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// (C) 2001-2014 Altera Corporation. All rights reserved.

// Your use of Altera Corporation's design tools, logic functions and other

// software and tools, and its AMPP partner logic functions, and any output

// files any of the foregoing (including device programming or simulation

// files), and any associated documentation or information are expressly subject

// to the terms and conditions of the Altera Program License Subscription

// Agreement, Altera MegaCore Function License Agreement, or other applicable

// license agreement, including, without limitation, that your use is for the

// sole purpose of programming logic devices manufactured by Altera and sold by

// Altera or its authorized distributors.  Please refer to the applicable

// agreement for further details.

// $Id: //acds/rel/14.0/ip/merlin/altera_merlin_multiplexer/altera_merlin_multiplexer.sv.terp#1 $

// $Revision: #1 $

// $Date: 2014/02/16 $

// $Author: swbranch $

// ------------------------------------------

// Merlin Multiplexer

// ------------------------------------------

`timescale 1 ns / 1 ns

// ------------------------------------------

// Generation parameters:

//   output_name:         DE0_NANO_SOC_QSYS_mm_interconnect_0_cmd_mux

//   NUM_INPUTS:          2

//   ARBITRATION_SHARES:  1 1

//   ARBITRATION_SCHEME   "round-robin"

//   PIPELINE_ARB:        1

//   PKT_TRANS_LOCK:      60 (arbitration locking enabled)

//   ST_DATA_W:           96

//   ST_CHANNEL_W:        6

// ------------------------------------------

module DE0_NANO_SOC_QSYS_mm_interconnect_0_cmd_mux

(

    // ----------------------

    // Sinks

    // ----------------------

    input                       sink0_valid,

    input [96-1   : 0]  sink0_data,

    input [6-1: 0]  sink0_channel,

    input                       sink0_startofpacket,

    input                       sink0_endofpacket,

    output                      sink0_ready,

    input                       sink1_valid,

    input [96-1   : 0]  sink1_data,

    input [6-1: 0]  sink1_channel,

    input                       sink1_startofpacket,

    input                       sink1_endofpacket,

    output                      sink1_ready,

    // ----------------------

    // Source

    // ----------------------

    output                      src_valid,

    output [96-1    : 0] src_data,

    output [6-1 : 0] src_channel,

    output                      src_startofpacket,

    output                      src_endofpacket,

    input                       src_ready,

    // ----------------------

    // Clock & Reset

    // ----------------------

    input clk,

    input reset

);

    localparam PAYLOAD_W        = 96 + 6 + 2;

    localparam NUM_INPUTS       = 2;

    localparam SHARE_COUNTER_W  = 1;

    localparam PIPELINE_ARB     = 1;

    localparam ST_DATA_W        = 96;

    localparam ST_CHANNEL_W     = 6;

    localparam PKT_TRANS_LOCK   = 60;

    // ------------------------------------------

    // Signals

    // ------------------------------------------

    wire [NUM_INPUTS - 1 : 0] request;

    wire [NUM_INPUTS - 1 : 0] valid;

    wire [NUM_INPUTS - 1 : 0] grant;

    wire [NUM_INPUTS - 1 : 0] next_grant;

    reg  [NUM_INPUTS - 1 : 0] saved_grant;

    reg  [PAYLOAD_W - 1 : 0]  src_payload;

    wire                      last_cycle;

    reg                       packet_in_progress;

    reg                       update_grant;

    wire [PAYLOAD_W - 1 : 0]  sink0_payload;

    wire [PAYLOAD_W - 1 : 0]  sink1_payload;

    assign valid[0] = sink0_valid;

    assign valid[1] = sink1_valid;

   wire [NUM_INPUTS - 1 : 0] eop;

      assign eop[0]   = sink0_endofpacket;

      assign eop[1]   = sink1_endofpacket;

    // ------------------------------------------

    // ------------------------------------------

    // Grant Logic & Updates

    // ------------------------------------------

    // ------------------------------------------

    reg [NUM_INPUTS - 1 : 0] lock;

    always @* begin

      lock[0] = sink0_data[60];

      lock[1] = sink1_data[60];

    end

    reg [NUM_INPUTS - 1 : 0] locked = '0;

    always @(posedge clk or posedge reset) begin

      if (reset) begin

        locked <= '0;

      end

      else begin

        locked <= next_grant & lock;

      end

    end

    assign last_cycle = src_valid & src_ready & src_endofpacket & ~(|(lock & grant));

    // ------------------------------------------

    // We're working on a packet at any time valid is high, except

    // when this is the endofpacket.

    // ------------------------------------------

    always @(posedge clk or posedge reset) begin

        if (reset) begin

            packet_in_progress <= 1'b0;

        end

        else begin

            if (last_cycle)

                packet_in_progress <= 1'b0;

            else if (src_valid)

                packet_in_progress <= 1'b1;

        end

    end

    // ------------------------------------------

    // Shares

    //

    // Special case: all-equal shares _should_ be optimized into assigning a

    // constant to next_grant_share.

