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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, | |
d9de20fa | 13 | xcorr_is_848, snoop, xcorr_quarter_freq, hi_read_rx_xcorr_amplitude |
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; | |
d9de20fa | 23 | input xcorr_is_848, snoop, xcorr_quarter_freq, hi_read_rx_xcorr_amplitude; |
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; | |
d9de20fa | 86 | |
51d4f6f1 | 87 | // clock and frame signal for communication to ARM |
88 | reg ssp_clk; | |
89 | reg ssp_frame; | |
90 | ||
91 | ||
d9de20fa | 92 | |
93 | // the amplitude of the subcarrier is sqrt(ci^2 + cq^2). | |
94 | // approximate by amplitude = max(|ci|,|cq|) + 1/2*min(|ci|,|cq|) | |
95 | reg [13:0] corr_amplitude, abs_ci, abs_cq, max_ci_cq, min_ci_cq; | |
96 | ||
97 | ||
98 | always @(corr_i_accum or corr_q_accum) | |
99 | begin | |
100 | if (corr_i_accum[13] == 1'b0) | |
101 | abs_ci <= corr_i_accum; | |
102 | else | |
103 | abs_ci <= -corr_i_accum; | |
104 | ||
105 | if (corr_q_accum[13] == 1'b0) | |
106 | abs_cq <= corr_q_accum; | |
107 | else | |
108 | abs_cq <= -corr_q_accum; | |
109 | ||
110 | if (abs_ci > abs_cq) | |
111 | begin | |
112 | max_ci_cq <= abs_ci; | |
113 | min_ci_cq <= abs_cq; | |
114 | end | |
115 | else | |
116 | begin | |
117 | max_ci_cq <= abs_cq; | |
118 | min_ci_cq <= abs_ci; | |
119 | end | |
120 | ||
121 | corr_amplitude <= max_ci_cq + min_ci_cq/2; | |
122 | ||
123 | end | |
124 | ||
125 | ||
315e18e6 | 126 | // The subcarrier reference signals |
127 | reg subcarrier_I; | |
128 | reg subcarrier_Q; | |
ba06a4b6 | 129 | |
315e18e6 | 130 | always @(corr_i_cnt or xcorr_is_848 or xcorr_quarter_freq) |
131 | begin | |
132 | if (xcorr_is_848 & ~xcorr_quarter_freq) // 848 kHz | |
133 | begin | |
134 | subcarrier_I = ~corr_i_cnt[3]; | |
135 | subcarrier_Q = ~(corr_i_cnt[3] ^ corr_i_cnt[2]); | |
136 | end | |
137 | else if (xcorr_is_848 & xcorr_quarter_freq) // 212 kHz | |
138 | begin | |
139 | subcarrier_I = ~corr_i_cnt[5]; | |
140 | subcarrier_Q = ~(corr_i_cnt[5] ^ corr_i_cnt[4]); | |
141 | end | |
142 | else | |
143 | begin // 424 kHz | |
144 | subcarrier_I = ~corr_i_cnt[4]; | |
145 | subcarrier_Q = ~(corr_i_cnt[4] ^ corr_i_cnt[3]); | |
146 | end | |
147 | end | |
d9de20fa | 148 | |
149 | ||
ba06a4b6 | 150 | // ADC data appears on the rising edge, so sample it on the falling edge |
151 | always @(negedge adc_clk) | |
152 | begin | |
153 | // These are the correlators: we correlate against in-phase and quadrature | |
d9de20fa | 154 | // versions of our reference signal, and keep the (signed) results or the |
155 | // resulting amplitude to send out later over the SSP. | |
705bfa10 | 156 | if(corr_i_cnt == 6'd0) |
ba06a4b6 | 157 | begin |
158 | if(snoop) | |
159 | begin | |
d9de20fa | 160 | if (hi_read_rx_xcorr_amplitude) |
161 | begin | |
162 | // send amplitude plus 2 bits reader signal | |
163 | corr_i_out <= corr_amplitude[13:6]; | |
164 | corr_q_out <= {corr_amplitude[5:0], after_hysteresis_prev_prev, after_hysteresis_prev}; | |
165 | end | |
166 | else | |
167 | begin | |
168 | // Send 7 most significant bits of in phase tag signal (signed), plus 1 bit reader signal | |
169 | if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111) | |
170 | corr_i_out <= {corr_i_accum[11:5], after_hysteresis_prev_prev}; | |
171 | else // truncate to maximum value | |
172 | if (corr_i_accum[13] == 1'b0) | |
173 | corr_i_out <= {7'b0111111, after_hysteresis_prev_prev}; | |
174 | else | |
175 | corr_i_out <= {7'b1000000, after_hysteresis_prev_prev}; | |
176 | // Send 7 most significant bits of quadrature phase tag signal (signed), plus 1 bit reader signal | |
