Usability Study of Available RealTime Operating and Communication Systems

1
Usability Study of Available Real-Time Operating
and Communication Systems
Dipl.-Ing. Andreas Kahmen Laboratory for Machine
Tools and Production EngineeringAachen
University of Technology 11 March 2003
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Contents of presentation

• Analysis of available Linux implementations
• Comparison of Linux real-time extensions
• Investigation of Linux networking and device
  support
• Comparison of Linux with standard operating
  systems
• Analysis of available CORBA implementations
• Comparison of CORBA implementations
• Interoperability between different ORBs
• Investigation of CORBA Component Model
• Time measurements for TAO

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Comparison of Linux implementations

• Suitable Linux real-time extensions are RTLinux
  and RTAI
• The comparison resulted that RTAI provides better
  real-time support than RTLinux
• soft real-time in user space along with hard
  real-time in kernel space
• excellent performance in terms of low jitter and
  low latency
• better C support and more complete feature set
• availability of LXRT which allows user space
  applications in kernel space
• RTAI has the better open source approach with
  frequent feedback from developers

4
Linux Networking and Device Support

• Linux support of network devices
• Ethernet (10 Mbps, Fast and Gigabit Ethernet)
• FDDI (Fiber Distributed Data Interface, 100 Mbps)
• Wireless LAN (Local Area Network)
• ISDN (Integrated Services Digital Network)
• WAN (Wide Area Network)
• Linux networking protocol support
• TCP/IP (standard and version 6)
• Fieldbus protocols (e.g. CAN, Profibus, Interbus,
  ControlNet, DeviceNet, AS-I, ...)
• PPP (Point-to-Point), SLIP (Serial Line IP), PLIP
  (Parallel Line IP)

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Benefits of Linux

• Linux has been ported to various platforms
• High level development and supporting tools are
  available
• Full control over source code and operating
  system functionality
• Open to all standards
• No royalties
• High reliability

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Comparison of Linux with standard OS

• Interrupt latency time and jitter are comparable
  to standards real-time OS
• The coupling of real-time part and non-real-time
  part is realised like for commercial real-time
  extensions
• More real-time drivers are available open source
  than for commercial solutions
• Development tools for open source real-time
  solutions are usually more powerful than
  commercial ones
• Linux with RTAI real-time extension is an
  excellent operating system for an Open Source
  control platform

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Comparison of CORBA implementations (I)

• Research for 11 different ORBs applying the
  following criteria
• Open source availablity
• CORBA version implemented
• Real-time capability and implemented RT CORBA
  features
• Available language bindings
• Implemented CORBA services
• Supported multithreading concept
• Supported protocols
• Tested Linux and compiler support

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Comparison of CORBA implementations (II)

• All ORBs except for JacORB and VisiBroker RT have
  been ported and tested on Linux platforms
• All ORBs except JacORB offer Language C
  bindings
• TAO and ROFES provide real-time capability
• Real-time versions of ORBExpress, eORB and
  VisiBroker are available only in commercial
  distributions
• Basic Services (e.g. Naming, Event, Trading) are
  provided by almost all ORBs
• Biggest range of implemented CORBA services are
  offered by TAO and ORBit

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Interoperability between different ORBs

• ORB interoperability is covered by OMG
  specifications since CORBA 2.0
• Interoperability is secured by General Inter-ORB
  Protocol (GIOP)
• Interoperable Object Reference (IOR) specifies
  standardised object reference format
• All ORBs of the research are implemented based on
  CORBA 2.0 or higher (IIOP available)
• Successful interoperability test have been
  reported for TAO, MICO and JacORB
• Projects for interoperability tests between
  different ORBs
• CORVAL2
• COST

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Investigation of CORBA Component Model

• CCM defines features and services for
  implementation, management, configuration and
  deployment of components with commonly used CORBA
  services
• Application of CCM eases software reuse
• CCM provides Quality of Service (QoS)
  capabilities
• monitoring and control of components behaviour
• Current CCM implementations are among others
• OpenCCM (ORBacus and VisiBroker for Java open
  source)
• MicoCCM (MICO for C GPL/LGPL)
• K2 (TAO, ORBacus, ORBIX for C commercial)
• CIAO (TAO for C open source)
• CIAO will be first implementation available with
  QoS RT-CCM

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Time measurements for TAO

• Test environment
• Hardware Motorola PowerPC (MPC604)
  333MHz
• Operating System VxWorks 5.4.2 Tornado
  2.0.2
• Compiler GCC Version cygnus-2.7.2
• ORB TAO 1.2a release of OCI
• Test conditions
• One server and one client
• methods provided by the server
• call_double_void( ) (return type double
  marshalling)
• call_double_long( long ) (return type double
  parameter type long marshalling)
• call_long_void( ) (return type long
  marshalling)
• call_double_sequence( sequenceltdoublegt )
• (parameter marshalling of a sequence
  of doubles return type double)

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Measurements for call_long_void()

• Server priority 6 Client priority
  7 Measurements for round trip times

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Conclusions for time measurements

• The round trip measurements reflect the minimum
  time for method calls using TAO
• Additional measurements with different
  configurations will be done in the future
• TAO fulfils the requirements for the real-time
  communication within the DCRF