module axil_crossbar_wr #
(
    // Number of AXI inputs (slave interfaces)
    parameter S_COUNT = 4,
    // Number of AXI outputs (master interfaces)
    parameter M_COUNT = 4,
    // Width of data bus in bits
    parameter DATA_WIDTH = 32,
    // Width of address bus in bits
    parameter ADDR_WIDTH = 32,
    // Width of wstrb (width of data bus in words)
    parameter STRB_WIDTH = (DATA_WIDTH/8),
    // Number of concurrent operations for each slave interface
    // S_COUNT concatenated fields of 32 bits
    parameter S_ACCEPT = {S_COUNT{32'd16}},
    // Number of regions per master interface
    parameter M_REGIONS = 1,
    // Master interface base addresses
    // M_COUNT concatenated fields of M_REGIONS concatenated fields of ADDR_WIDTH bits
    // set to zero for default addressing based on M_ADDR_WIDTH
    parameter M_BASE_ADDR = 0,
    // Master interface address widths
    // M_COUNT concatenated fields of M_REGIONS concatenated fields of 32 bits
    parameter M_ADDR_WIDTH = {M_COUNT{{M_REGIONS{32'd24}}}},
    // Write connections between interfaces
    // M_COUNT concatenated fields of S_COUNT bits
    parameter M_CONNECT = {M_COUNT{{S_COUNT{1'b1}}}},
    // Number of concurrent operations for each master interface
    // M_COUNT concatenated fields of 32 bits
    parameter M_ISSUE = {M_COUNT{32'd16}},
    // Secure master (fail operations based on awprot/arprot)
    // M_COUNT bits
    parameter M_SECURE = {M_COUNT{1'b0}},
    // Slave interface AW channel register type (input)
    // 0 to bypass, 1 for simple buffer, 2 for skid buffer
    parameter S_AW_REG_TYPE = {S_COUNT{2'd0}},
    // Slave interface W channel register type (input)
    // 0 to bypass, 1 for simple buffer, 2 for skid buffer
    parameter S_W_REG_TYPE = {S_COUNT{2'd0}},
    // Slave interface B channel register type (output)
    // 0 to bypass, 1 for simple buffer, 2 for skid buffer
    parameter S_B_REG_TYPE = {S_COUNT{2'd1}},
    // Master interface AW channel register type (output)
    // 0 to bypass, 1 for simple buffer, 2 for skid buffer
    parameter M_AW_REG_TYPE = {M_COUNT{2'd1}},
    // Master interface W channel register type (output)
    // 0 to bypass, 1 for simple buffer, 2 for skid buffer
    parameter M_W_REG_TYPE = {M_COUNT{2'd2}},
    // Master interface B channel register type (input)
    // 0 to bypass, 1 for simple buffer, 2 for skid buffer
    parameter M_B_REG_TYPE = {M_COUNT{2'd0}}
)
(
    input  wire                             clk,
    input  wire                             rst,

    /*
     * AXI lite slave interfaces
     */
    input  wire [S_COUNT*ADDR_WIDTH-1:0]    s_axil_awaddr,
    input  wire [S_COUNT*3-1:0]             s_axil_awprot,
    input  wire [S_COUNT-1:0]               s_axil_awvalid,
    output wire [S_COUNT-1:0]               s_axil_awready,
    input  wire [S_COUNT*DATA_WIDTH-1:0]    s_axil_wdata,
    input  wire [S_COUNT*STRB_WIDTH-1:0]    s_axil_wstrb,
    input  wire [S_COUNT-1:0]               s_axil_wvalid,
    output wire [S_COUNT-1:0]               s_axil_wready,
    output wire [S_COUNT*2-1:0]             s_axil_bresp,
    output wire [S_COUNT-1:0]               s_axil_bvalid,
    input  wire [S_COUNT-1:0]               s_axil_bready,

