MASE (Micro Architectural Simulation Environment) is a novel infrastructure that provides a flexible and capable environment to model modern microarchitectures. Many popular simulators, such as SimpleScalar, are predominately trace-based where the performance simulator is driven by a trace of instructions read from a file or generated on-the-fly by a functional simulator. Trace-driven simulators are well-suited for oracle studies and provide a clean division between performance modeling and functional emulation. A major problem with this approach, however, is that it does not accurately model timing dependent computations, an increasing trend in microarchitecture designs such as those found in multiprocessor systems. MASE implements a micro-functional performance model that combines timing and functional components into a single core. In addition, MASE incorporates a trace-driven functional component used to implement oracle studies and check the results of instructions as they commit. The check feature reduces the burden of correctness on the micro-functional core and also serves as a powerful debugging aid. MASE also implements a callback scheduling interface to support resources with non-deterministic latencies such as those found in highly concurrent memory systems. MASE was built on top of the current version of SimpleScalar. Analyses show that the performance statistics are comparable without a significant increase in simulation time.

We have developed Argus, a novel approach for providing low-cost, comprehensive error detection for simple cores. The key to Argus is that the operation of a von Neumann core consists of four fundamental tasks—control flow, dataflow, computation, and memory access—that can be checked separately. We prove that Argus can detect any error by observing whether any of these tasks are performed incorrectly. We describe a prototype implementation, Argus-1, based on a single-issue, 4-stage, in-order processor to illustrate the potential of our approach. Experiments show that Argus-1 detects transient and permanent errors in simple cores with much lower impact on performance (<4 % average overhead) and chip area (<17 % overhead)

Circuit reliability is an increasingly important design consideration for modern logic circuits. To this end, our work focuses on the evaluation of circuit reliability under probabilistic gate-level fault models that can capture both soft errors, e.g., radiation-related, and spatially-uniform manufacturing defects. This basic task can, in principle, be used (i) by synthesis procedures to select more reliable circuits, and (ii) to estimate yield for electronic nanotechnologies where high defect density is expected.

We introduce a new verification methodology for modern microprocessors that uses a simple checker processor to validate the execution of a companion high-performance processor. The checker can be viewed as an at-speed emulator that is formally verified to be compliant to an ISA specification. This verification approach enables the practical deployment of formal methods without impacting overall performance. 1.

The paper presents a sequence of three projects on design and formal verification of pipelined and superscalar processors. The projects were integrated—by means of lectures and preparatory homework exercises—into an existing advanced computer architecture course taught to both undergraduate and graduate students in a way that required them to have no prior knowledge of formal methods. The first project was on design and formal verification of a 5-stage pipelined DLX processor, implementing the six basic instruction types—register-register-ALU, registerimmediate-ALU, store, load, jump, and branch. The second project was on extending the processor from project one with ALU exceptions, a return-from-exception instruction, and branch prediction; each of the resulting models was formally verified. The third project was on design and formal verification of a dual-issue superscalar version of the DLX from project one. The preparatory homework problems included an exercise on design and formal verification of a staggered ALU, pipelined in the style of the integer ALUs in the Intel Pentium 4. The processors were described in the high-level hardware description language AbsHDL that allows the students to ignore the bit widths of word-level values and the internal implementations of functional units and memories, while focusing entirely on the logic that controls the pipelined or superscalar execution. The formal verification tool flow included the term-level symbolic simulator TLSim, the decision procedure EVC, and an efficient SAT-checker; this tool flow—combined with the same abstraction techniques for defining processors with exceptions and branch prediction, as used in the projects—was applied at Motorola to formally verify a model of the MCORE processor, and detected bugs. The course went through two iterations—offered at the Georgia Institute of Technology in the summer and fall of 2002—and was taught to 67 students, 25 of whom were undergraduates.

Ensuring correctness of execution of complex multi-core processor systems deployed in the field remains to this day an extremely challenging task. The major part of this effort is concentrated on design verification, where different pre- and post-silicon techniques are used to guarantee that devices behave exactly as stated in the specification. Unfortunately, the performance of even state-of-the-art validation tools lags behind the growing complexity of multi-core designs. Therefore, subtle bugs still slip into released components, causing incorrect computational results, or even compromising the security of the end-user systems. In this work we present Caspar – an approach for in-thefield patching of the memory subsystem hardware in multicore chips. Caspar relies on a checkpointing system, which periodically logs the state of the chip, and a novel error detection and recovery scheme, which uses a simplified mode of operation to bypass cache coherence and consistency errors. The implementation of Caspar employs hardware detectors: on-die programmable circuits to identify system’s configurations that may lead to bugs, and to trigger recovery and bypass. Our experimental results show that Caspar can be used effectively to detect and bypass a variety of memory subsystem bugs, with as little as 2 % performance impact and 6 % area overhead during bug-free operation. 1.

Abstract. This work-in-progress paper surveys error detection techniques for transient, timing, permanent and logical errors in system-on-chip (SoC) design and discusses their applicability in the design of monitors for our Autonomic SoC architecture framework. These monitors will be needed to deliver necessary signals to achieve fault-tolerance, self-healing and self-calibration in our Autonomic SoC architecture. The framework combines the monitors with a welltailored design methodology that explores how the Autonomic SoC (ASoC) can cope with malfunctioning subcomponents. 1

Shared memory consistency protocol verification against weak memory models: refinement via model-checking

...... Technological trends are leading to more hardware errors due to both transient and permanent physical phenomena. 1 The first and most important step in dealing with these errors is detecting them. Once an error is detected, the system can avoid silent data corruption and potentially recover to a pre-error state and resume execution. In this work, we focus on relatively simple cores, rather than speculative, out-of-order cores. Simple cores are becoming more attractive because of their low power consumption, particularly for multicore chips, embedded applications, and applications for which throughput is more important than latency.

Fault-tolerance has become an essential concern for processor designers due to increasing soft-error rates. In this study, we are motivated by the fact that Transactional Memory (TM) hardware provides an ideal base upon which to build a fault-tolerant system. We show how it is possible to provide low-cost faulttolerance for serial programs by using a minimallymodified Hardware Transactional Memory (HTM) that features lazy conflict detection, lazy data versioning. This scheme, called FaulTM, employs a hybrid hardware-software fault-tolerance technique. On the software side, FaulTM programming model is able to provide the flexibility for programmers to decide between performance and reliability. Our experimental results indicate that FaulTM produces relatively less performance overhead by reducing the number of comparisons and by leveraging already proposed TM hardware. We also conduct experiments which indicate that the baseline FaulTM design has a good error coverage. To the best of our knowledge, this is the first architectural fault-tolerance proposal using Hardware Transactional Memory.