Mach-Based Channel Library

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Quasi-Delay-Insensitive Circuits are Turing-Complete

Quasi-delay-insensitive (QDI) circuits are those whose correct operation does not depend on the delays of operators or wires, except for certain wires that form isochronic forks. In this paper we show that quasi-delay-insensitivity, stability and noninterference, and strong confluence are equivalent properties of a computation. In particular, this shows that QDI computations are deterministic. We show that the class of Turing-computable functions have QDI implementations by constructing a QDI Turing machine

The impact of asynchrony on computer architecture

The performance characteristics of asynchronous circuits are quite different from those of their synchronous counterparts. As a result, the best asynchronous design of a particular system does not necessarily correspond to the best synchronous design, even at the algorithmic level. The goal of this thesis is to examine certain aspects of computer architecture and design in the context of an asynchronous VLSI implementation. We present necessary and sufficient conditions under which the degree of pipelining of a component can be modified without affecting the correctness of an asynchronous computation. As an instance of the improvements possible using an asynchronous architecture, we present circuits to solve the prefix problem with average-case behavior better than that possible by any synchronous solution in the case when the prefix operator has a right zero. We show that our circuit implementations are area-optimal given their performance characteristics, and have the best possible average-case latency. At the level of processor design, we present a mechanism for the implementation of precise exceptions in asynchronous processors. The novel feature of this mechanism is that it permits the presence of a data-dependent number of instructions in the execution pipeline of the processor. Finally, at the level of processor architecture, we present the architecture of a processor with an independent instruction stream for branches. The instruction set permits loops and function calls to be executed with minimal control-flow overhead

Folded FIFOs

We present two distributed implementations of first-in first-out meassage buffers. The solutions presented reduce the delay between insert and delete operations on the bufer when the buffer is empty. The designs are then modified so as to offer bounded-response-time. The solutions presented use a CSP-like notation and are suitable for transformation into a VLSI circuit

Theory and Use of Conditional Composition

[No abstract available

HABIT: Hardware-Assisted Bluetooth-based Infection Tracking

The ongoing COVID-19 pandemic has caused health organizations to consider using digital contact tracing to help monitor and contain the spread of COVID-19. Due to this urgent need, many different groups have developed secure and private contact tracing phone apps. However, these apps have not been widely deployed, in part because they do not meet the needs of healthcare officials. We present HABIT, a contact tracing system using a wearable hardware device designed specifically with the goals of public health officials in mind. Unlike current approaches, we use a dedicated hardware device instead of a phone app for proximity detection. Our use of a hardware device allows us to substantially improve the accuracy of proximity detection, achieve strong security and privacy guarantees that cannot be compromised by remote attackers, and have a more usable system, while only making our system minimally harder to deploy compared to a phone app in centralized organizations such as hospitals, universities, and companies. The efficacy of our system is currently being evaluated in a pilot study at Yale University in collaboration with the Yale School of Public Health

Composing Processes Using Modified Rely-Guarantee Specifications

We present a specification notation for components of concurrent systems and an accompanying proof methodology for reasong about the composition of these components. The specification construct is motivated by rely-guarantee pairs and by any-component program properties. The proof technique is based on an implication ladder and on two basic properties from which more complex properties are derived. Two examples illustrate the simplicity and compositionality of the model, and demonstrate how the model can be used to create structured and reusable proofs of distributed systems

Field-programmable encoding for address-event representation

In conventional frame-based image sensors, every pixel records brightness information and sends this information to a receiver serially in a scanning fashion. This full-frame readout approach suffers from high bandwidth requirements and increased power consumption with the increasing size of the pixel array. Event-based image sensors are gaining popularity for reducing the bandwidth and power requirements by sending only meaningful data in an event-driven approach with the help of address-event representation (AER) communication protocol. However, the event-based readout suffers from increased latency and timing error when the number of pixels with an event increase. In this paper, we introduce a new field-programmable AER (FP-AER) encoding scheme which offers benefits of both frame-based and event-based approaches. The readout design can be configured “in the field” using configuration bits. We also compare the performance of the proposed design against existing AER-based approaches for imaging applications and show that FP-AER performs best in both scanning and event-based readout