/*

Copyright 2019, The Regents of the University of California.
All rights reserved.

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 REGENTS OF THE UNIVERSITY OF CALIFORNIA ''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 REGENTS OF THE UNIVERSITY OF CALIFORNIA 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
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OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those
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either expressed or implied, of The Regents of the University of California.

*/

// Language: Verilog 2001

`timescale 1ns / 1ps

/*
 * Descriptor operation mux
 */
module desc_op_mux #
(
    // Number of ports
    parameter PORTS = 2,
    // Select field width
    parameter SELECT_WIDTH = 1,
    // Queue index width
    parameter QUEUE_INDEX_WIDTH = 4,
    // Queue element pointer width
    parameter QUEUE_PTR_WIDTH = 16,
    // Completion queue index width
    parameter CPL_QUEUE_INDEX_WIDTH = 4,
    // Input request tag field width
    parameter S_REQ_TAG_WIDTH = 8,
    // Output request tag field width (towards descriptor module)
    // Additional bits required for response routing
    parameter M_REQ_TAG_WIDTH = S_REQ_TAG_WIDTH+$clog2(PORTS),
    // Width of AXI stream interface in bits
    parameter AXIS_DATA_WIDTH = 256,
    // AXI stream tkeep signal width (words per cycle)
    parameter AXIS_KEEP_WIDTH = AXIS_DATA_WIDTH/8,
    // arbitration type: "PRIORITY" or "ROUND_ROBIN"
    parameter ARB_TYPE = "PRIORITY",
    // LSB priority: "LOW", "HIGH"
    parameter LSB_PRIORITY = "HIGH"
)
(
    input  wire                                   clk,
    input  wire                                   rst,

    /*
     * Descriptor request output (to descriptor module)
     */
    output wire [SELECT_WIDTH-1:0]                m_axis_req_sel,
    output wire [QUEUE_INDEX_WIDTH-1:0]           m_axis_req_queue,
    output wire [M_REQ_TAG_WIDTH-1:0]             m_axis_req_tag,
    output wire                                   m_axis_req_valid,
    input  wire                                   m_axis_req_ready,

    /*
     * Descriptor request status input (from descriptor module)
     */
    input  wire [QUEUE_INDEX_WIDTH-1:0]           s_axis_req_status_queue,
    input  wire [QUEUE_PTR_WIDTH-1:0]             s_axis_req_status_ptr,
    input  wire [CPL_QUEUE_INDEX_WIDTH-1:0]       s_axis_req_status_cpl,
    input  wire [M_REQ_TAG_WIDTH-1:0]             s_axis_req_status_tag,
    input  wire                                   s_axis_req_status_empty,
    input  wire                                   s_axis_req_status_error,
    input  wire                                   s_axis_req_status_valid,

    /*
     * Descriptor data input (from descriptor module)
     */
    input  wire [AXIS_DATA_WIDTH-1:0]             s_axis_desc_tdata,
    input  wire [AXIS_KEEP_WIDTH-1:0]             s_axis_desc_tkeep,
    input  wire                                   s_axis_desc_tvalid,
    output wire                                   s_axis_desc_tready,
    input  wire                                   s_axis_desc_tlast,
    input  wire [M_REQ_TAG_WIDTH-1:0]             s_axis_desc_tid,
    input  wire                                   s_axis_desc_tuser,

    /*
     * Descriptor request input
     */
    input  wire [PORTS*SELECT_WIDTH-1:0]          s_axis_req_sel,
    input  wire [PORTS*QUEUE_INDEX_WIDTH-1:0]     s_axis_req_queue,
    input  wire [PORTS*S_REQ_TAG_WIDTH-1:0]       s_axis_req_tag,
    input  wire [PORTS-1:0]                       s_axis_req_valid,
    output wire [PORTS-1:0]                       s_axis_req_ready,

    /*
     * Descriptor request status output
     */
    output wire [PORTS*QUEUE_INDEX_WIDTH-1:0]     m_axis_req_status_queue,
    output wire [PORTS*QUEUE_PTR_WIDTH-1:0]       m_axis_req_status_ptr,
    output wire [PORTS*CPL_QUEUE_INDEX_WIDTH-1:0] m_axis_req_status_cpl,
    output wire [PORTS*S_REQ_TAG_WIDTH-1:0]       m_axis_req_status_tag,
    output wire [PORTS-1:0]                       m_axis_req_status_empty,
    output wire [PORTS-1:0]                       m_axis_req_status_error,
    output wire [PORTS-1:0]                       m_axis_req_status_valid,

