1 //-----------------------------------------------------------------------------
3 // Jonathan Westhues, April 2006
4 //-----------------------------------------------------------------------------
6 module hi_read_rx_xcorr(
7 pck0, ck_1356meg, ck_1356megb,
8 pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,
10 ssp_frame, ssp_din, ssp_dout, ssp_clk,
15 input pck0, ck_1356meg, ck_1356megb;
16 output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
20 output ssp_frame, ssp_din, ssp_clk;
21 input cross_hi, cross_lo;
23 input xcorr_is_848, snoop;
25 // Carrier is steady on through this, unless we're snooping.
26 assign pwr_hi = ck_1356megb & (~snoop);
27 assign pwr_oe1 = 1'b0;
28 assign pwr_oe3 = 1'b0;
29 assign pwr_oe4 = 1'b0;
31 wire adc_clk = ck_1356megb;
34 always @(negedge ck_1356megb)
35 fc_div_2 <= fc_div_2 + 1;
37 // When we're a reader, we just need to do the BPSK demod; but when we're an
38 // eavesdropper, we also need to pick out the commands sent by the reader,
39 // using AM. Do this the same way that we do it for the simulated tag.
40 reg after_hysteresis, after_hysteresis_prev, after_hysteresis_prev_prev;
41 reg [11:0] has_been_low_for;
42 always @(negedge adc_clk)
44 if(& adc_d[7:0]) after_hysteresis <= 1'b1;
45 else if(~(| adc_d[7:0])) after_hysteresis <= 1'b0;
49 has_been_low_for <= 7'b0;
53 if(has_been_low_for == 12'd4095)
55 has_been_low_for <= 12'd0;
56 after_hysteresis <= 1'b1;
59 has_been_low_for <= has_been_low_for + 1;
63 // Let us report a correlation every 4 subcarrier cycles, or 4*16 samples,
64 // so we need a 6-bit counter.
66 // And a couple of registers in which to accumulate the correlations.
67 // we would add at most 32 times adc_d, the result can be held in 13 bits.
68 // Need one additional bit because it can be negative as well
69 reg signed [13:0] corr_i_accum;
70 reg signed [13:0] corr_q_accum;
71 reg signed [7:0] corr_i_out;
72 reg signed [7:0] corr_q_out;
73 // clock and frame signal for communication to ARM
78 always @(negedge adc_clk)
80 if (xcorr_is_848 | fc_div_2)
81 corr_i_cnt <= corr_i_cnt + 1;
85 // ADC data appears on the rising edge, so sample it on the falling edge
86 always @(negedge adc_clk)
88 // These are the correlators: we correlate against in-phase and quadrature
89 // versions of our reference signal, and keep the (signed) result to
90 // send out later over the SSP.
91 if(corr_i_cnt == 6'd0)
95 // Send only 7 most significant bits of tag signal (signed), LSB is reader signal:
96 corr_i_out <= {corr_i_accum[13:7], after_hysteresis_prev_prev};
97 corr_q_out <= {corr_q_accum[13:7], after_hysteresis_prev};
98 after_hysteresis_prev_prev <= after_hysteresis;
102 // 8 most significant bits of tag signal
103 corr_i_out <= corr_i_accum[13:6];
104 corr_q_out <= corr_q_accum[13:6];
107 corr_i_accum <= adc_d;
108 corr_q_accum <= adc_d;
113 corr_i_accum <= corr_i_accum - adc_d;
115 corr_i_accum <= corr_i_accum + adc_d;
117 if(corr_i_cnt[3] == corr_i_cnt[2]) // phase shifted by pi/2
118 corr_q_accum <= corr_q_accum + adc_d;
120 corr_q_accum <= corr_q_accum - adc_d;
124 // The logic in hi_simulate.v reports 4 samples per bit. We report two
125 // (I, Q) pairs per bit, so we should do 2 samples per pair.
126 if(corr_i_cnt == 6'd32)
127 after_hysteresis_prev <= after_hysteresis;
129 // Then the result from last time is serialized and send out to the ARM.
130 // We get one report each cycle, and each report is 16 bits, so the
131 // ssp_clk should be the adc_clk divided by 64/16 = 4.
133 if(corr_i_cnt[1:0] == 2'b10)
136 if(corr_i_cnt[1:0] == 2'b00)
139 // Don't shift if we just loaded new data, obviously.
140 if(corr_i_cnt != 7'd0)
142 corr_i_out[7:0] <= {corr_i_out[6:0], corr_q_out[7]};
143 corr_q_out[7:1] <= corr_q_out[6:0];
147 // set ssp_frame signal for corr_i_cnt = 0..3 and corr_i_cnt = 32..35
148 // (send two frames with 8 Bits each)
149 if(corr_i_cnt[5:2] == 4'b0000 || corr_i_cnt[5:2] == 4'b1000)
156 assign ssp_din = corr_i_out[7];
158 assign dbg = corr_i_cnt[3];
161 assign pwr_lo = 1'b0;
162 assign pwr_oe2 = 1'b0;