6o Brazilian Conference on Dynamics, Control and Their Applications May 21-25, 2007 UNESP – Campus de São José do Rio Preto, SP, Brazil

Dincon’2007

FREE OPEN SOURCE TOOLS FOR REAL-TIME ROBOTICS & AUTOMATION SYSTEMS FOR THE 6th BRAZILIAN CONFERENCE ON DYNAMICS, CONTROL AND THEIR APPLICATIONS – DINCON 2007 Rafael Vidal Aroca 1 , Dalton Matsuo Tavares2 , Glauco Augusto de Paula Caurin 3 1

Mechatronics Laboratory - EESC - USP, São Carlos, Brazil, [email protected] Mechatronics Laboratory - EESC - USP, São Carlos, Brazil, [email protected] 3 Mechatronics Laboratory - EESC - USP, São Carlos, Brazil, [email protected]

2

Abstract: Real Time systems have several important characteristics and constraints that had always been related to enterprise-level solutions provided by well known software and hardware suppliers. Real Time Linux and Free Software are making success in this area through low cost and reliable solutions with high levels of flexibility. This paper explores Real Time Linux and other useful free open source tools for Real Time systems, concluding with a case study of a Real Time Linux based system controlling a SCARA Robot. Keywords: Open Source Software, Real Time Systems, Industrial Computers. 1. INTRODUCTION Real Time applications have always been highly related with expensive proprietary tools, because of the strongly reliable and deterministic constraints needed in such systems. Thanks to the Free Software philosophy [1], many open source tools have been successfully adopted in mission critical situations in the last years [2]. This article analyses the use of open source tools for Real Time tasks, with information of available resources. These tools are usually based in Linux Kernel with some modifications, to build a free Real Time system. Many efforts were made and proposed to transform Linux Kernel into a Real Time kernel, resulting in several flavors of Real Time Linux, such as RTLinux, KURT and RTAI, which are free implementations, and Montavista and BlueCat Linux which are commercial implementations based on the free ones. A Real Time System is focused on determinism [3, 4]. It may be not fast at all, but it must not break deadlines in any way. If a task must be executed at each second, a delay on that execution could cause fatal errors or even harm people. Soft Real Time Systems does not cause any drawback if a task is delayed. For example, a computer running a video consists on a Soft Real Time situation. Hard Real Time, in the other hand, can cause damage if minimum delays happen, such as stopping a robot that will collide against a human

being. Traditional RTOS (Real Time Operating System) are developed from scratch following rigorous requisites and concerns, to provide maximum reliability, determinism, and stability. Thus, converting an existent kernel originally designed for servers and desktops into a Real Time one [5] raises some technical problems. One interesting approach taken to create a Real Time Linux (RTL) System consists of writing a new simple, small, and deterministic kernel, and put it together with the common Linux kernel [6]. In this situation, the common Linux kernel, is nothing more than a task of the Real Time kernel. The Real Time kernel is responsible for scheduling all Real Time tasks and certify that all work is done on the correct timing. When there is an idle period of processing between the Real Time tasks, the Real Time kernel runs the common Linux kernel. This solution results in a flexible and powerful platform for several applications. Examples of such RTL approach can be found in different laboratories [7]. In this paper results obtained by the authors using RTL at the USP Mechatronics Laboratory are presented. The use of free open source software in Real Time systems has increased so much that many consolidated companies are offering free tools and solutions based on open source software, such as Linux. One example, is WindRiver, owner of VxWorks, which is now offering Linux as a product, that simply consists of a Linux distribution optimized for Real Time applications, with development tools, documentation, technical support, and other value added features [8]. 2. REAL TIME LINUX RELIABILITY Many developers ask themselves if they should move to RTL considering its development could lack technical support, or because there would be no consolidated companies behind the software to guarantee the reliability of the system and give all the help needed by the development team. One good way of trying to solve this conflicting question, is to look for successful cases in similar situations that already use RTL. In fact, there are several important systems

