WaveDrom
Rendering Beautiful Waveforms from Plain Text
Aliaksei Chapyzhenka
Jonah Probell
www.wavedrom.com
Abstract
WaveDrom is a tool for rendering digital timing diagrams, and other technical visualization, as SVG
or PNG images from an intuitive plain text language. It is easy to learn, easy to use, and browser-
based. WaveDrom is free open source software.
http://wavedrom.com/
This paper provides simple and complex examples of code and its resulting graphics. Also provided
are guidelines on integrating WaveDrom into source code, diffing waveforms, parameterizing
waveforms, describing and visualizing constraints, expressing design intent, and generating
assertions.
SNUG 2016
Page 2 WaveDrom: Rendering Beautiful Waveforms from Plain Text
Table of Contents
Introduction ............................................................................................................................................................................... 3
Problems with current practices ....................................................................................................................................... 3
Inspiration .................................................................................................................................................................................. 4
Exchange format (WaveJSON) ............................................................................................................................................ 5
Image rendering ....................................................................................................................................................................... 5
Waveforms in code comments ........................................................................................................................................... 8
Diffing waveforms ................................................................................................................................................................... 9
Parameterization ................................................................................................................................................................... 10
Representing constraints in WaveJSON ....................................................................................................................... 11
Generating assertions .......................................................................................................................................................... 13
Other users ............................................................................................................................................................................... 16
Conclusion ................................................................................................................................................................................ 16
SNUG 2016
Page 3 WaveDrom: Rendering Beautiful Waveforms from Plain Text
Introduction
Digital timing diagrams (“waveforms”) are the type of diagram that best describe how electronic
signals do, or should, behave. Chip designers naturally draw waveforms on whiteboards, and
routinely view waves when debugging simulations. When called upon to write a specification, we
know our word processing options. However, there has never been a simple, widely used tool for
rendering waveforms. That is until now.
WaveDrom is a tool for rendering waveforms as SVG or PNG images.
1
It defines a language that uses
textual symbols, which are easy to create with a keyboard, to represent the types of information
that waveforms present. WaveDrom follows the software development trend of running
applications in browsers for automatic portability across operating systems. The WaveDrom editor
(online and offline version) is WYSIWYG. The effect of changes to text describing waveforms is
immediately rendered, without a compilation step. Furthermore, since WaveDrom waveforms are
described as text, they can be embedded in source code comments, in source control metadata, and
diffed between versions.
WaveDrom was first created by this paper’s author, Aliaksei Chapyzhenka. It is available online, as
desktop application (Windows, Linux, OSX), and open source on github.
2
WaveDrom is well
documented online with a fun interactive tutorial.
3
Others have contributed ideas, and WaveDrom
has been extended for:
● drawing schematic diagrams
● generating register field documentation
● a translator to TikZ for TeX / LaTeX typesetting
4
This paper intends to stimulate ideas for other extensions and other uses.
Problems with current practices
Waveforms are a common, well understood, industry standard way to express hardware behavior.
When done well, they effectively communicate ideas visually, in a readable way.
5
Some readers of this paper draw waveforms as ASCII text. Some draw diagrams manually within a
word processor’s graphics tools. Some copy-paste lines and hexagons in drawing programs. Some
cleverly use cell outlining features in a spreadsheet, and some will even write Verilog with #delay
1
Scalable Vector Graphics (SVG) is a vector-based graphics format recognized by many document editing
programs. Portable Network Graphics (PNG) is a raster graphics format, recognized by many document
editing programs. PNG is comparable to the Joint Photographic Experts Group (JPEG) format.
2
https://github.com/drom/wavedrom
3
http://wavedrom.com/tutorial
4
TikZ is a description format for vector graphics rendered in TeX and LaTeX documents. Describing timing
diagrams in TikZ is not intuitive. See http://www.texample.net/tikz/examples/timing-diagram/.
5
Tufte, Edward. Envisioning Information, 1990, and
Tufte, Edward. The Visual Display of Quantitative Information, 2001.
SNUG 2016
Page 4 WaveDrom: Rendering Beautiful Waveforms from Plain Text
statements, run a simulation with a trace file, and take screenshots of the traces in a waveform
viewer GUI. Various commercial and freeware tools are available for download and installation on
PCs to produce waveforms, but none is widely used.
