Jacob Dahl
1888206a4e
* fix(uavcan): count a TX queue block only once the pool provides it LimitedPoolAllocator::allocate() incremented used_blocks_ before asking the underlying allocator, so an allocation the pool could not satisfy still spent quota. Nothing ever hands that block back, because deallocate() only runs for a pointer that was returned, so every queue that asked for memory while the pool was empty stays permanently smaller than its configured limit. The pool is shared between the RX side and one TX queue per interface, so it does empty transiently under load -- a DroneCAN node firmware update is enough. The damage accumulates and is only cleared by restarting the node. * feat(uavcan): report TX queue depth and why frames were dropped `uavcan status` gains, per interface: TX queue peak: 44/84 blocks TX rejected: 80 frames (78 expired, 2 no memory) CanTxQueue already counted rejected frames but tx_queues_ is private and CanIOManager exposed no accessor, so the count was unreachable. It also conflated three causes: a frame handed over with its deadline already passed, a queued frame evicted as expired to make room, and a frame dropped because the queue was at its block limit. Only the last two are memory pressure, and they call for opposite responses, so a single count sends you the wrong way. The peak is what makes the count actionable. The limit is pool_soft / (num_ifaces + 1) + 1, derived from the soft capacity in allocator.hpp, so a peak sitting at the limit says raising that capacity will help and a peak well under it says the frames are ageing out for some other reason and a larger pool will not. Measured on an FMU-v6XRT serving a DroneCAN node firmware update: one node holds 44 of 84 blocks and drops nothing, another pins the limit and drops hundreds. The counts alone did not distinguish those.
The autopilot stack the industry builds on.
About
PX4 is an open-source autopilot stack for drones and unmanned vehicles. It supports multirotors, fixed-wing, VTOL, rovers, and many more experimental platforms from racing quads to industrial survey aircraft. It runs on NuttX, Linux, and macOS. Licensed under BSD 3-Clause.
Why PX4
Modular architecture. PX4 is built around uORB, a DDS-compatible publish/subscribe middleware. Modules are fully parallelized and thread safe. You can build custom configurations and trim what you don't need.
Wide hardware support. PX4 runs on a wide range of autopilot boards and supports an extensive set of sensors, telemetry radios, and actuators through the Pixhawk ecosystem.
Developer friendly. First-class support for MAVLink and DDS / ROS 2 integration. Comprehensive SITL simulation, hardware-in-the-loop testing, and log analysis tools. An active developer community on Discord and the weekly dev call.
Vendor neutral governance. PX4 is hosted under the Dronecode Foundation, part of the Linux Foundation. Business-friendly BSD-3 license. No single vendor controls the roadmap.
Supported Vehicles
 Multicopter |
 Fixed Wing |
 VTOL |
 Rover |
…and many more: helicopters, autogyros, airships, submarines, boats, and other experimental platforms. These frames have basic support but are not part of the regular flight-test program. See the full airframe reference.
Try PX4
Run PX4 in simulation with a single command. No build tools, no dependencies beyond Docker:
docker run --rm -it -p 14550:14550/udp px4io/px4-sitl:latest
Open QGroundControl and fly. See PX4 Simulation Quickstart for more options.
Build from Source
git clone https://github.com/PX4/PX4-Autopilot.git --recursive
cd PX4-Autopilot
make px4_sitl
Note
See the Development Guide for toolchain setup and build options.
Documentation & Resources
| Resource | Description |
|---|---|
| User Guide | Build, configure, and fly with PX4 |
| Developer Guide | Modify the flight stack, add peripherals, port to new hardware |
| Airframe Reference | Full list of supported frames |
| Autopilot Hardware | Compatible flight controllers |
| Release Notes | What's new in each release |
| Contribution Guide | How to contribute to PX4 |
Community
- Weekly Dev Call — open to all developers (Dronecode calendar)
- Discord — Join the Dronecode server
- Discussion Forum — PX4 Discuss
- Maintainers — see
MAINTAINERS.md - Contributor Stats — LFX Insights
Contributing
We welcome contributions of all kinds — bug reports, documentation, new features, and code reviews. Please read the Contribution Guide to get started.
Citation
If you use PX4 in academic work, please cite it. BibTeX:
@software{px4_autopilot,
author = {Meier, Lorenz and {The PX4 Contributors}},
title = {{PX4 Autopilot}},
publisher = {Zenodo},
doi = {10.5281/zenodo.595432},
url = {https://px4.io}
}
The DOI above is a Zenodo concept DOI that always resolves to the latest release. For a version-pinned citation, see the Zenodo record or our CITATION.cff.
Governance
The PX4 Autopilot project is hosted by the Dronecode Foundation, a Linux Foundation Collaborative Project. Dronecode holds all PX4 trademarks and serves as the project's legal guardian, ensuring vendor-neutral stewardship — no single company owns the name or controls the roadmap. The source code is licensed under the BSD 3-Clause license, so you are free to use, modify, and distribute it in your own projects.
