Buttons in custom controller trigger events but do not set the value

I have one of those cheap one-hand controllers that I would like to get to work in Unity. I have been looking at the InputSystem examples and Reference, and I almost have it working. The controller generates events when the user hits the buttons on it, but I can't get the values from the buttons so that I can tell which button was pressed.

Here is the code I have so far:

Code (CSharp):

1. public struct OneHandDeviceState : IInputStateTypeInfo
2. {
3.      public FourCC format => new FourCC('O', 'H', 'C', 'F');
4.      public ushort unk1;
5.      public ushort unk2;
6.      [InputControl(name = "okButton", layout = "Button", bit = 12, displayName = "OK Button")]
7.      public ushort buttons;
8. }
9. #if UNITY_EDITOR
10. [InitializeOnLoad] // Call static class constructor in editor.
11. #endif
12. [InputControlLayout(stateType = typeof(OneHandDeviceState))]
13. public class OneHandController : InputDevice
14. {
15. #if UNITY_EDITOR
16.      static OneHandController()
17.      {
18.          // Trigger our RegisterLayout code in the editor.
19.          Initialize();
20.      }
21. #endif
22.      [RuntimeInitializeOnLoadMethod]
23.      private static void Initialize()
24.      {
25.          InputSystem.RegisterLayout<OneHandController>("Fortune Tech",
26.              matches: new InputDeviceMatcher()
27.                  .WithInterface("HID")
28.                  .WithProduct("Fortune Tech Wireless"));
29.          Debug.Log("Registered Fortune Tech.");
30.      }
31.      public ButtonControl okButton { get; private set; }
32.      protected override void FinishSetup()
33.      {
34.          base.FinishSetup();
35.          okButton = GetChildControl<ButtonControl>("okButton");
36.      }
37. }

I can tell this is working. The Input Debugger shows events coming in, and if I examine the events, I can see the okButton value is read correctly from the data. See in this screenshot how the value is different:


However, it does not appear in the live part of the Input Debugger:


This is different from the keyboard, for example, which correctly shows the value changing.

The same problem shows up in-game, if I use code like this:

Code (CSharp):

1. public class Movement : MonoBehaviour
2. {
3.      void Update()
4.      {
5.          var controller = OneHandController.current;
6.          var keyboard = Keyboard.current;
7.          ButtonControl keyButton = keyboard["#(a)"] as ButtonControl;
8.          ButtonControl conButton = controller.okButton;
9.          if (keyButton.ReadValue() != 0)
10.              Debug.Log("key a pressed");
11.          if (conButton.ReadValue() != 0)
12.              Debug.Log("OK button pressed");
13.      }
14. }

The keyboard button has a value when the key is pressed, but for the controller, ReadValue always comes out 0. Similarly, if I use code like this, ReadValueFromEvent returns 0, even though the event is being triggered.

It seems like I am missing one thing to make the Device correctly map the values from the Device State into the Input Controls. What is it?