module eth_demux #
(
    parameter M_COUNT = 4,
    parameter DATA_WIDTH = 8,
    parameter KEEP_ENABLE = (DATA_WIDTH>8),
    parameter KEEP_WIDTH = (DATA_WIDTH/8),
    parameter ID_ENABLE = 0,
    parameter ID_WIDTH = 8,
    parameter DEST_ENABLE = 0,
    parameter DEST_WIDTH = 8,
    parameter USER_ENABLE = 1,
    parameter USER_WIDTH = 1
)
(
    input  wire                          clk,
    input  wire                          rst,

    /*
     * Ethernet frame input
     */
    input  wire                          s_eth_hdr_valid,
    output wire                          s_eth_hdr_ready,
    input  wire [47:0]                   s_eth_dest_mac,
    input  wire [47:0]                   s_eth_src_mac,
    input  wire [15:0]                   s_eth_type,
    input  wire [DATA_WIDTH-1:0]         s_eth_payload_axis_tdata,
    input  wire [KEEP_WIDTH-1:0]         s_eth_payload_axis_tkeep,
    input  wire                          s_eth_payload_axis_tvalid,
    output wire                          s_eth_payload_axis_tready,
    input  wire                          s_eth_payload_axis_tlast,
    input  wire [ID_WIDTH-1:0]           s_eth_payload_axis_tid,
    input  wire [DEST_WIDTH-1:0]         s_eth_payload_axis_tdest,
    input  wire [USER_WIDTH-1:0]         s_eth_payload_axis_tuser,

    /*
     * Ethernet frame outputs
     */
    output wire [M_COUNT-1:0]            m_eth_hdr_valid,
    input  wire [M_COUNT-1:0]            m_eth_hdr_ready,
    output wire [M_COUNT*48-1:0]         m_eth_dest_mac,
    output wire [M_COUNT*48-1:0]         m_eth_src_mac,
    output wire [M_COUNT*16-1:0]         m_eth_type,
    output wire [M_COUNT*DATA_WIDTH-1:0] m_eth_payload_axis_tdata,
    output wire [M_COUNT*KEEP_WIDTH-1:0] m_eth_payload_axis_tkeep,
    output wire [M_COUNT-1:0]            m_eth_payload_axis_tvalid,
    input  wire [M_COUNT-1:0]            m_eth_payload_axis_tready,
    output wire [M_COUNT-1:0]            m_eth_payload_axis_tlast,
    output wire [M_COUNT*ID_WIDTH-1:0]   m_eth_payload_axis_tid,
    output wire [M_COUNT*DEST_WIDTH-1:0] m_eth_payload_axis_tdest,
    output wire [M_COUNT*USER_WIDTH-1:0] m_eth_payload_axis_tuser,

    /*
     * Control
     */
    input  wire                          enable,
    input  wire                          drop,
    input  wire [$clog2(M_COUNT)-1:0]    select
);

parameter CL_M_COUNT = $clog2(M_COUNT);

reg [CL_M_COUNT-1:0] select_reg = {CL_M_COUNT{1'b0}}, select_ctl, select_next;
reg drop_reg = 1'b0, drop_ctl, drop_next;
reg frame_reg = 1'b0, frame_ctl, frame_next;

reg s_eth_hdr_ready_reg = 1'b0, s_eth_hdr_ready_next;

reg s_eth_payload_axis_tready_reg = 1'b0, s_eth_payload_axis_tready_next;

reg [M_COUNT-1:0] m_eth_hdr_valid_reg = 0, m_eth_hdr_valid_next;
reg [47:0] m_eth_dest_mac_reg = 48'd0, m_eth_dest_mac_next;
reg [47:0] m_eth_src_mac_reg = 48'd0, m_eth_src_mac_next;
reg [15:0] m_eth_type_reg = 16'd0, m_eth_type_next;

