Exploiting Data-Dependent Slack Using Dynamic Multi-VDD to Minimize Energy Consumption in Datapath Circuits

Multiple Dynamic Supply Voltage (MDSV) is a technique that focuses on reducing the dynamic power. This technique is an evolution of the Multiple Supply Voltage (MSV). MSV and MDSV introduce some difference on traditional physical synthesis due to the different voltage operations of each region in the design. To convert the voltage among regions supplied by different voltages, these techniques insert a Level Shifter (LS) circuit. As a penalty consequence, traditional LS circuits insert a delay and extra power consumption in the design. The dynamical behavior of MDSV designs has brought a new condition, where LS inserted in the circuit can be in an idle state temporally. This work presents a new architecture to reduce the power consumption and delay, bypassing the LS. The architecture explores an alternative path to current flow in the cases that LS is idle. With this new approach we reduce up to 15% of power consumption and up to 75% and 15% of delay.

Multiple supply voltages are often utilized to decrease power dissipation in high performance integrated circuits. On-chip power distribution grids with multiple supply voltages are discussed in this paper. A power distribution grid with multiple supply voltages and multiple grounds is presented. The proposed power delivery scheme reduces power supply voltage drops as compared to conventional power distribution systems with dual supplies and a single ground by 17% on average (20% maximum). For an example power grid with decoupling capacitors placed between the power supply and ground, the proposed grid with multiple supply and multiple ground exhibits, respectively, 13% and 18% average performance improvement. The proposed power distribution grid can be an alternative to a single supply voltage and single ground power distribution system.

Recently, dynamic frequency scaling has been explored at the CPU and system levels for power optimization. Low-power datapath scheduling using multiple supply voltages has been well researched. In this work, we develop new datapath scheduling algorithms that use multiple supply voltages and dynamic frequency clocking in a coordinated manner in order to reduce the energy consumption of datapath circuits. In dynamic frequency clocking, the functional units can be operated at different frequencies depending on the computations occurring within the datapath during a given clock cycle. The strategy is to schedule high-energy units, such as multipliers at lower frequencies, so that they can be operated at lower voltages to reduce energy consumption and the low-energy units, such as adders at higher frequencies, to compensate for speed. The proposed time- and resource-constrained algorithms have been applied to various high-level synthesis benchmark circuits under different time and resource constraints. The experimental results show significant reduction in energy for both the algorithms.

Multiple supply voltages are commonly used in designs to enable better power performance through dedicated control of the supply voltage of the various functional units. In multiple supply voltage designs, circuits are partitioned into voltage islands that operate at their optimum supply voltages which necessitates the use of voltage level translators between them. This paper presents a high performance voltage level translator design aimed at minimizing insertion penalty by minimizing logic contention and thereby improving latency. In addition, the proposed voltage level translator design has an integrated logic multiplexer function built in through an enable signal. Simulation results of the proposed voltage level translator in comparison with the conventional voltage level translator shows upto 42% delay reduction, combined with a power benefit upto 15%, for supply voltage ranging from near-threshold to above-threshold levels.

Clock networks account for a significant fraction of the power dissipation of a chip and are critical to performance. This paper presents theory and algorithms for building a low-power clock tree by distributing the clock signal at a lower voltage and translating it to a higher voltage at the utilization points. Two low-power schemes are used: reduced swing and multiple-supply voltages. We analyze the issue of tree construction and present conclusions relevant to various technology generations according to the NTRS. Our experimental results show that power savings of an average of 45% are possible for a 0.25 /spl mu/m technology using multiple supply voltages, and about 32% using a single external supply voltage.

The use of multiple supply voltages for energy and average power reduction is well researched and several works have appeared in the literature. However, in low power design using deep submicron and nanometer technology, the peak power, peak power differential, average power and total energy are equally critical design constraints. In this work, we propose datapath scheduling algorithms for simultaneous minimization of peak and average power while maintaining performance by use of dynamic frequency clocking and multiple supply voltages. The algorithms use integer linear programming based models. The dynamic frequency clocking methodology is more useful for data intensive signal processing applications. The effectiveness of our scheduling technique is measured by estimating the peak power consumption, the average power consumption and the power delay product of the datapath circuit. Furthermore, the proposed scheduling scheme is compared with combined multiple supply voltages and multicycling scheme. Experimental results show that combined multiple supply voltages (3.3V,2.4V) and dynamic frequency clocking scheme achieves significant reductions in peak power (72% on the average), average power (71% on the average) and power delay product (54% on the average).