    // Special case: all-1's shares _should_ result in the share counter

    // being optimized away.

    // ------------------------------------------

    // Input  |  arb shares  |  counter load value

    // 0      |      1       |  0

    // 1      |      1       |  0

    wire [SHARE_COUNTER_W - 1 : 0] share_0 = 1'd0;

    wire [SHARE_COUNTER_W - 1 : 0] share_1 = 1'd0;

    // ------------------------------------------

    // Choose the share value corresponding to the grant.

    // ------------------------------------------

    reg [SHARE_COUNTER_W - 1 : 0] next_grant_share;

    always @* begin

        next_grant_share =

            share_0 & { SHARE_COUNTER_W {next_grant[0]} } |

            share_1 & { SHARE_COUNTER_W {next_grant[1]} };

    end

    // ------------------------------------------

    // Flag to indicate first packet of an arb sequence.

    // ------------------------------------------

    // ------------------------------------------

    // Compute the next share-count value.

    // ------------------------------------------

    reg [SHARE_COUNTER_W - 1 : 0] p1_share_count;

    reg [SHARE_COUNTER_W - 1 : 0] share_count;

    reg share_count_zero_flag;

    always @* begin

        // Update the counter, but don't decrement below 0.

        p1_share_count = share_count_zero_flag ? '0 : share_count - 1'b1;

    end

    // ------------------------------------------

    // Update the share counter and share-counter=zero flag.

    // ------------------------------------------

    always @(posedge clk or posedge reset) begin

        if (reset) begin

            share_count <= '0;

            share_count_zero_flag <= 1'b1;

        end

        else begin

            if (update_grant) begin

                share_count <= next_grant_share;

                share_count_zero_flag <= (next_grant_share == '0);

            end

            else if (last_cycle) begin

                share_count <= p1_share_count;

                share_count_zero_flag <= (p1_share_count == '0);

            end

        end

    end

    always @* begin

        update_grant = 0;

        // ------------------------------------------

        // The pipeline delays grant by one cycle, so

        // we have to calculate the update_grant signal

        // one cycle ahead of time.

        //

        // Possible optimization: omit the first clause

        //    "if (!packet_in_progress & ~src_valid) ..."

        //   cost: one idle cycle at the the beginning of each

        //     grant cycle.

        //   benefit: save a small amount of logic.

        // ------------------------------------------

        if (!packet_in_progress & !src_valid)

            update_grant = 1;

        if (last_cycle && share_count_zero_flag)

            update_grant = 1;

    end

    wire save_grant;

    assign save_grant = update_grant;

    assign grant      = saved_grant;

    always @(posedge clk, posedge reset) begin

        if (reset)

            saved_grant <= '0;

        else if (save_grant)

            saved_grant <= next_grant;

    end

    // ------------------------------------------

    // ------------------------------------------

    // Arbitrator

    // ------------------------------------------

    // ------------------------------------------

    // ------------------------------------------

    // Create a request vector that stays high during

    // the packet for unpipelined arbitration.

    //

    // The pipelined arbitration scheme does not require

    // request to be held high during the packet.

    // ------------------------------------------

    reg  [NUM_INPUTS - 1 : 0] prev_request;

    always @(posedge clk, posedge reset) begin

        if (reset)

            prev_request <= '0;

        else

            prev_request <= request & ~(valid & eop);

    end

    assign request = (PIPELINE_ARB == 1) ? valid | locked :

                                           prev_request | valid | locked;

    altera_merlin_arbitrator

    #(

        .NUM_REQUESTERS(NUM_INPUTS),

        .SCHEME        ("round-robin"),

        .PIPELINE      (1)

    ) arb (

        .clk                    (clk),

        .reset                  (reset),

        .request                (request),

        .grant                  (next_grant),

        .save_top_priority      (src_valid),

        .increment_top_priority (update_grant)

    );

    // ------------------------------------------

    // ------------------------------------------

    // Mux

    //

    // Implemented as a sum of products.

    // ------------------------------------------

    // ------------------------------------------

    assign sink0_ready = src_ready && grant[0];

    assign sink1_ready = src_ready && grant[1];

    assign src_valid = |(grant & valid);

    always @* begin

        src_payload =

            sink0_payload & {PAYLOAD_W {grant[0]} } |

            sink1_payload & {PAYLOAD_W {grant[1]} };

    end

    // ------------------------------------------

    // Mux Payload Mapping

    // ------------------------------------------

    assign sink0_payload = {sink0_channel,sink0_data,

        sink0_startofpacket,sink0_endofpacket};

    assign sink1_payload = {sink1_channel,sink1_data,

        sink1_startofpacket,sink1_endofpacket};

    assign {src_channel,src_data,src_startofpacket,src_endofpacket} = src_payload;

endmodule