// internal datapath
reg  [DATA_WIDTH-1:0] m_eth_payload_axis_tdata_int;
reg  [KEEP_WIDTH-1:0] m_eth_payload_axis_tkeep_int;
reg  [M_COUNT-1:0]    m_eth_payload_axis_tvalid_int;
reg                   m_eth_payload_axis_tready_int_reg = 1'b0;
reg                   m_eth_payload_axis_tlast_int;
reg  [ID_WIDTH-1:0]   m_eth_payload_axis_tid_int;
reg  [DEST_WIDTH-1:0] m_eth_payload_axis_tdest_int;
reg  [USER_WIDTH-1:0] m_eth_payload_axis_tuser_int;
wire                  m_eth_payload_axis_tready_int_early;

assign s_eth_hdr_ready = s_eth_hdr_ready_reg && enable;

assign s_eth_payload_axis_tready = s_eth_payload_axis_tready_reg && enable;

assign m_eth_hdr_valid = m_eth_hdr_valid_reg;
assign m_eth_dest_mac = {M_COUNT{m_eth_dest_mac_reg}};
assign m_eth_src_mac = {M_COUNT{m_eth_src_mac_reg}};
assign m_eth_type = {M_COUNT{m_eth_type_reg}};

integer i;

always @* begin
    select_next = select_reg;
    select_ctl = select_reg;
    drop_next = drop_reg;
    drop_ctl = drop_reg;
    frame_next = frame_reg;
    frame_ctl = frame_reg;

    s_eth_hdr_ready_next = 1'b0;

    s_eth_payload_axis_tready_next = 1'b0;

    m_eth_hdr_valid_next = m_eth_hdr_valid_reg & ~m_eth_hdr_ready;
    m_eth_dest_mac_next = m_eth_dest_mac_reg;
    m_eth_src_mac_next = m_eth_src_mac_reg;
    m_eth_type_next = m_eth_type_reg;

    if (s_eth_payload_axis_tvalid && s_eth_payload_axis_tready) begin
        // end of frame detection
        if (s_eth_payload_axis_tlast) begin
            frame_next = 1'b0;
            drop_next = 1'b0;
        end
    end

    if (!frame_reg && s_eth_hdr_valid && s_eth_hdr_ready) begin
        // start of frame, grab select value
        select_ctl = select;
        drop_ctl = drop;
        frame_ctl = 1'b1;

        select_next = select_ctl;
        drop_next = drop_ctl;
        frame_next = frame_ctl;

        s_eth_hdr_ready_next = 1'b0;

        m_eth_hdr_valid_next = (!drop_ctl) << select_ctl;
        m_eth_dest_mac_next = s_eth_dest_mac;
        m_eth_src_mac_next = s_eth_src_mac;
        m_eth_type_next = s_eth_type;
    end

    s_eth_hdr_ready_next = !frame_next && !m_eth_hdr_valid_next;

    s_eth_payload_axis_tready_next = (m_eth_payload_axis_tready_int_early || drop_ctl) && frame_ctl;

    m_eth_payload_axis_tdata_int  = s_eth_payload_axis_tdata;
    m_eth_payload_axis_tkeep_int  = s_eth_payload_axis_tkeep;
    m_eth_payload_axis_tvalid_int = (s_eth_payload_axis_tvalid && s_eth_payload_axis_tready && !drop_ctl) << select_ctl;
    m_eth_payload_axis_tlast_int  = s_eth_payload_axis_tlast;
    m_eth_payload_axis_tid_int    = s_eth_payload_axis_tid;
    m_eth_payload_axis_tdest_int  = s_eth_payload_axis_tdest;
    m_eth_payload_axis_tuser_int  = s_eth_payload_axis_tuser; 
end

always @(posedge clk) begin
    if (rst) begin
        select_reg <= 2'd0;
        drop_reg <= 1'b0;
        frame_reg <= 1'b0;
        s_eth_hdr_ready_reg <= 1'b0;
        s_eth_payload_axis_tready_reg <= 1'b0;
        m_eth_hdr_valid_reg <= 0;
    end else begin
        select_reg <= select_next;
        drop_reg <= drop_next;
        frame_reg <= frame_next;
        s_eth_hdr_ready_reg <= s_eth_hdr_ready_next;
        s_eth_payload_axis_tready_reg <= s_eth_payload_axis_tready_next;
        m_eth_hdr_valid_reg <= m_eth_hdr_valid_next;
    end

    m_eth_dest_mac_reg <= m_eth_dest_mac_next;
    m_eth_src_mac_reg <= m_eth_src_mac_next;
    m_eth_type_reg <= m_eth_type_next;
end

