Variation-aware resource sharing and binding in behavioral synthesis
As technology scales, the delay uncertainty caused by process variations has become increasingly pronounced in deep submicron designs. In the presence of process variations, worst-case timing analysis may lead to overly conservative synthesis, and may end up using excess resources to guarantee design constraints. In this paper, we propose an efficient variation-aware resource sharing and binding algorithm in behavioral synthesis, which takes into account the performance variations for functional units. The performance yield, which is defined as the probability that the synthesized hardware meets the target performance constraints, is used to evaluate the synthesis result. An efficient metric called statistical performance improvement, is used to guide resource sharing and binding. The proposed algorithm is evaluated within a commercial synthesis framework that generates optimized RTL netlists from behavioral specifications. The effectiveness of the proposed algorithm is demonstrated with a set of industrial benchmark designs, which consist of blocks that are commonly used in wireless and image processing applications. The experimental results show that our method achieves an average 33% area reduction over traditional methods, which are based on the worst-case delay analysis, with an average 10% run time overhead.

title: Embedded Multi-Processor System-on-chip (MPSoC) design considering process variations
abstract: As technology scales, the delay uncertainty caused by process variations has become increasingly pronounced in deep sub-micron designs. As a result, a paradigm shift from deterministic to statistical design methodology at all levels of the design hierarchy is inevitable (Borkar, 2005). As part of two NSF projects (NSF CNS CAREER 0643902 and NSF CNS 0720659), a variation-aware task allocation and scheduling method for multiprocessor system-on-chip (MPSoC) architectures is proposed, to mitigate the impact of parameter variations. A new design metric, called performance yield and defined as the probability of the assigned schedule meeting the predefined performance constraints, is used to guide the task allocation and scheduling procedure. An efficient yield computation method for task scheduling complements and significantly improves the effectiveness of the proposed variation-aware scheduling algorithm. Experimental results show that our variation-aware scheduler achieves significant yield improvements.

title: Variability-driven module selection with joint design time optimization and post-silicon tuning
abstract: Increasing delay and power variation are significant challenges to the designers as technology scales to the deep sub-micron (DSM) regime. Traditional module selection techniques in high level synthesis use worst case delay/power information to perform the optimization, and therefore may be too pessimistic such that extra resources are used to guarantee design requirements. Parametric yield, which is defined as the probability of the synthesized hardware meeting the performance/power constraints, can be used to guide design space exploration. The parametric yield can be effectively improved by combining both design-time variation-aware optimization and post silicon tuning techniques (such as adaptive body biasing (ABB)). In this paper, we propose a module selection algorithm that combines design-time optimization with post- silicon tuning (using ABB) to maximize design yield. A variation-aware module selection algorithm based on efficient performance and power yield gradient computation is developed. The post silicon optimization is formulated as an efficient sequential conic program to determine the optimal body bias distribution, which in turn affects design-time module selection. The experiment results show that significant yield can be achieved compared to traditional worst-case driven module selection technique. To the best of our knowledge, this is the first variability-driven high level synthesis technique that considers post-silicon tuning during design time optimization.

title: Optimal topology exploration for application-specific 3D architectures
abstract: As technology scales, increasing interconnect costs make it necessary to consider alternate ways of building integrated circuits. One promising option along this direction is 3D architectures where a stack of multiple device layers, with direct vertical tunneling through them, are put together on the same chip. In this paper, we explore how processor cores and storage blocks can be placed in a 3D architecture to minimize data access costs under temperature constraints. This process is referred to as the topology exploration. Using integer linear programming, we compare the best 2D placement with the best 3D placement, and show through experiments with both single-core and multicore systems that the 3D placement generates much better results (in terms of data access costs) under the same temperature bounds. We also discuss the tradeoffs between temperature constraint and data access costs

title: Soft Error Rate Analysis for Combinational Logic Using an Accurate Electrical Masking Model
abstract: Accurate electrical masking modeling represents a significant challenge in soft error rate analysis for combinational logic circuits. In this paper, we use table lookup MOSFET models to accurately capture the nonlinear properties of submicron MOS transistors. Based on these models, we propose and validate the transient pulse generation model and propagation model for soft error rate analysis. The pulse generated by our pulse generation model matches well with that of HSPICE simulation, and the pulse propagation model provides nearly one order of magnitude improvement in accuracy over the previous models. Using these two models, we propose an accurate and efficient block-based soft error rate analysis method for combinational logic circuits.

