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1//-----------------------------------------------------------------------------
2// Pretend to be an ISO 14443 tag. We will do this by alternately short-
3// circuiting and open-circuiting the antenna coil, with the tri-state
4// pins.
5//
6// We communicate over the SSP, as a bitstream (i.e., might as well be
7// unframed, though we still generate the word sync signal). The output
8// (ARM -> FPGA) tells us whether to modulate or not. The input (FPGA
9// -> ARM) is us using the A/D as a fancy comparator; this is with
10// (software-added) hysteresis, to undo the high-pass filter.
11//
12// At this point only Type A is implemented. This means that we are using a
13// bit rate of 106 kbit/s, or fc/128. Oversample by 4, which ought to make
14// things practical for the ARM (fc/32, 423.8 kbits/s, ~50 kbytes/s)
15//
16// Jonathan Westhues, October 2006
17//-----------------------------------------------------------------------------
18
19module hi_simulate(
20 pck0, ck_1356meg, ck_1356megb,
21 pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,
22 adc_d, adc_clk,
23 ssp_frame, ssp_din, ssp_dout, ssp_clk,
24 cross_hi, cross_lo,
25 dbg,
26 mod_type
27);
28 input pck0, ck_1356meg, ck_1356megb;
29 output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
30 input [7:0] adc_d;
31 output adc_clk;
32 input ssp_dout;
33 output ssp_frame, ssp_din, ssp_clk;
34 input cross_hi, cross_lo;
35 output dbg;
36 input [2:0] mod_type;
37
38// Power amp goes between LOW and tri-state, so pwr_hi (and pwr_lo) can
39// always be low.
40assign pwr_hi = 1'b0;
41assign pwr_lo = 1'b0;
42
43// The comparator with hysteresis on the output from the peak detector.
44reg after_hysteresis;
45assign adc_clk = ck_1356meg;
46
47always @(negedge adc_clk)
48begin
49 if(& adc_d[7:5]) after_hysteresis = 1'b1;
50 else if(~(| adc_d[7:5])) after_hysteresis = 1'b0;
51end
52
53
54// Divide 13.56 MHz by 32 to produce the SSP_CLK
55// The register is bigger to allow higher division factors of up to /128
56reg [10:0] ssp_clk_divider;
57
58always @(posedge adc_clk)
59 ssp_clk_divider <= (ssp_clk_divider + 1);
60
61reg ssp_clk;
62reg ssp_frame;
63always @(negedge adc_clk)
64begin
65 //If we're in 101, we only need a new bit every 8th carrier bit (53Hz). Otherwise, get next bit at 424Khz
66 if(mod_type == 3'b101)
67 begin
68 if(ssp_clk_divider[7:0] == 8'b00000000)
69 ssp_clk <= 1'b0;
70 if(ssp_clk_divider[7:0] == 8'b10000000)
71 ssp_clk <= 1'b1;
72
73 end
74 else
75 begin
76 if(ssp_clk_divider[4:0] == 5'd0)//[4:0] == 5'b00000)
77 ssp_clk <= 1'b1;
78 if(ssp_clk_divider[4:0] == 5'd16) //[4:0] == 5'b10000)
79 ssp_clk <= 1'b0;
80 end
81end
82
83
84//assign ssp_clk = ssp_clk_divider[4];
85
86// Divide SSP_CLK by 8 to produce the byte framing signal; the phase of
87// this is arbitrary, because it's just a bitstream.
88// One nasty issue, though: I can't make it work with both rx and tx at
89// once. The phase wrt ssp_clk must be changed. TODO to find out why
90// that is and make a better fix.
91reg [2:0] ssp_frame_divider_to_arm;
92always @(posedge ssp_clk)
93 ssp_frame_divider_to_arm <= (ssp_frame_divider_to_arm + 1);
94reg [2:0] ssp_frame_divider_from_arm;
95always @(negedge ssp_clk)
96 ssp_frame_divider_from_arm <= (ssp_frame_divider_from_arm + 1);
97
98
99
100always @(ssp_frame_divider_to_arm or ssp_frame_divider_from_arm or mod_type)
101 if(mod_type == 3'b000) // not modulating, so listening, to ARM
102 ssp_frame = (ssp_frame_divider_to_arm == 3'b000);
103 else
104 ssp_frame = (ssp_frame_divider_from_arm == 3'b000);
105
106// Synchronize up the after-hysteresis signal, to produce DIN.
107reg ssp_din;
108always @(posedge ssp_clk)
109 ssp_din = after_hysteresis;
110
111// Modulating carrier frequency is fc/16, reuse ssp_clk divider for that
112reg modulating_carrier;
113always @(mod_type or ssp_clk or ssp_dout)
114 if(mod_type == 3'b000)
115 modulating_carrier <= 1'b0; // no modulation
116 else if(mod_type == 3'b001)
117 modulating_carrier <= ssp_dout ^ ssp_clk_divider[3]; // XOR means BPSK
118 else if(mod_type == 3'b010)
119 modulating_carrier <= ssp_dout & ssp_clk_divider[5]; // switch 212kHz subcarrier on/off
120 else if(mod_type == 3'b100 || mod_type == 3'b101)
121 modulating_carrier <= ssp_dout & ssp_clk_divider[4]; // switch 424kHz modulation on/off
122 else
123 modulating_carrier <= 1'b0; // yet unused
124
125// This one is all LF, so doesn't matter
126assign pwr_oe2 = modulating_carrier;
127
128// Toggle only one of these, since we are already producing much deeper
129// modulation than a real tag would.
130assign pwr_oe1 = modulating_carrier;
131assign pwr_oe4 = modulating_carrier;
132
133// This one is always on, so that we can watch the carrier.
134assign pwr_oe3 = 1'b0;
135
136assign dbg = modulating_carrier;
137//reg dbg;
138//always @(ssp_dout)
139// dbg <= ssp_dout;
140
141endmodule
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