event_mux.v

/*

Copyright 2019, The Regents of the University of California.
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      this list of conditions and the following disclaimer.

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      and/or other materials provided with the distribution.

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IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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DISCLAIMED. IN NO EVENT SHALL THE REGENTS OF THE UNIVERSITY OF CALIFORNIA OR
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*/

// Language: Verilog 2001

`timescale 1ns / 1ps

/*
 * Event mux
 */
module event_mux #
(
    // Number of ports
    parameter PORTS = 2,
    // Queue index width
    parameter QUEUE_INDEX_WIDTH = 4,
    // Event type field width
    parameter EVENT_TYPE_WIDTH = 16,
    // Event source field width
    parameter EVENT_SOURCE_WIDTH = 16,
    // arbitration type: "PRIORITY" or "ROUND_ROBIN"
    parameter ARB_TYPE = "PRIORITY",
    // LSB priority: "LOW", "HIGH"
    parameter LSB_PRIORITY = "HIGH"
)
(
    input  wire                                clk,
    input  wire                                rst,

    /*
     * Event output
     */
    output wire [QUEUE_INDEX_WIDTH-1:0]        m_axis_event_queue,
    output wire [EVENT_TYPE_WIDTH-1:0]         m_axis_event_type,
    output wire [EVENT_SOURCE_WIDTH-1:0]       m_axis_event_source,
    output wire                                m_axis_event_valid,
    input  wire                                m_axis_event_ready,

    /*
     * Event input
     */
    input  wire [PORTS*QUEUE_INDEX_WIDTH-1:0]  s_axis_event_queue,
    input  wire [PORTS*EVENT_TYPE_WIDTH-1:0]   s_axis_event_type,
    input  wire [PORTS*EVENT_SOURCE_WIDTH-1:0] s_axis_event_source,
    input  wire [PORTS-1:0]                    s_axis_event_valid,
    output wire [PORTS-1:0]                    s_axis_event_ready
);

parameter CL_PORTS = $clog2(PORTS);

// eventriptor 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  [QUEUE_INDEX_WIDTH-1:0]  m_axis_event_queue_int;
reg  [EVENT_TYPE_WIDTH-1:0]   m_axis_event_type_int;
reg  [EVENT_SOURCE_WIDTH-1:0] m_axis_event_source_int;
reg                           m_axis_event_valid_int;
reg                           m_axis_event_ready_int_reg = 1'b0;
wire                          m_axis_event_ready_int_early;

assign s_axis_event_ready = (m_axis_event_ready_int_reg && grant_valid) << grant_encoded;

// mux for incoming packet
wire [QUEUE_INDEX_WIDTH-1:0]  current_s_event_queue   = s_axis_event_queue[grant_encoded*QUEUE_INDEX_WIDTH +: QUEUE_INDEX_WIDTH];
wire [EVENT_TYPE_WIDTH-1:0]   current_s_event_type    = s_axis_event_type[grant_encoded*EVENT_TYPE_WIDTH +: EVENT_TYPE_WIDTH];
wire [EVENT_SOURCE_WIDTH-1:0] current_s_event_source  = s_axis_event_source[grant_encoded*EVENT_SOURCE_WIDTH +: EVENT_SOURCE_WIDTH];
wire                          current_s_event_valid   = s_axis_event_valid[grant_encoded];
wire                          current_s_event_ready   = s_axis_event_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_event_valid & ~grant;
assign acknowledge = grant & s_axis_event_valid & s_axis_event_ready;

always @* begin
    m_axis_event_queue_int   = current_s_event_queue;
    m_axis_event_type_int    = current_s_event_type;
    m_axis_event_source_int  = current_s_event_source;
    m_axis_event_valid_int   = current_s_event_valid && m_axis_event_ready_int_reg && grant_valid;
end

// output datapath logic
reg [QUEUE_INDEX_WIDTH-1:0]  m_axis_event_queue_reg   = {QUEUE_INDEX_WIDTH{1'b0}};
reg [EVENT_TYPE_WIDTH-1:0]   m_axis_event_type_reg    = {EVENT_TYPE_WIDTH{1'b0}};
reg [EVENT_SOURCE_WIDTH-1:0] m_axis_event_source_reg  = {EVENT_SOURCE_WIDTH{1'b0}};
reg                          m_axis_event_valid_reg   = 1'b0, m_axis_event_valid_next;

reg [QUEUE_INDEX_WIDTH-1:0]  temp_m_axis_event_queue_reg   = {QUEUE_INDEX_WIDTH{1'b0}};
reg [EVENT_TYPE_WIDTH-1:0]   temp_m_axis_event_type_reg    = {EVENT_TYPE_WIDTH{1'b0}};
reg [EVENT_SOURCE_WIDTH-1:0] temp_m_axis_event_source_reg  = {EVENT_SOURCE_WIDTH{1'b0}};
reg                          temp_m_axis_event_valid_reg   = 1'b0, temp_m_axis_event_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_event_queue   = m_axis_event_queue_reg;
assign m_axis_event_type    = m_axis_event_type_reg;
assign m_axis_event_source  = m_axis_event_source_reg;
assign m_axis_event_valid   = m_axis_event_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_event_ready_int_early = m_axis_event_ready || (!temp_m_axis_event_valid_reg && (!m_axis_event_valid_reg || !m_axis_event_valid_int));

always @* begin
    // transfer sink ready state to source
    m_axis_event_valid_next = m_axis_event_valid_reg;
    temp_m_axis_event_valid_next = temp_m_axis_event_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_event_ready_int_reg) begin
        // input is ready
        if (m_axis_event_ready || !m_axis_event_valid_reg) begin
            // output is ready or currently not valid, transfer data to output
            m_axis_event_valid_next = m_axis_event_valid_int;
            store_axis_int_to_output = 1'b1;
        end else begin
            // output is not ready, store input in temp
            temp_m_axis_event_valid_next = m_axis_event_valid_int;
            store_axis_int_to_temp = 1'b1;
        end
    end else if (m_axis_event_ready) begin
        // input is not ready, but output is ready
        m_axis_event_valid_next = temp_m_axis_event_valid_reg;
        temp_m_axis_event_valid_next = 1'b0;
        store_axis_temp_to_output = 1'b1;
    end
end

always @(posedge clk) begin
    if (rst) begin
        m_axis_event_valid_reg <= 1'b0;
        m_axis_event_ready_int_reg <= 1'b0;
        temp_m_axis_event_valid_reg <= 1'b0;
    end else begin
        m_axis_event_valid_reg <= m_axis_event_valid_next;
        m_axis_event_ready_int_reg <= m_axis_event_ready_int_early;
        temp_m_axis_event_valid_reg <= temp_m_axis_event_valid_next;
    end

    // datapath
    if (store_axis_int_to_output) begin
        m_axis_event_queue_reg <= m_axis_event_queue_int;
        m_axis_event_type_reg <= m_axis_event_type_int;
        m_axis_event_source_reg <= m_axis_event_source_int;
    end else if (store_axis_temp_to_output) begin
        m_axis_event_queue_reg <= temp_m_axis_event_queue_reg;
        m_axis_event_type_reg <= temp_m_axis_event_type_reg;
        m_axis_event_source_reg <= temp_m_axis_event_source_reg;
    end

    if (store_axis_int_to_temp) begin
        temp_m_axis_event_queue_reg <= m_axis_event_queue_int;
        temp_m_axis_event_type_reg <= m_axis_event_type_int;
        temp_m_axis_event_source_reg <= m_axis_event_source_int;
    end
end

endmodule