Ola Redell

Exact best-case response time analysis of fixed priority scheduled tasks

We present a solution for exact calculation of the best-case response times of a periodic task set with fixed priorities. The solution is based on the identification of the best-case phasing of a low priority task compared to the higher priority tasks. This phasing occurs when the low priority task is released such that it finishes simultaneously with the releases of all the higher priority tasks, when these have experienced their maximum release jitter. A recurrence equation is applied to find the best-case response time. The dualism between worst-case and best-case response time calculation is characterized. The most important application of the solution is in the analysis of response jitter.

Analysis of tree-shaped transactions in distributed real time systems

A worst case response time analysis exploiting precedence constraints between fixed priority scheduled tasks in tree-shaped transactions is presented. The algorithm extends existing methods for analysis of linear transactions allowing a wider range of systems, in which tasks may trigger more than one succeeding task on their completion, i.e. the transactions form trees. It also improves existing methods, producing tighter response time bounds for tasks in both linear and tree-shaped transactions. The improvement is due to better exploitation of the precedence relations between tasks, which also makes the analysis faster than earlier. Simulation results show a significant reduction of estimated worst case response times when compared to earlier analysis methods for both linear and tree-shaped transactions. Such improvement leads to less pessimistic schedulability tests for distributed fixed priority scheduled systems.

Calculating exact worst case response times for static priority scheduled tasks with offsets and jitter

A method to perform exact worst case response time analysis for fixed priority tasks with offsets and release jitter is described. Available methods are either pessimistic or inefficient as they incorporate numerous time consuming schedule simulations in order to find the exact response times of tasks. The method presented here is based on the creation of the worst case conditions for the execution of each individual task instance within a hyperperiod. The worst case is built by choosing release jitter of higher priority tasks appropriately. Given these conditions, the corresponding task instance response time is calculated using partly iterative algorithms. Experiments comparing the efficiency of the proposed method to an alternative exact method based on schedule simulation show that the new method outperforms the latter. The analysis is expected to be particularly useful when analysing response times and schedulability of tasks that form transactions in distributed systems.

A tool integration platform for multi-disciplinary development

In multi-disciplinary development, where various domain specific tools are used by developers to specify and analyze a system, efficient system development requires that the models produced by these tools are well integrated into a whole, reducing any risks of inconsistencies and conflicts in the design information specified. In this paper, we present architecture for a model and tool integration platform that borrows its major components from well known and accepted standards from both computer and mechanical engineering. The architecture supports model integration, where models defined in different tools for different aspects of the same system are related such that they may share and exchange data. The integration platform also enables model management functionalities on a fine-grained level, suggesting a combination of the functionalities found in traditional data management systems such as product data management (PDM) and software configuration management (SCM).

The AIDA toolset for design and implementation analysis of distributed real-time control systems

This article introduces a toolset that integrates the design and performance analysis of control systems with embedded real-time system design. The toolset enables specification and analysis of rea ...

A modelling framework to support the design and analysis of distributed real-time control systems

Within the automatic control in distributed applications project a modelling framework has been developed to support design issues related to the implementation of control applications in embedded distributed computer systems. At a relatively high level of abstraction the models describe the structure and timing behaviour of a control application (in terms of functions and operational models) and its implementation (hardware, operating system threads and resources). The resource description allows the timing behaviour of the implementation to be analysed and fed back into the application models. The models form the basis for a decentralization tool-set, where a first prototype is under development. Examples of the models are given and the framework is compared to related modelling approaches.

Experiences from Model Supported Configuration Management and Production of Automotive Embedded Software

Configuration management of products containing software with complex interrelationships is a challenge for the automotive industry. Configurations are usually addressed through hierarchical produc ...

A Mechatronics Test-Bed for Embedded Distributed Control Systems

Abstract A testbed has been developed to be used for research in distributed real-time control systems. The testbed is modular both in mechanics and in control system, allowing a number of robot configurations, control system structures and execution strategies to be implemented and evaluated. The nodes of the control system are currently based on a microprocessor, CAN communication, interfaces to analog and digital I/O, and motor drive units. The modularity of the nodes allows changes of I/O and communication system, as well as the implementation of different resource structures. To give an idea of the experimental capabilities of the testbed, initial experiments in the area of time-varying control systems are described. The research goals include design and experimental evaluation of execution strategies, time-varying control systems and development tools for real-time implementation support.