Documentation

An Ember+ primer

What Ember+ is, the shape of its data, and how emberviewer maps onto it. No prior experience required.

What is Ember+?

Ember+ is an open control protocol from Lawo, widely used in broadcast and pro-audio gear to expose and control device parameters over the network. A device (or software) that publishes controllable data is a provider; a tool that connects to it - like emberviewer - is a consumer.

Under the hood it is three nested layers over a single TCP connection (default port 9000):

TCP  →  S101 frames  →  BER (TLV)  →  Glow tree

• S101 is the framing layer: packet boundaries, byte escaping, a CRC-16 checksum, and keep-alive.
• BER (the ASN.1 Basic Encoding Rules) encodes each message as nested tag/length/value bytes.
• Glow is the Ember+ schema carried inside that BER: the actual tree of nodes, parameters, matrices and functions.

emberviewer implements all three from scratch in Rust (the ember-proto and ember-net crates), so there is nothing closed in the stack.

The provider tree

A provider exposes its data as a tree. Every element sits at a numeric path such as 0.1.3 (encoded on the wire as a RELATIVE-OID). The element types you'll meet:

Node

A branch in the tree - a container that groups other elements. Has an identifier and an optional description.

Parameter

A single value: integer, real, string, boolean or enumeration. May be read-only or read/write, and can carry min/max, units, an enum map and more.

Matrix

A routing grid of sources × targets. Connections (crosspoints) are made by tying a target to one or more sources.

Function

A callable operation with typed arguments and results - invoke it to make the provider do something and return a value.

Stream

A high-rate value channel, typically used for audio meters and other live telemetry.

A small tree, as emberviewer shows it:

How emberviewer talks to a provider

Three operations cover almost everything emberviewer does:

getDirectory - browse

You never download the whole tree at once. emberviewer sends a getDirectory request for the children of a node, and the provider replies with that node's immediate children. Expanding a branch in the UI issues another getDirectory for it - this is the "lazy" browsing you see in the tree.

set - control

To change a writable parameter, emberviewer sends a set with the new value at that parameter's path. Booleans get dedicated set and pulse controls; other types are edited inline. The provider applies the change and reports the result back.

subscribe - watch live

Rather than polling, a consumer subscribes to a parameter and the provider pushes updates whenever the value changes. emberviewer subscribes to what you're viewing so the value column stays live, and records changes in the change log.

Mapping at a glance

• Address book entry → a provider's host + port.
• Tree row → a Glow node, parameter, matrix or function at a numeric path.
• Expanding a branch → a getDirectory for that node's children.
• Editing a value / toggling a crosspoint → a set.
• The live value column & change log → active subscribes.
• "Invoke" on a function → an Ember+ function invocation with its arguments.

Where to go next

• Lawo's reference implementation and spec discussion: github.com/Lawo/ember-plus.
• Try emberviewer against the bundled test provider - see Getting started.

← Back to home