proxmark3/fpga/hi_iso14443a.v

//-----------------------------------------------------------------------------
// ISO14443-A support for the Proxmark III
// Gerhard de Koning Gans, April 2008
//-----------------------------------------------------------------------------

// constants for the different modes:
`define SNIFFER			3'b000
`define TAGSIM_LISTEN	3'b001
`define TAGSIM_MOD		3'b010
`define READER_LISTEN	3'b011
`define READER_MOD		3'b100

module hi_iso14443a(
    pck0, ck_1356meg, ck_1356megb,
    pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,
    adc_d, adc_clk,
    ssp_frame, ssp_din, ssp_dout, ssp_clk,
    cross_hi, cross_lo,
    dbg,
    mod_type
);
    input pck0, ck_1356meg, ck_1356megb;
    output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
    input [7:0] adc_d;
    output adc_clk;
    input ssp_dout;
    output ssp_frame, ssp_din, ssp_clk;
    input cross_hi, cross_lo;
    output dbg;
    input [2:0] mod_type;


wire adc_clk = ck_1356meg;



////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Reader -> PM3:
// detecting and shaping the reader's signal. Reader will modulate the carrier by 100% (signal is either on or off). Use a 
// hysteresis (Schmitt Trigger) to avoid false triggers during slowly increasing or decreasing carrier amplitudes
reg after_hysteresis;
reg [11:0] has_been_low_for;

always @(negedge adc_clk)
begin
	if(adc_d >= 16) after_hysteresis <= 1'b1;			// U >= 1,14V 	-> after_hysteresis = 1
    else if(adc_d < 8) after_hysteresis <= 1'b0;  		// U < 	1,04V 	-> after_hysteresis = 0
	// Note: was >= 3,53V and <= 1,19V. The new trigger values allow more reliable detection of the first bit 
	// (it might not reach 3,53V due to the high time constant of the high pass filter in the analogue RF part).
	// In addition, the new values are more in line with ISO14443-2: "The PICC shall detect the ”End of Pause” after the field exceeds 
	// 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.
	
	
	// detecting a loss of reader's field (adc_d < 192 for 4096 clock cycles). If this is the case, 
	// set the detected reader signal (after_hysteresis) to '1' (unmodulated)
	if(adc_d >= 192)
    begin
        has_been_low_for <= 12'd0;
    end
    else
    begin
        if(has_been_low_for == 12'd4095)
        begin
            has_been_low_for <= 12'd0;
            after_hysteresis <= 1'b1;
        end
        else
		begin
            has_been_low_for <= has_been_low_for + 1;
		end	
    end
	
end



////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Reader -> PM3
// detect when a reader is active (modulating). We assume that the reader is active, if we see the carrier off for at least 8 
// carrier cycles. We assume that the reader is inactive, if the carrier stayed high for at least 256 carrier cycles. 
reg deep_modulation;
reg [2:0] deep_counter;
reg [8:0] saw_deep_modulation;

always @(negedge adc_clk)
begin
	if(~(| adc_d[7:0]))									// if adc_d == 0 (U <= 0,94V)
	begin
		if(deep_counter == 3'd7)						// adc_d == 0 for 8 adc_clk ticks -> deep_modulation (by reader)
		begin
			deep_modulation <= 1'b1;
			saw_deep_modulation <= 8'd0;
		end
		else
			deep_counter <= deep_counter + 1;
	end
	else							
	begin
		deep_counter <= 3'd0;
		if(saw_deep_modulation == 8'd255)				// adc_d != 0 for 256 adc_clk ticks -> deep_modulation is over, probably waiting for tag's response
			deep_modulation <= 1'b0;
		else
			saw_deep_modulation <= saw_deep_modulation + 1;
	end
end



////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Tag -> PM3
// filter the input for a tag's signal. The filter box needs the 4 previous input values and is a gaussian derivative filter
// 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;

always @(negedge adc_clk)
begin
	input_prev_4 <= input_prev_3;
	input_prev_3 <= input_prev_2;
	input_prev_2 <= input_prev_1;
	input_prev_1 <= adc_d;
end	

// 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};


	
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// internal FPGA timing. Maximum required period is 128 carrier clock cycles for a full 8 Bit transfer to ARM. (i.e. we need a 
// 7 bit counter). Adjust its frequency to external reader's clock when simulating a tag or sniffing.
reg pre_after_hysteresis; 
reg [3:0] reader_falling_edge_time;
reg [6:0] negedge_cnt;

always @(negedge adc_clk)
begin
	// detect a reader signal's falling edge and remember its timing:
	pre_after_hysteresis <= after_hysteresis;
	if (pre_after_hysteresis && ~after_hysteresis)
	begin
		reader_falling_edge_time[3:0] <= negedge_cnt[3:0];
	end

