Linux FCP (Focusrite Control Protocol) Support Tools

This repository provides the user-space components required for full functionality of Focusrite USB audio interfaces that use the Linux FCP driver.

System Overview

FCP support in Linux consists of several components that work together:

1. Kernel Driver (linux-fcp)

   • Allows fcp-server to communicate with the device

2. User-space Server (this repo: fcp-server)

   • Communicates with the device via the kernel driver
   • Creates ALSA controls and transfers control changes to and from the device
   • Allows fcp-tool to update the device firmware, reset the device configuration, and reboot the device

3. Firmware Update Tool (this repo: fcp-tool)

   • CLI utility for updating device firmware
   • Uploads firmware to fcp-server

4. GUI Application (alsa-scarlett-gui)

   • Provides a graphical interface for device control
   • Uses the ALSA controls created by fcp-server

Supported Devices

The currently supported devices are:

• Scarlett 4th Gen 16i16, 18i16, and 18i20

The FCP driver itself supports all Focusrite USB audio interfaces since the 2nd Gen Scarletts, so support for the other devices will be added here later. Until then, the Linux Scarlett2 driver supports all the other 2nd Gen and later Scarlett, Clarett USB, Clarett+, and Vocaster devices.

Prerequisites

1. The FCP kernel driver must be installed.

2. Required packages for building:

# Debian/Ubuntu
sudo apt-get install build-essential libasound2-dev libsystemd-dev \
  libssl-dev zlib1g-dev libjson-c-dev pkg-config

# Fedora
sudo dnf install make gcc alsa-lib-devel systemd-devel openssl-devel \
  zlib-devel json-c-devel pkgconfig

3. Audio group membership is required to use fcp-tool:

sudo usermod -a -G audio $USER

Log out and back in for the group membership change to take effect.

Installation

1. Build and install:

make
sudo make install

This will:

• Build fcp-server and fcp-tool
• Install binaries to /usr/local/bin/
• Install systemd service file to /usr/local/lib/systemd/system/
• Install udev rule to /usr/local/lib/udev/rules.d/
• Install data files to /usr/local/share/fcp-server/

2. Reload systemd and udev:

sudo systemctl daemon-reload
sudo udevadm control --reload-rules

Configuration

The installation process sets up:

1. Systemd Service: fcp-server@.service

   • Started automatically when a compatible device is detected
   • One instance per device (e.g., fcp-server@1.service)

2. Udev Rules:

   • Start systemd service when device is connected

Usage

Device Management

1. Normal operation:

• Plug in the device
• Server starts automatically
• Check status with systemctl status fcp-server@*

2. Troubleshooting:

• Watch the system log when connecting the device: journalctl -f
• Stop the FCP server: sudo systemctl stop fcp-server@*
• Get the card number with aplay -l
• Start the FCP server manually with debug logging: LOG_LEVEL=debug fcp-server <card-number>

Firmware Management

fcp-tool provides the following capabilities:

# View all commands
fcp-tool

# Update firmware (takes 1-2 minutes)
fcp-tool update <firmware.bin>

# Maintenance commands
fcp-tool erase-config   # Reset device configuration to firmware defaults
fcp-tool reboot         # Reboot device

Support

Report issues at: https://github.com/geoffreybennett/fcp-support/issues

Please include:

• Device model
• Linux distribution and version
• Output as per troubleshooting steps above

Contact

• Author: Geoffrey D. Bennett
• Email: g@b4.vu
• GitHub: https://github.com/geoffreybennett

Donations

This software, including the driver, tools, and GUI is Free Software that I’ve independently developed using my own resources. It represents hundreds of hours of development work.

If you find this software valuable, please consider making a donation. Your show of appreciation, more than the amount itself, motivates me to continue improving these tools.

You can donate via:

• LiberaPay: https://liberapay.com/gdb
• PayPal: https://paypal.me/gdbau
• Zelle: g@b4.vu