why is embedded software an issue for semiconductor...

1

SRC ETAB Summer StudyColorado Springs, June 25-26, 2001

Model-Based Approaches toEmbedded Software Design

Edward A. LeeUC Berkeley & GSRC

Edward A. Lee, Berkeley, 2

Why is Embedded Software an Issuefor Semiconductor Manufacturers?

Silicon without software is gettingrarer.

Time-to-volume is often dominatedby SW development.

Software requirements affecthardware design.

Embedded SW design is gettingharder (networking, complexity).

Mainstream SW engineering is notaddressing embedded SW well.

primeexample

today

2


Why is Embedded SW not justSoftware on Small Computers?

Interaction with physical processessensors, actuators, processes

Critical properties are not all functionalreal-time, fault recovery, power, security, robustness

Heterogeneoushardware/software, mixed architectures

Concurrentinteraction with multiple processes

Reactiveoperating at the speed of the environment

These feature look more like hardware!


Why not Leave This Problem to theSoftware Experts?E.g. Object-Oriented Design

Call/return imperative semanticsConcurrency is via ad-hoc calling conventions

band-aids: futures, proxies, monitorsPoorly models the environment

which does not have call/return semanticsLittle to say about time

ComponentEntityCompositeEntity

AtomicActor

CompositeActor

0..10..n

«Interface»Actor

+getDirector() : Director+getExecutiveDirector() : Director+getManager() : Manager+inputPortList() : List+newReceiver() : Receiver+outputPortList() : List

«Interface»Executable

+fire()+initialize()+postfire() : boolean+prefire() : boolean+preinitialize()+stopFire()+terminate()+wrapup()

Director

Object modelingemphasizes inheritanceand procedural interfaces.

We need to emphasizeconcurrency,communication, andtemporal abstractions.

3


Why not Leave This Problem to theSoftware Experts (cont)?

E.g. Real-Time CorbaComponent specification includes:

worst case execution timetypical execution timecached execution timepriorityfrequencyimportance

This is an elaborate prayer…


Hardware Experts Have Something toTeach to the Software World

Concurrencythe synchrony abstractionevent-driven modeling

Reusabilitycell librariesinterface definition

Reliabilityleveraging limited abstractionsleveraging verification

Heterogeneitymixing synchronous and asynchronous designsresource management

4


Alternative View of SW Architecture:Actors with Ports and Attributes

PortPort

Actor ActorLink

Relation

ActorPort

connection

connection conn

ectio

n

Link

Link

Attributes Attributes

Attributes

Model of Computation:

• Messaging schema• Flow of control• Concurrency

Examples:

• Synchronous circuits•Time triggered• Process networks• Discrete-event systems• Dataflow systems• Publish & subscribe

Key idea: The model of computation is part of the frameworkwithin which components are embedded rather than part of thecomponents themselves.


Examples of Actors+PortsSoftware Architectures

VHDL, Verilog, SystemC (Various)Simulink (The MathWorks)Labview (National Instruments)OCP, open control platform (Boeing)SPW, signal processing worksystem (Cadence)System studio (Synopsys)ROOM, real-time object-oriented modeling (Rational)Port-based objects (U of Maryland)I/O automata (MIT)Polis & Metropolis (UC Berkeley)Ptolemy & Ptolemy II (UC Berkeley)…

5


What an Embedded Program MightLook Like


Simple Example: Controlling anInverted Pendulum with Embedded SW

The Furuta pendulum hasa motor controlling theangle of an arm, fromwhich a free-swingingpendulum hangs. Theobjective is to swing thependulum up and thenbalance it.

6


Metaphor forDisk drive controllersManufacturing equipmentAutomotive:

Drive-by-wire devicesEngine controlAntilock braking systems, traction control

AvionicsFly-by-wire devicesNavigationflight control

Certain “software radio” functionsPrinting and paper handlingSignal processing (audio, video, radio)…


Execution

An execution of themodel displays varioussignals and at the bottomproduces a 3-D animationof the physical system.