    /*
     * Descriptor data output
     */
    output wire [PORTS*AXIS_DATA_WIDTH-1:0]       m_axis_desc_tdata,
    output wire [PORTS*AXIS_KEEP_WIDTH-1:0]       m_axis_desc_tkeep,
    output wire [PORTS-1:0]                       m_axis_desc_tvalid,
    input  wire [PORTS-1:0]                       m_axis_desc_tready,
    output wire [PORTS-1:0]                       m_axis_desc_tlast,
    output wire [PORTS*S_REQ_TAG_WIDTH-1:0]       m_axis_desc_tid,
    output wire [PORTS-1:0]                       m_axis_desc_tuser
);

parameter CL_PORTS = $clog2(PORTS);

// check configuration
initial begin
    if (M_REQ_TAG_WIDTH < S_REQ_TAG_WIDTH+$clog2(PORTS)) begin
        $error("Error: M_REQ_TAG_WIDTH must be at least $clog2(PORTS) larger than S_REQ_TAG_WIDTH (instance %m)");
        $finish;
    end
end

// request mux
wire [PORTS-1:0] request;
wire [PORTS-1:0] acknowledge;
wire [PORTS-1:0] grant;
wire grant_valid;
wire [CL_PORTS-1:0] grant_encoded;

// internal datapath
reg  [SELECT_WIDTH-1:0]      m_axis_req_sel_int;
reg  [QUEUE_INDEX_WIDTH-1:0] m_axis_req_queue_int;
reg  [M_REQ_TAG_WIDTH-1:0]   m_axis_req_tag_int;
reg                          m_axis_req_valid_int;
reg                          m_axis_req_ready_int_reg = 1'b0;
wire                         m_axis_req_ready_int_early;

assign s_axis_req_ready = (m_axis_req_ready_int_reg && grant_valid) << grant_encoded;

// mux for incoming packet
wire [SELECT_WIDTH-1:0]      current_s_desc_sel   = s_axis_req_sel[grant_encoded*SELECT_WIDTH +: SELECT_WIDTH];
wire [QUEUE_INDEX_WIDTH-1:0] current_s_desc_queue = s_axis_req_queue[grant_encoded*QUEUE_INDEX_WIDTH +: QUEUE_INDEX_WIDTH];
wire [S_REQ_TAG_WIDTH-1:0]   current_s_desc_tag   = s_axis_req_tag[grant_encoded*S_REQ_TAG_WIDTH +: S_REQ_TAG_WIDTH];
wire                         current_s_desc_valid = s_axis_req_valid[grant_encoded];
wire                         current_s_desc_ready = s_axis_req_ready[grant_encoded];

// arbiter instance
arbiter #(
    .PORTS(PORTS),
    .TYPE(ARB_TYPE),
    .BLOCK("ACKNOWLEDGE"),
    .LSB_PRIORITY(LSB_PRIORITY)
)
arb_inst (
    .clk(clk),
    .rst(rst),
    .request(request),
    .acknowledge(acknowledge),
    .grant(grant),
    .grant_valid(grant_valid),
    .grant_encoded(grant_encoded)
);

assign request = s_axis_req_valid & ~grant;
assign acknowledge = grant & s_axis_req_valid & s_axis_req_ready;

always @* begin
    // pass through selected packet data
    m_axis_req_sel_int   = current_s_desc_sel;
    m_axis_req_queue_int = current_s_desc_queue;
    m_axis_req_tag_int   = {grant_encoded, current_s_desc_tag};
    m_axis_req_valid_int = current_s_desc_valid && m_axis_req_ready_int_reg && grant_valid;
end

// output datapath logic
reg [SELECT_WIDTH-1:0]      m_axis_req_sel_reg   = {SELECT_WIDTH{1'b0}};
reg [QUEUE_INDEX_WIDTH-1:0] m_axis_req_queue_reg = {QUEUE_INDEX_WIDTH{1'b0}};
reg [M_REQ_TAG_WIDTH-1:0]   m_axis_req_tag_reg   = {M_REQ_TAG_WIDTH{1'b0}};
reg                         m_axis_req_valid_reg = 1'b0, m_axis_req_valid_next;

reg [SELECT_WIDTH-1:0]      temp_m_axis_req_sel_reg   = {SELECT_WIDTH{1'b0}};
reg [QUEUE_INDEX_WIDTH-1:0] temp_m_axis_req_queue_reg = {QUEUE_INDEX_WIDTH{1'b0}};
reg [M_REQ_TAG_WIDTH-1:0]   temp_m_axis_req_tag_reg   = {M_REQ_TAG_WIDTH{1'b0}};
reg                         temp_m_axis_req_valid_reg = 1'b0, temp_m_axis_req_valid_next;

