The scaling of microchip technologies has enabled large scale systems-on-chip (SoC). Network-on-chip (NoC) research addresses global communication in SoC, involving (i) a move from computation-centric to communication-centric design and (ii) the implementation of scalable communication structures. This survey presents a perspective on existing NoC research. We define the following abstractions: system, network adapter, network, and link to explain and structure the fundamental concepts. First, research relating to the actual network design is reviewed. Then system level design and modeling are discussed. We also evaluate performance analysis techniques. The research shows that NoC constitutes a unification of current trends of intrachip communication rather than an explicit new alternative.

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A survey of research and practices of Network-on-chip

Dynamic power management (DPM) is a design methodology for dynamically reconfiguring systems to provide the requested services and performance levels with a minimum number of active components or a minimum load on such components. DPM encompasses a set of techniques that achieves energy-efficient computation by selectively turning off (or reducing the performance of) system components when they are idle (or partially unexploited). In this paper, we survey several approaches to system-level dynamic power management. We first describe how systems employ power-manageable components and how the use of dynamic reconfiguration can impact the overall power consumption. We then analyze DPM implementation issues in electronic systems, and we survey recent initiatives in standardizing the hardware/software interface to enable software-controlled power management of hardware components.

A survey of design techniques for system-level dynamic power management : Special section on low-power electronics and design

Dynamic power management (DPM) is a design methodology for dynamically reconfiguring systems to provide the requested services and performance levels with a minimum number of active components or a minimum load on such components DPM encompasses a set of techniques that achieves energy-efficient computation by selectively turning off (or reducing the performance of) system components when they are idle (or partially unexploited) In this paper, we survey several approaches to system-level dynamic power management We first describe how systems employ power-manageable components and how the use of dynamic reconfiguration can impact the overall power consumption We then analyze DPM implementation issues in electronic systems, and we survey recent initiatives in standardizing the hardware/software interface to enable software-controlled power management of hardware components

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A survey of design techniques for system-level dynamic power management

The microprocessor system in portable electronic devices often has a time-varying computational load which is comprised of: (1) compute-intensive and low-latency processes, (2) background and high-latency processes, and (3) system idle. The key design objectives for the processor systems in these applications are providing the highest possible peak performance for the compute-intensive code (e.g., handwriting recognition, image decompression) while maximizing the battery life for the remaining low performance periods. If clock frequency and supply voltage are dynamically varied in response to computational load demands, then energy consumed per process can be reduced for the low computational periods, while retaining peak performance when required. This strategy, which achieves the highest possible energy efficiency for time-varying computational loads, is called dynamic voltage scaling (DVS).

A dynamic voltage scaled microprocessor system

The continuous advances in semiconductor technology enable the integration of increasing numbers of IP blocks in a single SoC. Interconnect infrastructures, such as buses, switches, and networks on chips (NoCs), combine the IPs into a working SoC. Moreover, the industry expects platform-based SoC design to evolve to communication-centric design, with NoCs as a central enabling technology. In this article, we introduce the AEthereal NoC. The tenet of the AEthereal NoC is that guaranteed services (GSs) - such as uncorrupted, lossless, ordered data delivery; guaranteed throughput; and bounded latency - are essential for the efficient construction of robust SoCs. To exploit the NoC capacity unused by the GS traffic, we provide best-effort services.

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AEthereal network on chip: concepts, architectures, and implementations

Principles of Asynchronous Circuit Design

On-chip networks for future system-on-chip designs need simple, high performance implementations. In order to promote system-level integrity, guaranteed services (GS) need to be provided. We propose a network-on-chip (NoC) router architecture to support this, and demonstrate with a CMOS standard cell design. Our implementation is based on clockless circuit techniques, and thus inherently supports a modular, GALS-oriented design flow. Our router exploits virtual channels to provide connection-oriented GS, as well as connection-less best-effort (BE) routing. The architecture is highly flexible, in that support for different types of BE routing and GS arbitration can be easily plugged into the router.

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A Router Architecture for Connection-Oriented Service Guarantees in the MANGO Clockless Network-on-Chip

Recent research has demonstrated that for certain types of applications like sampled audio systems, self-timed circuits can achieve very low power consumption, because unused circuit parts automatically turn into a stand-by mode. Additional savings may be obtained by combining the self-timed circuits with a mechanism that adaptively adjusts the supply voltage to the smallest possible, while maintaining the performance requirements. This paper describes such a mechanism, analyzes the possible power savings, and presents a demonstrator chip that has been fabricated and tested. The idea of voltage scaling has been used previously in synchronous circuits, and the contributions of the present paper are: 1) the combination of supply scaling and self-timed circuitry which has some unique advantages, and 2) the thorough analysis of the power savings that are possible using this technique. >

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Low-power operation using self-timed circuits and adaptive scaling of the supply voltage

Real-time systems need time-predictable platforms to allow static analysis of the worst-case execution time (WCET). Standard multi-core processors are optimized for the average case and are hardly analyzable. Within the T-CREST project we propose novel solutions for time-predictable multi-core architectures that are optimized for the WCET instead of the average-case execution time. The resulting time-predictable resources (processors, interconnect, memory arbiter, and memory controller) and tools (compiler, WCET analysis) are designed to ease WCET analysis and to optimize WCET performance. Compared to other processors the WCET performance is outstanding.The T-CREST platform is evaluated with two industrial use cases. An application from the avionic domain demonstrates that tasks executing on different cores do not interfere with respect to their WCET. A signal processing application from the railway domain shows that the WCET can be reduced for computation-intensive tasks when distributing the tasks on several cores and using the network-on-chip for communication. With three cores the WCET is improved by a factor of 1.8 and with 15 cores by a factor of 5.7.The T-CREST project is the result of a collaborative research and development project executed by eight partners from academia and industry. The European Commission funded T-CREST.

Jens Sparsø

Papers

Principles of Asynchronous Circuit Design

A Router Architecture for Connection-Oriented Service Guarantees in the MANGO Clockless Network-on-Chip

Low-power operation using self-timed circuits and adaptive scaling of the supply voltage

T-crest

Delay-insensitive multi-ring structures