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;
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,
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
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
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;
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];
assign dbg = corr_i_cnt[3];
-// Unused.
-assign pwr_lo = 1'b0;
-assign pwr_oe2 = 1'b0;
-
endmodule
projects / proxmark3-svn / blobdiff