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

module tt_um_shivam (
    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 uo_out  = ui_in + uio_in;  // Example: ou_out is the sum of ui_in and uio_in
  assign uio_out = 0;
  assign uio_oe  = 0;
  assign uo_out = PWM_OUT;
	
 wire slow_clk_enable; // slow clock enable signal for debouncing FFs
 reg[27:0] counter_debounce=0;// counter for creating slow clock enable signals 
 wire tmp1,tmp2,duty_inc;// temporary flip-flop signals for debouncing the increasing button
 wire tmp3,tmp4,duty_dec;// temporary flip-flop signals for debouncing the decreasing button
 reg[3:0] counter_PWM=0;// counter for creating 10Mhz PWM signal
 reg[3:0] DUTY_CYCLE=5; // initial duty cycle is 50%
  // Debouncing 2 buttons for inc/dec duty cycle 
  // Firstly generate slow clock enable for debouncing flip-flop (4Hz)
 always @(posedge clk)
 begin
   counter_debounce <= counter_debounce + 1;
   //if(counter_debounce>=25000000) then  
   // for running on FPGA -- comment when running simulation
   if(counter_debounce>=1) 
   // for running simulation -- comment when running on FPGA
    counter_debounce <= 0;
 end
 // assign slow_clk_enable = counter_debounce == 25000000 ?1:0;
 // for running on FPGA -- comment when running simulation 
 assign slow_clk_enable = counter_debounce == 1 ?1:0;
 // for running simulation -- comment when running on FPGA
 // debouncing FFs for increasing button
	DFF_PWM PWM_DFF1(clk,slow_clk_enable,ui_in[0],tmp1);
 DFF_PWM PWM_DFF2(clk,slow_clk_enable,tmp1, tmp2); 
 assign duty_inc =  tmp1 & (~ tmp2) & slow_clk_enable;
 // debouncing FFs for decreasing button
	DFF_PWM PWM_DFF3(clk,slow_clk_enable,ui_in[1], tmp3);
 DFF_PWM PWM_DFF4(clk,slow_clk_enable,tmp3, tmp4); 
 assign duty_dec =  tmp3 & (~ tmp4) & slow_clk_enable;
 // vary the duty cycle using the debounced buttons above
 always @(posedge clk)
 begin
   if(duty_inc==1 && DUTY_CYCLE <= 9) 
    DUTY_CYCLE <= DUTY_CYCLE + 1;// increase duty cycle by 10%
   else if(duty_dec==1 && DUTY_CYCLE>=1) 
    DUTY_CYCLE <= DUTY_CYCLE - 1;//decrease duty cycle by 10%
 end 
// Create 10MHz PWM signal with variable duty cycle controlled by 2 buttons 
 always @(posedge clk)
 begin
   counter_PWM <= counter_PWM + 1;
   if(counter_PWM>=9) 
    counter_PWM <= 0;
 end
 assign PWM_OUT = counter_PWM < DUTY_CYCLE ? 1:0;
endmodule
// Debouncing DFFs for push buttons on FPGA
module DFF_PWM(clk,en,D,Q);
// >>> Module Implementation Begin

// <<< Module Implementation End
endmodule




Reference solution:
rtl/generated.v: input clk,en,D;
output reg Q;
always @(posedge clk)
begin 
 if(en==1) // slow clock enable signal 
  Q <= D;
end