//======================================================================
//
// montprod.v
// ---------
// Montgomery product calculator for the modular exponentiantion core.
//
//
// Author: Peter Magnusson, Joachim Strombergson
// Copyright (c) 2015, 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 montprod(
                input wire           clk,
                input wire           reset_n,

                input wire           calculate,
                output wire          ready,

                input   [7 : 0]      length,

                output wire [7 : 0]  opa_addr,
                input wire [31 : 0]  opa_data,

                output wire [7 : 0]  opb_addr,
                input wire [31 : 0]  opb_data,

                output wire [7 : 0]  opm_addr,
                input wire [31 : 0]  opm_data,

                output wire [7 : 0]  result_addr,
                output wire [31 : 0] result_data,
                output wire          result_we
               );


  //----------------------------------------------------------------
  // Internal constant and parameter definitions.
  //----------------------------------------------------------------
  localparam CTRL_IDLE            = 4'h0;
  localparam CTRL_INIT_S          = 4'h1;
  localparam CTRL_WAIT            = 4'h2;
  localparam CTRL_LOOP_ITER       = 4'h3;
  localparam CTRL_LOOP_BQ         = 4'h4;
  localparam CTRL_CALC_ADD        = 4'h5;
  localparam CTRL_STALLPIPE_ADD   = 4'h6;
  localparam CTRL_CALC_SDIV2      = 4'h7;
  localparam CTRL_STALLPIPE_SDIV2 = 4'h8;
  localparam CTRL_L_STALLPIPE_ES  = 4'h9;
  localparam CTRL_EMIT_S          = 4'ha;

  localparam SMUX_0               = 2'h0;
  localparam SMUX_ADD             = 2'h1;
  localparam SMUX_SHR             = 2'h2;


  //----------------------------------------------------------------
  // Registers including update variables and write enable.
  //----------------------------------------------------------------
  reg [07 : 0] opa_addr_reg;
  reg [07 : 0] opb_addr_reg;
  reg [07 : 0] opm_addr_reg;

  reg [07 : 0] result_addr_reg;
  reg [31 : 0] result_data_reg;

  reg          ready_reg;
  reg          ready_new;
  reg          ready_we;

  reg [3 : 0]  montprod_ctrl_reg;
  reg [3 : 0]  montprod_ctrl_new;
  reg          montprod_ctrl_we;

  reg  [1 : 0] s_mux_new;
  reg  [1 : 0] s_mux_reg;

  reg [31 : 0]  s_mem_new;
  reg           s_mem_we_reg;
  reg           s_mem_we_new;
  reg [07 : 0]  s_mem_addr;
  reg [07 : 0]  s_mem_wr_addr_reg;
  wire [31 : 0] s_mem_read_data;

  reg           q_new;
  reg           q_reg;
  reg           b_new;
  reg           b_reg;
  reg           bq_we;

  reg [12 : 0] loop_ctr_reg;
  reg [12 : 0] loop_ctr_new;
  reg          loop_ctr_we;
  reg          loop_ctr_set;
  reg          loop_ctr_dec;

  reg [07 : 0] b_word_index; //loop counter as a word index

  reg [04 : 0] b_bit_index_reg;
  reg [04 : 0] b_bit_index_new;
  reg          b_bit_index_we;

  reg [07 : 0] word_index_reg; //register of what word is being read
  reg [07 : 0] word_index_new; //calculation of what word to be read
  reg [07 : 0] word_index_prev_reg; //register of what word was read previously (result address to emit)
  reg [07 : 0] length_m1;

  reg          add_carry_in_sa_reg;
  reg          add_carry_in_sa_new;
  reg          add_carry_in_sm_reg;
  reg          add_carry_in_sm_new;

  reg          shr_carry_in_reg;
  reg          shr_carry_in_new;

  reg          first_iteration_reg;
  reg          first_iteration_new;
  reg          first_iteration_we;


  //----------------------------------------------------------------
  // Wires.
  //----------------------------------------------------------------
  reg           tmp_result_we;
  wire [31 : 0] add_result_sa;
  wire          add_carry_out_sa;
  wire [31 : 0] add_result_sm;
  wire          add_carry_out_sm;

  reg  [31 : 0] shr_data_in;
  wire          shr_carry_out;
  wire [31 : 0] shr_data_out;

  reg           reset_word_index_lsw;
  reg           reset_word_index_msw;

  reg [31 : 0]  sa_adder_data_in;
  reg [31 : 0]  muxed_s_mem_read_data;



