (value) < ((target)+(fuzz)))
-
-/* Generate Keystream */
-static uint32_t get_key_stream(int skip, int count)
-{
-  uint32_t key=0; int i;
-
-  /* Use int to enlarge timer tc to 32bit */
-  legic_prng_bc += prng_timer->TC_CV;
-  prng_timer->TC_CCR = AT91C_TC_SWTRG;
-
-  /* If skip == -1, forward prng time based */
-  if(skip == -1) {
-     i  = (legic_prng_bc+SIM_SHIFT)/SIM_DIVISOR; /* Calculate Cycles based on timer */
-     i -= legic_prng_count(); /* substract cycles of finished frames */
-     i -= count; /* substract current frame length, rewidn to bedinning */
-     legic_prng_forward(i);
-  } else {
-     legic_prng_forward(skip);
+//-----------------------------------------------------------------------------
+// Demodulation (Reader)
+//-----------------------------------------------------------------------------
+
+// Returns a demedulated bit
+//
+// The FPGA running xcorrelation samples the subcarrier at ~13.56 MHz. The mode
+// was initialy designed to receive BSPK/2-PSK. Hance, it reports an I/Q pair
+// every 4.7us (8 bits i and 8 bits q).
+//
+// The subcarrier amplitude can be calculated using Pythagoras sqrt(i^2 + q^2).
+// To reduce CPU time the amplitude is approximated by using linear functions:
+//   am = MAX(ABS(i),ABS(q)) + 1/2*MIN(ABS(i),ABSq))
+//
+// The bit time is 99.1us (21 I/Q pairs). The receiver skips the first 5 samples
+// and averages the next (most stable) 8 samples. The final 8 samples are dropped
+// also.
+//
+// The demodulated should be alligned to the bit period by the caller. This is
+// done in rx_bit and rx_ack.
+static inline bool rx_bit() {
+  int32_t sum_cq = 0;
+  int32_t sum_ci = 0;
+
+  // skip first 5 I/Q pairs
+  for(size_t i = 0; i<5; ++i) {
+    (void)rx_frame_from_fpga();

   }
 
   }
 

-  /* Write Time Data into LOG */
-  if(count == 6) { i = -1; } else { i = legic_read_count; }
-  ((uint8_t*)BigBuf)[OFFSET_LOG+128+i] = legic_prng_count();
-  ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4]   = (legic_prng_bc >> 0) & 0xff;
-  ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4+1] = (legic_prng_bc >> 8) & 0xff;
-  ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4+2] = (legic_prng_bc >>16) & 0xff;
-  ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4+3] = (legic_prng_bc >>24) & 0xff;
-  ((uint8_t*)BigBuf)[OFFSET_LOG+384+i] = count;
-
-  /* Generate KeyStream */
-  for(i=0; i<count; i++) {
-    key |= legic_prng_get_bit() << i;
-    legic_prng_forward(1);
+  // sample next 8 I/Q pairs
+  for(size_t i = 0; i<8; ++i) {
+    uint16_t iq = rx_frame_from_fpga();
+    int8_t ci = (int8_t)(iq >> 8);
+    int8_t cq = (int8_t)(iq & 0xff);
+    sum_ci += ci;
+    sum_cq += cq;

   }
   }

-  return key;
-}

 
 

-/* Send a frame in tag mode, the FPGA must have been set up by
- * LegicRfSimulate
- */
-static void frame_send_tag(uint16_t response, int bits, int crypt)
-{
-   /* Bitbang the response */
-   AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
-   AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
-   AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
-        
-   /* Use time to crypt frame */
-   if(crypt) {
-      legic_prng_forward(2); /* TAG_TIME_WAIT -> shift by 2 */
-      int i; int key = 0;
-      for(i=0; i<bits; i++) {
-         key |= legic_prng_get_bit() << i;
-         legic_prng_forward(1);
-      }
-      //Dbprintf("key = 0x%x", key);
-      response = response ^ key;
-   }
-
-   /* Wait for the frame start */
-   while(timer->TC_CV < (TAG_TIME_WAIT - 30)) ;
-       
-   int i;
-   for(i=0; i<bits; i++) {
-      int nextbit = timer->TC_CV + TAG_TIME_BIT;
-      int bit = response & 1;
-      response = response >> 1;
-      if(bit) {
-         AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
-      } else {
-         AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
-      }
-      while(timer->TC_CV < nextbit) ;
-   }
-   AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
-}
+  // calculate power
+  int32_t power = (MAX(ABS(sum_ci), ABS(sum_cq)) + MIN(ABS(sum_ci), ABS(sum_cq))/2);

 
 

