//======================================================================
//
// trng.v
// --------
// Top level wrapper for the True Random Number Generator.
//
//
// Author: Joachim Strombergson
// Copyright (c) 2014, NORDUnet A/S All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// - Redistributions of source code must retain the above copyright notice,
//   this list of conditions and the following disclaimer.
//
// - Redistributions in binary form must reproduce the above copyright
//   notice, this list of conditions and the following disclaimer in the
//   documentation and/or other materials provided with the distribution.
//
// - Neither the name of the NORDUnet nor the names of its contributors may
//   be used to endorse or promote products derived from this software
//   without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
// TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//======================================================================

module trng(
            // Clock and reset.
            input wire           clk,
            input wire           reset_n,

            input wire           avalanche_noise,

            input wire           cs,
            input wire           we,
            input wire  [11 : 0] address,
            input wire  [31 : 0] write_data,
            output wire [31 : 0] read_data,
            output wire          error,

            output wire  [7 : 0] debug,
            input wire           debug_update,

            output wire          security_error
           );


  //----------------------------------------------------------------
  // Internal constant and parameter definitions.
  //----------------------------------------------------------------
  parameter TRNG_PREFIX             = 4'h0;
  parameter ENTROPY1_PREFIX         = 4'h5;
  parameter ENTROPY2_PREFIX         = 4'h6;
  parameter MIXER_PREFIX            = 4'ha;
  parameter CSPRNG_PREFIX           = 4'hb;

  parameter DEBUG_ENTROPY0          = 3'h0;
  parameter DEBUG_ENTROPY1          = 3'h1;
  parameter DEBUG_ENTROPY2          = 3'h2;
  parameter DEBUG_MIXER             = 3'h3;
  parameter DEBUG_CSPRNG            = 3'h4;

  parameter ADDR_NAME0              = 8'h00;
  parameter ADDR_NAME1              = 8'h01;
  parameter ADDR_VERSION            = 8'h02;

  parameter ADDR_TRNG_CTRL          = 8'h10;
  parameter TRNG_CTRL_DISCARD_BIT   = 0;
  parameter TRNG_CTRL_TEST_MODE_BIT = 1;

  parameter ADDR_TRNG_STATUS        = 8'h11;
  parameter ADDR_DEBUG_CTRL         = 8'h12;

  parameter TRNG_NAME0              = 32'h74726e67; // "trng"
  parameter TRNG_NAME1              = 32'h20202020; // "    "
  parameter TRNG_VERSION            = 32'h302e3031; // "0.01"


  //----------------------------------------------------------------
  // Registers including update variables and write enable.
  //----------------------------------------------------------------
  reg discard_reg;
  reg discard_new;

  reg test_mode_reg;
  reg test_mode_new;
  reg test_mode_we;

  reg [2 : 0] debug_mux_reg;
  reg [2 : 0] debug_mux_new;
  reg [2 : 0] debug_mux_we;


  //----------------------------------------------------------------
  // Wires.
  //----------------------------------------------------------------
  reg            trng_api_cs;
  reg            trng_api_we;
  reg [31 : 0]   trng_api_read_data;
  reg            trng_api_error;

  wire           mixer_more_seed;
  wire [511 : 0] mixer_seed_data;
  wire           mixer_seed_syn;
  wire           mixer_seed_ack;
  reg            mixer_api_cs;
  reg            mixer_api_we;
  wire [31 : 0]  mixer_api_read_data;
  wire           mixer_api_error;
  wire [7 : 0]   mixer_debug;
  reg            mixer_debug_update;

  wire           csprng_more_seed;
  wire           csprng_seed_ack;
  reg            csprng_api_cs;
  reg            csprng_api_we;
  wire [31 : 0]  csprng_api_read_data;
  wire           csprng_api_error;
  wire [7 : 0]   csprng_debug;
  reg            csprng_debug_update;

  wire           entropy0_entropy_enabled;
  wire [31 : 0]  entropy0_entropy_data;
  wire           entropy0_entropy_syn;
  wire           entropy0_entropy_ack;

  reg            entropy1_api_cs;
  reg            entropy1_api_we;
  wire [31 : 0]  entropy1_api_read_data;
  wire           entropy1_api_error;
  wire           entropy1_entropy_enabled;
  wire [31 : 0]  entropy1_entropy_data;
  wire           entropy1_entropy_syn;
  wire           entropy1_entropy_ack;
  wire           entropy1_test_mode;
  wire [7 : 0]   entropy1_debug;
  reg            entropy1_debug_update;
  wire           entropy1_security_error;

  reg            entropy2_api_cs;
  reg            entropy2_api_we;
  wire [31 : 0]  entropy2_api_read_data;
  wire           entropy2_api_error;
  wire           entropy2_entropy_enabled;
  wire [31 : 0]  entropy2_entropy_data;
  wire           entropy2_entropy_syn;
  wire           entropy2_entropy_ack;
  wire           entropy2_test_mode;
  wire [7 : 0]   entropy2_debug;
  reg            entropy2_debug_update;
  wire           entropy2_security_error;

  reg [7 : 0]    api_address;
  reg [31 : 0]   tmp_read_data;
  reg            tmp_error;
  reg [7 : 0]    tmp_debug;


