Crate meterbus_wired_datalink 

Wired M-Bus data-link fields and frame codecs.

This crate represents and encodes the wired M-Bus frames exchanged by masters and slaves. Its wire formats and message types follow the link-layer portion of EN 13757-2:2018+A1:2023, which uses the FT1.2 format class defined by the EN 60870-5 series.

The API is suitable for M-Bus masters, meters, bridges, and diagnostic tools. It is no_std and supports encoding without dynamic allocation.

Scope

The crate provides:

• typed control and address fields;
• ACK and NACK acknowledgement frames;
• fixed-length short frames;
• variable-format control frames without user data; and
• variable-format long frames containing user data.

Constructors and decoders validate each frame’s structure, checksum, and supported control-field use. Address values remain representable even when they are reserved or inappropriate for a particular exchange; callers can inspect Address::kind and Address::expects_response when applying protocol rules.

This crate does not implement:

• the wired electrical interface or UART configuration;
• byte timing, collision handling, retries, or response timeouts;
• master or slave state machines;
• application-layer interpretation of the control-information byte or user data.

Those concerns belong to the surrounding physical, transport, and application layers. In particular, application data carried by a LongFrame is specified separately by EN 13757-3.

Choosing a frame

Type	Wire form	Typical role
AckFrame	One byte, 0xe5	Positively acknowledge an accepted request
NackFrame	One byte, 0xa2	Reject an unsupported SND-UD2 request
ShortFrame	Five-byte fixed format	Send SND-NKE, REQ-UD1, or REQ-UD2
ControlFrame	Nine-byte variable format with no user data	Carry control and control-information fields without an application payload
LongFrame	Variable format with 1 to 252 user-data bytes	Send or respond with application data

A frame constructor rejects a Control value that is incompatible with that frame format. CommunicationType identifies the supported communication type represented by a raw control field.

Encoding and decoding

Every decode function consumes a slice containing exactly one complete frame. It rejects truncated input, trailing bytes, invalid delimiters, invalid lengths, checksum mismatches, and incompatible control fields as applicable to that frame type. decoder::stream identifies boundaries across arbitrary chunks and can recover from noise without allocation.

Every frame provides encode_into, which writes into a caller-owned buffer and returns only the initialized portion. When the alloc feature is enabled, frames also provide encode, which returns an allocated Vec.

Example

The following constructs the standard five-byte shape of a REQ-UD2 request for slave address 1, encodes it without allocation, and decodes it again:

use meterbus_wired_datalink::{Address, Control, ShortFrame};

let request = ShortFrame::new(Control::req_ud2(false), Address::new(1))?;
let mut storage = [0_u8; ShortFrame::LEN];
let encoded = request.encode_into(&mut storage)?;

assert_eq!(encoded, [0x10, 0x5b, 0x01, 0x5c, 0x16]);
assert_eq!(ShortFrame::decode(encoded)?, request);

Allocation and crate features

The crate itself always uses #![no_std].

• the default feature set is allocation-free;
• alloc adds allocating encode methods and the collecting decoder::stream::StreamDecoder::push convenience method.

Without alloc, encode with encode_into and stream with push_into.

A valid frame is not necessarily the right frame for the current exchange. Callers must still manage message order, timing, retries, and application data according to EN 13757-2 and EN 13757-3.

Modules

decoder

Frame decoders.

Structs

AckFrame

A positive acknowledgement frame.

Address

A data-link address.

Control

A data-link control field.

ControlFrame

A variable-format frame without user data.

FrameEncodeError

Error returned when a buffer cannot hold an encoded Frame.

LongFrame

A variable-format frame containing user data.

NackFrame

A negative acknowledgement frame.

ShortFrame

A fixed-length short frame.

Enums

AckFrameError

Error produced while encoding or decoding an acknowledgement frame.

AddressKind

The protocol-defined use of a data-link address.

CommunicationType

A supported wired M-Bus communication type.

ControlError

Error produced when a control field is incompatible with a frame.

ControlFrameError

Error produced while constructing, encoding, or decoding a control frame.

Direction

Direction of a supported data-link communication.

Frame

Any supported wired M-Bus frame.

FrameKind

The wire format represented by a Frame.

LongFrameError

Error produced while constructing, encoding, or decoding a long frame.

NackFrameError

Error produced while encoding or decoding a negative acknowledgement frame.

ShortFrameError

Error produced while constructing, encoding, or decoding a short frame.