Macbook Desktop Mode

---
name: macbook-desktop-mode
description: Configure a MacBook as an always-on-AC desktop workstation with USB device resilience, battery longevity, and self-healing audio device.
allowed-tools: Read, Bash, Write, Edit, Glob, Grep, AskUserQuestion, WebSearch
---

# MacBook Desktop Mode

A holistic configuration guide for running a MacBook as an always-on-AC desktop workstation. Solves two interconnected problems: USB devices (especially USB 1.1 audio) disappearing during sleep/wake cycles, and unnecessary battery degradation from constant charge cycling.

> **Self-Evolving Skill**: This skill improves through use. If instructions are wrong, parameters drifted, or a workaround was needed — fix this file immediately, don't defer. Only update for real, reproducible issues.

## When to Use This Skill

- USB microphone or audio device disappears after sleep/wake
- Battery is cycling unnecessarily on a plugged-in Mac
- Setting up a MacBook as a permanent desktop workstation
- Configuring `pmset` for always-on-AC use
- Setting up a powered USB hub with `uhubctl` for software-controlled USB resets
- Enhancing the AudioDeviceMonitor Swift daemon with self-healing recovery

## Root Cause Diagnosis Framework

Before applying fixes, diagnose the specific failure mode. This framework was developed from empirical analysis of a MacBook Pro M3 Max with an Antlion USB Microphone (VID `0x2F96`, PID `0x0200`).

### DarkWake Cycling

macOS performs frequent DarkWake (partial maintenance wake) cycles — typically every 15 minutes overnight. During DarkWake:

- CPU wakes for Power Nap, network keepalive, Siri
- USB bus is partially powered but devices aren't fully re-enumerated
- USB 1.1 Full Speed devices lack Link Power Management (LPM) and can't negotiate graceful resume
- After multiple cycles, the XHCI controller drops the device from the IO registry

**Diagnostic command** — check sleep/wake history:

```bash
pmset -g log | grep -E "Sleep |Wake |DarkWake" | tail -30
```

### USB 1.1 Device Limitations

USB 1.1 devices (12 Mbps, `USBSpeed = 1`) are the most fragile across sleep/wake:

- No Link Power Management protocol
- No USB selective suspend negotiation
- Often lack serial numbers (`iSerialNumber = 0`), making re-identification after bus reset unreliable

**Diagnostic command** — check device properties:

```bash
ioreg -r -c IOUSBHostDevice -l | grep -A 20 "DEVICE_NAME"
```

Key fields: `USBSpeed` (1=Full, 2=High, 3=Super), `iSerialNumber` (0 = no serial), `IOPowerManagement.DriverPowerState`.

### USB Handle Contention

Applications like Chrome hold direct USB user client handles (`AppleUSBHostDeviceUserClient`) for WebRTC/WebAudio. These stale handles prevent clean re-initialization after sleep.

**Diagnostic command** — check who has USB handles:

```bash
ioreg -r -c IOUSBHostDevice -l | grep -B5 "IOUserClientCreator"
```

### Battery Micro-Cycling

On an always-AC Mac with no charge limit, the battery cycles between the ML-predicted level and actual charge. DarkWake cycles consume power, causing repeated charge/discharge micro-cycles.

**Diagnostic command** — check daily charge range:

```bash
ioreg -r -c AppleSmartBattery -l | grep -E "DailyMinSoc|DailyMaxSoc|Temperature|CycleCount"
```

- `Temperature` is in centidegrees (divide by 100 for Celsius)
- `DailyMinSoc`/`DailyMaxSoc` show today's charge swing range

## Phase 1: Power Configuration for Desktop Mode

### 1.1 Set Charge Limit to 80%

**System Settings → Battery → Charging Optimization → "Limit to 80%"**

On Apple Silicon, once at the limit the Mac enters AC bypass mode — power flows directly from charger to system board. The battery sits electrically disconnected, eliminating both calendar aging and cycle aging.

