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

   1 //-----------------------------------------------------------------------------
   2 // The way that we connect things in low-frequency read mode. In this case
   3 // we are generating the 134 kHz or 125 kHz carrier, and running the
   4 // unmodulated carrier at that frequency. The A/D samples at that same rate,
   5 // and the result is serialized.
   6 //
   7 // Jonathan Westhues, April 2006
   8 //-----------------------------------------------------------------------------
   9
  10 module lo_read(
  11     pck0, ck_1356meg, ck_1356megb,
  12     pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,
  13     adc_d, adc_clk,
  14     ssp_frame, ssp_din, ssp_dout, ssp_clk,
  15     cross_hi, cross_lo,
  16     dbg,
  17     lo_is_125khz
  18 );
  19     input pck0, ck_1356meg, ck_1356megb;
  20     output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
  21     input [7:0] adc_d;
  22     output adc_clk;
  23     input ssp_dout;
  24     output ssp_frame, ssp_din, ssp_clk;
  25     input cross_hi, cross_lo;
  26     output dbg;
  27     input lo_is_125khz;
  28
  29 // The low-frequency RFID stuff. This is relatively simple, because most
  30 // of the work happens on the ARM, and we just pass samples through. The
  31 // PCK0 must be divided down to generate the A/D clock, and from there by
  32 // a factor of 8 to generate the carrier (that we apply to the coil drivers).
  33 //
  34 // This is also where we decode the received synchronous serial port words,
  35 // to determine how to drive the output enables.
  36
  37 // PCK0 will run at (PLL clock) / 4, or 24 MHz. That means that we can do
  38 // 125 kHz by dividing by a further factor of (8*12*2), or ~134 kHz by
  39 // dividing by a factor of (8*11*2) (for 136 kHz, ~2% error, tolerable).
  40
  41 reg [3:0] pck_divider;
  42 reg clk_lo;
  43
  44 always @(posedge pck0)
  45 begin
  46     if(lo_is_125khz)
  47     begin
  48         if(pck_divider == 4'd11)
  49         begin
  50             pck_divider <= 4'd0;
  51             clk_lo = !clk_lo;
  52         end
  53         else
  54             pck_divider <= pck_divider + 1;
  55     end
  56     else
  57     begin
  58         if(pck_divider == 4'd10)
  59         begin
  60             pck_divider <= 4'd0;
  61             clk_lo = !clk_lo;
  62         end
  63         else
  64             pck_divider <= pck_divider + 1;
  65     end
  66 end
  67
  68 reg [2:0] carrier_divider_lo;
  69
  70 always @(posedge clk_lo)
  71 begin
  72     carrier_divider_lo <= carrier_divider_lo + 1;
  73 end
  74
  75 assign pwr_lo = carrier_divider_lo[2];
  76
  77 // This serializes the values returned from the A/D, and sends them out
  78 // over the SSP.
  79
  80 reg [7:0] to_arm_shiftreg;
  81
  82 always @(posedge clk_lo)
  83 begin
  84     if(carrier_divider_lo == 3'b000)
  85         to_arm_shiftreg <= adc_d;
  86     else
  87         to_arm_shiftreg[7:1] <= to_arm_shiftreg[6:0];
  88 end
  89
  90 assign ssp_clk = clk_lo;
  91 assign ssp_frame = (carrier_divider_lo == 3'b001);
  92 assign ssp_din = to_arm_shiftreg[7];
  93
  94 // The ADC converts on the falling edge, and our serializer loads when
  95 // carrier_divider_lo == 3'b000.
  96 assign adc_clk = ~carrier_divider_lo[2];
  97
  98 assign pwr_hi = 1'b0;
  99
 100 assign dbg = adc_clk;
 101
 102 endmodule