// output datapath logic
reg [DATA_WIDTH-1:0] m_eth_payload_axis_tdata_reg  = {DATA_WIDTH{1'b0}};
reg [KEEP_WIDTH-1:0] m_eth_payload_axis_tkeep_reg  = {KEEP_WIDTH{1'b0}};
reg [M_COUNT-1:0]    m_eth_payload_axis_tvalid_reg = {M_COUNT{1'b0}}, m_eth_payload_axis_tvalid_next;
reg                  m_eth_payload_axis_tlast_reg  = 1'b0;
reg [ID_WIDTH-1:0]   m_eth_payload_axis_tid_reg    = {ID_WIDTH{1'b0}};
reg [DEST_WIDTH-1:0] m_eth_payload_axis_tdest_reg  = {DEST_WIDTH{1'b0}};
reg [USER_WIDTH-1:0] m_eth_payload_axis_tuser_reg  = {USER_WIDTH{1'b0}};

reg [DATA_WIDTH-1:0] temp_m_eth_payload_axis_tdata_reg  = {DATA_WIDTH{1'b0}};
reg [KEEP_WIDTH-1:0] temp_m_eth_payload_axis_tkeep_reg  = {KEEP_WIDTH{1'b0}};
reg [M_COUNT-1:0]    temp_m_eth_payload_axis_tvalid_reg = {M_COUNT{1'b0}}, temp_m_eth_payload_axis_tvalid_next;
reg                  temp_m_eth_payload_axis_tlast_reg  = 1'b0;
reg [ID_WIDTH-1:0]   temp_m_eth_payload_axis_tid_reg    = {ID_WIDTH{1'b0}};
reg [DEST_WIDTH-1:0] temp_m_eth_payload_axis_tdest_reg  = {DEST_WIDTH{1'b0}};
reg [USER_WIDTH-1:0] temp_m_eth_payload_axis_tuser_reg  = {USER_WIDTH{1'b0}};

// datapath control
reg store_axis_int_to_output;
reg store_axis_int_to_temp;
reg store_eth_payload_axis_temp_to_output;

assign m_eth_payload_axis_tdata  = {M_COUNT{m_eth_payload_axis_tdata_reg}};
assign m_eth_payload_axis_tkeep  = KEEP_ENABLE ? {M_COUNT{m_eth_payload_axis_tkeep_reg}} : {M_COUNT*KEEP_WIDTH{1'b1}};
assign m_eth_payload_axis_tvalid = m_eth_payload_axis_tvalid_reg;
assign m_eth_payload_axis_tlast  = {M_COUNT{m_eth_payload_axis_tlast_reg}};
assign m_eth_payload_axis_tid    = ID_ENABLE   ? {M_COUNT{m_eth_payload_axis_tid_reg}}   : {M_COUNT*ID_WIDTH{1'b0}};
assign m_eth_payload_axis_tdest  = DEST_ENABLE ? {M_COUNT{m_eth_payload_axis_tdest_reg}} : {M_COUNT*DEST_WIDTH{1'b0}};
assign m_eth_payload_axis_tuser  = USER_ENABLE ? {M_COUNT{m_eth_payload_axis_tuser_reg}} : {M_COUNT*USER_WIDTH{1'b0}};