    /*
     * AXI lite master interfaces
     */
    output wire [M_COUNT*ADDR_WIDTH-1:0]    m_axil_awaddr,
    output wire [M_COUNT*3-1:0]             m_axil_awprot,
    output wire [M_COUNT-1:0]               m_axil_awvalid,
    input  wire [M_COUNT-1:0]               m_axil_awready,
    output wire [M_COUNT*DATA_WIDTH-1:0]    m_axil_wdata,
    output wire [M_COUNT*STRB_WIDTH-1:0]    m_axil_wstrb,
    output wire [M_COUNT-1:0]               m_axil_wvalid,
    input  wire [M_COUNT-1:0]               m_axil_wready,
    input  wire [M_COUNT*2-1:0]             m_axil_bresp,
    input  wire [M_COUNT-1:0]               m_axil_bvalid,
    output wire [M_COUNT-1:0]               m_axil_bready
);

parameter CL_S_COUNT = $clog2(S_COUNT);
parameter CL_M_COUNT = $clog2(M_COUNT);
parameter M_COUNT_P1 = M_COUNT+1;
parameter CL_M_COUNT_P1 = $clog2(M_COUNT_P1);

integer i;

// check configuration
initial begin
    for (i = 0; i < M_COUNT*M_REGIONS; i = i + 1) begin
        if (M_ADDR_WIDTH[i*32 +: 32] && (M_ADDR_WIDTH[i*32 +: 32] < 12 || M_ADDR_WIDTH[i*32 +: 32] > ADDR_WIDTH)) begin
            $error("Error: value out of range (instance %m)");
            $finish;
        end
    end
end

wire [S_COUNT*ADDR_WIDTH-1:0]    int_s_axil_awaddr;
wire [S_COUNT*3-1:0]             int_s_axil_awprot;
wire [S_COUNT-1:0]               int_s_axil_awvalid;
wire [S_COUNT-1:0]               int_s_axil_awready;

wire [S_COUNT*M_COUNT-1:0]       int_axil_awvalid;
wire [M_COUNT*S_COUNT-1:0]       int_axil_awready;

wire [S_COUNT*DATA_WIDTH-1:0]    int_s_axil_wdata;
wire [S_COUNT*STRB_WIDTH-1:0]    int_s_axil_wstrb;
wire [S_COUNT-1:0]               int_s_axil_wvalid;
wire [S_COUNT-1:0]               int_s_axil_wready;

wire [S_COUNT*M_COUNT-1:0]       int_axil_wvalid;
wire [M_COUNT*S_COUNT-1:0]       int_axil_wready;

wire [M_COUNT*2-1:0]             int_m_axil_bresp;
wire [M_COUNT-1:0]               int_m_axil_bvalid;
wire [M_COUNT-1:0]               int_m_axil_bready;

wire [M_COUNT*S_COUNT-1:0]       int_axil_bvalid;
wire [S_COUNT*M_COUNT-1:0]       int_axil_bready;

generate

    genvar m, n;

    for (m = 0; m < S_COUNT; m = m + 1) begin : s_ifaces
        // response routing FIFO
        localparam FIFO_ADDR_WIDTH = $clog2(S_ACCEPT[m*32 +: 32])+1;

        reg [FIFO_ADDR_WIDTH+1-1:0] fifo_wr_ptr_reg = 0;
        reg [FIFO_ADDR_WIDTH+1-1:0] fifo_rd_ptr_reg = 0;

        reg [CL_M_COUNT-1:0] fifo_select[(2**FIFO_ADDR_WIDTH)-1:0];
        reg fifo_decerr[(2**FIFO_ADDR_WIDTH)-1:0];
        wire [CL_M_COUNT-1:0] fifo_wr_select;
        wire fifo_wr_decerr;
        wire fifo_wr_en;
        wire fifo_rd_en;
        reg fifo_half_full_reg = 1'b0;

        wire fifo_empty = fifo_rd_ptr_reg == fifo_wr_ptr_reg;

        integer i;

        initial begin
            for (i = 0; i < 2**FIFO_ADDR_WIDTH; i = i + 1) begin
                fifo_select[i] = 0;
                fifo_decerr[i] = 0;
            end
        end

