]>
Commit | Line | Data |
---|---|---|
ba06a4b6 | 1 | //----------------------------------------------------------------------------- |
2 | // | |
3 | // Jonathan Westhues, April 2006 | |
4 | //----------------------------------------------------------------------------- | |
5 | ||
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, | |
9 | adc_d, adc_clk, | |
10 | ssp_frame, ssp_din, ssp_dout, ssp_clk, | |
11 | cross_hi, cross_lo, | |
12 | dbg, | |
3f7aaf24 | 13 | xcorr_is_848, snoop, xcorr_quarter_freq |
ba06a4b6 | 14 | ); |
15 | input pck0, ck_1356meg, ck_1356megb; | |
16 | output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4; | |
17 | input [7:0] adc_d; | |
18 | output adc_clk; | |
19 | input ssp_dout; | |
20 | output ssp_frame, ssp_din, ssp_clk; | |
21 | input cross_hi, cross_lo; | |
22 | output dbg; | |
3f7aaf24 | 23 | input xcorr_is_848, snoop, xcorr_quarter_freq; |
ba06a4b6 | 24 | |
25 | // Carrier is steady on through this, unless we're snooping. | |
26 | assign pwr_hi = ck_1356megb & (~snoop); | |
27 | assign pwr_oe1 = 1'b0; | |
ba06a4b6 | 28 | assign pwr_oe3 = 1'b0; |
29 | assign pwr_oe4 = 1'b0; | |
315e18e6 | 30 | // Unused. |
31 | assign pwr_lo = 1'b0; | |
32 | assign pwr_oe2 = 1'b0; | |
33 | ||
34 | assign adc_clk = ck_1356megb; // sample frequency is 13,56 MHz | |
ba06a4b6 | 35 | |
ba06a4b6 | 36 | // When we're a reader, we just need to do the BPSK demod; but when we're an |
37 | // eavesdropper, we also need to pick out the commands sent by the reader, | |
38 | // using AM. Do this the same way that we do it for the simulated tag. | |
51d4f6f1 | 39 | reg after_hysteresis, after_hysteresis_prev, after_hysteresis_prev_prev; |
ba06a4b6 | 40 | reg [11:0] has_been_low_for; |
41 | always @(negedge adc_clk) | |
42 | begin | |
43 | if(& adc_d[7:0]) after_hysteresis <= 1'b1; | |
44 | else if(~(| adc_d[7:0])) after_hysteresis <= 1'b0; | |
45 | ||
46 | if(after_hysteresis) | |
47 | begin | |
48 | has_been_low_for <= 7'b0; | |
49 | end | |
50 | else | |
51 | begin | |
52 | if(has_been_low_for == 12'd4095) | |
53 | begin | |
54 | has_been_low_for <= 12'd0; | |
55 | after_hysteresis <= 1'b1; | |
56 | end | |
57 | else | |
58 | has_been_low_for <= has_been_low_for + 1; | |
59 | end | |
60 | end | |
61 | ||
315e18e6 | 62 | |
63 | // Let us report a correlation every 64 samples. I.e. | |
64 | // one Q/I pair after 4 subcarrier cycles for the 848kHz subcarrier, | |
65 | // one Q/I pair after 2 subcarrier cycles for the 424kHz subcarriers, | |
66 | // one Q/I pair for each subcarrier cyle for the 212kHz subcarrier. | |
67 | // We need a 6-bit counter for the timing. | |
ba06a4b6 | 68 | reg [5:0] corr_i_cnt; |
315e18e6 | 69 | always @(negedge adc_clk) |
70 | begin | |
71 | corr_i_cnt <= corr_i_cnt + 1; | |
72 | end | |
73 | ||
74 | // And a couple of registers in which to accumulate the correlations. From the 64 samples | |
75 | // we would add at most 32 times the difference between unmodulated and modulated signal. It should | |