  //----------------------------------------------------------------
  // Concurrent connectivity for ports etc.
  //----------------------------------------------------------------
  assign read_data      = tmp_read_data;
  assign error          = tmp_error;
  assign security_error = entropy1_security_error | entropy2_security_error;
  assign debug          = tmp_debug;

  // Patches to get our first version to work.
  assign entropy0_entropy_enabled = 0;
  assign entropy0_entropy_syn     = 0;
  assign entropy0_entropy_data    = 32'h00000000;


  //----------------------------------------------------------------
  // core instantiations.
  //----------------------------------------------------------------
  trng_mixer mixer(
                   .clk(clk),
                   .reset_n(reset_n),

                   .cs(mixer_api_cs),
                   .we(mixer_api_we),
                   .address(api_address),
                   .write_data(write_data),
                   .read_data(mixer_api_read_data),
                   .error(mixer_api_error),

                   .discard(discard_reg),
                   .test_mode(test_mode_reg),

                   .more_seed(csprng_more_seed),

                   .entropy0_enabled(entropy0_entropy_enabled),
                   .entropy0_syn(entropy0_entropy_syn),
                   .entropy0_data(entropy0_entropy_data),
                   .entropy0_ack(entropy0_entropy_ack),

                   .entropy1_enabled(entropy1_entropy_enabled),
                   .entropy1_syn(entropy1_entropy_syn),
                   .entropy1_data(entropy1_entropy_data),
                   .entropy1_ack(entropy1_entropy_ack),

                   .entropy2_enabled(entropy2_entropy_enabled),
                   .entropy2_syn(entropy2_entropy_syn),
                   .entropy2_data(entropy2_entropy_data),
                   .entropy2_ack(entropy2_entropy_ack),

                   .seed_data(mixer_seed_data),
                   .seed_syn(mixer_seed_syn),
                   .seed_ack(csprng_seed_ack),

                   .debug(mixer_debug),
                   .debug_update(mixer_debug_update)
                  );

  trng_csprng csprng(
                     .clk(clk),
                     .reset_n(reset_n),

                     .cs(csprng_api_cs),
                     .we(csprng_api_we),
                     .address(api_address),
                     .write_data(write_data),
                     .read_data(csprng_api_read_data),
                     .error(csprng_api_error),

                     .discard(discard_reg),
                     .test_mode(test_mode_reg),

                     .more_seed(csprng_more_seed),

                     .seed_data(mixer_seed_data),
                     .seed_syn(mixer_seed_syn),
                     .seed_ack(csprng_seed_ack),

                     .debug(csprng_debug),
                     .debug_update(csprng_debug_update)
                    );

  avalanche_entropy entropy1(
                             .clk(clk),
                             .reset_n(reset_n),

                             .noise(avalanche_noise),

                             .cs(entropy1_api_cs),
                             .we(entropy1_api_we),
                             .address(api_address),
                             .write_data(write_data),
                             .read_data(entropy1_api_read_data),
                             .error(entropy1_api_error),

                             .discard(discard_reg),
                             .test_mode(test_mode_reg),
                             .security_error(entropy1_security_error),

                             .entropy_enabled(entropy1_entropy_enabled),
                             .entropy_data(entropy1_entropy_data),
                             .entropy_valid(entropy1_entropy_syn),
                             .entropy_ack(entropy1_entropy_ack),

                             .debug(entropy1_debug),
                             .debug_update(entropy1_debug_update)
                            );

  rosc_entropy entropy2(
                        .clk(clk),
                        .reset_n(reset_n),

                        .cs(entropy2_api_cs),
                        .we(entropy2_api_we),
                        .address(api_address),
                        .write_data(write_data),
                        .read_data(entropy2_api_read_data),
                        .error(entropy2_api_error),

                        .discard(discard_reg),
                        .test_mode(test_mode_reg),
                        .security_error(entropy2_security_error),

                        .entropy_enabled(entropy2_entropy_enabled),
                        .entropy_data(entropy2_entropy_data),
                        .entropy_valid(entropy2_entropy_syn),
                        .entropy_ack(entropy2_entropy_ack),

                        .debug(entropy2_debug),
                        .debug_update(entropy2_debug_update)
                       );


  //----------------------------------------------------------------
  // reg_update
  //
  // Update functionality for all registers in the core.
  // All registers are positive edge triggered with asynchronous
  // active low reset.
  //----------------------------------------------------------------
  always @ (posedge clk or negedge reset_n)
    begin
      if (!reset_n)
        begin
          discard_reg   <= 0;
          test_mode_reg <= 0;
          debug_mux_reg <= DEBUG_ENTROPY1;
        end
      else
        begin
          discard_reg <= discard_new;

          if (test_mode_we)
            begin
              test_mode_reg <= test_mode_new;
            end

          if (debug_mux_we)
            begin
              debug_mux_reg <= debug_mux_new;
            end
        end
    end // reg_update


