Budgeting Under-Specified Tasks for Weakly-Hard Real-Time Systems

In this paper, we present an extension of slack analysis for budgeting in the design of weakly-hard real-time systems. During design, it often happens that some parts of a task set are fully specified while other parameters, e.g. regarding recovery or monitoring tasks, will be available only much later. In such cases, slack analysis can help anticipate how these missing parameters can influence the behavior of the whole system so that a resource budget can be allocated to them. It is, however, sufficient in many application contexts to budget these tasks in order to preserve weakly-hard rather than hard guarantees. We thus present an extension of slack analysis for deriving task budgets for systems with hard and weakly-hard requirements. This work is motivated by and validated on a realistic case study inspired by industrial practice

Bounding Deadline Misses in Weakly-Hard Real-Time Systems with Task Dependencies

International audienceReal-time systems with functional dependencies between tasks often require end-to-end (as opposed to task-level) guarantees. For many of these systems, it is even possible to accept the possibility of longer end-to-end delays if one can bound their frequency. Such systems are called weakly-hard. In this paper we provide end-to-end deadline miss models for systems with task chains using Typical Worst-Case Analysis (TWCA). This bounds the number of potential deadline misses in a given sequence of activations of a task chain. To achieve this we exploit task chain properties which arise from the priority assignment of tasks in static-priority preemptive systems. This work is motivated by and validated on a realistic case study inspired by industrial practice and derived synthetic test cases

Deadline-Überschreitungsmodell für Temporär Überlastete Systeme

A wide range of embedded systems falls into the category of safety-critical systems. Such systems impose different levels of safety requirements depending on how critical the functions assigned to the system are and on how humans interact with the system. Safety requirements involve timing constraints, the violation of which may lead to a system failure. Timing constraints are graded from soft to hard real-time constraints. While satisfying soft real-time constraints requires only best-efforts guarantees, hard real-time constraints are best-treated with worst-case analysis methods for verifying all timing constraints. Weakly-hard real-time systems have extra demands on the timing verification as they tolerate few deadline-misses in certain distributions. Applying worst-case analysis methods, in which a task is schedulable only when it can meet its deadline in the worst-case, to weakly-hard real-time systems questions the expressiveness of the computed guarantees. Considering tolerable deadline-misses raises the need for weakly-hard schedulability analyses to verify weakly-hard real-time constraints and to provide more expressive guarantees. This thesis addresses the schedulability analysis problem of weakly-hard real-time systems. It presents an efficient analysis to compute weakly-hard real-time guarantees in the form of a deadline miss model for various system models. The first contribution is a deadline miss model for a temporarily overloaded uniprocessor system with independent tasks under the Fixed Priority Preemptive and NonPreemptive scheduling policy (FPP & FPNP) using Typical Worst-Case Analysis. In our application context, the transient overload is due to sporadic tasks, for example, interrupt service routines. We adopt the proposed analysis to compute deadline miss models for independent tasks under the Earliest Deadline First (EDF) and Weighted Round-Robin (WRR) scheduling policies. In the second contribution, we extend the analysis to compute deadline miss models for task chains. The extension is motivated by an industrial case study. The third contribution of this thesis targets the system extensibility to budget under-specified tasks in a weakly-hard real-time system. Adding recovery or reconfiguration tasks such that the system still meets its weakly-hard timing constraints is of interest of an industrial case study (satellite on-board software) that is considered in this thesis.Eine große Zahl von eingebetteten Systemen fällt in die Kategorie der sicherheitskritischen Systeme. Solche Systeme stellen unterschiedliche Sicherheitsanforderungen, je nachdem wie kritisch die dem System zugewiesenen Funktionen sind und wie Menschen mit dem System interagieren. Sicherheitsanforderungen beschreiben insbesondere das geforderte Echtzeitverhalten, dessen Verletzung zu einem Systemausfall führen kann. Anforderungen an das Echtzeitverhalten können unterschiedlich strikte Echtzeitbedingungen umfassen. Während die Erfüllung weicher Echtzeitbedingungen nur wenn möglich gefordert ist, braucht es zur Gewährleistung harter Echtzeitbedingungen die Anwendung von Worst-Case-Analysen zur Überprüfung der zeitlichen Bedingungen in allen Fällen. Die besondere Kategorie der schwach-harten Echtzeitsysteme hat zusätzliche Anforderungen an die Timing-Verifikation, da sie wenige Deadline-Überschreitungen mit bestimmten Mustern tolerieren. Das stellt die Aussagekraft der mit Methoden der Antwortzeitanalyse berechneten Grenzen in Frage und erhöht den Bedarf an Analysen, um die schwach-harten Echtzeitbeschränkungen zu verifizieren und aussagekräftigere Garantien zu liefern. Diese Arbeit befasst sich mit dem Problem der Scheduling-Analyse von schwach-harten Echtzeitsystemen. Es stellt eine effiziente Analyse zur Berechnung von schwach-harten Echtzeitgarantien in Form eines Deadline Miss Modells für verschiedene Systemmodelle dar. Der erste Beitrag ist ein Deadline-Überschreitungsmodell für ein temporär überlastetes Uniprozess-System mit eigenständigen Aufgaben im Rahmen der Fixed Priority Scheduling Policy mittels Typical Worst-Case Analysis. In unserem Anwendungskontext sind sporadische Tasks die Ursache von temporärer Überlast, wie zum Beispiel Interrupt Service Routines. Wir adaptieren die vorgeschlagene Analyse für Earliest Deadline First (EDF) und gewichtete Round-Robin (WRR) Scheduling. Zweitens erweitern wir die Analyse, um ein Deadline-Überschreitungsmodell für Taskketten zu berechnen. Die Erweiterung wird durch eine industrielle Fallstudie motiviert. Der dritte Beitrag dieser Arbeit zielt auf die Erweiterbarkeit des Systems bei unterdefinierte Tasks in einem schwach-harten Echtzeitsystem ab. Ziel ist es, ein Budget für Wiederherstellungs- oder Rekonfigurationstasks herzuleiten, so dass das System immer noch seine schwach-harten Echtzeitbedingungen erfüllt. Dies ist von Interesse für eine industrielle Fallstudie, die in dieser Arbeit berücksichtigt wird

