Rust on STM32

Hardware Baseline

• Default board: STM32F103C8T6 Blue Pill, Cortex-M3
• Default target: thumbv7m-none-eabi
• Default probe-rs chip name: STM32F103C8
• Default probe: ST-Link v2
• Also supported in docs: Rusty Probe and other probe-rs compatible probes
• Onboard LED: usually PC13, active-low on most Blue Pill boards

See blue-pill.md for wiring notes.

Attached Hardware

• internal LED: PC13
• RGB LED:
  • PA5 = red
  • PA6 = green
  • PA7 = blue
  • PA4 = drive low for the LED return path
• 5-way button board:
  • PB12 = GND, drive low
  • PA10 = VCC, drive high
  • PB13 = right
  • PB14 = down
  • PB15 = left
  • PA8 = center
  • PA9 = up
• HMC5883L module:
  • PB4 = VCC, drive high
  • PB5 = GND, drive low
  • PB6 = SCL
  • PB7 = SDA
  • PB8 = DRDY

Important Target Note

• Blue Pill STM32F103 is Cortex-M3 and uses thumbv7m-none-eabi.
• STM32F0 is Cortex-M0 and uses thumbv6m-none-eabi.
• Do not mix them.
• This repo leaves room for STM32F0 later, but the default path is STM32F103 only.

Repo Layout

• Cargo.toml - workspace root and pinned shared dependencies
• flake.nix - reproducible development shell
• .cargo/config.toml - default target and linker settings
• memory.x - conservative Blue Pill memory map
• justfile - build, flash, run, and lint commands
• examples/README.md - example index

Nix Setup

Use Nix flakes. No global rustup. No global cargo install.

nix develop

The dev shell provides:

• pinned Rust toolchain
• cargo, rustc, rustfmt, clippy
• rust-src
• targets for thumbv7m-none-eabi and thumbv6m-none-eabi
• probe-rs
• flip-link
• cargo-binutils
• just

First Commands

nix develop
just build
just flash-blinky
just run-blinky

If your chip name differs from the default, override it:

PROBE_RS_CHIP=STM32F103C8 just flash-blinky

If you need to inspect available names:

probe-rs chip list | rg STM32F103

Examples

• blinky-basic - plain no_std blink with a simple delay
• blinky-timer - periodic blink driven by a timer abstraction
• button-input - poll the center button on PA8, mirror state on the LED, log transitions
• embassy-blinky - minimal async blink with Embassy
• embassy-button - minimal Embassy polling loop for the center button on PA8

The button examples assume the 5-way board is wired like this:

• PB12 forced low for ground
• PA10 forced high for power
• PA8 used as the center button input
• internal pull-down enabled in firmware
• common ground still required for the probe

ST-Link Setup

Typical SWD wiring:

• SWDIO -> SWDIO
• SWCLK -> SWCLK
• GND -> GND
• 3V3 -> 3V3 reference

Keep BOOT0 low for normal flash-and-run.

Rusty Probe / probe-rs Note

• probe-rs is the primary flash, run, and debug path in this repo.
• Rusty Probe works if the host sees it as a probe-rs compatible probe.
• Start with probe-rs list to confirm the probe is visible.

Memory Note

Many Blue Pill boards have 64K or 128K flash despite markings. This repo uses a conservative 64K flash map in memory.x.

Troubleshooting

Probe not found

• Run probe-rs list.
• Check USB cable and power.
• Check SWDIO, SWCLK, GND, and 3V3.

Linux udev permissions

• You may need udev rules for ST-Link or your probe.
• Install the vendor or distro rules, then replug the probe.

Wrong chip selected

• Run probe-rs chip list | rg STM32F103.
• Override the default with PROBE_RS_CHIP=....

No RTT or defmt output

• Use just run-blinky or just run-embassy-blinky.
• Confirm the firmware did not crash early.
• Confirm the probe stays attached.
• Confirm BOOT0 is low.

Blue Pill LED looks inverted

• That is expected on most boards.
• PC13 is usually active-low, so driving it low turns the LED on.

Safety

• Check board voltage before connecting anything.
• Check SWDIO, SWCLK, GND, and 3V3 wiring before flashing.
• Do not assume a random button or LED pinout without checking the board.

Contribution

• Keep examples independent.
• Keep demo reliability first.
• Keep nix develop, just fmt, just check, and just build working.
• Document hardware assumptions when they matter.
• Do not claim hardware-tested behavior unless it was actually tested on hardware.