EmbeddedSpacePacket

Minimal, embedded-optimized implementation of the CCSDS Space Packet Protocol primary header in C99, targeting small-scale academic missions.

Standards Alignment

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”).

Features

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

Protocol Notes

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.

Project Structure

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

Building

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 tests

Coverage (requires `gcovr`)

sudo apt install gcovr
make coverage-html   # → build/coverage/index.html

Clean

make clean

Quick Start

Look at the example/.

Memory Footprint (estimated, 64-bit host)

Item	Size
`sp_packet_t` struct	~28 bytes
Library code (stripped)	< 1 KB
Serialization buffer	6 + `data_len` bytes
Heap usage	none

Limitations

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

References

License

See LICENSE file.