Computational Models in Embedded Design

Computational Models
In Embedded Design
1
Computational Models prepared by
Anand H. D. Dr. AIT,Bengaluru

• Data Flow Graph/Diagram (DFG) Model
• Control Data Flow Graph/Diagram (CDFG)
Model
• State Machine Model
• Sequential Program Model
• Concurrent/Communicating Process Model
• Object Oriented Model
Definition: a model is a formal system consisting of objects & composition rules.
It is hard to make a decision on which model should be followed in particular
system design.
Most often designers switch between variety of models from requirement
specification to implementation.
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Data Flow Graph/Diagram (DFG)
Model
• Translates the data processing requirements into a data
flow graph.
• It is data driven model in which program execution is
determined by data.
• It emphasizes on data and operation on data which
transform the input data to output data.
• It is visual model in which operation on data(Process) is
represented using a block(Circle) and data flow is
represented by arrows(inward arrow => i/p to process
and outward arrow=> o/p of process)
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Data Flow Graph/Diagram (DFG)
Model cont…
• Embedded application which are computational intensive &
data driven are modeled using DFG Eg.: DSP
• For example suppose computation x = a + b & y = x - c needs
to be carried out, then
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• Acyclic DFG: doesn’t contain
multiple values for i/p variables
and multiple values for o/p
variables.

Control Data Flow Graph (CDFG)
Model
• Is used for applications involving control
program execution.
• Contains both data operation and control
operation.
Data nodes-> elements
control nodes-> decision makers
• For example, if Flag=1, x=a+b else y=a-b. This
requires decision making
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Control node is represented by a Diamond
Block
X
y

State Machine Model
• Used for modeling reactive or event-driven embedded
systems, whose behavior are dependent on state
transistions.
• State machine model describes the system behavior
with ‘State’, ‘Event’, ‘Action’ & ‘Transistion’.
State -> representation of current situation.
Event -> i/p to state, acts as stimuli for state transistion.
Action ->activity to be performed by state machine.
Transistion -> movement from one state to another.
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State Machine Model cont.
Example-1: SEAT BELT WARNING SYSTEM
Requirements:
1. When vehicle ignition is turned ON & seat belt is
not fastened within 10 secs of Ignition ON, the
system generates an alarm signal for 5 secs.
2. The alarm is turned OFF when the seat belt is
fastened / alarm time expires / the ignition is
off== whichever happens first.
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SEAT BELT WARNING SYSTEM:
Events:
‘Ignition_Key_ON’
‘Ignition_Key_OFF’,
‘Time Expire’,
‘Alarm Time Expire’ and
‘Seat_Belt_ON’.
States:
‘Alarm_OFF’,
‘Waiting’, and
’Alarm_ON’.
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SEAT BELT WARNING SYSTEM: cont..
The timer used in Seat Belt Warning System can also be
modeled as a Finite State Machine
States: ‘Idle’,
‘Ready’, and
’Running’.
Events: ‘Load Timer’
‘Start Timer’,
‘Stop Timer’ and
‘Timer Expire’
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Example-2: Automatic Tea/Coffee vending
Machine
Requirements:
1. Tea/Coffee vending machine is initiated by
user by inserting 5 Rs. Coin.
2. After inserting Coin, user can select either
coffee /tea / press cancel order and take back
the coin.
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Automatic Tea/Coffee vending Machine:
Events:
‘Insert Coin’
‘Tea Button Pressed’,
‘Coffee Button Pressed’,
‘Cancel Button Pressed’,
‘Coffee Dispensed’ and
‘Tea Dispensed’
States:
A= ‘OFF/wait for coin’,
B= ‘wait for user i/p’,
C= ’Dispense Tea’ and
D= ’Dispense Coffee’.
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Automatic Tea/Coffee vending Machine:
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Example-3: Coin Operated Public Telephone Unit
Requirements:
1. Call is initiated by lifting the receiver.
2. After lifting user needs to insert 1 Rs. Coin
3. If line is busy, coin is returned on placing the receiver back.
4. If line is through/free user is allowed to talk for 60 secs & at the end of
45th sec prompt for inserting another if want to continue call.
5. If doesn’t insert coin, call is terminated after completing 60 secs .
6. The system is ready to take up new call when receiver is placed back on
hook.
7. The system goes Out of order state when there is line fault.
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Coin Operated Public Telephone Unit :
Events:
‘Rceiver lifted’
‘Coin inserted’,
‘Valid Number’,
’Line available’,
’Line busy’,
‘Time out’,
‘Place Receiver’,
‘Invalid Number’,
‘Line fault’ and
‘Line OK’
States:
A= ‘Ready’,
B=‘wait for coin’,
C=‘wait for number’,
D=’Dialing’
E=’Call in Progress’
F=’Call Terminated’
G=’Unable to make call’
H=’Invalid Number’ and
I=’Out of Order’.
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Coin Operated Public Telephone Unit :
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Sequential Program Model
• The functions or processing requirements are executed in
sequence.
• Program instructions are iterated and executed
conditionally and data gets transformed through a series of
operations.
• FSMs are good choice for sequential Program modeling.
• Flow charts are also good tool for modeling sequential
program.
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FSMs represents States, events, transistions and actions
Flow charts model the execution flow

Example: Seat Belt Warning System
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#define ON 1
#define OFF 0
#define YES 1
#define ON 0
Void Seat_belt_warn()
{
Wait_10sec();
If (Check_ignition_key()==ON)
{
If (Check_seat_belt()==OFF)
{
Set_timer(5);
Start_alarm;
While (Check_seat_belt() == ON || Check_ignition_key() == OFF || Timer_expire()==YES)
Stop_alarm();
}
}
}

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Concurrent/Communicating Process
Model
• Models concurrently executing tasks/processes
• Sequential models leads to poor utilization of
processor, when the tasks waits for I/O
Sleeping.
• here a task is subdivided into multiple sub tasks &
CPU is effectively used.
• but requires additional overhead like task
scheduling, task synchronization &
communication
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Tasks can be split into:
• 1.) timer task for waiting 10 secs
Wait_timer_task
• 2.) tasks for checking the ignition key status
Ignition_status_monitoring task
• 3.) tasks for checking the seat belt status
seat_belt_status_monitoring task
• 4.) task for starting & stopping of alarm
alarm_control_task
• 5.) alarm timer task for waiting 5 sec
alarm_timer_task
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Example: Seat Belt Warning System

These tasks cannot be executed randomly or sequentially instead
they need to be synchronized through some mechanism 
events
Events associated with tasks are:
• Wait_timer_task  wait_timer_expire
• Ignition_status_monitoring task  Ignition key ON
 Ignition key OFF
• seat_belt_status_monitoring task  Seat belt ON
 Seat belt OFF
• Alarm_timer_task  alarm_timer_start
alarm_timer_stop
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Set & Reset by
alarm_control_task

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Object Oriented Model
• Complex overall program/software requirement is
divided into simple well defined pieces called
objects.
• A class is abstract description of a set of objects &
can be considered as blueprint of objects.
• State of object=member variable
• Object behavior= member function
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Private, Public or
Protected
Private= ->accessible only within the class
Public-> accessible within as well as outside the class
Protected-> external access is prohibited

Reference
• Shibu K V, “Introduction to Embedded
Systems”, First Edition, Tata McGraw Hill
Education Private Limited, 2009
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Prof. Anand H. D.
M. Tech. (PhD.)
Assistant Professor,
Department of Electronics & Communication Engineering
Dr. Ambedkar Institute of Technology, Bengaluru-56
Email: anandhdece@dr-ait.org
Phone: 9844518832

Computational Models in Embedded Design

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