177 | if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111) | |
178 | corr_q_out <= {corr_q_accum[11:5], after_hysteresis_prev}; | |
179 | else // truncate to maximum value | |
180 | if (corr_q_accum[13] == 1'b0) | |
181 | corr_q_out <= {7'b0111111, after_hysteresis_prev}; | |
182 | else | |
183 | corr_q_out <= {7'b1000000, after_hysteresis_prev}; | |
184 | end | |
ba06a4b6 | 185 | end |
186 | else | |
187 | begin | |
d9de20fa | 188 | if (hi_read_rx_xcorr_amplitude) |
189 | begin | |
190 | // send amplitude | |
191 | corr_i_out <= {2'b00, corr_amplitude[13:8]}; | |
192 | corr_q_out <= corr_amplitude[7:0]; | |
193 | end | |
194 | else | |
195 | begin | |
196 | // Send 8 bits of in phase tag signal | |
197 | if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111) | |
198 | corr_i_out <= corr_i_accum[11:4]; | |
199 | else // truncate to maximum value | |
200 | if (corr_i_accum[13] == 1'b0) | |
201 | corr_i_out <= 8'b01111111; | |
202 | else | |
203 | corr_i_out <= 8'b10000000; | |
204 | // Send 8 bits of quadrature phase tag signal | |
205 | if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111) | |
206 | corr_q_out <= corr_q_accum[11:4]; | |
207 | else // truncate to maximum value | |
208 | if (corr_q_accum[13] == 1'b0) | |
209 | corr_q_out <= 8'b01111111; | |
210 | else | |
211 | corr_q_out <= 8'b10000000; | |
212 | end | |
ba06a4b6 | 213 | end |
d9de20fa | 214 | |
215 | // for each Q/I pair report two reader signal samples when sniffing. Store the 1st. | |
216 | after_hysteresis_prev_prev <= after_hysteresis; | |
315e18e6 | 217 | // Initialize next correlation. |
218 | // Both I and Q reference signals are high when corr_i_nct == 0. Therefore need to accumulate. | |
219 | corr_i_accum <= $signed({1'b0,adc_d}); | |
220 | corr_q_accum <= $signed({1'b0,adc_d}); | |
ba06a4b6 | 221 | end |
222 | else | |
223 | begin | |
315e18e6 | 224 | if (subcarrier_I) |
225 | corr_i_accum <= corr_i_accum + $signed({1'b0,adc_d}); | |
ba06a4b6 | 226 | else |
315e18e6 | 227 | corr_i_accum <= corr_i_accum - $signed({1'b0,adc_d}); |
ba06a4b6 | 228 | |
315e18e6 | 229 | if (subcarrier_Q) |
230 | corr_q_accum <= corr_q_accum + $signed({1'b0,adc_d}); | |
51d4f6f1 | 231 | else |
315e18e6 | 232 | corr_q_accum <= corr_q_accum - $signed({1'b0,adc_d}); |
ba06a4b6 | 233 | end |
234 | ||
d9de20fa | 235 | // for each Q/I pair report two reader signal samples when sniffing. Store the 2nd. |
705bfa10 | 236 | if(corr_i_cnt == 6'd32) |
ba06a4b6 | 237 | after_hysteresis_prev <= after_hysteresis; |
238 | ||
239 | // Then the result from last time is serialized and send out to the ARM. | |
240 | // We get one report each cycle, and each report is 16 bits, so the | |
d9de20fa | 241 | // ssp_clk should be the adc_clk divided by 64/16 = 4. |
242 | // ssp_clk frequency = 13,56MHz / 4 = 3.39MHz | |
ba06a4b6 | 243 | |
244 | if(corr_i_cnt[1:0] == 2'b10) | |
245 | ssp_clk <= 1'b0; | |
246 | ||
247 | if(corr_i_cnt[1:0] == 2'b00) | |
248 | begin | |
249 | ssp_clk <= 1'b1; | |
250 | // Don't shift if we just loaded new data, obviously. | |
b535053a | 251 | if(corr_i_cnt != 6'd0) |
ba06a4b6 | 252 | begin |
253 | corr_i_out[7:0] <= {corr_i_out[6:0], corr_q_out[7]}; | |
254 | corr_q_out[7:1] <= corr_q_out[6:0]; | |
255 | end | |
256 | end | |
257 | ||
6a5d4e17 | 258 | // set ssp_frame signal for corr_i_cnt = 0..3 |
259 | // (send one frame with 16 Bits) | |
260 | if(corr_i_cnt[5:2] == 4'b0000) | |
ba06a4b6 | 261 | ssp_frame = 1'b1; |
262 | else | |
263 | ssp_frame = 1'b0; | |
264 | ||
265 | end | |
266 | ||
267 | assign ssp_din = corr_i_out[7]; | |
268 | ||
269 | assign dbg = corr_i_cnt[3]; | |
270 | ||
ba06a4b6 | 271 | endmodule |