// datapath control
reg store_axis_int_to_output;
reg store_axis_int_to_temp;
reg store_axis_temp_to_output;

assign m_axis_req_sel   = m_axis_req_sel_reg;
assign m_axis_req_queue = m_axis_req_queue_reg;
assign m_axis_req_tag   = m_axis_req_tag_reg;
assign m_axis_req_valid = m_axis_req_valid_reg;

// enable ready input next cycle if output is ready or the temp reg will not be filled on the next cycle (output reg empty or no input)
assign m_axis_req_ready_int_early = m_axis_req_ready || (!temp_m_axis_req_valid_reg && (!m_axis_req_valid_reg || !m_axis_req_valid_int));

always @* begin
    // transfer sink ready state to source
    m_axis_req_valid_next = m_axis_req_valid_reg;
    temp_m_axis_req_valid_next = temp_m_axis_req_valid_reg;

    store_axis_int_to_output = 1'b0;
    store_axis_int_to_temp = 1'b0;
    store_axis_temp_to_output = 1'b0;

    if (m_axis_req_ready_int_reg) begin
        // input is ready
        if (m_axis_req_ready || !m_axis_req_valid_reg) begin
            // output is ready or currently not valid, transfer data to output
            m_axis_req_valid_next = m_axis_req_valid_int;
            store_axis_int_to_output = 1'b1;
        end else begin
            // output is not ready, store input in temp
            temp_m_axis_req_valid_next = m_axis_req_valid_int;
            store_axis_int_to_temp = 1'b1;
        end
    end else if (m_axis_req_ready) begin
        // input is not ready, but output is ready
        m_axis_req_valid_next = temp_m_axis_req_valid_reg;
        temp_m_axis_req_valid_next = 1'b0;
        store_axis_temp_to_output = 1'b1;
    end
end

always @(posedge clk) begin
    if (rst) begin
        m_axis_req_valid_reg <= 1'b0;
        m_axis_req_ready_int_reg <= 1'b0;
        temp_m_axis_req_valid_reg <= 1'b0;
    end else begin
        m_axis_req_valid_reg <= m_axis_req_valid_next;
        m_axis_req_ready_int_reg <= m_axis_req_ready_int_early;
        temp_m_axis_req_valid_reg <= temp_m_axis_req_valid_next;
    end

    // datapath
    if (store_axis_int_to_output) begin
        m_axis_req_sel_reg <= m_axis_req_sel_int;
        m_axis_req_queue_reg <= m_axis_req_queue_int;
        m_axis_req_tag_reg <= m_axis_req_tag_int;
    end else if (store_axis_temp_to_output) begin
        m_axis_req_sel_reg <= temp_m_axis_req_sel_reg;
        m_axis_req_queue_reg <= temp_m_axis_req_queue_reg;
        m_axis_req_tag_reg <= temp_m_axis_req_tag_reg;
    end

    if (store_axis_int_to_temp) begin
        temp_m_axis_req_sel_reg <= m_axis_req_sel_int;
        temp_m_axis_req_queue_reg <= m_axis_req_queue_int;
        temp_m_axis_req_tag_reg <= m_axis_req_tag_int;
    end
end

// request status demux
reg [QUEUE_INDEX_WIDTH-1:0] m_axis_req_status_queue_reg = {QUEUE_INDEX_WIDTH{1'b0}}, m_axis_req_status_queue_next;
reg [QUEUE_PTR_WIDTH-1:0] m_axis_req_status_ptr_reg = {QUEUE_PTR_WIDTH{1'b0}}, m_axis_req_status_ptr_next;
reg [CPL_QUEUE_INDEX_WIDTH-1:0] m_axis_req_status_cpl_reg = {CPL_QUEUE_INDEX_WIDTH{1'b0}}, m_axis_req_status_cpl_next;
reg [S_REQ_TAG_WIDTH-1:0] m_axis_req_status_tag_reg = {S_REQ_TAG_WIDTH{1'b0}}, m_axis_req_status_tag_next;
reg m_axis_req_status_empty_reg = 1'b0, m_axis_req_status_empty_next;
reg m_axis_req_status_error_reg = 1'b0, m_axis_req_status_error_next;
reg [PORTS-1:0] m_axis_req_status_valid_reg = {PORTS{1'b0}}, m_axis_req_status_valid_next;

