1 //-----------------------------------------------------------------------------
2 // ISO14443-A support for the Proxmark III
3 // Gerhard de Koning Gans, April 2008
4 //-----------------------------------------------------------------------------
6 // constants for the different modes:
8 `define TAGSIM_LISTEN 3'b001
9 `define TAGSIM_MOD 3'b010
10 `define READER_LISTEN 3'b011
11 `define READER_MOD 3'b100
14 pck0, ck_1356meg, ck_1356megb,
15 pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,
17 ssp_frame, ssp_din, ssp_dout, ssp_clk,
22 input pck0, ck_1356meg, ck_1356megb;
23 output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
27 output ssp_frame, ssp_din, ssp_clk;
28 input cross_hi, cross_lo;
33 wire adc_clk = ck_1356meg;
37 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
39 // detecting and shaping the reader's signal. Reader will modulate the carrier by 100% (signal is either on or off). Use a
40 // hysteresis (Schmitt Trigger) to avoid false triggers during slowly increasing or decreasing carrier amplitudes
42 reg [11:0] has_been_low_for;
44 always @(negedge adc_clk)
46 if(adc_d >= 16) after_hysteresis <= 1'b1; // U >= 1,14V -> after_hysteresis = 1
47 else if(adc_d < 8) after_hysteresis <= 1'b0; // U < 1,04V -> after_hysteresis = 0
48 // Note: was >= 3,53V and <= 1,19V. The new trigger values allow more reliable detection of the first bit
49 // (it might not reach 3,53V due to the high time constant of the high pass filter in the analogue RF part).
50 // In addition, the new values are more in line with ISO14443-2: "The PICC shall detect the ”End of Pause” after the field exceeds
51 // 5% of H_INITIAL and before it exceeds 60% of H_INITIAL." Depending on the signal strength, 60% might well be less than 3,53V.
54 // detecting a loss of reader's field (adc_d < 192 for 4096 clock cycles). If this is the case,
55 // set the detected reader signal (after_hysteresis) to '1' (unmodulated)
58 has_been_low_for <= 12'd0;
62 if(has_been_low_for == 12'd4095)
64 has_been_low_for <= 12'd0;
65 after_hysteresis <= 1'b1;
69 has_been_low_for <= has_been_low_for + 1;
77 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
79 // detect when a reader is active (modulating). We assume that the reader is active, if we see the carrier off for at least 8
80 // carrier cycles. We assume that the reader is inactive, if the carrier stayed high for at least 256 carrier cycles.
82 reg [2:0] deep_counter;
83 reg [8:0] saw_deep_modulation;
85 always @(negedge adc_clk)
87 if(~(| adc_d[7:0])) // if adc_d == 0 (U <= 0,94V)
89 if(deep_counter == 3'd7) // adc_d == 0 for 8 adc_clk ticks -> deep_modulation (by reader)
91 deep_modulation <= 1'b1;
92 saw_deep_modulation <= 8'd0;
95 deep_counter <= deep_counter + 1;
100 if(saw_deep_modulation == 8'd255) // adc_d != 0 for 256 adc_clk ticks -> deep_modulation is over, probably waiting for tag's response
101 deep_modulation <= 1'b0;
103 saw_deep_modulation <= saw_deep_modulation + 1;
109 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
111 // filter the input for a tag's signal. The filter box needs the 4 previous input values and is a gaussian derivative filter
112 // for noise reduction and edge detection.
