2024 Offseason Updates

Docs/Architecture/AKitStructureReference.md

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+# AdvantageKit Code Structure Reference
+
+This document contains a quick reference for how we structure our code.
+It should be used when planning out the structure of a subsystem.
+
+## Basic Layout
+
+```mermaid
+flowchart TD
+    subgraph Subsystem
+        A[Subsystem]
+    end
+    Subsystem-->IO
+    subgraph IO
+        direction LR
+        B[IO]-->E[IOInputs]
+    end
+    IO-->IOImpl
+    subgraph IOImpl
+        C[IO Implementation Real]
+        D[IO Implementation Sim]
+    end
+```
+
+This diagram shows the basic structure of an AKit Subsystem.
+It includes 3 layers:
+
+### Subsystem
+
+- The "subsystem" layer is a class which `extends SubsystemBase`.
+- This class should contain methods that return Commands for this subsystem.
+- This class should contain all higher-level control flow within this mechanism.
+  - For instance, it could contain a `SwerveDriveOdometry` object to track a drivetrain's position.
+  - It might contain information about the current target of a mechanism, or whether or not the mechanism has homed its position yet.
+  - *Generally, this information should all be **"processed" information** that we derive from our IOInputs.
+- The `Subsystem` file will contain one `IO` instance and one `IOInputs` instance, conventionally called `io` and `inputs` respectively.
+
+### IO
+
+- The "IO" layer defines the interface with our hardware, as well as all the values we will log.
+- This includes an `interface` called `SubsystemIO` which defines a set of methods to interact with the hardware, such as `setVoltage` or `getPosition`.
+However, it doesn't define *how* to do them, because that's specific to each implementation.
+The interface just provides a template.
+- This class will also include an `updateInputs` method, which takes in an `IOInputs` object and updates it with the latest sensor data from the mechanism.
+- The `IOInputs` object is a class that contains various measurements and sensor data about the mechanism, like current draw, encoder position, and voltage output.
+- It is marked with `@AutoLog` which means all the inputs and outputs for the subsystem will be automatically recorded in the log, so we can play it back later.
+
+### IO Implementations
+
+- These are classes which `implement` the aforementioned `IO` class.
+- This means they will specify how to do all of the methods defined in the `IO` class.
+- Generally we will have 2 types of `IOImplementation`, `IOSim` and `IOReal`.
+  - `IOReal` defines its methods to command real hardware to have real outputs.
+  - `IOSim` often looks similar to `IOReal`, but will have some behaviour added to fake the behaviour of real world physics.
+    This can include a physics sim which approximates physical behaviour, setting outputs which we can't sim to a default value (like temperature), or other ways of "faking" real world behaviour.
+- `IOImplementation`s will contain the actual objects such as `TalonFX`s (for `IOReal`) or `DCMotorSim`s (for `IOSim`).
+
+## Intake Example
+
+<img src="../../Assets/2025OffsznIntake.png" alt="A cad render of the intake from our 2025 offseason robot" width="600"/>
+
+This example will cover how the code for an intake such as the one above might be set up.
+
+```mermaid
+flowchart TD
+    subgraph Subsystem
+        A[IntakeSubsystem]
+    end
+    Subsystem-->IO
+    subgraph IO
+        direction LR
+        B[IntakeIO]-->E[IntakeIOInputs]
+    end
+    IO-->IOImpl
+    subgraph IOImpl
+        C[IntakeIOReal]
+        D[IntakeIOSim]
+    end
+```
+
+Let's start by defining the methods in the `IntakeIO` interface.
+There are two motors on this slapdown intake--one that controls the pivot, and one that controls the rollers.
+The intake needs to set its position (extended or retracted), so we will need a `setAngle(Rotation2d angle)` method.
+We will also need a way to set the rollers' output, so let's add a `setRollerVoltage(double volts)` method.
+For convenience, let's add a method `stop()` that calls `setRollerVoltage()` with a voltage of 0.
+
+We also need to add our `IntakeIOInputs` to the `IntakeIO` file.
+This should contain all of the sensor information we need to know about our intake so that we can debug its behaviour with logs.
+Then we can add our logged fields for the motor.
