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.

/*
 * Copyright (c) 2024 Your Name
 * SPDX-License-Identifier: Apache-2.0
 */

`define default_netname none
//`include "chip.v"

module tt_um_fdc_chip (
    input  wire [7:0] ui_in,    // Dedicated inputs
    output wire [7:0] uo_out,   // Dedicated outputs
    input  wire [7:0] uio_in,   // IOs: Input path
    output wire [7:0] uio_out,  // IOs: Output path
    output wire [7:0] uio_oe,   // IOs: Enable path (active high: 0=input, 1=output)
    input  wire       ena,      // will go high when the design is enabled
    input  wire       clk,      // clock
    input  wire       rst_n     // reset_n - low to reset
);

  // All output pins must be assigned. If not used, assign to 0.
  assign uio_oe = 8'b0;
  assign uio_out = 8'b0;
  assign uo_out[7:5] = 3'b0;

  wire reset = !rst_n; // Consistent use of reset signal

  /* verilator lint_off UNUSEDSIGNAL */
  wire dummy0 = ena;
  wire dummy2 = |uio_in[7:0];
  /* verilator lint_on UNUSEDSIGNAL */

  chip chip(
    .reset(ui_in[3]),
    .selec(ui_in[0]),
    .clk_ref(ui_in[1]),
    .VCO(ui_in[2]),
    .out(uo_out[4:0])
  );

endmodule


module chip (
    input wire  reset,selec,clk_ref,VCO,
    output wire [4:0] out
    );

    wire VCO_S, VCO_A, CLK_S, CLK_A;
    wire [4:0] S;
    wire [4:0] A;
    
    demux dmx1(
    .selec(selec),
    .a(VCO), 
    .x(VCO_S), 
    .y(VCO_A));
    demux dmx2(
    .selec(selec),
    .a(clk_ref), 
    .x(CLK_S), 
    .y(CLK_A));
    fdc_sincronico sfdc(
    .VCO(VCO_S), 
    .clk(CLK_S), 
    .reset(reset),
    .D_out(S));
    fdc_asincrono asfdc(
    .reset(reset),
    .FPTAT(VCO_A), 
    .FREF(CLK_A), 
    .data(A));
    
    assign out = (selec)? S:A;

endmodule



module fdc_sincronico(
    input wire VCO, clk, reset,
    output reg [4:0] D_out
);
    wire [4:0] count, q1, q2;

    counter counter_1(.clk(VCO), .reset(reset), .count(count));
    register register_1(.clk(clk), .reset(reset), .d(count), .q(q1));
    register register_2(.clk(clk), .reset(reset), .d(q1), .q(q2));

    always @* 
        D_out = q1 - q2;
endmodule



module fdc_asincrono #(parameter ref_N = 2, ptat_N = 5)(
    input wire reset, FPTAT, FREF,
    output wire [ptat_N-1:0] data
    );
    wire [ptat_N-1:0] data_prev;
    wire [ref_N-1:0] ref_data;
    
    assign done = ref_data[ref_N-1];
    
    ripple_counter #(ref_N) REF_COUNT (
        .clk(~done&FREF),
        .reset(reset),
        .count(ref_data)
    );
    ripple_counter #(ptat_N) PTAT_COUNT (
        .clk(~done&FPTAT),
        .reset((ref_data == 0) ? 1'b1 : 1'b0),
        .count(data_prev)
    );
    reg_file #(ptat_N) Reg_Data (
        .clk(done),
        .reset(reset),
        .D(data_prev),
        .Q(data)
    );
endmodule



module demux (
    input wire selec,
    input wire a,
    output wire x,
    output wire y
);
// >>> Module Implementation Begin

// <<< Module Implementation End
endmodule





module ripple_counter#(parameter N=8)(
    input wire clk, reset,
    output wire [N-1:0] count
    );
    
    wire qclk[N-1:0];
    
    genvar i;
    generate
        for (i = 0; i < N; i = i + 1) begin : counter_gen
            ff_d_fdc dff_instance (
                .clk((i == 0) ? clk:qclk[i-1]),
                .reset(reset),
                .D(count[i]),
                .Q(qclk[i]),
                .not_Q(count[i])
            );
        end
    endgenerate
    
endmodule



module reg_file #(parameter N = 5)(
    input wire clk, reset,
    input wire [N-1:0]D,
    output reg [N-1:0]Q
    );
    
    always@(posedge clk or posedge reset)
    begin
        if(reset)
            Q <= 0;
        else
            Q <= D;
    end
    
endmodule



module ff_d_fdc(
    input wire clk, reset,
    input wire D,
    output reg Q,
    output wire not_Q
    );
    
    always @(posedge clk or posedge reset) begin
        if (reset) begin
            Q <= 1'b1;
        end
        else begin
            Q <= D;
        end
    end
    
    assign not_Q = ~Q;

endmodule



module counter(
    input wire clk, reset,
    output reg [4:0] count
);
    always @(posedge clk) begin
        if (reset) 
            count <= 5'd0;
        else 
            count <= count + 1;
        end
endmodule


module register(
    input wire clk, reset,
    input wire [4:0] d,
    output reg [4:0] q
);
    always @(posedge clk) begin
        if (reset) 
            q <= 5'd0;
        else 
            q <= d;
    end
endmodule


Reference solution:
rtl/generated.v: 
assign {x,y} = selec? {a,1'b0}:{1'b0,a};