+ end
+
+end
+
+
+
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// Tag+Reader -> PM3
+// sample 4 bits reader data and 4 bits tag data for sniffing
+reg [3:0] reader_data;
+reg [3:0] tag_data;
+
+always @(negedge adc_clk)
+begin
+ if(negedge_cnt[3:0] == 4'd0)
+ begin
+ reader_data[3:0] <= {reader_data[2:0], after_hysteresis};
+ tag_data[3:0] <= {tag_data[2:0], curbit};
+ end
+end
+
+
+
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// PM3 -> Tag:
+// 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;
+reg mod_sig;
+
+always @(negedge adc_clk)
+begin
+ if(negedge_cnt[3:0] == 4'd0) // sample data at rising edge of ssp_clk - ssp_dout changes at the falling edge.
+ begin
+ mod_sig_buf[31:2] <= mod_sig_buf[30:1]; // shift
+ if (~ssp_dout && ~mod_sig_buf[1])
+ mod_sig_buf[1] <= 1'b0; // delete the correction bit (a single 1 preceded and succeeded by 0)
+ else
+ mod_sig_buf[1] <= mod_sig_buf[0];
+ mod_sig_buf[0] <= ssp_dout; // add new data to the delay line
+
+ mod_sig = mod_sig_buf[mod_sig_ptr]; // the delayed signal.
+ end
+end
+
+
+
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// PM3 -> Tag, 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
+// a correction bit (before the start bit). The correction bit will be coded as 00010000, i.e. it adds 4 bits to the
+// transmission stream, causing the required additional delay.
+reg [10:0] fdt_counter;
+reg fdt_indicator, fdt_elapsed;
+reg [3:0] mod_sig_flip;
+reg [3:0] sub_carrier_cnt;
+
+// we want to achieve a delay of 1172. The RF part already has delayed the reader signals's rising edge
+// 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
+// count to 1172 - 9 - 3 - 32 = 1128
+`define FDT_COUNT 11'd1128
+
+// 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
+
+// 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;
+
+always @(negedge adc_clk)
+begin
+ if (fdt_reset)
+ begin
+ fdt_counter <= 11'd0;
+ fdt_elapsed <= 1'b0;
+ fdt_indicator <= 1'b0;
+ end
+ else
+ begin
+ if(fdt_counter == `FDT_COUNT)
+ begin
+ if(~fdt_elapsed) // just reached fdt.
projects / proxmark3-svn / blobdiff