running RTL for several years. Though commercial solutions based on RTL are not always published, we can find some interesting examples in the academic and research environments. Complex telescopes, for example, rely heavily on Hard Real Time Operating Systems [2]. The SOAR Telescope, is one of the biggest and most powerful telescopes for state-of-the-art astrophysics research, and its control and supervisory systems were developed using RTL, and common Linux systems, with a distributed architecture and specialized hardware for instruments control, monitoring and data acquisition [7, 9]. RTL was also used to control a proton therapy room designed for human patients, in treatments involving X-Rays [10]. Again, Linux was used here in several machines, from the user interface to the machine controlling the beam, patient security, and the emergency stop if needed. Another open source tool used in this application was Comedi. Before start using RTL, it should also be interesting to gather some comparative studies about open source and commercially available RTOS. A systematic comparative study made between VxWorks, a market highly consolidated and adopted RTOS, and RTL [11], concludes that both operating systems are suitable for Hard Real Time applications. Nevertheless, VxWorks is more predictable and deterministic, which may be required in some applications. The US National Institute of Standards and Technology (NIST) published a report about RTLinux and made it available on the Internet with more reports and Linux articles [12]. According to the report, RTL works, but before start using it, developers and organizations might consider that, although the tools are free, some considerable work will be taken to setup the platform, and write code. About this problem, the report concludes that:

“The enthusiasm of real-time Linux converts is one form of evidence that many find this an agreeable trade-off.” [7]

The report also provides several case studies of successful solutions inside and outside NIST already using RTL, such as machine and robot control systems. National Aeronautics and Space Administration (NASA) is another well known organization, with great Real Time challenges. The agency has several projects using RTL, such as FlightLinux, that consists on the Linux operating system embedded in control computers of spacecrafts and satellites [13]. Scientists at Jet Propulsion Laboratory (JPL) that usually use VxWorks, are porting their C Real Time applications to a version of Real Time Linux, RTAI [2]. Their intentions with this change is to obtain better performance levels, and of course, reduce costs. NASA’s research areas also have meetings, where RTL is discussed [14]. According to Weinberg [15], RTL is scalable enough for up to 95% of the Real Time projects requirements and also highlights Linux for its superior reliability, cost effectiveness and its open source Application Programming Interfaces (APIs) compared to existent systems.

3. REAL TIME LINUX IMPLEMENTATIONS The increasing concern in Real Time Linux implementations has called attention of many companies, resulting in commercial distributions of Real Time Linux. Some examples of commercial versions are: BlueCat Linux: Developed and maintained by LynxWorks, company that develops and maintains Hard Real Time applications for avionics and other mission critical tasks. BlueCat is based on Linux Kernel 2.6 and compatible with LynxOS, allowing direct and transparent migration. BlueCat Linux is also tested according to ISO 9001:2000, which increases quality through accountability and welldefined procedures [16]; Montavista Linux: Consists of a Linux highly optimized and customized for Real Time tasks, and according to the developers, offers impressive response times when compared to free RTLinux implementations [17]; Wind River Linux: Developed and maintained by WindRiver, the company that develops and maintains VxWorks and Tornado. Wind River Linux brings an Eclipse based Workbench [8]; FSMLabs: Finite State Machine (FSM) Labs provides a commercial version of RTLinux, one of the oldest versions of RTL. The company has a significative number of success cases using Linux available On-Line at the company website [18]. These commercial versions of RTL provide development tools, platforms, documentation, APIs, and technical support as any other RTOS company offers. However, there are also well deployed and reliable versions of RTL completely free of charge. Some examples are: KURT: Kansas University Real Time Linux, consists of a project created to completely implement the POSIX Real Time extensions to Linux Kernel [19]; RTAI: Originally based on RTLinux, but evolved to completely different and reliable RTOS, with the ability of user and kernel space Real Time execution modes, that could be selected by the user [20]; FSMLabs RTLinux: FSMLabs also provides a Free version of its Real Time Linux, but without technical support, development tools, and development APIs [21]. 4. OPEN SOURCE INFRASTRUCTURE TOOLS Free Software means not only that the Software is free of charge, but specially that the users have the freedom to modify the software, and give the modifications back to a motivated community of developers, increasing even more the quality and features of the free software. As mentioned already, there are plenty of high quality free open source tools, even for Real Time development. In this section some interesting tools are studied, to support development of Real Time systems with free software, and increase developers productivity.