-/* Send a frame in reader mode, the FPGA must have been set up by
- * LegicRfReader
- */
-static void frame_send_rwd(uint32_t data, int bits)
-{
-       /* Start clock */
-       timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
-       while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
-
-       int i;
-       for(i=0; i<bits; i++) {
-               int starttime = timer->TC_CV;
-               int pause_end = starttime + RWD_TIME_PAUSE, bit_end;
-               int bit = data & 1;
-               data = data >> 1;
-
-               if(bit ^ legic_prng_get_bit()) {
-                       bit_end = starttime + RWD_TIME_1;
-               } else {
-                       bit_end = starttime + RWD_TIME_0;
-               }
-
-               /* RWD_TIME_PAUSE time off, then some time on, so that the complete bit time is
-                * RWD_TIME_x, where x is the bit to be transmitted */
-               AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
-               while(timer->TC_CV < pause_end) ;
-               AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
-               legic_prng_forward(1); /* bit duration is longest. use this time to forward the lfsr */
-
-               while(timer->TC_CV < bit_end) ;
-       }
-
-       {
-               /* One final pause to mark the end of the frame */
-               int pause_end = timer->TC_CV + RWD_TIME_PAUSE;
-               AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
-               while(timer->TC_CV < pause_end) ;
-               AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
-       }
-
-       /* Reset the timer, to measure time until the start of the tag frame */
-       timer->TC_CCR = AT91C_TC_SWTRG;
-       while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
+  // compare average (power / 8) to threshold
+  return ((power >> 3) > INPUT_THRESHOLD);

 }
 
 }
 

-/* Receive a frame from the card in reader emulation mode, the FPGA and
- * timer must have been set up by LegicRfReader and frame_send_rwd.
- *
- * The LEGIC RF protocol from card to reader does not include explicit
- * frame start/stop information or length information. The reader must
- * know beforehand how many bits it wants to receive. (Notably: a card
- * sending a stream of 0-bits is indistinguishable from no card present.)
- *
- * Receive methodology: There is a fancy correlator in hi_read_rx_xcorr, but
- * I'm not smart enough to use it. Instead I have patched hi_read_tx to output
- * the ADC signal with hysteresis on SSP_DIN. Bit-bang that signal and look
- * for edges. Count the edges in each bit interval. If they are approximately
- * 0 this was a 0-bit, if they are approximately equal to the number of edges
- * expected for a 212kHz subcarrier, this was a 1-bit. For timing we use the
- * timer that's still running from frame_send_rwd in order to get a synchronization
- * with the frame that we just sent.
- *
- * FIXME: Because we're relying on the hysteresis to just do the right thing
- * the range is severely reduced (and you'll probably also need a good antenna).
- * So this should be fixed some time in the future for a proper receiver.
- */
-static void frame_receive_rwd(struct legic_frame * const f, int bits, int crypt)
-{
-       uint32_t the_bit = 1;  /* Use a bitmask to save on shifts */
-       uint32_t data=0;
-       int i, old_level=0, edges=0;
-       int next_bit_at = TAG_TIME_WAIT;
-       
-       if(bits > 32) {
-               bits = 32;
-    }
+//-----------------------------------------------------------------------------
+// Modulation (Reader)
+//
+// I've tried to modulate the Legic specific pause-puls using ssc and the default
+// ssc clock of 105.4 kHz (bit periode of 9.4us) - previous commit. However,
+// the timing was not precise enough. By increasing the ssc clock this could
+// be circumvented, but the adventage over bitbang would be little.
+//-----------------------------------------------------------------------------

 
 

-       AT91C_BASE_PIOA->PIO_ODR = GPIO_SSC_DIN;
-       AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DIN;
-
-       /* we have some time now, precompute the cipher
-     * since we cannot compute it on the fly while reading */
-       legic_prng_forward(2);
-
-       if(crypt)
-       {
-               for(i=0; i<bits; i++) {
-                       data |= legic_prng_get_bit() << i;
-                       legic_prng_forward(1);
-               }
-       }
-
-       while(timer->TC_CV < next_bit_at) ;
-
-       next_bit_at += TAG_TIME_BIT;
-
-       for(i=0; i<bits; i++) {
-               edges = 0;
-               while(timer->TC_CV < next_bit_at) {
-                       int level = (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_DIN);
-                       if(level != old_level)
-                               edges++;
-                       old_level = level;
-               }
-               next_bit_at += TAG_TIME_BIT;
-               
-               if(edges > 20 && edges < 60) { /* expected are 42 edges */
-                       data ^= the_bit;
-               }
-               the_bit <<= 1;
-       }
-
-       f->data = data;
-       f->bits = bits;
-
-       /* Reset the timer, to synchronize the next frame */
-       timer->TC_CCR = AT91C_TC_SWTRG;
-       while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
-}
+static inline void tx_bit(bool bit) {
+  // insert pause
+  HIGH(GPIO_SSC_DOUT);
+  last_frame_end += RWD_TIME_PAUSE;
+  while(GET_TICKS < last_frame_end) { };

