Refreshing

A macOS menu bar app that prevents kernel panics (DCPEXT PANIC) on Apple Silicon Macs with external monitors running above 120Hz.

The Problem

macOS Sequoia (and versions of macOS since then) have a bug in the Display Coprocessor (DCP) firmware that causes kernel panics when Apple Silicon Macs wake from sleep or reconnect to external monitors running at refresh rates above 120Hz. This primarily affects 4K 240Hz QD-OLED panels (Samsung, ASUS ROG, MSI MPG, etc.) and manifests as DCPEXT2 PANIC - apt firmware: dual_pipe in crash logs.

The issue is a regression introduced in Sequoia - it does not occur on Sonoma.

How It Works

Refreshing allows you to run the monitor at refresh rates above 120Hz but ensures that whenever the monitor is reconnected or the machine wakes from sleep the default refresh rate on initialisation is kept at 120Hz. The app then upshifts back to 240Hz after the initial connection, avoiding the codepath that triggers the panic.

During reconnection, the app displays a full-screen overlay to prevent interaction while the refresh rate handshake completes. This avoids the confusing flash of the desktop at an intermediate rate.

It uses a two-layer strategy to achieve this:

Permanent 120Hz in the WindowServer plist

When the app sets the display to 120Hz, it uses CGCompleteDisplayConfiguration(.permanently), which writes the mode to macOS's display preferences plist. This means WindowServer will request 120Hz when negotiating with the display on reconnection, avoiding the dangerous >120Hz DCP code path.

When upshifting to 240Hz for active use, it uses .forSession - a temporary change that is not written to the plist. If the display disconnects while at 240Hz, the plist still says 120Hz, so the next connection is safe.

Display reconfiguration callback

The app registers a CGDisplayRegisterReconfigurationCallback to react immediately when an external display is connected or disconnected:

1. Display connected → immediately set 120Hz (permanently)
2. Wait 3 seconds for the display link to stabilize
3. Upshift to 240Hz (session-only) at the target resolution

Sleep/wake safety net

As a secondary defense, the app uses IORegisterForSystemPower to intercept sleep events with acknowledgement gating - the system cannot sleep until the refresh rate change completes. On sleep, it applies the pre-cached 120Hz mode permanently.

Requirements

• macOS 15 (Sequoia) or later
• Apple Silicon Mac
• External monitor with refresh rate above 120Hz
• Xcode Command Line Tools (xcode-select --install)

Building

make

This builds Refreshing.app in the project directory and ad-hoc signs it.

To install to /Applications:

make install

To clean:

make clean

Installing a Pre-built Release

If you download a pre-built Refreshing.app, macOS Gatekeeper will block it because it is not notarized. To allow it to run:

1. Move Refreshing.app to /Applications (or wherever you want it)
2. Do not double-click it - it will just show a warning with no option to open
3. Instead, right-click (or Control-click) the app and select Open
4. A dialog will appear saying the app is from an unidentified developer - click Open
5. macOS will remember this choice and the app will launch normally from now on

Alternatively, from Terminal:

xattr -c Refreshing.app
open Refreshing.app

Usage

Run the app - a display icon appears in the menu bar. The menu provides:

• Enable/disable the automatic refresh rate management
• Display picker if multiple external monitors are connected
• Resolution - defaults to native, can be changed if desired
• Sleep Hz - the safe refresh rate (default: 120Hz)
• Wake Hz - the active refresh rate (default: 240Hz)
• Launch at Login - uses SMAppService for login item registration

All settings persist across app restarts.

Debugging

The app logs to the system log with the [Refreshing] prefix. To watch in real time:

log stream --predicate 'eventMessage CONTAINS "[Refreshing]"' --level debug

Architecture

File	Purpose
RefreshingApp.swift	@main entry point, MenuBarExtra scene
DisplayManager.swift	CoreGraphics display enumeration, mode switching, resolution detection
SleepWakeManager.swift	IOKit sleep/wake callbacks with acknowledgement gating
AppState.swift	ObservableObject - state coordination, UserDefaults persistence, display connect/disconnect handling
MenuBarView.swift	SwiftUI menu bar UI