Normally-Off Computing and Checkpoint/Rollback for Fast, Low-Power, and Reliable Devices

International audienceSince the advent of complementary metal oxide semiconductors (CMOS), the number of transistors per die has continued to increase, reaching today several billion transistors. As a result, it has been possible to design and fabricate smart devices able to run at high speed. However, the power consumption of systems-on-chip has significantly increased due to the high density integration and the high leakage power of current CMOS transistors. As a result, the limits of heat dissipation make further improvement in performance difficult. A high level of autonomy for battery-powered devices is a real challenge. To deal with these issues, spin-transfer-torque magnetic random-access memory (STT-MRAM) technology is seen as a promising solution. In addition to its attractive performance features, STT-MRAM can bring nonvolatility to a system to allow full data retention after a complete shutdown while maintaining a fast wake-up time. Considering two 32-bit embedded processors, this letter shows how STT-MRAM can improve energy efficiency and reliability of future embedded systems thanks to normally-off computing and checkpointing/rollback techniques. A detailed analysis is performed to evaluate the cost related to the backup/recovery of the system. Index Terms—Spintronic memory and logic, embedded processor, spin-transfer-torque, magnetic random-access memory

Loop Optimization in Presence of STT-MRAM Caches: a Study of Performance-Energy Tradeoffs

International audienceEnergy-efficiency is one of the most challenging design issues in both embedded and high-performance computing domains. The aim is to reduce as much as possible the energy consumption of considered systems while providing them with the best computing performance. Finding an adequate solution to this problem certainly requires a cross-disciplinary approach capable of addressing the energy/performance trade-off at different system design levels. In this paper, we present an empirical impact analysis of the integration of Spin Transfer Torque Magnetic Random Access Memory (STT-MRAM) technologies in multicore architectures when applying some existing compiler optimizations. For that purpose, we use three well-established architecture and NVM evaluation tools: NVSim, gem5 and McPAT. Our results show that the integration of STT-MRAM at cache memory levels enables a significant reduction of the energy consumption (up to 24.2 % and 31 % on the considered multicore and monocore platforms respectively) while preserving the performance improvement provided by typical code optimizations. We also identify how the choice of the clock frequency impacts the relative efficiency of the considered memory technologies