 
 

-static void frame_append_bit(struct legic_frame * const f, int bit)
-{
-   if(f->bits >= 31) {
-       return; /* Overflow, won't happen */
-   }
-   f->data |= (bit<<f->bits);
-   f->bits++;
+  // return to carrier on, wait for bit periode to end
+  LOW(GPIO_SSC_DOUT);
+  last_frame_end += (bit ? RWD_TIME_1 : RWD_TIME_0) - RWD_TIME_PAUSE;
+  while(GET_TICKS < last_frame_end) { };

 }
 
 }
 

-static void frame_clean(struct legic_frame * const f)
-{
-       f->data = 0;
-       f->bits = 0;
+//-----------------------------------------------------------------------------
+// Frame Handling (Reader)
+//
+// The LEGIC RF protocol from card to reader does not include explicit frame
+// start/stop information or length information. The reader must know beforehand
+// how many bits it wants to receive.
+// Notably: a card sending a stream of 0-bits is indistinguishable from no card
+// present.
+//-----------------------------------------------------------------------------
+
+static void tx_frame(uint32_t frame, uint8_t len) {
+  FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_MODE_SEND_FULL_MOD);
+
+  // wait for next tx timeslot
+  last_frame_end += RWD_FRAME_WAIT;
+  while(GET_TICKS < last_frame_end) { };
+
+  // transmit frame, MSB first
+  for(uint8_t i = 0; i < len; ++i) {
+    bool bit = (frame >> i) & 0x01;
+    tx_bit(bit ^ legic_prng_get_bit());
+    legic_prng_forward(1);
+  };
+
+  // add pause to mark end of the frame
+  HIGH(GPIO_SSC_DOUT);
+  last_frame_end += RWD_TIME_PAUSE;
+  while(GET_TICKS < last_frame_end) { };
+  LOW(GPIO_SSC_DOUT);

 }
 
 }
 

-static uint32_t perform_setup_phase_rwd(int iv)
-{
+static uint32_t rx_frame(uint8_t len) {
+  FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_212_KHZ | FPGA_HF_READER_MODE_RECEIVE_IQ);

 
 

-       /* Switch on carrier and let the tag charge for 1ms */
-       AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
-       SpinDelay(1);
+  // hold sampling until card is expected to respond
+  last_frame_end += TAG_FRAME_WAIT;
+  while(GET_TICKS < last_frame_end) { };

 
 

-       legic_prng_init(0); /* no keystream yet */
-       frame_send_rwd(iv, 7);
-       legic_prng_init(iv);
+  uint32_t frame = 0;
+  for(uint8_t i = 0; i < len; ++i) {
+    frame |= (rx_bit() ^ legic_prng_get_bit()) << i;
+    legic_prng_forward(1);

 
 

-       frame_clean(&current_frame);
-       frame_receive_rwd(&current_frame, 6, 1);
-       legic_prng_forward(1); /* we wait anyways */
-       while(timer->TC_CV < 387) ; /* ~ 258us */
-       frame_send_rwd(0x19, 6);
+    // rx_bit runs only 95us, resync to TAG_BIT_PERIOD
+    last_frame_end += TAG_BIT_PERIOD;
+    while(GET_TICKS < last_frame_end) { };
+  }

 
 

-       return current_frame.data;
+  return frame;

 }
 
 }
 

-static void LegicCommonInit(void) {
-       SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
-       FpgaSetupSsc();
-       FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
+static bool rx_ack() {
+  // change fpga into rx mode
+  FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_212_KHZ | FPGA_HF_READER_MODE_RECEIVE_IQ);

 
 

-       /* Bitbang the transmitter */
-       AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
-       AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
-       AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
+  // hold sampling until card is expected to respond
+  last_frame_end += TAG_FRAME_WAIT;
+  while(GET_TICKS < last_frame_end) { };

 
 

-       setup_timer();
+  uint32_t ack = 0;
+  for(uint8_t i = 0; i < TAG_WRITE_TIMEOUT; ++i) {
+    // sample bit
+    ack = rx_bit();
+    legic_prng_forward(1);

 
 

-       crc_init(&legic_crc, 4, 0x19 >> 1, 0x5, 0);
-}
+    // rx_bit runs only 95us, resync to TAG_BIT_PERIOD
+    last_frame_end += TAG_BIT_PERIOD;
+    while(GET_TICKS < last_frame_end) { };

 
 

-static void switch_off_tag_rwd(void)
-{
-       /* Switch off carrier, make sure tag is reset */
-       AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
-       SpinDelay(10);
+    // check if it was an ACK
+    if(ack) {
+      break;
+    }
+  }

