Lua Scripting Interface


MAME provides Lua script bindings for a useful set of core functionality. This feature first appeared in version 0.148, when a minimal Lua interface was implemented. Today, the Lua interface is rich enough to let you inspect and manipulate device state, access CPU registers, read and write memory, and draw custom graphical overlays.

There are three ways to use MAME’s Lua scripting capabilities:

Internally, MAME makes extensive use of Sol3 to implement Lua bindings.

The Lua API is not yet declared stable and may suddenly change without prior notice. However, we expose methods to let you know at runtime which API version you are running against, and most objects support some level of runtime introspection.


The API is not yet complete, but this is a partial list of capabilities exposed to Lua scripts:

  • Session information (application version, current emulated system)

  • Session control (starting, pausing, resetting, stopping)

  • Event hooks (on frame painting and on user events)

  • Device introspection (device tree listing, memory and register enumeration)

  • Screen introspection (screens listing, screen details, frame counting)

  • Screen overlay drawing (text, lines, boxes on multiple screens)

  • Memory read/write (8/16/32/64 bits, signed and unsigned)

  • Register and state control (state enumeration, get and set)

API reference

Interactive Lua console tutorial

First run an arcade game in MAME at the command prompt with the -console and -window options to enable the Lua console:

$ mame -console -window YOUR_SYSTEM
       /|  /|    /|     /|  /|    _______
      / | / |   / |    / | / |   /      /
     /  |/  |  /  |   /  |/  |  /  ____/
    /       | /   |  /       | /  /_
   /        |/    | /        |/  __/
  /  /|  /|    /| |/  /|  /|    /____
 /  / | / |   / |    / | / |        /
/ _/  |/  /  /  |___/  |/  /_______/
         /  /
        / _/

mame 0.255
Copyright (C) Nicola Salmoria and the MAME team

Lua 5.4
Copyright (C), PUC-Rio


At this point, your game is probably running in attract mode. Let’s pause it:

[MAME]> emu.pause()

Even without textual feedback on the console, you’ll notice the game is now paused. In general, commands are quiet and only print error messages.

You can check the version of MAME you are running with:

[MAME]> print(emu.app_name() .. " " .. emu.app_version())
mame 0.255

Let’s examine the emulated screens. First, enumerate the screen devices in the system:

[MAME]> for tag, screen in pairs(manager.machine.screens) do print(tag) end

manager.machine is the running machine object for the current emulation session. We will be using this frequently. screens is a device enumerator that yields all emulated screens in the system. Most arcade games only have one main screen. In our case, the main and only screen has the absolute tag :screen. We can examine it further:

[MAME]> -- keep a reference to the main screen in a variable
[MAME]> s = manager.machine.screens[':screen']
[MAME]> print(s.width .. 'x' .. s.height)

Several methods are available for drawing an overlay on the screen using lines, rectangles and text:

[MAME]> -- define a function for drawing an overlay and call it
[MAME]> function draw_overlay()
[MAME]>> s:draw_text(40, 40, 'foo') -- (x0, y0, msg)
[MAME]>> s:draw_box(20, 20, 80, 80, 0xff00ffff, 0) -- (x0, y0, x1, y1, line-color, fill-color)
[MAME]>> s:draw_line(20, 20, 80, 80, 0xff00ffff) -- (x0, y0, x1, y1, line-color)
[MAME]>> end
[MAME]> draw_overlay()

This will draw some useless lines and text over the screen. However, when the emulated system is resumed, your overlay needs to be refreshed or it will just disappear. In order to do this, you have to register your function to be called on every video update:

[MAME]> emu.register_frame_done(draw_overlay, 'frame')

All colors are specified in ARGB format (eight bits per channel). The coordinate origin (0,0) normally corresponds to the top-left corner of the screen.

As with screens, you can examine all the emulated devices in the running system:

[MAME]> for tag, device in pairs(manager.machine.devices) do print(tag) end

For some of them, you can also inspect and manipulate memory and state:

[MAME]> cpu = manager.machine.devices[':maincpu']
[MAME]> -- enumerate, read and write register state
[MAME]> for k, v in pairs(cpu.state) do print(k) end
[MAME]> print(cpu.state["D0"].value)
[MAME]> cpu.state['D0'].value = 255
[MAME]> print(cpu.state['D0'].value)
[MAME]> -- inspect memory
[MAME]> for name, space in pairs(cpu.spaces) do print(name) end
[MAME]> mem = cpu.spaces['program']
[MAME]> print(mem:read_i8(0xc000))

Note that many objects support symbol completion if you type part of a method or property name and press the Tab key: