CRC Variants

CRC Variant Selection for CRUMBS Protocol (ATmega328P Target).

Variant Flash (bytes) RAM (bytes) Speed (Ξs/kiB) Suitability
crc8_bit ~80 0 7800–18000 Too slow
crc8_nibble ~130 0 5300–7600 Best balance
crc8_nibblem ~130 16 4900–7200 Slightly faster, costs RAM
crc8_byte ~300 0 900–2200 Fastest, wasteful on flash-limited MCUs

Choice: crc8_nibble (use crc8_nibble_calculate() API)
Reason: Optimal tradeoff between flash size, speed, and zero RAM use for AVR-class MCUs (e.g., ATmega328P).
CRC field: 1 byte, calculated over first 31 bytes of message payload.

CRC Code Generation

The CRC generation workflow has been simplified and consolidated into a single script:

  • scripts/generate_crc8.py — generates C99 outputs via pycrc and optionally stages variants into src/crc so the library compiles against a chosen CRC-8 implementation.

What it produces:

  • Generated C99 outputs (per-variant):

    • dist/crc/c99/crc8_<variant>.h
    • dist/crc/c99/crc8_<variant>.c

  • Staged (copied) files (if staging enabled):

    • src/crc/crc8_<variant>.h
    • src/crc/crc8_<variant>.c

Usage examples and notes:

# Generate the default variant (nibble) and stage it into src/crc
python scripts/generate_crc8.py

# Generate nibble+byte variants and *don't* stage them into src/ (writes only to dist/)
python scripts/generate_crc8.py --algos nibble,byte --no-stage

# Generate all variants and stage them (bit,nibble,nibblem,byte)
python scripts/generate_crc8.py --algos bit,nibble,nibblem,byte

By default the script stages nibble (the variant chosen by the project) to keep the repository in a consistent state. The generator is driven by pycrc and produces portable, C99-compatible implementations.

If you previously relied on separate conversion or staging scripts (generate_crc8_c99.py, validate_and_stage_crc8.py, generate_crc8_arduino.py) note that this new script replaces the common C99 generation + staging flow. The Arduino conversion script remains available for specialized Arduino-friendly conversions but is no longer part of the default generation + staging workflow.

Refer to scripts/generate_crc8.py --help for full options and usage.