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1 | //-----------------------------------------------------------------------------\r | |
2 | //\r | |
3 | // Jonathan Westhues, April 2006\r | |
4 | //-----------------------------------------------------------------------------\r | |
5 | \r | |
6 | module hi_read_rx_xcorr(\r | |
7 | pck0, ck_1356meg, ck_1356megb,\r | |
8 | pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,\r | |
9 | adc_d, adc_clk,\r | |
10 | ssp_frame, ssp_din, ssp_dout, ssp_clk,\r | |
11 | cross_hi, cross_lo,\r | |
12 | dbg,\r | |
13 | xcorr_is_848, snoop, xcorr_quarter_freq\r | |
14 | );\r | |
15 | input pck0, ck_1356meg, ck_1356megb;\r | |
16 | output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;\r | |
17 | input [7:0] adc_d;\r | |
18 | output adc_clk;\r | |
19 | input ssp_dout;\r | |
20 | output ssp_frame, ssp_din, ssp_clk;\r | |
21 | input cross_hi, cross_lo;\r | |
22 | output dbg;\r | |
23 | input xcorr_is_848, snoop, xcorr_quarter_freq;\r | |
24 | \r | |
25 | // Carrier is steady on through this, unless we're snooping.\r | |
26 | assign pwr_hi = ck_1356megb & (~snoop);\r | |
27 | assign pwr_oe1 = 1'b0;\r | |
28 | assign pwr_oe2 = 1'b0;\r | |
29 | assign pwr_oe3 = 1'b0;\r | |
30 | assign pwr_oe4 = 1'b0;\r | |
31 | \r | |
32 | reg ssp_clk;\r | |
33 | reg ssp_frame;\r | |
34 | \r | |
35 | reg fc_div_2;\r | |
36 | always @(posedge ck_1356meg)\r | |
37 | fc_div_2 = ~fc_div_2;\r | |
38 | \r | |
39 | reg fc_div_4;\r | |
40 | always @(posedge fc_div_2)\r | |
41 | fc_div_4 = ~fc_div_4;\r | |
42 | \r | |
43 | reg fc_div_8;\r | |
44 | always @(posedge fc_div_4)\r | |
45 | fc_div_8 = ~fc_div_8;\r | |
46 | \r | |
47 | reg adc_clk;\r | |
48 | \r | |
49 | always @(xcorr_is_848 or xcorr_quarter_freq or ck_1356meg)\r | |
50 | if(~xcorr_quarter_freq)\r | |
51 | begin\r | |
52 | if(xcorr_is_848)\r | |
53 | // The subcarrier frequency is fc/16; we will sample at fc, so that \r | |
54 | // means the subcarrier is 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 ...\r | |
55 | adc_clk <= ck_1356meg;\r | |
56 | else\r | |
57 | // The subcarrier frequency is fc/32; we will sample at fc/2, and\r | |
58 | // the subcarrier will look identical.\r | |
59 | adc_clk <= fc_div_2;\r | |
60 | end\r | |
61 | else\r | |
62 | begin\r | |
63 | if(xcorr_is_848)\r | |
64 | // The subcarrier frequency is fc/64\r | |
65 | adc_clk <= fc_div_4;\r | |
66 | else\r | |
67 | // The subcarrier frequency is fc/128\r | |
68 | adc_clk <= fc_div_8;\r | |
69 | end\r | |
70 | \r | |
71 | // When we're a reader, we just need to do the BPSK demod; but when we're an\r | |
72 | // eavesdropper, we also need to pick out the commands sent by the reader,\r | |
73 | // using AM. Do this the same way that we do it for the simulated tag.\r | |
74 | reg after_hysteresis, after_hysteresis_prev;\r | |
75 | reg [11:0] has_been_low_for;\r | |
76 | always @(negedge adc_clk)\r | |
77 | begin\r | |
78 | if(& adc_d[7:0]) after_hysteresis <= 1'b1;\r | |
79 | else if(~(| adc_d[7:0])) after_hysteresis <= 1'b0;\r | |
80 | \r | |
81 | if(after_hysteresis)\r | |
82 | begin\r | |
83 | has_been_low_for <= 7'b0;\r | |
84 | end\r | |
85 | else\r | |
86 | begin\r | |
87 | if(has_been_low_for == 12'd4095)\r | |
88 | begin\r | |
89 | has_been_low_for <= 12'd0;\r | |
90 | after_hysteresis <= 1'b1;\r | |
91 | end\r | |
