System-level design issues become critical as implementation technology evolves toward increasingly complex integrated circuits and the time-to-market pressure continues relentlessly. To cope with these issues, new methodologies that emphasize re-use at all levels of abstraction are a "must", and this is a major focus of our work in the Gigascale Silicon Research Center. We present some important concepts for system design that are likely to provide at least some of the gains in productivity postulated above. In particular, we focus on a method that separates parts of the design process and makes them nearly independent so that complexity could be mastered. In this domain, architecture-function co-design and communication-based design are introduced and motivated. Platforms are essential elements of this design paradigm. We define system platforms and we argue about their use and relevance. Then we present an application of the design methodology to the design of wireless systems. Finally, we present a new approach to platform-based design called modern embedded systems, compilers, architectures and languages, based on highly concurrent and software programmable architectures and associated design tools.

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System-level design: orthogonalization of concerns and platform-based design

This paper focuses on the challenges of modeling cyber-physical systems (CPSs) that arise from the intrinsic heterogeneity, concurrency, and sensitivity to timing of such systems. It uses a portion of an aircraft vehicle management system (VMS), specifically the fuel management subsystem, to illustrate the challenges, and then discusses technologies that at least partially address the challenges. Specific technologies described include hybrid system modeling and simulation, concurrent and heterogeneous models of computation, the use of domain-specific ontologies to enhance modularity, and the joint modeling of functionality and implementation architectures.

Modeling Cyber–Physical Systems

Today, the design chain lacks adequate support, with most system-level designers using a collection of unlinked tools. The implementation then proceeds with informal techniques involving numerous human-language interactions that create unnecessary and unwanted iterations among groups of designers in different companies or different divisions. The move toward programmable platforms shifts the design implementation task toward embedded software design. When embedded software reaches the complexity typical of today's designs, the risk that the software will not function correctly increases exponentially. The Metropolis project seeks to develop a unified framework that can cope with this challenge. Based on a metamodel with formal semantics that developers can use to capture designs, Metropolis provides an environment for complex electronic-system design that supports simulation, formal analysis, and synthesis.

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Metropolis: an integrated electronic system design environment

We present a methodology for modeling heterogeneous real-time components. 
Components are obtained as the superposition of three layers :
Behavior, specified as a set of transitions; Interactions between transitions
of the behavior; Priorities, used to choose amongst possible interactions. 
A parameterized binary composition operator is used to compose components layer by layer.

We present the BIP language for the description and composition of layered components as well 
as associated tools for executing and analyzing components on a dedicated platform. The language
provides a powerful mechanism for structuring interactions involving rendezvous and broadcast.
We show that synchronous and timed systems are particular classes of components. Finally, we
provide examples showing the utility of the BIP framework in heterogeneous component
modeling.

Modeling Heterogeneous Real-time Components in BIP

In this paper, we present a polymorphic processor paradigm incorporating both general-purpose and custom computing processing. The proposal incorporates an arbitrary number of programmable units, exposes the hardware to the programmers/designers, and allows them to modify and extend the processor functionality at will. To achieve the previously stated attributes, we present a new programming paradigm, a new instruction set architecture, a microcode-based microarchitecture, and a compiler methodology. The programming paradigm, in contrast with the conventional programming paradigms, allows general-purpose conventional code and hardware descriptions to coexist in a program: In our proposal, for a given instruction set architecture, a onetime instruction set extension of eight instructions, is sufficient to implement the reconfigurable functionality of the processor. We propose a microarchitecture based on reconfigurable hardware emulation to allow high-speed reconfiguration and execution. To prove the viability of the proposal, we experimented with the MPEG-2 encoder and decoder and a Xilinx Virtex II Pro FPGA. We have implemented three operations, SAD, DCT, and IDCT. The overall attainable application speedup for the MPEG-2 encoder and decoder is between 2.64-3.18 and between 1.56-1.94, respectively, representing between 93 percent and 98 percent of the theoretically obtainable speedups.

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The MOLEN polymorphic processor

Embedded systems are informally defined as a collection of programmable parts surrounded by ASICs and other standard components, that interact continuously with an environment through sensors and actuators. The programmable parts include micro-controllers and Digital Signal Processors (DSPs). Embedded systems are often used in life-critical situations, where reliability and safety are more important criteria than performance. Today, embedded systems are designed with an ad hoc approach that is heavily based on earlier experience with similar products and on manual design. Use of higher-level languages such as C helps structure the design somewhat, but with increasing complexity it is not sufficient. Formal verification and automatic synthesis of implementations are the surest ways to guarantee safety. Thus, the POLIS system which is a co-design environment for embedded systems is based on a formal model of computation. POLIS was initiated in 1988 as a research project at the University of California at Berkeley and, over the years, grew into a full design methodology with a software system supporting it. Hardware-Software Co-Design of Embedded Systems: The POLIS Approach is intended to give a complete overview of the POLIS system including its formal and algorithmic aspects. Hardware-Software Co-Design of Embedded Systems: The POLIS Approach will be of interest to embedded system designers (automotive electronics, consumer electronics and telecommunications), micro-controller designers, CAD developers and students.

Hardware-software co-design of embedded systems: the POLIS approach

Hardware-software co design of embedded systems

We present the modeling mechanism employed in Metropolis, a design environment for heterogeneous embedded systems, and a design methodology based on the mechanism experimented for wireless communication systems. It is developed to favor the reusability of components in the systems, by decoupling the specification of orthogonal aspects explicitly over a set of abstraction levels. It uses a single model to represent designs specified this way, to which not only simulation but also analysis and synthesis algorithms can be applied relatively easily. The model uses executable code as well as denotational formulas, classes of temporal and predicate logic, so that the right level of details of the design can be defined at each abstraction.

Modeling and Designing Heterogeneous Systems

Hardware/software co-simulation is generally performed withseparate simulation models.This makes trade-off evaluationdifficult, because the models must be re-compiled wheneversome architectural choice is changed.We propose a techniqueto simulate hardware and software that is almost cycle-accurate,and uses the same model for both types of components.Only the timing information used for synchronizationneeds to be changed to modify the processor choice, the implementationchoice, or the scheduling policy.We show howthis technique can be used to decide the implementation of areal-life example, a car dashboard controller.

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Claudio Passerone

Papers

Hardware-software co-design of embedded systems: the POLIS approach

Metropolis: an integrated electronic system design environment

Hardware-software co design of embedded systems

Modeling and Designing Heterogeneous Systems

Fast hardware/software co-simulation for virtual prototyping and trade-off analysis