d372569b | 76 | // be safe to assume that a tag will not be able to modulate the carrier signal by more than 25%. |
77 | // 32 * 255 * 0,25 = 2040, which can be held in 11 bits. Add 1 bit for sign. | |
315e18e6 | 78 | // Temporary we might need more bits. For the 212kHz subcarrier we could possible add 32 times the |
79 | // maximum signal value before a first subtraction would occur. 32 * 255 = 8160 can be held in 13 bits. | |
80 | // Add one bit for sign -> need 14 bit registers but final result will fit into 12 bits. | |
81 | reg signed [13:0] corr_i_accum; | |
82 | reg signed [13:0] corr_q_accum; | |
d372569b | 83 | // we will report maximum 8 significant bits |
ba06a4b6 | 84 | reg signed [7:0] corr_i_out; |
85 | reg signed [7:0] corr_q_out; | |
51d4f6f1 | 86 | // clock and frame signal for communication to ARM |
87 | reg ssp_clk; | |
88 | reg ssp_frame; | |
89 | ||
90 | ||
315e18e6 | 91 | // The subcarrier reference signals |
92 | reg subcarrier_I; | |
93 | reg subcarrier_Q; | |
ba06a4b6 | 94 | |
315e18e6 | 95 | always @(corr_i_cnt or xcorr_is_848 or xcorr_quarter_freq) |
96 | begin | |
97 | if (xcorr_is_848 & ~xcorr_quarter_freq) // 848 kHz | |
98 | begin | |
99 | subcarrier_I = ~corr_i_cnt[3]; | |
100 | subcarrier_Q = ~(corr_i_cnt[3] ^ corr_i_cnt[2]); | |
101 | end | |
102 | else if (xcorr_is_848 & xcorr_quarter_freq) // 212 kHz | |
103 | begin | |
104 | subcarrier_I = ~corr_i_cnt[5]; | |
105 | subcarrier_Q = ~(corr_i_cnt[5] ^ corr_i_cnt[4]); | |
106 | end | |
107 | else | |
108 | begin // 424 kHz | |
109 | subcarrier_I = ~corr_i_cnt[4]; | |
110 | subcarrier_Q = ~(corr_i_cnt[4] ^ corr_i_cnt[3]); | |
111 | end | |
112 | end | |
113 | ||
ba06a4b6 | 114 | // ADC data appears on the rising edge, so sample it on the falling edge |
115 | always @(negedge adc_clk) | |
116 | begin | |
117 | // These are the correlators: we correlate against in-phase and quadrature | |
118 | // versions of our reference signal, and keep the (signed) result to | |
119 | // send out later over the SSP. | |
705bfa10 | 120 | if(corr_i_cnt == 6'd0) |
ba06a4b6 | 121 | begin |
122 | if(snoop) | |
123 | begin | |
d372569b | 124 | // Send 7 most significant bits of tag signal (signed), plus 1 bit reader signal |
315e18e6 | 125 | if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111) |
126 | corr_i_out <= {corr_i_accum[11:5], after_hysteresis_prev_prev}; | |
127 | else // truncate to maximum value | |
128 | if (corr_i_accum[13] == 1'b0) | |
129 | corr_i_out <= {7'b0111111, after_hysteresis_prev_prev}; | |
130 | else | |
131 | corr_i_out <= {7'b1000000, after_hysteresis_prev_prev}; | |
132 | if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111) | |
133 | corr_q_out <= {corr_q_accum[11:5], after_hysteresis_prev}; | |
134 | else // truncate to maximum value | |
135 | if (corr_q_accum[13] == 1'b0) | |
136 | corr_q_out <= {7'b0111111, after_hysteresis_prev}; | |
