PyARINC429

PyARINC429 is a maintained fork of the original work by Jason Hodge.
It provides Python types for encoding and decoding ARINC 429 words:

• BCD
• BNR
• Discrete
• Mixed fields
• Bit‑field extraction and validation
• Parity computation
• Label bit‑reversal
• Optional label metadata
• A fluent WordBuilder

The library targets Python 3.12 and uses type annotations.

Installation

git clone https://github.com/yourusername/PyARINC429
cd PyARINC429
pip install .

Tests:

pip install .[test]
pytest

Package structure

arinc429/
    word.py
    bitfields.py
    errors.py
    builder.py
    definitions.py
    datatypes/
        base.py
        bcd.py
        bnr.py
        discrete.py

Word

Represents a 32‑bit ARINC 429 word.

Properties

• label — octal label (0o000–0o377), bit‑reversed on write
• sdi — 2‑bit SDI
• data — bits 11–29 (19 bits)
• ssm — 2‑bit SSM
• parity — stored parity bit
• parity_type — ODD_PARITY or EVEN_PARITY
• parity_ok — computed parity check
• raw — underlying integer

Methods

• get_bit_field(lsb, msb)
• set_bit_field(lsb, msb, value)
• from_int(value, parity_type)
• to_int()
• copy()
• with_fields(label=…, sdi=…, data=…, ssm=…)
• as_dict()
• validate(raise_on_error=False)

Bit‑field rules

• All bitfields use signed two’s‑complement range checks.
• Overflow raises FieldOverflowError.
• Parity is recomputed after every write.

Data‑field integer semantics

int(BNR|BCD|Discrete) returns the encoded on‑wire integer.
float(...), str(...), and .decoded return the semantic value.

WordBuilder

Fluent builder for constructing words.

from arinc429.builder import WordBuilder

w = (
    WordBuilder()
    .label(0o123)
    .sdi(1)
    .data(0x55AA)
    .ssm(2)
    .parity_type(Word.EVEN_PARITY)
    .build()
)

Builder rules

• Unknown private attributes (e.g., b._unexpected = 1) raise ValueError.
• FieldOverflowError propagates.
• Other exceptions are wrapped in ValueError.

BCD

BCD(value, resolution)

Attributes:

• decoded
• encoded
• resolution
• sign

Methods:

• decode(bcd_value, ssm, resolution)
• copy()
• with_resolution(r)
• as_dict()

BNR

BNR(value, resolution)

Attributes:

• decoded
• encoded
• resolution

Methods:

• decode(value, bit_length, resolution)
• copy()
• with_resolution(r)
• as_dict()

Discrete

Discrete(value)

Attributes:

• decoded
• encoded

Methods:

• decode(value)
• copy()
• as_dict()

definitions

Metadata for optional label‑based decoding.

LabelDefinition(name, type, resolution, unit=None)
EQUIP_ADC
EQUIP_IRS

Helper:

decode_word(word, definitions) -> (data_field, definition) | None

ARINC615 Packetizer

• Splits a byte stream into ARINC 429 words.
• SOF carries payload length.
• DATA words carry 2 bytes each.
• EOF always has data field = 0.
• Padding is removed on decode.

WilliamsburgTransmitter / WilliamsburgReceiver

Simple SOF/DATA/EOF framing.

Rules:

• Unexpected label aborts the frame.
• EOF after abort returns None.
• Padding trimmed using SOF length.

Example:

from arinc429 import WilliamsburgTransmitter, WilliamsburgReceiver

tx = WilliamsburgTransmitter()
words = tx.encode(b"HELLO")

rx = WilliamsburgReceiver()
out = None
for w in words:
    r = rx.process_word(w)
    if r is not None:
        out = r

assert out == b"HELLO"

Decoding with metadata

from arinc429 import Word
from arinc429.definitions import EQUIP_ADC, decode_word

w = Word()
w.label = 0o203
decoded = decode_word(w, EQUIP_ADC)

Validation

w = Word()
errors = w.validate(raise_on_error=False)
if errors:
    print(errors)