All such methods have important limitations:
1. Not everyone is a visual artist, especially at work, and especially during routine
work
2. It takes time to make a good drawing
3. Different authors draw with different and inconsistent styles
4. Drawing waveforms directly intermingles presentation and content
5. It is difficult to version control, change control, and compare waveforms
6. Waveforms are not interactive
7. It is difficult to assemble or concatenate multiple waveforms
8. Waveforms are not parameterized
As a result, designers avoid drawing waveforms where they could be helpful. When designers draw
waveforms, they require editors and technical writers to redo the drawings for clarity.
WaveDrom resolves all of these limitations. Furthermore, because WaveDrom uses a textual
language it can serve as a modeling language that computers can parse. Designers at several
companies use WaveDrom descriptions as part of hardware design entry, design capture, or test
case entry. Furthermore, some designers parse simulation traces to generate WaveDrom
waveforms for selected signals.
Inspiration
The concept of using textual (markup) language as a source for diagram rendering engine is not
new. Many domain specific language exist to drive or hint diagram rendering process. There is full
spectrum of language approaches.
One approach is to provide some domain specific computer language that can be utilize standard
computer language processing tools like lexer and parser, and processed than as abstract syntax
tree. For example DOT to describe graphs or PlantUML to describe UML diagrams.
Another approach is to employs the fact that block of monospace font text can have meaningful
alignment that can be understood by the computer program. The ASCII graphics type descriptions
like ditaa or shaape rely on fact of 2D alignment to render sophisticated block diagrams with
desired spacial relationship of it’s parts, and certain color, shape, size effects.
Some of the diagram languages employ standard mark languages (typically XML) to capture
structure and content. For example: CML (Chemical Markup Language) For graphic rendering of the
molecular structure of chemical compounds, or MathML (Mathematical Markup Language) to
describe mathematical notations. JSON is new emerging standard for data object representation
replacing XML in many areas.
SNUG 2016
Page 5 WaveDrom: Rendering Beautiful Waveforms from Plain Text
Exchange format (WaveJSON)
WaveJSON is the compact exchange format used by WaveDrom to render waveforms.
6
It is based on
the JSON language syntax. WaveJSON is an Embedded Domain Specific Language.
7
It uses the
industry-standard JSON format with additional semantics embedded into the JavaScript object
structure syntax.
8
WaveJSON satisfies the following criteria for a useful waveform exchange format:
● Text format
○ Plain text editor can be used
○ Waveform code can be inserted into HDL or software code as comment
○ Code can be inserted into wiki, markdown, literate, or Asciidoctor documents
9
● Machine readable
○ JSON data object notation language
○ Has JSON schema: https://github.com/wavedrom/wavedrom-schema that can be
used for data validation.
● Domain specific language (DSL)
○ Great expressive power within the domain
○ Exhibits minimum redundancy of domain specific knowledge definition
○ Is an extension of a general purpose language (i.e. JavaScript)
● Open Source format and tools
○ WaveDrom : WaveJSON → SVG rendering engine in JavaScript
https://github.com/drom/wavedrom
○ WaveDromEditor : WaveJSON editor for Desktop and Browser
https://github.com/wavedrom/wavedrom.github.io
Image rendering
The first and most natural use for WaveDrom is rendering of images for publishing purposes.
10
Here is a code example:
6
The WaveJSON format specification is at https://github.com/drom/wavedrom/wiki/WaveJSON
7
Mernik, Marjan, Jan Heering, and Anthony M. Sloane. "When and how to develop domain-specific languages."
ACM computing surveys (CSUR) 37.4 (2005): 316-344.
Knuth, Donald Ervin. The texbook. Vol. 1993. Reading, Massachusetts: Addison-Wesley, 1986.
Spinellis, Diomidis. "Notable design patterns for domain-specific languages."Journal of systems and software
56.1 (2001): 91-99.
8
JavaScript Object Notation (JSON) is an open standard format that uses human-readable text to transmit
data objects consisting of attribute–value pairs. More information at http://json.org/.
9
Knuth, Donald E. "Literate programming." CSLI Lecture Notes, Stanford, CA: Center for the Study of Language
and Information (CSLI), 1992 1 (1992).
Asciidoctor diagram extension at https://github.com/asciidoctor/asciidoctor-diagram
10
The online editor is available at http://wavedrom.com/editor.html.
The desktop application is available at https://github.com/wavedrom/wavedrom.github.io/releases.