Extending typical worst-case analysis using response-time dependencies to bound deadline misses

International audienceWeakly-hard time constraints have been proposed for applications where occasional deadline misses are permitted. Recently, a new approach called Typical Worst-Case Analysis (TWCA) has been introduced which exploits similar constraints to bound response times of systems with sporadic overload. In this paper, we extend that approach for static priority preemptive and non-preemptive scheduling to determine the maximum number of deadline misses for a given deadline. The approach is based on an optimization problem which trades off higher priority interference versus miss count. We formally derive a lattice structure for the possible combinations that lays the ground for an integer linear programming (ILP) formulation. The ILP solution is evaluated showing effectiveness of the approach and far better results than previous TWCA

Improved Deadline Miss Models for Real-Time Systems Using Typical Worst-Case Analysis

International audienceWe focus on the problem of computing tight deadline miss models for real-time systems, which bound the number of potential deadline misses in a given sequence of activations of a task. In practical applications, such guarantees are often sufficient because many systems are in fact not hard real-time. Our major contribution is a general formulation of that problem in the context of systems where some tasks occasionally experience sporadic overload. Based on this new formulation, we present an algorithm that can take into account fine-grained effects of overload at the input of different tasks when computing deadline miss bounds. Finally, we show in experiments with synthetic as well as industrial data that ouralgorithm produces bounds that are much tighter than in previous work, in sufficiently short time

Event-Driven Multithreading Execution Platform for Real-Time On-Board Software Systems

The high computational demand and the modularity of future space applications make the effort of developing multithreading reusable middlewares worthwhile. In this paper, we present a multihreading execution platform and a Software development framework that consists of abstract classes with virtual methods. The presented work is written in C++ following the event-driven programming paradigm and based on the inverse of control programming principle. The platform is portable over different operating systems, e.g., Linux and RTEMS. This platform is supported with a modeling language to automatically generate the code from the given requirements. Our platform has been used in already flying satellites, e.g., Eu:CROPIS. We present in this paper an example that illustrates how to use the proposed platform in designing and implementing an on-board software system