parameterized_gray_counter.v

/**
 * Parameterized Gray Code Counter
 * 
 * This module implements a configurable Gray code counter that can count up or down.
 * Gray code ensures only one bit changes between consecutive values, making it ideal
 * for clock domain crossing, reducing glitches, and improving reliability.
 * 
 * Key Features:
 * - Configurable width: Any bit width via WIDTH parameter
 * - Bidirectional: Count up or down based on COUNT_MODE
 * - Initial value: Configurable starting value
 * - Dual output: Both Gray code and binary representations
 * 
 * Gray Code Benefits:
 * - Single bit transitions: Reduces power consumption and glitches
 * - CDC safety: Safer for clock domain crossing (reduces metastability)
 * - Error detection: Multiple bit changes indicate errors
 * 
 * Conversion:
 * - Binary to Gray: gray = binary ^ (binary >> 1)
 * - Maintained internally in binary for easy increment/decrement
 * 
 * @param WIDTH Counter width in bits (default: 4)
 * @param COUNT_MODE 0 = count up, 1 = count down (default: 0)
 * @param INITIAL_VALUE Initial counter value on reset (default: 0)
 * 
 * @input clk Clock signal
 * @input rst_n Active-low synchronous reset
 * @input enable Counter enable (high to count)
 * @output gray_out[WIDTH-1:0] Gray code output (only one bit changes per count)
 * @output binary_out[WIDTH-1:0] Binary counter value (for reference/convenience)
 */
module parameterized_gray_counter #(
    parameter WIDTH = 4,                 // Counter width in bits
    parameter COUNT_MODE = 0,            // 0: Up counter, 1: Down counter
    parameter INITIAL_VALUE = 0          // Initial counter value
)(
    input wire clk,                      // Clock input
    input wire rst_n,                    // Active-low synchronous reset
    input wire enable,                   // Counter enable signal
    output wire [WIDTH-1:0] gray_out,    // Gray code output
    output wire [WIDTH-1:0] binary_out   // Binary counter value (for reference)
);

    // ============================================================================
    // Internal State
    // ============================================================================
    // Binary counter register: maintained internally for easy increment/decrement
    // We convert to Gray code for output, but binary is easier to manipulate
    reg [WIDTH-1:0] binary_count;

    // ============================================================================
    // Output Generation
    // ============================================================================
    // Convert binary count to Gray code using standard formula
    // Formula: gray = binary ^ (binary >> 1)
    // This ensures only one bit changes between consecutive values
    assign gray_out = binary_count ^ (binary_count >> 1);
    
    // Also provide binary output for applications that need it
    assign binary_out = binary_count;

    // ============================================================================
    // Counter Logic
    // ============================================================================
    // Binary counter with synchronous reset and enable control
    always @(posedge clk) begin
        if (!rst_n) begin
            // ====================================================================
            // Reset State
            // ====================================================================
            // Initialize counter to configured initial value
            binary_count <= INITIAL_VALUE;
        end else if (enable) begin
            // ====================================================================
            // Count Operation
            // ====================================================================
            if (COUNT_MODE == 0) begin
                // Up counting: increment binary counter
                binary_count <= binary_count + 1'b1;
            end else begin
                // Down counting: decrement binary counter
                binary_count <= binary_count - 1'b1;
            end
        end
        // Note: If enable is low, counter holds current value
    end

endmodule