#run #probe #knurling #backtrace #devices #ones #cargo-runner

no-std app probe-run

Runs embedded programs just like native ones

28 releases

0.3.11 Jan 30, 2024
0.3.10 Aug 1, 2023
0.3.9 May 5, 2023
0.3.7 Mar 29, 2023
0.1.7 Nov 26, 2020

#1901 in Embedded development

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271 downloads per month


2.5K SLoC

Contains (ELF exe/lib, 1.5MB) tests/test_elfs/levels-with-timestamp, (ELF exe/lib, 1MB) tests/test_elfs/hello-raw, (ELF exe/lib, 1MB) tests/test_elfs/hello-rzcobs, (ELF exe/lib, 1.5MB) tests/test_elfs/levels-rzcobs, (ELF exe/lib, 1MB) tests/test_elfs/overflow-no-flip-link, (ELF exe/lib, 1MB) tests/test_elfs/overflow-rzcobs and 2 more.

⚠️ As of 11.10.2023 probe-run is in maintainance mode. We recommend everyone to switch to probe-rs. Read following article on the why and on how to migrate: https://ferrous-systems.com/blog/probe-run-deprecation/


Runs embedded programs just like native ones

probe-run is a custom Cargo runner that transparently runs Rust firmware on an embedded device.

probe-run is powered by probe-rs and thus supports all the devices and probes supported by probe-rs.


  • Acts as a Cargo runner, integrating into cargo run.
  • Displays program output streamed from the device via RTT.
  • Exits the firmware and prints a stack backtrace on hardware breakpoints (e.g. bkpt), Rust panics and unrecoverable hardware exceptions (e.g. HardFault).


To install probe-run, use cargo install probe-run.

On Linux, you might have to install libudev and libusb from your package manager before installing probe-run.

# ubuntu
$ sudo apt install -y libusb-1.0-0-dev libudev-dev

# fedora
$ sudo dnf install -y libusbx-devel systemd-devel

Using the latest probe-rs

probe-run inherits device support from the probe-rs library. If your target chip does not appear in the output of probe-run --list-chips it could be that:

  1. The latest git version probe-rs supports your chip but the latest version on crates.io does not. You could try building probe-run against the latest probe-rs version; see instructions below.
  2. probe-rs does not yet support the device. You'll need to request support in the probe-rs issue tracker.

To build probe-run against the latest git version probe-rs and install it follow these steps:

$ # clone the latest version of probe-run; line below uses version v0.3.3
$ git clone --depth 1 --branch v0.3.3 https://github.com/knurling-rs/probe-run

$ cd probe-run

$ # modify Cargo.toml to use the git version of probe-rs
$ # append these lines to Cargo.toml; command below is UNIX-y
$ cat >> Cargo.toml << STOP
probe-rs = { git = "https://github.com/probe-rs/probe-rs" }

$ # install this patched version
$ cargo install --path .

Note that you may need to modify probe-rs-rtt and/or probe-run itself to get probe-run to compile. As we only support the crates.io version of probe-rs in the unmodified Cargo.toml we cannot provide further assistance in that case.


NOTE for new Cargo projects we recommend starting from app-template

1. Set the Cargo runner

The recommend way to use probe-run is to set as the Cargo runner of your application.

Add these two lines to your Cargo configuration file (.cargo/config.toml) and set the particular --chip value for your target. In this case it is nRF52840_xxAA for the nRF52840:

[target.'cfg(all(target_arch = "arm", target_os = "none"))']
runner = "probe-run --chip nRF52840_xxAA"
#                          ^^^^^^^^^^^^^

To list all supported chips run probe-run --list-chips.

1.1 Env variable

To support multiple devices, or permit overriding default behavior, you may prefer to:

  1. set the ${PROBE_RUN_CHIP} environment variable, and
  2. set runner (or CARGO_TARGET_${TARGET_ARCH}_RUNNER) to probe-run:
[target.'cfg(all(target_arch = "arm", target_os = "none"))']
runner = "probe-run"

1.2 Multiple probes

If you have several probes connected, you can specify which one to use by adding the --probe option to the runner or setting the ${PROBE_RUN_PROBE} environment variable with a value containing either ${VID}:${PID} or ${VID}:${PID}:${SERIAL}:

// --probe
$ probe-run --probe '0483:3748' --chip ${PROBE_RUN_CHIP}

$ PROBE_RUN_PROBE='1366:0101:123456' cargo run

To list all connected probes, run probe-run --list-probes.

