// retroDE_ps2 — de25_nano_pll_stub (Ch151)
//
// Sim-friendly stub matching the Quartus IOPLL "pll" module signature
// used by sibling cores (retroDE_nes/ip/pll/pll_bb.v and
// retroDE_splash/ip/sys_pll/sys_pll_bb.v). Real synthesis swaps this
// stub for Terasic-supplied IP via Quartus's IP catalog and a
// `\`ifdef USE_PLL_IP` gate in the board top.
//
// Behavior:
//   - `outclk_0` is a direct pass-through of `refclk` (no PLL
//     multiplication; sim doesn't need a different frequency, and a
//     pass-through still exercises the PLL-gated reset bridge in the
//     Ch149 board top).
//   - `locked` rises after a small post-reset delay (~32 cycles),
//     mimicking real-IP behavior where lock acquires after rst goes
//     low. Held LOW while `rst` is HIGH.
//
// The signature matches Quartus's IOPLL exactly so swapping in the
// real IP is a single `\`ifdef` at instantiation; the rest of the
// board top is unchanged.

`timescale 1ns/1ps

module de25_nano_pll_stub (
    input  wire  refclk,   // reference clock from CLOCK2_50
    input  wire  rst,      // active-HIGH async reset (Quartus convention)
    output wire  outclk_0, // pass-through of refclk
    output wire  locked    // high once "lock" is acquired
);

    assign outclk_0 = refclk;

    // Lock counter — tick up while rst is low; saturate at 32 and hold
    // `locked` high. While rst is high, hold counter at 0 and locked low.
    logic [5:0] lock_cnt;
    always_ff @(posedge refclk or posedge rst) begin
        if (rst)
            lock_cnt <= 6'd0;
        else if (lock_cnt < 6'd32)
            lock_cnt <= lock_cnt + 6'd1;
    end

    assign locked = (lock_cnt == 6'd32);

endmodule : de25_nano_pll_stub