  //----------------------------------------------------------------
  // Concurrent connectivity for ports etc.
  //----------------------------------------------------------------
  assign opa_addr    = opa_addr_reg;
  assign opb_addr    = opb_addr_reg;
  assign opm_addr    = opm_addr_reg;

  assign result_addr = result_addr_reg;
  assign result_data = result_data_reg;
  assign result_we   = tmp_result_we;

  assign ready       = ready_reg;


  //----------------------------------------------------------------
  // Instantions
  //----------------------------------------------------------------
  blockmem1r1w s_mem(
                     .clk(clk),
                     .read_addr(s_mem_addr),
                     .read_data(s_mem_read_data),
                     .wr(s_mem_we_reg),
                     .write_addr(s_mem_wr_addr_reg),
                     .write_data(s_mem_new)
                    );


  adder32 s_adder_sm(
                     .a(muxed_s_mem_read_data),
                     .b(opm_data),
                     .carry_in(add_carry_in_sm_reg),
                     .sum(add_result_sm),
                     .carry_out(add_carry_out_sm)
                    );


  adder32 s_adder_sa(
                     .a(sa_adder_data_in),
                     .b(opa_data),
                     .carry_in(add_carry_in_sa_reg),
                     .sum(add_result_sa),
                     .carry_out(add_carry_out_sa)
                    );

  shr32 shifter(
                .a(s_mem_read_data),
                .carry_in(shr_carry_in_reg),
                .adiv2(shr_data_out),
                .carry_out(shr_carry_out)
               );


  //----------------------------------------------------------------
  // reg_update
  //
  // Update functionality for all registers in the core.
  // All registers are positive edge triggered with asynchronous
  // active low reset. All registers have write enable.
  //----------------------------------------------------------------
  always @ (posedge clk or negedge reset_n)
    begin : reg_update
      if (!reset_n)
        begin
          ready_reg           <= 1'b1;
          loop_ctr_reg        <= 13'h0;
          word_index_reg      <= 8'h0;
          word_index_prev_reg <= 8'h0;
          add_carry_in_sa_reg <= 1'b0;
          add_carry_in_sm_reg <= 1'b0;
          shr_carry_in_reg    <= 1'b0;
          b_reg               <= 1'b0;
          q_reg               <= 1'b0;
          s_mux_reg           <= SMUX_0;
          s_mem_we_reg        <= 1'b0;
          s_mem_wr_addr_reg   <= 8'h0;
          b_bit_index_reg     <= 5'h0;
          first_iteration_reg <= 1'b0;
          montprod_ctrl_reg   <= CTRL_IDLE;
        end
      else
        begin
          s_mem_wr_addr_reg   <= s_mem_addr;
          s_mem_we_reg        <= s_mem_we_new;
          s_mux_reg           <= s_mux_new;

          word_index_reg      <= word_index_new;
          word_index_prev_reg <= word_index_reg;

          shr_carry_in_reg    <= shr_carry_in_new;
          add_carry_in_sa_reg <= add_carry_in_sa_new;
          add_carry_in_sm_reg <= add_carry_in_sm_new;

          if (first_iteration_we)
            first_iteration_reg <= first_iteration_new;

          if (b_bit_index_we)
            b_bit_index_reg <= b_bit_index_new;

          if (bq_we)
            begin
              b_reg <= b_new;
              q_reg <= q_new;
            end

          if (ready_we)
            ready_reg <= ready_new;

          if (loop_ctr_we)
            loop_ctr_reg <= loop_ctr_new;

          if (montprod_ctrl_we)
            begin
               montprod_ctrl_reg <= montprod_ctrl_new;
             end
        end
    end // reg_update