2. Enable debug info

Next check that debug info is enabled for all profiles. If you are using the cortex-m-quickstart template then this is already the case. If not check or add these lines to Cargo.toml.

panic-probe = { version = "0.2", features = ["print-rtt"] }

# Cargo.toml
debug = 1 # default is `true`; not needed if not already overridden

debug = 1 # default is `false`; using `true` is also OK as symbols reside on the host, not the target

3. Look out for old dependencies

The cortex-m dependency must be version 0.6.3 or newer. Older versions are not supported. Check your Cargo.lock for old versions. Run cargo update to update the cortex-m dependency if an older one appears in Cargo.lock.

4. Run

You are all set. You can now run your firmware using cargo run. For example,

use cortex_m::asm;
use cortex_m_rt::entry;
use panic_probe as _;
use rtt_target::rprintln;

fn main() -> ! {
    rtt_init_print!(); // You may prefer to initialize another way
    rprintln!("Hello, world!");
    loop { asm::bkpt() }

would output

$ cargo run --bin hello
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s
     Running `probe-run --chip nRF52840_xxAA target/thumbv7em-none-eabihf/debug/hello`
  (HOST) INFO  flashing program (30.22 KiB)
  (HOST) INFO  success!
INFO:hello -- Hello, world!
  (HOST) INFO  exiting because the device halted.
To see the backtrace at the exit point repeat this run with
`probe-run --chip nRF52840_xxAA target/thumbv7em-none-eabihf/debug/hello --force-backtrace`

Stack backtraces

When the device raises a hard fault exception, indicating e.g. a panic or a stack overflow, probe-run will print a backtrace and exit with a non-zero exit code.

This backtrace follows the format of the std backtraces you get from std::panic! but includes <exception entry> lines to indicate where an exception/interrupt occurred.


use cortex_m::asm;
fn main() -> ! {
    // trigger a hard fault exception with the UDF instruction.
    Finished dev [optimized + debuginfo] target(s) in 0.04s
     Running `probe-run --chip nRF52840_xxAA target/thumbv7em-none-eabihf/debug/hard-fault`
  (HOST) INFO  flashing program (30.08 KiB)
  (HOST) INFO  success!
stack backtrace:
   0: HardFaultTrampoline
      <exception entry>
   1: __udf
   2: cortex_m::asm::udf
        at /<...>/cortex-m-0.6.4/src/asm.rs:104
   3: panic::__cortex_m_rt_main
        at src/bin/hard-fault.rs:12
   4: main
        at src/bin/hard-fault.rs:8
   5: ResetTrampoline
        at /<...>3/cortex-m-rt-0.6.13/src/lib.rs:547
   6: Reset
        at /<...>/cortex-m-rt-0.6.13/src/lib.rs:550

If we look at the return code emitted by this cargo run, we'll see that it is non-0:

$ echo $?

⚠️ NOTE when you run your application with probe-run, the HardFault handler (default or user-defined) will NOT be executed.

Backtrace options


The --backtrace flag is optional and can get passed the following values:

  • --backtrace=always - forced backtrace (if you'd like to see a backtrace at the end of successful program run)
  • --backtrace=never - suppresed backtrace
  • --backtrace=auto - default, shows a backtrace if the program panics or the stack overflows

Run it like this (example for a forced backtrace):

$ cargo run --bin hello --backtrace=always


The --backtrace-limit flag is optional and defaults to 50. It is possible to set any number.

--backtrace-limit=0 is accepted and means "no limit".

To show a shortened backtrace showing 5 frames, run:

$ cargo run --bin panic --backtrace-limit=5

Note: if --backtrace=never is set, setting --backtrace-limit has no effect.


"Error: no probe was found."

