EmbeddedCUCTime

A minimal, embedded-friendly C library implementing the CCSDS Unsegmented Time Code (CUC) — a pure binary count of seconds and binary fractions of a second from a defined epoch.

The library is deliberately small and dependency-free (only <stdint.h>, <stddef.h>, <stdbool.h>), uses caller-supplied buffers (no heap), and keeps its core encode/decode path integer-only so it fits comfortably on microcontrollers.

Standards Compliance

• CCSDS 301.0-B-4 — Time Code Formats, Section 3.2 (CCSDS Unsegmented Time Code). See docs/ccsds_cuc.md for a field-by-field summary.

Features

• Encode/decode the P-field (1 or 2 octets) and T-field separately, or as a combined self-identified code.
• Full format range: 1–7 basic (second) octets, 0–10 fractional octets.
• Both CCSDS 1958 TAI epoch (Level 1) and agency-defined epoch (Level 2).
• Format-independent time value (cuc_time_t) using a Q0.64 binary fraction.
• Optional double conversion helpers, removable with -DCUC_NO_FLOAT.
• Explicit, checked error codes; no dynamic allocation.

Project Structure

EmbeddedCUCTime/
├── include/
│ └── cuc.h # Public API
├── src/
│ └── cuc.c # Implementation
├── examples/
│ └── cuc_example.c # Encode/decode demo
├── tests/
│ ├── cunit.h # Minimal test framework
│ └── unit_tests.c # Unit tests
├── docs/
│ └── ccsds_cuc.md # CUC format reference notes
├── tools/
│ └── coverage-html.sh # Coverage report helper
├── Makefile
└── README.md

Building

Build everything

make # static library, example and test binaries in build/

Build the library only

make lib # produces build/libcuc.a

Build and run the example

make example
./build/examples/cuc_example

Run the tests

make run # or: make ctest && ./build/tests/ctest

Coverage (HTML)

Requires gcovr (pip install gcovr):

make coverage-html # writes build/coverage/index.html

Clean

make clean

Quick Start

See the examples.

Memory Usage

• No heap usage: all buffers are caller-supplied.
• Largest CUC code: CUC_OCTETS_MAX = 19 octets (2 P-field + 17 T-field).
• State: cuc_time_t and cuc_format_t are small plain structs.

Notes and Limitations

• CUC is not UTC-based; leap-second corrections do not apply (use CDS/CCS for UTC-based time — not yet implemented here).
• The fractional value is stored to 64 bits (Q0.64). Encodings that request more than 8 fractional octets carry those extra low octets as zero.
• Integer seconds fit in uint64_t; a field configured for fewer octets rolls over modulo 256 per octet, exactly as the standard specifies.
• This library implements the CUC format only. CDS, CCS and ASCII time codes from CCSDS 301.0-B-4 are out of scope for this initial version.

References

• CCSDS 301.0-B-4, Time Code Formats, Blue Book, Issue 4, November 2010.

License

See the LICENSE file.