        always @(posedge clk) begin
            if (fifo_wr_en) begin
                fifo_select[fifo_wr_ptr_reg[FIFO_ADDR_WIDTH-1:0]] <= fifo_wr_select;
                fifo_decerr[fifo_wr_ptr_reg[FIFO_ADDR_WIDTH-1:0]] <= fifo_wr_decerr;
                fifo_wr_ptr_reg <= fifo_wr_ptr_reg + 1;
            end
            if (fifo_rd_en) begin
                fifo_rd_ptr_reg <= fifo_rd_ptr_reg + 1;
            end

            fifo_half_full_reg <= $unsigned(fifo_wr_ptr_reg - fifo_rd_ptr_reg) >= 2**(FIFO_ADDR_WIDTH-1);

            if (rst) begin
                fifo_wr_ptr_reg <= 0;
                fifo_rd_ptr_reg <= 0;
            end
        end

        // address decode and admission control
        wire [CL_M_COUNT-1:0] a_select;

        wire m_axil_avalid;
        wire m_axil_aready;

        wire [CL_M_COUNT-1:0] m_wc_select;
        wire m_wc_decerr;
        wire m_wc_valid;
        wire m_wc_ready;

        wire [CL_M_COUNT-1:0] m_rc_select;
        wire m_rc_decerr;
        wire m_rc_valid;
        wire m_rc_ready;

        axil_crossbar_addr #(
            .S(m),
            .S_COUNT(S_COUNT),
            .M_COUNT(M_COUNT),
            .ADDR_WIDTH(ADDR_WIDTH),
            .M_REGIONS(M_REGIONS),
            .M_BASE_ADDR(M_BASE_ADDR),
            .M_ADDR_WIDTH(M_ADDR_WIDTH),
            .M_CONNECT(M_CONNECT),
            .M_SECURE(M_SECURE),
            .WC_OUTPUT(1)
        )
        addr_inst (
            .clk(clk),
            .rst(rst),

            /*
             * Address input
             */
            .s_axil_aaddr(int_s_axil_awaddr[m*ADDR_WIDTH +: ADDR_WIDTH]),
            .s_axil_aprot(int_s_axil_awprot[m*3 +: 3]),
            .s_axil_avalid(int_s_axil_awvalid[m]),
            .s_axil_aready(int_s_axil_awready[m]),

            /*
             * Address output
             */
            .m_select(a_select),
            .m_axil_avalid(m_axil_avalid),
            .m_axil_aready(m_axil_aready),

            /*
             * Write command output
             */
            .m_wc_select(m_wc_select),
            .m_wc_decerr(m_wc_decerr),
            .m_wc_valid(m_wc_valid),
            .m_wc_ready(m_wc_ready),

            /*
             * Response command output
             */
            .m_rc_select(m_rc_select),
            .m_rc_decerr(m_rc_decerr),
            .m_rc_valid(m_rc_valid),
            .m_rc_ready(m_rc_ready)
        );

        assign int_axil_awvalid[m*M_COUNT +: M_COUNT] = m_axil_avalid << a_select;
        assign m_axil_aready = int_axil_awready[a_select*S_COUNT+m];

        // write command handling
        reg [CL_M_COUNT-1:0] w_select_reg = 0, w_select_next;
        reg w_drop_reg = 1'b0, w_drop_next;
        reg w_select_valid_reg = 1'b0, w_select_valid_next;

        assign m_wc_ready = !w_select_valid_reg;

        always @* begin
            w_select_next = w_select_reg;
            w_drop_next = w_drop_reg && !(int_s_axil_wvalid[m] && int_s_axil_wready[m]);
            w_select_valid_next = w_select_valid_reg && !(int_s_axil_wvalid[m] && int_s_axil_wready[m]);

            if (m_wc_valid && !w_select_valid_reg) begin
                w_select_next = m_wc_select;
                w_drop_next = m_wc_decerr;
                w_select_valid_next = m_wc_valid;
            end
        end

        always @(posedge clk) begin
            if (rst) begin
                w_select_valid_reg <= 1'b0;
            end else begin
                w_select_valid_reg <= w_select_valid_next;
            end

            w_select_reg <= w_select_next;
            w_drop_reg <= w_drop_next;
        end