  //----------------------------------------------------------------
  // prodcalc
  //----------------------------------------------------------------
  always @*
    begin : prodcalc
      opa_addr_reg  = word_index_reg;
      opb_addr_reg  = b_word_index;
      opm_addr_reg  = word_index_reg;
      s_mem_addr    = word_index_reg;
      tmp_result_we = 1'b0;


      result_addr_reg  = word_index_prev_reg;
      result_data_reg  = s_mem_read_data;


      if (montprod_ctrl_reg == CTRL_LOOP_ITER)
        opa_addr_reg = length_m1;

      if (montprod_ctrl_reg == CTRL_LOOP_ITER)
          s_mem_addr = length_m1;

      if (montprod_ctrl_reg == CTRL_EMIT_S)
        tmp_result_we = 1'b1;


      if (reset_word_index_lsw == 1'b1)
        word_index_new = length_m1;

      else if (reset_word_index_msw == 1'b1)
        word_index_new = 8'h0;

      else if (montprod_ctrl_reg == CTRL_CALC_SDIV2)
        word_index_new = word_index_reg + 1'b1;

      else
        word_index_new = word_index_reg - 1'b1;
    end // prodcalc


  //----------------------------------------------------------------
  // s_logic
  //----------------------------------------------------------------
  always @*
    begin : s_logic
      shr_carry_in_new      = 1'b0;
      muxed_s_mem_read_data = 32'h0;
      sa_adder_data_in      = 32'h0;
      add_carry_in_sa_new   = 1'b0;
      add_carry_in_sm_new   = 1'b0;
      s_mem_new             = 32'h0;
      s_mem_we_new          = 1'b0;


      case (montprod_ctrl_reg)
        CTRL_INIT_S:
          begin
            s_mem_we_new = 1'b1;
          end

        CTRL_CALC_ADD:
          begin
            //s = (s + q*M + b*A) >>> 1;, if(b==1) S+= A. Takes (1..length) cycles.
            s_mem_we_new = b_reg | q_reg | first_iteration_reg;
          end

        CTRL_CALC_SDIV2:
          begin
            //s = (s + q*M + b*A) >>> 1; s>>=1.  Takes (1..length) cycles.
            s_mem_we_new  = 1'b1;
          end

        default:
          begin
          end
      endcase


      case (s_mux_reg)
        SMUX_ADD:
          begin
            if (first_iteration_reg)
              muxed_s_mem_read_data = 32'h0;
            else
              muxed_s_mem_read_data = s_mem_read_data;


            if (q_reg)
                sa_adder_data_in = add_result_sm;
            else
              sa_adder_data_in = muxed_s_mem_read_data;

            if (b_reg)
              s_mem_new = add_result_sa;
            else if (q_reg)
              s_mem_new = add_result_sm;
            else
              s_mem_new = muxed_s_mem_read_data;

            add_carry_in_sa_new = add_carry_out_sa;
            add_carry_in_sm_new = add_carry_out_sm;
          end

        SMUX_SHR:
          begin
            shr_data_in      = s_mem_read_data;
            s_mem_new        = shr_data_out;
            shr_carry_in_new = shr_carry_out;
          end

        default:
          begin
          end
      endcase
    end // s_logic


  //----------------------------------------------------------------
  // bq
  //
  // Extract b and q bits.
  // b: current bit of B used.
  // q = (s - b * A) & 1
  //----------------------------------------------------------------
  always @*
   begin : bq
     b_new = opb_data[b_bit_index_reg];
     q_new = s_mem_read_data[0] ^ (opa_data[0] & b_new);
   end // bq


  //----------------------------------------------------------------
  // loop_ctr
  // Logic for updating the loop counter and
  // setting related B indices.
  //----------------------------------------------------------------
  always @*
   begin : loop_ctr
     loop_ctr_new     = 13'h0;
     loop_ctr_we      = 1'b0;
     length_m1        = length - 1'b1;

     b_bit_index_new  = 5'h1f - loop_ctr_reg[4:0];
     b_word_index     = loop_ctr_reg[12:5];

     if (loop_ctr_set)
         begin
           loop_ctr_new = {length, 5'b00000} - 1'b1;
           loop_ctr_we  = 1'b1;
         end

     if (loop_ctr_dec)
       begin
           loop_ctr_new = loop_ctr_reg - 1'b1;
           loop_ctr_we  = 1'b1;
       end
   end


