42676253
Synchronization of large sequential circuits by partial reset
In this paper, we present a technique to synchronize large synchronous sequential circuits, which uses partial reset to break feedback loops in the circuits such that they become synchronizable. The method also provides a synchronizing sequence. Experimental results for ISCAS'89 benchmark circuits are presented, including the largest circuits, which were not synchronized previously.
6121809
Tree-like counterexamples in model checking
Counter examples for specification violations provide engineers with important debugging information. Although counterexamples are considered one of the main advantages of model checking, state-of the art model checkers are restricted to relatively simple counterexamples, and surprisingly little research effort has been put into counterexamples. In this paper, we introduce a new general framework for counterexamples. The paper has three main contributions: (i) We determine the general form of ACTL counterexamples. To this end, we investigate the notion of counterexample and show that a large class of temporal logics beyond ACTL admits counterexamples with a simple tree-like transition relation. We show that the existence of tree-like counterexamples is related to a universal fragment of extended branching time logic based on w-regular temporal operators. (ii) We present new symbolic algorithms to generate tree-like counterexamples for ACTL specifications. (iii) Based on tree-like counterexamples we extend the abstraction refinement methodology developed recently by Clarke et al. (CAV'2000) to full ACTL. This demonstrates the conceptual simplicity and elegance of tree-like counterexamples.
18404090
Dynamic frequency scaling with buffer insertion for mixed workloads
This paper presents a method to reduce the energy of interactive systems for mixed workloads: multimedia applications that require constant output rates and sporadic jobs that need prompt responses. The authors' method divides multimedia programs into stages and inserts data buffers between them. Data buffering has three purposes: (1) to support constant output rates; (2) to allow frequency scaling for energy reduction; and (3) to shorten the response times of sporadic jobs. The authors construct frequency-assignment graphs. Each vertex represents the current state of the buffers and the frequencies of the processor. The authors develop an efficient graph-walk algorithm that assigns frequencies to reduce energy. The same method. can be applied to perform voltage scaling and the combination of frequency and voltage scaling. The authors' experimental results on a Strong-ARM-based computer show that four discrete frequencies are sufficient to achieve nearly maximum energy saving. The method reduces the power consumption of an MPEG program by 46%. The authors also demonstrate a case that shortens the response time of a sporadic job by 55%.
2412225
Dynamic Voltage Scaling for Multitasking Real-Time Systems With Uncertain Execution Time
Dynamic voltage and frequency scaling can save energy for real-time systems. Frequencies are generally assumed proportional to voltages. Previous studies consider the probabilistic distributions of tasks' execution time to assist dynamic voltage scaling in task scheduling. These studies use probability information for intratask voltage scheduling but do not sufficiently explore the opportunities for intertask scheduling to save more energy. This paper presents a new approach to combine intra- and intertask voltage scheduling for better energy savings in hard real-time systems with uncertain task execution time. Our approach takes three steps: 1) We calculate statistically the optimal voltage schedules for multiple concurrent tasks, using earliest deadline first scheduling for an ideal processor that can change the frequency continuously; 2) we then adapt the solution to a processor with a limited range of discrete frequencies, using a polynomial-time heuristic algorithm; and 3) finally, we improve our solution, considering the time and energy overheads of frequency switching for schedulability and energy reduction. Our simulation shows that the new approach can save more energy than existing solutions while meeting hard deadlines.
1552056
Pama: a Fast String Matching Algorithm
String matching is a fundamental operation in computer science, and its performance has great impact on many applications including database query, text processing, DNA and protein sequence analysis. In this paper, we propose a fast string matching algorithm, PAMA (PAttern MAtching). The shift rule used by PAMA not only subsumes both the bad character rule and the good suffix rule employed by the well-known Boyer-Moore algorithm, but also employs an additional key observation to enable faster shifting during the string matching process. Theoretically, we prove that from the same alignment, the next shift of PAMA will be at least as much as that of the Boyer-Moore algorithm. Experimentally, we show that PAMA indeed significantly outperforms the original Boyer-Moore algorithm in almost all cases, and outperforms other Boyer-Moore variants such as Tuned-BM, Turbo-BM and Horspool for long patterns (length ≥ 128) or for small alphabets (size < 8).
2733921
Joint power management of memory and disk
The paper presents a scheme to combine memory and power management for achieving better energy reduction. Our method periodically adjusts the size of physical memory and the timeout value to shut down a hard disk for reducing the average power consumption. We use Pareto distributions to model the distributions of idle time. The parameters of the distributions are adjusted at run-time for calculating the corresponding timeout value of the disk power management. The memory size is changed based on the inclusion property to predict the number of disk accesses at different memory sizes. Experimental results show more than 50% energy savings compared to a 2-competitive fixed-timeout method.
14054770
A new approach for ground moving target indication in foliage environment
Ground moving target indication (GMTI) in foliage environment is a challenging problem, because the strong echoes from dense foliage environment and big attenuation of the radar microwave often make it difficult for traditional time frequency distributions to clearly and locally represent the Doppler frequency. This paper introduced a new approach to improve the performance of GMTI. This so-called Hilbert Huang Transform (HHT) method composes of empirical mode decomposition (EMD) and Hilbert transform technique. EMD is applied to extract target signal from interference and the associated Hilbert transform calculates the instantaneous Doppler frequency, representing a novel Hilbert spectrum in time frequency domain. Both simulative and experimental signals are used to validate the efficiency of HHT. This adaptive approach offers higher signal to disturbance ratio and higher resolution in the time frequency distribution.