Uninitialized Inputs

Timestamps & Driver Station

Before calling Logger.start(), AdvantageKit's built-in input logging is not active. This means that Driver Station data (e.g. from the DriverStation or joystick classes) and timestamp data (e.g. Timer.getTimestamp()) are not deterministic and should not be accessed by the robot code.

tip

Wait to create subsystems or button bindings until after Logger.start() is called. For most projects, this can be achieved by instantiating RobotContainer at the end of the Robot constructor.

public class Robot extends LoggedRobot {
    // DANGER: The Intake constructor runs before Logger.start(),
    // so it can access non-deterministic timestamps and DS data.
    private final Intake intake = new Intake();

    // Better: The Flywheel constructor is not called until after
    // Logger.start() has been called in the Robot constructor.
    private final Flywheel flywheel;

    public Robot() {
        // ... (AdvantageKit configuration)
        Logger.start();

        // Since Logger.start() has been called, the Flywheel
        // constructor is free to use timestamps and DS data.
        flywheel = new Flywheel();
    }
}

Subsystems

Typically, inputs from subsystems are only updated during calls to periodic. Note that this means updated (non-default) input data is not available in the constructor. The solution is to either wait for the first periodic call or call periodic from within the constructor.

public class Example extends SubsystemBase {
    private final ExampleIO io;
    private final ExampleIOInputs inputs = new ExampleIOInputs();

    public Example(ExampleIO io) {
        this.io = io;

        // Inputs are not updated yet
        inputs.position;
    }

    @Override
    public void periodic() {
        io.updateInputs(inputs);
        Logger.processInputs("Example", inputs);

        // Inputs are now updated
        inputs.position;
    }
}