+
+Here is a list of common logged fields for motors:
+
+- Velocity (Often but not always in rotations per second)
+  - This is the main field we care about to see if the motor is moving.
+- Current draw (Amps)
+  - This lets us see if the motor is stalling (trying to move but stuck) as well as how much energy the motor is using.
+- Temperature (Celsius)
+  - If a motor gets too hot it will turn itself off to protect its electronics.
+    This lets us see if we are having issues related to that.
+    In addition, motors are less efficient as they heat up.
+- Voltage (Voltage)
+  - This lets us see how much we are commanding our motors to move.
+- Position (Rotations or inches, often after a gear reduction)
+  - This lets us track the position of the motor and its corresponding mechanism.
+
+We can add all of these values into our `IntakeIOInputs` class.
+
+Finally, add a `updateInputs(IntakeIOInputs inputs)` method that our `IOImplementation`s can call to record these values.
+Our `IntakeIO` file should look something like this now:
+
+```Java
+// Imports go here
+
+public interface IntakeIO {
+    @AutoLog
+    public class IntakeIOInputs {
+
+        // Pivot motor values
+        public double pivotVelocityRotationsPerSec;
+        public double pivotCurrentDrawAmps;
+        public double pivotTemperatureCelsius;
+        public double pivotVoltage;
+        public Rotation2d pivotMotorPosition;
+
+        // Roller motor values
+        public double rollerVelocityRotationsPerSec;
+        public double rollerCurrentDrawAmps;
+        public double rollerTemperatureCelsius;
+        public double rollerVoltage;
+    }
+
+    // Methods that IOImplementations will implement
+    public void setAngle(Rotation2d angle);
+
+    public void setRollerVoltage(double volts);
+
+    // Note the use of "default"
+    // This means that we don't have to re-implement this method in each IOImplementation, because it will default to
+    // whatever the specific implementation of setVoltage() is
+    public default void stop() {
+        setRollerVoltage(0);
+    }
+
+    public void updateInputs(IntakeIOInputs inputs);
+}
+```
+
+Next, let's write `IntakeIOReal`.
+This will contain all of the hardware we want to interact with on the real robot.
+
+First, we will need to define the hardware we want to use.
+In this case, they will be two `TalonFX`s.
+
+```Java
+private final TalonFX pivot = new TalonFX(IntakeSubsystem.PIVOT_MOTOR_ID);
+private final TalonFX roller = new TalonFX(IntakeSubsystem.ROLLER_MOTOR_ID);
+```
+
+Next we will need to implement each of the methods from `IntakeIO`.
+Each should `@Override` the template method.
+For the sake of brevity, I won't cover that in detail here. *MAKE SUBSYSTEM WALKTHROUGH AND LINK HERE*
+
+In the end you should have something like:
+
+```Java
+public class IntakeIOReal implements IntakeIO {
+    private final TalonFX pivot = new TalonFX(IntakeSubsystem.PIVOT_MOTOR_ID);
+    private final TalonFX roller = new TalonFX(IntakeSubsystem.ROLLER_MOTOR_ID);
+
+    @Override
+    public void updateInputs(IntakeIOInputs inputs) {
+        // Note that the exact calls here are just examples, and might not work if copy-pasted
+
+        inputs.pivotVelocityRotationsPerSec = pivot.getVelocity();
+        inputs.pivotCurrentDrawAmps = pivot.getStatorCurrent();
+        inputs.pivotTemperatureCelsius = pivot.getDeviceTemp();
+        inputs.pivotVoltage = pivot.getMotorVoltage();
+        inputs.pivotMotorPosition = pivot.getMotorPosition();
+
+        // Roller motor values
+        inputs.rollerVelocityRotationsPerSec = roller.getVelocity();
+        inputs.rollerCurrentDrawAmps = roller.getStatorCurrent();
+        inputs.rollerTemperatureCelsius = roller.getDeviceTemp();
+        inputs.rollerVoltage = roller.getMotorVoltage();
+    }
+
+  @Override
+  public void setRollerVoltage(double volts) {
+    roller.setVoltage(volts);
+  }
+
+  // Note how we don't need to define stop() because it has a default implementation that does what we want
+
+  @Override
+  public void setAngle(Rotation2d angle) {
+    pivot.setAngle(angle);
+  }
+}
+```
+
+We can make a similar class for `IntakeIOSim`, although instead of getting motor outputs directly we would have to use `motor.getSimState()`.
