// for noise reduction and edge detection.
// store 4 previous samples:
reg [7:0] input_prev_4, input_prev_3, input_prev_2, input_prev_1;
-// convert to signed signals (and multiply by two for samples at t-4 and t)
-wire signed [10:0] input_prev_4_times_2 = {0, 0, input_prev_4, 0};
-wire signed [10:0] input_prev_3_times_1 = {0, 0, 0, input_prev_3};
-wire signed [10:0] input_prev_1_times_1 = {0, 0, 0, input_prev_1};
-wire signed [10:0] adc_d_times_2 = {0, 0, adc_d, 0};
-
-wire signed [10:0] tmp_1, tmp_2;
-wire signed [10:0] adc_d_filtered;
-integer i;
-
-assign tmp_1 = input_prev_4_times_2 + input_prev_3_times_1;
-assign tmp_2 = input_prev_1_times_1 + adc_d_times_2;
-
+
always @(negedge adc_clk)
begin
- // for (i = 3; i > 0; i = i - 1)
- // begin
- // input_shift[i] <= input_shift[i-1];
- // end
- // input_shift[0] <= adc_d;
input_prev_4 <= input_prev_3;
input_prev_3 <= input_prev_2;
input_prev_2 <= input_prev_1;
input_prev_1 <= adc_d;
end
-// assign adc_d_filtered = (input_shift[3] << 1) + input_shift[2] - input_shift[0] - (adc_d << 1);
-assign adc_d_filtered = tmp_1 - tmp_2;
+// adc_d_filtered = 2*input_prev4 + 1*input_prev3 + 0*input_prev2 - 1*input_prev1 - 2*input
+// = (2*input_prev4 + input_prev3) - (2*input + input_prev1)
+wire [8:0] input_prev_4_times_2 = input_prev_4 << 1;
+wire [8:0] adc_d_times_2 = adc_d << 1;
+
+wire [9:0] tmp1 = input_prev_4_times_2 + input_prev_3;
+wire [9:0] tmp2 = adc_d_times_2 + input_prev_1;
+
+// convert intermediate signals to signed and calculate the filter output
+wire signed [10:0] adc_d_filtered = {1'b0, tmp1} - {1'b0, tmp2};
+
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
always @(negedge adc_clk)
begin
if (mod_type == `READER_LISTEN)
- // (our) reader signal changes at t=1, tag response expected n*16+4 ticks later, further delayed by
- // 3 ticks ADC conversion.
- // 1 + 4 + 3 = 8
+ // (our) reader signal changes at negedge_cnt[3:0]=9, tag response expected to start n*16+4 ticks later, further delayed by
+ // 3 ticks ADC conversion. The maximum filter output (edge detected) will be detected after subcarrier zero crossing (+7 ticks).
+ // To allow some timing variances, we want to have the maximum filter outputs well within the detection window, i.e.
+ // at mod_detect_reset_time+4 and mod_detect_reset_time+12 (-4 ticks).
+ // 9 + 4 + 3 + 7 - 4 = 19. 19 mod 16 = 3
begin
- mod_detect_reset_time <= 4'd8;
+ mod_detect_reset_time <= 4'd4;
end
else
if (mod_type == `SNIFFER)
if (~pre_after_hysteresis && after_hysteresis && deep_modulation)
// reader signal rising edge detected at negedge_cnt[3:0]. This signal had been delayed
// 9 ticks by the RF part + 3 ticks by the A/D converter + 1 tick to assign to after_hysteresis.
- // The tag will respond n*16 + 4 ticks later + 3 ticks A/D converter delay.
- // - 9 - 3 - 1 + 4 + 3 = -6
+ // Then the same as above.