137 | else | |
138 | corr_q_out <= {7'b1000000, after_hysteresis_prev}; | |
51d4f6f1 | 139 | after_hysteresis_prev_prev <= after_hysteresis; |
ba06a4b6 | 140 | end |
141 | else | |
142 | begin | |
315e18e6 | 143 | // Send 8 bits of tag signal |
144 | if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111) | |
145 | corr_i_out <= corr_i_accum[11:4]; | |
146 | else // truncate to maximum value | |
147 | if (corr_i_accum[13] == 1'b0) | |
148 | corr_i_out <= 8'b01111111; | |
149 | else | |
150 | corr_i_out <= 8'b10000000; | |
151 | if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111) | |
152 | corr_q_out <= corr_q_accum[11:4]; | |
153 | else // truncate to maximum value | |
154 | if (corr_q_accum[13] == 1'b0) | |
155 | corr_q_out <= 8'b01111111; | |
156 | else | |
157 | corr_q_out <= 8'b10000000; | |
ba06a4b6 | 158 | end |
315e18e6 | 159 | // Initialize next correlation. |
160 | // Both I and Q reference signals are high when corr_i_nct == 0. Therefore need to accumulate. | |
161 | corr_i_accum <= $signed({1'b0,adc_d}); | |
162 | corr_q_accum <= $signed({1'b0,adc_d}); | |
ba06a4b6 | 163 | end |
164 | else | |
165 | begin | |
315e18e6 | 166 | if (subcarrier_I) |
167 | corr_i_accum <= corr_i_accum + $signed({1'b0,adc_d}); | |
ba06a4b6 | 168 | else |
315e18e6 | 169 | corr_i_accum <= corr_i_accum - $signed({1'b0,adc_d}); |
ba06a4b6 | 170 | |
315e18e6 | 171 | if (subcarrier_Q) |
172 | corr_q_accum <= corr_q_accum + $signed({1'b0,adc_d}); | |
51d4f6f1 | 173 | else |
315e18e6 | 174 | corr_q_accum <= corr_q_accum - $signed({1'b0,adc_d}); |
ba06a4b6 | 175 | |
ba06a4b6 | 176 | end |
177 | ||
315e18e6 | 178 | // for each Q/I pair report two reader signal samples when sniffing |
705bfa10 | 179 | if(corr_i_cnt == 6'd32) |
ba06a4b6 | 180 | after_hysteresis_prev <= after_hysteresis; |
181 | ||
182 | // Then the result from last time is serialized and send out to the ARM. | |
183 | // We get one report each cycle, and each report is 16 bits, so the | |
184 | // ssp_clk should be the adc_clk divided by 64/16 = 4. | |
185 | ||
186 | if(corr_i_cnt[1:0] == 2'b10) | |
187 | ssp_clk <= 1'b0; | |
188 | ||
189 | if(corr_i_cnt[1:0] == 2'b00) | |
190 | begin | |
191 | ssp_clk <= 1'b1; | |
192 | // Don't shift if we just loaded new data, obviously. | |
b535053a | 193 | if(corr_i_cnt != 6'd0) |
ba06a4b6 | 194 | begin |
195 | corr_i_out[7:0] <= {corr_i_out[6:0], corr_q_out[7]}; | |
196 | corr_q_out[7:1] <= corr_q_out[6:0]; | |
197 | end | |
198 | end | |
199 | ||
09c66f1f | 200 | // set ssp_frame signal for corr_i_cnt = 0..3 and corr_i_cnt = 32..35 |
51d4f6f1 | 201 | // (send two frames with 8 Bits each) |
09c66f1f | 202 | if(corr_i_cnt[5:2] == 4'b0000 || corr_i_cnt[5:2] == 4'b1000) |
ba06a4b6 | 203 | ssp_frame = 1'b1; |
204 | else | |
205 | ssp_frame = 1'b0; | |
206 | ||
207 | end | |
208 | ||
209 | assign ssp_din = corr_i_out[7]; | |
210 | ||
211 | assign dbg = corr_i_cnt[3]; | |
212 | ||
ba06a4b6 | 213 | endmodule |