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
  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
  56 reg [10:0] ssp_clk_divider;
  57
  58 always @(posedge adc_clk)
  59     ssp_clk_divider <= (ssp_clk_divider + 1);
  60
  61 reg ssp_clk;
  62 reg ssp_frame;
  63 always @(negedge adc_clk)
  64 begin
  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
  81 end
  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.
  91 reg [2:0] ssp_frame_divider_to_arm;
  92 always @(posedge ssp_clk)
  93     ssp_frame_divider_to_arm <= (ssp_frame_divider_to_arm + 1);
  94 reg [2:0] ssp_frame_divider_from_arm;
  95 always @(negedge ssp_clk)
  96     ssp_frame_divider_from_arm <= (ssp_frame_divider_from_arm + 1);
  97
  98
  99
 100 always @(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.
 107 reg ssp_din;
 108 always @(posedge ssp_clk)
 109     ssp_din = after_hysteresis;
 110
 111 // Modulating carrier frequency is fc/16, reuse ssp_clk divider for that
 112 reg modulating_carrier;
 113 always @(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
 126 assign 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.
 130 assign pwr_oe1 = modulating_carrier;
 131 assign pwr_oe4 = modulating_carrier;
 132
 133 // This one is always on, so that we can watch the carrier.
 134 assign pwr_oe3 = 1'b0;
 135
 136 assign dbg = modulating_carrier;
 137 //reg dbg;
 138 //always @(ssp_dout)
 139 //    dbg <= ssp_dout;
 140
 141 endmodule