//======================================================================
//
// blockmem2r1wptr.v
// -----------------
// Synchronous block memory with two read ports and one write port.
// For port 1 the address is implicit and instead given by the
// internal pointer. But write address is explicitly given.
//
// The memory is used in the modexp core.
//
//
// Author: 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 blockmem2rptr1w(
                       input wire           clk,
                       input wire           reset_n,

                       input wire  [07 : 0] read_addr0,
                       output wire [31 : 0] read_data0,

                       output wire [31 : 0] read_data1,

                       input wire           rst,
                       input wire           cs,
                       input wire           wr,
                       input wire  [07 : 0] write_addr,
                       input wire  [31 : 0] write_data
                      );


  //----------------------------------------------------------------
  // Memories and regs including update variables and write enable.
  //----------------------------------------------------------------
  reg [31 : 0] mem [0 : 255];
  reg [31 : 0] tmp_read_data0;
  reg [31 : 0] tmp_read_data1;

  reg [7 : 0] ptr_reg;
  reg [7 : 0] ptr_new;
  reg         ptr_we;


  //----------------------------------------------------------------
  // Concurrent connectivity for ports etc.
  //----------------------------------------------------------------
  assign read_data0 = tmp_read_data0;
  assign read_data1 = tmp_read_data1;


  //----------------------------------------------------------------
  // mem_update
  //
  // Clocked update of memory This should cause
  // the memory to be implemented as a block memory.
  //----------------------------------------------------------------
  always @ (posedge clk)
    begin : mem_update
      if (wr)
        mem[write_addr] <= write_data;

      tmp_read_data0 <= mem[read_addr0];
      tmp_read_data1 <= mem[ptr_reg];
    end


  //----------------------------------------------------------------
  // reg_update
  //----------------------------------------------------------------
  always @ (posedge clk or negedge reset_n)
    begin : reg_mem_update
      if (!reset_n)
        ptr_reg <= 8'h00;

      else
        if (ptr_we)
          ptr_reg <= ptr_new;
    end


  //----------------------------------------------------------------
  // ptr_logic
  //----------------------------------------------------------------
  always @*
    begin : ptr_logic
      ptr_new = 8'h00;
      ptr_we  = 1'b0;

      if (rst)
        begin
          ptr_new = 8'h00;
          ptr_we  = 1'b1;
        end

      if (cs)
        begin
          ptr_new = ptr_reg + 1'b1;
          ptr_we  = 1'b1;
        end
    end

endmodule // blockmem2r1wptr

//======================================================================
// EOF blockmem2r1wptr.v
//======================================================================