WaveDrom

WaveDrom takes a list of signals, each with a wave string, and draws a timing diagram. Characters in the wave string mean clock edges, held values, transitions and don't-care periods.

It also draws register field diagrams, which is a useful second job.

#What it is good at

• Hardware and protocol timing documentation.

• Firmware notes comparing expected and observed behaviour.

• Register layouts, using its reg mode.

#What it draws

#A worked example

An I2C-style transfer with a gap in the middle:

The source, which you can paste into a new diagram and edit:

{ "signal": [
  { "name": "clk",   "wave": "p......|..." },
  { "name": "start", "wave": "01.....|0.." },
  { "name": "addr",  "wave": "x2.....|x..", "data": ["0x3C"] },
  { "name": "rw",    "wave": "x0.....|x.." },
  { "name": "ack",   "wave": "x.0....|x.." },
  { "name": "data",  "wave": "x...345|6..", "data": ["d0","d1","d2","dn"] }
]}

#A few things that catch people out

• The wave string is per character, so all signals must be the same length to line up.

• p is a positive-edge clock, n a negative one; . holds the previous value.

• Use x for don't-care; a flat 0 claims the line is actually low.

#Related

Thirty-one languages. Nobody knows them all.