Lecture 4: State Machines for Real-Time Embedded Systems

Transcription

1 SWE 760 Lecture 4: State Machines for Real-Time Embedded Systems Hassan Gomaa Department of Computer Science George Mason University References: H. Gomaa, Chapter 7 - Real-Time Software Design for Embedded Systems, Cambridge University Press, 2016 Copyright 2016 Hassan Gomaa All rights reserved. No part of this document may be reproduced in any form or by any means, without the prior written permission of the author. 1 Figure 4.1 COMET/RTE life cycle model User System Structural Requirements Analysis Design Incremental Software Construction Incremental Software Integration Incremental Prototyping System Testing Customer Copyright 2016 Hassan Gomaa 2 1

2 Analysis Static Define entity classes and relationships Dynamic State Machine Real-time systems are highly state dependent Actions depend on input event AND current state Object Structuring Determine objects that realize each use case Dynamic Interaction Determine sequence of interactions among objects 3 State Machines Conceptual machine with finite number of states a.k.a. finite state machine Graphical representation of State Machine States are rounded boxes Transitions are arcs State Machine Relates events and states Event Causes change of state Referred to as state transition State A recognizable situation Exists over an interval of time Represents an interval between successive events 4 2

3 Events and Actions State transition label Event [condition] / action(s) Event When event occurs, condition must be true for state transition to occur. If condition is false, state transition does not occur Action Executed as a result of state transition Executes instantaneously at state transition Terminates itself 5 Example of events and actions Microwave Control - Cook Food main sequence Door Opened Door Shut Door Closed Door Open Item Placed Item Removed Door Open With Item Door Closed Door Opened Cooking Timer Expired/ Stop Cooking Start/Start Cooking, Start Timer Cooking Time Entered/ Display Cooking time, Update Cooking Time Door Shut With Item Ready To Cook 6 3

4 Example of alternative state transitions and actions in Cook Food use case 7 Entry and Exit Actions Entry action Action executed on entry into state Entry / action E.g., Start Cooking Exit action Action executed on exit from state Exit / action E.g, Stop Cooking Copyright 2012 H. Gomaa fsm-8 4

5 Example of entry action Fig a: Actions on state transitions Fig b: Entry action 9 Example of exit action Actions on state transitions Exit action 10 5

6 State Machine for Microwave Oven Control with entry and exit actions Door Opened Door Shut Door Closed Door Open Cancel/Cancel Timer Item Placed Item Removed Door Closed [Time Remaining] Door Opened/ Stop Timer Door Closed [Zero Time] Door Open With Item Door Opened Door Opened Cooking entry/ Start Cooking Timer Expired Door Shut With Item exit/ Stop Cooking Cancel/ Stop Timer Cooking Time Entered/ Display Cooking Time, Update Cooking Time Cancel/ Cancel Timer Start/ Start Timer Ready To Cook Cooking Time Entered/ Display Cooking Time, Update Cooking Time 11 Activities Activity Executes for duration of state do / Activity in state Examples of activities in Cruise Control State Machine Increase Speed Executes for duration of Accelerating state Maintain Speed Executes for duration of Cruising state Reduce Speed Executes for duration of Decelerating state Stop Train Executes for duration of Stopping state 12 6

7 Cruise Control State Machine with activities 13 Hierarchical State Machines Sequential State (OR) decomposition When object is in composite state (superstate) It is in one and only one of substates Transition into composite state Must be to one and only one of substates Aggregation of state transitions If same event causes transition out of every substate Then aggregate into transition out of composite state History state When composite state is re-entered Enter substate that was previously active Prior to previous exit from composite state Example: Microwave Oven Control 14 7

8 15 Orthogonal State Machines Concurrent State Machines State of an object described by more than one state machine Orthogonal State Machine Used to depict states of different aspects of object Uses concurrent state machine Concurrent state (AND) decomposition Object is in one substate on each lower level state machine Object s state is union of all substates Same event May cause transitions on more than one state machine Output event on one state machine May be input event on other state machine Substate on one state machine May be condition on other state machine Example: Microwave Oven Control 16 8

9 Orthogonal State Machines for Microwave Oven Control 17 Variability in State Machines - Inherited State Machines When a state machine is specialized Child state machine inherits properties of parent state machine Child state machine can: Add new states New states at same level of hierarchy as inherited states New substates of new or inherited states New orthogonal (concurrent) states Add new events and transitions Add or remove actions and activities Child state machine Must not delete states or events defined in parent 18 9

10 Inherited State Machines Examples from Microwave Oven SPL Superclass: Microwave Oven Control Subclass with all features: Enhanced Microwave Oven Control Added functionality Light, Turntable, Beeper, Minute Plus, Time of Day (TOD) Example of new states added TOD 3 substates of inherited Door Shut state Example of new transitions added Minute Plus Example of new actions added Turntable, Beeper 19 Inheritance of State Dependent Control Class «state dependent control» MicrowaveOvenControl «state dependent control» EnhancedMicrowaveOvenControl 20 10

11 Inherited State Machine for Enhanced Microwave Oven Control Door Opened / Switch On Door Shut Door Closed / Switch Off Door Open Cancel / Cancel Timer Item Placed Item Removed Door Closed [Time Remaining] / Switch Off Minute Plus / Add Minute Cooking Entry / Start Cooking, Start Turning, Switch On Exit / Stop Cooking, Beep, Stop Turning Door Opened/ Stop Timer Timer Expired / Switch Off Minute Plus / Start Minute Cancel / Stop Timer, Switch Off Door Open With Item Door Closed [Zero Time] / Door Opened / Switch Off Switch On Door Shut With Item Cooking Time Entered / Cancel / Display Cooking, Cancel Timer Update Cooking Time Door Opened / Switch On Start / Start Timer Ready To Cook Cooking Time Entered / Display Cooking Time, Update Cooking Time 21 Cooperating State Machines Cooperating state-dependent control objects Each control object executes a state machine Cooperating state machines Action on one state machine corresponds to event on another state machine E.g., Microwave Oven Control, Oven Timer state machines Microwave Oven Control state machine Action: Start Timer -> Oven Timer state machine Event: Timer Expired Oven Timer state machine Event: Start Timer Action: Timer Expired -> Microwave Oven Control state machine 22 11

12 Cooperating State Machines: Oven Timer State Machine Cook Food use case 23 Figure 4.1 COMET/RTE life cycle model User System Structural Requirements Analysis Design Incremental Software Construction Incremental Software Integration Incremental Prototyping System Testing Customer Copyright 2016 Hassan Gomaa 24 12

13 Analysis Static Define entity classes and relationships Dynamic State Machine Real-time systems are highly state dependent Object Structuring Determine objects that realize each use case Dynamic Interaction Determine sequence of interactions among objects 25 13