X-Git-Url: http://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/bf7ebb7b208a3b95f28a9a40f2e560a56e121794..351d6d17b3fa82a82b2205c69dcc024884d0b146:/fpga/hi_read_rx_xcorr.v

diff --git a/fpga/hi_read_rx_xcorr.v b/fpga/hi_read_rx_xcorr.v
index afaf7cb6..8233960f 100644
--- a/fpga/hi_read_rx_xcorr.v
+++ b/fpga/hi_read_rx_xcorr.v
@@ -10,7 +10,7 @@ module hi_read_rx_xcorr(
     ssp_frame, ssp_din, ssp_dout, ssp_clk,
     cross_hi, cross_lo,
     dbg,
-    xcorr_is_848, snoop
+    xcorr_is_848, snoop, xcorr_quarter_freq
 );
     input pck0, ck_1356meg, ck_1356megb;
     output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
@@ -20,19 +20,18 @@ module hi_read_rx_xcorr(
     output ssp_frame, ssp_din, ssp_clk;
     input cross_hi, cross_lo;
     output dbg;
-    input xcorr_is_848, snoop;
+    input xcorr_is_848, snoop, xcorr_quarter_freq;
 
 // Carrier is steady on through this, unless we're snooping.
 assign pwr_hi = ck_1356megb & (~snoop);
 assign pwr_oe1 = 1'b0;
 assign pwr_oe3 = 1'b0;
 assign pwr_oe4 = 1'b0;
+// Unused.
+assign pwr_lo = 1'b0;
+assign pwr_oe2 = 1'b0;
 
-wire adc_clk = ck_1356megb;
-
-reg fc_div_2;
-always @(negedge ck_1356megb)
-    fc_div_2 <= fc_div_2 + 1;
+assign adc_clk = ck_1356megb;  // sample frequency is 13,56 MHz
 
 // When we're a reader, we just need to do the BPSK demod; but when we're an
 // eavesdropper, we also need to pick out the commands sent by the reader,
@@ -60,14 +59,28 @@ begin
     end
 end
 
-// Let us report a correlation every 4 subcarrier cycles, or 4*16 samples,
-// so we need a 6-bit counter.
+
+// Let us report a correlation every 64 samples. I.e.
+// one Q/I pair after 4 subcarrier cycles for the 848kHz subcarrier,
+// one Q/I pair after 2 subcarrier cycles for the 424kHz subcarriers,
+// one Q/I pair for each subcarrier cyle for the 212kHz subcarrier.
+// We need a 6-bit counter for the timing.
 reg [5:0] corr_i_cnt;
-// And a couple of registers in which to accumulate the correlations.
-// we would add at most 32 times adc_d, the result can be held in 13 bits. 
-// Need one additional bit because it can be negative as well
+always @(negedge adc_clk)
+begin
+	corr_i_cnt <= corr_i_cnt + 1;
+end		
+
+// And a couple of registers in which to accumulate the correlations. From the 64 samples
+// we would add at most 32 times the difference between unmodulated and modulated signal. It should
+// be safe to assume that a tag will not be able to modulate the carrier signal by more than 25%.
+// 32 * 255 * 0,25 = 2040, which can be held in 11 bits. Add 1 bit for sign.
+// Temporary we might need more bits. For the 212kHz subcarrier we could possible add 32 times the
+// maximum signal value before a first subtraction would occur. 32 * 255 = 8160 can be held in 13 bits. 
+// Add one bit for sign -> need 14 bit registers but final result will fit into 12 bits.
 reg signed [13:0] corr_i_accum;
 reg signed [13:0] corr_q_accum;
+// we will report maximum 8 significant bits
 reg signed [7:0] corr_i_out;
 reg signed [7:0] corr_q_out;
 // clock and frame signal for communication to ARM
@@ -75,13 +88,29 @@ reg ssp_clk;
 reg ssp_frame;
 
 
-always @(negedge adc_clk)
-begin
-	if (xcorr_is_848 | fc_div_2)
-		corr_i_cnt <= corr_i_cnt + 1;
-end		
-		
+// The subcarrier reference signals
+reg subcarrier_I;
+reg subcarrier_Q;
 
