$this->load->driver('cache', array('adapter' => 'file'));
$cache_id = hash('sha256', $_SERVER['REQUEST_URI']);
if ( $html = $this->cache->get($cache_id) ){
	echo $html;
	echo "\n<!-- cached --> \n";
	return;
}

// html 生成処理
$html = '..................';

// キャッシュを保存 60*60*24*7(sec) = 7日
$this->cache->save($cache_id, $html, 60*60*24*7);