# One-Key KVM: Mac ↔ Nobara

**Status:** WIP - Nobara → Mac working, Mac → Nobara needs work
**Hardware:** Dell U3821DW, MX Keys S, MX Master 4 for Mac
**Updated:** 2026-02-01

## Overview

Software KVM solution to switch the Dell U3821DW ultrawide monitor and Logitech MX peripherals between Mac (MacBook Air M3) and Nobara Linux using DDC/CI and HID++ commands.

## Hardware Mapping

### Monitor Inputs
| Input | Code | Port | Computer |
|-------|------|------|----------|
| USB-C | 27 | USB-C | Mac |
| HDMI 2 | 18 | HDMI 2 | Nobara |

### Peripheral Hosts (Logi Bolt)
| Host | Index (HID++) | Connection | Computer |
|------|---------------|------------|----------|
| 1 | 0x00 | Bolt #1 | MacBook Air (Bluetooth?) |
| 2 | 0x01 | Bolt #1 | Nobara (xtrm-pc) |
| 3 | 0x02 | Bolt #2 | MacBook Air (via monitor hub) |

### Devices
- **Monitor:** Dell U3821DW (38" Ultrawide, DDC/CI enabled)
- **Keyboard:** Logitech MX Keys S (Easy-Switch capable)
- **Mouse:** Logitech MX Master 4 for Mac (Easy-Switch capable)
- **Receiver:** Logi Bolt USB (PID: 046d:c548)

## Nobara Setup

### 1. Install dependencies
```bash
sudo dnf install ddcutil
```

### 2. Add user to i2c group (requires reboot)
```bash
sudo usermod -aG i2c $USER
```

### 3. Install hidapitester
```bash
curl -sL https://github.com/todbot/hidapitester/releases/latest/download/hidapitester-linux-amd64.zip -o /tmp/hidapitester.zip
unzip -o /tmp/hidapitester.zip -d ~/bin/
chmod +x ~/bin/hidapitester
```

### 4. Udev rule for non-root HID access
```bash
echo 'SUBSYSTEM=="usb", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="c548", MODE="0666"' | \
  sudo tee /etc/udev/rules.d/99-logitech-bolt.rules
sudo udevadm control --reload-rules && sudo udevadm trigger
```

### 5. Reboot
```bash
sudo reboot
```

### 6. Verify setup
```bash
# Check i2c group membership
groups | grep i2c

# Check monitor detection
ddcutil detect

# Check Bolt receiver
~/bin/hidapitester --vidpid 046d/c548 --list-detail
```

### 7. Copy script and set up shortcut
```bash
# Copy script
mkdir -p ~/scripts
cp /path/to/xtrm/infrastructure/scripts/kvm/to_mac.sh ~/scripts/
chmod +x ~/scripts/to_mac.sh

# Set up keyboard shortcut (Ctrl+Shift+Up)
gsettings set org.gnome.settings-daemon.plugins.media-keys custom-keybindings \
  "$(gsettings get org.gnome.settings-daemon.plugins.media-keys custom-keybindings | sed "s/]$/, '\/org\/gnome\/settings-daemon\/plugins\/media-keys\/custom-keybindings\/custom-kvm\/']/")"

gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom-kvm/ name 'KVM Switch to Mac'
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom-kvm/ command '/home/jazzymc/scripts/to_mac.sh'
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom-kvm/ binding '<Shift><Control>Up'
```

## Mac Setup

### 1. Install dependencies
```bash
# Install m1ddc (DDC control for Apple Silicon)
brew install m1ddc

# Install hidapitester
curl -sL https://github.com/todbot/hidapitester/releases/latest/download/hidapitester-macos-arm64.zip -o /tmp/hidapitester.zip
unzip -o /tmp/hidapitester.zip -d ~/bin/
chmod +x ~/bin/hidapitester
```

### 2. Copy script
```bash
mkdir -p ~/scripts
cp /path/to/xtrm/infrastructure/scripts/kvm/to_nobara.sh ~/scripts/
chmod +x ~/scripts/to_nobara.sh
```