113 // store 4 previous samples:
114 reg [7:0] input_prev_4, input_prev_3, input_prev_2, input_prev_1;
116 always @(negedge adc_clk)
118 input_prev_4 <= input_prev_3;
119 input_prev_3 <= input_prev_2;
120 input_prev_2 <= input_prev_1;
121 input_prev_1 <= adc_d;
124 // adc_d_filtered = 2*input_prev4 + 1*input_prev3 + 0*input_prev2 - 1*input_prev1 - 2*input
125 // = (2*input_prev4 + input_prev3) - (2*input + input_prev1)
126 wire [8:0] input_prev_4_times_2 = input_prev_4 << 1;
127 wire [8:0] adc_d_times_2 = adc_d << 1;
129 wire [9:0] tmp1 = input_prev_4_times_2 + input_prev_3;
130 wire [9:0] tmp2 = adc_d_times_2 + input_prev_1;
132 // convert intermediate signals to signed and calculate the filter output
133 wire signed [10:0] adc_d_filtered = {1'b0, tmp1} - {1'b0, tmp2};
137 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
138 // internal FPGA timing. Maximum required period is 128 carrier clock cycles for a full 8 Bit transfer to ARM. (i.e. we need a
139 // 7 bit counter). Adjust its frequency to external reader's clock when simulating a tag or sniffing.
140 reg pre_after_hysteresis;
141 reg [3:0] reader_falling_edge_time;
142 reg [6:0] negedge_cnt;
144 always @(negedge adc_clk)
146 // detect a reader signal's falling edge and remember its timing:
147 pre_after_hysteresis <= after_hysteresis;
148 if (pre_after_hysteresis && ~after_hysteresis)
150 reader_falling_edge_time[3:0] <= negedge_cnt[3:0];
153 // adjust internal timer counter if necessary:
154 if (negedge_cnt[3:0] == 4'd13 && (mod_type == `SNIFFER || mod_type == `TAGSIM_LISTEN) && deep_modulation)
156 if (reader_falling_edge_time == 4'd1) // reader signal changes right after sampling. Better sample earlier next time.
158 negedge_cnt <= negedge_cnt + 2; // time warp
160 else if (reader_falling_edge_time == 4'd0) // reader signal changes right before sampling. Better sample later next time.
162 negedge_cnt <= negedge_cnt; // freeze time
166 negedge_cnt <= negedge_cnt + 1; // Continue as usual
168 reader_falling_edge_time[3:0] <= 4'd8; // adjust only once per detected edge
170 else if (negedge_cnt == 7'd127) // normal operation: count from 0 to 127
176 negedge_cnt <= negedge_cnt + 1;
181 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
183 // determine best possible time for starting/resetting the modulation detector.
184 reg [3:0] mod_detect_reset_time;
186 always @(negedge adc_clk)
188 if (mod_type == `READER_LISTEN)
189 // (our) reader signal changes at negedge_cnt[3:0]=9, tag response expected to start n*16+4 ticks later, further delayed by
190 // 3 ticks ADC conversion. The maximum filter output (edge detected) will be detected after subcarrier zero crossing (+7 ticks).
191 // To allow some timing variances, we want to have the maximum filter outputs well within the detection window, i.e.
192 // at mod_detect_reset_time+4 and mod_detect_reset_time+12 (-4 ticks).
193 // 9 + 4 + 3 + 7 - 4 = 19. 19 mod 16 = 3
195 mod_detect_reset_time <= 4'd4;
198 if (mod_type == `SNIFFER)
200 // detect a rising edge of reader's signal and sync modulation detector to the tag's answer:
201 if (~pre_after_hysteresis && after_hysteresis && deep_modulation)
202 // reader signal rising edge detected at negedge_cnt[3:0]. This signal had been delayed
203 // 9 ticks by the RF part + 3 ticks by the A/D converter + 1 tick to assign to after_hysteresis.
204 // Then the same as above.
205 // - 9 - 3 - 1 + 4 + 3 + 7 - 4 = -3
207 mod_detect_reset_time <= negedge_cnt[3:0] - 4'd3;
213 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
215 // modulation detector. Looks for the steepest falling and rising edges within a 16 clock period. If there is both a significant
216 // falling and rising edge (in any order), a modulation is detected.
