Software engineering for real-time systems

Software engineering for real-time systems
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003)
Section 7
Data flow design concepts
Simple example - materials flow model
Robot 1 Robot 2 Robot 3
Data flow design concepts - slide 1
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 3
Materials flow model - single work resource
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 5
To:
Introduction to data flow design
Objectives
Explain the basic concept of materials flow processing of data.
Show how systems can be described in terms of collaborating data
processing machines (‘data transformations’).
Give a detailed view of design structuring and levelling using data
flow constructs.
Introduce the need for and use of control transformations
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 2
Data in to DT1
Sonar
echo
return
Simple DFD example - multiprocessor implementation
Data out from DT1
Process sonar
signal
(Processor 1)
Processed
sonar
signal
Data in to DT2
Perform
spectral
analysis
(Processor 2)
Sonar
spectral
data
Data
transformation 1 Data
transformation 2 Data
transformation 3
Evaluate threat
(processor 3)
Threat
data
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 4
Uncut
bar
Measure
and mark bar
DFD example (part) - single work resource
Marked
bar
Cut bar
Basic
bar
Heat and
shape bar
Shaped
bar
Tempered
Quench bar
bar
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 6
1

External
item 1
External
item 2
DFD design - the context diagram
Data 1 in
Data 2 in
The system
software
Data 3 out
Data 4 out
External
item 3
External
item 4
The purpose of a context diagram is to show the relationship of the system software with its
environment.
It portrays the complete system in its simplest form: a set of external items connected to a
software ‘black box’.
It contains:
- A single processing unit (the ‘bubble’) representing the complete software system.
- The external items which this software interfaces to.
- Data flows into and out of the software.
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 7
Data 1 in
Data 2 in
DT
1
DT
2
First-level DFD - general form
Data X
Data Y
Data Z
DT
3
DT
4
Data A
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 9
DT
5
Data 4 out
Data B Data 3 out
Second-level DFD - levelled form of the DT ‘Compute braking signals’
Speed 1
Speed 2
Compute wheel
accel/decel
2.1
Compute wheel
accel/decel
2.2
Wheel 1 accel/decel
Wheel 2 accel/decel
Compute
braking correction
signals
2.3
Stored values
Accel/decel
profiles
valve 1 signal
valve 2 signal
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 11
Speed sensor 1
Speed sensor 2
Tyre pressure 1
Tyre pressure 2
Context diagram - anti-skid braking system
Wheel 1 speed
Wheel 2 speed
Tyre 1 pressure
Tyre 2 pressure
Anti-skid
braking
system
Valve 1 signal
Valve 2 signal
Display data
Valve 1
Valve 2
Vehicle dash
display
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 8
Wheel 1 speed
Wheel 2 speed
Tyre 1 pressure
Tyre 2 pressure
Example first-level DFD - anti-skid braking system
Measure wheel
speeds
1
Measure tyre
pressures
3
Pressure 1
Pressure 2
Speed 1
Speed 2
Compute
braking signals
2
Control dash
display
4
Braking 1
signal
Braking 2
signal
Control servo
value 1
5
Control servo
valve 2
6
Valve 1 signal
Valve 2 signal
Display
data
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 10
A
B
B
Entity 1
Levelling and balancing in DFD design
A
Entity 2 Software system
B
DT1
DT2
D
E
DT3
F
2.1 2.2
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 12
C
C
E
Entity 3
Context
diagram
First level
DFD
Second
level DFD
2

Combining data and control transformations
DT 1
DT 2
DT 3
E/D
E/D
E/D
CT 1
Data transformation enable/
disable commands
Control
transformation
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 13
A more complex control transformation
Set loop counter to 0
Loop:
If loop counter = 0 then
Run DT1
Else if loop counter = 1 then
Run DT1
Run DT2
Else if loop counter = 2 then
Run DT2
Run DT3
Increment Loop Counter by one
When Loop Counter = 3 reset to 0
End Loop;
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 15
CT1
Control transformation - icon and specification
Icon
Specification
of CT1
Loop:
Enable DT1
Wait Time T1
Disable DT1
Enable DT2
Wait Time T2
Disable DT2
Enable DT3
Wait Time 3
Disable DT3
End Loop
Run DT1
Run DT2
Run DT3
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 14
Review of ‘Data flow design concepts’
Review of section
You should now:
Realize that the data flow model of software presents a materials flow
view of the process.
Understand how to structure a design using DFD techniques.
Know the meaning and use of context diagrams, levelled data flow
diagrams, data flows, data transformations and control transformations.
Be competent to assess real designs that are based on DFD methods.
End of section ‘Data flow design concepts’
SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Data flow design concepts - slide 16
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