A PROPOSAL FOR A DISTRIBUTED REAL TIME OPERATING SYSTEM SUPPORTING THE CLIENT/SERVER CONCEPT

Design and implementation of an MMS environment on ISODE

We introduce a specification of a distributed transaction processing facility for the Manufacturing Message Specification (MMS) which is an application service element of the Manufacturing Automation Protocol (MAP) standardized by the International Standard Organization (ISO) to support messaging communication to and from programmable devices in a computer integrated manufacturing (CIM) environment. The proposed facility permits the organization of a distributed transaction in terms of a set of MMS services encapsulated together to perform the manufacturing or the production tasks. The services provided by the transaction processing (TP) standard, presented by the ISO, are used as well as new services are defined to guarantee the coherent behavior of the MMS distributed transactions. This guarantee is based on the satisfaction of the Atomicity, Consistency, Isolation, and Durability (ACID) properties defined by the ISO. The distributed transaction processing facility is specified as finite state automata represented by Nutt evaluation networks notations. A validation technique based on the Calculus of Communicating Systems (CCS) introduced by Milner is used to prove the coherent behavior of the transactions.

Distributed real-time operating system (DRTOS) modeling in SpecC

This paper addresses the problems concerning the fault-tolerant distributed replication of a controlling application in an automated system. The Manufacturing Message Specification (MMS) is used as a communication protocol between the controlling application (MMS client) and the automated industrial equipment (MMS servers). A distributed systems toolkit (DST) is used to manage the replication of the controlling application. We identify potential obstacles in the MMS environment when passive client replication is used. We suggest methods that the recovering client can use to overcome these obstacles. The solutions and alternatives proposed are discussed with respect to their conformance to the MMS standard.

Deadline scheduling policies based on stochastic computation times perform well in average but fail in presence of transient overloads, causing already scheduled tasks to miss their deadline. This paper presents an approach using medium-term scheduling policies to cope with the problem of transient overload in dynamic real-time systems. The proposed approach has been implemented in a Real-Time Distributed Operating System (RTDOS) running on a Transputer network. >

The manufacturing message specification (MMS) is an application layer protocol (ISO IS 9506) which specifies services for distributed manufacturing applications design. It enables communication between heterogeneous devices. An important topic in application design process is the performance issues, because some applications present performance constraints such as maximal service response time. This paper presents some performance models for evaluating the MMS response time by taking into account among others the real characteristics of a MAP/MMS implementation. Colored stochastic Petri nets formalism was used for models representation on the one hand and simulation for their resolution on the other hand. This choice has been established following the analysis of characteristics of MMS. We have built our models in a progressive way until we obtained the global MMS model. The major problem posed in this work, is the lower layers' model parameters. These parameters are mainly probability distributions of processing time for each network layer. These distributions are different and specific to each implementation. Their determination is necessary for the quantitative validation of the models. However these indices are inaccessible in the used implementation. To show the behavior of our models, we have therefore put forward hypotheses on the various missing indices.

A Distributed Real-Time Transaction Processing Environment For the CIM Applications

The implementation of an icon-based manufacturing message specification (MMS) messaging system for system control in a manufacturing automation protocol (MAP environment) is described. The system was designed with a four-layer hierarchy. The top layer acts as a user interface and essentially provides a data manipulation service. The next layer invokes the appropriate firmware calls to manage the communication process. The third layer consists of the firmware that handles the actual transmission of data across the network. The lowest level is the actual network hardware. Twelve MMS services were implemented in order to provide the capability to carry out a typical control session. The system was tested using software that simulates the external communications of an MMS virtual manufacturing device. The LabVIEW MAP environment used imposed at least two limitations on the operation of the system. First, LabVIEW makes no provision for data structures; therefore, each parameter had to be passed from the MMS layer to the code VI layer as a variable of a specific data type. Second, LabVIEW provides no convenient way to maintain global variables throughout a diagram. >

IEC 61850 is an international standard developed by the International Electrotechnical Commission TC57 substation automation communication networks and systems. It uses MMS (Manufacturing Message Specification) as a real-time communication protocol of the application layer, and achieves the communication between the substation layer and the spacer layer. This paper describes the features and functions of the IEC 61850 and MMS technology and focuses on the principle of MMS mapping in the application of IEC 61850 , then preliminarily leads to the overall design framework of the IEC 61850 gateway.

Manufacturing equipments should be integrated to construct CIM (Computer Integrated Manufacturing) environment, but several economical and technological difficulties may be arisen in case heterogeneous systems are integrated into each other. MMS (Manufacturing Message Specification) can be effective in such a case, but the problem is that MMS-related products are comparatively expensive and the existing manufacturing equipments mostly do not support MMS. This study was focused on developing a gateway suitable to a non-MMS-compatible CNC machine-tool, and on implementing OSI (Open System Interconnection) upper layer on TCP/IP. The development system was applied to a cell controller by means of heterogeneous equipments under CIM environment, and to evaluate interoperability and portability.

14 - UCA protocol

This paper presents an overview of a proposed protocol to provide application---transparent fault tolerant services in a Real Time Operating system. Fault tolerance is achieved by saving checkpoints of the processes belonging to a real time application. This approach proposes the extension of some real time system calls in order to save a recovery point when the user invokes them. This protocol allows a real time application designer to know the temporal specifications of every system call. Current real time applications are composed of several Real Time processes and they have to share data by using interprocess communication facilities provided by the operating system. The operating system has to take into account these interactions to ensure the consistency of checkpoints. This is done by tracking the communications performed since the last checkpoint and forcing dependent processes to perform a checkpoint at the same time.

This paper presents the basics of an operating systems plus RTOS(Real Time Operating System) specific features. Readers are expected to have an overview of the foundations of embedded operating systems and especially RTOS. Operating systems have been evaluated by different commercial and non profit organizations. It can be seen the main lines of different operating systems.

A real-time operating system (RTOS) is software which ensures that time critical events are processed as efficiently as possible. In this paper, an attempt has been taken to develop a real time operating system, named Preemptive Real Time Operating System (pRTOS), in which all of the important issues regarding to a real time application have been considered. In this pRTOS, strictly preemptive scheduling algorithm has been used. This scheduling policy makes sure that important tasks are handled first and the less important later. The Bitmap technique has been used to find out the highest priority task from the unsorted ready list. The complexity of this technique for selecting the highest priority task is O(1), which is much faster than the linear search technique having complexity of O(n). This pRTOS can support 64 priority levels ranges from 0 to 63. In addition with this, it is a highly configurable RTOS. Moreover, it can be adopted in a board range of hardware platform, say, Intel x86, MIPS, Hitachi SH, Power PC and Strong ARM processors. This RTOS has been tested on Intel x86 and from the obtained result, it has been found that our developed pRTOS can be used for various application, say, for automated industrial systems, control-systems, high-tech electronics/electrical products and home applications.

A simulation study of the performances of MiniMAP networks is presented. The two network models used in the simulation take into account the effect of the maximum number of outstanding requests set for each manufacturing message specification (MMS) application association. Three different situations are considered. In the first, all the messages are generated at the same priority level, whereas in the other two, four priority classes that are directly mapped onto channel priorities are introduced. However, the second situation considers the use of priorities only on the client side of MMS, whereas the third uses priorities on both sides.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>