 
 

-       WDT_HIT();
-}
-/* calculate crc for a legic command */
-static int LegicCRC(int byte_index, int value, int cmd_sz) {
-       crc_clear(&legic_crc);
-       crc_update(&legic_crc, 1, 1); /* CMD_READ */
-       crc_update(&legic_crc, byte_index, cmd_sz-1);
-       crc_update(&legic_crc, value, 8);
-       return crc_finish(&legic_crc);
+  return ack;

 }
 
 }
 

-int legic_read_byte(int byte_index, int cmd_sz) {
-       int byte;
+//-----------------------------------------------------------------------------
+// Legic Reader
+//-----------------------------------------------------------------------------
+
+static int init_card(uint8_t cardtype, legic_card_select_t *p_card) {
+  p_card->tagtype = cardtype;
+
+  switch(p_card->tagtype) {
+    case 0x0d:
+      p_card->cmdsize = 6;
+      p_card->addrsize = 5;
+      p_card->cardsize = 22;
+      break;
+    case 0x1d:
+      p_card->cmdsize = 9;
+      p_card->addrsize = 8;
+      p_card->cardsize = 256;
+      break;
+    case 0x3d:
+      p_card->cmdsize = 11;
+      p_card->addrsize = 10;
+      p_card->cardsize = 1024;
+      break;
+    default:
+      p_card->cmdsize = 0;
+      p_card->addrsize = 0;
+      p_card->cardsize = 0;
+      return 2;
+  }
+  return 0;
+}

 
 

-       legic_prng_forward(4); /* we wait anyways */
-       while(timer->TC_CV < 387) ; /* ~ 258us + 100us*delay */
+static void init_reader(bool clear_mem) {
+  // configure FPGA
+  FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
+  FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_212_KHZ | FPGA_HF_READER_MODE_RECEIVE_IQ);
+  SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
+  LED_D_ON();

 
 

-       frame_send_rwd(1 | (byte_index << 1), cmd_sz);
-       frame_clean(&current_frame);
+  // configure SSC with defaults
+  FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER);

 
 

-       frame_receive_rwd(&current_frame, 12, 1);
+  // re-claim GPIO_SSC_DOUT as GPIO and enable output
+  AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
+  AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
+  LOW(GPIO_SSC_DOUT);

 
 

-       byte = current_frame.data & 0xff;
-       if( LegicCRC(byte_index, byte, cmd_sz) != (current_frame.data >> 8) ) {
-               Dbprintf("!!! crc mismatch: expected %x but got %x !!!", 
-           LegicCRC(byte_index, current_frame.data & 0xff, cmd_sz), current_frame.data >> 8);
-               return -1;
-       }
+  // init crc calculator
+  crc_init(&legic_crc, 4, 0x19 >> 1, 0x05, 0);

 
 

-       return byte;
+  // start us timer
+  StartTicks();

 }
 
 }
 

-/* legic_write_byte() is not included, however it's trivial to implement
- * and here are some hints on what remains to be done:
- *
- *  * assemble a write_cmd_frame with crc and send it
- *  * wait until the tag sends back an ACK ('1' bit unencrypted)
- *  * forward the prng based on the timing
- */
-int legic_write_byte(int byte, int addr, int addr_sz) {
-    //do not write UID, CRC, DCF
-    if(addr <= 0x06) { 
-               return 0;
-       }
-
-       //== send write command ==============================
-       crc_clear(&legic_crc);
-       crc_update(&legic_crc, 0, 1); /* CMD_WRITE */
-       crc_update(&legic_crc, addr, addr_sz);
-       crc_update(&legic_crc, byte, 8);
-
-       uint32_t crc = crc_finish(&legic_crc);
-       uint32_t cmd = ((crc     <<(addr_sz+1+8)) //CRC
-                   |(byte    <<(addr_sz+1))   //Data
-                   |(addr    <<1)             //Address
-                   |(0x00    <<0));           //CMD = W
-    uint32_t cmd_sz = addr_sz+1+8+4;          //crc+data+cmd
-
-    legic_prng_forward(2); /* we wait anyways */
-    while(timer->TC_CV < 387) ; /* ~ 258us */
-       frame_send_rwd(cmd, cmd_sz);
-
-       //== wait for ack ====================================
-    int t, old_level=0, edges=0;
-    int next_bit_at =0;
-       while(timer->TC_CV < 387) ; /* ~ 258us */
-    for(t=0; t<80; t++) {
-        edges = 0;
-               next_bit_at += TAG_TIME_BIT;
-        while(timer->TC_CV < next_bit_at) {
-            int level = (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_DIN);
-            if(level != old_level) {
-                edges++;
-                       }
-            old_level = level;
-        }
-        if(edges > 20 && edges < 60) { /* expected are 42 edges */
-                       int t = timer->TC_CV;
-                       int c = t/TAG_TIME_BIT;
-                       timer->TC_CCR = AT91C_TC_SWTRG;
-                       while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
-                       legic_prng_forward(c);
-               return 0;
-        }
-    }
-    timer->TC_CCR = AT91C_TC_SWTRG;
-    while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
-       return -1;
+// Setup reader to card connection
+//
+// The setup consists of a three way handshake:
+//  - Transmit initialisation vector 7 bits
+//  - Receive card type 6 bits
+//  - Transmit Acknowledge 6 bits
+static uint32_t setup_phase(uint8_t iv) {
+  // init coordination timestamp
+  last_frame_end = GET_TICKS;
+
+  // Switch on carrier and let the card charge for 5ms.
+  last_frame_end += 7500;
+  while(GET_TICKS < last_frame_end) { };
+
+  legic_prng_init(0);
+  tx_frame(iv, 7);
+
+  // configure prng
+  legic_prng_init(iv);
+  legic_prng_forward(2);
+
+  // receive card type
+  int32_t card_type = rx_frame(6);
+  legic_prng_forward(3);
+
+  // send obsfuscated acknowledgment frame
+  switch (card_type) {
+    case 0x0D:
+      tx_frame(0x19, 6); // MIM22 | READCMD = 0x18 | 0x01
+      break;
+    case 0x1D:
+    case 0x3D:
+      tx_frame(0x39, 6); // MIM256 | READCMD = 0x38 | 0x01
+      break;
+  }
+
+  return card_type;