Exploration d'architecture de processeur à technologie mémoire non volatile MRAM

With the downscaling of the complementary metal-oxide semiconductor (CMOS) technology,designing dense and energy-efficient systems-on-chip (SoC) is becoming a realchallenge. Concerning the density, reducing the CMOS transistor size faces up to manufacturingconstraints while the cost increases exponentially. Regarding the energy, a significantincrease of the power density and dissipation obstructs further improvement inperformance. This issue is mainly due to the growth of the leakage current of the CMOStransistors, which leads to an increase of the static energy consumption. Observing currentSoCs, more and more area is occupied by embedded volatile memories, such as staticrandom access memory (SRAM) and dynamic random access memory (DRAM). As a result,a significant proportion of total power is spent into memory systems. In the past twodecades, alternative memory technologies have emerged with attractive characteristics tomitigate the aforementioned issues. Among these technologies, magnetic random accessmemory (MRAM) is a promising candidate as it combines simultaneously high densityand very low static power consumption while its performance is competitive comparedto SRAM and DRAM. Moreover, MRAM is non-volatile. This capability, if present inembedded memories, has the potential to add new features to SoCs to enhance energyefficiency and reliability. In this thesis, an area, performance and energy exploration ofembedding the MRAM technology in the memory hierarchy of a processor architectureis investigated. A first fine-grain exploration was made at cache level for multi-core architectures.A second study evaluated the possibility to design a non-volatile processorintegrating MRAM at register level. Within the context of internet of things, new featuresand the benefits brought by the non-volatility were investigated.De par la réduction continuelle des dimensions du transistor CMOS, concevoir des systèmes sur puce (SoC) à la fois très denses et énergétiquement efficients devient un réel défi. Concernant la densité, réduire la dimension du transistor CMOS est sujet à de fortes contraintes de fabrication tandis que le coût ne cesse d'augmenter. Concernant l'aspect énergétique, une augmentation importante de la puissance dissipée par unité de surface frêne l'évolution en performance. Ceci est essentiellement dû à l'augmentation du courant de fuite dans les transistors CMOS, entraînant une montée de la consommation d'énergie statique. En observant les SoCs actuels, les mémoires embarquées volatiles tels que la SRAM et la DRAM occupent de plus en plus de surface silicium. C'est la raison pour laquelle une partie significative de la puissance totale consommée provient des composants mémoires. Ces deux dernières décennies, de nouvelles mémoires non volatiles sont apparues possédant des caractéristiques pouvant aider à résoudre les problèmes des SoCs actuels. Parmi elles, la MRAM est une candidate à fort potentiel car elle permet à la fois une forte densité d'intégration et une consommation d'énergie statique quasi nulle, tout en montrant des performances comparables à la SRAM et à la DRAM. De plus, la MRAM a la capacité d'être non volatile. Ceci est particulièrement intéressant pour l'ajout de nouvelles fonctionnalités afin d'améliorer l'efficacité énergétique ainsi que la fiabilité. Ce travail de thèse a permis de mener une exploration en surface, performance et consommation énergétique de l'intégration de la MRAM au sein de la hiérarchie mémoire d'un processeur. Une première exploration fine a été réalisée au niveau mémoire cache pour des architectures multicoeurs. Une seconde étude a permis d'évaluer la possibilité d'intégrer la MRAM au niveau registre pour la conception d'un processeur non volatile. Dans le cadre d'applications des objets connectés, de nouvelles fonctionnalités ainsi que les intérêts apportés par la non volatilité ont été étudiés et évalués

Exploration of magnetic memory for ultra low-power systems-on-chip

National audienceMemories are currently a real bottleneck to design high speed, low area and energy-efficient systems-on-chip (SoC). An important proportion of total power is spent on memory systems. Ultra low-power (ULP) SoC often use different memory technologies to keep the advantages of each one (area, energy consumption, latency and non-volatility), however there are still penalties and this add more complexity at every development levels. MRAM (Magnetic Random Access Memory) is seen as a promising alternative solution to replace both traditional SRAM (Static Random Access Memory) and NVM (Non Volatile Memory), thanks to its high density, low read/right latency, non-volatility and negligible leakage current. The aim of this work is to explore the possibilities of using MRAM in ULP SoC at various memory levels

MAGPIE Software: Manycore Architecture enerGy and Performance evaluatIon Environment

MAGPIE is a collaborative framework that mainly targets an easy design evaluation for multicore systems, by applying selected existing tools, which are popular. It is made available to the research community as an open-source code to which any contribution is welcome for improvements and/or extension. Finally, it has been developed in the framework of the CONTINUUM ANR project, in a joint collaboration with the GREAT (heteroGeneous integRated magnetic tEchnology using multifunctional stAndardized sTack) H2020 European project.Homepage: http://www.lirmm.fr/continuum-project/pages/magpie.htm

Exploring MRAM Technologies for Energy Efficient Systems-On-Chip

International audienceIt has become increasingly challenging to respect Moore's well-known law in recent years. Energy efficiency and manufacturing constraints are among the main challenges to current integrated circuits today. The energy efficiency issue is mainly due to the high leakage current from the CMOS transistors that are used to build almost all logic devices. As a result, performance is limited to a few gigahertz due to high power dissipation. A significant proportion of total power is spent on memory systems due to the increasing trend of embedding volatile memory into systems-on-chip devices. New non-volatile memory technologies are one possible way to solve the energy efficiency issue. Among these technologies, magnetic memory is a promising candidate to replace current memories since it combines non-volatility, high density, low latency and low leakage. This paper describes an approach to obtain large, fine-grained exploration of how magnetic memory can be included in the memory hierarchy of processor-based systems by analyzing both performance and energy consumption

