Regulated DSDL definitions

This repository contains definitions of the regulated Cyphal data types. Cyphal is an open technology for real-time intravehicular distributed computing and communication based on modern networking standards.

Contributors must obey the guidelines defined in this document. Feedback and proposals are welcome on the Cyphal forum.

A web-based DSDL compiler is available at nunaweb.opencyphal.org.

Namespaces

Regulated data types include the standard data types and domain-specific public definitions.

Per the specification, standard data types are contained in the root namespace uavcan, and domain-specific public regulated definitions are in the root namespace reg. The latter contains nested namespaces named after the domain.

Vendors are encouraged to define interfaces to their products or systems using the definitions available in this repository instead of defining custom types in order to facilitate reusability and reduce the fragmentation of the ecosystem.

If a fixed regulated port-ID is needed for a new type, developers are free to choose any unoccupied identifier from the ranges defined by the specification before submitting the pull request.

Identifier ranges

Refer to the specification for background information and motivation. The limits specified here are inclusive.

The upper part of the non-standard ranges may be repurposed for standard types shall that become necessary, so new non-standard regulated fixed port-ID allocations should be done near the bottom. Likewise, the non-standard ranges may be expanded into the unregulated area if their exhaustion becomes imminent.

Subjects

From	To	Purpose
0	6143	Unregulated identifiers
6144	7167	Non-standard regulated identifiers (namespace reg)
7168	8191	Standard regulated identifiers (namespace uavcan)

Services

From	To	Purpose
0	255	Unregulated identifiers
256	383	Non-standard regulated identifiers (namespace reg)
384	511	Standard regulated identifiers (namespace uavcan)

Standard data types

The standard data types are contained in the root namespace uavcan.

Standard fixed identifier allocation

Subjects

Ordered by priority from high to low.

Namespace	Lower bound (inclusive)
uavcan.time	7168
uavcan.node	7509
uavcan.pnp	8164
uavcan.internet	8174
uavcan.diagnostic	8184

The value 7509 contains the longest possible sequence of alternating bits, which can be leveraged for automatic bit rate detection (depending on the physical layer).

Services

Ordered by priority from high to low.

Namespace	Lower bound (inclusive)
uavcan.register	384
uavcan.pnp	390
uavcan.file	400
uavcan.node	430
uavcan.internet	500
uavcan.time	510

Generic data type definitions

SI

The namespace uavcan.si contains a collection of generic data types describing commonly used physical quantities. The namespace uavcan.si.unit contains basic units that can be used as type-safe wrappers over native float32 and other scalar and array types. The namespace uavcan.si.sample contains time-stamped versions of these.

All units follow the International System of Units. All units are unscaled basic units of measure -- meters rather than kilometers, kilograms rather than milligrams.

All coordinate systems are right-handed. In relation to body, the preferred standard is as follows: X -- forward, Y -- right, Z -- down. In case of cameras, the following convention should be preferred: Z -- forward, X -- right, Y -- down. For world frames, the North-East-Down (NED) notation should be preferred.

Primitives

A collection of primitive data types is intended as a very generic solution for odd use cases and prototyping. They permit the user to broadcast a completely arbitrary value via the bus while not having to deal with custom data type design and distribution.

Since these types lack any semantic information, their usage in production environments is discouraged.

Another important application of these types is in the schemaless register protocol defined in the namespace uavcan.register.

Registers

The register protocol provides a highly generic interface to vendor-specific functionality and configuration parameters via named registers.

Non-standard data types

Non-standard regulated data types are contained in the root namespace reg. The root namespace contains nested namespaces, one per application domain, named after the domain.

Note for authors of unregulated data type definitions: the Cyphal specification explicitly bans namespaces that share the same name but differ in their contents. Users seeking to define unregulated data types shall not put those into the regulated namespace; instead, a new root namespace (named after the vendor) shall be used.

Guidelines for data type authors

Follow the interface design guidelines provided in The Cyphal Guide.

Every data type definition should have a header comment. Every field should be followed by a comment, unless it is certain that it is completely self-explanatory. An exception is made for trivial definitions where the comment would not add useful information.

When using void fields for alignment, insert them after the alignee. For example, bool foo followed by void7 is the recommended sequence; the opposite is to be avoided. To understand the motivation, read the DSDL serialization specification.

Attributes shall be separated by exactly one blank line, excepting tightly related attributes and void fields used for post-alignment (e.g., after bit fields), in which case blank lines are not necessary. More than one blank line is never allowed. There shall be exactly one blank line at the end of the file.

The lines of text should not be longer than 120 characters.

Here is an example:

# This is a header comment.
# It explains what this data type definition is for and why do we need it.

void48  # This space is reserved for future use.

uint8 VALUE_A = 1       # A comment describing the constant.
uint8 VALUE_B = 2       # Another one. Constants go before the field they relate to.
uint8 value
# This is an enumeration.
# We don't need blank lines because the items are tightly related.

float32[<100] aligned_array
# This is a new field, mind the blank line above.

Remember, the set of standard data types is an important part of the protocol specification, so the quality of the documentation is very important.

IDE setup

For editing DSDL definitions, we recommend Visual Studio Code. See .vscode/ for recommended extensions and workspace settings.