92 | else\r | |
93 | has_been_low_for <= has_been_low_for + 1;\r | |
94 | end\r | |
95 | end\r | |
96 | \r | |
97 | // Let us report a correlation every 4 subcarrier cycles, or 4*16 samples,\r | |
98 | // so we need a 6-bit counter.\r | |
99 | reg [5:0] corr_i_cnt;\r | |
100 | reg [5:0] corr_q_cnt;\r | |
101 | // And a couple of registers in which to accumulate the correlations.\r | |
102 | reg signed [15:0] corr_i_accum;\r | |
103 | reg signed [15:0] corr_q_accum;\r | |
104 | reg signed [7:0] corr_i_out;\r | |
105 | reg signed [7:0] corr_q_out;\r | |
106 | \r | |
107 | // ADC data appears on the rising edge, so sample it on the falling edge\r | |
108 | always @(negedge adc_clk)\r | |
109 | begin\r | |
110 | // These are the correlators: we correlate against in-phase and quadrature\r | |
111 | // versions of our reference signal, and keep the (signed) result to\r | |
112 | // send out later over the SSP.\r | |
113 | if(corr_i_cnt == 7'd63)\r | |
114 | begin\r | |
115 | if(snoop)\r | |
116 | begin\r | |
117 | corr_i_out <= {corr_i_accum[12:6], after_hysteresis_prev};\r | |
118 | corr_q_out <= {corr_q_accum[12:6], after_hysteresis};\r | |
119 | end\r | |
120 | else\r | |
121 | begin\r | |
122 | // Only correlations need to be delivered.\r | |
123 | corr_i_out <= corr_i_accum[13:6];\r | |
124 | corr_q_out <= corr_q_accum[13:6];\r | |
125 | end\r | |
126 | \r | |
127 | corr_i_accum <= adc_d;\r | |
128 | corr_q_accum <= adc_d;\r | |
129 | corr_q_cnt <= 4;\r | |
130 | corr_i_cnt <= 0;\r | |
131 | end\r | |
132 | else\r | |
133 | begin\r | |
134 | if(corr_i_cnt[3])\r | |
135 | corr_i_accum <= corr_i_accum - adc_d;\r | |
136 | else\r | |
137 | corr_i_accum <= corr_i_accum + adc_d;\r | |
138 | \r | |
139 | if(corr_q_cnt[3])\r | |
140 | corr_q_accum <= corr_q_accum - adc_d;\r | |
141 | else\r | |
142 | corr_q_accum <= corr_q_accum + adc_d;\r | |
143 | \r | |
144 | corr_i_cnt <= corr_i_cnt + 1;\r | |
145 | corr_q_cnt <= corr_q_cnt + 1;\r | |
146 | end\r | |
147 | \r | |
148 | // The logic in hi_simulate.v reports 4 samples per bit. We report two\r | |
149 | // (I, Q) pairs per bit, so we should do 2 samples per pair.\r | |
150 | if(corr_i_cnt == 6'd31)\r | |
151 | after_hysteresis_prev <= after_hysteresis;\r | |
152 | \r | |
153 | // Then the result from last time is serialized and send out to the ARM.\r | |
154 | // We get one report each cycle, and each report is 16 bits, so the\r | |
155 | // ssp_clk should be the adc_clk divided by 64/16 = 4.\r | |
156 | \r | |
157 | if(corr_i_cnt[1:0] == 2'b10)\r | |
158 | ssp_clk <= 1'b0;\r | |
159 | \r | |
160 | if(corr_i_cnt[1:0] == 2'b00)\r | |
161 | begin\r | |
162 | ssp_clk <= 1'b1;\r | |
163 | // Don't shift if we just loaded new data, obviously.\r | |
164 | if(corr_i_cnt != 7'd0)\r | |
165 | begin\r | |
166 | corr_i_out[7:0] <= {corr_i_out[6:0], corr_q_out[7]};\r | |
167 | corr_q_out[7:1] <= corr_q_out[6:0];\r | |
168 | end\r | |
169 | end\r | |
170 | \r | |
171 | if(corr_i_cnt[5:2] == 4'b000 || corr_i_cnt[5:2] == 4'b1000)\r | |
172 | ssp_frame = 1'b1;\r | |
173 | else\r | |
174 | ssp_frame = 1'b0;\r | |
175 | \r | |
176 | end\r | |
177 | \r | |
178 | assign ssp_din = corr_i_out[7];\r | |
179 | \r | |
180 | assign dbg = corr_i_cnt[3];\r | |
181 | \r | |
182 | // Unused.\r | |
183 | assign pwr_lo = 1'b0;\r | |
184 | \r | |
185 | endmodule\r |