### 3. Set up keyboard shortcut
TODO: Configure via Logi Options+ or macOS Shortcuts app

## Scripts

### Switch to Mac (Run on Nobara) - WORKING
**Location:** `~/scripts/to_mac.sh`

```bash
#!/bin/bash
# KVM Switch: Nobara → Mac
# Switches monitor to USB-C and peripherals to Host 3 (Mac)
#
# Host mapping (0-indexed in HID++):
#   Host 1 (0x01): Nobara (xtrm-pc)
#   Host 3 (0x02): Mac (Kaloyan's MacBook Air)
#
# HID++ command format: ReportID, DeviceIdx, FeatureIdx, Function, HostIdx, 0, 0
#   Mouse:    device 0x03, feature 0x0E (CHANGE_HOST)
#   Keyboard: device 0x02, feature 0x0A (CHANGE_HOST)
#   Function 0x10 = setCurrentHost (function 0 << 4)

HIDAPITESTER="$HOME/bin/hidapitester"

echo "Switching to Mac..."

# 1. Switch Mouse (MX Master 4) to Host 3 (Mac)
echo "  Mouse -> Mac..."
"$HIDAPITESTER" --vidpid 046d/c548 --usage 0x0001 --usagePage 0xff00 \
    --open --length 7 --send-output 0x10,0x03,0x0E,0x10,0x02,0x00,0x00 2>/dev/null || \
    echo "  [WARN] Mouse switch failed"

# 2. Switch Keyboard (MX Keys S) to Host 3 (Mac)
echo "  Keyboard -> Mac..."
"$HIDAPITESTER" --vidpid 046d/c548 --usage 0x0001 --usagePage 0xff00 \
    --open --length 7 --send-output 0x10,0x02,0x0A,0x10,0x02,0x00,0x00 2>/dev/null || \
    echo "  [WARN] Keyboard switch failed"

# 3. Switch Monitor to USB-C (Dell U3821DW input code: 27)
echo "  Monitor -> USB-C..."
if command -v ddcutil &>/dev/null; then
    ddcutil setvcp 60 27 2>/dev/null || \
        echo "  [WARN] Monitor switch failed (DDC/CI disabled or permissions issue)"
else
    echo "  [WARN] ddcutil not installed"
fi

echo "Done!"
```

### Switch to Nobara (Run on Mac) - NEEDS WORK
**Location:** `~/scripts/to_nobara.sh`

```bash
#!/bin/bash
# KVM Switch: Mac → Nobara
# TODO: Needs correct HID++ feature indices for Mac's Bolt receiver

echo "Switching to Nobara..."

# Switch Monitor to HDMI 2
m1ddc set input 18

# TODO: Find correct HID++ commands for Mac
# The feature indices may differ on Mac's Bolt receiver
# Use: hidapitester --vidpid 046d/c548 --list-detail
# Then use solaar (if available) or HID++ protocol to find feature indices

echo "Done!"
```

## HID++ Command Reference

### Command Format
| Byte | Purpose | Description |
|------|---------|-------------|
| 0 | Report ID | 0x10 (short report) |
| 1 | Device Index | Device slot on Bolt receiver (0x01-0x06) |
| 2 | Feature Index | **Device-specific** - must be discovered per device |
| 3 | Function | 0x10 = setCurrentHost (function 0 << 4) |
| 4 | Host Index | 0x00=Host1, 0x01=Host2, 0x02=Host3 |
| 5-6 | Padding | 0x00, 0x00 |

### Current Device Configuration (Nobara Bolt Receiver)
| Device | Solaar Index | HID++ Device Index | CHANGE_HOST Feature Index |
|--------|--------------|-------------------|---------------------------|
| MX Keys S | 2 | 0x02 | 0x0A (10) |
| MX Master 4 for Mac | 3 | 0x03 | 0x0E (14) |

### Finding Feature Indices
The CHANGE_HOST feature index varies per device. To find it:
```bash
# On Linux with solaar
solaar show <device_number> 2>&1 | strings | grep "CHANGE HOST"
# Look for: "14: CHANGE HOST {1814}" - the number before the colon is the feature index
```

## DDC Input Codes (Dell U3821DW)

| Input | Code | Hex |
|-------|------|-----|
| DisplayPort 1 | 15 | 0x0F |
| DisplayPort 2 | 16 | 0x10 |
| HDMI 1 | 17 | 0x11 |
| HDMI 2 | 18 | 0x12 |
| USB-C | 27 | 0x1B |

## Troubleshooting

### Monitor doesn't switch
- **DDC/CI disabled:** Monitor Menu → Others → DDC/CI → On
- **Linux permissions:** Ensure user in `i2c` group, reboot after adding
- **Verify:** `ddcutil detect` should show monitor

### Peripherals don't switch
- **Wrong feature index:** Feature indices are device-specific and must be discovered
- **Device offline:** Move mouse/press key to wake device before switching
- **Wrong device index:** Check `solaar show` for correct device numbers

### Solaar vs hidapitester
- `solaar config` doesn't reliably switch hosts on some devices
- Use `hidapitester` with correct HID++ commands instead
- Solaar is useful for discovering device info and feature indices

## Files Location

**Nobara:**
- `~/scripts/to_mac.sh` - Switch to Mac (working)
- `~/bin/hidapitester` - HID control tool

**Mac:**
- `~/scripts/to_nobara.sh` - Switch to Nobara (needs work)
- `~/bin/hidapitester` - HID control tool

**Repository:**
- `infrastructure/scripts/kvm/to_mac.sh`
- `infrastructure/scripts/kvm/to_nobara.sh`

## TODO

- [x] Nobara → Mac switching (working)
- [x] Set up keyboard shortcut on Nobara (Ctrl+Shift+Up)
- [ ] **Mac → Nobara switching** - needs correct HID++ feature indices for Mac's Bolt receiver
- [ ] Set up keyboard shortcut on Mac
- [ ] Test monitor switching from Mac side