        // write data forwarding
        assign int_axil_wvalid[m*M_COUNT +: M_COUNT] = (int_s_axil_wvalid[m] && w_select_valid_reg && !w_drop_reg) << w_select_reg;
        assign int_s_axil_wready[m] = int_axil_wready[w_select_reg*S_COUNT+m] || w_drop_reg;

        // response handling
        assign fifo_wr_select = m_rc_select;
        assign fifo_wr_decerr = m_rc_decerr;
        assign fifo_wr_en = m_rc_valid && !fifo_half_full_reg;
        assign m_rc_ready = !fifo_half_full_reg;

        // write response handling
        wire [CL_M_COUNT-1:0] b_select = M_COUNT > 1 ? fifo_select[fifo_rd_ptr_reg[FIFO_ADDR_WIDTH-1:0]] : 0;
        wire b_decerr = fifo_decerr[fifo_rd_ptr_reg[FIFO_ADDR_WIDTH-1:0]];
        wire b_valid = !fifo_empty;

        // write response mux
        wire [1:0]  m_axil_bresp_mux  = b_decerr ? 2'b11 : int_m_axil_bresp[b_select*2 +: 2];
        wire        m_axil_bvalid_mux = (b_decerr ? 1'b1 : int_axil_bvalid[b_select*S_COUNT+m]) && b_valid;
        wire        m_axil_bready_mux;

        assign int_axil_bready[m*M_COUNT +: M_COUNT] = (b_valid && m_axil_bready_mux) << b_select;

        assign fifo_rd_en = m_axil_bvalid_mux && m_axil_bready_mux && b_valid;

        // S side register
        axil_register_wr #(
            .DATA_WIDTH(DATA_WIDTH),
            .ADDR_WIDTH(ADDR_WIDTH),
            .STRB_WIDTH(STRB_WIDTH),
            .AW_REG_TYPE(S_AW_REG_TYPE[m*2 +: 2]),
            .W_REG_TYPE(S_W_REG_TYPE[m*2 +: 2]),
            .B_REG_TYPE(S_B_REG_TYPE[m*2 +: 2])
        )
        reg_inst (
            .clk(clk),
            .rst(rst),
            .s_axil_awaddr(s_axil_awaddr[m*ADDR_WIDTH +: ADDR_WIDTH]),
            .s_axil_awprot(s_axil_awprot[m*3 +: 3]),
            .s_axil_awvalid(s_axil_awvalid[m]),
            .s_axil_awready(s_axil_awready[m]),
            .s_axil_wdata(s_axil_wdata[m*DATA_WIDTH +: DATA_WIDTH]),
            .s_axil_wstrb(s_axil_wstrb[m*STRB_WIDTH +: STRB_WIDTH]),
            .s_axil_wvalid(s_axil_wvalid[m]),
            .s_axil_wready(s_axil_wready[m]),
            .s_axil_bresp(s_axil_bresp[m*2 +: 2]),
            .s_axil_bvalid(s_axil_bvalid[m]),
            .s_axil_bready(s_axil_bready[m]),
            .m_axil_awaddr(int_s_axil_awaddr[m*ADDR_WIDTH +: ADDR_WIDTH]),
            .m_axil_awprot(int_s_axil_awprot[m*3 +: 3]),
            .m_axil_awvalid(int_s_axil_awvalid[m]),
            .m_axil_awready(int_s_axil_awready[m]),
            .m_axil_wdata(int_s_axil_wdata[m*DATA_WIDTH +: DATA_WIDTH]),
            .m_axil_wstrb(int_s_axil_wstrb[m*STRB_WIDTH +: STRB_WIDTH]),
            .m_axil_wvalid(int_s_axil_wvalid[m]),
            .m_axil_wready(int_s_axil_wready[m]),
            .m_axil_bresp(m_axil_bresp_mux),
            .m_axil_bvalid(m_axil_bvalid_mux),
            .m_axil_bready(m_axil_bready_mux)
        );
    end // s_ifaces

    for (n = 0; n < M_COUNT; n = n + 1) begin : m_ifaces
        // response routing FIFO
        localparam FIFO_ADDR_WIDTH = $clog2(M_ISSUE[n*32 +: 32])+1;

