New FPGA code for bidirectional LF emulation

[proxmark3-svn] / fpga / hi_read_rx_xcorr.v

//-----------------------------------------------------------------------------\r
//\r
// Jonathan Westhues, April 2006\r
//-----------------------------------------------------------------------------\r
\r
module hi_read_rx_xcorr(\r
    pck0, ck_1356meg, ck_1356megb,\r
    pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,\r
    adc_d, adc_clk,\r
    ssp_frame, ssp_din, ssp_dout, ssp_clk,\r
    cross_hi, cross_lo,\r
    dbg,\r
    xcorr_is_848, snoop\r
);\r
    input pck0, ck_1356meg, ck_1356megb;\r
    output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;\r
    input [7:0] adc_d;\r
    output adc_clk;\r
    input ssp_dout;\r
    output ssp_frame, ssp_din, ssp_clk;\r
    input cross_hi, cross_lo;\r
    output dbg;\r
    input xcorr_is_848, snoop;\r
\r
// Carrier is steady on through this, unless we're snooping.\r
assign pwr_hi = ck_1356megb & (~snoop);\r
assign pwr_oe1 = 1'b0;\r
assign pwr_oe2 = 1'b0;\r
assign pwr_oe3 = 1'b0;\r
assign pwr_oe4 = 1'b0;\r
\r
reg ssp_clk;\r
reg ssp_frame;\r
\r
reg fc_div_2;\r
always @(posedge ck_1356meg)\r
    fc_div_2 = ~fc_div_2;\r
\r
reg adc_clk;\r
\r
always @(xcorr_is_848 or fc_div_2 or ck_1356meg)\r
    if(xcorr_is_848)\r
        // The subcarrier frequency is fc/16; we will sample at fc, so that \r
        // means the subcarrier is 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 ...\r
        adc_clk <= ck_1356meg;\r
    else\r
        // The subcarrier frequency is fc/32; we will sample at fc/2, and\r
        // the subcarrier will look identical.\r
        adc_clk <= fc_div_2;\r
\r
// When we're a reader, we just need to do the BPSK demod; but when we're an\r
// eavesdropper, we also need to pick out the commands sent by the reader,\r
// using AM. Do this the same way that we do it for the simulated tag.\r
reg after_hysteresis, after_hysteresis_prev;\r
reg [11:0] has_been_low_for;\r
always @(negedge adc_clk)\r
begin\r
    if(& adc_d[7:0]) after_hysteresis <= 1'b1;\r
    else if(~(| adc_d[7:0])) after_hysteresis <= 1'b0;\r
\r
    if(after_hysteresis)\r
    begin\r
        has_been_low_for <= 7'b0;\r
    end\r
    else\r
    begin\r
        if(has_been_low_for == 12'd4095)\r
        begin\r
            has_been_low_for <= 12'd0;\r
            after_hysteresis <= 1'b1;\r
        end\r
        else\r
            has_been_low_for <= has_been_low_for + 1;\r
    end\r
end\r
\r
// Let us report a correlation every 4 subcarrier cycles, or 4*16 samples,\r
// so we need a 6-bit counter.\r
reg [5:0] corr_i_cnt;\r
reg [5:0] corr_q_cnt;\r
// And a couple of registers in which to accumulate the correlations.\r
reg signed [15:0] corr_i_accum;\r
reg signed [15:0] corr_q_accum;\r
reg signed [7:0] corr_i_out;\r
reg signed [7:0] corr_q_out;\r
\r
// ADC data appears on the rising edge, so sample it on the falling edge\r
always @(negedge adc_clk)\r
begin\r
    // These are the correlators: we correlate against in-phase and quadrature\r
    // versions of our reference signal, and keep the (signed) result to\r
    // send out later over the SSP.\r
    if(corr_i_cnt == 7'd63)\r
    begin\r
        if(snoop)\r
        begin\r
            corr_i_out <= {corr_i_accum[12:6], after_hysteresis_prev};\r
            corr_q_out <= {corr_q_accum[12:6], after_hysteresis};\r
        end\r
        else\r
        begin\r
            // Only correlations need to be delivered.\r
            corr_i_out <= corr_i_accum[13:6];\r
            corr_q_out <= corr_q_accum[13:6];\r
        end\r
\r
        corr_i_accum <= adc_d;\r
        corr_q_accum <= adc_d;\r
        corr_q_cnt <= 4;\r
        corr_i_cnt <= 0;\r
    end\r
    else\r
    begin\r
        if(corr_i_cnt[3])\r
            corr_i_accum <= corr_i_accum - adc_d;\r
        else\r
            corr_i_accum <= corr_i_accum + adc_d;\r
\r
        if(corr_q_cnt[3])\r
            corr_q_accum <= corr_q_accum - adc_d;\r
        else\r
            corr_q_accum <= corr_q_accum + adc_d;\r
\r
        corr_i_cnt <= corr_i_cnt + 1;\r
        corr_q_cnt <= corr_q_cnt + 1;\r
    end\r
\r
    // The logic in hi_simulate.v reports 4 samples per bit. We report two\r
    // (I, Q) pairs per bit, so we should do 2 samples per pair.\r
    if(corr_i_cnt == 6'd31)\r
        after_hysteresis_prev <= after_hysteresis;\r
\r
    // Then the result from last time is serialized and send out to the ARM.\r
    // We get one report each cycle, and each report is 16 bits, so the\r
    // ssp_clk should be the adc_clk divided by 64/16 = 4.\r
\r
    if(corr_i_cnt[1:0] == 2'b10)\r
        ssp_clk <= 1'b0;\r
\r
    if(corr_i_cnt[1:0] == 2'b00)\r
    begin\r
        ssp_clk <= 1'b1;\r
        // Don't shift if we just loaded new data, obviously.\r
        if(corr_i_cnt != 7'd0)\r
        begin\r
            corr_i_out[7:0] <= {corr_i_out[6:0], corr_q_out[7]};\r
            corr_q_out[7:1] <= corr_q_out[6:0];\r
        end\r
    end\r
\r
    if(corr_i_cnt[5:2] == 4'b000 || corr_i_cnt[5:2] == 4'b1000)\r
        ssp_frame = 1'b1;\r
    else\r
        ssp_frame = 1'b0;\r
\r
end\r
\r
assign ssp_din = corr_i_out[7];\r
\r
assign dbg = corr_i_cnt[3];\r
\r
// Unused.\r
assign pwr_lo = 1'b0;\r
\r
endmodule\r