### 1.2 Set sleep=0 on AC

For an always-on-AC desktop, system sleep creates more problems than it solves:

```bash
# Disable system sleep on AC only (battery settings unchanged)
sudo pmset -c sleep 0

# Verify
pmset -g custom | grep -A1 "AC Power" | grep sleep
```

**What this preserves:**

- Display sleep still works (`displaysleep=10` on AC)
- Battery sleep settings unchanged (`sleep=1` for travel)
- `ttyskeepawake=1` still honored

**What this eliminates:**

- DarkWake cycling (root cause of USB dropout)
- Battery micro-cycling during maintenance wakes
- Thermal cycling (repeated cold↔warm transitions)

**Cost:** ~5-8W idle draw on Apple Silicon. No fan spin. ~$5-8/year in electricity.

### 1.3 Verify Power Configuration

```bash
# Full power settings
pmset -g custom

# Battery health snapshot
ioreg -r -c AppleSmartBattery -l | grep -E "Temperature|CycleCount|DailyMinSoc|DailyMaxSoc|MaxCapacity|IsCharging"

# Active power assertions
pmset -g assertions
```

## Phase 2: Hardware Layer — Powered USB Hub

### 2.1 Why a Powered Hub

A powered USB hub creates a **USB session boundary**. The Mac's XHCI controller maintains a session with the hub (a robust USB 2.0+ device with serial number). The hub independently maintains sessions with connected devices. Sleep/wake only stresses the Mac↔Hub link.

Additionally, the hub enables **software-controlled USB port reset** via `uhubctl` — the equivalent of a physical unplug/replug without touching hardware.

### 2.2 Hub Selection Criteria

Requirements:

- **Externally powered** (not bus-powered) — must have its own power supply
- **uhubctl-compatible** chipset — supports per-port power switching
- **USB 2.0+ hub** with serial number for reliable re-identification

Compatible chipsets (from the uhubctl project):

- VIA VL805/VL812/VL817
- Realtek RTS5411
- Genesys Logic GL850G/GL3510

### 2.3 uhubctl Setup

```bash
# Install
brew install uhubctl

# List compatible hubs (must have powered hub connected)
uhubctl

# Cycle all ports (2-second off period)
uhubctl -a cycle -d 2

# Cycle specific port on specific hub
uhubctl -a cycle -p 1 -l 1-1 -d 2
```

## Phase 3: Software Layer — AudioDeviceMonitor Enhancement

The reference implementation is a Swift daemon (`AudioDeviceMonitorRunner.swift`) deployed as a macOS launchd KeepAlive agent. It combines:

1. **Priority enforcement** (original) — sets default input/output to highest-priority available device
2. **Device guardian** (v2) — state machine tracking, disappearance detection, recovery cascade
3. **Wake detection** — IOKit power notifications via `IORegisterForSystemPower`
4. **Heartbeat** — 60-second periodic check for silent drops
5. **Recovery cascade** — uhubctl port cycle → retry → Telegram notification

### 3.1 State Machine

```
                    ┌──────────┐
          ┌────────▶│ PRESENT  │◀──────────────┐
          │         └────┬─────┘               │
          │              │ device gone          │
          │              ▼                      │
          │     ┌──────────────┐               │
          │     │ DISAPPEARED  │               │
          │     │  (3s debounce)│               │
          │     └──────┬───────┘               │
          │            │ still missing          │
          │            ▼                        │
          │     ┌──────────────┐     found     │
          │     │  RECOVERING  │───────────────┘
          │     │ uhubctl cycle│
          │     └──────┬───────┘
          │            │ max attempts
          │            ▼
          │     ┌──────────────┐
          │     │     DEAD     │
          └─────│  (Telegram)  │
          replug└──────────────┘
```

### 3.2 Key Architecture Decisions

- **IOKit power callbacks** instead of `NSWorkspace` — no AppKit dependency, works in headless launchd daemons
- **IOKit message constants defined manually** — Swift can't import `iokit_common_msg()` C macros; values computed from `sys_iokit (0xe0000000) | message_code`
- **Synchronous uhubctl/curl calls** — acceptable because the main RunLoop queues CoreAudio callbacks during blocking; no events lost, just delayed by recovery time
- **Telegram via curl subprocess** — no library dependency; credentials loaded from a dotenv file at startup
- **Single-threaded via main queue** — all CoreAudio callbacks, heartbeat, and power notifications dispatch to `.main`; no locks needed

### 3.3 Build and Deploy

The daemon is a single-file Swift program compiled into a self-contained binary:

```bash
# Compile
swiftc -O -framework CoreAudio -framework IOKit \
    -o /path/to/output/audio-device-monitor \
    AudioDeviceMonitorRunner.swift

# Codesign for launchd (ad-hoc, no Apple Developer account needed)
codesign -s - -f -i com.yourorg.audio-device-monitor /path/to/output/audio-device-monitor
```

