Working without hardware

nxt-rs includes a simulated brick. It’s always compiled in and needs no feature flag. It answers every protocol command plausibly:

• Motors with a rotation limit finish instantly and update their counters.
• Sensors report whatever values you set.
• Files, mailboxes, I²C registers and the screen live in memory.

use nxt_rs::{prelude::*, transport::mock::Simulator};

fn main() -> nxt_rs::Result<()> {
let sim = Simulator::new();
let brick = Brick::mock_with(sim.clone());   // keep `sim` to control the brick

let motor = brick.motor(A)?;
motor.run(power!(50)).degrees(degrees!(720)).wait().block()?;
assert_eq!(sim.output(OutputPort::A).rotation_count, 720);

let touch = brick.touch(S1).block()?;
assert!(!touch.read().block()?);
sim.set_sensor(InputPort::S1, 1023, 1);      // press the button
assert!(touch.read().block()?);
Ok(()) }

Brick::mock() is shorthand for a simulator you don’t need to control.

Use the simulator to:

• try the library before your brick arrives,
• unit-test robot logic in CI,
• develop on a laptop away from the robot.

Write your functions against a generic Brick<T> so that the same code runs on the real brick and in tests:

use nxt_rs::{prelude::*, transport::{Transport, mock::Simulator}};

/// Turns in small steps until the ultrasonic sensor sees something close.
async fn face_obstacle<T: Transport>(brick: &Brick<T>) -> nxt_rs::Result<()> {
    let (motor, sonar) = brick.take((A.motor(), S4.ultrasonic())).await?;
    while sonar.read().await?.is_none_or(|d| d > Centimeters(20)) {
        motor.run(power!(30)).degrees(degrees!(10)).wait().await?;
    }
    Ok(())
}

fn main() -> nxt_rs::Result<()> {
let sim = Simulator::new();
sim.set_ultrasonic_distance(InputPort::S4, 15);
face_obstacle(&Brick::mock_with(sim)).block()?;
Ok(()) }

The Testing chapter covers the simulator in depth, including byte-exact scripted tests.

Run cargo run --example simulator in the nxt-rs repository to see a complete program running against it.