Dynamic power is the main source of power consumption in CMOS circuits. It depends on the square of the supply voltage. It may significantly be reduced by scaling down the supply voltage of some computational elements in the circuit, with the penalty of an increase of their execution delay. To reduce the dynamic power consumption, without degrading the performance determined assuming that the circuit operates at the highest available supply voltage, the supply voltage of computational elements off critical paths can be scaled down. Defined here as MinP/sub dyn/, the problem of minimizing the dynamic power consumption, under performance constraints, by scaling down the supply voltage of computational elements on non-critical paths is NP-hard in general. Solving MinP/sub dyn/ for multi-phase clocked sequential circuits may allow to reduce their power consumption and the required number of registers. Reducing the number of registers also allows to reduce the power consumption, the number of control signals, and the area of the circuit. In this paper, we focus on devising methods to efficiently solve MinP/sub dyn/ for designs modeled as cyclic or acyclic graphs. More precisely, once the circuit is optimized for timing constraints, then we look for schedules that allow the computational elements of the circuit to operate at the lowest possible supply voltage. We present an integer linear programming formulation for that problem, which we use to devise a polynomial time solvable method and an exact algorithm based on a branch-and-bound technique. Experimental results confirm the effectiveness of the method and power reduction factors as high as 53.84% were obtained. Also, they show that the exact algorithm produces optimal results in a small number of tries, which is due to the rules used to prune useless solutions.

In this paper, we first propose a huddle-based distributed-register architecture (HDR architecture), an island-based distributed-register architecture for multi-cycle interconnect communications where we can develop several energy-saving techniques. Next, we propose an energy-efficient high-level synthesis algorithm for HDR architectures focusing on multiple supply voltages. Our algorithm is based on iterative improvement of scheduling/binding and floorplanning. In the iteration process, huddles, each of which is composed of functional units, registers, controller, and level converters, are very naturally generated using floorplanning results. By assigning high supply voltage to critical huddles and low supply voltage to non-critical huddles, we can finally have energy-efficient floorplan-aware high-level synthesis. Experimental results show that our algorithm achieves 45% energy-saving compared with the conventional distributed-register architectures and conventional algorithms.

We present an algorithm called MOVER (Multiple Operating Voltage Energy Reduction) to minimize datapath energy dissipation through use of multiple supply voltages. In a single voltage design, the critical path length, clock period, and number of control steps limit minimization of voltage and power. Multiple supply voltages permit localized voltage reductions to take up remaining schedule slack. MOVER initially finds one minimum voltage for an entire datapath. It then determines a second voltage for operations where there is still schedule slack. New voltages con be introduced and minimized until no schedule slack remains. MOVER was exercised for a variety of DSP datapath examples. Energy savings ranged from 0% to 50% when comparing dual to single voltage results. The benefit of going from two to three voltages never exceeded 15%. Power supply costs are not reflected in these savings, but a simple analysis shows that energy savings can be achieved even with relatively inefficient DC-DC converters. Datapath resource requirements were found to vary greatly with respect to number of supplies. Area penalties ranged from 0% to 170%. Implications of multiple voltage design for IC layout and power supply requirements are discussed.

The mobile computing device market has been growing rapidly. This brings the technologies that optimize system energy to the forefront. As circuits continue to scale in the future, it would be important to optimize both leakage and dynamic energy. Effective optimization of leakage and dynamic energy consumption requires a vertical integration of techniques spanning from circuit to software levels. Schedule slacks in codes executing in VLIW architectures present an opportunity for such an integration. In this paper, we present three compiler-directed techniques that take advantage of schedule slacks to optimize leakage and dynamic energy consumption. Integer ALU (IALU) components operating with multiple supply voltages are designed to provide different low-energy versions that possess different operational latencies. The goal of the first technique explored is to maximize the number of operations mapped to IALU components with the lowest energy consumption without extending the schedule length. We also consider a variant of this technique that saves more energy at the cost of some performance loss. The second technique uses two leakage-control mechanisms to reduce leakage energy consumption when no operations are scheduled in the component. Our evaluation of these two approaches, using fifteen benchmarks, shows that based on the number and duration of slacks, the availability of low-energy functional units and the relative magnitude of leakage and dynamic energy, either leakage or dynamic energy consumption, will provide more energy gains. Finally, we provide a unified energy-optimization strategy that integrates both dynamic and leakage energy-reduction schemes. The proposed techniques have been incorporated into a cycle accurate simulator using parameters extracted from circuit-level simulation. Our results show that the unified scheme generates better results than using either of dynamic and leakage energy-reduction techniques independently.

