# 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=STM32F103C8`.

## No Firmware Output

- Use `run-04` or `run-08` from `nix develop`.
- Confirm the firmware did not crash early.
- Confirm the probe stays attached.
- Confirm `BOOT0` is low.

## Host Chapter Does Not Run

- Use `run-00`, `run-01`, `run-02`, or `run-03`.
- If you skipped Nix, make sure `rustup toolchain install 1.95.0` and `rustup target add thumbv7m-none-eabi` are done.
- If you skipped Nix, make sure `flip-link` is on your `PATH` for embedded builds.

## 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 `nix develop`, `fmt`, `check`, and the chapter build or run aliases working.
- Document hardware assumptions when they matter.
- Do not claim hardware-tested behavior unless it was actually tested on hardware.