217 reg signed [10:0] rx_mod_falling_edge_max;
218 reg signed [10:0] rx_mod_rising_edge_max;
221 `define EDGE_DETECT_THRESHOLD 5
223 always @(negedge adc_clk)
225 if(negedge_cnt[3:0] == mod_detect_reset_time)
227 // detect modulation signal: if modulating, there must have been a falling AND a rising edge
228 if ((rx_mod_falling_edge_max > `EDGE_DETECT_THRESHOLD) && (rx_mod_rising_edge_max < -`EDGE_DETECT_THRESHOLD))
229 curbit <= 1'b1; // modulation
231 curbit <= 1'b0; // no modulation
232 // reset modulation detector
233 rx_mod_rising_edge_max <= 0;
234 rx_mod_falling_edge_max <= 0;
236 else // look for steepest edges (slopes)
238 if (adc_d_filtered > 0)
240 if (adc_d_filtered > rx_mod_falling_edge_max)
241 rx_mod_falling_edge_max <= adc_d_filtered;
245 if (adc_d_filtered < rx_mod_rising_edge_max)
246 rx_mod_rising_edge_max <= adc_d_filtered;
254 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
256 // sample 4 bits reader data and 4 bits tag data for sniffing
257 reg [3:0] reader_data;
260 always @(negedge adc_clk)
262 if(negedge_cnt[3:0] == 4'd0)
264 reader_data[3:0] <= {reader_data[2:0], after_hysteresis};
265 tag_data[3:0] <= {tag_data[2:0], curbit};
271 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
273 // a delay line to ensure that we send the (emulated) tag's answer at the correct time according to ISO14443-3
274 reg [31:0] mod_sig_buf;
275 reg [4:0] mod_sig_ptr;
278 always @(negedge adc_clk)
280 if(negedge_cnt[3:0] == 4'd0) // sample data at rising edge of ssp_clk - ssp_dout changes at the falling edge.
282 mod_sig_buf[31:2] <= mod_sig_buf[30:1]; // shift
283 if (~ssp_dout && ~mod_sig_buf[1])
284 mod_sig_buf[1] <= 1'b0; // delete the correction bit (a single 1 preceded and succeeded by 0)
286 mod_sig_buf[1] <= mod_sig_buf[0];
287 mod_sig_buf[0] <= ssp_dout; // add new data to the delay line
289 mod_sig = mod_sig_buf[mod_sig_ptr]; // the delayed signal.
295 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
296 // PM3 -> Reader, internal timing:
297 // a timer for the 1172 cycles fdt (Frame Delay Time). Start the timer with a rising edge of the reader's signal.
298 // set fdt_elapsed when we no longer need to delay data. Set fdt_indicator when we can start sending data.
299 // Note: the FPGA only takes care for the 1172 delay. To achieve an additional 1236-1172=64 ticks delay, the ARM must send
300 // a correction bit (before the start bit). The correction bit will be coded as 00010000, i.e. it adds 4 bits to the
301 // transmission stream, causing the required additional delay.
302 reg [10:0] fdt_counter;
303 reg fdt_indicator, fdt_elapsed;
304 reg [3:0] mod_sig_flip;
305 reg [3:0] sub_carrier_cnt;
307 // we want to achieve a delay of 1172. The RF part already has delayed the reader signals's rising edge
308 // by 9 ticks, the ADC took 3 ticks and there is always a delay of 32 ticks by the mod_sig_buf. Therefore need to
309 // count to 1172 - 9 - 3 - 32 = 1128
310 `define FDT_COUNT 11'd1128
312 // The ARM must not send too early, otherwise the mod_sig_buf will overflow, therefore signal that we are ready
313 // with fdt_indicator. The mod_sig_buf can buffer 29 excess data bits, i.e. a maximum delay of 29 * 16 = 464 adc_clk ticks.
314 // fdt_indicator is assigned to sendbit after at least 1 tick, the transfer to ARM needs minimum 8 ticks. Response from
315 // ARM could appear at ssp_dout 8 ticks later.
316 // 1128 - 464 - 1 - 8 - 8 = 647
317 `define FDT_INDICATOR_COUNT 11'd647
318 // Note: worst case, assignment to sendbit takes 15 ticks more, and transfer to ARM needs 7*16 = 112 ticks more.
