af79fe6f7f
Verified workflow (not first-principles): host udev rules with uaccess ACL (maps by UID into the toolbox; group access shows nobody:nobody), prebuilt probe-rs in the toolbox, probe-rs run --chip RP235x pm-kit.elf for flash+RTT defmt streaming. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
76 lines
4.1 KiB
Markdown
76 lines
4.1 KiB
Markdown
# Flashing & debugging pm-kit with the Raspberry Pi Debug Probe
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How to flash the Rust RP2350 firmware (`rust/pm-kit`) and watch its `defmt` logs live, from a
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**Fedora Silverblue `toolbox`**. This replaces the BOOTSEL/UF2 drag for development — over SWD you
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get one-command flash + reset + RTT log streaming, and panics print their message and `file:line`.
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Wiring and chip name were verified against the official docs (links at the bottom); don't guess them.
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## 0. Hardware wiring (once)
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- **Probe "D" port → Pico 2 DEBUG connector** with the included 3-pin JST-SH cable
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(SC=SWCLK / SD=SWDIO / GND — connector is keyed). The "U" port is UART, not used here.
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- **Probe USB → computer.** **Pico 2 USB → power** (the probe does SWD only, not power).
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- Connect **GND first** when the target is separately powered.
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- If `probe-rs` can't see the chip later, the **probe's own firmware** may predate the Pico 2 —
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update it: hold BOOTSEL on the *probe*, plug it in (mounts `RPI-RP2`), drag the latest
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`debugprobe.uf2` from github.com/raspberrypi/debugprobe/releases.
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## 1. Host udev rules (once, on the Silverblue HOST — not inside toolbox)
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The host's `udevd` sets the device permissions; the rule's `TAG+="uaccess"` grants *your UID* an
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ACL, which is what maps correctly into the toolbox (group-based access shows as `nobody:nobody`).
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```sh
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sudo curl -L https://probe.rs/files/69-probe-rs.rules -o /etc/udev/rules.d/69-probe-rs.rules
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sudo udevadm control --reload
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sudo udevadm trigger
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# then unplug/replug the probe
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```
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(`/etc` is writable on Silverblue. If your terminal opens inside a toolbox, run these on the host,
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e.g. `flatpak-spawn --host sudo …`.)
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## 2. Install probe-rs in the toolbox (once)
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```sh
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toolbox enter # or: toolbox create probe && toolbox enter probe
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sudo dnf install -y libusb1 # runtime lib the prebuilt binary links against
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curl --proto '=https' --tlsv1.2 -LsSf \
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https://github.com/probe-rs/probe-rs/releases/latest/download/probe-rs-tools-installer.sh | sh
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# follow the installer's PATH note (it lands in ~/.cargo/bin) or restart the shell
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probe-rs --version
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probe-rs list # should show the CMSIS-DAP Debug Probe
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```
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## 3. Flash + watch logs
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```sh
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curl -O https://metronome.varasys.io/pm-kit.elf
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probe-rs run --chip RP235x pm-kit.elf
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```
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`probe-rs run` flashes the ELF, resets, and streams `defmt` over RTT. We ship the **ELF** (not the
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UF2) because defmt decodes its log strings from the ELF's symbol table. The firmware narrates:
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`== pm-kit boot ==` → `display init ok` → `parsed groove 0` → `entering main loop` →
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`alive: …` (~2×/sec). A `panic`/`HardFault` prints its location.
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> Building from source instead of the prebuilt ELF? `.cargo/config.toml` already sets
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> `runner = "probe-rs run --chip RP235x"`, so inside the **pm-rust build image** `cargo run --release`
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> does build+flash+log in one — but that image needs probe-rs + USB passthrough too; the toolbox
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> route above is simpler for just flashing what we ship.
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## Troubleshooting
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- **`No probe was found`** → udev rules not applied (re-plug after step 1), or the device shows
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`nobody:nobody` in the toolbox. Quick unblock without re-plugging:
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`sudo setfacl -m u:$USER:rw $(readlink -f /dev/serial/by-id/*Debug_Probe* 2>/dev/null)` on the host,
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or just run `sudo probe-rs run …` inside the toolbox (it's privileged, so root can open the node).
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- **`chip RP235x not found`** → your probe-rs is too old (RP2350 support landed Feb 2025);
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reinstall. Confirm the exact name with `probe-rs chip list | grep -i rp23`.
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- **Connects but can't halt/flash the core** → update the **probe firmware** (step 0).
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## References
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- Raspberry Pi Debug Probe docs — https://www.raspberrypi.com/documentation/microcontrollers/debug-probe.html
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- probe-rs install — https://probe.rs/docs/getting-started/installation/
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- probe-rs probe setup / udev — https://probe.rs/docs/getting-started/probe-setup/
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- probe-rs RP235x support — https://github.com/probe-rs/probe-rs/issues/2787
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- Toolbox USB ACL gotcha — https://discussion.fedoraproject.org/t/accessing-a-usb-device-in-toolbox-via-udev-rule/127904
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