  //----------------------------------------------------------------
  // debug_mux
  //----------------------------------------------------------------
  always @*
    begin : debug_mux
      entropy1_debug_update = 0;
      entropy2_debug_update = 0;
      mixer_debug_update    = 0;
      csprng_debug_update   = 0;

      tmp_debug = 8'h00;

      case(debug_mux_reg)
        DEBUG_ENTROPY1:
          begin
            entropy1_debug_update = debug_update;
            tmp_debug             = entropy1_debug;
          end

        DEBUG_ENTROPY2:
          begin
            entropy2_debug_update = debug_update;
            tmp_debug             = entropy2_debug;
          end

        DEBUG_MIXER:
          begin
            mixer_debug_update = debug_update;
            tmp_debug          = mixer_debug;
          end

        DEBUG_CSPRNG:
          begin
            csprng_debug_update = debug_update;
            tmp_debug           = csprng_debug;
          end

        default:
          begin

          end
      endcase // case (debug_mux_reg)

    end // debug_mux


  //----------------------------------------------------------------
  // api_mux
  //
  // This is a simple decoder that looks at the top 4 bits of
  // the given api address and selects which of the sub modules
  // or the top level mux that gets to handle any API
  // operations.
  //----------------------------------------------------------------
  always @*
    begin : api_mux
      trng_api_cs     = 0;
      trng_api_we     = 0;

      entropy1_api_cs = 0;
      entropy1_api_we = 0;

      entropy2_api_cs = 0;
      entropy2_api_we = 0;

      mixer_api_cs    = 0;
      mixer_api_we    = 0;

      csprng_api_cs   = 0;
      csprng_api_we   = 0;

      api_address     = address[7 : 0];
      tmp_read_data   = 32'h00000000;
      tmp_error       = 0;

      case (address[11 : 8])
        TRNG_PREFIX:
          begin
            trng_api_cs   = cs;
            trng_api_we   = we;
            tmp_read_data = trng_api_read_data;
            tmp_error     = trng_api_error;
          end

        ENTROPY1_PREFIX:
          begin
            entropy1_api_cs = cs;
            entropy1_api_we = we;
            tmp_read_data   = entropy1_api_read_data;
            tmp_error       = entropy1_api_error;
          end

        ENTROPY2_PREFIX:
          begin
            entropy2_api_cs = cs;
            entropy2_api_we = we;
            tmp_read_data   = entropy2_api_read_data;
            tmp_error       = entropy2_api_error;
          end

        MIXER_PREFIX:
          begin
            mixer_api_cs  = cs;
            mixer_api_we  = we;
            tmp_read_data = mixer_api_read_data;
            tmp_error     = mixer_api_error;
          end

        CSPRNG_PREFIX:
          begin
            csprng_api_cs = cs;
            csprng_api_we = we;
            tmp_read_data = csprng_api_read_data;
            tmp_error     = csprng_api_error;
          end

        default:
          begin

          end
      endcase // case (address[11 : 8])
    end // api_mux


  //----------------------------------------------------------------
  // trng_api_logic
  //
  // Implementation of the top level api logic.
  //----------------------------------------------------------------
  always @*
    begin : trng_api_logic
      discard_new        = 0;
      test_mode_new      = 0;
      test_mode_we       = 0;
      debug_mux_new      = 3'h0;
      debug_mux_we       = 0;
      trng_api_read_data = 32'h00000000;
      trng_api_error     = 0;

      if (trng_api_cs)
        begin
          if (trng_api_we)
            begin
              // Write operations.
              case (api_address)
                // Write operations.
                ADDR_TRNG_CTRL:
                  begin
                    discard_new   = write_data[TRNG_CTRL_DISCARD_BIT];
                    test_mode_new = write_data[TRNG_CTRL_TEST_MODE_BIT];
                    test_mode_we  = 1;
                  end

                ADDR_DEBUG_CTRL:
                  begin
                    debug_mux_new = write_data[2 : 0];
                    debug_mux_we  = 1;
                  end

                default:
                  begin
                    trng_api_error = 1;
                  end
              endcase // case (address)
            end // if (we)

          else
            begin
              // Read operations.
              case (api_address)
                // Read operations.
                ADDR_NAME0:
                  begin
                    trng_api_read_data = TRNG_NAME0;
                  end

                ADDR_NAME1:
                  begin
                    trng_api_read_data = TRNG_NAME1;
                  end

                ADDR_VERSION:
                  begin
                    trng_api_read_data = TRNG_VERSION;
                  end

                ADDR_TRNG_CTRL:
                  begin
                  end

                ADDR_TRNG_STATUS:
                  begin

                  end

                ADDR_DEBUG_CTRL:
                  begin
                    trng_api_read_data = debug_mux_new;
                  end

                default:
                  begin
                    trng_api_error = 1;
                  end
              endcase // case (address)
            end
        end
    end // trng_api_logic
endmodule // trng

//======================================================================
// EOF trng.v
//======================================================================