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_roy1707018 (
    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
);

 // Instantiate the ro_buffer_counter module
  wire [7:0] buffer_out;
  wire [4:0] ascon_sbox_out;


  ro_buffer_counter ro_buffer_counter_inst (.rst_n(~rst_n),
                            .clk(clk),
                            .ro_activate_1(ui_in[0]),
                            .ro_activate_2(ui_in[1]),
			    .out_sel(ui_in[4:2]),
                            .out(buffer_out)
                           );
	
  ascon_sbox ascon_inst (.rst_n(~rst_n),
                            .clk(clk),
			    .activate_sbox(ui_in[7]),
			    .sbox_in(ui_in[6:2]),
                            .sbox_out(ascon_sbox_out)
                           );

  // Example: Output assignments (update based on your design needs)
  assign uo_out  = buffer_out ^ {3'b000,ascon_sbox_out};  // Example: take lower 8 bits of buffer_out ^ ascon sbox output
  assign uio_out = 0;
  assign uio_oe  = 0;

  // List all unused inputs to prevent warnings
  wire _unused = &{ena, uio_in, 1'b0};

endmodule



module ring_osc(input wire  rst_n,
          input wire  clk,
          input wire  ro_activate,
          output wire   ro_out);

   reg                en;
   (*keep = "true" *) wire q;
   (*keep = "true" *) wire q0;
   (*keep = "true" *) wire q1;
   (*keep = "true" *) wire q2;
   (*keep = "true" *) wire q3;
   (*keep = "true" *) wire q4;
   (* keep = "true" *) wire cq4;

   
   assign ro_out = en ? q : 1'b0;
   
   always @(posedge clk or posedge rst_n) begin
    if (rst_n)
        en <= 1'b0;
    else if (ro_activate)
        en <= 1'b1;
    else
        en <= 1'b0;
    end

   assign cq4 = (en & q4);
   (* keep = 1 *) cinv cinv1(.a(cq4),.q(q0));
   (* keep = 1 *) cinv cinv2(.a(q0), .q(q1));
   (* keep = 1 *) cinv cinv3(.a(q1), .q(q2));
   (* keep = 1 *) cinv cinv4(.a(q2), .q(q3));
   (* keep = 1 *) cinv cinv5(.a(q3), .q(q4));
   assign q  = q4;
endmodule



module ro_buffer_counter (
    input wire rst_n,
    input wire clk,
    input wire ro_activate_1,
    input wire ro_activate_2,
    input wire [2:0] out_sel,
    output reg [7:0] out
);

   // Wires to connect the outputs of the two ring oscillators
   // Wires for RO1 outputs
wire ro1_out_A;
wire ro1_out_B;
wire ro1_out_C;
wire ro1_out_D;
wire ro1_out_E;
wire ro1_out_F;
wire ro1_out_G;
wire ro1_out_H;

// Wires for RO2 outputs (unique names for each wire)
wire ro2_out_A;
wire ro2_out_B;
wire ro2_out_C;
wire ro2_out_D;
wire ro2_out_E;
wire ro2_out_F;
wire ro2_out_G;
wire ro2_out_H;

// Registers for RO1 outputs
reg ro_1_reg_A;
reg ro_1_reg_B;
reg ro_1_reg_C;
reg ro_1_reg_D;
reg ro_1_reg_E;
reg ro_1_reg_F;
reg ro_1_reg_G;
reg ro_1_reg_H;

// Registers for RO2 outputs
reg ro_2_reg_A;
reg ro_2_reg_B;
reg ro_2_reg_C;
reg ro_2_reg_D;
reg ro_2_reg_E;
reg ro_2_reg_F;
reg ro_2_reg_G;
reg ro_2_reg_H;
 wire       xor_out;
   reg[63:0]    shift_register;

   // Instantiate the first ring oscillator 8 times
ring_osc ro1_A (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_A)
);

ring_osc ro1_B (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_B)
);

ring_osc ro1_C (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_C)
);

ring_osc ro1_D (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_D)
);

ring_osc ro1_E (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_E)
);

ring_osc ro1_F (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_F)
);

ring_osc ro1_G (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_G)
);

ring_osc ro1_H (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_1),
   .ro_out(ro1_out_H)
);

// Instantiate the second ring oscillator 8 times
ring_osc ro2_A (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_A)
);

ring_osc ro2_B (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_B)
);

ring_osc ro2_C (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_C)
);

ring_osc ro2_D (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_D)
);

ring_osc ro2_E (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_E)
);

ring_osc ro2_F (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_F)
);

ring_osc ro2_G (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_G)
);

ring_osc ro2_H (
   .rst_n(rst_n),
   .clk(clk),
   .ro_activate(ro_activate_2),
   .ro_out(ro2_out_H)
);
           

   
   // Store the ro1 out result in a register (DFF) on the clock edge
   
always @(posedge clk or posedge rst_n) begin
    if (rst_n) begin
        ro_1_reg_A <= 1'b0;
        ro_1_reg_B <= 1'b0;
        ro_1_reg_C <= 1'b0;
        ro_1_reg_D <= 1'b0;
        ro_1_reg_E <= 1'b0;
        ro_1_reg_F <= 1'b0;
        ro_1_reg_G <= 1'b0;
        ro_1_reg_H <= 1'b0;
    end else begin
        ro_1_reg_A <= ro1_out_A;
        ro_1_reg_B <= ro1_out_B;
        ro_1_reg_C <= ro1_out_C;
        ro_1_reg_D <= ro1_out_D;
        ro_1_reg_E <= ro1_out_E;
        ro_1_reg_F <= ro1_out_F;
        ro_1_reg_G <= ro1_out_G;
        ro_1_reg_H <= ro1_out_H;
    end
end


