Properties Of Real-time Systems Research Articles

Computing Accumulated Delays in Real-time Systems

We present a verification algorithm for duration properties of real-time systems. While simple real-time properties constrain the total elapsed time between events, duration properties constrain the accumulated satisfaction time of state predicates. We formalize the concept of durations by introducing duration measures for timed automata. A duration measure assigns to each finite run of a timed automaton a real number —the duration of the run— which may be the accumulated satisfaction time of a state predicate along the run. Given a timed automaton with a duration measure, an initial and a final state, and an arithmetic constraint, the duration-bounded reachability problem asks if there is a run of the automaton from the initial state to the final state such that the duration of the run satisfies the constraint. Our main result is an (optimal) PSPACE decision procedure for the duration-bounded reachability problem.

UPPAAL in 1995

UPPAAL is a tool suite for automatic verification of safety and<br />bounded liveness properties of real-time systems modeled as networks of timed automata<br />[12, 9, 4], developed during the past two years. In this paper, we summarize<br />the main features of UPPAAL in particular its various extensions developed in 1995<br />as well as applications to various case-studies, review and provide pointers to the<br />theoretical foundation.

UPPAAL—a Tool Suite for Automatic Verification of Real–Time Systems

Uppaal is a tool suite for automatic verification of safety and<br />bounded liveness properties of real-time systems modeled as networks of<br />timed automata. It includes: a graphical interface that supports graphical<br />and textual representations of networks of timed automata, and automatic<br />transformation from graphical representations to textual format,<br />a compiler that transforms a certain class of linear hybrid systems to<br />networks of timed automata, and a model-checker which is implemented<br />based on constraint-solving techniques. Uppaal also supports diagnostic<br />model-checking providing diagnostic information in case verification of a<br />particular real-time systems fails.<br />The current version of Uppaal is available on the World Wide Web via<br />the Uppaal home page http://www.docs.uu.se/docs/rtmv/uppaal.

The benefits of relaxing punctuality

The most natural, compositional, way of modeling real-time systems uses a dense domain for time. The satisfiability of timing constraints that are capable of expressing punctuality in this model, however, is known to be undecidable. We introduce a temporal language that can constrain the time difference between events only with finite, yet arbitrary, precision and show the resulting logic to be EXPSPACE-complete. This result allows us to develop an algorithm for the verification of timing properties of real-time systems with a dense semantics.

An accurate worst case timing analysis for RISC processors

An accurate and safe estimation of a task's worst case execution time (WCET) is crucial for reasoning about the timing properties of real time systems. In RISC processors, the execution time of a program construct (e.g., a statement) is affected by various factors such as cache hits/misses and pipeline hazards, and these factors impose serious problems in analyzing the WCETs of tasks. To analyze the timing effects of RISC's pipelined execution and cache memory, we propose extensions to the original timing schema where the timing information associated with each program construct is a simple time bound. In our approach, associated with each program construct is worst case timing abstraction, (WCTA), which contains detailed timing information of every execution path that might be the worst case execution path of the program construct. This extension leads to a revised timing schema that is similar to the original timing schema except that concatenation and pruning operations on WCTAs are newly defined to replace the add and max operations on time bounds in the original timing schema. Our revised timing schema accurately accounts for the timing effects of pipelined execution and cache memory not only within but also across program constructs. The paper also reports on preliminary results of WCET analysis for a RISC processor. Our results show that tight WCET bounds (within a maximum of about 30% overestimation) can be obtained by using the revised timing schema approach. >

Comparing RTL and FNLOG- timing properties in real-time systems

The specification and verification of real-time systems is an important component in the reliable development of such systems. Formal techniques of specification and verification have the advantage of formal analysis and design, as well as the possibility of automating some of the processes. FNLOG is a logic-based specification language for real-time systems, which is based on first order predicate logic with arithmetic extended by quantified temporal operators. FNLOG semantics is based on an underlying statechart, and a sound and relatively complete proof system for FNLOG exists. This paper presents extensions to FNLOG, inspired by Real Time Logic (RTL), to facilitate the specification of periodic and sporadic properties of real-time systems.

Proving properties of real-time systems through logical specifications and Petri net models

Addresses the problem of formally analyzing the properties of real-time systems. We propose a method based on modeling the system as a timed Petri net and on specifying its properties in TRIO, an extension of temporal logic suitable for dealing explicitly with time and for measuring it. Timed Petri nets are axiomatized in terms of TRIO, so that their properties can be derived as theorems in the same spirit as the classical Hoare method allows one to prove properties of programs coded in a Pascal-like language. The method is also illustrated through an example. >

Trends in artificial intelligence applications for real-time control (a speculative study)

Some of the theory-bound evolutional trends in real-time AI applications are pointed out based on analysis of essential properties of real-time systems as well as AI based systems. The evolutional mainstream is increasing interdisciplinary integration. Three subtrends are illustrated on examples: mechanical combination of methods, AI methods used for approximate solution of “classical” problems, and abstract methods applied in new domains. In addition similarity between integrated circuits and real-time systems design and increased use of formal verification at the early stages of systems development are pointed out.

AN EVENT-BASED REAL-TIME LOGIC FOR THE SPECIFICATION AND ANALYSIS OF REAL-TIME SYSTEMS

Research on real-time systems now focuses on formal approaches to specify and analyze the behavior of real-time systems. Temporal logic is a natural candidate for this since it can specify properties of event and state sequences. However, “pure” temporal logic cannot specify “quantitative” aspect of time. The concepts of eventuality, fairness, etc. are essentially “qualitative” treatment of time. The pure temporal logic makes no reference to absolute time. For real-time systems, the pure qualitative specification and analysis of time are inadequate. In this paper, we present a modification of temporal logic—Event-based Real-time Logic (ERL), based on our event-based conceptual model. The ERL provides a high-level framework for specifying timing properties of real-time systems, and it can be implemented using Prolog programming language. In our approach to testing and debugging of real-time systems, the ERL is used to specify both expected behavior (specification) and actual behavior (execution traces) of the target system and to verify that the target system achieves the specification. In this paper, a method is presented to implement the ERL using Prolog programming language for testing and debugging real-time systems.

A KNOWLEDGE-BASED APPROACH FOR THE SPECIFICATION AND ANALYSIS OF REAL-TIME SOFTWARE SYSTEMS

FRORL (Frame-and-Rule Oriented Requirements specification Language) was proposed to exploit knowledge representation techniques as an aid in the specification, analysis, and development of a software system. With the real-time software systems as our target systems, the merely mechanisms provided by FRORL cannot meet the specific demands on real-time software systems. As a result, in this paper, we propose RT-FRORL (Real-Time FRORL) as an extension of FRORL. RT-FRORL not only inherits FRORL's basic structure but also includes those language constructs needed to support the specification of real-time systems. The syntax of RT-FRORL is based on frames and production rules. The semantics of RT-FRORL is defined through the integration of first order logic and temporal logic extension. Using RT-FRORL, concurrent and absolute time properties of real-time systems can be easily specified.

Specifying real-time properties with metric temporal logic

This paper is motivated by the need for a formal specification method for real-time systems. In these systemsquantitative temporal properties play a dominant role. We first characterize real-time systems by giving a classification of such quantitative temporal properties. Next, we extend the usual models for temporal logic by including a distance function to measure time and analyze what restrictions should be imposed on such a function. Then we introduce appropriate temporal operators to reason about such models by turning qualitative temporal operators into (quantitative) metric temporal operators and show how the usual quantitative temporal properties of real-time systems can be expressed in this metric temporal logic. After we illustrate the application of metric temporal logic to real-time systems by several examples, we end this paper with some conclusions.