+always @(corr_i_cnt or xcorr_is_848 or xcorr_quarter_freq)
+begin
+	if (xcorr_is_848 & ~xcorr_quarter_freq)				// 848 kHz
+		begin
+			subcarrier_I = ~corr_i_cnt[3];
+			subcarrier_Q = ~(corr_i_cnt[3] ^ corr_i_cnt[2]);
+		end
+	else if (xcorr_is_848 & xcorr_quarter_freq)			// 212 kHz	
+		begin
+			subcarrier_I = ~corr_i_cnt[5];
+			subcarrier_Q = ~(corr_i_cnt[5] ^ corr_i_cnt[4]);
+		end
+	else
+		begin											// 424 kHz
+			subcarrier_I = ~corr_i_cnt[4];
+			subcarrier_Q = ~(corr_i_cnt[4] ^ corr_i_cnt[3]);
+		end
+end
+	
 // ADC data appears on the rising edge, so sample it on the falling edge
 always @(negedge adc_clk)
 begin
@@ -92,37 +121,61 @@ begin
     begin
         if(snoop)
         begin
-			// Send only 7 most significant bits of tag signal (signed), LSB is reader signal:
-            corr_i_out <= {corr_i_accum[13:7], after_hysteresis_prev_prev};
-            corr_q_out <= {corr_q_accum[13:7], after_hysteresis_prev};
+			// Send 7 most significant bits of tag signal (signed), plus 1 bit reader signal
+			if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111) 
+				corr_i_out <= {corr_i_accum[11:5], after_hysteresis_prev_prev};
+			else // truncate to maximum value
+				if (corr_i_accum[13] == 1'b0)
+					corr_i_out <= {7'b0111111, after_hysteresis_prev_prev};
+				else
+					corr_i_out <= {7'b1000000, after_hysteresis_prev_prev};
+			if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111) 
+				corr_q_out <= {corr_q_accum[11:5], after_hysteresis_prev};
+			else // truncate to maximum value
+				if (corr_q_accum[13] == 1'b0)
+					corr_q_out <= {7'b0111111, after_hysteresis_prev};
+				else
+					corr_q_out <= {7'b1000000, after_hysteresis_prev};
 			after_hysteresis_prev_prev <= after_hysteresis;
         end
         else
         begin
-            // 8 most significant bits of tag signal
-            corr_i_out <= corr_i_accum[13:6];
-            corr_q_out <= corr_q_accum[13:6];
+            // Send 8 bits of tag signal
+			if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111) 
+				corr_i_out <= corr_i_accum[11:4];
+			else // truncate to maximum value
+				if (corr_i_accum[13] == 1'b0)
+					corr_i_out <= 8'b01111111;
+				else
+					corr_i_out <= 8'b10000000;
+			if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111) 
+				corr_q_out <= corr_q_accum[11:4];
+			else // truncate to maximum value
+				if (corr_q_accum[13] == 1'b0)
+					corr_q_out <= 8'b01111111;
+				else
+					corr_q_out <= 8'b10000000;
         end
-
-        corr_i_accum <= adc_d;
-        corr_q_accum <= adc_d;
+		// Initialize next correlation. 
+		// Both I and Q reference signals are high when corr_i_nct == 0. Therefore need to accumulate.
+        corr_i_accum <= $signed({1'b0,adc_d});
+        corr_q_accum <= $signed({1'b0,adc_d});
     end
     else
     begin
-        if(corr_i_cnt[3])
-            corr_i_accum <= corr_i_accum - adc_d;
+        if (subcarrier_I)
+            corr_i_accum <= corr_i_accum + $signed({1'b0,adc_d});
         else
-            corr_i_accum <= corr_i_accum + adc_d;
+            corr_i_accum <= corr_i_accum - $signed({1'b0,adc_d});
 
-        if(corr_i_cnt[3] == corr_i_cnt[2])			// phase shifted by pi/2
-            corr_q_accum <= corr_q_accum + adc_d;
+        if (subcarrier_Q)
+            corr_q_accum <= corr_q_accum + $signed({1'b0,adc_d});
         else
-            corr_q_accum <= corr_q_accum - adc_d;
+            corr_q_accum <= corr_q_accum - $signed({1'b0,adc_d});
 
     end
 
-    // The logic in hi_simulate.v reports 4 samples per bit. We report two
-    // (I, Q) pairs per bit, so we should do 2 samples per pair.
+	// for each Q/I pair report two reader signal samples when sniffing
     if(corr_i_cnt == 6'd32)
         after_hysteresis_prev <= after_hysteresis;
 
@@ -137,16 +190,16 @@ begin
     begin
         ssp_clk <= 1'b1;
         // Don't shift if we just loaded new data, obviously.
-        if(corr_i_cnt != 7'd0)
+        if(corr_i_cnt != 6'd0)
         begin
             corr_i_out[7:0] <= {corr_i_out[6:0], corr_q_out[7]};
             corr_q_out[7:1] <= corr_q_out[6:0];
         end
     end
 
-	// set ssp_frame signal for corr_i_cnt = 0..3 and corr_i_cnt = 32..35
-	// (send two frames with 8 Bits each)
-    if(corr_i_cnt[5:2] == 4'b0000 || corr_i_cnt[5:2] == 4'b1000)
+    // set ssp_frame signal for corr_i_cnt = 0..3
+    // (send one frame with 16 Bits)
+    if(corr_i_cnt[5:2] == 4'b0000)
         ssp_frame = 1'b1;
     else
         ssp_frame = 1'b0;
@@ -157,8 +210,4 @@ assign ssp_din = corr_i_out[7];
 
 assign dbg = corr_i_cnt[3];
 
-// Unused.
-assign pwr_lo = 1'b0;
-assign pwr_oe2 = 1'b0;
-
 endmodule