4.1. Etherboot: No Disks Etherboot is a General Public License (GPL) tool [22, 23], commonly used in computer cluster systems, allowing complete diskless operation of several machines. To be direct, etherboot can be considered a network boot loader, that will retrieve an operating system kernel or a disk image from a trivial ftp server (TFTP) located on a server, and boot the machine with the downloaded software. RTL systems can be deployed in completely diskless situations, where all the system files and even the RTOS kernel stay on a server. Additionally, a remote filesystem could be set over the network with NFS (Network File System), or RamFS could be used to create the system main filesystem in memory after the network boot process. This way of booting could be very useful in situations where disks may suffer damage and constantly break due to industrial environments. The remote disk, can be installed on a safe and controlled place, with backups and other tools to make the data more reliable and available, and the client machine accesses its disk over a network. Etherboot can also help booting other operating systems over networks, such as VxWorks, and Windows CE, allowing easy development and testing. A set of simple Linux scripts in a server, can reboot the target machine with any desired OS. Etherboot provides two important tools, that are: • ROMs: to be inserted in the Network Interface Cards (NICs) of the target machines, which will get a valid IP Address and load the operating system. These ROMs are available on Etherboot project’s website, and can be downloaded and installed in the NIC’s Boot ROM; • mknbi: make network boot image, which consists of a program that will get an operating system kernel, or boot disk, and specially prepare to boot over the Local Area Network (LAN). 4.2. Comedi Comedi stands for Linux Control and Measurement Device Interface and implements several drivers for I/O boards [24]. The drivers, as any other Linux Device Driver, are implemented as Linux kernel modules, that can be dynamically loaded when needed. Comedi project also provides a userspace library called Comedilib that provides a developerfriendly interface to Comedi devices. This library also provides several sample programs, documentation, and highlevel, developer functions to use the I/O. For Real Time development, Kcomedilib can be used, consisting of a Linux kernel module with similar functions of comedilib, but in kernel space, suitable for Real Time tasks. It is effectively a "kernel library" for using Comedi from Real Time tasks. Comedi already supports more than 330 different I/O boards. It also provides a framework to easily develop new drivers where there is no comedi driver for a needed board.

4.3. Orocos Orocos means Open RObot COntrol System [25], and consists of a complete and general purpose framework for robotics [26]. The fact that Orocos is a framework means that it offers support and libraries for new systems development, in a way, that Orocos is a tool to be used when developing applications. As Orocos project grew, and started to be used by several applications other than robotics, the project was divided into two different but integrated sub-projects, in April of 2006. Orocos provides typical library routines for robot positioning and control tasks like direct and inverse kinematics calculation. It also offer several other features for robots mechanical manipulation tasks, such as trajectory generator and state estimator based on Kalman filters, for example [27]. Orocos also supports distributed computation and control using CORBA, allowing scalable and flexible distributed control of several robots and machines in a coordinate way. 4.4. Xenomai Xenomai [28] consists of another free framework for Real Time applications development and debugging. The APIs provided by Xenomai includes emulators that can run other Real Time Operating Systems programs, allowing easy and fast migration from other RTOS to RTL [29]. Some RTOS emulators present in Xenomai APIs supports VxWorks, pSOS+, and VRTXsa [30]. The Real Time layers of Xenomai depends and works with RTAI to provide Real Time functions. 4.5. RTLab RTLab [31] is a free software developed to support scientific experimentation in laboratories. Its development started to help biomedical research and experiments [32], but it can be applied to many other research areas. This scientific software can be used on top of RTAI or RTLinux, and provides Hard Real Time data acquisition, through Comedi libraries and drivers. RTLab also have an intuitive Graphical User Interface (GUI) to display the read data in several formats and graphs, allowing on-line observation of the experiment. A fully functional version of a Live-CD can be downloaded from the project website. The Live-CD can be used in any PC with a data acquisition card, allowing easy and practical use of RTLab, Comedi and RTLinux for non computer scientists or specialists. 4.6. RTNet RTNet [33] consists on an open source project to add determinism guarantees to the Ethernet. The project adds Hard Real Time capabilities to the Ethernet, that could even be used for example as a fieldbus, permitting Real Time control, monitoring and distributed Real Time computing. Confident Real Time communication with RTNet can only be assured if all the nodes in the Ethernet bus are using the RTNet network layer driver, otherwise, collisions and non deterministic data can be sent by hosts not running RTNet, interfering in the deterministic network.

