How To Understand The Behavior Of A Coke Machine

Size: px

Start display at page:

Download "How To Understand The Behavior Of A Coke Machine"

Sabina Montgomery
3 years ago
Views:

1 NPTEL Course on Human Computer Interaction - An Introduction Dr. Pradeep Yammiyavar Professor, Dept. of Design, IIT Guwahati, Assam, India Dr. Samit Bhattacharya Assistant Professor, Dept. of Computer Science and Engineering, IIT Guwahati, Assam, India Indian Institute of Technology Guwahati

2 Module 7: Dialog Design Lecture 2: StateCharts Dr. Samit Bhattacharya

3 Objective In the previous lecture, we introduced the need for dialog design We also learned about the advantages about formal modeling of dialogs We discussed how to use STNs for the purpose

4 Objective As we mentioned, STNs are good for modeling simple systems; for complex systems as well as systems having concurrency, STNs fail In this lecture, we shall learn about the statechart formalism that can overcome the problems with STNs

5 StateCharts Proposed by David Harel (1987) to represent complex reactive systems Extends finite state machines (FSM) Better handle concurrency Adds memory, conditional statements to FSM Simplifies complex system representation (states and arcs) to a great extent

6 Definitions Active state: the current state of the underlying FSM Basic states: states that are not composed of other states Super states: states that are composed of other states For each basic state b, the super state containing b is called the ancestor state A super state is called OR super state if exactly one of its sub states is active, whenever it is active

7 Definitions Super state Ancestor state of A to E Sub states

8 Super State Advantage It allows us to represent complex FSM in a nice way, by clustering states

9 Default State Mechanism Indicates the sub state entered whenever super state is entered represented using a filled circle Not a state by itself

10 History Mechanism For input m, S enters the state it was in before S was left If S is entered for the very first time, the default mechanism applies History and default mechanisms can be used hierarchically

11 Combining History and Default State Mechanism same meaning

12 Concurrency StateCharts supports concurrency using the notion of the AND super states In AND super states, the FSM is active in all (immediate) sub states simultaneously A S11 S12 S21 S22 S 2

13 Timing Constraints StateChart supports delay/timeout modeling using special edges Do we need it?? If event a does not happen while the system is in the left state for 20 ms, a timeout will take place.

14 Example: Coke Machine Version 1.0 Suppose you have a coke vending machine: When turned on, the machine waits for money When Rs. 5/- coin is deposited, the machine waits for another Rs. 5/- coin When the second coin is deposited, the machine waits for a selection When the user presses COKE, a coke is d

15 Example: Coke Machine Version 1.0 Suppose you have a coke vending machine: When the user takes the bottle, the machine waits again When the user presses either SPRITE or DIET COKE, a Sprite or a diet Coke is d When the user takes the bottle, the machine waits again Let us represent this behavior using FSM

16 Coke Machine 1.0 take bottle Select coke Insert Insert coin coin idle 5/- 5/- take bottle take bottle coke Select diet coke Select sprite sprite diet coke

17 Coke Machine, Version 2.0 Let s include some more features in the machine The Bottles can get stuck in the machine An automatic indicator will notify the system when a bottle is stuck When this occurs, the machine will not accept any money or issue any bottles until the bottle is cleared When the bottle is cleared, the machine will wait for money again

18 Coke Machine, Version 2.0 State machine changes How many new states are required? How many new transitions?

19 Coke Machine 2.0 idle 5/- 5/- take bottle take bottle Insert coin Insert coin Select coke take bottle clear bottle coke Select sprite Select diet coke sprite stuck bottle diet coke

20 Coke Machine, Version 3.0 Let s add some more features Bottles sometimes shake loose An additional, automatic indicator will indicate that the bottle is cleared When the bottles are cleared, the machine will return to the same state it was in before the bottle got stuck

21 Coke Machine, Version 3.0 State machine changes How many new states are required? How many new transitions?

22 Coke Machine, Version 4.0 We can add even more features Automatic bottle filler If a button is pressed, the machine will toggle between bottle filling and dispensing modes When in bottle filling mode Bottles may be inserted if the Coke machine is ready When a bottle is inserted, the machine will NOT be ready to accept another bottle and will check the bottle

23 Coke Machine, Version 4.0 We can add even more features Automatic bottle filler If a button is pressed, the machine will toggle between bottle filling and dispensing modes When in bottle filling mode If the bottle check finds a Coke was inserted, it will signal Coke_OK and return to ready If the bottle check finds a Diet Coke was inserted, the coke machine will signal Diet_OK and return to ready Otherwise, the bottle will be immediately d

24 Coke Machine, Version 4.0 State machine changes How many new states are required? How many new transitions?

25 StateChart Construction: Bottle Dispenser collecting dispensing button take bottle

26 StateChart Construction: Bottle Dispenser collecting Insert coin idle 5/- 5/- Insert coin Select coke Select diet coke Select sprite take bottle dispensing coke diet coke sprite

27 StateChart Construction: Bottle Dispenser clear bottle Insert coin collecting idle 5/- 5/- Insert coin stuck bottle stick Select coke Select diet coke Select sprite take bottle stick dispensing coke diet coke sprite

28 StateChart Construction: Adding History clear bottle collecting H Insert coin idle 5/- 5/- Insert coin stuck bottle stick Select coke Select diet coke Select sprite take bottle stick dispensing coke diet coke sprite H

29 StateChart Pros Large number of commercial simulation tools available (StateMate, StateFlow, BetterState,...) Available back-ends translate StateCharts into C or VHDL, thus enabling software or hardware implementations

Design and Implementation of Vending Machine using Verilog HDL

2011 2nd International Conference on Networking and Information Technology IPCSIT vol.17 (2011) (2011) IACSIT Press, Singapore Design and Implementation of Vending Machine using Verilog HDL Muhammad Ali