Configuration

This page covers all configuration options for the Open Apollo driver, including kernel module parameters, PipeWire/WirePlumber integration, UCM2 profiles, and systemd service setup.

Module Parameters

The ua_apollo module accepts the following parameters, which can be set when loading the module with insmod or modprobe.

Channel Count Override

By default, the driver auto-detects channel counts from the device model:

To override (e.g., to limit to stereo for testing):

sudo modprobe ua_apollo play_ch=2 rec_ch=2

If only play_ch is specified, rec_ch defaults to the same value. When overriding channel counts, preamp ALSA controls are disabled.

Warm Boot Mode

If the Apollo was previously initialized by another operating system in a dual-boot configuration, you can skip firmware loading:

sudo modprobe ua_apollo warm_boot=1

This skips both firmware upload and the ACEFACE connection handshake, assuming the DSP is already running. The driver will still re-program the DMA scatter-gather table (since the previous OS's physical addresses are invalid) and create the ALSA card.

Debug Mode (no_connect)

For crash debugging, you can load the driver without attempting the DSP connection:

sudo modprobe ua_apollo no_connect=1

The driver will probe the device, map registers, and create the chardev, but will not start audio transport. Audio will not work in this mode.

Making Parameters Persistent

Create a modprobe configuration file:

sudo tee /etc/modprobe.d/ua-apollo.conf <<EOF
options ua_apollo play_ch=24 rec_ch=22
EOF

PipeWire Configuration

WirePlumber Rules

The project includes a WirePlumber configuration file that sets optimal defaults for Apollo interfaces. Deploy it to /etc/wireplumber/main.lua.d/51-ua-apollo.lua:

sudo cp configs/wireplumber/51-ua-apollo.lua /etc/wireplumber/main.lua.d/

This configuration applies the following properties to all Apollo ALSA nodes:

Pro-Audio Profile

WirePlumber does not auto-select the pro-audio profile. After PipeWire starts, set it manually:

# Find the Apollo device ID
wpctl status

# Set pro-audio profile (replace <id> with the device ID)
wpctl set-profile <id> pro-audio

To make this automatic, you can create a WirePlumber script or a systemd user service that runs after wireplumber.service.

UCM2 Profiles

UCM2 (Use Case Manager 2) profiles tell ALSA and PipeWire about the device's channel layout and capabilities.

Deployment

sudo mkdir -p /usr/share/alsa/ucm2/ua_apollo
sudo mkdir -p /usr/share/alsa/ucm2/conf.d/ua_apollo
sudo cp configs/ucm2/ua_apollo/ua_apollo.conf /usr/share/alsa/ucm2/ua_apollo/
sudo cp configs/ucm2/ua_apollo/HiFi.conf /usr/share/alsa/ucm2/ua_apollo/
sudo ln -sf ../../ua_apollo/ua_apollo.conf \
    /usr/share/alsa/ucm2/conf.d/ua_apollo/ua_apollo.conf

Or use the included deployment script:

sudo bash configs/deploy.sh

Channel Layout (Apollo x4)

The HiFi profile exposes all DMA channels:

Playback (24 channels):

Capture (22 channels):

ALSA Controls

The driver registers ALSA mixer controls dynamically based on the detected model. Use amixer or alsamixer to view and modify them.

List All Controls

amixer -c Apollo contents

Per-Preamp Controls

For each preamp channel (e.g., 4 channels on Apollo x4), the following controls are created:

Monitor Controls

Routing Controls

Device Controls

Example: Set Gain and Enable Phantom Power

# Set preamp 1 gain to 40 dB
amixer -c Apollo cset name='Line 1 Capture Volume' 40

# Enable 48V phantom power on channel 1
amixer -c Apollo cset name='Mic 1 48V Phantom Power Switch' 1

# Set monitor volume to -10 dB (raw value = 192 + (-10 * 2) = 172)
amixer -c Apollo cset name='Monitor Playback Volume' 172

Systemd Service for the Mixer Daemon

The mixer daemon (ua_mixer_daemon.py) bridges the hardware driver with network control protocols (TCP:4710 and WS:4720). To run it as a system service:

Create the Service File

sudo tee /etc/systemd/system/ua-mixer-daemon.service <<EOF
[Unit]
Description=Universal Audio Apollo Mixer Daemon
After=sound.target
Wants=sound.target
ConditionPathExists=/dev/ua_apollo0

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

[Install]
WantedBy=multi-user.target
EOF

Enable and Start

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

Check Status

sudo systemctl status ua-mixer-daemon.service
journalctl -u ua-mixer-daemon.service -f

Running Without Hardware

For development or testing without the Apollo connected:

python3 mixer-engine/ua_mixer_daemon.py --no-hardware --no-bonjour -v

Audio Routing Basics

The Apollo's internal mixer operates independently from the ALSA PCM streams. Audio routing is controlled through the mixer daemon, which translates high-level mix commands into hardware register writes.

Signal Flow

Physical Inputs → DSP Mixer → Monitor Outputs
                            → Headphone Outputs
                            → S/PDIF / ADAT Outputs

DAW Playback (Virtual Inputs) → DSP Mixer → Outputs

Physical Inputs → DMA Capture → DAW Recording

Key Concepts

• Monitor outputs are the main line outputs, controlled by the Monitor Volume/Mute/Dim controls
• CUE mixes are independent headphone/aux mixes that can be assigned to headphone outputs
• Virtual inputs are DAW playback channels routed through the DSP mixer before reaching outputs
• The hardware monitor knob controls the analog output level independently from PipeWire's software volume