319 // When the ARM's response then appears, the fdt_count is already 647 + 15 + 112 = 774, which still allows the ARM a possible
320 // response window of 1128 - 774 = 354 ticks.
322 // reset on a pause in listen mode. I.e. the counter starts when the pause is over:
323 assign fdt_reset = ~after_hysteresis && mod_type == `TAGSIM_LISTEN;
325 always @(negedge adc_clk)
329 fdt_counter <= 11'd0;
331 fdt_indicator <= 1'b0;
335 if(fdt_counter == `FDT_COUNT)
337 if(~fdt_elapsed) // just reached fdt.
339 mod_sig_flip <= negedge_cnt[3:0]; // start modulation at this time
340 sub_carrier_cnt <= 4'd0; // subcarrier phase in sync with start of modulation
345 sub_carrier_cnt <= sub_carrier_cnt + 1;
350 fdt_counter <= fdt_counter + 1;
354 if(fdt_counter == `FDT_INDICATOR_COUNT) fdt_indicator <= 1'b1;
358 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
359 // PM3 -> Reader or Tag
360 // assign a modulation signal to the antenna. This signal is either a delayed signal (to achieve fdt when sending to a reader)
361 // or undelayed when sending to a tag
364 always @(negedge adc_clk)
366 if (mod_type == `TAGSIM_MOD) // need to take care of proper fdt timing
368 if(fdt_counter == `FDT_COUNT)
372 if(negedge_cnt[3:0] == mod_sig_flip) mod_sig_coil <= mod_sig;
376 mod_sig_coil <= mod_sig; // just reached fdt. Immediately assign signal to coil
380 else // other modes: don't delay
382 mod_sig_coil <= ssp_dout;
388 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
390 // determine the required delay in the mod_sig_buf (set mod_sig_ptr).
391 reg temp_buffer_reset;
393 always @(negedge adc_clk)
398 temp_buffer_reset = 1'b0;
402 if(fdt_counter == `FDT_COUNT && ~fdt_elapsed) // if we just reached fdt
403 if(~(| mod_sig_ptr[4:0]))
404 mod_sig_ptr <= 5'd8; // ... but didn't buffer a 1 yet, delay next 1 by n*128 ticks.
406 temp_buffer_reset = 1'b1; // else no need for further delays.
408 if(negedge_cnt[3:0] == 4'd0) // at rising edge of ssp_clk - ssp_dout changes at the falling edge.
410 if((ssp_dout || (| mod_sig_ptr[4:0])) && ~fdt_elapsed) // buffer a 1 (and all subsequent data) until fdt is reached.
411 if (mod_sig_ptr == 5'd31)
412 mod_sig_ptr <= 5'd0; // buffer overflow - data loss.
414 mod_sig_ptr <= mod_sig_ptr + 1; // increase buffer (= increase delay by 16 adc_clk ticks). mod_sig_ptr always points ahead of first 1.
415 else if(fdt_elapsed && ~temp_buffer_reset)
417 // wait for the next 1 after fdt_elapsed before fixing the delay and starting modulation. This ensures that the response can only happen
418 // at intervals of 8 * 16 = 128 adc_clk ticks (as defined in ISO14443-3)
420 temp_buffer_reset = 1'b1;
421 if(mod_sig_ptr == 5'd1)
422 mod_sig_ptr <= 5'd8; // still nothing received, need to go for the next interval
424 mod_sig_ptr <= mod_sig_ptr - 1; // decrease buffer.
432 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
433 // FPGA -> ARM communication:
434 // buffer 8 bits data to be sent to ARM. Shift them out bit by bit.
437 always @(negedge adc_clk)
439 if (negedge_cnt[5:0] == 6'd63) // fill the buffer
441 if (mod_type == `SNIFFER)
443 if(deep_modulation) // a reader is sending (or there's no field at all)
445 to_arm <= {reader_data[3:0], 4'b0000}; // don't send tag data
449 to_arm <= {reader_data[3:0], tag_data[3:0]};
454 to_arm[7:0] <= {mod_sig_ptr[4:0], mod_sig_flip[3:1]}; // feedback timing information
458 if(negedge_cnt[2:0] == 3'b000 && mod_type == `SNIFFER) // shift at double speed
460 // Don't shift if we just loaded new data, obviously.
