EmbeddedSpaceWire

Minimal, embedded-optimized implementation of the SpaceWire packet and network layers (ECSS-E-ST-50-12C) carrying the CCSDS Packet Transfer Protocol (ECSS-E-ST-50-53C).

Standards Compliance

• ECSS-E-ST-50-12C Rev.1: SpaceWire — links, nodes, routers and networks
• ECSS-E-ST-50-53C: SpaceWire — CCSDS packet transfer protocol
• ECSS-E-ST-50-51C: SpaceWire — protocol identification (Protocol ID 0x02)
• CCSDS 133.0-B-2: Space Packet Protocol

Features

Core Protocol Implementation

• Network layer: SpaceWire packets and routing — path (0–31) and logical (32–254) addressing with header deletion (ECSS-E-ST-50-12C §5.6)
• CCSDS Packet Transfer Protocol: encapsulation/extraction of CCSDS Space Packets with EOP/EEP receive status (ECSS-E-ST-50-53C)
• CCSDS Integration: built on the EmbeddedSpacePacket library

Scope (hardware boundary)

This is a packet- and network-layer library. The character/signal and data-link levels — character encoding and parity, data-strobe signalling, link initialisation and flow control, and EOP/EEP generation and detection — are provided by the SpaceWire hardware CODEC. EOP/EEP are exchanged with this library as out-of-band metadata, not as bytes within packet buffers.

Design Principles

• Minimal footprint: small static library, no dynamic allocation
• Zero allocation: stack- and caller-owned buffers only
• Embedded-optimized: no external dependencies except EmbeddedSpacePacket
• Portable: pure C99, big-endian network byte order
• Standards-driven: no non-standard framing or checksums on the wire

Project Structure

EmbeddedSpaceWire/
├── include/
│   ├── spacewire.h          # SpaceWire packet + network (routing) layer
│   └── spacewire_packet.h   # CCSDS packet transfer protocol (ECSS-E-ST-50-53C)
├── src/
│   ├── spacewire_frame.c    # SpaceWire packet builder
│   ├── spacewire_router.c   # Routing switch + link state
│   └── spacewire_packet.c   # CCSDS packet transfer protocol
├── external/
│   └── EmbeddedSpacePacket/ # CCSDS Space Packet library (submodule)
├── examples/
│   └── main.c               # End-to-end usage
├── tests/
│   ├── cunit.h              # Tiny C test helpers
│   ├── test_frame.c         # Packet-builder tests
│   ├── test_router.c        # Routing + link tests
│   ├── test_packet.c        # CCSDS PTP tests (+ golden wire vector)
│   └── unit_tests.c         # Test runner
├── tools/
│   └── coverage_html.sh     # HTML coverage generator
├── Makefile
└── README.md

Building

Prerequisites

This repository vendors the CCSDS Space Packet library as a git submodule. After cloning, initialise it:

git submodule update --init --recursive

Build Everything

make all

Build Library Only

make lib
# Produces: build/lib/libspacewire.a (static) and build/lib/libspacewire.so (shared)

Build Example

make example
./build/bin/spacewire_example

Run Tests

make test

Test binary path: build/bin/spacewire_tests.

Coverage (HTML)

make coverage-html

Coverage report is generated at build/coverage/index.html.

Clean

make clean      # Remove build/ artifacts
make distclean  # Deep clean including object files

Quick Start

See examples/main.c.

Memory Usage

• Library code: ~3 KB (.text); no dynamic allocation, all buffers caller-owned
• sw_packet_frame_t: 40 bytes (CCSDS PTP packet state)
• sw_router_t: ~1.4 KB — a 256-entry routing table (3 B/entry) plus per-port link state; set -DSW_NUM_PORTS=n to shrink the per-router footprint

Thread Safety

Packet, routing and link operations work entirely on caller-owned state passed by pointer and take no internal locks, so independent objects can be used from independent tasks. The one shared item is the library's statistics block: sw_packet_encode and sw_packet_decode update a process-global counter (read via sw_get_statistics, cleared via sw_reset_statistics), which is not thread-safe. In a multi-task system, serialise the encode/decode/statistics calls or confine them to a single task.

Limitations and Extensions

The library implements the packet and network layers; the following are out of scope or not yet implemented:

• Character/signal and data-link levels — provided by the SpaceWire hardware CODEC
• Time-codes, broadcast codes and distributed interrupts (ECSS-E-ST-50-12C §5.6)
• Group adaptive routing (one output port per logical address)
• Guaranteed delivery — per ECSS-E-ST-50-53C the service is unconfirmed and incomplete (no acknowledgement, retransmission or QoS)

These can be added as needed for specific mission requirements.

References

• ECSS-E-ST-50-12C Rev.1 — SpaceWire: links, nodes, routers and networks
• ECSS-E-ST-50-53C — SpaceWire: CCSDS packet transfer protocol
• ECSS-E-ST-50-51C — SpaceWire: protocol identification
• CCSDS 133.0-B-2 — Space Packet Protocol
• https://www.spacewire.esa.int — SpaceWire website

License

See LICENSE file.