git.zerfleddert.de Git - proxmark3-svn/blob - fpga/hi_simulate.v

   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
  19 module 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.
  40 assign pwr_hi = 1'b0;
  41 assign pwr_lo = 1'b0;
  42
  43 // The comparator with hysteresis on the output from the peak detector.
  44 reg after_hysteresis;
  45 assign adc_clk = ck_1356meg;
  46
  47 always @(negedge adc_clk)
  48 begin
  49     if(& adc_d[7:5]) after_hysteresis = 1'b1;
  50     else if(~(| adc_d[7:5])) after_hysteresis = 1'b0;
  51 end
  52
  53 // Divide 13.56 MHz by 32 to produce the SSP_CLK
  54 reg [4:0] ssp_clk_divider;
  55 always @(posedge adc_clk)
  56     ssp_clk_divider <= (ssp_clk_divider + 1);
  57 assign ssp_clk = ssp_clk_divider[4];
  58
  59 // Divide SSP_CLK by 8 to produce the byte framing signal; the phase of
  60 // this is arbitrary, because it's just a bitstream.
  61 // One nasty issue, though: I can't make it work with both rx and tx at
  62 // once. The phase wrt ssp_clk must be changed. TODO to find out why
  63 // that is and make a better fix.
  64 reg [2:0] ssp_frame_divider_to_arm;
  65 always @(posedge ssp_clk)
  66     ssp_frame_divider_to_arm <= (ssp_frame_divider_to_arm + 1);
  67 reg [2:0] ssp_frame_divider_from_arm;
  68 always @(negedge ssp_clk)
  69     ssp_frame_divider_from_arm <= (ssp_frame_divider_from_arm + 1);
  70
  71 reg ssp_frame;
  72 always @(ssp_frame_divider_to_arm or ssp_frame_divider_from_arm or mod_type)
  73     if(mod_type == 3'b000) // not modulating, so listening, to ARM
  74         ssp_frame = (ssp_frame_divider_to_arm == 3'b000);
  75     else
  76         ssp_frame = (ssp_frame_divider_from_arm == 3'b000);
  77
  78 // Synchronize up the after-hysteresis signal, to produce DIN.
  79 reg ssp_din;
  80 always @(posedge ssp_clk)
  81     ssp_din = after_hysteresis;
  82
  83 // Modulating carrier frequency is fc/16, reuse ssp_clk divider for that
  84 reg modulating_carrier;
  85 always @(mod_type or ssp_clk or ssp_dout)
  86     if(mod_type == 3'b000)
  87         modulating_carrier <= 1'b0;                          // no modulation
  88     else if(mod_type == 3'b001)
  89         modulating_carrier <= ssp_dout ^ ssp_clk_divider[3]; // XOR means BPSK
  90     else
  91         modulating_carrier <= 1'b0;                           // yet unused
  92
  93 // This one is all LF, so doesn't matter
  94 assign pwr_oe2 = modulating_carrier;
  95
  96 // Toggle only one of these, since we are already producing much deeper
  97 // modulation than a real tag would.
  98 assign pwr_oe1 = modulating_carrier;
  99 assign pwr_oe4 = modulating_carrier;
 100
 101 // This one is always on, so that we can watch the carrier.
 102 assign pwr_oe3 = 1'b0;
 103
 104 assign dbg = after_hysteresis;
 105
 106 endmodule