 }
 
 }
 

-int LegicRfReader(int offset, int bytes) {
-       int byte_index=0, cmd_sz=0, card_sz=0;
-
-       LegicCommonInit();
-
-       memset(BigBuf, 0, 1024);
-
-       DbpString("setting up legic card");
-       uint32_t tag_type = perform_setup_phase_rwd(SESSION_IV);
-       switch_off_tag_rwd(); //we lose to mutch time with dprintf
-       switch(tag_type) {
-               case 0x1d:
-                       DbpString("MIM 256 card found, reading card ...");
-            cmd_sz = 9;
-                       card_sz = 256;
-                       break;
-               case 0x3d:
-                       DbpString("MIM 1024 card found, reading card ...");
-            cmd_sz = 11;
-                       card_sz = 1024;
-                       break;
-               default:
-                       Dbprintf("Unknown card format: %x",tag_type);
-                       return -1;
-       }
-       if(bytes == -1) {
-               bytes = card_sz;
-       }
-       if(bytes+offset >= card_sz) {
-               bytes = card_sz-offset;
-       }
-
-       perform_setup_phase_rwd(SESSION_IV);
-
-       LED_B_ON();
-       while(byte_index < bytes) {
-               int r = legic_read_byte(byte_index+offset, cmd_sz);
-               if(r == -1 ||BUTTON_PRESS()) {
-               DbpString("operation aborted");
-                       switch_off_tag_rwd();
-               LED_B_OFF();
-                       LED_C_OFF();
-               return -1;
-               }
-               ((uint8_t*)BigBuf)[byte_index] = r;
-        WDT_HIT();
-               byte_index++;
-               if(byte_index & 0x10) LED_C_ON(); else LED_C_OFF();
-       }
-       LED_B_OFF();
-    LED_C_OFF();
-       switch_off_tag_rwd();
-       Dbprintf("Card read, use 'hf legic decode' or");
-    Dbprintf("'data hexsamples %d' to view results", (bytes+7) & ~7);
-    return 0;
+static uint8_t calc_crc4(uint16_t cmd, uint8_t cmd_sz, uint8_t value) {
+  crc_clear(&legic_crc);
+  crc_update(&legic_crc, (value << cmd_sz) | cmd, 8 + cmd_sz);
+  return crc_finish(&legic_crc);

