嵌入式系统导论-实验课-3-solution.pdfVIP

Institut für Technische Informatik und Kommunikationsnetze 1.1 StateCharts The lecture has introduced Harel’s StateChart formalism. StateCharts are a popular specification model for embedded systems. 1.1.a) Advantages of StateCharts What are the most important extensions of the StateChart model in comparison to an ordinary finite state machine (FSM)? Solution: StateCharts can model hierarchy and concurrency. Transitions can be guarded (conditionally enabled). Furthermore, transitions can be associated with actions. Actions can perform computations on variables, as well as generate new events. 1.1.b) Disadvantages of StateCharts What are the disadvantages of the StateChart formalism? Solution: Although StateCharts scale better than ordinary FSMs, they grow in size for large systems and tend to be hard to understand. There is only limited potential for re-use. Actions associated with transitions provide a powerful extension, but on the other hand, the extensive use of actions moves parts of the system state information from the states themselves to the variables. This hidden state makes system analysis difficult. 1.1.c) Tree of states for StateChart Given the StateChart in Figure 1. Draw the state space of the StateChart as a tree, which shows the hierarchy CB e d a/c ec b[D2] A 1 2 G D1 D D2 Figure 1: StateChart of states and denotes the state types (basic state, sequential states, and parallel states). Solution: The state space is shown in Figure 2. 1.1.d) Formal computation of state space How would you formally compute the set of states? Compute the set of states for the hierarchical automata which is defined by the StateChart from Fig. 1. 1 Kai Huang Introduction to Embedded Systems Solution for Exercise Sheet 3 Issue Date: 14.11. 2014 paralleler Zustand sequentieller Zustand Basiszustand B 2 G C D D1 D2 1 A Figure 2: State tree: hierarchy and type of states Solution: ZA = ZB × ZC = (Z1 ∪ Z2)× (ZG ∪ ZD) = (Z1 ∪ Z2)× (ZG ∪ (ZD1 ∪ ZD2)) = (Z1, ZG) ∪ (Z1, ZD1) ∪ (Z1,