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annotate fpga/sniffer-basic/sniff_rx.v @ 6:7db5fd6646df

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fpga/sniffer-basic: initial version
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 21 Aug 2023 00:52:00 +0000
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children db8acc067542
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7db5fd6646df fpga/sniffer-basic: initial version
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1 /*
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2 * This Verilog module captures the ISO 7816-3 character sniffing receiver.
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3 */
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4
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5 module sniff_rx (IntClk, SIM_RST_sync, SIM_CLK_sync, SIM_IO_sync,
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6 Rx_strobe, Rx_error, Rx_char, Rx_start_bit, Rx_parity_bit);
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7
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8 input IntClk;
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9 input SIM_RST_sync, SIM_CLK_sync, SIM_IO_sync;
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10 output Rx_strobe, Rx_error;
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11 output [7:0] Rx_char;
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12 output Rx_start_bit, Rx_parity_bit;
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13
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14 wire SIM_CLK_edge;
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16 clk_edge clk_edge (IntClk, SIM_CLK_sync, SIM_CLK_edge);
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17
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18 wire [9:0] etu_0p5, etu_1p0, etu_1p5;
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19
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20 /* Fi/Di=372 only for now */
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21 assign etu_0p5 = 10'd185;
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22 assign etu_1p0 = 10'd371;
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23 assign etu_1p5 = 10'd557;
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24
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25 reg rx_active;
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26 reg [9:0] clk_count;
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27 reg [3:0] bit_count;
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28 reg [9:0] shift_reg;
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29
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30 always @(posedge IntClk)
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31 if (!SIM_RST_sync)
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32 rx_active <= 1'b0;
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33 else if (!rx_active && !SIM_IO_sync)
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34 begin
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35 rx_active <= 1'b1;
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36 clk_count <= etu_0p5;
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37 bit_count <= 4'd0;
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38 end
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39 else if (rx_active && SIM_CLK_edge)
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40 begin
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41 if (clk_count != 10'd0)
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42 clk_count <= clk_count - 10'd1;
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43 else begin
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44 shift_reg <= {SIM_IO_sync,shift_reg[9:1]};
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45 bit_count <= bit_count + 4'd1;
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46 if (bit_count == 4'd9)
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47 clk_count <= etu_1p5;
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48 else
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49 clk_count <= etu_1p0;
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50 if (bit_count == 4'd10)
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51 rx_active <= 1'b0;
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52 end
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53 end
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54
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55 assign Rx_strobe = rx_active && SIM_CLK_edge && clk_count == 10'd0 &&
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56 bit_count == 4'd10;
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57 assign Rx_error = Rx_strobe && !SIO_IO_sync;
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58 assign Rx_char = shift_reg[8:1];
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59 assign Rx_start_bit = shift_reg[0];
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60 assign Rx_parity_bit = shift_reg[9];
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61
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62 endmodule