  //----------------------------------------------------------------
  // montprod_ctrl
  //
  // Control FSM for the montgomery product calculator.
  //----------------------------------------------------------------
  always @*
    begin : montprod_ctrl
      ready_new            = 1'b0;
      ready_we             = 1'b0;
      loop_ctr_set         = 1'b0;
      loop_ctr_dec         = 1'b0;
      b_bit_index_we       = 1'b0;
      bq_we                = 1'b0;
      s_mux_new            = SMUX_0;
      reset_word_index_lsw = 1'b0;
      reset_word_index_msw = 1'b0;
      first_iteration_new  = 1'b0;
      first_iteration_we   = 1'b0;
      montprod_ctrl_new    = CTRL_IDLE;
      montprod_ctrl_we     = 1'b0;

      case (montprod_ctrl_reg)
        CTRL_IDLE:
          begin
            if (calculate)
              begin
                ready_new            = 1'b0;
                ready_we             = 1'b1;
                first_iteration_new  = 1'b0;
                first_iteration_we   = 1'b1;
                reset_word_index_lsw = 1'b1;
                montprod_ctrl_new    = CTRL_INIT_S;
                montprod_ctrl_we     = 1'b1;
              end
          end

        CTRL_INIT_S:
          begin
            s_mux_new    = SMUX_0; // write 0

            if (word_index_reg == 8'h0)
              begin
                montprod_ctrl_new = CTRL_WAIT;
                montprod_ctrl_we  = 1'b1;
              end
          end

        CTRL_WAIT:
          begin
            loop_ctr_set      = 1'b1;
            montprod_ctrl_new = CTRL_LOOP_ITER;
            montprod_ctrl_we  = 1'b1;
          end

        //calculate q = (s - b * A) & 1;.
        // Also abort loop if done.
        CTRL_LOOP_ITER:
          begin
            b_bit_index_we       = 1'b1;
            reset_word_index_lsw = 1'b1;
            montprod_ctrl_new    = CTRL_LOOP_BQ;
            montprod_ctrl_we     = 1'b1;
          end

        CTRL_LOOP_BQ:
          begin
            reset_word_index_lsw = 1'b1;
            bq_we                = 1'b1;
            montprod_ctrl_new    = CTRL_CALC_ADD;
            montprod_ctrl_we     = 1'b1;
          end

        CTRL_CALC_ADD:
          begin
            s_mux_new = SMUX_ADD;

            if (word_index_reg == 8'h0)
              begin
                reset_word_index_lsw = 1'b1;
                first_iteration_new  = 1'b0;
                first_iteration_we   = 1'b1;
                montprod_ctrl_new    = CTRL_STALLPIPE_ADD;
                montprod_ctrl_we     = 1'b1;
              end
          end

        CTRL_STALLPIPE_ADD:
          begin
            montprod_ctrl_new    = CTRL_CALC_SDIV2;
            montprod_ctrl_we     = 1'b1;
            reset_word_index_msw = 1'b1;
          end

        CTRL_CALC_SDIV2:
          begin
            s_mux_new = SMUX_SHR;

            if (word_index_reg == length_m1)
              begin
                montprod_ctrl_new = CTRL_STALLPIPE_SDIV2;
                montprod_ctrl_we  = 1'b1;
              end
          end

        CTRL_STALLPIPE_SDIV2:
          begin
            loop_ctr_dec         = 1'b1;
            montprod_ctrl_new    = CTRL_LOOP_ITER;
            montprod_ctrl_we     = 1'b1;
            reset_word_index_lsw = 1'b1;

            if (loop_ctr_reg == 0)
              begin
                montprod_ctrl_new = CTRL_L_STALLPIPE_ES;
                montprod_ctrl_we  = 1'b1;
              end
          end

        CTRL_L_STALLPIPE_ES:
          begin
            montprod_ctrl_new = CTRL_EMIT_S;
            montprod_ctrl_we  = 1'b1;
          end

        CTRL_EMIT_S:
           begin
             if (word_index_prev_reg == 8'h0)
               begin
                 ready_new         = 1'b1;
                 ready_we          = 1'b1;
                 montprod_ctrl_new = CTRL_IDLE;
                 montprod_ctrl_we  = 1'b1;
               end
           end

        default:
          begin
          end

      endcase // case (montprod_ctrl_reg)
    end // montprod_ctrl

endmodule // montprod

//======================================================================
// EOF montprod.v
//======================================================================