1. 6/26/2015Page 1 Software Requirements Engineering Ch.5 B. Ramamurthy

2. 6/26/2015Page 2 Topics Requirements engineering process State machines Event-driven programming Table-driven methods Mealy Machines Petri nets for representing behavior of multiprocessors Use case diagrams

3. 6/26/2015Page 3 Requirements-Engineering Process Deals with determining the goals, functions, and constraints of systems, and with representation of these aspects in forms amenable to modeling and analysis.

4. 6/26/2015Page 4 Types of requirements Standard scheme for realtime systems is defined by IEEE standard IEEE830. It defines the following kind of requirements: I.Functional II.Non-functional 1.External interfaces 2.Performance 3.Logical database 4.Design constraints (ex: standards compliance) 5.Software system attributes Reliability, availability, security, maintainability, portability

5. 6/26/2015Page 5 Design methods: Finite state machines Finite state automaton (FSA), finite state machine (FSM) or state transition diagram (STD) is a formal method used in the specification and design of wide range of embedded and realtime systems. The system in this case would be represented by a finite number of states. Lets design the avionics for a fighter aircraft.

6. 6/26/2015Page 6 Fighter aircraft avionics TAK LAN NAA NAE NAV else MA else TD else LO else EE ED MC

7. 6/26/2015Page 7 Finite State Machine (FSM) M = five tuple  { S, i, T, Σ, δ } S = set of states i = initial state T = terminal state (s) Σ = events that bring about transitions δ = transitions Lets do this exercise for the avionics for fighter aircraft

8. 6/26/2015Page 8 State Transition table MALOTDMCEEED TAKNAV NAELAN NAENAA NAENAV LAN

9. 6/26/2015Page 9 Lets write the embedded system Use the table to code a function with case statement Or write a table-driven code Which is better and why?