EMBEDDED RUST · no_std → WASM

The decision that stays on the machine

The engine has four outcomes and the match handles three. What happens?

Write the relocated decision in no_std Rust, with every case handled, including the one it refuses.

01Challenge

You have priced the miss. Now write the engine that produces it. Four outcomes, one of them an honest refusal, and a compiler that will not let you leave a case unhandled.

Predict firstThe engine has four outcomes and the match handles three. What happens?

02Model

Python measured the claim; Rust is where the claim has to hold. On the machine the relocated decision is a total function over a small enum, running no_std with no allocation and no round trip, and it is the compiler rather than a test that proves every case is handled. That matters more here than in ordinary code, because the unhandled case is not a crash: it is a decision quietly taking the generative path while your ledger still counts it as relocated. Rust will not compile a partial match, which is the language enforcing the thing lesson two priced.

03Guided practice

Read the compiler error before changing anything. It names the unhandled variant. Then decide what the machine should physically do when the engine refuses a decision, and write that arm.

04Feedback

PASS WHEN The firmware compiles as no_std with a total match over all four cases, and the rover reaches the pad without the escalation case falling through.

If your run fails, check:

A partial match is a decision leaking to the expensive path with nobody counting it.
Read error[E0004]: it names the variant you left out.

05Retrieve & space

Why is an unhandled decision case worse than a crash, in an energy ledger?
What does the compiler guarantee here that a unit test would not?

06Mastery & project

You can write a relocated decision as a total function on the machine, and say what it does when it refuses.

Take one decision your system currently sends off-machine. Write it as an enum with an explicit refusal case, and say what the machine does in that case.

GO FURTHER · THE LIVE PLAYGROUND

PAI-140 · Rust for Physical AI ↗ · If enums and matching are new, this is where the language is taught.
What a decision costs: the instrument ↗ · Move the router and watch the ceiling move with it.

← The miss pays twice Readout is the term you forgot →

EMBEDDED RUST · no_std → WASM

The decision that stays on the machine

no_std Rust against the rover HAL, compiled to WASM and run as the real control loop. This starter does not compile on purpose: one decision case is unhandled.

You read

You change

the firmware you write in the control loop

Fixed

the emulated chip, its peripherals, and the wiring