Minimal, embedded-optimized implementation of the CCSDS Space Packet Protocol primary header in C99, targeting small-scale academic missions.
- CCSDS 133.0-B-2 — Space Packet Protocol (Blue Book, June 2020)
- CCSDS 130.3-G-1 — Space Packet Protocols Informational Report (Green Book, April 2023)
The library implements the 6-byte Primary Header exactly as specified. The Packet Data Field (everything that follows the primary header) is treated as an opaque, application-owned byte sequence. Its internal layout — secondary header, user data, any integrity check — is mission-specific and outside the library's scope, consistent with CCSDS §4.1.4.2 ("contents of the Packet Secondary Header shall be specified by the source end user").
- Primary Header serializer / parser — big-endian, bit-exact per CCSDS §4.1.3
- Sequence Flags — wire values match the standard (
UNSEGMENTED = 0b11 = 3) - Version enforcement — always serializes Packet Version Number as
000(§4.1.3.2) - Zero allocation — no dynamic memory inside the library; caller supplies all buffers
- Minimal footprint — single header + single source file, no external dependencies
- Pure C99 — no OS primitives, suitable for bare-metal targets
Primary header (6 bytes):
| Bits | Field | Notes |
|---|---|---|
| 0–2 | Packet Version Number | Always 000 (§4.1.3.2) |
| 3 | Packet Type | 0 = TM (telemetry), 1 = TC (telecommand) |
| 4 | Secondary Header Flag | 1 if Packet Data Field starts with a secondary header |
| 5–15 | APID | 11-bit application process identifier |
| 16–17 | Sequence Flags | See table below |
| 18–31 | Packet Sequence Count | Modulo-16384 per APID (§4.1.3.4.3) |
| 32–47 | Packet Data Length | (Packet Data Field octets) − 1 (§4.1.3.5) |
Sequence Flags wire values (§4.1.3.4.2):
| Value | Meaning |
|---|---|
00 = 0 | Continuation segment |
01 = 1 | First segment |
10 = 2 | Last segment |
11 = 3 | Unsegmented (standalone packet) |
Packet Data Field: Follows the primary header immediately. Contains an optional secondary header and user data (§4.1.4). Structure is entirely mission-defined. The library copies it verbatim on serialization and exposes a pointer into the wire buffer on parsing.
CRC / integrity:
CCSDS SPP defines no checksum at the Space Packet level. If a mission requires data
integrity checking (e.g. CRC-16-CCITT), it should be computed by the application and
appended to the Packet Data Field before calling sp_packet_serialize. See
examples/main.c for a complete example.
EmbeddedSpacePacket/
├── include/
│ └── space_packet.h # Public API and types
├── src/
│ └── space_packet.c # Serializer, parser, helpers
├── examples/
│ └── main.c # Example: build and parse a packet with app-level CRC
├── tests/
│ ├── cunit.h # Minimal unit test framework
│ ├── test_runners.h # Suite runner declarations
│ ├── test_space_packet.c # Space Packet test suite
│ └── unit_tests.c # Test entry point
├── tools/
│ └── coverage_html.sh # gcovr HTML coverage report
├── build/ # Build artifacts (git-ignored)
├── docs/ # CCSDS reference PDFs
├── Makefile
└── README.md
make # library + example + tests
make lib # static library only → build/libspacepacket.a
make example # example binary → build/examples/spacepacket_example
make test# build and run testssudo apt install gcovr
make coverage-html # → build/coverage/index.htmlmake cleanLook at the example/.
| Item | Size |
|---|---|
sp_packet_t struct | ~28 bytes |
| Library code (stripped) | < 1 KB |
| Serialization buffer | 6 + data_len bytes |
| Heap usage | none |
- No fragmentation / reassembly — sequence flag tracking is the application's responsibility
- No thread safety — external locking required in multi-threaded contexts
- Parser does not copy the Packet Data Field; caller must keep the source buffer alive
See LICENSE file.