As silicon technologies move into the nanometer regime, transistor reliability is expected to wane as devices become subject to extreme process variation, particle-induced transient errors, and transistor wear-out. Unless these challenges are addressed, computer vendors can expect low yields and short mean-timesto-failure. In this paper, we examine the challenges of designing complex computing systems in the presence of transient and permanent faults. We select one small aspect of a typical chip multiprocessor (CMP) system to study in detail, a single CMP router switch. To start, we develop a unified model of faults, based on the time-tested bathtub curve. Using this convenient abstraction, we analyze the reliability versus area tradeoff across a wide spectrum of CMP switch designs, ranging from unprotected designs to fully protected designs with online repair and recovery capabilities. Protection is considered at multiple levels from the entire system down through arbitrary partitions of the design. To better understand the impact of these faults, we evaluate our CMP switch designs using circuit-level timing on detailed physical layouts. Our experimental results are quite illuminating. We find that designs are attainable that can tolerate a larger number of defects with less overhead than naïve triple-modular redundancy, using domain-specific techniques such as end-to-end error detection, resource sparing, automatic circuit decomposition, and iterative diagnosis and reconfiguration.

Abstract-Extreme transistor technology scaling is causing increasing concerns in device reliability: the expected lifetime of individual transistors in complex chips is quickly decreasing, and the problem is expected to worsen at future technology nodes. With complex designs increasingly relying on Networks-on-Chip (NoCs) for on-chip data transfers, a NoC must continue to operate even in the face of many transistor failures. Specifically, it must be able to reconfigure and reroute packets around faults to enable continued operation, i.e., generate new routing paths to replace the old ones upon a failure. In addition to these reliability requirements, NoCs must maintain low latency and high throughput at very low area budget.In this work, we propose a distributed reconfiguration solution named Ariadne, targeting large, aggressively scaled, unreliable NoCs. Ariadne utilizes up*/down* for fast routing at high bandwidth, and upon any number of concurrent network failures in any location, it reconfigures to discover new resilient paths to connect the surviving nodes. Experimental results show that Ariadne provides a 40%-140% latency improvement (when subject to 50 faults in a 64-node NoC) over other on-chip state-of-the-art fault tolerant solutions, while meeting the low area budget of on-chip routers with an overhead of just 1.97%.

Abstract-Post-silicon validation has become a crucial part of modern integrated circuit design to capture and eliminate functional bugs that escape pre-silicon verification. The most critical roadblock in post-silicon validation is the limited observability of internal signals of a design, since this aspect hinders the ability to diagnose detected bugs. A solution to address this issue leverage trace buffers: these are register buffers embedded into the design with the goal of recording the value of a small number of state elements, over a time interval, triggered by a user-specified event. Due to the trace buffer's area overhead, only a very small fraction of signals can be traced. Thus, the selection of which signals to trace is of paramount importance in post-silicon debugging and diagnosis. Ideally, we would like to select signals enabling the maximum amount of reconstruction of internal signal values. Several signal selection algorithms for post-silicon debug have been proposed in the literature: they rely on a probability-based state-restoration capacity metric coupled with a greedy algorithm. In this work we propose a more accurate restoration capacity metric, based on simulation information, and present a novel algorithm that overcomes some key shortcomings of previous solutions. We show that our technique provides up to 34% better state restoration compared to all previous techniques while showing a much better trend with increasing trace buffer size.

The sustained push toward smaller and smaller technology sizes has reached a point where device reliability has moved to the forefront of concerns for next-generation designs. Silicon failure mechanisms, such as transistor wearout and manufacturing defects, are a growing challenge that threatens the yield and product lifetime of future systems. In this paper we introduce the BulletProof pipeline, the first ultra low-cost mechanism to protect a microprocessor pipeline and on-chip memory system from silicon defects. To achieve this goal we combine area-frugal on-line testing techniques and system-level checkpointing to provide the same guarantees of reliability found in traditional solutions, but at much lower cost. Our approach utilizes a microarchitectural checkpointing mechanism which creates coarse-grained epochs of execution, during which distributed on-line built in self-test (BIST) mechanisms validate the integrity of the underlying hardware. In case a failure is detected, we rely on the natural redundancy of instructionlevel parallel processors to repair the system so that it can still operate in a degraded performance mode. Using detailed circuit-level and architectural simulation, we find that our approach provides very high coverage of silicon defects (89%) with little area cost (5.8%). In addition, when a defect occurs, the subsequent degraded mode of operation was found to have only moderate performance impacts, (from 4% to 18% slowdown).

