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
 */

`default_nettype none

module tt_um_ronikant_jeremykam_tinyregisters (
    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,      // always 1 when the design is powered, so you can ignore it
    input  wire       clk,      // clock
    input  wire       rst_n     // reset_n - low to reset
);

    // uio pins: 
    // 7:6 chip select inputs
    // 5:4 extra inputs
    // 3:0 extra outputs
    assign uio_oe  = 8'b00001111;

    // Decoder
    wire [2:0] decoder_out_n;
    wire [1:0] select_register = uio_in[7:6];
    assign decoder_out_n = (select_register == 0) ? 3'b110 :
        (select_register == 1) ? 3'b101 : 
        (select_register == 2) ? 3'b011 : 3'b111;

    // Mux
    wire [7:0] register_out;
    wire [7:0] MAR_data_out;
    wire [3:0] MAR_addr_out;
    wire [7:0] IR_bus_out;
    wire [3:0] IR_opcode_out;
    assign uo_out = (select_register == 0) ? register_out :
        (select_register == 1) ? MAR_data_out :
        (select_register == 2) ? IR_bus_out : 8'b00000000;
    assign uio_out[3:0] = (select_register == 1) ? MAR_addr_out :
        (select_register == 2) ? IR_opcode_out : 4'b0000;
    
    // Register
    register register(.clk(clk),.n_load(uio_in[4] | decoder_out_n[0]),.bus(ui_in),.value(register_out));

    // Input and MAR Register
    input_mar_register im_register( .clk(clk), .n_load_data(uio_in[4] | decoder_out_n[1]), .n_load_addr(uio_in [5] | decoder_out_n[1]), .bus(ui_in), .data(MAR_data_out), .addr(MAR_addr_out) );

    // Instruction Register Start
    wire [7:0] bus;
    instruction_register instr_register( .clk(clk), .clear(rst_n), .n_load(uio_in [4] | decoder_out_n[2]), .n_enable(uio_in [5] | decoder_out_n[2]), .bus(bus), .opcode(IR_opcode_out) );
    assign bus = ((uio_in [5] | decoder_out_n[2]) == 0) ? 8'bz : ui_in;           // Input path
    assign IR_bus_out = bus;                                // Output path

    
    // All output pins must be assigned. If not used, assign to 0.
    assign uio_out[7:4] = 0;
    
    // List all unused inputs to prevent warnings
    wire _unused = &{ena, uio_in[3:0], 1'b0};
    // Register Test End
    
    
endmodule


module register(
  input clk, n_load,
  input [7:0] bus,
  output reg [7:0] value
);
  
  always@(posedge clk) begin
    if (!n_load) value <= bus;
  end

endmodule

module input_mar_register(
  input clk, n_load_data, n_load_addr,
  input [7:0] bus,
  output reg [7:0] data,
  output reg [3:0] addr
);
  
  always@(posedge clk) begin
    if(!n_load_data) data <= bus;
    if(!n_load_addr) addr <= bus[3:0];
  end
endmodule

module instruction_register(
  input clk, clear, n_load, n_enable,
  inout [7:0] bus,
  output [3:0] opcode
);
// >>> Module Implementation Begin

// <<< Module Implementation End
endmodule





Reference solution:
rtl/generated.v:   reg [7:0] instruction;
  
  assign bus[3:0] = !n_enable ? instruction[3:0] : 4'bZ;
  assign opcode = instruction[7:4];
  
  always@(posedge clk) begin
    if (clear) instruction <= 8'b0;
    else if (!n_load) instruction <= bus;
  end