CSCI1600: Embedded and Real Time Software Lecture 10: Modeling IV: Compositions of State Machines Steven Reiss, Fall 2015

Modeling Tasks  We can model individual tasks using FSMs  Extended FSMs, Timed automata, …  Hybrid automata to reflect state of outside world  This is sufficient for coding  We need to model the overall application  We need this to prove properties of the system  We need this to understand overall system behavior  What was in chapter 5

Statecharts  We saw this last week  Lets look at it in more detail  Lets be able to understand it formally  Map to a single FSM

Example : Concurrent Machines

Example: concurrency

Example: Concurrency

Example : communicating tasks

Example: hierarchical

Example: Hierarchical

Example

 Tic-Tac-Toe

Issues  Handling concurrency  The FSM is in multiple states  What does this mean formally (single FSA)  What does this mean in a statechart  What do you do with an input  How is this implemented  What if the results are contradictory (set x = 1, set x = 0)  What does this mean for your implementation

Mapping to Code  Direct sequential coding  Determine state from various conditions  Act accordingly  Allows common operations for multiple states  Explicit state variable  switch (state) { … }  Table-driven  Approximate the state machine

Homework  Read 6.1, 6.2, 6.4