EMBEDDED RUST · no_std → WASM

GPIO, Peripherals & the Control Loop

Write your first no_std Rust firmware: own the rover's peripherals, blink a GPIO LED, and drive the motors from the control loop to reach the goal.

01Challenge

The Bench opens on firmware whose control() only blinks the LED, so the rover sits still. Press Compile & Run: it builds real Rust to WASM and the rover doesn't move. Your job: make this firmware drive to the green pad.

02Model

On the Python tier you called set_motor(...). What ran underneath? A control loop on a chip, talking to motor and sensor peripherals it OWNS. In Rust that ownership is literal: you take() the Peripherals once, as a value, and the compiler then guarantees no two parts of your code fight over the same motor. The loop runs every tick like a heartbeat: read sensors, decide, drive. The same embodied loop you've known since the blocks tier, now you're writing the metal that runs it.

Firmware owns the board's peripherals.

03Guided practice

1. Take the peripherals. control_loop!(control) exports the tick; inside, p is your &mut Peripherals. 2. Read the goal beacon. p.goal.distance() (m) and p.goal.bearing() (rad, + = left). 3. Drive the motors. p.motors.set(left, right) in [-1, 1]. 4. Steer + go. let turn = 1.2 * bearing; then let forward = if dist > 0.2 { 0.6 } else { 0.0 }; and p.motors.set(forward - turn, forward + turn); 5. GPIO. Keep p.led.set(dist > 0.2).

04Feedback

PASS WHEN The firmware compiles as no_std and drives the rover within 0.2 m of the pad.

If your run fails, check:

Closest approach barely changed. Your motors are still set(0.0, 0.0). Compute turn from bearing and a forward term, then p.motors.set(forward - turn, forward + turn).
Rover spun/veered away. The steering sign is flipped. bearing is + when the goal is LEFT: set(forward - turn, forward + turn).
rustc error 'cannot find value `bearing`': you read it into `_bearing`; drop the underscore to use it.

05Retrieve & space

Ownership: why does take() hand you the peripherals exactly once? (single guaranteed owner of each motor/pin).
Units: p.goal.bearing() is in ____ and + means the goal is to your ____ (radians; left).
What does control_loop!(control) generate? (a #[no_mangle] tick() the host calls each period).

06Mastery & project

Compile-and-run firmware (no_std, no emulator) that owns the peripherals and drives the rover into the pad.

Foundation of the metal capstone: every later firmware builds on this take → read → drive loop.

← Imitation and Sim-to-Real Timers, PWM & Proportional Drive →

EMBEDDED RUST · no_std → WASM

GPIO, Peripherals & the Control Loop

Write no_std embedded Rust against the rover HAL. It compiles to WASM and runs as the real control loop.

You read

You change

the firmware you write in the control loop

Fixed

the emulated chip, its peripherals, and the wiring