| 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 | // The register is bigger to allow higher division factors of up to /128 |
| 55 | reg [6:0] ssp_clk_divider; |
| 56 | always @(posedge adc_clk) |
| 57 | ssp_clk_divider <= (ssp_clk_divider + 1); |
| 58 | assign ssp_clk = ssp_clk_divider[4]; |
| 59 | |
| 60 | // Divide SSP_CLK by 8 to produce the byte framing signal; the phase of |
| 61 | // this is arbitrary, because it's just a bitstream. |
| 62 | // One nasty issue, though: I can't make it work with both rx and tx at |
| 63 | // once. The phase wrt ssp_clk must be changed. TODO to find out why |
| 64 | // that is and make a better fix. |
| 65 | reg [2:0] ssp_frame_divider_to_arm; |
| 66 | always @(posedge ssp_clk) |
| 67 | ssp_frame_divider_to_arm <= (ssp_frame_divider_to_arm + 1); |
| 68 | reg [2:0] ssp_frame_divider_from_arm; |
| 69 | always @(negedge ssp_clk) |
| 70 | ssp_frame_divider_from_arm <= (ssp_frame_divider_from_arm + 1); |
| 71 | |
| 72 | reg ssp_frame; |
| 73 | always @(ssp_frame_divider_to_arm or ssp_frame_divider_from_arm or mod_type) |
| 74 | if(mod_type == 3'b000) // not modulating, so listening, to ARM |
| 75 | ssp_frame = (ssp_frame_divider_to_arm == 3'b000); |
| 76 | else |
| 77 | ssp_frame = (ssp_frame_divider_from_arm == 3'b000); |
| 78 | |
| 79 | // Synchronize up the after-hysteresis signal, to produce DIN. |
| 80 | reg ssp_din; |
| 81 | always @(posedge ssp_clk) |
| 82 | ssp_din = after_hysteresis; |
| 83 | |
| 84 | // Modulating carrier frequency is fc/16, reuse ssp_clk divider for that |
| 85 | reg modulating_carrier; |
| 86 | always @(mod_type or ssp_clk or ssp_dout) |
| 87 | if(mod_type == 3'b000) |
| 88 | modulating_carrier <= 1'b0; // no modulation |
| 89 | else if(mod_type == 3'b001) |
| 90 | modulating_carrier <= ssp_dout ^ ssp_clk_divider[3]; // XOR means BPSK |
| 91 | else if(mod_type == 3'b010) |
| 92 | modulating_carrier <= ssp_dout & ssp_clk_divider[5]; // switch 212kHz subcarrier on/off |
| 93 | else if(mod_type == 3'b100) |
| 94 | modulating_carrier <= ssp_dout & ssp_clk_divider[4]; // switch 424kHz modulation on/off |
| 95 | else |
| 96 | modulating_carrier <= 1'b0; // yet unused |
| 97 | |
| 98 | // This one is all LF, so doesn't matter |
| 99 | assign pwr_oe2 = modulating_carrier; |
| 100 | |
| 101 | // Toggle only one of these, since we are already producing much deeper |
| 102 | // modulation than a real tag would. |
| 103 | assign pwr_oe1 = modulating_carrier; |
| 104 | assign pwr_oe4 = modulating_carrier; |
| 105 | |
| 106 | // This one is always on, so that we can watch the carrier. |
| 107 | assign pwr_oe3 = 1'b0; |
| 108 | |
| 109 | assign dbg = after_hysteresis; |
| 110 | //reg dbg; |
| 111 | //always @(ssp_dout) |
| 112 | // dbg <= ssp_dout; |
| 113 | |
| 114 | endmodule |