461 if(negedge_cnt[5:0] != 6'd0)
463 to_arm[7:1] <= to_arm[6:0];
467 if(negedge_cnt[3:0] == 4'b0000 && mod_type != `SNIFFER)
469 // Don't shift if we just loaded new data, obviously.
470 if(negedge_cnt[6:0] != 7'd0)
472 to_arm[7:1] <= to_arm[6:0];
479 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
480 // FPGA <-> ARM communication:
481 // generate a ssp clock and ssp frame signal for the synchronous transfer from/to the ARM
485 always @(negedge adc_clk)
487 if(mod_type == `SNIFFER)
488 // SNIFFER mode (ssp_clk = adc_clk / 8, ssp_frame clock = adc_clk / 64)):
490 if(negedge_cnt[2:0] == 3'd0)
492 if(negedge_cnt[2:0] == 3'd4)
495 if(negedge_cnt[5:0] == 6'd0) // ssp_frame rising edge indicates start of frame
497 if(negedge_cnt[5:0] == 6'd8)
501 // all other modes (ssp_clk = adc_clk / 16, ssp_frame clock = adc_clk / 128):
503 if(negedge_cnt[3:0] == 4'd0)
505 if(negedge_cnt[3:0] == 4'd8)
508 if(negedge_cnt[6:0] == 7'd7) // ssp_frame rising edge indicates start of frame
510 if(negedge_cnt[6:0] == 7'd23)
517 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
518 // FPGA -> ARM communication:
519 // select the data to be sent to ARM
523 always @(negedge adc_clk)
525 if(negedge_cnt[3:0] == 4'd0)
527 // What do we communicate to the ARM
528 if(mod_type == `TAGSIM_LISTEN)
529 sendbit = after_hysteresis;
530 else if(mod_type == `TAGSIM_MOD)
531 /* if(fdt_counter > 11'd772) sendbit = mod_sig_coil; // huh?
533 sendbit = fdt_indicator;
534 else if (mod_type == `READER_LISTEN)
541 if(mod_type == `SNIFFER)
542 // send sampled reader and tag data:
543 bit_to_arm = to_arm[7];
544 else if (mod_type == `TAGSIM_MOD && fdt_elapsed && temp_buffer_reset)
545 // send timing information:
546 bit_to_arm = to_arm[7];
548 // send data or fdt_indicator
549 bit_to_arm = sendbit;
555 assign ssp_din = bit_to_arm;
557 // Subcarrier (adc_clk/16, for TAGSIM_MOD only).
559 assign sub_carrier = ~sub_carrier_cnt[3];
561 // in READER_MOD: drop carrier for mod_sig_coil==1 (pause); in READER_LISTEN: carrier always on; in other modes: carrier always off
562 assign pwr_hi = (ck_1356megb & (((mod_type == `READER_MOD) & ~mod_sig_coil) || (mod_type == `READER_LISTEN)));
565 // Enable HF antenna drivers:
566 assign pwr_oe1 = 1'b0;
567 assign pwr_oe3 = 1'b0;
569 // TAGSIM_MOD: short circuit antenna with different resistances (modulated by sub_carrier modulated by mod_sig_coil)
570 // for pwr_oe4 = 1 (tristate): antenna load = 10k || 33 = 32,9 Ohms
571 // for pwr_oe4 = 0 (active): antenna load = 10k || 33 || 33 = 16,5 Ohms
572 assign pwr_oe4 = mod_sig_coil & sub_carrier & (mod_type == `TAGSIM_MOD);
574 // This is all LF, so doesn't matter.
575 assign pwr_oe2 = 1'b0;
576 assign pwr_lo = 1'b0;
579 assign dbg = negedge_cnt[3];