   // Store the ro2 out result in a register (DFF) on the clock edge
   always @(posedge clk or posedge rst_n) begin
    if (rst_n) begin
        ro_2_reg_A <= 1'b0;
        ro_2_reg_B <= 1'b0;
        ro_2_reg_C <= 1'b0;
        ro_2_reg_D <= 1'b0;
        ro_2_reg_E <= 1'b0;
        ro_2_reg_F <= 1'b0;
        ro_2_reg_G <= 1'b0;
        ro_2_reg_H <= 1'b0;
    end else begin
        ro_2_reg_A <= ro2_out_A;
        ro_2_reg_B <= ro2_out_B;
        ro_2_reg_C <= ro2_out_C;
        ro_2_reg_D <= ro2_out_D;
        ro_2_reg_E <= ro2_out_E;
        ro_2_reg_F <= ro2_out_F;
        ro_2_reg_G <= ro2_out_G;
        ro_2_reg_H <= ro2_out_H;
    end
end


   // Perform bitwise XOR across all the registers from RO1 and RO2
assign xor_out = ro_1_reg_A ^ ro_2_reg_A ^ 
                 ro_1_reg_B ^ ro_2_reg_B ^ 
                 ro_1_reg_C ^ ro_2_reg_C ^ 
                 ro_1_reg_D ^ ro_2_reg_D ^ 
                 ro_1_reg_E ^ ro_2_reg_E ^ 
                 ro_1_reg_F ^ ro_2_reg_F ^ 
                 ro_1_reg_G ^ ro_2_reg_G ^ 
                 ro_1_reg_H ^ ro_2_reg_H;

   // Shift in the XOR result on the clock edge
   always @(posedge clk or posedge rst_n) begin
      if (rst_n)
         shift_register <= 64'b0;
      else
      if (ro_activate_1 | ro_activate_2)
         shift_register <= {shift_register[62:0], xor_out};
      else
         shift_register <= shift_register;
   end

   // Store the XOR result in the register on the clock edge
   always @(posedge clk or posedge rst_n) begin
      if (rst_n)
          out <= 8'h00;
      else begin
          if (out_sel == 3'b111)
              out <= shift_register[63:56];
          else if (out_sel == 3'b110)
              out <= shift_register[55:48];
          else if (out_sel == 3'b101)
              out <= shift_register[47:40];
          else if (out_sel == 3'b100)
              out <= shift_register[39:32];
          else if (out_sel == 3'b011)
              out <= shift_register[31:24];
          else if (out_sel == 3'b010)
              out <= shift_register[23:16];
          else if (out_sel == 3'b001)
              out <= shift_register[15:8];
          else if (out_sel == 3'b000)
              out <= shift_register[7:0];
          else
              out <= 8'h00;
      end
   end

endmodule


(* keep_hierarchy = "yes" *)
module cinv(input a,
            output q);
// >>> Module Implementation Begin

// <<< Module Implementation End
endmodule




module ascon_sbox(input wire  rst_n,
          input wire  clk,
          input wire  activate_sbox,
          input wire [4:0]  sbox_in,
          output wire [4:0]  sbox_out);

   reg  en;
   
   assign sbox_out = en ? ps(sbox_in) : 5'b00000;
   
   always @(posedge clk or posedge rst_n) begin
    if (rst_n)
        en <= 1'b0;
    else if (activate_sbox)
        en <= 1'b1;
    else
        en <= 1'b0;
    end

   function [4 : 0] ps(input [4 : 0] x);
    begin : ps_inst
      reg x0, x0_1, x0_2, x0_3, x0_4;
      reg x1, x1_1, x1_2, x1_3;
      reg x2, x2_1, x2_2, x2_3, x2_4;
      reg x3, x3_1, x3_2, x3_3;
      reg x4, x4_1, x4_2, x4_3;

      x0 = x[4];
      x1 = x[3];
      x2 = x[2];
      x3 = x[1];
      x4 = x[0];

      x0_1 = x0 ^ x4;
      x2_1 = x2 ^ x1;
      x4_1 = x4 ^ x3;

      x0_2 = ~x0_1 & x1;
      x1_1 = ~x1 & x2_1;
      x2_2 = ~x2_1 & x3;
      x3_1 = ~x3 & x4_1;
      x4_2 = ~x4_1 & x0_1;

      x0_3 = x0_1 ^ x1_1;
      x1_2 = x1 ^ x2_2;
      x2_3 = x2_1 ^ x3_1;
      x3_2 = x3 ^ x4_2;
      x4_3 = x4_1 ^ x0_2;

      x0_4 = x0_3 ^ x4_3;
      x1_3 = x1_2 ^ x0_3;
      x2_4 = ~x2_3;
      x3_3 = x3_2 ^ x2_3;

      ps = {x0_4, x1_3, x2_4, x3_3, x4_3};
    end
  endfunction // ps
   
endmodule


Reference solution:
rtl/generated.v: 
`ifdef SIM
   assign #1 q =  ~a;
`else
   assign q = ~a;
`endif