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Generating Packets

The spac-generate command creates valid CCSDS packets for testing parsers, data pipelines, and ground software.

Basic Usage

Generate all packets:

spac-generate --output test.bin

Generate specific APIDs:

spac-generate --output test.bin --apid 100 200

Generate by module:

spac-generate --output test.bin --module europa_clipper.ecm

Command-Line Options

Required:

-o FILE, --output FILE
Output file path

Optional:

-a APID [APID ...], --apid APID [APID ...]
Generate specific APID(s) only
-m MODULE [MODULE ...], --module MODULE [MODULE ...]
Generate specific module(s). Can specify full module path (europa_clipper.ecm) or specific packet (europa_clipper.ecm.fg1_low). The ccsds.packets prefix is optional.
-n COUNT, --count COUNT
Number of packets per definition (default: 1)
-z, --zeros
Generate zero-initialized data instead of random

Examples

Multiple packets with zeros:

spac-generate --output test.bin --apid 100 200 --count 10 --zeros

Specific packet by module:

spac-generate --output test.bin --module europa_clipper.ecm.fg1_low

List available packets:

spac-ls

Output Statistics

The generator provides file statistics:

Generating packets to: test.bin
  Generated 1 packet(s) for APID 100 (SensorPacket)

Success! Generated packets written to test.bin
  2,048 bytes, entropy: 7.98 bits/byte (99.8%), chi-squared: p=0.54 (uniform)
  • Entropy: 0.0 (all same byte) to 8.0 (perfectly random)
  • Chi-squared p-value: > 0.05 suggests uniform distribution

Python API

Basic generation:

import ccsdspy
from spac_kit.generator import PacketGenerator

# Define packet structure
fields = [
    ccsdspy.PacketField(name="status", data_type="uint", bit_length=8),
    ccsdspy.PacketField(name="temperature", data_type="float", bit_length=32),
]
packet_def = ccsdspy.VariableLength(fields, apid=100, name="SensorPacket")

# Generate packets
generator = PacketGenerator(packet_def)
with open("packets.bin", "wb") as f:
    generator.write_packet(f, count=5, use_random=True)

Generate with plugin packets:

from spac_kit.generator import PacketGenerator
from spac_kit.parser.util import import_ccsds_packet_packages

# Load all packet definitions from plugins
packets = import_ccsds_packet_packages()

# Generate for specific APID
packet_info = next(p for p in packets if p["packet"].apid == 100)
generator = PacketGenerator(packet_info["packet"])

with open("output.bin", "wb") as f:
    generator.write_packet(f, count=10, use_random=False)  # zeros

Test fixture example:

import pytest
from io import BytesIO
from spac_kit.generator import PacketGenerator

@pytest.fixture
def test_packet_data():
    """Generate test CCSDS packets."""
    buf = BytesIO()
    generator = PacketGenerator(my_packet_def)
    generator.write_packet(buf, count=5, use_random=False)
    return buf.getvalue()