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2. Specification and Modeling

2. Specification and Modeling. 2.5 Data Flow 2.6 Petri nets 2.7 Discrete event based languages 2.8 Von-Neumann languages. 2.5 Data flow. 2.5.1 Scope

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2. Specification and Modeling

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  1. 2. Specification and Modeling 2. Spec. & Modeling 2.5 Data Flow 2.6 Petri nets 2.7 Discrete event based languages 2.8 Von-Neumann languages

  2. 2.5 Data flow 2.5.1 Scope • Def: Data flow modeling “is the process of identifying modeling and documenting how data moves around an information system. Data flow modeling examines processes, data stores, external entities, data flows”. • A data flow diagram is specified by a directed graph where the nodes, called actors, represent computation and the arc represent communication channels. 2.5.2 Kahn process networks • KPNs consist of nodes and edges. Nodes correspond to computations performed by some program or task. Edges imply communication via channels containing potentially infinite FIFOs. • Fig. 2.40 shows a graphical representation of the KPN (p. 63). 2. Spec. & Modeling

  3. 2.5.3 Synchronous data flow • SDF can best be introduced by referring to its graphical notation. • Graphical representation of synchronous data flow • For each execution for computation in a node is called a firing. For each firing, a number of token, representing data, is consumed and produced. • Constant edge labels denote the corresponding numbers of tokens. • Multi-rate SDF model • Let ns be the number of tokens produced by some sender per firing, and let fr be the corresponding rate. 1 A B 1 A B 1 1 * + * 1 + D 1 1 1 1 2. Spec. & Modeling FIFO nr fs ns fr

  4. 2.6 Petri Nets 2.6.1 Introduction • Petri nets model only control and control dependencies. • Conditions, events and a flow relation are the key elements of Petri nets. • Conditions are either satisfied or not satisfied. • Events can happens. • The flow relation describes the condition that must be met before events can happen and it also describes the conditions that become true if events happen. 2. Spec. & Modeling

  5. 2.7 Discrete event based language • The discrete event-based model of computation is based on the idea of simulating the generation of events and the processing of event over time. 2.7.1 VHDL • VHDL uses processors for modeling concurrency. 2. Spec. & Modeling

  6. 2.7.2 SystemC and SystemVerilog • SystemC is a C++ class library designed to solve these problems: concurrency, time, multiple-valued logic and determinate behavior. • Verilog is another hardware description language. Verilog versions 3.0 and 3.1 are also known as SystemVerilog. They include numerous extensions to Verilog 2.0. (p.99) 2. Spec. & Modeling

  7. 2.8 Von-Neumann language 2.8.1 CSP • CSP (communicating sequential processes) is one of the first language comprising mechanisms for inter-process communication. • Both processes will wait for the other process to service at the input or output statement. This is a case of rendez-vous-based, blocking or synchronous message passing. 2.8.2 ADA 2. Spec. & Modeling

  8. 2.8.3 Java 2. Spec. & Modeling

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