The progressive trend of fabrication technologies towards the nanometer regime has created a number of new physical design challenges for computer architects. Design complexity, uncertainty in environmental and fabrication conditions, and single-event upsets all conspire to compromise system correctness and reliability. Recently, researchers have begun to advocate a new design strategy called Better Than Worst-Case design that couples a complex core component with a simple reliable checker mechanism. By delegating the responsibility for correctness and reliability of the design to the checker, it becomes possible to build provably correct designs that effectively address the challenges of deep submicron design. In this paper, we present the concepts of Better Than Worst-Case design and highlight two exemplary designs: the DIVA checker and Razor logic. We show how this approach to system implementation relaxes design constraints on core components, which reduces the effects of physical design challenges and creates opportunities to optimize performance and power characteristics. We demonstrate the advantages of relaxed design constraints for the core components by applying typical-case optimization (TCO) techniques to an adder circuit. Finally, we discuss the challenges and opportunities posed to CAD tools in the context of Better Than Worst-Case design. In particular, we describe the additional support required for analyzing run-time characteristics of designs and the many opportunities which are created to incorporate typical-case optimizations into synthesis and verification.

The progressive trend of fabrication technologies towards the nanometer regime has created a number of new physical design challenges for computer architects. Design complexity, uncertainty in environmental and fabrication conditions, and single-event upsets all conspire to compromise system correctness and reliability. Recently, researchers have begun to advocate a new design strategy called Better Than Worst-Case design that couples a complex core component with a simple reliable checker mechanism. By delegating the responsibility for correctness and reliability of the design to the checker, it becomes possible to build provably correct designs that effectively address the challenges of deep submicron design. In this paper, we present the concepts of Better Than Worst-Case design and highlight two exemplary designs: the DIVA checker and Razor logic. We show how this approach to system implementation relaxes design constraints on core components, which reduces the effects of physical design challenges and creates opportunities to optimize performance and power characteristics. We demonstrate the advantages of relaxed design constraints for the core components by applying typical-case optimization (TCO) techniques to an adder circuit. Finally, we discuss the challenges and opportunities posed to CAD tools in the context of Better Than Worst-Case design. In particular, we describe the additional support required for analyzing run-time characteristics of designs and the many opportunities which are created to incorporate typical-case optimizations into synthesis and verification.

Abstract-In this work we propose a resynthesis framework, called CoRé, that automatically corrects errors in digital designs. The framework is based on a simulation-based abstraction technique and performs error correction through two innovative circuit resynthesis solutions: Distinguishing-Power Search (DPS) and Goal-Directed Search (GDS), which modify the functionality of a circuit's internal nodes to match the correct behavior. In addition, we propose a compact encoding of resynthesis information, called Pairs of Bits to be Distinguished (PBDs), which is a key enabler for our resynthesis techniques. Compared with previous solutions, CoRé is more powerful in that: (1) it can fix a broader range of error types because it is not bounded by specific error models; (2) it derives the correct functionality from simulation vectors, without requiring golden netlists; and (3) it can be applied with a broad range of verification flows, including formal and simulation-based.

Abstract-SAT sweeping is the activity of merging two or more functionally equivalent nodes in a circuit by selecting one of them to represent the entire equivalence class. This provides significant advantages in synthesis because it can reduce circuit size and provides additionaly flexibility in technology mapping which could be crucial in post-synthesis optimizations. In addition, it is also critical in verification because it can reduce the complexity of the netlist to be analyzed in equivalence checking. Most algorithms available to this end do not exploit observability don't cares (ODCs) since they do not lend themselves to symmetric transformations. Although a few recent approaches have proposed solutions that can exploit ODCs by overcoming this limitation, they limit their analysis to just a few levels of surrounding logic due to the elevated computational complexity.We develop an ODC-based node merging algorithm that performs efficient global ODC analysis (considering the entire netlist) through simulation and SAT. Our contributions which enable global ODC-based optimizations are: (1) a fast ODC-aware simulator and (2) an incremental verification strategy that limits computational complexity. In addition, our techniques operate on arbitrarily mapped netlists, allowing for powerful post-synthesis optimizations. We show that global ODC analysis discovers up to 60% more (and 25% on average) node-merging opportunities than current state-of-the-art solutions based on local ODC analysis.