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Embedded Systems December 2000 Vol13_13

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A configuration is a set of PBOs that are interconnected to provide the required open-loop or closed-loop system. FIGURE 4 Comp-arison of traditional . . . Traditional RealĀ·Time Process processO { POSIX - RT - }/*end process * / _ = System (RTOS or Framework) Code }/*end pboframe* / = User Code ... PortĀ· Based Object Process pboframe(*pboX pbo ",,/ Configurations N; defin ed by Dorf, "a control system is an inte rconnection of components forming a system configuration which will provide a desired sys tem response."141 Each component can be mathematical ly modeled using a trans- fer function to compute an output response fo r any given input response. The port-automaton theory provides an algebraic model for these types of contI-ol systems. By incorporating the model in to the PBO, the PBOs pro- vide a model sui table for control engi- neers. PBOs are configured to form a control system in the same way that a control engineer configures a system using transfer functions and block dia- grams. This approach allows th e framework to satisfy an important cri- terion: to make it easy to program for a target audience of control engineers who do not have extensive train ing in software engineering or real-time sys- tems programming. A conjigumtion is a set of PBOs that one of the PBOs in the s~stem pboframe(*pbo) { pbo n pboframeO { pb01 pbo2 pbo3 A pboframe(*pbo) { pbo1 pboframe(*pbo) { pbo2 B pboframe(*pbo) { pbo3 are interconnected to provide the required open-loop or closed-loop sys- tem. A configuration is valid only if for every PBO selected, any data that it requires at its input ports is pmduced by one of the other PBOs as output. N; per the port-automaton theory, the contI'ol engineer does not have to be concerned with how data gets from the output of one PBO to the input of another PBO. The communication is embedded in the framework, such that it is u'ansparent to the conu'ol engineer. A configuration also cannot have two PBOs that produce the same output, othe rwise a confl ict may arise as to which output should be used at a given time. Port names a re used to perform the bindings betwe(,!n input and out- put ports. Whenever two PBOs exist with matching input and output ports , the framework creates a communica- tions link from the output to the input. If necessary, the output can be fanned into multiple inputs. Our framework uses an internal/ external name separation for the ports, such 108 DECEMBER 2000 Embedded Systems Programming

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