Code for creating order comment in magento and display in backend

Add code in config.xml in module in etc folder(Path : app/local/namespace/modulename/etc)

<events>
            <checkout_type_onepage_save_order>
                <observers>
                    <onestepcheckout_save_order_comment>
                        <type>helper</type>
                        <class>DCKAP_Onestepcheckout_Helper_Data</class>
                        <method>setOrderCommentCompatible1</method>
                    </onestepcheckout_save_order_comment>
                </observers>
            </checkout_type_onepage_save_order>     
            <checkout_type_onepage_save_order_after>
                <observers>
                    <onestepcheckout_save_order_comment>
                        <type>helper</type>
                        <class>DCKAP_Onestepcheckout_Helper_Data</class>
                        <method>setOrderCommentCompatible2</method>
                    </onestepcheckout_save_order_comment>
                </observers>
            </checkout_type_onepage_save_order_after>     
            <sales_model_service_quote_submit_after>
                <observers>
                    <onestepcheckout_service_quote_submit_order_comment>
                        <type>helper</type>
                        <class>DCKAP_Onestepcheckout_Helper_Data</class>
                        <method>setOrderCommentCompatible2</method>
                    </onestepcheckout_service_quote_submit_order_comment>
                </observers>
            </sales_model_service_quote_submit_after>    
        </events>


Add code in helper (path : app/code/local/namespace/modulename/helper)



public function isOrderComment() {
       
        return Mage::getStoreConfig('onestepcheckout/general/comment');
    }

public function setOrderCommentCompatible1($observer) {

        if ($this->getCompatibility() != self::COMPATIBILITY_TYPE1) {
           return;
        }
        if ($this->isOrderComment()) {
            $orderComment = trim($this->_getRequest()->getPost('order_comment'));
            if ($orderComment != "") {
                $observer->getEvent()->getOrder()->addStatusHistoryComment($orderComment,true);
            } else {
                $observer->getEvent()->getOrder()->setOrderComment(Mage::getSingleton('checkout/session')->getOpcheckoutOrderComment());
                Mage::getSingleton('checkout/session')->unsOpcheckoutOrderComment();
            }
        }
    }


    public function setOrderCommentCompatible2($observer) {

        if ($this->getCompatibility() != self::COMPATIBILITY_TYPE2) {
         return;
        }
        if ($this->isOrderComment()) {

            $orderComment = trim($this->_getRequest()->getPost('order_comment'));
            if ($orderComment == "") {
                $orderComment = Mage::getSingleton('checkout/session')->getOpcheckoutOrderComment();
                Mage::getSingleton('checkout/session')->unsOpcheckoutOrderComment();
            }
            $order = $observer->getEvent()->getOrder();
            if ($order && ($orderComment != "")) {
                if ($order->getId()) {
                    $resource = Mage::getSingleton('core/resource');
                    $sales_order = $resource->getTableName('sales_order');
                    $resource->getConnection('core_write')->update($sales_order, array('order_comment' => $orderComment), array('entity_id = ?' => $order->getId()));
                }
            }
        }
    }