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Embedded Systems November 2000 Vol13_12

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I I point of failure potentially reducing the level of availabili ty that can be achieved in the system. One approach that can alleviate the latter problem is to define a fau lt- tolerant arbiter. This can be done by defining a set of processors all equally capable of playing the arbiter role and then electing one to be the active a rbite r. Usuall y, only one level of redundancy is sufficient (one active and one standby), which greatly sim- plifies the election protocol. [5] Distributed system technologies In recent years, a number of pre-pack- aged distributed software technologies have become available in the market- place. Perhaps the most widely used are the ones based on the CORBA industry standard maintained by the Object Management Group (OMG) consortium. CORBA (Common Object Request Broker Architecture) defines a standard for interoperability of distributed appli- cations. At its core is a distributed com- munication facility, called the object request broker (ORB) , that allows individ- ual objects to locate and in teract with each other. [11] For this reason, the ORB is often referred to as the "object bus." The interacting objects might even be implemented in different program- ming languages, which means that the systems based on an ORB can be het- erogeneous. This is achieved by defining a language-neuu·al fmmat, called tl1e interface definition language (IDL). IDL is used to define tl1e interfaces of remote objects, representing func- tions that may be invoked by clients and attributes that are publicly accessi- ble. These interface specifications can then be automatically translated into an implementation language by a suit- able IDL compiler. You a.twa:ys believed there were mo,re intetUgen embedded toots out there People doubted their existence - yet you continued to search - and now you've found them. COSMIC C compilers are fa st, efficient, reliable, and produce the tightest object code available. Cosmic Software's embedded development tools offer portability for a complete line of micro- controllers. All toolkits include IDEA, our intuitive IDE that provides everything you need in a single, seamless Windows framework. You we e right. G MIC Software E-mail: c-tools@cosmic-us.com www.cosmic-software.com Phone: US ....... .781 932-2556 France ..... 33 1 4399 5390 UK ........ 44 01256 843400 Germany ... 49 0711 4204062 Sweden . . .46 31704 3920 Add ZAP, our non-intrusive source- level debuggers and minimize your test cycle too. Want proof of their existence? Download a free evaluation copy of our development tools at www.cosmic-software.com or call Cosmic today. Cosmic supports the Motorola family of microcontrollers: 6BHC05, 68HC08, 68HC11, 68HC12, 68HC16, 68300 and STMicroelectronics' ST7 Family. The key compone nts of the CORBA model and its basic opera- tion are described in Figure 3. The IDL stub is a local agent of the remote server and has the same inte rface as the remote server, but is specified in the implementa tion la n- guage of the client. This "native" specification is actually generated by the IDL compiler based on the IDL specification of the server. The IDL skeleton encapsulates the server at the remote end and invokes the server on behalf of the client. The object adapter provides an interface to the serve r fo r accessing the faci li t ies of the ORB as well as other CORBA ser- vices, such as a name service (used to locate d istributed objects during sys- tem establishment). These services may be used by the server to realize its function . The client simply makes a synchro- nous call via the IDL stub. The stub appears like a simple object that has the appropriate service interface. However, it hides a remote call to the ser·ver, executed via the ORB and an up-call through the IDL skeleton (in some cases, the object adapter may also be involved). When the reply information is returned, the client proceeds normally. The entire com- plex transaction is completely trans- parent to the client. There are many more detai ls and variants of th is basic scheme, but they are beyond the scope of this article. Interested readers should refer to the OMG spec.[ll] CORBA is just one example of the new gen eration of technologies and accompanying tools that a re becom- ing availabl e to distributed system developers. Their primary purpose is to hide some of the complexity of distributed systems development by providing standard solutions to com- mon distributed system problems. From that perspective it is useful to characterize the different kinds of "transparencies" (that is, complexity hiding) that such technologies can provide: [8] 142 NOVEMBER 2000 Embedded Systems Programming

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