//======================================================================
//
// sha1_w_mem_reg.v
// -----------------
// The SHA-1 W memory. This memory includes functionality to 
// expand the block into 80 words.
//
//
// Author: Joachim Strombergson
// Copyright (c) 2014 SUNET
// 
// Redistribution and use in source and binary forms, with or 
// without modification, are permitted provided that the following 
// conditions are met: 
// 
// 1. Redistributions of source code must retain the above copyright 
//    notice, this list of conditions and the following disclaimer. 
// 
// 2. 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. 
// 
// 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 OWNER 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 sha1_w_mem(
                  input wire           clk,
                  input wire           reset_n,

                  input wire           init,
                  input wire [511 : 0] block,

                  input wire [6 : 0]   addr,
                  output wire [31 : 0] w
                 );

  
  //----------------------------------------------------------------
  // Internal constant and parameter definitions.
  //----------------------------------------------------------------
  parameter SHA1_ROUNDS = 79;

  parameter CTRL_IDLE   = 1'b0;
  parameter CTRL_UPDATE = 1'b1;

  
  //----------------------------------------------------------------
  // Registers including update variables and write enable.
  //----------------------------------------------------------------
  reg [31 : 0] w_mem [0 : 79];
  reg [31 : 0] w_mem_new;
  reg          w_mem_we;
  
  reg [6 : 0] w_ctr_reg;
  reg [6 : 0] w_ctr_new;
  reg         w_ctr_we;
  reg         w_ctr_inc;
  reg         w_ctr_set;
  
  reg         sha1_w_mem_ctrl_reg;
  reg         sha1_w_mem_ctrl_new;
  reg         sha1_w_mem_ctrl_we;
  
  
  //----------------------------------------------------------------
  // Wires.
  //----------------------------------------------------------------
  reg [31 : 0] w_tmp;
  reg [31 : 0] w_new;
  reg [6 : 0]  w_addr;
  reg          w_update;
  
  
  //----------------------------------------------------------------
  // Concurrent connectivity for ports etc.
  //----------------------------------------------------------------
  assign w     = w_tmp;
  
  
  //----------------------------------------------------------------
  // reg_update
  //
  // Update functionality for all registers in the core.
  // All registers are positive edge triggered with synchronous
  // active low reset. All registers have write enable.
  //----------------------------------------------------------------
  always @ (posedge clk)
    begin : reg_update
      if (!reset_n)
        begin
          w_ctr_reg           <= 7'b0000000;
          sha1_w_mem_ctrl_reg <= CTRL_IDLE;
        end
      else
        begin
          if (init)
            begin
              w_mem[00] <= block[511 : 480];
              w_mem[01] <= block[479 : 448];
              w_mem[02] <= block[447 : 416];
              w_mem[03] <= block[415 : 384];
              w_mem[04] <= block[383 : 352];
              w_mem[05] <= block[351 : 320];
              w_mem[06] <= block[319 : 288];
              w_mem[07] <= block[287 : 256];
              w_mem[08] <= block[255 : 224];
              w_mem[09] <= block[223 : 192];
              w_mem[10] <= block[191 : 160];
              w_mem[11] <= block[159 : 128];
              w_mem[12] <= block[127 :  96];
              w_mem[13] <= block[95  :  64];
              w_mem[14] <= block[63  :  32];
              w_mem[15] <= block[31  :   0];
            end

          if (w_mem_we)
            begin
              w_mem[w_addr] <= w_mem_new;
            end
          
          if (w_ctr_we)
            begin
              w_ctr_reg <= w_ctr_new;
            end
          
          if (sha1_w_mem_ctrl_we)
            begin
              sha1_w_mem_ctrl_reg <= sha1_w_mem_ctrl_new;
            end

        end
    end // reg_update

  
  //----------------------------------------------------------------
  // external_addr_mux
  //
  // Mux for the external read operation. This is where we exract
  // the W variable.
  //----------------------------------------------------------------
  always @*
    begin : external_addr_mux
      w_tmp = w_mem[addr];
    end // external_addr_mux
  

  //----------------------------------------------------------------
  // w_schedule
  //
  // W word expansion logic.
  //----------------------------------------------------------------
  always @*
    begin : w_schedule
      reg [31 : 0] w_new_tmp;
      
      w_mem_we  = 0;
      w_new_tmp = 32'h00000000;
      w_mem_new = 32'h00000000;
      w_addr    = 0;

      if (w_update)
        begin
          w_new_tmp = w_mem[(w_ctr_reg - 3)] ^ w_mem[(w_ctr_reg - 8)] ^
                      w_mem[(w_ctr_reg - 14)] ^ w_mem[(w_ctr_reg - 16)];
          w_mem_new = {w_new_tmp[30 : 0], w_new_tmp[31]};
          w_addr    = w_ctr_reg;
          w_mem_we  = 1;
        end
    end // w_schedule

  
  //----------------------------------------------------------------
  // w_ctr
  //
  // W schedule adress counter. Counts from 0x10 to 0x3f and
  // is used to expand the block into words.
  //----------------------------------------------------------------
  always @*
    begin : w_ctr
      w_ctr_new = 0;
      w_ctr_we  = 0;
      
      if (w_ctr_set)
        begin
          w_ctr_new = 6'h10;
          w_ctr_we  = 1;
        end

      if (w_ctr_inc)
        begin
          w_ctr_new = w_ctr_reg + 6'h01;
          w_ctr_we  = 1;
        end
    end // w_ctr

  
  //----------------------------------------------------------------
  // sha1_w_mem_fsm
  //
  // Logic for the w shedule FSM.
  //----------------------------------------------------------------
  always @*
    begin : sha1_w_mem_fsm
      w_ctr_set = 0;
      w_ctr_inc = 0;
      w_update  = 0;
      
      sha1_w_mem_ctrl_new = CTRL_IDLE;
      sha1_w_mem_ctrl_we  = 0;
      
      case (sha1_w_mem_ctrl_reg)
        CTRL_IDLE:
          begin
            if (init)
              begin
                w_ctr_set           = 1;
                sha1_w_mem_ctrl_new = CTRL_UPDATE;
                sha1_w_mem_ctrl_we  = 1;
              end
          end
        
        CTRL_UPDATE:
          begin
            w_update  = 1;
            w_ctr_inc = 1;

            if (w_ctr_reg == SHA1_ROUNDS)
              begin
                sha1_w_mem_ctrl_new = CTRL_IDLE;
                sha1_w_mem_ctrl_we  = 1;
              end
          end
      endcase // case (sha1_ctrl_reg)
    end // sha1_ctrl_fsm
endmodule // sha1_w_mem

//======================================================================
// sha1_w_mem.v
//======================================================================