+For more information about that, check the [CTRE docs](https://pro.docs.ctr-electronics.com/en/stable/docs/api-reference/simulation/simulation-intro.html).
+
+Finally, let's write the `IntakeSubsystem` class.
+This class will include an instance of `IntakeIO` and an instance of `IntakeIOInputs`.
+It will also contain Command factories to allow the rest of our code to interface with it.
+
+Add the io and io inputs to the class:
+
+```Java
+// Snip imports
+
+public class IntakeSubsystem extends SubsystemBase {
+    private final IntakeIO io;
+    private final IntakeIOInputsAutoLogged inputs = new IntakeIOInputsAutoLogged();
+
+    public IntakeSubsystem(IntakeIO io) {
+        // Pass in either the sim io or real io
+        this.io = io;
+    }
+}
+```
+
+Then we can add a few Command factories to control the subsystem:
+
+```Java
+public Command intake(double volts) {
+    return Commands.run(() -> {
+        io.setAngle(INTAKE_ANGLE);
+        io.setRollerVoltage(volts);
+    });
+}
+
+public Command stop() {
+    return Commands.runOnce(() -> {
+        io.setAngle(RETRACTED_ANGLE);
+        io.stop();
+    });
+}
+```
+
+Finally, let's add our `periodic()` method to update and log our inputs.
+
+```Java
+@Override
+public void periodic() {
+    io.updateInputs();
+    // Make sure to import the "littletonRobotics" Logger, not one of the other ones.
+    Logger.processInputs("Intake", inputs);
+}
+```
+
+Overall, `IntakeSubsystem` should roughly look like:
+
+```Java
+// Snip imports
+
+public class IntakeSubsystem extends SubsystemBase {
+    IntakeIO io;
+    IntakeIOInputsAutoLogged inputs;
+
+    public IntakeSubsystem(IntakeIO io) {
+        // Pass in either the sim io or real io
+        this.io = io;
+        inputs = new IntakeIOInputsAutoLogged();
+    }
+
+    public Command intake(double volts) {
+        return Commands.run(() -> {
+            io.setAngle(INTAKE_ANGLE);
+            io.setRollerVoltage(volts);
+        });
+    }
+
+    public Command stop() {
+        return Commands.runOnce(() -> {
+            io.setAngle(RETRACTED_ANGLE);
+            io.stop();
+        });
+    }
+
+    @Override
+    public void periodic() {
+        io.updateInputs();
+        // Make sure to import the "littletonRobotics" Logger, not one of the other ones.
+        Logger.processInputs("Intake", inputs);
+    }
+}
+```
+
+### More complex subsystems
+
+The intake is a very simple to program subsystem, but more complex ones exist.
+A swerve drive might have the following set of classes:
+
+```mermaid
+flowchart TD
+    subgraph Subsystem
+        A[SwerveSubsystem]
+    end
+
+    Subsystem--- 4x -->SwerveModuleIO
+    subgraph SwerveModuleIO
+        direction LR
+        B[SwerveModuleIO]-->E[SwerveModuleIOInputs]
+    end
+    SwerveModuleIO-->SwerveModuleIOImpl
+    subgraph SwerveModuleIOImpl
+        C[SwerveModuleIOReal]
+        D[SwerveModuleIOSim]
+    end
+
+    Subsystem--->GyroIO
+    subgraph GyroIO
+        direction LR
+        X[GyroIO]-->GyroIOInputs
+    end
+    GyroIO-->GyroIOImpl
+    subgraph GyroIOImpl
+        GyroIOReal
+        GyroIOSim
+    end
+```
+
+This means that we will have one `SwerveSubsystem` class.
+Within that class, we will have 4 instances of `SwerveModuleIO` and its corresponding `SwerveModuleIOInputs`, one for each module.
+We will also have an instance of `GyroIO` and `GyroIOInputs`.
+The `SwerveSubsystem` file handles coordinating and combining data from these `IO`s, and each `IO` handles turning the control signals from the `Subsystem` into motion in the hardware (or sim!).