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Struct Frame

Advanced Features

This page covers advanced scenarios for special use cases.

Package IDs for Extended Addressing

Package IDs enable 16-bit message addressing for large systems.

When to use:

  • Systems with more than 255 messages
  • Multi-package systems requiring namespace separation

Frame compatibility: Use Extended or ExtendedMultiSystemStream payload types with package IDs.

Message ID encoding:

  • Without pkgid: 8-bit (0-255)
  • With pkgid: 16-bit = (package_id << 8) | msg_id

See Message Definitions for usage details.

Minimal Frames (Bandwidth-Limited Scenarios)

Minimal frames remove length and checksum fields for lowest overhead.

Requirements:

  • All messages must be fixed-size (no max_size, only size)
  • Parser needs message length lookup function

The generator creates a get_msg_info function automatically:

from struct_frame.frame_profiles import get_profile, Profile
from messages import get_msg_info


# Get minimal profile
profile = get_profile(Profile.SENSOR)  # TinyMinimal


# Parser uses auto-generated get_msg_info
parser = profile.create_parser(get_msg_info)
 
#include "FrameProfiles.hpp"
#include "messages.structframe.hpp"


// Use sensor profile with minimal frames
ProfileSensorAccumulatingReader reader(get_msg_info);

See Framing for more on minimal frames.

Large Messages

For messages > 255 bytes, use Extended payload type:

Terminal window
python -m struct_frame large.proto --build_c

Use BasicExtended or Network frame profile when encoding.

Variable-Length Encoding

Use option variable = true; for efficient encoding of messages with variable-length arrays or strings:

message LogEntry {
  option msgid = 10;
  option variable = true;
  uint64 timestamp = 1;
  string message = 2 [max_size=256];
  repeated uint8 data = 3 [max_size=128];
}

Only used bytes are transmitted instead of full max_size. See Message Definitions for details.