title: Dependability analysis of nano-scale FinFET circuits
abstract: FinFET technology has been proposed as a promising alternative for deep sub-micro bulk CMOS technology, because of its better scalability. Previous works have studied the performance or power advantages of FinFET circuits over bulk CMOS circuits. This paper provides the dependability analysis of FinFET circuits, studying the soft error vulnerability of FinFET circuits and the impact of process variation. Our experiments compare FinFET circuits against bulk CMOS circuits in both 32 nm and 45 nm technologies, showing that FinFET circuits have better dependability and scalability, which is indicated by better soft error immunity and less impact of process variation. It is concluded that FinFET-based circuit design is more robust than the bulk CMOS based circuit design

title: On greedy construction of connected dominating sets in wireless networks
abstract: Since no fixed infrastructure and no centralized management present in wireless networks, a connected dominating set (CDS) of the graph representing the network is widely used as a virtual backbone. Constructing a minimum CDS is NP-hard. In this paper, we propose a new greedy algorithm, called S-MIS, with the help of Steiner tree that can construct a CDS within a factor of 4:8 þ ln5 from the optimal solution. We also introduce the distributed version of this algorithm. We prove that the proposed algorithm is better than the current best performance ratio which is 6.8. A simulation is conducted to compare S-MIS with its variation which is rS-MIS. The simulation shows that the sizes of the CDSs generated by S-MIS and rS-MIS are almost the same.

title: Fault-Tolerant Topology Control for All-to-One and One-to-All Communication in Wireles Networks
abstract: This paper introduces the problem of fault-tolerant topology control for all-to-one and one-to-all communication in static wireless networks with asymmetric wireless links. This problem is important in both theoretical and practical aspects. We investigate two approaches, namely, the minimum-weight-based approach and the augmentation-based approach, to address this problem. Furthermore, we prove that the minimum-weight-based approach has a k-approximation algorithm for all-to-one fault-tolerant topology control, where k is the number of node-disjoint paths. When k = 1, this approach solves the minimum power sink tree problem. To the best of our knowledge, this paper is the first to study the fault-tolerant topology control for all-to-one and one-to-all communication in asymmetric static wireless networks and is also the first to demonstrate that the minimum power sink tree problem has a polynomial time optimal solution.

title: A Note on Optical Network with Nonsplitting Nodes
abstract: We study the problem of computing the minimum total weight multicast route in an optical network with both nonsplitting and splitting nodes, and present a simple approximation with performance ratio 3, which is better than existing one in the literature.

title: On the construction of 2-connected virtual backbone in wireless networks
abstract: Virtual backbone has been proposed as the routing infrastructure to alleviate the broadcasting storm problem in ad hoc networks. Since the nodes in the virtual backbone need to carry other node's traffic, and node and link failure are inherent in wireless networks, it is desirable that the virtual backbone is fault tolerant. In this paper, we propose a new algorithm called Connecting Dominating Set Augmentation (CDSA) to construct a 2-connected virtual backbone which can resist the failure of one wireless node. We show that CDSA has guaranteed quality by proving that the size of the CDSA constructed 2-connected backbone is within a constant factor of the optimal 2-connected virtual backbone size. Through extensive simulations, we demonstrate that in practice, CDSA can build a 2-connected virtual backbone with only small overhead.

title: Greedy Approximation Algorithms
abstract: Greedy strategy is a simple and natural method in the design of approximation algorithms. This chapter presents greedy approximation algorithms for very broad classes of maximization problems and minimization problems and analyzes their approximation bounds. A number of applications of these greedy approximation algorithms are also described in this chapter. For many applications, the greedy approximation algorithm can achieve the best known approximation bound in a straightforward manner. For some applications, they have different formulations, and the corresponding greedy approximation algorithms have different approximation bounds. In addition, some applications can have better approximation algorithm than the greedy approximation algorithm.