+ // - 9 - 3 - 1 + 4 + 3 + 7 - 4 = -3
begin
- mod_detect_reset_time <= negedge_cnt[3:0] - 4'd4;
+ mod_detect_reset_time <= negedge_cnt[3:0] - 4'd3;
end
end
end
reg signed [10:0] rx_mod_rising_edge_max;
reg curbit;
+`define EDGE_DETECT_THRESHOLD 5
+
always @(negedge adc_clk)
begin
if(negedge_cnt[3:0] == mod_detect_reset_time)
begin
// detect modulation signal: if modulating, there must have been a falling AND a rising edge
- if (rx_mod_falling_edge_max > 5 && rx_mod_rising_edge_max > 5)
+ if ((rx_mod_falling_edge_max > `EDGE_DETECT_THRESHOLD) && (rx_mod_rising_edge_max < -`EDGE_DETECT_THRESHOLD))
curbit <= 1'b1; // modulation
else
curbit <= 1'b0; // no modulation
end
else
begin
- if (-adc_d_filtered > rx_mod_rising_edge_max)
- rx_mod_rising_edge_max <= -adc_d_filtered;
+ if (adc_d_filtered < rx_mod_rising_edge_max)
+ rx_mod_rising_edge_max <= adc_d_filtered;
end
end
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-// PM3 -> Tag:
+// PM3 -> Reader:
// a delay line to ensure that we send the (emulated) tag's answer at the correct time according to ISO14443-3
reg [31:0] mod_sig_buf;
reg [4:0] mod_sig_ptr;
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-// PM3 -> Tag, internal timing:
+// PM3 -> Reader, internal timing:
// a timer for the 1172 cycles fdt (Frame Delay Time). Start the timer with a rising edge of the reader's signal.
// set fdt_elapsed when we no longer need to delay data. Set fdt_indicator when we can start sending data.
// Note: the FPGA only takes care for the 1172 delay. To achieve an additional 1236-1172=64 ticks delay, the ARM must send
// The ARM must not send too early, otherwise the mod_sig_buf will overflow, therefore signal that we are ready
// 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.
-// fdt_indicator could appear at ssp_din after 1 tick, the transfer needs 16 ticks, the ARM can send 128 ticks later.
-// 1128 - 464 - 1 - 128 - 8 = 535
-`define FDT_INDICATOR_COUNT 11'd535
+// fdt_indicator is assigned to sendbit after at least 1 tick, the transfer to ARM needs minimum 8 ticks. Response from
+// ARM could appear at ssp_dout 8 ticks later.
+// 1128 - 464 - 1 - 8 - 8 = 647
+`define FDT_INDICATOR_COUNT 11'd647
+// Note: worst case, assignment to sendbit takes 15 ticks more, and transfer to ARM needs 7*16 = 112 ticks more.
+// When the ARM's response then appears, the fdt_count is already 647 + 15 + 112 = 774, which still allows the ARM a possible
+// response window of 1128 - 774 = 354 ticks.
// reset on a pause in listen mode. I.e. the counter starts when the pause is over:
assign fdt_reset = ~after_hysteresis && mod_type == `TAGSIM_LISTEN;
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-// FPGA -> ARM communication:
+// FPGA <-> ARM communication:
// generate a ssp clock and ssp frame signal for the synchronous transfer from/to the ARM
reg ssp_clk;
reg ssp_frame;
-reg [2:0] ssp_frame_counter;
always @(negedge adc_clk)
begin
// TAGSIM_MOD: short circuit antenna with different resistances (modulated by sub_carrier modulated by mod_sig_coil)
// for pwr_oe4 = 1 (tristate): antenna load = 10k || 33 = 32,9 Ohms
// for pwr_oe4 = 0 (active): antenna load = 10k || 33 || 33 = 16,5 Ohms
-assign pwr_oe4 = ~(mod_sig_coil & sub_carrier & (mod_type == `TAGSIM_MOD));
+assign pwr_oe4 = mod_sig_coil & sub_carrier & (mod_type == `TAGSIM_MOD);
// This is all LF, so doesn't matter.
assign pwr_oe2 = 1'b0;
projects / proxmark3-svn / blobdiff