You are an expert Verilog hardware designer working on a complete FPGA or ASIC project. You are given the full source code of a Verilog project. One of the modules in the project is incomplete — its implementation is missing and marked with:

// >>> Module Implementation Begin

// <<< Module Implementation End

Your task is to complete the missing implementation so that the entire project functions correctly. You must infer what the missing module or logic is supposed to do by analyzing the rest of the codebase: module names, signal connections, instantiations, comments, and usage patterns.

Follow these rules:

1. Only generate Verilog code to go between the `// >>> Module Implementation Begin` and `// <<< Module Implementation End` comments.
2. Use Verilog-2001 syntax. Ensure the code is synthesizable.
3. Assume the goal is a working, integrated hardware design — your code must make the whole system function as intended.
4. Analyze the naming, I/O ports, and how the module is instantiated or used in other parts of the project.
5. Implement correct behavior based on design context. Do not guess randomly — reason it out.
6. Avoid vendor-specific features unless explicitly required.
7. Do not output comments, explanation, or anything outside the required code region unless explicitly asked.

Your output should contain **only the Verilog code** that fits inside the marked region.

`timescale 1ns/1ps

module tt_um_Xgamer1999_LIF (
  input  wire        clk,
  input  wire        rst_n,
  input  wire        ena,         // required by TT
  input  wire [7:0]  ui_in,
  output wire [7:0]  uo_out,
  input  wire [7:0]  uio_in,
  output wire [7:0]  uio_out,
  output wire [7:0]  uio_oe
);
  // Optionally gate behavior with ena (good TT hygiene)
  wire user_in  = ui_in[0] & ena;
  wire out_bit;

  tt_um_top_lvl u_top (
    .clk(clk),
    .rst_n(rst_n),
    .signal_in(user_in),
    .signal_out(out_bit)
  );

  assign uo_out[0]   = out_bit;
  assign uo_out[7:1] = 7'b0;
  assign uio_out     = 8'b0;
  assign uio_oe      = 8'b0;


endmodule


`timescale 1ns/1ps

//LIF_Accumulator.v
//Accumulator that adds and subtracts values to hit threshold voltage necessary for neuron spike

module LIF_Accumulator #(
    parameter WIDTH = 8,//bit width of bus used in design
    parameter [WIDTH-1:0] THRESH = 8'd100//defines what the required threshold is to send an impulse
)(
    input wire clk,//clock cycle
    input wire rst_n,//reset active low to prevent reset while register has values
    input wire add_en,//enable bit to turn on adding portion of accumulator
    input wire sub_en,//enable bit to turn on subtracting portion of the accumulator
    input wire load_reset,//enable bit to determine if the register needs to be reset to zero
    input wire [WIDTH-1:0] add,//bus that determines how many bits are added to the accumulator
    input wire [WIDTH-1:0] sub,//bus that determines how many bits are subtracted from the accumulator
    input wire [WIDTH-1:0] VRESET,//bus that holds the value 8'b00000000 and resets the accumulator to that value
    output reg [WIDTH-1:0] acc,//bus that holds the accumulator's value in 8 bits
    output wire thresh_hit//threshold has been met flag that tells design to send an impulse
);

reg [WIDTH-1:0] acc_n;
wire [WIDTH-1:0] sum = acc + add;
wire [WIDTH-1:0] dec = (acc > sub) ? (acc - sub) : {WIDTH{1'b0}};//If accumulator value greater than subtractor value then subtract from accumulator and if not then reset to 0
wire ovf = (sum < acc);//1 bit overflow flag
assign thresh_hit = (acc > THRESH);

always @* begin
    acc_n = acc;

    if(load_reset) begin
        acc_n = VRESET;//If load_reset is true then reset the accumulator to all zeroes
    end
    else if(add_en) begin
        acc_n = ovf ? {WIDTH{1'b1}} : sum;//test overflow flag, if overflow is true then saturate bus with 1 and if not then add to sum
    end
    else if(sub_en)  begin
        acc_n = dec;//decrement accumulator, dont need underflow code bc underflow code is incorporated into dec design
    end
end

always @(posedge clk) begin
    if(!rst_n) begin
        acc <= VRESET;
    end
    else begin
        acc <= acc_n;
    end
end
endmodule