 }
 
 }
 

-void LegicRfWriter(int bytes, int offset) {
-       int byte_index=0, addr_sz=0;
-       
-       LegicCommonInit();
-       
-       DbpString("setting up legic card");
-       uint32_t tag_type = perform_setup_phase_rwd(SESSION_IV);
-       switch_off_tag_rwd();
-       switch(tag_type) {
-               case 0x1d:
-                       if(offset+bytes > 0x100) {
-                               Dbprintf("Error: can not write to 0x%03.3x on MIM 256", offset+bytes);
-                               return;
-                       }
-                       addr_sz = 8;
-                       Dbprintf("MIM 256 card found, writing 0x%02.2x - 0x%02.2x ...", offset, offset+bytes);
-                       break;
-               case 0x3d:
-                       if(offset+bytes > 0x400) {
-                       Dbprintf("Error: can not write to 0x%03.3x on MIM 1024", offset+bytes);
-                       return;
-               }
-                       addr_sz = 10;
-                       Dbprintf("MIM 1024 card found, writing 0x%03.3x - 0x%03.3x ...", offset, offset+bytes);
-                       break;
-               default:
-                       Dbprintf("No or unknown card found, aborting");
-            return;
-       }
-
-    LED_B_ON();
-       perform_setup_phase_rwd(SESSION_IV);
-    legic_prng_forward(2);
-       while(byte_index < bytes) {
-               int r = legic_write_byte(((uint8_t*)BigBuf)[byte_index+offset], byte_index+offset, addr_sz);
-               if((r != 0) || BUTTON_PRESS()) {
-                       Dbprintf("operation aborted @ 0x%03.3x", byte_index);
-                       switch_off_tag_rwd();
-                       LED_B_OFF();
-                       LED_C_OFF();
-                       return;
-               }
-        WDT_HIT();
-               byte_index++;
-        if(byte_index & 0x10) LED_C_ON(); else LED_C_OFF();
-       }
-    LED_B_OFF();
-    LED_C_OFF();
-    DbpString("write successful");
+static int16_t read_byte(uint16_t index, uint8_t cmd_sz) {
+  uint16_t cmd = (index << 1) | LEGIC_READ;
+
+  // read one byte
+  LED_B_ON();
+  legic_prng_forward(2);
+  tx_frame(cmd, cmd_sz);
+  legic_prng_forward(2);
+  uint32_t frame = rx_frame(12);
+  LED_B_OFF();
+
+  // split frame into data and crc
+  uint8_t byte = BYTEx(frame, 0);
+  uint8_t crc = BYTEx(frame, 1);
+
+  // check received against calculated crc
+  uint8_t calc_crc = calc_crc4(cmd, cmd_sz, byte);
+  if(calc_crc != crc) {
+    Dbprintf("!!! crc mismatch: %x != %x !!!",  calc_crc, crc);
+    return -1;
+  }
+
+  legic_prng_forward(1);
+
+  return byte;