First, check your hardware:

  • make sure that your development board has an on-board hardware debugger. If it doesn't, you'll need a separate hardware debugger that works with the JTAG or SWD interface. Some boards have a USB micro-B or Type-C connector but only come with bootloader firmware that lets you load new program over USB Mass Storage, instead of having a dedicated on-board JTAG or SWD to USB chip; probe-run cannot be used with these boards.
  • make sure that it is connected to the right port on your development board
  • make sure that you are using a data cable– some cables are built for charging only! When in doubt, try using a different cable.
  • make sure you have the right drivers for the debugger installed (st-link or j-link)

If this doesn't resolve the issue, try the following:

[Linux only] udev rules haven't been set

Check if your device shows up in lsusb:

$ lsusb
Bus 001 Device 008: ID 1366:1015 SEGGER J-Link

If your device shows up like in the example, skip to the next troubleshooting section

If it doesn't show up, you need to give your system permission to access the device as a non-root user so that probe-run can find your device.

In order to grant these permissions, you'll need to add a new set of udev rules.

To learn how to do this for the nRF52840 Development Kit, check out the installation instructions in our embedded training materials.

afterwards, your device should show up in probe-run --list-probes similar to this:

$ probe-run --list-probes
The following devices were found:
[0]: J-Link (J-Link) (VID: 1366, PID: 1015, Serial: <redacted>, JLink)

No external or on-board debugger present

To use probe-run you need a "probe" (also known as "debugger") that sits between your PC and the microcontroller.

Most development boards, especially the bigger ones, have a probe "on-board": If the product description of your board mentions something like a J-Link or ST-Link on-board debugger you're good to go. With these boards, all you need to do is connect your PC to the dev board using a USB cable you are all set to use probe-run!

If this is not the case for your board, check in the datasheet if it exposes exposes SWD or JTAG pins. If they are exposed, you can connect a "stand alone" probe device to the microcontroller and then connect the probe to your PC via USB. Some examples of stand alone probes are: the ST-Link and the J-Link.

Note that this may involve some soldering if your board does not come with a pre-attached header to plug your debugger into.

Error: RTT up channel 0 not found

This may instead present as Error: RTT control block not found in target memory.

Your code, or a library you're using (e.g. RTIC) might be putting your CPU to sleep when idle. You can verify that this is the problem by busy looping instead of sleeping. When using RTIC, this can be achieved by adding an idle handler to your app:

fn idle(_ctx: idle::Context) -> ! {
     loop {}

Assuming you'd like to still sleep in order to save power, you need to configure your microcontroller so that RTT can still be handled even when the CPU is sleeping. How to do this varies between microcontrollers.

On an STM32G0 running RTIC it can be done by amending your init function to set the dmaen bit on RCC.ahbenr. e.g.:

fn init(ctx: init::Context) -> init::LateResources {
     ctx.device.RCC.ahbenr.write(|w| w.dmaen().set_bit());

defmt version mismatch


Follow the instructions in the error message to resolve the mismatch.


If you are hacking around with probe-run, you can disable the version check by setting the PROBE_RUN_IGNORE_VERSION environment variable to true or 1 at runtime.

Developer Information

running your locally modified probe-run

For easier copy-paste-ability, here's an example how to try out your local probe_run modifications.

$ cd probe-run/
$ PROBE_RUN_IGNORE_VERSION=1 cargo run -- --chip nRF52840_xxAA --backtrace-limit=10 hello
  ˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆ                                   ˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆˆ ˆˆˆˆˆ
  environment variables                                        extra flags             binary to be
  (optional)                                                   (optional)              flashed & run

running snapshot tests

To check whether your change has altered probe-run in unexpected ways, please run the snapshot tests in tests before opening a PR if at all possible.

You can do so by connecting a nrf52840 Development Kit and running

$ cargo test -- --ignored

Support Us

probe-run is part of the Knurling project, Ferrous Systems' effort at improving tooling used to develop for embedded systems.

If you think that our work is useful, consider sponsoring it via GitHub Sponsors.


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be licensed as above, without any additional terms or conditions.


~533K SLoC