4.7. BusyBox

5.1.1 Hardware

BusyBox [34] is a GPL software specially made to be used in small and embedded systems. It provides the function of more than 107 different programs in a single and small binary file [35]. The technology used by BusyBox is called multi-call binary, which means that depending on how BusyBox is called, it acts as a different program. BusyBox offers several applications in a few hundreds of kilobytes ranging from file copy commands and system initialization utilities to ftp and telnet servers. 5. CASE STUDY One interesting case study developed at the Mechatronics Laboratory consists of a system that allows network control of a retrofited IBM SCARA Robot using an industrial PC and Real Time Linux. It is clear that Real Time Linux, specifically RTAI, is more than adequate to control a robot with 6 degrees of freedom [36], with very low scheduling jitter, which is less than 10 µs in the worst case. A critical decision to be taken here, is which Real Time Linux version to use. Using a comparative study made by Aarno [3], we conclude that we should use either RTAI or RTLinux from FSMLabs, but preferably RTAI, which is completely open source, and showed a better performance on stress situations, with maximum deviation of 10 µs, while RTLinux had 5 ms. Using Linux flexibility, the robot software could even be changed while the robot is running [37]. The general system architecture is shown on Figure 1.

An industrial PC was used for the Real Time System, consisting of a CompactPCI rack, with the following boards: • Inova AMD K6 CPU Board: The CPU board can be inserted in any slot of the industrial PC. More than one CPU board can be inserted for parallel processing or redundant processing. A picture of the CPU board inserted on the CompactPCI rack can be seen on Figure 2; • Acromag Carriers: The CompactPCI carriers are boards that act as a bridge between the Industry Packs (IPs) and the CompactPCI Bus on the PC. Two carriers were used with two slots each; • National Instruments I/O Board: CompactPCI board with 48 digital and analog inputs, which are adopted to read data provided by the six axis force/torque sensor placed at robot wrist;

Remote Control using TCP/IP

IPs

Remote Control Server

Carriers

Robot Control Software

DAQs

Orocos Framework

Sensors

Network

BusyBox

CompactPCI Bus

Comedi Drivers

Actuators

WatchDog Timer Robot

Hardware

Real Time Line Kernel Software

Figure 1 – The Real Time Linux SCARA Robot control system

5.1. Assets and Methods The development was based on a host-target scheme, where all the software were developed on a Linux workstation, and transparently sent to the target machine running RTL.

Figure 2 – Inova Industrial PC with the CPU board connected

On the industrial PC world, the carrier boards can hold several smaller boards, each with a specific function. These small boards are called IPs or Industry Packs. The used industry Packs were: • Tews 48 Digital I/O IP: Industry Pack with digital input and outputs to read data from digital sensors and output digital data; • Tews IP Quadrature IP: Industry Pack to read encoders values, and inform the software “where” are the robot’s axis; • Tews DAC IP: Industry Pack to convert digital data into analog signals, providing information to control the motors; Other items used in the project were: • Power Interface: Power boards to interface the analog I/Os from the IPs with the robot’s motors;

• SCARA Robot: A SCARA robot from IBM, that went through a retrofit process in the Mechatronics Laboratory. Figure 3 shows a graphical overview of all the subsystems and their integration with the SCARA Robot. The industrial PC Software running on RTL reads robot position from 4 encoders using the quadrature industry pack, that is connected to the CompactPCI Carrier Card. The motor control is accomplished generating analog signals using an industry pack to feed an Analog/PWM Converter, which controls the motor drivers. The real time software allows the programmer to implement different motor command strategies, sensor data access and fusion. It constitutes further a flexible environment for implementing and testing any kind of control theory including conventional model based approaches and also soft-computing methods like artificial Neural Networks, Fuzzy Logic and Genetic Algorithms. A six axis force-torque sensor is also attached to the robot’s wrist allowing future research on robot-environment interaction. Data from this sensor is read using the National Instruments Board. Encoder 1 Motor 2

Motor 1

Encoder 2

Position Data (4 axes)

Motor Control Tensions (4 axes)

described, running RTL. Both computers are connected in an Ethernet network, which is used for control, debugging, monitoring, and new software transfer. The host machine main software consists of: gcc to compile the target applications and the target kernel; mknbi: to make the kernel images network bootable; dhcp daemon: to provide automatic IP configuration for the target; tftp server: to upload the target kernel to the industrial PC, and nfs server to host the target filesystem. The target machine consists of a Linux Kernel compiled with Real Time patches, and with kernel level IP auto configuration, which allows the target machine to boot its kernel, get an IP address, and mount a remote root filesystem without any external program. Some interesting tools present in the target machine are BusyBox and Comedi. The target system can be remotely accessed with telnet for tests and control. Most of the hardware device drivers were already available for Linux from the vendors, or using Comedi drivers, but still some driver needed to be developed to interface the Industry Packs to the CompactPCI carrier, and today the system already have a working Real Time network controlled I/O system. As this is an ongoing project, next steps covers Orocos deployment to the target machine for kinematic control, and Real Time software development to control the SCARA Robot. 6. CONCLUSION

