Eli Arbel

Resurrecting infeasible clock-gating functions

In this paper we consider the problem of exploiting infeasible clock gating functions. Analysis of industrial designs reveals a large margin of potential for power saving based on clock gating functions that initially appear to be useless due to timing violation or excessive power consumption. We propose two optimization techniques for resurrecting such functions that can be used as a generic post-processing phase in an automatic clock gating tool. The first provides timing-aware approximation and the second aims at generating large gating domains by clustering similar clock gating functions. Our experimental results show that the combination of these two techniques yields an additional power saving of up to 78% in industrial designs.

SAT-based synthesis of clock gating functions using 3-valued abstraction

Clock gating is a power reduction technique for digital circuits that works by eliminating unnecessary switching of parts of the clock network, a power-hungry component in hardware designs. An effective approach to clock gating synthesis is based on a functional analysis of the design using BDDs. Algorithms of this type attempt to build a BDD for a clock gating circuit and then reduce its size with an approximation. If the BDD of a particular latch grows too large the attempt to gate that latch is aborted. We replace BDDs with a SAT-based technique combined with 3-valued abstraction. Our technique generates the approximation directly from the circuit, and thus avoids the explosion. Furthermore, our technique is incremental in the sense that it produces a partial result (a weaker approximation) if time or memory limits are exceeded. Our experimentation shows that more than 70% of latches that could not be gated using the BDD-based approach were gated by the SAT-based method.

Gating Aware Error Injection

Error injection is one of the most commonly used techniques for estimating the reliability of a given hardware design. While error injection in dynamic simulation is widely used in the industry, other methods exist as well, e.g. hardware error injection and fault-tolerance analysis using formal verification. As covering the entire space of all possible fault injections is impractical, nearly all workload-based error injection methods (e.g. simulation or emulation techniques) use a statistical approach for error injection, i.e. they only inject a fraction of all possible faults. As a result, the statistical fault injection approach is much more efficient in characterizing the overall reliability of the design than in finding particular reliability-related bugs. On the other hand, the formal-based approach guarantees full coverage of the design space, including under all possible faults, granted the formal analysis can be completed. However, performing formal verification on design hierarchies with error detection and recovery logic is usually unfeasible. To address the challenge of effectively finding reliability-related bugs on large industrial designs, this paper proposes a novel approach which is aimed at finding a particular kind of design bugs related to gating conditions which correspond to error detection logic. We present an automated method for identifying those gating conditions and generating a gating-aware fault injection module. Experimental results on a real microprocessor arithmetical unit demonstrates the effectiveness of our method in finding real design bugs using relatively small amount of error injection tests.

Designing reliable cyber-physical systems overview associated to the special session at FDL'16

CPS, that consist of a cyber part – a computing system – and a physical part – the system in the physical environment – as well as the respective interfaces between those parts, are omnipresent in our daily lives. The application in the physical environment drives the overall requirements that must be respected when designing the computing system. Here, reliability is a core aspect where some of the most pressing design challenges are: monitoring failures throughout the computing system, determining the impact of failures on the application constraints, and ensuring correctness of the computing system with respect to application-driven requirements rooted in the physical environment. This paper provides an overview of techniques discussed in the special session to tackle these challenges throughout the stack of layers of the computing system while tightly coupling the design methodology to the physical requirements.

Facilitating timing debug by logic path correspondence

Synthesis tools for high-performance VLSI designs employ aggressive logic optimization techniques in order to meet physical requirements such as area and cycle time. During these optimizations, the original structure of the design, which is usually written in a hardware description language (HDL), is lost. It is difficult, and often impossible, to relate signals after synthesis to the original signals in the HDL code. Some signals only lose their names while for others there are no equivalent counterparts in the design after synthesis. Debugging timing problems is based on timing reports which are usually represented in terms of the post-synthesis design. Hence, it is difficult to relate critical paths in the timing reports to the relevant paths in the HDL code when a logic fix is needed. In this paper, we propose a different approach for dealing with the correspondence problem: instead of trying to relate signals we relate paths. Given a critical path in a post-synthesis representation, our method is able to find all corresponding paths in the pre-synthesis (HDL) representation. As a result, locating the parts in the HDL which are relevant to the given timing problem becomes trivial. A novel Sat-based algorithm for dealing with the path-correspondence problem is described. Experimental results on various industrial high-end processor designs show the effectiveness of our algorithm in substantially reducing the amount of paths in the HDL which one will have to consider when debugging a given critical path.

Designing Reliable Cyber-Physical Systems

Cyber-physical systems, that consist of a cyber part—a computing system—and a physical part—the system in the physical environment—as well as the respective interfaces between those parts, are omnipresent in our daily lives. The application in the physical environment drives the overall requirements that must be respected when designing the computing system. Here, reliability is a core aspect where some of the most pressing design challenges are: monitoring failures throughout the computing system, determining the impact of failures on the application constraints, and ensuring correctness of the computing system with respect to application-driven requirements rooted in the physical environment.

Hardware and Software: Verification and Testing

Current Trends and Future Direction in Eco-system of Hardware Formal Verification: A Technical and Business Perspective