 }
 
 }
 

-int timestamp;
-
-/* Handle (whether to respond) a frame in tag mode */
-static void frame_handle_tag(struct legic_frame const * const f)
-{
-   /* First Part of Handshake (IV) */
-   if(f->bits == 7) {
-     if(f->data == SESSION_IV) {
-        LED_C_ON();
-        prng_timer->TC_CCR = AT91C_TC_SWTRG;
-        legic_prng_init(f->data);
-        frame_send_tag(0x3d, 6, 1); /* 0x3d^0x26 = 0x1b */
-        legic_state = STATE_IV;
-        legic_read_count = 0;
-        legic_prng_bc = 0;
-        legic_prng_iv = f->data;
- 
-        /* TIMEOUT */
-        timer->TC_CCR = AT91C_TC_SWTRG;
-        while(timer->TC_CV > 1);
-        while(timer->TC_CV < 280);
-        return;
-      } else if((prng_timer->TC_CV % 50) > 40) {
-        legic_prng_init(f->data);
-        frame_send_tag(0x3d, 6, 1);
-        SpinDelay(20);
-        return;
-     }
-   }
-
-   /* 0x19==??? */
-   if(legic_state == STATE_IV) {
-      if((f->bits == 6) && (f->data == (0x19 ^ get_key_stream(1, 6)))) {
-         legic_state = STATE_CON;
-
-         /* TIMEOUT */
-         timer->TC_CCR = AT91C_TC_SWTRG;
-         while(timer->TC_CV > 1);
-         while(timer->TC_CV < 200);
-         return;
-      } else {
-         legic_state = STATE_DISCON;
-         LED_C_OFF();
-         Dbprintf("0x19 - Frame: %03.3x", f->data);
-         return;
-      }
-   }
-
-   /* Read */
-   if(f->bits == 11) {
-      if(legic_state == STATE_CON) {
-         int key   = get_key_stream(-1, 11); //legic_phase_drift, 11);
-         int addr  = f->data ^ key; addr = addr >> 1;
-         int data = ((uint8_t*)BigBuf)[addr];
-         int hash = LegicCRC(addr, data, 11) << 8;
-         ((uint8_t*)BigBuf)[OFFSET_LOG+legic_read_count] = (uint8_t)addr;
-         legic_read_count++;
-
-         //Dbprintf("Data:%03.3x, key:%03.3x, addr: %03.3x, read_c:%u", f->data, key, addr, read_c);
-         legic_prng_forward(legic_reqresp_drift);
-
-         frame_send_tag(hash | data, 12, 1);
-
-         /* SHORT TIMEOUT */
-         timer->TC_CCR = AT91C_TC_SWTRG;
-         while(timer->TC_CV > 1);
-         legic_prng_forward(legic_frame_drift);
-         while(timer->TC_CV < 180);
-         return;
-      }
-   }
-
-   /* Write */
-   if(f->bits == 23) {
-      int key   = get_key_stream(-1, 23); //legic_frame_drift, 23);
-      int addr  = f->data ^ key; addr = addr >> 1; addr = addr & 0x3ff;
-      int data  = f->data ^ key; data = data >> 11; data = data & 0xff;
-
-      /* write command */
-      legic_state = STATE_DISCON;
-      LED_C_OFF();
-      Dbprintf("write - addr: %x, data: %x", addr, data);
-      return;
-   }
-
-   if(legic_state != STATE_DISCON) {
-      Dbprintf("Unexpected: sz:%u, Data:%03.3x, State:%u, Count:%u", f->bits, f->data, legic_state, legic_read_count);
-      int i;
-      Dbprintf("IV: %03.3x", legic_prng_iv);
-      for(i = 0; i<legic_read_count; i++) {
-         Dbprintf("Read Nb: %u, Addr: %u", i, ((uint8_t*)BigBuf)[OFFSET_LOG+i]);
-      }
-
-      for(i = -1; i<legic_read_count; i++) {
-         uint32_t t;
-         t  = ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4];
-         t |= ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4+1] << 8;
-         t |= ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4+2] <<16;
-         t |= ((uint8_t*)BigBuf)[OFFSET_LOG+256+i*4+3] <<24;
-
-         Dbprintf("Cycles: %u, Frame Length: %u, Time: %u", 
-            ((uint8_t*)BigBuf)[OFFSET_LOG+128+i],
-            ((uint8_t*)BigBuf)[OFFSET_LOG+384+i],
-            t);
-      }
-   }
-   legic_state = STATE_DISCON; 
-   legic_read_count = 0;
-   SpinDelay(10);
-   LED_C_OFF();
-   return; 
+// Transmit write command, wait until (3.6ms) the tag sends back an unencrypted
+// ACK ('1' bit) and forward the prng time based.
+bool write_byte(uint16_t index, uint8_t byte, uint8_t addr_sz) {
+  uint32_t cmd = index << 1 | LEGIC_WRITE;          // prepare command
+  uint8_t  crc = calc_crc4(cmd, addr_sz + 1, byte); // calculate crc
+  cmd |= byte << (addr_sz + 1);                     // append value
+  cmd |= (crc & 0xF) << (addr_sz + 1 + 8);          // and crc
+
+  // send write command
+  LED_C_ON();
+  legic_prng_forward(2);
+  tx_frame(cmd, addr_sz + 1 + 8 + 4); // sz = addr_sz + cmd + data + crc
+  legic_prng_forward(3);
+  LED_C_OFF();
+
+  // wait for ack
+  return rx_ack();

 }
 
 }
 

-/* Read bit by bit untill full frame is received
- * Call to process frame end answer
- */
-static void emit(int bit)
-{
-  if(bit == -1) {
-     if(current_frame.bits <= 4) {
-        frame_clean(&current_frame);
-     } else {
-        frame_handle_tag(&current_frame);
-        frame_clean(&current_frame);
-     }
-     WDT_HIT();
-  } else if(bit == 0) {
-    frame_append_bit(&current_frame, 0);
-  } else if(bit == 1) {
-    frame_append_bit(&current_frame, 1);
+//-----------------------------------------------------------------------------
+// Command Line Interface
+//
+// Only this functions are public / called from appmain.c
+//-----------------------------------------------------------------------------
+void LegicRfReader(int offset, int bytes) {
+  uint8_t *BigBuf = BigBuf_get_addr();
+  memset(BigBuf, 0, 1024);
+
+  // configure ARM and FPGA
+  init_reader(false);
+
+  // establish shared secret and detect card type
+  DbpString("Reading card ...");
+  uint8_t card_type = setup_phase(SESSION_IV);
+  uint8_t result = 0;
+  if(init_card(card_type, &card) != 0) {
+    result = 1;
+    goto OUT;
+  }
+
+  // if no argument is specified create full dump
+  if(bytes == -1) {
+    bytes = card.cardsize;

   }
   }

-}

 
 