Encoder 3 Motor 3 Torque Sensor

Encoder 4

Motor 4

Sensor Data

Quadrature Industry Pack Motors Drivers

Digital Torque Data

PWM 1

PWM 2

PWM 3

Digital Analog Conveter (DAC) Industry Pack

PWM 4

Analog/PWM Converter Data Acquisition Board

Analog

Industrial PC (Target)

CompactPCI Bus

CompactPCI Bus Industry Pack Carrier Card

Real Time Linux and open source tools brings powerful flexibility and resources, permitting low-cost development of highly sophisticated Real Time systems that can be used for Robotics and automation control systems. Beyond the cost reduction, these systems can be easily modified to each situation, and integrated with other proprietary and legacy systems, thanks to open standards and implementations. Linux, as other free software, projects informally creates a community of self-helping developers, offering plenty of documentation, compared to other proprietary solutions. Next steps in the laboratory research activities involves concluding the SCARA Control system, providing a flexible framework for robotics tests and research. ACKNOWLEDGMENTS This work was developed in the Mechatronics Laboratory at University of São Paulo (USP). Thanks to Leonardo Marquez Pedro, who helped with the mechanics of the SCARA Robot.

Ethernet Bus

Remote Workstation Control/Development (Host)

Figure 3 – SCARA Robot Control System

5.1.2 Software Software architecture of the proposed system consists of a host computer running Linux, and a target computer, already

REFERENCES [1] Free Software Foundation, “GNU GENERAL PUBLIC LICENSE,” March 2007. Available at: http://www.gnu.org/licenses/gpl.html [2] P. C. Irwin, L. Richard, L. Johnson Jr., “Real-time control using open source RTOS,” Advanced Telescope and Instrumentation Control Soft-

ware II, Vol. 4848, No. 1, 2002. Available at: http://link.aip.org/link/?PSI/4848/560/1 [3] D. Aarno, “Evaluation of Real-Time Linux Derivatives for Use in Robotic Control,” 2004. Available at: http://www.nada.kth.se/ bishop/resources/rtos.pdf [4] P. A. Laplante, “Real-Time Systems Design and Analysis,” Willey Interscience,2004. [5] A. Lennon, “Embedding Linux,” IEE Review, pp. 33 37, Vol. 47, No. 3, May 2001. [6] V. Yodaiken, “The RTLinux Manifesto,” Proceedings of The 5th Linux Expo, Raleigh, NC, Mar 1999. Available at: http://citeseer.ist.psu.edu/yodaiken99rtlinux.html [7] National Instutute of Standards and Technology - NIST, “Introduction to Linux for Real-Time Control,” 2002. Available at: http://www.isd.mel.nist.gov/projects/rtlinux/intrortl.pdf [8] Wind River Linux Center, Last Access on Mar 2007. Available at: http://www.windriver.com/linux/ [9] G. Schumacher, S. Heathcote, V. Krabbendam, “SOAR TCS: from implementation to operation,” Advanced Software, Control, and Communication Systems for Astronomy, pp. 32-37, Vol. 5496, No. 1, Glasgow, Scotland, United Kingdom, 2004. Last Access on Mar 2007. Available at: http://link.aip.org/link/?PSI/5496/32/1 [10] J. Katuin, “Proton therapy treatment room controls using a Linux control system,” Proceedings of the Particle Accelerator Conference 2003, pp. 12-16, Vol. 2, May 2003.

- Robust embedded-Linux operating system based on Linux 2.6 kernel,” Last Access on Mar 2007. Available at: http://www.lynuxworks.com/embeddedlinux/embedded-linux.php [17] MontaVista Software, “Real-Time Linux,” Last Access on Mar 2007. Available at: http://www.mvista.com/products/realtime.html [18] FSMLabs, “FSMLabs to bring Real-Time Technology to Enterprise, Security and Financial Markets,” Feb 2007. Last Access on Mar 2007. Available at: http://www.fsmlabs.com/docs/fsmlabs-pr-070220enterprise.pdf [19] KURT-Linux: Kansas University Real-Time Linux, “KURT-Linux User Manual - DRAFT,” Last Access on Mar 2007. Available at: http://www.ittc.ku.edu/kurt/papers/user-manualDRAFT.pdf [20] RTAI: the RealTime Application Interface for Linux from DIAPM, “RTAI 3.4 User Manual rev 0.3,” Last Access on Mar 2007. Available at: https://www.rtai.org/ [21] RTLinux Free, “RTLinux Free, the free software edition of RTlinux,” Last Access on Mar 2007. Available at: http://www.rtlinuxfree.com/ [22] LinuxFocus.org, “An Introduction to Network Booting and Etherboot,” Last Access on Mar 2007. Available at: http://www.linuxfocus.org/English/September1998/ [23] EtherBoot.org, “Etherboot Project,” Last Access on Mar 2007. Available at: http://www.etherboot.org [24] Comedi.org, “Comedi - Linux COntrol and MEasurement Device Interface,” Last Access on Mar 2007. Available at: http://www.comedi.org

