//------------------------------------------------------------------------------
//
// mw_mover.v
// -----------------------------------------------------------------------------
// Multi-word data mover.
//
// Authors: Pavel Shatov
//
// Copyright (c) 2015-2016, NORDUnet A/S
//
// 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 mw_mover
(
    clk, rst_n,
    ena, rdy,
    x_addr, y_addr, y_wren,
    x_din, y_dout
);


    //
    // Parameters
    //
    parameter WORD_COUNTER_WIDTH    = 3;
    parameter OPERAND_NUM_WORDS     = 8;


    //
    // Handy Numbers
    //
    localparam  [WORD_COUNTER_WIDTH-1:0]    WORD_INDEX_ZERO = 0;
    localparam  [WORD_COUNTER_WIDTH-1:0]    WORD_INDEX_LAST = OPERAND_NUM_WORDS - 1;


    //
    // Handy Functions
    //
    function [WORD_COUNTER_WIDTH-1:0] WORD_INDEX_NEXT_OR_ZERO;
    input    [WORD_COUNTER_WIDTH-1:0] WORD_INDEX_CURRENT;
    begin
        WORD_INDEX_NEXT_OR_ZERO = (WORD_INDEX_CURRENT < WORD_INDEX_LAST) ?
            WORD_INDEX_CURRENT + 1'b1 : WORD_INDEX_ZERO;
    end
    endfunction


    //
    // Ports
    //
    input   clk;    // system clock
    input   rst_n;  // active-low async reset

    input   ena;    // enable input
    output  rdy;    // ready output

    output  [WORD_COUNTER_WIDTH-1:0]    x_addr;     // address of current X word
    output  [WORD_COUNTER_WIDTH-1:0]    y_addr;     // address of current Y word
    output                              y_wren;     // store current Y word

    input   [                32-1:0]    x_din;      // current X word
    output  [                32-1:0]    y_dout;     // current Y word


    //
    // Word Indices
    //
    reg [WORD_COUNTER_WIDTH-1:0] index_x;
    reg [WORD_COUNTER_WIDTH-1:0] index_y;


    //
    // Output Mapping
    //
    assign x_addr   = index_x;
    assign y_addr   = index_y;


    //
    // FSM
    //
    localparam FSM_SHREG_WIDTH = 1 * OPERAND_NUM_WORDS + 2;
    localparam [FSM_SHREG_WIDTH-1:0] FSM_SHREG_INIT = {{(FSM_SHREG_WIDTH-1){1'b0}}, 1'b1};
    
    reg [FSM_SHREG_WIDTH-1:0] fsm_shreg = FSM_SHREG_INIT;

    assign rdy = fsm_shreg[0];

    wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_inc_index_x = fsm_shreg[FSM_SHREG_WIDTH - (0 * OPERAND_NUM_WORDS + 1) : FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 0)];
    wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_inc_index_y = fsm_shreg[FSM_SHREG_WIDTH - (0 * OPERAND_NUM_WORDS + 2) : FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 1)];

    wire inc_index_x    = |fsm_shreg_inc_index_x;
    wire inc_index_y    = |fsm_shreg_inc_index_y;
    wire store_word_y   = |fsm_shreg_inc_index_x;


    always @(posedge clk or negedge rst_n)
        //
        if (rst_n == 1'b0)  fsm_shreg <= FSM_SHREG_INIT;
        else begin
            if (rdy)        fsm_shreg <= {ena, {FSM_SHREG_WIDTH-2{1'b0}}, ~ena};
            else            fsm_shreg <= {1'b0, fsm_shreg[FSM_SHREG_WIDTH-1:1]};
        end


    //
    // Word Index Increment Logic
    //
    always @(posedge clk)
    //
    if (rdy) begin
        index_x <= WORD_INDEX_ZERO;
        index_y <= WORD_INDEX_ZERO;
    end else begin
        if (inc_index_x)    index_x <= WORD_INDEX_NEXT_OR_ZERO(index_x);
        if (inc_index_y)    index_y <= WORD_INDEX_NEXT_OR_ZERO(index_y);
    end


    //
    // Write Enable Logic
    //
    reg y_wren_reg;

    assign y_wren = y_wren_reg;

    always @(posedge clk)
    //
    if (rdy)    y_wren_reg  <= 1'b0;
    else        y_wren_reg  <= store_word_y;


    //
    // Output Logic
    //
    assign y_dout = x_din;


endmodule


//------------------------------------------------------------------------------
// End-of-File
//------------------------------------------------------------------------------