To write “Hello, world!” in embedded Rust, build a no_std firmware project for a specific microcontroller, give the linker that chip’s flash and RAM layout, then flash and debug the program using board-compatible tools. The official Embedded Rust Book’s STM32F3DISCOVERY example is a concrete route through those steps: it targets an STM32F303VCT6 and uses OpenOCD and GDB to run the firmware and observe its debug output.
What “Hello, world!” means on a microcontroller
On a desktop, a Rust program can use the operating system and standard library. Bare-metal firmware starts without an operating system already loaded. The Embedded Rust Book puts it plainly: “In a bare metal environment no code has been loaded before your program.” For this reason, the example uses #![no_std] rather than Rust’s standard library. That means it links against core; it does not provide the OS integration or standard heap a typical std program expects. A heap can be added when needed by using alloc together with an allocator, but a first firmware example generally does not require one. Read the Embedded Rust Book’s explanation of no_std.
A firmware “print” also needs a destination. A microcontroller does not automatically have a terminal: output might be routed through a debugger, serial connection, or another board-specific interface. In the walkthrough below, the example’s debug-output mechanism sends “Hello, world!” to the OpenOCD console while GDB is attached. Programming the chip and viewing text are related but distinct jobs: the probe and OpenOCD handle the debug transport, while the example configuration determines where its output goes.
Choose the board and target before creating the project
Reference path: STM32F3DISCOVERY
The Embedded Rust Book’s reproducible walkthrough uses the STM32F3DISCOVERY board, which has an STM32F303VCT6 Cortex-M4F microcontroller. The book documents 256 KiB of flash and 40 KiB of RAM for this board. Those memory figures are specific to the named chip and board; they are not safe defaults for a different STM32 or another manufacturer’s MCU. See the book’s board and hardware setup.
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Select the Rust target triple for the chip
A target triple encodes the processor and relevant compilation assumptions, so it is part of the hardware contract rather than a generic setting to copy between projects. For this STM32F3 example, use thumbv7em-none-eabihf. Other Cortex-M families require different triples; floating-point support also affects the suffix. Confirm the correct target for the actual MCU before compiling. The Embedded Rust Book lists target installation guidance.
Create and configure the firmware project
The classic book workflow uses the cortex-m-quickstart template. A template is useful because bare-metal firmware needs more than a Rust source file: it supplies or organizes target configuration, startup/runtime integration, and linker settings. The book also documents cargo-generate for creating a project and cargo-binutils as part of the embedded tooling ecosystem. Review the book’s tooling overview.
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Install Rust with
rustup, then add the target for this board:rustup target add thumbv7em-none-eabihf. If you choose a different MCU, substitute its documented Rust target instead. The installation chapter covers target selection.Rank #2
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Generate or create a project from
cortex-m-quickstart(or an equivalent embedded template), then retain its runtime and linker integration rather than treating it as an ordinary host application. The template is a starting point, not proof that its memory settings match every board.What’s actually slowing this PC down?
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Set the build target in
.cargo/config.tomltothumbv7em-none-eabihffor the STM32F3DISCOVERY example. This ensures Cargo builds for the microcontroller rather than for the computer running the command. -
Configure
memory.xwith the chip’s actual flash and RAM regions. For the documented STM32F303VCT6 board, the book’s memory map corresponds to 256 KiB flash and 40 KiB RAM. If using another board, consult its MCU datasheet or reference manual and update the addresses and sizes: a project can compile with an incorrect map yet fail to run because the linker placed code or data in nonexistent memory.Rank #3
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Use the example’s embedded entry point and debug-output mechanism to emit “Hello, world!” once, then leave the firmware in
loop {}. For physical hardware, remove or comment out the QEMU-onlydebug::exitcall: the book warns that it should not be run on hardware. The hardware chapter contains the hello example and board-specific cautions.
Build, flash, and see the message
For the book’s STM32F3DISCOVERY setup, the high-level sequence is to build the hello example, connect to the board through its ST-LINK interface using OpenOCD, then use GDB to load and run the firmware. The exact probe configuration and GDB commands depend on the project and installed versions of the tooling, so use the configuration provided by the selected template and the board walkthrough rather than assuming one universal command line.
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From the project directory, build the example with
cargo build --example hello. Resolve target or linker errors before attempting to flash; in particular, check the configured target and the flash/RAM values inmemory.x.Rank #4
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Connect the STM32F3DISCOVERY board to the computer through its ST-LINK interface and start OpenOCD with the board-compatible configuration described by the project and tooling instructions.
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Start GDB with the firmware artifact, connect it to the OpenOCD server, load the program, and continue execution using the commands for the template’s debug setup. The hardware walkthrough demonstrates this OpenOCD/GDB flow.
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Read the OpenOCD console for “Hello, world!” The example then remains in
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Choose between the classic book workflow and Embassy
The classic Embedded Rust Book route is useful when the goal is to understand how target selection, startup support, linker scripts, memory maps, flashing, and debugging fit together. Embassy is a framework-oriented route with board examples and async support; its getting-started guidance recommends rustup and either probe-run or OpenOCD, and names STM32 Nucleo, STM32 Discovery, and nRF kits among possible hardware. Explore the Embassy Book and its getting-started guidance.
| Decision point | Classic Embedded Rust Book path | Embassy path |
|---|---|---|
| What you learn first | More direct exposure to target triples, startup/runtime setup, linker scripts, memory maps, OpenOCD, and GDB. | Framework-oriented setup, board examples, and async support. |
| Board choice | The cited hello walkthrough is specifically for STM32F3DISCOVERY and its STM32F303VCT6. | The getting-started page names STM32 Nucleo, STM32 Discovery, and nRF kits; check its examples for support for the exact board and MCU you own. |
| First “hello” style | A bare-metal debug-output example that emits text through the configured debug path. | The Embassy Book calls blinky “the embedded world’s equivalent of ‘Hello World’,” reflecting the common LED-first approach. |
| Flashing/debug tools | The cited walkthrough uses OpenOCD and GDB with the board’s ST-LINK interface. | The getting-started guidance recommends probe-run or OpenOCD; follow the instructions for the selected board. |
Choose the classic route if you want the mechanics of bare-metal startup and memory placement to be visible. Choose Embassy when you want to begin with its framework and board examples, especially if an async application is your next step. Either way, verify target and board support for the exact MCU rather than assuming all Cortex-M devices share one setup.
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