[11] B. Ip, “Performance Analysis of VxWorks and RTLinux,” Technical Report for COMS W49952, Languages of Embedded Systems, Depart[25] ment of Computer Science, Columbia University, NY. Last Access on Mar 2007. Available at: http://www1.cs.columbia.edu/ sedwards/classes/2001/w499502/reports/ip.pdf [26] [12] F. Proctor, “Real-Time Linux,” Last Access on Mar 2007. Available at: http://www.isd.mel.nist.gov/projects/rtlinux/ [13] D. Hardison, “FlightLinux,” Last Access on Mar 2007. Available at: http://flightlinux.gsfc.nasa.gov/ [14] B. Kalynnda, “Real-Time Linux Evaluation,” Technical report, Glen Research center, NASA, 2002. [15] B. Weinberg, “Embedded Linux - Ready for Real Time,” Proceedings of the Third Real-Time Linux Workshop, No. 3, Milan, Italy, Sept 2001. Available at: http://www.realtimelinuxfoundation.org/events/rtlws2001/agenda.html#AGENDA_Weinberg [16] BlueCat Linux, “Embedded Linux: BlueCat Linux

H. Bruyninckx, “Open robot control software: the OROCOS project,” Proceedings of the IEEE International Conference on Robotics and Automation ICRA 2001, pp. 2523-2528, Vol. 3, No. 3, 2001. H. Bruyninckx, “OROCOS: design and implementation of a robot control software framework,” Proceedings of the IEEE International Conference on Robotics and Automation - ICRA 2002, Apr 2002.

[27] H. Bruyninckx, P. Soetens, B. Koninckx, “The realtime motion control core of the Orocos project,” Proceedings of the IEEE International Conference on Robotics and Automation - ICRA 2003, Sep 2003. [28] Xenomai, “Xenomai: Real-Time framework for linux,” Last Access on Mar 2007. Available at: http://www.xenomai.org [29] Xenomai, “Xenomai Implementing a RTOS emulation framework on GNU/Linux,” Last Access on Mar 2007. Available at: http://download.gna.org/rtai/documentation/vesuvio/

pdf/xenomai.pdf [30] Xenomai, “An Introduction to UVMs - What is this?,” Last Access on Mar 2007. Available at: http://www.xenomai.org/documentation/branches/ v2.2.x/pdf/Introduction-to-UVMs-rev-B.pdf [31] D. Christini, “Real-Time Linux BiologicalExperiment Control project,” Last Access on Mar 2007. Available at: http://rtlab.org/index.jsp [32] C.A. Culianu & D.J. Christini, “Real-time Linux experiment interface system: RTLab,” Proceedings of the IEEE 29th Annual Bioengineering Conference, pp. 52 - 53, Mar 2003. Available at: http://rtlab.org/index.php [33] RTnet, “RTnet: hard real-time networking for RealTime Linux,” Last Access on Mar 2007. Available at: http://www.rts.uni-hannover.de/rtnet/ [34] BusyBox, “BusyBox,” Last Access on Mar 2007. Available at: http://www.busybox.net [35] BusyBox, “Building Tiny Linux Systems with Busybox – Part I,” Last Access on Mar 2007. Available at: http://www.linuxjournal.com/node/4335/print [36] D. Aarno, “Control of a PUMA 560 Using Linux Real-Time Application Interface (RTAI),” 2004. Available at: http://www.nada.kth.se/ bishop/resources/rtcontrol.pdf [37] E. Horiuchi, “Nonstop Update of Running Robot Controllers,” Proceedings of the 2004 IEEE/RSJ International Conference on Intelligent Robots and Systems, Sendai, Japan, Oct 2004.