EmbeddedSDLP

Minimal, embedded-optimized implementation of CCSDS Space Data Link Protocol (SDLP) for TM (Telemetry) and TC (Telecommand) frame handling, following international standards.

Standards Compliance

• CCSDS 132.0-B-3: TM Space Data Link Protocol
• CCSDS 232.0-B-4: TC Space Data Link Protocol

Features

Core Protocol Implementation

• Telemetry (TM) Frame Handling: Create, encode, and decode TM frames
• Telecommand (TC) Frame Handling: Create, encode, and decode TC frames
• Frame Error Control Field (FECF): 2-byte FECF carried verbatim in the wire format; computing/validating the value (e.g. CRC-16) is left to the application
• Configurable: Support for virtual channels, spacecraft IDs, and frame sequence numbers
• TM Secondary Header: Optional Transfer Frame Secondary Header (1–63 data octets) via sdlp_tm_set_secondary_header, signaled by the Secondary Header Flag and parsed automatically on decode
• TM Operational Control Field: Optional 4-octet OCF carried verbatim via sdlp_tm_set_ocf (the caller decides whether to set the OCF Flag); its content, e.g. a CLCW, is mission-specific and left to the application
• TC Frame Types: Type-AD/BD/BC frames via sdlp_tc_set_frame_type, plus Unlock and Set V(R) control-command helpers (sdlp_tc_create_unlock_frame, sdlp_tc_create_set_vr_frame)
• TC Segment Header: Optional MAP-based segmentation support (enabled with SDLP_TC_SEGMENT_HEADER_ENABLED)

Design Principles

• Minimal footprint: Small library size (stripped)
• Zero allocation: Stack-based, no dynamic memory
• Embedded-optimized: Pure C99, no external dependencies
• Portable: Standard C99, big-endian network byte order

Project Structure

EmbeddedSDLP/
├── .github/
│   └── workflows/
│       └── ci.yml       # CI: unit tests, coverage gate, sanitizers
├── include/
│   ├── sdlp_common.h    # Common definitions and error codes
│   ├── sdlp_tm.h        # TM frame definitions
│   └── sdlp_tc.h        # TC frame definitions
├── src/
│   ├── sdlp_tm.c        # TM frame implementation
│   └── sdlp_tc.c        # TC frame implementation
├── examples/
│   ├── example_crc.h    # CRC-16 helper used only by the examples
│   ├── tm_example.c     # TM frame example
│   └── tc_example.c     # TC frame example
├── tests/
│   ├── cunit.h          # Minimal unit-test assertion helpers
│   ├── test_runners.h   # Per-module test runner interface
│   ├── test_tm.c        # TM unit tests
│   ├── test_tc.c        # TC unit tests
│   └── unit_tests.c     # Test entry point (aggregates per-module results)
├── tools/
│   └── coverage_html.sh # Coverage (HTML) report generator
├── Makefile
└── README.md

Building

Warnings are treated as errors (-Werror). The build is checked with both gcc and clang; select the compiler with make CC=clang.

Build Everything

make all

This will create:

• build/libsdlp.a - Static library
• build/bin/tm_example - TM frame example
• build/bin/tc_example - TC frame example
• build/segment_header/tm_example and build/segment_header/tc_example - the same examples built with the optional TC Segment Header (SDLP_TC_SEGMENT_HEADER_ENABLED)

Build Library Only

make lib
# Produces: build/libsdlp.a (static)

Build Examples

make examples   # build only
make example    # build, then run tm_example and tc_example

Run Tests

make test

The unit tests are built and run twice: against the library as make lib builds it, and again with the optional TC Segment Header compiled in (SDLP_TC_SEGMENT_HEADER_ENABLED).

Coverage (HTML)

Requires gcovr installed in your system:

sudo apt install gcovr

Generate coverage report:

make coverage-html

The command fails unless line and branch coverage of src/ are both 100% in each of the two build configurations (without and with the TC Segment Header). It rebuilds the unit tests from scratch with the Makefile's own flags plus coverage instrumentation.

Output report:

build/coverage/index.html

Sanitizers (ASan + UBSan)

make sanitize   # rebuild with ASan + UBSan, run tests and examples, then clean up

The target starts from a clean build and removes build/ again when it finishes, so a coverage report generated earlier is deleted with it.

Clean

make clean      # Remove build artifacts

Quick Start

Look at the examples/

Memory Usage (Estimated)

• Library (stripped): < 5 KB
• Per TM frame buffer: SDLP_TM_PRIMARY_HEADER_SIZE (6) + optional secondary header (≤ 64) + data + optional OCF (4) + 2 bytes FECF
• Per TC frame buffer: SDLP_TC_PRIMARY_HEADER_SIZE (5) + optional segment header (1) + data + 2 bytes FECF
• Maximum data per frame: SDLP_TM_MAX_DATA_SIZE = 1024 bytes (TM); SDLP_TC_MAX_DATA_SIZE = 1017 bytes (TC — the whole frame is capped at 1024 octets per CCSDS 232.0-B-4; one less when the TC segment header is enabled)

Limitations and Extensions

Current implementation focuses on core protocol features:

• No automatic retransmission handling (COP-1 FOP/FARM)
• No flow control or bandwidth management
• No segmentation beyond optional TC segment header
• No SDLS (Space Data Link Security) option
• No TM Only-Idle-Data (OID) frame generation or PN randomization
• TM Transfer Frames are variable length; the mission-fixed frame length must be enforced by the caller
• The 2-octet FECF is always emitted, although both standards make it optional
• The TC Segment Header is a build-time switch for all Virtual Channels, not per Virtual Channel; it changes sdlp_tc_frame_t, so build the library and the application with the same setting
• Decoders do not check the Transfer Frame Version Number
• TM frame counts are kept per Master Channel / Virtual Channel in fixed static state (not thread-safe). At most SDLP_TM_MAX_MASTER_CHANNELS (default 8) Spacecraft IDs are tracked; sdlp_tm_create_frame returns SDLP_ERROR_NO_RESOURCE for one more, and sdlp_tm_reset_frame_counts empties the table

These can be extended as needed for specific mission requirements.

References

• CCSDS 132.0-B-3: TM Space Data Link Protocol
• CCSDS 232.0-B-4: TC Space Data Link Protocol

License

Apache License 2.0 - See LICENSE file for details.