Magento – Custom action GetUrl

Ok, this is the follow up to a other question of mine. I just can't figure out the last detail.

I created a custom extension to set a order status to "Ready for Pickup". The button shows and is clickable but does not generate the correct action.

/app/code/local/Mymodule/Pickup/etc/config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
<modules>
    <Mymodule_Pickup>
        <version>0.0.1</version>
    </Mymodule_Pickup>
</modules>
<global>
    <blocks>
         <adminhtml>
            <rewrite>
                <sales_order_view>Mymodule_Pickup_Block_Adminhtml_Sales_Order_View</sales_order_view>
            </rewrite>
        </adminhtml>
    </blocks>
</global>
</config>  

/app/code/local/Mymodule/Pickup/controllers/Adminhtml/IndexController.php

<?php
class Mymodule_Pickup_Adminhtml_IndexController extends Mage_Adminhtml_Controller_Action

public function pickupAction()
{
  $orderId = $this->getRequest()->getParam('order_id');
  $order = Mage::getModel('sales/order')->load($orderId);
  $order->setStatus("pickup_ready");
  $order->save();
  // redirect to your sales order view page back
}
?>

/app/code/local/Mymodule/Pickup/Block/Adminhtml/Sales/Order/View.php

<?
class Mymodule_Pickup_Block_Adminhtml_Sales_Order_View extends Mage_Adminhtml_Block_Sales_Order_View 
{
public function  __construct() {

parent::__construct();

$order = $this->getOrder();

    $this->_addButton('inform_pickup', array(
        'label'     => Mage::helper('sales')->__('Custom Pickup Button'),
        'onclick'   => 'setLocation(\'' . $this->getPickupUrl($order) . '\')',
    ));
}

public function getPickupUrl($order)
{
   return $this->getUrl('pickup/adminhtml_index/pickup', array('order_id' => $order->getId()));
}
}
?>

The problem is that my

return $this->getUrl('pickup/adminhtml_index/pickup', array('order_id' => $order->getId()));

is not working. It redirects me to a front page 404. What am I doing wrong in this Url?

UPDATE

Added /app/code/local/Mymodule/Pickup/etc/adminhtml.xml

<?xml version="1.0"?>
<config>
<acl>
    <resources>
        <admin>
            <children>
                <system>
                    <children>
                        <config>
                            <children>
                                <pickup translate="title" module="pickup">
                                    <title>Pickup</title>
                                    <sort_order>100</sort_order>
                                </pickup>
                            </children>
                        </config>
                    </children>
                </system>
            </children>
        </admin>
    </resources>
</acl>
</config>