	// adjust internal timer counter if necessary:
	if (negedge_cnt[3:0] == 4'd13 && (mod_type == `SNIFFER || mod_type == `TAGSIM_LISTEN) && deep_modulation)
	begin
		if (reader_falling_edge_time == 4'd1) 			// reader signal changes right after sampling. Better sample earlier next time. 
		begin
			negedge_cnt <= negedge_cnt + 2;				// time warp
		end	
		else if (reader_falling_edge_time == 4'd0)		// reader signal changes right before sampling. Better sample later next time.
		begin
			negedge_cnt <= negedge_cnt;					// freeze time
		end
		else
		begin
			negedge_cnt <= negedge_cnt + 1;				// Continue as usual
		end
		reader_falling_edge_time[3:0] <= 4'd8;			// adjust only once per detected edge
	end
	else if (negedge_cnt == 7'd127)						// normal operation: count from 0 to 127
	begin
		negedge_cnt <= 0;
	end	
	else
	begin
		negedge_cnt <= negedge_cnt + 1;
	end
end	


////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Tag -> PM3:
// determine best possible time for starting/resetting the modulation detector.
reg [3:0] mod_detect_reset_time;

always @(negedge adc_clk)
begin
	if (mod_type == `READER_LISTEN) 
	// (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'd4;
	end
	else
	if (mod_type == `SNIFFER)
	begin
		// detect a rising edge of reader's signal and sync modulation detector to the tag's answer:
		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.
		// Then the same as above.
		// - 9 - 3 - 1 + 4 + 3 + 7 - 4 = -3
		begin
			mod_detect_reset_time <= negedge_cnt[3:0] - 4'd3;
		end
	end
end


////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Tag -> PM3:
// modulation detector. Looks for the steepest falling and rising edges within a 16 clock period. If there is both a significant
// falling and rising edge (in any order), a modulation is detected.
reg signed [10:0] rx_mod_falling_edge_max;
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 > `EDGE_DETECT_THRESHOLD) && (rx_mod_rising_edge_max < -`EDGE_DETECT_THRESHOLD))
				curbit <= 1'b1;	// modulation
			else
				curbit <= 1'b0;	// no modulation
		// reset modulation detector
		rx_mod_rising_edge_max <= 0;
		rx_mod_falling_edge_max <= 0;
	end
	else											// look for steepest edges (slopes)
	begin
		if (adc_d_filtered > 0)
		begin
			if (adc_d_filtered > rx_mod_falling_edge_max)
				rx_mod_falling_edge_max <= adc_d_filtered;
		end
		else
		begin
			if (adc_d_filtered < rx_mod_rising_edge_max)
				rx_mod_rising_edge_max <= adc_d_filtered;
		end
	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 -> 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;
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 -> 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
// 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 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;

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.
			begin
				mod_sig_flip <= negedge_cnt[3:0];		// start modulation at this time
				sub_carrier_cnt <= 4'd0;				// subcarrier phase in sync with start of modulation
				fdt_elapsed <= 1'b1;
			end
			else
			begin
				sub_carrier_cnt <= sub_carrier_cnt + 1;
			end	
		end	
		else
		begin
			fdt_counter <= fdt_counter + 1;
		end
	end
	
	if(fdt_counter == `FDT_INDICATOR_COUNT) fdt_indicator <= 1'b1;
end


////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// PM3 -> Reader or Tag
// assign a modulation signal to the antenna. This signal is either a delayed signal (to achieve fdt when sending to a reader)
// or undelayed when sending to a tag
reg mod_sig_coil;

always @(negedge adc_clk)
begin
	if (mod_type == `TAGSIM_MOD)			 // need to take care of proper fdt timing
	begin
		if(fdt_counter == `FDT_COUNT)
		begin
			if(fdt_elapsed)
			begin
				if(negedge_cnt[3:0] == mod_sig_flip) mod_sig_coil <= mod_sig;
			end
			else
			begin
				mod_sig_coil <= mod_sig;	// just reached fdt. Immediately assign signal to coil
			end
		end
	end
	else 									// other modes: don't delay
	begin
		mod_sig_coil <= ssp_dout;
	end	
end



////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// PM3 -> Reader
// determine the required delay in the mod_sig_buf (set mod_sig_ptr).
reg temp_buffer_reset;

always @(negedge adc_clk)
begin
	if(fdt_reset)
	begin
		mod_sig_ptr <= 5'd0;
		temp_buffer_reset = 1'b0;
	end	
	else
	begin
		if(fdt_counter == `FDT_COUNT && ~fdt_elapsed)							// if we just reached fdt
			if(~(| mod_sig_ptr[4:0])) 
				mod_sig_ptr <= 5'd8;  											// ... but didn't buffer a 1 yet, delay next 1 by n*128 ticks.
			else 
				temp_buffer_reset = 1'b1; 										// else no need for further delays.

		if(negedge_cnt[3:0] == 4'd0) 											// at rising edge of ssp_clk - ssp_dout changes at the falling edge.
		begin
			if((ssp_dout || (| mod_sig_ptr[4:0])) && ~fdt_elapsed)				// buffer a 1 (and all subsequent data) until fdt is reached.
				if (mod_sig_ptr == 5'd31) 
					mod_sig_ptr <= 5'd0;										// buffer overflow - data loss.
				else 
					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.
			else if(fdt_elapsed && ~temp_buffer_reset)							
			begin
				// wait for the next 1 after fdt_elapsed before fixing the delay and starting modulation. This ensures that the response can only happen
				// at intervals of 8 * 16 = 128 adc_clk ticks (as defined in ISO14443-3)
				if(ssp_dout) 
					temp_buffer_reset = 1'b1;							
				if(mod_sig_ptr == 5'd1) 
					mod_sig_ptr <= 5'd8;										// still nothing received, need to go for the next interval
				else 
					mod_sig_ptr <= mod_sig_ptr - 1;								// decrease buffer.
			end
		end
	end
end