In this paper, a tabu search-based behavior level synthesis scheme is proposed to minimize power consumption with resource operating at multiple voltages under the timing and the resource constraints. Unlike the conventional methods where only scheduling is considered, our synthesis scheme considers both scheduling and partitioning simultaneously to reduce power consumption due to the functional units as well as the interconnects among them. More importantly, our approach tends to efficiently address a few practical layout problems inherent to multiple voltage designs. In particular, we have configured our solutions as a three-tuple vector to account for both the timing and the partition. Cycling of the same solutions is prevented by applying a tabu list with an update mechanism enhanced with an aspiration function. In this way, the algorithm can search a large solution space with modest computation effort and fast convergence rate. Experiments with a number of DSP benchmarks show that the proposed algorithms achieve an average power reduction by 49.6%.

Multiple supply voltage (MSV) is an effective scheme to achieve low power. Recent works in MSV are based on physical level and aim at reducing physical overheads, but all of them do not consider level converter, which is one of the most important issues in dual-vdd design. In this work, a logic and layout aware methodology and related algorithms combining voltage assignment and placement are proposed to minimize the number of level converters and to implement voltage islands with minimal physical overheads. Experimental results show that our approach uses much fewer level converters (reduced by 83.23% on average) and improves the power savings by 16% on average compared to the previous approach [1]. Furthermore, the methodology is able to produce feasible placement with a small impact to traditional placement goals.

Core-to-core variability in future many-core chip multi-processors (CMPs) negatively impacts energy. Under-performing cores necessitate increasing the system voltage to maintain homogeneous core performance, introducing an energy overhead. Multiple supply voltages can be used to mitigate the impact of delay variation in CMPs. In this paper, we carefully analyze the use of a local search algorithm to pick near-optimal supply voltages while meeting a fixed performance target. With two system voltages, we prove our algorithm selects the global optimum and in the more general multiple voltage case we develop quantitative bounds. Using a custom simulation methodology on a real processor core, we show that two system voltages provide the most incremental benefit, reducing the energy overhead relative to a single voltage by 59-75% and total energy by 6-16%. Additionally, the worst 5-15% of cores in such systems necessitate increasingly larger amounts of incremental energy for a constant incremental performance gain. Therefore, turning off or disabling these cores is beneficial to a joint performance-energy metric.

Clock networks account for a significant fraction of the power dissipation of a chip and are critical to the performance. This paper presents theory and algorithms for building a low power clock tree. Two low power schemes are used: a reduced swing scheme and one using multiple supply voltages. We analyze the issue of tree construction and present conclusions relevant to various technology generations according to the National Technology Roadmap of Semiconductors (NTRS). Our experimental results show that the power could be saved an average of 45% for a 0.25 /spl mu/m technology using multiple supply voltages, and 31% using reduced swing buffers.

The scaling trend of semiconductor devices has raised several issues such as energy consumption and heat dissipation, as well as the increasing probabilistic behavior of devices. Motivated by the necessity to consider probabilistic approaches to future designs, probabilistic CMOS (PCMOS) based computing has been proposed. PCMOS devices are inherently probabilistic devices that compute correctly with a probability <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> . This paper investigates the tradeoffs between the energy, speed (or performance), and probability of correctness ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> ) of PCMOS circuits. For given constraints on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> , performance, and energy delay product (EDP), and using analytical models of energy, delay, and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> , the optimum values of EDP and probability are found for PCMOS circuits. The analytical models are validated using circuit simulations for PCMOS circuits designed in a 0.13-mum process. The results show that, to minimize EDP, it is preferable to operate PCMOS circuits at lower supply voltages. On the other hand, to maximize <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> , the highest possible supply voltage under the given constraints is preferable. Our analysis makes it possible to achieve an optimal circuit design that satisfies the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> , performance, and EDP requirements for a given application. An analysis of the impact of variations in temperature, threshold voltage, and supply voltage on optimal EDP and probability values is also included.