Deploy as a launchd agent (user-level, KeepAlive):

```xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.yourorg.audio-device-monitor</string>
    <key>ProgramArguments</key>
    <array>
        <string>/path/to/output/audio-device-monitor</string>
    </array>
    <key>KeepAlive</key>
    <true/>
    <key>RunAtLoad</key>
    <true/>
    <key>ProcessType</key>
    <string>Background</string>
    <key>EnvironmentVariables</key>
    <dict>
        <key>HOME</key>
        <string>/Users/yourusername</string>
    </dict>
    <key>StandardOutPath</key>
    <string>/path/to/logs/audio-device-monitor-stdout.log</string>
    <key>StandardErrorPath</key>
    <string>/path/to/logs/audio-device-monitor-stderr.log</string>
</dict>
</plist>
```

Load: `launchctl load ~/Library/LaunchAgents/com.yourorg.audio-device-monitor.plist`

### 3.4 Configuration (in Swift source)

Priority lists and guarded devices are defined as constants at the top of the Swift source:

1. `inputPriorities` / `outputPriorities` — ordered arrays, highest priority first
2. `guardedDevices` — array of `GuardedDevice(name:, isInput:)` for disappearance monitoring
3. Tuning constants: `heartbeatInterval` (60s), `disappearDebounce` (3s), `maxRecoveryAttempts` (3)
4. Notification credentials: loaded from a dotenv file (path configured in `loadCredentials()`)

After changes, recompile and restart the launchd agent.

## Phase 4: Verification and Monitoring

### 4.1 Battery Health Monitoring

```bash
# Quick battery snapshot
ioreg -r -c AppleSmartBattery -l | grep -E "Temperature|CycleCount|DailyMinSoc|DailyMaxSoc|MaxCapacity"

# Full power state
pmset -g batt
system_profiler SPPowerDataType | grep -E "Cycle|Condition|Maximum|Charging"
```

With the 80% charge limit set and `sleep=0` on AC:

- `DailyMinSoc` and `DailyMaxSoc` should converge (no swing)
- `Temperature` should stay under 3500 (35°C) at steady state
- `CycleCount` accumulation should slow dramatically

### 4.2 USB Device Health

```bash
# Current USB device tree
system_profiler SPUSBDataType

# IOKit details for a specific device
ioreg -r -c IOUSBHostDevice -l | grep -A 25 "DEVICE_NAME"

# Kernel USB assertions (shows which devices prevent sleep)
pmset -g assertions | grep USB
```

### 4.3 Audio Monitor Logs

```bash
# Tail live logs (adjust path to your log location)
tail -50 /path/to/logs/audio-device-monitor-stderr.log

# Key log patterns to watch for:
# "Starting v2 — device guardian mode"     → v2 features active
# "System woke — checking devices"         → wake detection working
# "ALERT: '<device>' disappeared"          → device dropout detected
# "recovered via uhubctl!"                 → automated recovery succeeded
# "recovery FAILED"                        → manual replug needed
```

## Anti-Patterns

| Anti-Pattern                             | Why It Fails                                                 | Correct Approach                                   |
| ---------------------------------------- | ------------------------------------------------------------ | -------------------------------------------------- |
| Changing `powernap=0` to reduce DarkWake | Trades USB stability for missed iCloud sync, Find My, etc.   | Set `sleep=0` on AC — eliminates DarkWake entirely |
| Disabling Optimized Battery Charging     | Allows battery to charge to 100% — worse for longevity       | Set explicit 80% charge limit                      |
| Killing Chrome to release USB handles    | Whack-a-mole; any WebRTC app can grab handles                | Powered hub creates session boundary               |
| Polling `system_profiler` for USB status | Expensive subprocess, 2-3 second latency                     | CoreAudio property listeners are instant           |
| Using `NSWorkspace.didWakeNotification`  | Requires AppKit/NSApplication — won't work in launchd daemon | `IORegisterForSystemPower` callback                |
| Resetting USB via IOKit when device gone | Can't reset a device that's already dropped from IO registry | uhubctl power-cycles the physical port             |

## See Also

- **`kokoro-tts:realtime-audio-architecture`** — Complementary skill covering audio _playback_ patterns (PortAudio, GIL contention, jitter elimination, device hot-switching). This skill handles the system/USB layer; that one handles the application/playback layer.

## Post-Execution Reflection

After this skill completes, reflect before closing the task:

0. **Locate yourself.** — Find this SKILL.md's canonical path before editing.
1. **What failed?** — Fix the instruction that caused it.
2. **What worked better than expected?** — Promote to recommended practice.
3. **What drifted?** — Fix any script, reference, or dependency that no longer matches reality.
4. **Log it.** — Evolution-log entry with trigger, fix, and evidence.

Do NOT defer. The next invocation inherits whatever you leave behind.