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_oe3 = 1'b0;
assign pwr_oe4 = 1'b0;
-(* clock_signal = "yes" *) reg fc_div_2;
+reg [2:0] fc_div;
always @(negedge ck_1356megb)
- fc_div_2 <= fc_div_2 + 1;
-
-(* clock_signal = "yes" *) reg adc_clk;
-always @(xcorr_is_848, ck_1356megb, fc_div_2)
-if (xcorr_is_848)
- // The subcarrier frequency is fc/16; we will sample at fc, so that
- // means the subcarrier is 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 ...
- adc_clk <= ck_1356megb;
-else
- // The subcarrier frequency is fc/32; we will sample at fc/2, and
- // the subcarrier will look identical.
- adc_clk <= fc_div_2;
-
-
+ fc_div <= fc_div + 1;
+
+(* clock_signal = "yes" *) reg adc_clk; // sample frequency, always 16 * fc
+always @(ck_1356megb, xcorr_is_848, xcorr_quarter_freq, fc_div)
+ if (xcorr_is_848 & ~xcorr_quarter_freq) // fc = 847.5 kHz, standard ISO14443B
+ adc_clk <= ck_1356megb;
+ else if (~xcorr_is_848 & ~xcorr_quarter_freq) // fc = 423.75 kHz
+ adc_clk <= fc_div[0];
+ else if (xcorr_is_848 & xcorr_quarter_freq) // fc = 211.875 kHz
+ adc_clk <= fc_div[1];
+ else // fc = 105.9375 kHz
+ adc_clk <= fc_div[2];
+
// 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,
// using AM. Do this the same way that we do it for the simulated tag.
end
end
-// Let us report a correlation every 4 subcarrier cycles, or 4*16 samples,
+// Let us report a correlation every 4 subcarrier cycles, or 4*16=64 samples,
// so we need a 6-bit counter.
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
-reg signed [13:0] corr_i_accum;
-reg signed [13:0] corr_q_accum;
+// 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.
+reg signed [11:0] corr_i_accum;
+reg signed [11:0] 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
+ corr_i_cnt <= corr_i_cnt + 1;
+end
+
// ADC data appears on the rising edge, so sample it on the falling edge
always @(negedge adc_clk)
begin
- corr_i_cnt <= corr_i_cnt + 1;
-
// These are the correlators: we correlate against in-phase and quadrature
// versions of our reference signal, and keep the (signed) result to
// send out later over the SSP.
- if(corr_i_cnt == 7'd0)
+ if(corr_i_cnt == 6'd0)
begin
if(snoop)
begin
- // 7 most significant bits of tag signal (signed), 1 bit 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
+ corr_i_out <= {corr_i_accum[11:5], after_hysteresis_prev_prev};
+ corr_q_out <= {corr_q_accum[11:5], 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];
+ // 8 bits of tag signal
+ corr_i_out <= corr_i_accum[11:4];
+ corr_q_out <= corr_q_accum[11:4];
end
corr_i_accum <= adc_d;
// 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.
- if(corr_i_cnt == 6'd31)
+ if(corr_i_cnt == 6'd32)
after_hysteresis_prev <= after_hysteresis;
// Then the result from last time is serialized and send out to the ARM.
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];
projects / proxmark3-svn / blobdiff