OA

Mixer Daemon

Daemon Setup

The mixer daemon (ua_mixer_daemon.py) bridges the kernel driver and network control clients. It serves two TCP protocols and an optional WebSocket endpoint, allowing UA Console, ConsoleLink, and custom clients to control the Apollo mixer without modification.

What the daemon does

The daemon provides:

  • TCP:4710 — UA Mixer Engine protocol (null-terminated JSON text). Used by ConsoleLink (iOS/iPad).
  • TCP:4720 — UA Mixer Helper protocol (text commands, UBJSON binary responses). Used by UA Console / UA Connect.
  • WS:4721 — WebSocket server for UA Connect (Electron app).
  • State tree — Maintains 11,000+ mixer controls mirroring the structure expected by UA client software.
  • Hardware router — Translates state tree changes into ioctl calls to /dev/ua_apollo0.
  • Metering — Computes per-channel audio level meters from ALSA PCM capture data.
  • Bonjour/mDNS — Advertises _uamixer._tcp. so ConsoleLink auto-discovers the daemon.

Python dependencies

The daemon requires Python 3.10+ and the following packages:

# Required
pip install websockets    # WebSocket server for UA Connect

# Optional (enable Bonjour auto-discovery)
pip install zeroconf

# Optional (enable ALSA metering)
pip install pyalsaaudio

The daemon runs without optional dependencies — WebSocket, Bonjour, and hardware metering degrade gracefully when packages are missing.

Running the daemon

Basic usage

cd mixer-engine
python3 ua_mixer_daemon.py

This starts the daemon with auto-detected device map and hardware. It binds to 0.0.0.0 on ports 4710, 4720, and 4721.

With verbose logging

python3 ua_mixer_daemon.py -v

Protocol trace (log every message)

python3 ua_mixer_daemon.py -v -t

Software-only mode (no hardware)

For development and testing without an Apollo connected:

python3 ua_mixer_daemon.py --no-hardware --no-bonjour -v

This starts the full protocol server with simulated hardware. Clients can connect and interact with the state tree, but no ioctl calls are made.

Custom device map

python3 ua_mixer_daemon.py --device-map device_maps/device_map_apollo_x4.json

Custom ports

python3 ua_mixer_daemon.py --port 4711 --helper-port 4721 --ws-port 4722

Systemd service

Create a service file for automatic startup:

# /etc/systemd/system/ua-mixer-daemon.service
[Unit]
Description=UA Mixer Engine Daemon
After=sound.target
Wants=sound.target

[Service]
Type=simple
User=root
WorkingDirectory=/opt/open-apollo/mixer-engine
ExecStart=/usr/bin/python3 ua_mixer_daemon.py -v
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target

Enable and start:

sudo systemctl daemon-reload
sudo systemctl enable ua-mixer-daemon
sudo systemctl start ua-mixer-daemon

The daemon requires root (or appropriate permissions) to open /dev/ua_apollo0 for ioctl communication with the kernel driver.

Verifying it works

Check daemon is listening

ss -tlnp | grep -E '4710|4720|4721'

Test with the included test client

The repository includes a ConsoleLink simulator:

python3 test_client.py

This replays the exact command sequence that ConsoleLink sends on connection. Use --host to test against a remote daemon:

python3 test_client.py --host 192.168.1.100 -v

Test with netcat

# Connect and send a GET request
echo -ne 'get /devices/0/DeviceOnline/value\0' | nc localhost 4710

You should receive a JSON response:

{"path":"/devices/0/DeviceOnline/value","data":true}

Check Bonjour advertisement

If zeroconf is installed, the daemon advertises itself. On another machine:

avahi-browse -r _uamixer._tcp

Persistent state

The daemon saves modified control values to disk and restores them on restart. State files are stored in mixer-engine/state/ alongside the device map name.

This means mixer settings (preamp gain, monitor volume, fader positions) survive daemon restarts.

Next steps

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Sample Rates
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Protocol Reference