Lecture Building reliable component-based systems - Chapter 16: Component-based embedded systems

Chapter 16

Component based embedded
systems

Building Reliable Component­based 


Overview
Introduction
Component technology in embedded systems
Case study – ABB’s Field Devices
Prerequisites for effective development of Componentbased embedded systems
Summary

Building Reliable Component­based 


Where is the problem?
Huge market arises for embedded devices, and thus for
software for them
Similar basic functionalities are repeated
New functionalities are added constantly
Shorter development time is required

Building Reliable Component­based 


Introduction

Building Reliable Component­based 

Embedded vs. Component-based
Monolithic approach
requires re-implementing
the functionalities

Embedded devices 
are too small for 
component off­the­
shelf technologies

Component based SE
provides a mean to reuse
the functionalities

Component based SE 
can provide a 
framework instead of 
technology

Building Reliable Component­based 


Component technology in embedded
world
Contractually specified interfaces
Component as a unit of composition and independent
deployment
Explicit context dependencies

Component granularity
Reuse
Location transparency
Component wiring
Portability, platform independence

Building Reliable Component­based 


Contractually specified interfaces
State-of-the-art technologies approach:
Interfaces as pure collection of methods.

•  Embedded environment constraint:
Non­functional specifications are equally 
important part of the contract
Building Reliable Component­based 


Interfaces II
Component interfaces support:
Late binding,
Polymorphism,
Semantic specification
Pre conditions,
Post conditions,
Invariants

Building Reliable Component­based 

Unit of composition and independent
deployment
Run-time composition
Component model,
Run-time environment,
Dynamic communication,

Design-time composition
Capable of generating
monolithic firmware from
component-based design,
Optimization

Building Reliable Component­based 


Explicit context dependencies
What is a context in embedded world?
Other components and interfaces
Run-time environment
CPU,
RTOS,
Component implementation language,
Resource constraints

Building Reliable Component­based 


Component granularity

Coarse-grained components,

Fine-grained components,

Too heavy bag of
unnecessary functionality,

Light, unneeded functionality
reduced,

Too much resources used,

Scarcer uses of resources,
Greater communication
overhead,

Building Reliable Component­based 


Reuse
Black-box reuse
From component’s user point of view,
White-box reuse
From composition environment point of view
Gray-box reuse (composition environment)
If clear conventions for knowledge about implementation
are introduced

Building Reliable Component­based 

Architecture and frameworks
Defining components alone will not lead to reuse
Common architecture for family of embedded devices
Framework for development

Building Reliable Component­based 


Portability, Platform independence
Source level portability suffices,
Design-time composition,
Run-time environment restrictions
Source level portability requires:
Agreement on implementation language,
Agreement on available libraries,
Providing proper abstractions (i.e. RTOS API)

Building Reliable Component­based 


Other issues
Location transparency
For embedded devices there is a single location,
Component wiring
Needed for flexible composition of software,
Optimizes component interaction,
Component ”glue code” should be in implementation
language

Building Reliable Component­based 


Case study – ABB’s Field devices

Synchronous approach
Architecture of the field devices
Dynamic behavior
Inter-component communication

Building Reliable Component­based 


Synchronous approach
Synchronous languages have been developed to simplify
the programming of reactive systems
Provide the mean to handle concurrency, determinism,
response time control
Based on synchrony hypothesis

Building Reliable Component­based 


Architecture of the field device
Block Container
Scheduler

AO Function Block
SP

AO
Algorithm

Transducer Block
OUT

MODE

OUT_CHAN

READBACK

IN_CHAN

POS_VALUE
CTRL_PAR

I/O
HW
FEEDBACK

Profibus PA Mapper

Pos
Control

Pos
Measure.

AccessManager

Profibus PA Stack

Display, Buttons

Local Operation

Persistent Storage

PC/Handheld-Interface

Building Reliable Component­based 


Dynamic behavior
manipulated
variable
(3)

a)
setpoint

Controlled
System

Controller
(2)
actual
value

(1)

b)

Sensors
(1)

PID
(2)

Building Reliable Component­based 

out

out

error

Setpoint

Tv,Tv,kp

speed

speed

Signalbus

Actuator
(3)

Inter-component communication
Based on Signal Bus
Signal Bus communication is maintained by Object
Manager
Communication itself is based on signals
One source per signal

Building Reliable Component­based 


Types of Interfaces
User
Interface
(1)
(4)
Communication
Link

(2)
Real­time
System

(3)

Mass storage
Interface

Building Reliable Component­based 

Process
Interface


Prerequisites for effective development
Component model
Additionally must address non functional properties,
Allow for code generation,
Allow for efficient functional interfaces,
Allow for specification of architectural styles that
describe component connections and containment
relations,

Building Reliable Component­based 


Framework

Component
Model

Component-based
Architecture for
field devices

Component
Repository

Composition

environment

Building Reliable Component­based 

Run-time
environment


Prerequisites II
Component-based architecture for field devices
Framework,
Compile time optimizations,
Field-bus architecture,
Repository
Storage and retrieval of components,
Storage of non-functional properties, implementation,
support and test scripts,
Versioning

Building Reliable Component­based 


Prerequisites III
Composition environment
Constraint verification,
Component adaptation and code generation,
Composition techniques,
Definition of composition rules

Building Reliable Component­based