// enable ready input next cycle if output is ready or if both output registers are empty
assign m_eth_payload_axis_tready_int_early = (m_eth_payload_axis_tready & m_eth_payload_axis_tvalid) || (!temp_m_eth_payload_axis_tvalid_reg && !m_eth_payload_axis_tvalid_reg);

always @* begin
    // transfer sink ready state to source
    m_eth_payload_axis_tvalid_next = m_eth_payload_axis_tvalid_reg;
    temp_m_eth_payload_axis_tvalid_next = temp_m_eth_payload_axis_tvalid_reg;

    store_axis_int_to_output = 1'b0;
    store_axis_int_to_temp = 1'b0;
    store_eth_payload_axis_temp_to_output = 1'b0;

    if (m_eth_payload_axis_tready_int_reg) begin
        // input is ready
        if ((m_eth_payload_axis_tready & m_eth_payload_axis_tvalid) || !m_eth_payload_axis_tvalid) begin
            // output is ready or currently not valid, transfer data to output
            m_eth_payload_axis_tvalid_next = m_eth_payload_axis_tvalid_int;
            store_axis_int_to_output = 1'b1;
        end else begin
            // output is not ready, store input in temp
            temp_m_eth_payload_axis_tvalid_next = m_eth_payload_axis_tvalid_int;
            store_axis_int_to_temp = 1'b1;
        end
    end else if (m_eth_payload_axis_tready & m_eth_payload_axis_tvalid) begin
        // input is not ready, but output is ready
        m_eth_payload_axis_tvalid_next = temp_m_eth_payload_axis_tvalid_reg;
        temp_m_eth_payload_axis_tvalid_next = 1'b0;
        store_eth_payload_axis_temp_to_output = 1'b1;
    end
end

always @(posedge clk) begin
    m_eth_payload_axis_tvalid_reg <= m_eth_payload_axis_tvalid_next;
    m_eth_payload_axis_tready_int_reg <= m_eth_payload_axis_tready_int_early;
    temp_m_eth_payload_axis_tvalid_reg <= temp_m_eth_payload_axis_tvalid_next;

    // datapath
    if (store_axis_int_to_output) begin
        m_eth_payload_axis_tdata_reg <= m_eth_payload_axis_tdata_int;
        m_eth_payload_axis_tkeep_reg <= m_eth_payload_axis_tkeep_int;
        m_eth_payload_axis_tlast_reg <= m_eth_payload_axis_tlast_int;
        m_eth_payload_axis_tid_reg   <= m_eth_payload_axis_tid_int;
        m_eth_payload_axis_tdest_reg <= m_eth_payload_axis_tdest_int;
        m_eth_payload_axis_tuser_reg <= m_eth_payload_axis_tuser_int;
    end else if (store_eth_payload_axis_temp_to_output) begin
        m_eth_payload_axis_tdata_reg <= temp_m_eth_payload_axis_tdata_reg;
        m_eth_payload_axis_tkeep_reg <= temp_m_eth_payload_axis_tkeep_reg;
        m_eth_payload_axis_tlast_reg <= temp_m_eth_payload_axis_tlast_reg;
        m_eth_payload_axis_tid_reg   <= temp_m_eth_payload_axis_tid_reg;
        m_eth_payload_axis_tdest_reg <= temp_m_eth_payload_axis_tdest_reg;
        m_eth_payload_axis_tuser_reg <= temp_m_eth_payload_axis_tuser_reg;
    end

    if (store_axis_int_to_temp) begin
        temp_m_eth_payload_axis_tdata_reg <= m_eth_payload_axis_tdata_int;
        temp_m_eth_payload_axis_tkeep_reg <= m_eth_payload_axis_tkeep_int;
        temp_m_eth_payload_axis_tlast_reg <= m_eth_payload_axis_tlast_int;
        temp_m_eth_payload_axis_tid_reg   <= m_eth_payload_axis_tid_int;
        temp_m_eth_payload_axis_tdest_reg <= m_eth_payload_axis_tdest_int;
        temp_m_eth_payload_axis_tuser_reg <= m_eth_payload_axis_tuser_int;
    end

    if (rst) begin
        m_eth_payload_axis_tvalid_reg <= {M_COUNT{1'b0}};
        m_eth_payload_axis_tready_int_reg <= 1'b0;
        temp_m_eth_payload_axis_tvalid_reg <= 1'b0;
    end
end

endmodule