How to setup an automatic function?

[eluser]Corey Freeman[/eluser]
For my game, the player's stamina needs to replenish itself automatically once every 6 hours. I thought setting up a cron job would work, but it won't run the controller that way. So I'm not sure how to go about doing this.

Here's the code I have for the stamina update:

Code:

<?php

class Stamina extends Controller {

    function Stamina()
    {
        parent::Controller();    
    }
    
    function index()
    {
         $query = $this->db->get('players');
         foreach($query->result() as $row):
         $max = $row->max_stamina;
         $data = array('stamina' => $max);
         $this->db->where('id', $row->id);
         $this->db->update('players', $data);
         endforeach;
    }
}

This is really important so any help is majorly appreciated!