        reg [FIFO_ADDR_WIDTH+1-1:0] fifo_wr_ptr_reg = 0;
        reg [FIFO_ADDR_WIDTH+1-1:0] fifo_rd_ptr_reg = 0;

        reg [CL_S_COUNT-1:0] fifo_select[(2**FIFO_ADDR_WIDTH)-1:0];
        wire [CL_S_COUNT-1:0] fifo_wr_select;
        wire fifo_wr_en;
        wire fifo_rd_en;
        reg fifo_half_full_reg = 1'b0;

        wire fifo_empty = fifo_rd_ptr_reg == fifo_wr_ptr_reg;

        integer i;

        initial begin
            for (i = 0; i < 2**FIFO_ADDR_WIDTH; i = i + 1) begin
                fifo_select[i] = 0;
            end
        end

        always @(posedge clk) begin
            if (fifo_wr_en) begin
                fifo_select[fifo_wr_ptr_reg[FIFO_ADDR_WIDTH-1:0]] <= fifo_wr_select;
                fifo_wr_ptr_reg <= fifo_wr_ptr_reg + 1;
            end
            if (fifo_rd_en) begin
                fifo_rd_ptr_reg <= fifo_rd_ptr_reg + 1;
            end

            fifo_half_full_reg <= $unsigned(fifo_wr_ptr_reg - fifo_rd_ptr_reg) >= 2**(FIFO_ADDR_WIDTH-1);

            if (rst) begin
                fifo_wr_ptr_reg <= 0;
                fifo_rd_ptr_reg <= 0;
            end
        end

        // address arbitration
        reg [CL_S_COUNT-1:0] w_select_reg = 0, w_select_next = 0;
        reg w_select_valid_reg = 1'b0, w_select_valid_next;
        reg w_select_new_reg = 1'b0, w_select_new_next;

        wire [S_COUNT-1:0] a_request;
        wire [S_COUNT-1:0] a_acknowledge;
        wire [S_COUNT-1:0] a_grant;
        wire a_grant_valid;
        wire [CL_S_COUNT-1:0] a_grant_encoded;

        arbiter #(
            .PORTS(S_COUNT),
            .ARB_TYPE_ROUND_ROBIN(1),
            .ARB_BLOCK(1),
            .ARB_BLOCK_ACK(1),
            .ARB_LSB_HIGH_PRIORITY(1)
        )
        a_arb_inst (
            .clk(clk),
            .rst(rst),
            .request(a_request),
            .acknowledge(a_acknowledge),
            .grant(a_grant),
            .grant_valid(a_grant_valid),
            .grant_encoded(a_grant_encoded)
        );

        // address mux
        wire [ADDR_WIDTH-1:0]  s_axil_awaddr_mux   = int_s_axil_awaddr[a_grant_encoded*ADDR_WIDTH +: ADDR_WIDTH];
        wire [2:0]             s_axil_awprot_mux   = int_s_axil_awprot[a_grant_encoded*3 +: 3];
        wire                   s_axil_awvalid_mux  = int_axil_awvalid[a_grant_encoded*M_COUNT+n] && a_grant_valid;
        wire                   s_axil_awready_mux;

        assign int_axil_awready[n*S_COUNT +: S_COUNT] = (a_grant_valid && s_axil_awready_mux) << a_grant_encoded;

        for (m = 0; m < S_COUNT; m = m + 1) begin
            assign a_request[m] = int_axil_awvalid[m*M_COUNT+n] && !a_grant[m] && !fifo_half_full_reg && !w_select_valid_next;
            assign a_acknowledge[m] = a_grant[m] && int_axil_awvalid[m*M_COUNT+n] && s_axil_awready_mux;
        end

        assign fifo_wr_select = a_grant_encoded;
        assign fifo_wr_en = s_axil_awvalid_mux && s_axil_awready_mux && a_grant_valid;

