Accessibility profiles

The umi profiles generate a workstation usable without a keyboard or mouse, controlled by gaze, voice or touch. It is intended for people with motor disabilities.

They consist of two parts: an umi host profile that declares the hardware and the session, and a umi user profile that sets up the user’s environment.

The principle

Common peripherals (keyboard, mouse) can be replaced by voice, gaze or touch. Accessibility tools can be configured according to the user’s characteristics.

The hardware

Item	Requirement
Eye tracker	Tobii Eye Tracker 5 (USB, manufacturer ID 2104)
Architecture	x86_64-linux only (Talon does not provide another binary)
Microphone	Needed for voice commands
Speakers	Sound feedback for visual keyboard keystrokes
Screen	A good touchscreen for controlling the desktop and applications

First boot under Windows

The Tobii 5 firmware must be initialized once on a Windows machine, with the Tobii Experience app. Without this step, the tracker stays silent under Linux.

Setting up a workstation

1. Declare the host and its user in etc/config.yaml, both with the umi profile:

   etc/config.yaml

   users:
     alice:
       uid: 1010
       name: "Alice"
       profile: "umi"
       groups: ["global"]
   
   hosts:
     - hostname: "umi-desktop"
       name: "Poste accessible"
       zone: "maison:2.3"
       profile: "umi"
       users: ["alice"]

   The user profile adds the account to the input and uinput groups, without which Talon cannot inject events.

2. Enable automatic login in the machine configuration, if the user cannot use a keyboard to identify themselves:

   usr/machines/poste-regard/default.nix

   darkone.host.umi.autoLoginUser = "alice";

3. Generate and deploy:

   just generate
   just apply umi-desktop

4. Test and configure

   Eye tracker: calibrate on first launch

   Unplug then replug the tracker (the udev rules only apply at plug-in), relaunch Talon, then run the calibration from its menu.

Multiple users on the same machine

Only the account listed in autoLoginUser opens its session on its own. The other UMI accounts declare themselves in gazeUsers to inherit the Cinnamon session. Regular accounts keep their usual GNOME Wayland session.

Configuring the host

darkone.host.umi options, to set in usr/machines/<host>/default.nix.

Option	Default	Role
enable	enabled by the profile	Enables the host profile
autoLoginUser	null	Account opened automatically at startup
gazeUsers	[ ]	Other accounts whose GDM session is Cinnamon/X11
package	pkgs.talon	Talon package, or null to install it manually

Talon absent or not wanted

With package = null, everything else is configured (udev, uinput, accessibility) and Talon can be launched manually from the upstream archive, which preserves its automatic update.

Configuring the user

darkone.home.umi options, to set in usr/users/<login>/default.nix.

Option	Default	Role
enable	enabled by the profile	Enables the user profile
enableTalonAutostart	true	Launches Talon at session start
communityScripts	null	talonhub/community tree deployed in ~/.talon/user/community
enableDwell	false	Click by pointer dwell
dwellTime	1.2	Dwell click delay, in seconds

Dwell click remains optional

enableDwell triggers a click as soon as the pointer stays still. It is essential for gaze, but unsettling for the mouse: a pointer left on the accessibility menu or on the visual keyboard clicks on its own. Only enable it on a workstation equipped with a tracker.

Community contributions

The talonhub/community community scripts bring mouse zoom and click by tongue click. They are declared reproducibly:

usr/users/alice/default.nix

{ pkgs, ... }:
{
  darkone.home.umi.communityScripts = pkgs.fetchFromGitHub {
    owner = "talonhub";
    repo = "community";
    rev = "…";
    hash = "…";
  };
}

What the profile changes

The workstation is deliberately stripped of anything that requires a keyboard or a mouse.

Change	Reason
Cinnamon session on X11	Talon (unfortunately) does not work under Wayland
Automatic sign-in	No password that could be typed
Locking and sleep disabled	A locked screen is a dead end
Keyring without password	Avoids a prompt that cannot be satisfied (unencrypted host only)
Enlarged cursor and text	Eye-tracking accuracy limited to a few dozen pixels
On-screen keyboard anchored at the bottom	Always available, large targets, word prediction

The workstation is not protected at startup

Automatic sign-in, no screen locking : anyone turning on the machine is in the session. The only useful barrier is disk encryption, to plan from installation if the workstation is mobile.

Face recognition sign-in is on the TODO list.

The keyring follows disk encryption

Session keyring handling depends on the host :

• unencrypted workstation : the keyring is created without a password, otherwise the session would open on a prompt that no one can satisfy ;
• encrypted workstation (LUKS) : the passphrase entered at startup is passed to the keyring by the PAM stack of automatic sign-in. The keyring stays protected, and nothing is requested.

Consequence on an encrypted workstation : changing the LUKS passphrase without changing the keyring one triggers the message “the login password no longer matches your keyring’s”. Then delete ~/.local/share/keyrings/login.keyring and open the session again.

Diagnostics

Symptom	Lead
Talon does not see the tracker	Replug the tracker, then relaunch Talon (udev rule applied on connection)
Firmware not initialized	Run through Tobii Experience under Windows once
Session opened under GNOME	Check that the account is in gazeUsers or in autoLoginUser
The pointer clicks on its own	enableDwell enabled without a tracker, disable it

Expected kernel messages

The tracker exposes two video interfaces that uvcvideo cannot handle, hence the Unknown video format, No supported video formats found and probe with driver uvcvideo failed with error -22 messages. They are normal and desirable: no kernel driver claims the interfaces, which leaves them free for Talon.