A novel SRAM -STT-MRAM hybrid cache implementation improving cache performance

International audienceMemories are currently a real bottleneck to design high speed and energy-efficient systems-on-chip. A significant increase of the performance gap between processors and memories is observed. On the other hand, an important proportion of total power is spent on memory systems due to the increasing trend of embedding volatile memory into systems-on-chip. For these reasons, STT-MRAM (Spin-Transfer Torque Magnetic Random Access Memory) is seen as a promising alternative solution to traditional SRAM (Static Random Access Memory) thanks to its negligible leakage current, high density, and non-volatility. Nevertheless, the strategy of the same footprint replacement is constrained by the high write energy/latency of STT-MRAM. This paper performs a fine-grained evaluation of the cache organization to propose a hybrid cache memory architecture including both SRAM and STT-MRAM technologies

Design and Evaluation of a 28-nm FD-SOI STT-MRAM for Ultra-Low Power microcontrollers

International audienceThe complexity of embedded devices increases as today's applications request always more services. However, the power consumption of systems-on-chip has significantly increased due to the high-density integration and the high leakage power of current CMOS transistors. To address these issues, emerging technologies are considered. Spin-Transfer Torque Magnetic Random Access Memory (STT-MRAM) is seen as a promising alternative solution to traditional memories thanks to its negligible leakage current, high density, and non-volatility. In this work, we present the design and evaluation of a 128 kB STT-RAM in 28-nm FD-SOI technology with SRAM-like interface for ultra-low power microcontrollers. With 0.9 pJ/bit read in 5 ns and 3 pJ/bit write in 10 ns, this embedded non-volatile memory is suitable for devices that run at frequencies under 100 MHz. Considering low-power application with duty-cycled behaviour, we evaluate the STT-MRAM as a replacement of embedded Flash and SRAM by comparing single and multi-memory architecture scenarios

Embedded Memory Hierarchy Exploration Based on Magnetic Random Access Memory

International audienceStatic random access memory (SRAM) is the most commonly employed semiconductor in the design of on-chip processor memory. However, it is unlikely that the SRAM technology will have a cell size that will continue to scale below 45 nm, due to the leakage current that is caused by the quantum tunneling effect. Magnetic random access memory (MRAM) is a candidate technology to replace SRAM, assuming appropriate dimensioning given an operating threshold voltage. The write current of spin transfer torque (STT)-MRAM is a known limitation; however, this has been recently mitigated by leveraging perpendicular magnetic tunneling junctions. In this article, we present a comprehensive comparison of spin transfer torque-MRAM (STT-MRAM) and SRAM cache set banks. The non-volatility of STT-MRAM allows the definition of new instant on/off policies and leakage current optimizations. Through our experiments, we demonstrate that STT-MRAM is a candidate for the memory hierarchy of embedded systems, due to the higher densities and reduced leakage of MRAM.We demonstrate that adopting STT-MRAM in L1 and L2 caches mitigates the impact of higher write latencies and increased current draw due to the use of MRAM. With the correct system-on-chip (SoC) design, we believe that STT-MRAM is a viable alternative to SRAM, which minimizes leakage current and the total power consumed by the SoC

Embedded systems to high performance computing using STT-MRAM

International audienceThe scaling limits of CMOS have pushed many researchers to explore alternative technologies for beyond CMOS circuits. In addition to the increased device variability and process complexity led by the continuous decreasing size of CMOS transistors, heat dissipation effects limit the density and speed of current systems-on-chip. For beyond CMOS systems, the emerging memory technology STT-MRAM is seen as a promising alternative solution. This paper shows first how STT-MRAM can improve energy efficiency and reliability of future embedded systems. Then, a hybrid design exploration framework is presented to investigate the potential of STT-MRAM for high performance computing