        // write data mux
        wire [DATA_WIDTH-1:0]  s_axil_wdata_mux   = int_s_axil_wdata[w_select_reg*DATA_WIDTH +: DATA_WIDTH];
        wire [STRB_WIDTH-1:0]  s_axil_wstrb_mux   = int_s_axil_wstrb[w_select_reg*STRB_WIDTH +: STRB_WIDTH];
        wire                   s_axil_wvalid_mux  = int_axil_wvalid[w_select_reg*M_COUNT+n] && w_select_valid_reg;
        wire                   s_axil_wready_mux;

        assign int_axil_wready[n*S_COUNT +: S_COUNT] = (w_select_valid_reg && s_axil_wready_mux) << w_select_reg;

        // write data routing
        always @* begin
            w_select_next = w_select_reg;
            w_select_valid_next = w_select_valid_reg && !(s_axil_wvalid_mux && s_axil_wready_mux);
            w_select_new_next = w_select_new_reg || !a_grant_valid || a_acknowledge;

            if (a_grant_valid && !w_select_valid_reg && w_select_new_reg) begin
                w_select_next = a_grant_encoded;
                w_select_valid_next = a_grant_valid;
                w_select_new_next = 1'b0;
            end
        end

        always @(posedge clk) begin
            if (rst) begin
                w_select_valid_reg <= 1'b0;
                w_select_new_reg <= 1'b1;
            end else begin
                w_select_valid_reg <= w_select_valid_next;
                w_select_new_reg <= w_select_new_next;
            end

            w_select_reg <= w_select_next;
        end

        // write response forwarding
        wire [CL_S_COUNT-1:0] b_select = S_COUNT > 1 ? fifo_select[fifo_rd_ptr_reg[FIFO_ADDR_WIDTH-1:0]] : 0;

        assign int_axil_bvalid[n*S_COUNT +: S_COUNT] = int_m_axil_bvalid[n] << b_select;
        assign int_m_axil_bready[n] = int_axil_bready[b_select*M_COUNT+n];

        assign fifo_rd_en = int_m_axil_bvalid[n] && int_m_axil_bready[n];

        // M side register
        axil_register_wr #(
            .DATA_WIDTH(DATA_WIDTH),
            .ADDR_WIDTH(ADDR_WIDTH),
            .STRB_WIDTH(STRB_WIDTH),
            .AW_REG_TYPE(M_AW_REG_TYPE[n*2 +: 2]),
            .W_REG_TYPE(M_W_REG_TYPE[n*2 +: 2]),
            .B_REG_TYPE(M_B_REG_TYPE[n*2 +: 2])
        )
        reg_inst (
            .clk(clk),
            .rst(rst),
            .s_axil_awaddr(s_axil_awaddr_mux),
            .s_axil_awprot(s_axil_awprot_mux),
            .s_axil_awvalid(s_axil_awvalid_mux),
            .s_axil_awready(s_axil_awready_mux),
            .s_axil_wdata(s_axil_wdata_mux),
            .s_axil_wstrb(s_axil_wstrb_mux),
            .s_axil_wvalid(s_axil_wvalid_mux),
            .s_axil_wready(s_axil_wready_mux),
            .s_axil_bresp(int_m_axil_bresp[n*2 +: 2]),
            .s_axil_bvalid(int_m_axil_bvalid[n]),
            .s_axil_bready(int_m_axil_bready[n]),
            .m_axil_awaddr(m_axil_awaddr[n*ADDR_WIDTH +: ADDR_WIDTH]),
            .m_axil_awprot(m_axil_awprot[n*3 +: 3]),
            .m_axil_awvalid(m_axil_awvalid[n]),
            .m_axil_awready(m_axil_awready[n]),
            .m_axil_wdata(m_axil_wdata[n*DATA_WIDTH +: DATA_WIDTH]),
            .m_axil_wstrb(m_axil_wstrb[n*STRB_WIDTH +: STRB_WIDTH]),
            .m_axil_wvalid(m_axil_wvalid[n]),
            .m_axil_wready(m_axil_wready[n]),
            .m_axil_bresp(m_axil_bresp[n*2 +: 2]),
            .m_axil_bvalid(m_axil_bvalid[n]),
            .m_axil_bready(m_axil_bready[n])
        );
    end // m_ifaces

endgenerate

endmodule