Model by Johan Eker

7


Top-Level Model

The top-level is a continuous-time model that specifies thedynamics of the physical system as a set of nonlinear ordinarydifferential equations, and encapsulates a closed loop controller.

Framework by Jie Liu


A Modal Controller

The controlleritself is modal,with three modesof operation,where a differentcontrol law isspecified foreach mode.

Framework by Xiaojun Liu

8


The Discrete Controllers

Three discretesubmodels(dataflowmodels) specifycontrol laws foreach of threemodes ofoperation.

Framework by Steve Neuendorffer


This is System-Level ModelingSRC funding in system-level modeling, simulation, anddesign work 5-10 years ago has had demonstrable impactvia:

SystemCVSIA standards effortsCadence SPW & VSSSynopsys Cocentric StudioAgilent ADS (RF + DSP)…

Much of this work is now starting to address embeddedsoftware issues.

9


The Key Idea

Components are actors with portsInteraction is governed by a model of computation

flow of controlmessaging protocolsnon-functional properties (timing, resource management, …)

So what is a model of computation?

It is the “laws of physics” governing the interaction betweencomponentsIt is the modeling paradigm


Model of Computation

What is a component? (ontology)States? Processes? Threads? Differential equations?Constraints? Objects (data + methods)?

What knowledge do components share? (epistemology)Time? Name spaces? Signals? State?

How do components communicate? (protocols)Rendezvous? Message passing? Continuous-time signals?Streams? Method calls? Events in time?

What do components communicate? (lexicon)Objects? Transfer of control? Data structures? ASCII text?

10


Domains – Realizations of Models ofComputation

CSP – concurrent threads with rendezvousCT – continuous-time modelingDE – discrete-event systemsDDE – distributed discrete-event systemsDT – discrete time (cycle driven)FSM – finite state machinesGiotto – time driven cyclic modelsGR – graphicsPN – process networksSDF – synchronous dataflowxDF – other dataflow

Each of these defines a component ontology and an interactionsemantics between components. There are many morepossibilities!


Domain

Domain

Domain

Hierarchical, Compositional Models

Actors with ports arebetter than objectswith methods forembedded systemdesign.

11


Heterogeneity – Hierarchical Mixturesof Models of Computation

Modal ModelsFSM + anything

Hybrid systemsFSM + CT

Mixed-signal systemsDE + CTDT + CT

Complex systemsResource managementSignal processingReal time


Key Advantages

Domains are specializedleantargetedoptimizableunderstandable

Domains are mixable (hierarchically)structureddisciplined interactionunderstandable interaction

12


Model = DesignWe need modeling “languages” for humans to

realize complex functionalityunderstand the designformulate the questionspredict the behavior

The issue is “model” or “design” not “hardware” or “software”

Invest in:modeling “languages” for systemsfinding the useful abstractionscomputational systems theorycomposable abstractionsexpressing time, concurrency, power, etc.


Composing SystemsWe need systematic methods for composing systems

component frameworkscomposition semanticson-the-fly composition, admission controllegacy component integration

Invest in:methods and toolsreference implementationssemantic frameworks and theoriesdefining architectural frameworksstrategies for distribution, partitioningstrategies for controlling granularity and modularity

13


TransformationsWe need theory of transformations between abstractions

relationships between abstractionsgenerators (transformers, synthesis tools)multi-view abstractionsmodel abstractors (create reduced-order models)abstractions of physical environmentsverifiable transformations

Invest in:open generator infrastructure (methods, libraries)theories of generatorsmethods for correct by construction transformersco-compilation


Conclusions

Semiconductor manufacturers should not ignoreembedded software.

Software experts are unlikely to solve theembedded software problem on their own.

Actors with ports are better than objects withmethods for embedded system design.

Well-founded models of computation matter agreat deal, and specialization can help.

why is embedded software an issue for semiconductor...

Documents