libLua

Lua interpreter library for Arduino boards. Used official Lua sources from https://www.lua.org/. The library provides standard Lua C API, so you can learn more about Lua and its API here https://www.lua.org/manual/5.4/.

How to

To convert your Lua scripts just put them in "lua_scripts" folder and run Python script "prepareScripts.py". It will convert .lua files in headers. You can find converted scripts in "src/scripts" folder.

Simple C++ Arduino example:

#include <Arduino.h>
// Include library
#include <lua.hpp>
// Include script
#include <scripts/hello_world_lua.h>

// Function to be run from Lua
int luaprint_func(lua_State *L)
{
  // Get amount of provided arguments
  int n = lua_gettop(L);

  if (n < 0)
  {
    lua_pushstring(L, "Not enough parameter.");
    return lua_error(L);
  }

  // Get first string argument and print it
  Serial.println(lua_tostring(L, 1));
  
  return 0;
};

void setup()
{
  // Open serial
  Serial.begin(115200);
  
  // Create Lua state
  lua_State *L = luaL_newstate();
  if (L == NULL)
  {
    Serial.println("Cannot create Lua state: not enough memory.");
    while(1);
  }
  
  // Register custom println function
  lua_register(L, "println", luaprint_func);
  
  // Register standard Lua libraries
  luaL_openlibs(L);
  
  // Execute script
  luaL_dostring(L, LuaScripts::hello_world_lua.content);
}

void loop() {
  
}

For an easier way to call lua script you may use this:

LuaScripts::hello_world_lua.call(L);

Compilation

prepareScripts.py takes an argument specifying what to do with the Lua scripts. It can have one of four values:

• PlainText (Default) - Just remove duplicate spaces and comments;
• Compiled - Compile scripts to bytecode with Luac. Compiled scripts take up more space but take less time to start;
• Compressed - (Not implemented yet) - compressed plain text;
• CompiledAndCompressed - (Not implemented yet) - compressed bytecode.

Usage example:

py ./prepareScripts.py Compiled

Performance

Tested on ESP32 WROOM DevKit v1 board with 240 MHz Core clock.

Test code

static double benchCalc(void)
{
  double t = 8521.0234;
  double s = sin(t) + 21000;

  s = t * sqrt(s);
  t = log(t);

  double sum = t;
  for (int i = 0; i < 256; ++i)
  {
    sum += log(t);
  }

  return (t / s) + sum;
}

The analog functions were written in Lua and MicroPython using the standard math library.

Test results

Language	Time (us)	Function output
C++	76	572.966329
Lua	1940	572.9656
MicroPython	13832	570.7628