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.

/*
 * MAC with SPST adder (TinyTapeout compliant)
 * SPDX-License-Identifier: Apache-2.0
 */

`default_nettype none

// ============================================================
// Top-level TinyTapeout wrapper
// ============================================================
module tt_um_mac_spst_tiny (
    input  wire [7:0] ui_in,    // Dedicated inputs: operand A
    output wire [7:0] uo_out,   // Dedicated outputs: accumulator low byte
    input  wire [7:0] uio_in,   // IOs: input path (operand B / ext high byte in)
    output wire [7:0] uio_out,  // IOs: output path (accumulator high byte)
    output wire [7:0] uio_oe,   // IOs: enable path (1=drive output)
    input  wire       ena,      // always 1 when powered
    input  wire       clk,      // clock
    input  wire       rst_n     // reset, active low
);

    // Internal signals
    wire [7:0] out_low;
    wire [7:0] out_high;
    wire       out_high_oe;

    // Operand mapping
    wire [7:0] operand_a = ui_in;
    wire [7:0] operand_b = uio_in;

    // Instantiate the MAC core
    mac_spst_tiny dut (
        .clk(clk),
        .rst_n(rst_n),
        .acc_en(ena),
        .in_a(operand_a),
        .in_b(operand_b),
        .out_low(out_low),
        .out_high(out_high),
        .out_high_oe(out_high_oe)
    );

    // Outputs
    assign uo_out  = out_low;                  // low byte
    assign uio_out = out_high;                 // high byte
    assign uio_oe  = {8{out_high_oe}};         // enable mask

endmodule


// ============================================================
// Core MAC with SPST Adder (no inout)
// ============================================================
module mac_spst_tiny (
    input  wire        clk,
    input  wire        rst_n,
    input  wire        acc_en,
    input  wire [7:0]  in_a,
    input  wire [7:0]  in_b,
    output wire [7:0]  out_low,
    output wire [7:0]  out_high,
    output wire        out_high_oe
);
    reg [15:0] acc;
    wire [15:0] mult_out;
    wire [15:0] sum;

    // Multiplier
    array_mult8x8 u_mult (
        .a(in_a),
        .b(in_b),
        .y(mult_out)
    );

    // SPST Adder
    spst_adder16 u_adder (
        .a(acc),
        .b(mult_out),
        .sum(sum)
    );

    // Accumulator update
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            acc <= 16'd0;
        end else if (acc_en) begin
            acc <= sum;
        end
    end

    // Outputs
    assign out_low    = acc[7:0];
    assign out_high   = acc[15:8];
    assign out_high_oe = 1'b1;   // always drive high byte

endmodule


// ============================================================
// 8x8 Array Multiplier
// ============================================================
module array_mult8x8 (
    input  wire [7:0] a,
    input  wire [7:0] b,
    output wire [15:0] y
);
    assign y = a * b;
endmodule


// ============================================================
// 16-bit SPST Adder
// ============================================================
module spst_adder16 (
    input  wire [15:0] a,
    input  wire [15:0] b,
    output wire [15:0] sum
);
// >>> Module Implementation Begin

// <<< Module Implementation End
endmodule




Reference solution:
rtl/generated.v:     assign sum = a + b; // Replace with SPST optimized logic if needed