Minimizing System Modification in an
Incremental Design Approach
Paul Pop, Petru Eles, Traian Pop, Zebo Peng
Department of Computer and Information Science, Linköpings universitet, Sweden
Summary
I/O Interface
RAM
Incremental Design
Future
applications
Map and schedule
so that the
future applications
will have a chance
to fit.
N-1
Existing
applications
Modify (re-map)
so that the
current applications
will fit.
ROM
CPU
ASIC
Comm. Controller
 Static cyclic scheduling of processes and messages,
 Bus access scheme: time-division multiple-access.
Node
 Incremental design process
 Already existing system,
 Implement new functionality,
 a) Existing system modified as little as possible,
b) new functionality can be easily added to the system.
S0
S1
S2
S0
S3
S1
S2
S3
Slot
N
Version N+1
Current
applications
Do not exist yet
at Version N!
 Mapping and scheduling of distributed
embedded systems for hard-real time applications
TDMA Round
 Mapping strategy
Cycle of two rounds
 a) Subset selection to minimize modification time,
 b) Two design criteria, objective function.
 Start from an already existing system with applications
 Implement new functionality on this system
Mapping and Scheduling
Problem Formulation
 To reduce design and testing time:
As few as possible modifications of the existing applications
 After the new functionality has been implemented:
It should be easy to add functionality in the future
Characterizing existing applications:
 Input
150
 A set of existing applications.
 A current application to be mapped.
 The system architecture.
 Output
 Requirements
a)
b)
c)
50
G3
70
G4
50
G5
G6
G9
G10
20
G7
Characterizing future applications:
 Typical WCETs
 Typical message sizes
 Smallest expected period Tmin
 Expected necessary processor time tneed
 Expected necessary bandwidth bneed
 a) constraints of the current application are satisfied
and minimal modifications are performed to the
existing applications.
C1P,
Mapping Strategy
C1m
 First criterion:
How well the resulted slack sizes
accommodate a future application
 Initial mapping and scheduling
360 ms
Periodic slack
min(40, 80, 0) = 0ms
min(40, 0, 80) = 0ms
min(80, 80, 40) = 40ms
S1 S2 S3 S1 S2 S3 S1 S2 S3 S1 S2 S3
C P2 = 40ms
Tmin
P1
Round 0 Round 1 Round 2 Round 3
Period 0
Period 1
Period 2
a)
min(40, 40, 40) = 40ms
min(40, 40, 40) = 40ms
min(80, 80, 40) = 40ms
S1 S2 S3 S1 S2 S3 S1 S2 S3 S1 S2 S3
C P2 = 120ms
Round 0 Round 1 Round 2 Round 3
b)
 Second criterion: C2P, C2m
How well the slack is distributed in time to
accommodate Tmin, tneed and bneed
Paul Pop, Petru Eles, Traian Pop, Zebo Peng:
An approach to Incremental Design of
Distributed Embedded Systems,
Design Automation Conference, 2001
 Requirement a)
Subset selection problem
Select that subset  of existing applications so that
the current application fits and the modification
cost R() is minimized:
R() 
 Ri
Gi 
Three approaches to the subset selection problem
 Exhaustive Search (ES)
 Ad-Hoc Solution (AH)
 Subset Selection Heuristic (SH)
1200
AH
SH
ES
1000
800
600
400
200
0
320
400
480
560
640
Number of processes
140
Average Execution Time [min]
P2
Average Modification Cost R()
Slack
 Requirement b)
Objective function minimization:
AH
SH
ES
120
100
80
60
40
20
0
320
400
480
560
640
Number of processes
C  w1P (C1P )  w1m (C1m )  w2P max( 0, t need  C2P )  w2m max( 0, bneed  C2m )
Percentage of future applications [%]
Current
Future: P1
N1
N2
N3
Bus
G2
 b) new future applications can be mapped
on the resulted system.
Existing
N1
N2
N3
Bus
70
G8
 A mapping and scheduling of the current application,
so that the incremental design requirements are satisfied.
Design Criteria
G1
120
MS*
100
AD
80
60
40
20
0
40
1 of240 16
April 25, 2006
80
160
Number of processes in the current application