Copyright © 2006, by the author(s).

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This paper gives an overview of methods used for Design Space Exploration (DSE) at the system- and micro-architecture levels. The DSE problem is considered to be two orthogonal issues: (I) How could a single design point be evaluated, (II) how could the design space be covered during the exploration process? The latter question arises since an exhaustive exploration of the design space by evaluating every possible design point is usually prohibitive due to the sheer size of the design space. We therefore reveal trade-o#s linked to the choice of appropriate evaluation and coverage methods. The designer has to balance the following issues: the accuracy of the evaluation, the time it takes to evaluate one design point (including the implementation of the evaluation model), the precision/granularity of the design space coverage, and last but not least the possibilities for automating the exploration process. We also list common representations of the design space and compare current system and micro-architecture level design frameworks. This review thus eases the choice of a decent exploration policy by providing a comprehensive survey and classification of recent related work. It is focused on System-on-a-Chip designs, particularly those used for network processors. These systems are heterogeneous in nature using multiple computation, communication, memory, and peripheral resources.

The problem of optimal software synthesis for concurrent processes to be implemented on a single processor is addressed. The approach calls for the representation of the concurrent processes with Petri nets that give a theoretical foundation for the scheduling algorithm that sequentializes the concurrent processes and for the code generation step. The approach maximizes the amount of static scheduling to reduce the need of context switch and operating system intervention. Experimental results show the potential of our method to reduce software design time and errors. 1 Introduction We address the problem of optimal software synthesis for a set of concurrently communicating sequential processes to be executed on a single processor. This concurrent specification mechanism permits the underlying implementation architecture (number of processors, scheduling policy, implementation of communication, HW/SW partitioning, etc.) to be varied for a given functional specification, thus requiri...

In this paper we present and evaluate the SPADE (System level Performance Analysis and Design space Exploration) methodology through an illustrative case study. SPADE is a method and tool for architecture exploration of heterogeneous signal processing systems. In this case study we start from an M-JPEG application and use SPADE to evaluate alternative multi-processor architectures for implementing this application. SPADE follows the Y-chart paradigm for system level design; application and architecture are modeled separately and mapped onto each other in an explicit design step. SPADE permits architectures to be modeled at an abstract level using a library of generic building blocks, thereby reducing the cost of model construction and simulation. The case study shows that SPADE supports efficient exploration of candidate architectures; models can be easily constructed, modified and simulated in order to quickly evaluate alternative system implementations.

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The Sesame environment provides modeling and simulation methods and tools for the efficient design space exploration of heterogeneous embedded multimedia systems. In this paper we describe the Sesame software system and demonstrate its capabilities using several examples. We show that Sesame significantly reduces model construction time through the use of modeling component libraries, hierarchy, and advanced model structure description features.

We consider a dynamic application running on a multiprocessor network-on-chip as a set of independent jobs, each job possibly running on multiple processors. To provide guaranteed quality and performance, the scheduling of jobs, jobs themselves and the hardware must be amenable to timing analysis. For a certain class of applications and multiprocessor architectures, we propose exact timing models that effectively co-model both the computation and communication of a job. The models are based on interprocessor communication (IPC) graphs [4]. Our main contribution is a precise model of network-on-chip communication, including buffer models. We use a JPEG-decoder job as an example to demonstrate that our models can be used in practice to derive upper bounds on the job execution time and to reason about optimal buffer sizes.

The design of high-performance stream-processing systems is a fast growing domain, driven by markets such like high-end TV, gaming, 3D animation and medical imaging. It is also a surprisingly demanding task, with respect to the algorithmic and conceptual simplicity of streaming applications. It needs the close cooperation between numerical analysts, parallel programming experts, realtime control experts and computer architects, and incurs a very high level of quality insurance and optimization. In search for improved productivity, we propose a programming model and language dedicated to high-performance stream processing. This language builds on the synchronous programming model and on domain knowledge — the periodic evolution of streams — to allow correct-by-construction properties to be proven by the compiler. These properties include resource requirements and delays between input and output streams. Automating this task avoids tedious and error-prone engineering, due to the combinatorics of the composition of filters with multiple data rates and formats. Correctness of the implementation is also difficult to assess with traditional (asynchronous, simulation-based) approaches. This language is thus provided with a relaxed notion of synchronous composition, called n-synchrony: two processes are n-synchronous if they can communicate in the ordinary (0-)synchronous model with a FIFO buffer of size n. Technically, we extend a core synchronous data-flow language with a notion of periodic clocks, and design a relaxed clock calculus (a type system for clocks) to allow non strictly synchronous processes to be composed or correlated. This relaxation is associated with two sub-typing rules in the clock calculus. Delay, buffer insertion and control code for these buffers are automatically inferred from the clock types through a systematic transformation into a standard synchronous program. We formally define the se-

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