assign m_axis_req_status_queue = {PORTS{m_axis_req_status_queue_reg}};
assign m_axis_req_status_ptr = {PORTS{m_axis_req_status_ptr_reg}};
assign m_axis_req_status_cpl = {PORTS{m_axis_req_status_cpl_reg}};
assign m_axis_req_status_tag = {PORTS{m_axis_req_status_tag_reg}};
assign m_axis_req_status_empty = {PORTS{m_axis_req_status_empty_reg}};
assign m_axis_req_status_error = {PORTS{m_axis_req_status_error_reg}};
assign m_axis_req_status_valid = m_axis_req_status_valid_reg;

always @* begin
    m_axis_req_status_queue_next = s_axis_req_status_queue;
    m_axis_req_status_ptr_next = s_axis_req_status_ptr;
    m_axis_req_status_cpl_next = s_axis_req_status_cpl;
    m_axis_req_status_tag_next = s_axis_req_status_tag;
    m_axis_req_status_empty_next = s_axis_req_status_empty;
    m_axis_req_status_error_next = s_axis_req_status_error;
    m_axis_req_status_valid_next = s_axis_req_status_valid << (PORTS > 1 ? (s_axis_req_status_tag >> S_REQ_TAG_WIDTH) : 0);
end

always @(posedge clk) begin
    if (rst) begin
        m_axis_req_status_valid_reg <= {PORTS{1'b0}};
    end else begin
        m_axis_req_status_valid_reg <= m_axis_req_status_valid_next;
    end

    m_axis_req_status_queue_reg <= m_axis_req_status_queue_next;
    m_axis_req_status_ptr_reg <= m_axis_req_status_ptr_next;
    m_axis_req_status_cpl_reg <= m_axis_req_status_cpl_next;
    m_axis_req_status_tag_reg <= m_axis_req_status_tag_next;
    m_axis_req_status_empty_reg <= m_axis_req_status_empty_next;
    m_axis_req_status_error_reg <= m_axis_req_status_error_next;
end

// descriptor data demux

// internal datapath
reg  [AXIS_DATA_WIDTH-1:0] m_axis_desc_tdata_int;
reg  [AXIS_KEEP_WIDTH-1:0] m_axis_desc_tkeep_int;
reg  [PORTS-1:0]           m_axis_desc_tvalid_int;
reg                        m_axis_desc_tready_int_reg = 1'b0;
wire                       m_axis_desc_tready_int_early;
reg                        m_axis_desc_tlast_int;
reg  [S_REQ_TAG_WIDTH-1:0] m_axis_desc_tid_int;
reg                        m_axis_desc_tuser_int;

assign s_axis_desc_tready = m_axis_desc_tready_int_reg;

always @* begin
    m_axis_desc_tdata_int  = s_axis_desc_tdata;
    m_axis_desc_tkeep_int  = s_axis_desc_tkeep;
    m_axis_desc_tvalid_int = (s_axis_desc_tvalid && s_axis_desc_tready) << (PORTS > 1 ? (s_axis_desc_tid >> S_REQ_TAG_WIDTH) : 0);
    m_axis_desc_tlast_int  = s_axis_desc_tlast;
    m_axis_desc_tid_int    = s_axis_desc_tid;
    m_axis_desc_tuser_int  = s_axis_desc_tuser;
end

// output datapath logic
reg [AXIS_DATA_WIDTH-1:0] m_axis_desc_tdata_reg  = {AXIS_DATA_WIDTH{1'b0}};
reg [AXIS_KEEP_WIDTH-1:0] m_axis_desc_tkeep_reg  = {AXIS_KEEP_WIDTH{1'b0}};
reg [PORTS-1:0]           m_axis_desc_tvalid_reg = {PORTS{1'b0}}, m_axis_desc_tvalid_next;
reg                       m_axis_desc_tlast_reg  = 1'b0;
reg [S_REQ_TAG_WIDTH-1:0] m_axis_desc_tid_reg    = {S_REQ_TAG_WIDTH{1'b0}};
reg                       m_axis_desc_tuser_reg  = 1'b0;

reg [AXIS_DATA_WIDTH-1:0] temp_m_axis_desc_tdata_reg  = {AXIS_DATA_WIDTH{1'b0}};
reg [AXIS_KEEP_WIDTH-1:0] temp_m_axis_desc_tkeep_reg  = {AXIS_KEEP_WIDTH{1'b0}};
reg [PORTS-1:0]           temp_m_axis_desc_tvalid_reg = {PORTS{1'b0}}, temp_m_axis_desc_tvalid_next;
reg                       temp_m_axis_desc_tlast_reg  = 1'b0;
reg [S_REQ_TAG_WIDTH-1:0] temp_m_axis_desc_tid_reg    = {S_REQ_TAG_WIDTH{1'b0}};
reg                       temp_m_axis_desc_tuser_reg  = 1'b0;

