Loopa

Header-only library to easily implement feedback loops with Lua in C

Usage

1. Download locally loopa.h

2. Include loopa.h

#define LOOPA_IMPLEMENTATION
// optional
// #define LOOPA_ACTUATOR_TYPE uint64_t
// #define LOOPA_SENSOR_TYPE double
#include "loopa.h"

3. Initialize the loopa_State

loopa_State* L = loopa_init("your_lua_file.lua");
// ...
function(L);
// ...
loopa_close(L);

4. Define your controller in Lua

The Lua class is expected to be named Controller, but this can be overloaded with the LOOPA_CLASS_NAME macro.

#define LOOPA_CLASS_NAME "MyControllerClass"
//...
#include "loopa.h"

The class must implement at least the following methods:

• Controller:init(): initialize the controller

• Controller:recv_sensor(sensor): receive the new sensor value and update the inner state of the controller

• Controller:send_actuator(): return the new value of the actuator

Here is an example for a PI Controller:

-- your_lua_file.lua
Controller = {}

function Controller:init() 
  local ret = { u = 0, kp = 2000, ki = 1000, ref = 0.02, cumerror = 0.0 }
  setmetatable(ret, Controller)
  return ret
end

function Controller:recv_sensor(sensor)
  local error = self.ref - sensor
  self.cumerror = self.cumerror + error
  self.u = self.kp * error + self.ki * self.cumerror
  if self.u < 0 then
    self.u = 0
  end
end

function Controller:send_actuator()
  return math.floor(self.u)
end

5. Call the controller from C

For example:

// function(L)
// ...
cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;
loopa_send_sensor(L, cpu_time_used);
iterations = loopa_recv_actuator(L);
// ...

Features

Hot reloading of the Lua file

Loopa provides a way to reload the Lua file when a modification occurs.

void loopa_try_reload(loopa_State* L, char* filename);

for now there is no check that the reload is successful or not, so a file saved with an error might crash the main program.

Examples

examples/mandelbrot

This example compute the Mandelbrot set. The maximum depth of convergence is controlled with respect to the iteration speed. The control loop is executed at the end of each iteration.

examples/monte_carlo_pi

This example computes an estimation of PI via a Monte Carlo simulation. The number of concurrent threads is controlled with respect to the loadavg of the host machine. The control loop is running in another thread.