////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// FPGA -> ARM communication:
// buffer 8 bits data to be sent to ARM. Shift them out bit by bit.
reg [7:0] to_arm;

always @(negedge adc_clk)
begin
	if (negedge_cnt[5:0] == 6'd63)							// fill the buffer
	begin
		if (mod_type == `SNIFFER)
		begin
			if(deep_modulation) 							// a reader is sending (or there's no field at all)
			begin
				to_arm <= {reader_data[3:0], 4'b0000};		// don't send tag data
			end
			else
			begin
				to_arm <= {reader_data[3:0], tag_data[3:0]};
			end			
		end
		else
		begin
			to_arm[7:0] <= {mod_sig_ptr[4:0], mod_sig_flip[3:1]}; // feedback timing information
		end
	end	

	if(negedge_cnt[2:0] == 3'b000 && mod_type == `SNIFFER)	// shift at double speed
	begin
		// Don't shift if we just loaded new data, obviously.
		if(negedge_cnt[5:0] != 6'd0)
		begin
			to_arm[7:1] <= to_arm[6:0];
		end
	end

	if(negedge_cnt[3:0] == 4'b0000 && mod_type != `SNIFFER)
	begin
		// Don't shift if we just loaded new data, obviously.
		if(negedge_cnt[6:0] != 7'd0)
		begin
			to_arm[7:1] <= to_arm[6:0];
		end
	end
	
end


////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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;

always @(negedge adc_clk)
begin
	if(mod_type == `SNIFFER)
	// SNIFFER mode (ssp_clk = adc_clk / 8, ssp_frame clock = adc_clk / 64)):
	begin
		if(negedge_cnt[2:0] == 3'd0)
			ssp_clk <= 1'b1;
		if(negedge_cnt[2:0] == 3'd4)
			ssp_clk <= 1'b0;

		if(negedge_cnt[5:0] == 6'd0)	// ssp_frame rising edge indicates start of frame
			ssp_frame <= 1'b1;
		if(negedge_cnt[5:0] == 6'd8)	
			ssp_frame <= 1'b0;
	end
	else
	// all other modes (ssp_clk = adc_clk / 16, ssp_frame clock = adc_clk / 128):
	begin
		if(negedge_cnt[3:0] == 4'd0)
			ssp_clk <= 1'b1;
		if(negedge_cnt[3:0] == 4'd8) 
			ssp_clk <= 1'b0;

		if(negedge_cnt[6:0] == 7'd7)	// ssp_frame rising edge indicates start of frame
			ssp_frame <= 1'b1;
		if(negedge_cnt[6:0] == 7'd23)
			ssp_frame <= 1'b0;
	end	
end



////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// FPGA -> ARM communication:
// select the data to be sent to ARM
reg bit_to_arm;
reg sendbit;

always @(negedge adc_clk)
begin
	if(negedge_cnt[3:0] == 4'd0)
	begin
		// What do we communicate to the ARM
		if(mod_type == `TAGSIM_LISTEN) 
			sendbit = after_hysteresis;
		else if(mod_type == `TAGSIM_MOD)
			/* if(fdt_counter > 11'd772) sendbit = mod_sig_coil; // huh?
			else */ 
			sendbit = fdt_indicator;
		else if (mod_type == `READER_LISTEN)
			sendbit = curbit;
		else
			sendbit = 1'b0;
	end


	if(mod_type == `SNIFFER)
		// send sampled reader and tag data:
		bit_to_arm = to_arm[7];
	else if (mod_type == `TAGSIM_MOD && fdt_elapsed && temp_buffer_reset)
		// send timing information:
		bit_to_arm = to_arm[7];
	else
		// send data or fdt_indicator
		bit_to_arm = sendbit;
end




assign ssp_din = bit_to_arm;

// Subcarrier (adc_clk/16, for TAGSIM_MOD only).
wire sub_carrier;
assign sub_carrier = ~sub_carrier_cnt[3];

// in READER_MOD: drop carrier for mod_sig_coil==1 (pause); in READER_LISTEN: carrier always on; in other modes: carrier always off
assign pwr_hi = (ck_1356megb & (((mod_type == `READER_MOD) & ~mod_sig_coil) || (mod_type == `READER_LISTEN)));	


// Enable HF antenna drivers:
assign pwr_oe1 = 1'b0;
assign pwr_oe3 = 1'b0;

// 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);

// This is all LF, so doesn't matter.
assign pwr_oe2 = 1'b0;
assign pwr_lo = 1'b0;


assign dbg = negedge_cnt[3];

endmodule