395 research outputs found
Language Design for Reactive Systems: On Modal Models, Time, and Object Orientation in Lingua Franca and SCCharts
Reactive systems play a crucial role in the embedded domain. They continuously interact with their environment, handle concurrent operations, and are commonly expected to provide deterministic behavior to enable application in safety-critical systems. In this context, language design is a key aspect, since carefully tailored language constructs can aid in addressing the challenges faced in this domain, as illustrated by the various concurrency models that prevent the known pitfalls of regular threads. Today, many languages exist in this domain and often provide unique characteristics that make them specifically fit for certain use cases. This thesis evolves around two distinctive languages: the actor-oriented polyglot coordination language Lingua Franca and the synchronous statecharts dialect SCCharts. While they take different approaches in providing reactive modeling capabilities, they share clear similarities in their semantics and complement each other in design principles. This thesis analyzes and compares key design aspects in the context of these two languages. For three particularly relevant concepts, it provides and evaluates lean and seamless language extensions that are carefully aligned with the fundamental principles of the underlying language. Specifically, Lingua Franca is extended toward coordinating modal behavior, while SCCharts receives a timed automaton notation with an efficient execution model using dynamic ticks and an extension toward the object-oriented modeling paradigm
LIPIcs, Volume 251, ITCS 2023, Complete Volume
LIPIcs, Volume 251, ITCS 2023, Complete Volum
Bridging Causal Reversibility and Time Reversibility: A Stochastic Process Algebraic Approach
Causal reversibility blends reversibility and causality for concurrent
systems. It indicates that an action can be undone provided that all of its
consequences have been undone already, thus making it possible to bring the
system back to a past consistent state. Time reversibility is instead
considered in the field of stochastic processes, mostly for efficient analysis
purposes. A performance model based on a continuous-time Markov chain is time
reversible if its stochastic behavior remains the same when the direction of
time is reversed. We bridge these two theories of reversibility by showing the
conditions under which causal reversibility and time reversibility are both
ensured by construction. This is done in the setting of a stochastic process
calculus, which is then equipped with a variant of stochastic bisimilarity
accounting for both forward and backward directions
A multi-level functional IR with rewrites for higher-level synthesis of accelerators
Specialised accelerators deliver orders of magnitude higher energy-efficiency than
general-purpose processors. Field Programmable Gate Arrays (FPGAs) have become
the substrate of choice, because the ever-changing nature of modern workloads, such
as machine learning, demands reconfigurability. However, they are notoriously hard
to program directly using Hardware Description Languages (HDLs). Traditional High-Level Synthesis (HLS) tools improve productivity, but come with their own problems.
They often produce sub-optimal designs and programmers are still required to write
hardware-specific code, thus development cycles remain long.
This thesis proposes Shir, a higher-level synthesis approach for high-performance
accelerator design with a hardware-agnostic programming entry point, a multi-level
Intermediate Representation (IR), a compiler and rewrite rules for optimisation.
First, a novel, multi-level functional IR structure for accelerator design is described.
The IRs operate on different levels of abstraction, cleanly separating different hardware
concerns. They enable the expression of different forms of parallelism and standard
memory features, such as asynchronous off-chip memories or synchronous on-chip
buffers, as well as arbitration of such shared resources. Exposing these features at the
IR level is essential for achieving high performance.
Next, mechanical lowering procedures are introduced to automatically compile
a program specification through Shir’s functional IRs until low-level HDL code for
FPGA synthesis is emitted. Each lowering step gradually adds implementation details.
Finally, this thesis presents rewrite rules for automatic optimisations around parallelisation, buffering and data reshaping. Reshaping operations pose a challenge to
functional approaches in particular. They introduce overheads that compromise performance or even prevent the generation of synthesisable hardware designs altogether.
This fundamental issue is solved by the application of rewrite rules.
The viability of this approach is demonstrated by running matrix multiplication
and 2D convolution on an Intel Arria 10 FPGA. A limited design space exploration is
conducted, confirming the ability of the IR to exploit various hardware features. Using
rewrite rules for optimisation, it is possible to generate high-performance designs
that are competitive with highly tuned OpenCL implementations and that outperform
hardware-agnostic OpenCL code. The performance impact of the optimisations is
further evaluated showing that they are essential to achieving high performance, and
in many cases also necessary to produce hardware that fits the resource constraints
An Efficient Canonical Narrowing Implementation with Irreducibility and SMT Constraints for Generic Symbolic Protocol Analysis
Narrowing and unification are very useful tools for symbolic analysis of
rewrite theories, and thus for any model that can be specified in that way. A
very clear example of their application is the field of formal cryptographic
protocol analysis, which is why narrowing and unification are used in tools
such as Maude-NPA, Tamarin and Akiss. In this work we present the
implementation of a canonical narrowing algorithm, which improves the standard
narrowing algorithm, extended to be able to process rewrite theories with
conditional rules. The conditions of the rules will contain SMT constraints,
which will be carried throughout the execution of the algorithm to determine if
the solutions have associated satisfiable or unsatisfiable constraints, and in
the latter case, discard them.Comment: 41 pages, 7 tables, 1 algorithm, 9 example
Safe Session-Based Concurrency with Shared Linear State
Publisher Copyright: © 2023, The Author(s).We introduce CLASS, a session-typed, higher-order, core language that supports concurrent computation with shared linear state.publishersversionpublishe
Proof-theoretic Semantics for Intuitionistic Multiplicative Linear Logic
This work is the first exploration of proof-theoretic semantics for a substructural logic. It focuses on the base-extension semantics (B-eS) for intuitionistic multiplicative linear logic (IMLL). The starting point is a review of Sandqvist’s B-eS for intuitionistic propositional logic (IPL), for which we propose an alternative treatment of conjunction that takes the form of the generalized elimination rule for the connective. The resulting semantics is shown to be sound and complete. This motivates our main contribution, a B-eS for IMLL
, in which the definitions of the logical constants all take the form of their elimination rule and for which soundness and completeness are established
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Examining university student satisfaction and barriers to taking online remote exams
Recent years have seen a surge in the popularity of online exams at universities, due to the greater convenience and flexibility they offer both students and institutions. Driven by the dearth of empirical data on distance learning students' satisfaction levels and the difficulties they face when taking online exams, a survey with 562 students at The Open University (UK) was conducted to gain insights into their experiences with this type of exam. Satisfaction was reported with the environment and exams, while work commitments and technical difficulties presented the greatest barriers. Gender, race and disability were also associated with different levels of satisfaction and barriers. This study adds to the increasing number of studies into online exams, demonstrating how this type of exam can still have a substantial effect on students experienced in online learning systems and
technologies
Open Source Law, Policy and Practice
This book examines various policies, including the legal and commercial aspects of the Open Source phenomenon. Here, ‘Open Source’ is adopted as convenient shorthand for a collection of diverse users and communities, whose differences can be as great as their similarities. The common thread is their reliance on, and use of, law and legal mechanisms to govern the source code they write, use, and distribute. The central fact of open source is that maintaining control over source code relies on the existence and efficacy of intellectual property (‘IP’) laws, particularly copyright law. Copyright law is the primary statutory tool that achieves the end of openness, although implemented through private law arrangements at varying points within the software supply chain. This dependent relationship is itself a cause of concern for some philosophically in favour of ‘open’, with some predicting (or hoping) that the free software movement will bring about the end of copyright as a means for protecting software
LIPIcs, Volume 244, ESA 2022, Complete Volume
LIPIcs, Volume 244, ESA 2022, Complete Volum
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