`timescale 1ns/1ps

//LIF_neuron_FSM.v
//General FSM that dictates direction in which logic is going

module LIF_neuron_FSM #(
    parameter WIDTH = 8
)(
    input wire clk,
    input wire rst_n,
    input wire signal_in,
    input wire thresh_hit,
    output reg add_en,
    output reg sub_en,
    output reg load_reset,
    output reg signal_out
);

    reg [2:0] state, state_n;
    localparam ini = 3'b000;
    localparam charge = 3'b001;
    localparam leak = 3'b010;
    localparam impulse = 3'b100;
    
    always @* begin
    state_n = state;
    signal_out = 1'b0;
    add_en = 1'b0;
    sub_en = 1'b0;
    load_reset = 1'b0;

        case(state)
            ini: begin
                load_reset = 1;
                if(signal_in) begin
                    state_n = charge;
                end
                else begin
                    state_n = ini;
                end
            end
            charge: begin
                add_en = signal_in;
                //assign +1 to accumulator
                if(thresh_hit) begin
                    state_n = impulse;
                end
                else begin
                    state_n = leak;
                end
            end
            leak: begin
                sub_en = 1;
                //use subtractor to subtract values from accumulator
                if(thresh_hit) begin
                    state_n = impulse;
                end
                else if(signal_in) begin
                    state_n = charge;//add value to accumulator
                end
                else begin
                state_n = leak;
                end
            end
            impulse: begin
                signal_out = 1;
                load_reset = 1;
                state_n = ini;
            end
            default: state_n = ini;
        endcase
    end

    always @(posedge clk) begin
        if(!rst_n) begin
            state = ini;
        end else begin
            state = state_n;
        end
    end
endmodule


`timescale 1ns/1ps

// TT wrapper for your LIF design
module LIF_neuron (
  input  wire        clk,
  input  wire        rst_n,
  input  wire        ena,
  input  wire [7:0]  ui_in,
  output wire [7:0]  uo_out,
  input  wire [7:0]  uio_in,
  output wire [7:0]  uio_out,
  output wire [7:0]  uio_oe
);
  // pick simple mappings
  wire signal_in  = ui_in[0];        // user drives switch 0
  wire signal_out;

  // instantiate your actual top
  tt_um_top_lvl u_top (
    .clk(clk),
    .rst_n(rst_n),
    .signal_in(signal_in),
    .signal_out(signal_out)
  );

  // drive outputs
  assign uo_out[0] = signal_out;
  assign uo_out[7:1] = 7'b0;

  // not using bidirectional bus
  assign uio_out = 8'b0;
  assign uio_oe  = 8'b0;
endmodule


`timescale 1ns/1ps

//tt_um_top_lvl.v
//Top level design file, this will instantiate the design files and wire the ports together

module tt_um_top_lvl(
    input wire clk,
    input wire rst_n,
    input wire signal_in,//signal provided by the user
    output wire signal_out//output to an LED on board
);
// >>> Module Implementation Begin

// <<< Module Implementation End
endmodule




Reference solution:
rtl/generated.v: 

wire add_en, sub_en, load_reset;
wire thresh_hit;
wire [7:0] acc;


LIF_Accumulator #(
    .WIDTH(8),
    .THRESH(8'd100)
) u_acc(
    .clk(clk),
    .rst_n(rst_n),
    .add_en(add_en),
    .sub_en(sub_en),
    .load_reset(load_reset),
    .add(8'd25),
    .sub(8'd1),
    .VRESET(8'd0),
    .acc(acc),
    .thresh_hit(thresh_hit)
);


LIF_neuron_FSM #(
    .WIDTH(8)
) u_fsm(
    .clk(clk),
    .rst_n(rst_n),
    .signal_in(signal_in),
    .add_en(add_en),
    .sub_en(sub_en),
    .load_reset(load_reset),
    .thresh_hit(thresh_hit),
    .signal_out(signal_out)
);