Ethos Lua Docs¶

Lua scripting for FrSky Ethos radios: the complete API reference with examples, practical guides, and the RAM and CPU habits that keep scripts fast on real hardware.

Getting started

Write, install and run your first widget in ten minutes, then learn how widgets, tools, tasks and sources fit together.

First widget
API reference

Every function, object and constant, one page each. Each page has its parameters, return values, examples and real code from open-source projects.

Browse the API
Best practice

Radios have a few hundred KB of Lua heap and a fixed instruction budget per cycle. These patterns come from measurements on real radios.

Saving RAM
Cookbook

Complete, commented scripts you can copy: telemetry widgets, alert tasks, system tools, Lua sources. Plus every official FrSky example.

Recipes
VS Code template

A ready-made project: press ▶ to deploy to the simulator or a USB radio, stream print() output, translate, and publish release zips from a git tag.

Project template
AI agents

Let Claude Code (or another agent) boot a simulated radio, deploy your script, take screenshots and check its own work with ethos-tools.

Agent setup

scripts/hello/main.lua
local function create()
  return { source = system.getSource("RSSI"), last = nil }  -- (1)!
end

local function wakeup(widget)
  local v = widget.source and widget.source:value()
  if v ~= widget.last then          -- only redraw when something changed (2)
    widget.last = v
    lcd.invalidate()
  end
end

local function paint(widget)
  local w, h = lcd.getWindowSize()
  lcd.font(FONT_L)
  lcd.drawText(w / 2, h / 2 - 10, widget.last and tostring(widget.last) or "--", CENTERED)
end

local function init()
  system.registerWidget({ key = "hello", name = "Hello RSSI", create = create, wakeup = wakeup, paint = paint })
end

return { init = init }

create() runs once when the widget is placed on a screen. Look up sources here, never in paint().
wakeup() runs many times a second; paint() only runs after lcd.invalidate(). Checking for a change before invalidating is the most important performance habit in Ethos Lua. See Saving CPU.

Where this documentation comes from¶

Part	Source	Refreshed
API reference	FrSky's `lua-doc.zip` (Doxygen output from the Ethos firmware), parsed into one page per function	By the scheduled update workflow, see Updating
Official examples	ETHOS-Feedback-Community/lua/examples	Same workflow
Real-world usage on API pages	Public open-source Ethos Lua projects, see Real-world usage	Same workflow
Guides, best practice, cookbook	Written for this site, with RAM figures taken from on-radio measurements	By hand

Check the version

Every API page shows the Ethos version that introduced the call (for example since 1.5.0). Calls added in the newest release are highlighted. To support older radios, check before calling: if lcd.setWindowTitle then ... end.

Ethos Lua Docs¶

A whole widget in 20 lines¶

Where this documentation comes from¶