Cyphal/UDP transport in C

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LibUDPard is a robust implementation of the Cyphal/UDP transport layer in C99/C11 for high-integrity real-time systems.

Cyphal is an open technology for real-time intravehicular distributed computing and communication based on modern networking standards (Ethernet, CAN FD, etc.). It was created to address the challenge of on-board deterministic computing and data distribution in next-generation intelligent vehicles: manned and unmanned aircraft, spacecraft, robots, and cars.

Features

• Zero-copy RX pipeline -- payload is moved from the NIC driver all the way to the application without copying.
• ≤1-copy TX pipeline with deduplication across multiple interfaces and scattered input buffer support.
• Support for redundant network interfaces with seamless interface aggregation and zero fail-over delay.
• Robust message reassembler supporting highly distorted datagram streams: out-of-order fragments, message ordering recovery, fragment/message deduplication, interleaving, variable MTU, ...
• Robust message ordering recovery for ordering-sensitive applications (e.g., state estimators, control loops) with well-defined deterministic recovery in the event of lost messages.
• Packet loss mitigation via:
  • reliable topics (retransmit until acknowledged; callback notifications for successful/failed deliveries).
  • redundant interfaces (packet lost on one interface may be received on another, transparent to the application);
• Heap not required (but supported); the library can be used with fixed-size block pool allocators.
• Detailed time complexity and memory requirement models for the benefit of real-time high-integrity applications.
• Highly scalable: designed to handle thousands of topics and hundreds of concurrent transfers with minimal resources.
• Runs anywhere out of the box, including extremely resource-constrained baremetal environments with ~100K ROM/RAM. No porting required.
• Partial MISRA C compliance (reach out to https://forum.opencyphal.org).
• Full implementation in a single C file with only 2k lines of straightforward C99!
• Extensive verification suite.

Usage

An application using this library will need to provide a third-party UDP/IP stack with multicast/IGMP support (TCP not needed). In the most straightforward case, the network layer can be based on the standard Berkeley socket API or a lightweight embedded stack such as LwIP.

%%{init: {"fontFamily": "Ubuntu Mono, monospace", "flowchart": {"curve": "basis"}}}%%
flowchart TD
    classDef OpenCyphal color:#00DAC6,fill:#1700b3,stroke:#00DAC6,stroke-width:2px,font-weight:600
    Application <-->|messages| LibUDPard[fa:fa-code LibUDPard]
    class LibUDPard OpenCyphal
    LibUDPard <-->|datagrams| UDP
    subgraph domain_udpip["3rd-party UDP/IP+IGMP stack"]
        UDP <--> IP["IPv4, IGMPv1+"] <--> MAC
    end
    MAC <--> PHY

Loading

To integrate the library into your application, simply copy udpard.c and udpard.h from libudpard/ into your project tree, or add this entire repository as a submodule; also ensure you have cavl2.h somewhere in your include paths.

The library contains only one translation unit named udpard.c; no special compiler options are needed to build it. The library should be compatible out of the box with all conventional computer architectures where a standards-compliant C99 compiler is available.

Read the API docs in libudpard/udpard.h.

Revisions

v3.0 -- WORK IN PROGRESS

The library has been redesigned from scratch to support Cyphal v1.1, named topics, and reliable transfers. No porting guide is provided since the changes are too significant; please refer to the new API docs in libudpard/udpard.h.

v2.0

• Updating from LibUDPard v1 to v2 involves several significant changes to improve memory management and payload handling.
• Please follow MIGRATION_v1.x_to_v2.0.md guide (available in v2 tree).

v1.0

Initial release.