// datapath control
reg store_axis_req_int_to_output;
reg store_axis_req_int_to_temp;
reg store_axis_req_temp_to_output;

assign m_axis_desc_tdata  = {PORTS{m_axis_desc_tdata_reg}};
assign m_axis_desc_tkeep  = {PORTS{m_axis_desc_tkeep_reg}};
assign m_axis_desc_tlast  = {PORTS{m_axis_desc_tlast_reg}};
assign m_axis_desc_tid    = {PORTS{m_axis_desc_tid_reg}};
assign m_axis_desc_tuser  = {PORTS{m_axis_desc_tuser_reg}};
assign m_axis_desc_tvalid = m_axis_desc_tvalid_reg;

// enable ready input next cycle if output is ready or the temp reg will not be filled on the next cycle (output reg empty or no input)
assign m_axis_desc_tready_int_early = (m_axis_desc_tready & m_axis_desc_tvalid) || (!temp_m_axis_desc_tvalid_reg && (!m_axis_desc_tvalid || !m_axis_desc_tvalid_int));

always @* begin
    // transfer sink ready state to source
    m_axis_desc_tvalid_next = m_axis_desc_tvalid_reg;
    temp_m_axis_desc_tvalid_next = temp_m_axis_desc_tvalid_reg;

    store_axis_req_int_to_output = 1'b0;
    store_axis_req_int_to_temp = 1'b0;
    store_axis_req_temp_to_output = 1'b0;

    if (m_axis_desc_tready_int_reg) begin
        // input is ready
        if ((m_axis_desc_tready & m_axis_desc_tvalid) || !m_axis_desc_tvalid) begin
            // output is ready or currently not valid, transfer data to output
            m_axis_desc_tvalid_next = m_axis_desc_tvalid_int;
            store_axis_req_int_to_output = 1'b1;
        end else begin
            // output is not ready, store input in temp
            temp_m_axis_desc_tvalid_next = m_axis_desc_tvalid_int;
            store_axis_req_int_to_temp = 1'b1;
        end
    end else if (m_axis_desc_tready & m_axis_desc_tvalid) begin
        // input is not ready, but output is ready
        m_axis_desc_tvalid_next = temp_m_axis_desc_tvalid_reg;
        temp_m_axis_desc_tvalid_next = {PORTS{1'b0}};
        store_axis_req_temp_to_output = 1'b1;
    end
end

always @(posedge clk) begin
    if (rst) begin
        m_axis_desc_tvalid_reg <= {PORTS{1'b0}};
        m_axis_desc_tready_int_reg <= 1'b0;
        temp_m_axis_desc_tvalid_reg <= {PORTS{1'b0}};
    end else begin
        m_axis_desc_tvalid_reg <= m_axis_desc_tvalid_next;
        m_axis_desc_tready_int_reg <= m_axis_desc_tready_int_early;
        temp_m_axis_desc_tvalid_reg <= temp_m_axis_desc_tvalid_next;
    end

    // datapath
    if (store_axis_req_int_to_output) begin
        m_axis_desc_tdata_reg <= m_axis_desc_tdata_int;
        m_axis_desc_tkeep_reg <= m_axis_desc_tkeep_int;
        m_axis_desc_tlast_reg <= m_axis_desc_tlast_int;
        m_axis_desc_tid_reg <= m_axis_desc_tid_int;
        m_axis_desc_tuser_reg <= m_axis_desc_tuser_int;
    end else if (store_axis_req_temp_to_output) begin
        m_axis_desc_tdata_reg <= temp_m_axis_desc_tdata_reg;
        m_axis_desc_tkeep_reg <= temp_m_axis_desc_tkeep_reg;
        m_axis_desc_tlast_reg <= temp_m_axis_desc_tlast_reg;
        m_axis_desc_tid_reg <= temp_m_axis_desc_tid_reg;
        m_axis_desc_tuser_reg <= temp_m_axis_desc_tuser_reg;
    end

    if (store_axis_req_int_to_temp) begin
        temp_m_axis_desc_tdata_reg <= m_axis_desc_tdata_int;
        temp_m_axis_desc_tkeep_reg <= m_axis_desc_tkeep_int;
        temp_m_axis_desc_tlast_reg <= m_axis_desc_tlast_int;
        temp_m_axis_desc_tid_reg <= m_axis_desc_tid_int;
        temp_m_axis_desc_tuser_reg <= m_axis_desc_tuser_int;
    end
end

endmodule
