module blink #(
    // Input clock frequency in Hz
    parameter integer F_CLK = 50_000_000  // 50 MHz
)(
    input  wire clk,
    output wire led,
    output wire pin,
    output wire pin_10
);

    //---------------------------------------------------------
    // Step duration:
    //  - for 0 Hz   : 8 s
    //  - for others : 4 s
    //---------------------------------------------------------
    localparam integer STEP_4SEC_MAX = (F_CLK * 4) - 1;
    localparam integer STEP_8SEC_MAX = (F_CLK * 8) - 1;

    // Step timer counter
    reg [31:0] step_cnt = 32'd0;

    // Frequency index: 0..5 → 0,10,20,30,40,50 Hz
    reg [2:0] freq_idx = 3'd0;

    // Half-period counter and current half-period length in clock cycles
    reg [31:0] blink_cnt   = 32'd0;
    reg [31:0] max_count   = 32'd0;

    // Base LED signal (before output inversions)
    reg led_base = 1'b0;

    //---------------------------------------------------------
    // Function to calculate half-period in clock cycles
    //---------------------------------------------------------
    function [31:0] calc_max_count;
        input [2:0] idx;
        integer f;
    begin
        // Frequency in Hz: 0, 10, 20, 30, 40, 50
        f = idx * 10;
        if (f == 0) begin
            // Special case: 0 Hz → no blinking
            calc_max_count = 32'd0;
        end else begin
            // Half-period: F_CLK / (2 * f)
            calc_max_count = (F_CLK / (2 * f)) - 1;
        end
    end
    endfunction

    //---------------------------------------------------------
    // Main process: step timing, frequency selection,
    //               blink generation
    //---------------------------------------------------------
    always @(posedge clk) begin
        //-----------------------------------------------------
        // Step timer: change frequency every 4 or 8 seconds
        //-----------------------------------------------------
        if (step_cnt >= (freq_idx == 3'd0 ? STEP_8SEC_MAX : STEP_4SEC_MAX)) begin
            step_cnt <= 32'd0;

            // Cycle through 0→1→2→3→4→5→0...
            if (freq_idx == 3'd5)
                freq_idx <= 3'd0;
            else
                freq_idx <= freq_idx + 3'd1;
        end else begin
            step_cnt <= step_cnt + 32'd1;
        end

        //-----------------------------------------------------
        // Recalculate half-period for current frequency
        //-----------------------------------------------------
        max_count <= calc_max_count(freq_idx);

        //-----------------------------------------------------
        // Blink generation
        //-----------------------------------------------------
        if (max_count == 32'd0) begin
            // 0 Hz: hold current state, no blinking
            blink_cnt <= 32'd0;
            // led_base keeps its last value
        end else begin
            if (blink_cnt >= max_count) begin
                blink_cnt <= 32'd0;
                led_base  <= ~led_base;
            end else begin
                blink_cnt <= blink_cnt + 32'd1;
            end
        end
    end

    //---------------------------------------------------------
    // Outputs:
    //  led     = inverted base signal
    //  pin     = same as led
    //  pin_10  = inverted pin
    //---------------------------------------------------------
    assign led    = ~led_base;
    assign pin    = led;
    assign pin_10 = ~pin;

endmodule