-void LegicRfSimulate(int phase, int frame, int reqresp)
-{
-  /* ADC path high-frequency peak detector, FPGA in high-frequency simulator mode, 
-   * modulation mode set to 212kHz subcarrier. We are getting the incoming raw
-   * envelope waveform on DIN and should send our response on DOUT.
-   *
-   * The LEGIC RF protocol is pulse-pause-encoding from reader to card, so we'll
-   * measure the time between two rising edges on DIN, and no encoding on the
-   * subcarrier from card to reader, so we'll just shift out our verbatim data
-   * on DOUT, 1 bit is 100us. The time from reader to card frame is still unclear,
-   * seems to be 300us-ish.
-   */
-
-   if(phase < 0) {
-      int i;
-      for(i=0; i<=reqresp; i++) {
-         legic_prng_init(SESSION_IV);
-         Dbprintf("i=%u, key 0x%3.3x", i, get_key_stream(i, frame));
-      }
-      return;
-   }
-
-   legic_phase_drift = phase;
-   legic_frame_drift = frame;
-   legic_reqresp_drift = reqresp;
-
-   SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
-   FpgaSetupSsc();
-   FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR | FPGA_HF_SIMULATOR_MODULATE_212K);
-   
-   /* Bitbang the receiver */
-   AT91C_BASE_PIOA->PIO_ODR = GPIO_SSC_DIN;
-   AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DIN;
-   
-   setup_timer();
-   crc_init(&legic_crc, 4, 0x19 >> 1, 0x5, 0);
-   
-   int old_level = 0;
-   int active = 0;
-   legic_state = STATE_DISCON;
-
-   LED_B_ON();
-   DbpString("Starting Legic emulator, press button to end");
-   while(!BUTTON_PRESS()) {
-      int level = !!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_DIN);
-      int time = timer->TC_CV;
-                
-      if(level != old_level) {
-         if(level == 1) {
-            timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
-            if(FUZZ_EQUAL(time, RWD_TIME_1, RWD_TIME_FUZZ)) {
-               /* 1 bit */
-               emit(1);
-               active = 1;
-               LED_A_ON();
-            } else if(FUZZ_EQUAL(time, RWD_TIME_0, RWD_TIME_FUZZ)) {
-               /* 0 bit */
-               emit(0);
-               active = 1;
-               LED_A_ON();
-            } else if(active) {
-               /* invalid */
-               emit(-1);
-               active = 0;
-               LED_A_OFF();
-            }
-         }
-      }
-
-      if(time >= (RWD_TIME_1+RWD_TIME_FUZZ) && active) {
-         /* Frame end */
-         emit(-1);
-         active = 0;
-         LED_A_OFF();
-      }
-                
-      if(time >= (20*RWD_TIME_1) && (timer->TC_SR & AT91C_TC_CLKSTA)) {
-         timer->TC_CCR = AT91C_TC_CLKDIS;
-      }
-                
-      old_level = level;
-      WDT_HIT();
-   }
-   DbpString("Stopped");
-   LED_B_OFF();
-   LED_A_OFF();
-   LED_C_OFF();
+  // do not read beyond card memory
+  if(bytes + offset > card.cardsize) {
+    bytes = card.cardsize - offset;
+  }
+
+  for(uint16_t i = 0; i < bytes; ++i) {
+    int16_t byte = read_byte(offset + i, card.cmdsize);
+    if(byte == -1) {
+      result = 2;
+      goto OUT;
+    }
+    BigBuf[i] = byte;
+  }
+
+OUT:
+  cmd_send(CMD_ACK, result, bytes, 0, &card, sizeof(card));
+  FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+  LED_B_OFF();
+  LED_C_OFF();
+  LED_D_OFF();
+  StopTicks();

 }
 
 }
 

+void LegicRfWriter(int bytes, int offset) {
+  uint8_t *BigBuf = BigBuf_get_addr();
+
+  // configure ARM and FPGA
+  init_reader(false);
+
+  // uid is not writeable
+  if(offset <= WRITE_LOWERLIMIT) {
+    goto OUT;
+  }
+
+  // establish shared secret and detect card type
+  Dbprintf("Writing 0x%02.2x - 0x%02.2x ...", offset, offset+bytes);
+  uint8_t card_type = setup_phase(SESSION_IV);
+  if(init_card(card_type, &card) != 0) {
+    Dbprintf("No or unknown card found, aborting");
+    goto OUT;
+  }
+
+  // do not write beyond card memory
+  if(bytes + offset > card.cardsize) {
+    bytes = card.cardsize - offset;
+  }
+
+  // write in reverse order, only then is DCF (decremental field) writable
+  while(bytes-- > 0 && !BUTTON_PRESS()) {
+    if(!write_byte(bytes + offset, BigBuf[bytes + offset], card.addrsize)) {
+      Dbprintf("operation failed @ 0x%03.3x", bytes);
+      goto OUT;
+    }
+  }
+
+  // OK
+  DbpString("Write successful");
+
+OUT:
+  FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+  LED_B_OFF();
+  LED_C_OFF();
+  LED_D_OFF();
+  StopTicks();
+}