public function feed()
{
    // creating rss feed with our most recent 20 posts in variable $post

    // first load the library
    $this->load->library('feed');

    // create new instance
    $feed = new Feed();

    // set your feed's title, description, link, pubdate and language
    $feed->title = 'Your title';
    $feed->description = 'Your description';
    $feed->link = 'http://yoursite.com';
    $feed->lang = 'en';
    $feed->pubdate = $posts[0]->created; // date of your last update (in this example create date of your latest post)

    // add posts to the feed
    foreach ($posts as $post)
    {
        // set item's title, author, url, pubdate and description
        $feed->add($post->title, $post->author, $post->slug, $post->created, $post->description);
    }

    // show your feed (options: 'atom' (recommended) or 'rss')
    $feed->render('atom');
}