Jacob Illum Rasmussen

Optimal scheduling using priced timed automata

This contribution reports on the considerable effort made recently towards extending and applying well-established timed automata technology to optimal scheduling and planning problems. The effort of the authors in this direction has to a large extent been carried out as part of the European projects VHS [20] and AMETIST [16] and are available in the recently released UPPAAL CORA [12], a variant of the real-time verification tool UPPAAL [18, 5] specialized for cost-optimal reachability for the extended model of so-called priced timed automata.

Priced timed automata: algorithms and applications

This contribution reports on the considerable effort made recently towards extending and applying well-established timed automata technology to optimal scheduling and planning problems. The effort of the authors in this direction has to a large extent been carried out as part of the European projects Vhs [22] and Ametist [17] and are available in the recently released Uppaal Cora [12], a variant of the real-time verification tool Uppaal [20,5] specialized for cost-optimal reachability for the extended model of priced timed automata.

Resource-Optimal Scheduling Using Priced Timed Automata

In this paper, we show how the simple structure of the linear programs encountered during symbolic minimum-cost reachability analysis of priced timed automata can be exploited in order to substantially improve the performance of the current algorithm. The idea is rooted in duality of linear programs and we show that each encountered linear program can be reduced to the dual problem of an instance of the min-cost flow problem. Thus, we only need to solve instances of the much simpler min-cost flow problem during minimum-cost reachability analysis. Experimental results using Uppaal show a 70-80 percent performance gain. As a main application area, we show how to solve energy-optimal task graph scheduling problems using the framework of priced timed automata.

Guided controller synthesis for climate controller using UPPAAL TIGA

We present a complete tool chain for automatic controller synthesis using Uppaal Tiga and Simulink. The tool chain is explored using an industrial case study for climate control in a pig stable. The problem is modeled as a game, and we use Uppaal Tiga to automatically synthesize safe strategies that are transformed for input to Simulink, which is used to run simulations on the controller and generate code that can be executed in an actual pig stable provided by industrial partner Skov A/S. The model allows for guiding the synthesis process and generate different strategies that are compared through simulations.

Optimal conditional reachability for multi-priced timed automata

In this paper, we prove decidability of the optimal conditional reachability problem for multi-priced timed automata, an extension of timed automata with multiple cost variables evolving according to given rates for each location. More precisely, we consider the problem of determining the minimal cost of reaching a given target state, with respect to some primary cost variable, while respecting upper bound constraints on the remaining (secondary) cost variables. Decidability is proven by constructing a zone-based algorithm that always terminates while synthesizing the optimal cost with a single secondary cost variable. The approach is then lifted to any number of secondary cost variables.

Optimal reachability for multi-priced timed automata

In this paper, we prove the decidability of the minimal and maximal reachability problems for multi-priced timed automata, an extension of timed automata with multiple cost variables evolving according to given rates for each location. More precisely, we consider the problems of synthesizing the minimal and maximal costs of reaching a given target location. These problems generalize conditional optimal reachability, i.e., the problem of minimizing one primary cost under individual upper bound constraints on the remaining, secondary, costs, and the problem of maximizing the primary cost under individual lower bound constraints on the secondary costs. Furthermore, under the liveness constraint that all traces eventually reach the goal location, we can synthesize all costs combinations that can reach the goal. The decidability of the minimal reachability problem is proven by constructing a zone-based algorithm that always terminates while synthesizing the optimal cost tuples. For the corresponding maximization problem, we construct two zone-based algorithms, one with and one without the above liveness constraint. All algorithms are presented in the setting of two cost variables and then lifted to an arbitrary number of cost variables.

Schedulability analysis using Uppaal: Herschel-Planck case study

We propose a modeling framework for performing schedulability analysis by using UPPAAL real-time model-checker [2]. The framework is inspired by a case study where schedulability analysis of a satellite system is performed. The framework assumes a single CPU hardware where a fixed priority preemptive scheduler is used in a combination with two resource sharing protocols and in addition voluntary task suspension is considered. The contributions include the modeling framework, its application on an industrial case study and a comparison of results with classical response time analysis.

Almost optimal strategies in one clock priced timed games

We consider timed games extended with cost information, and prove computability of the optimal cost and of e-optimal memoryless strategies in timed games with one clock. In contrast, this problem has recently been proved undecidable for timed games with three clocks.

On using priced timed automata to achieve optimal scheduling

In this paper, we describe an approach for solving the general class of energy-optimal task graph scheduling problems using priced timed automata. We provide an efficient zone-based algorithm for minimum-cost reachability. Furthermore, we show how the simple structure of the linear programs encountered during symbolic minimum-cost reachability analysis of priced timed automata can be exploited in order to substantially improve the performance of the current algorithm. The idea is rooted in duality of linear programs and we show that each encountered linear program can be reduced to the dual problem of an instance of the min-cost flow problem. Experimental results using Uppaal show a 70–80 percent performance gain. We provide priced timed automata models for the scheduling problems and provide experimental results illustrating the potential competitiveness of our approach compared to existing approaches such as mixed integer linear programming.

Beyond liveness: efficient parameter synthesis for time bounded liveness

In this paper, we deal with the problem of parameter synthesis for a subset of parameterised TCTL over timed automata. The problem was proved decidable by V. Bruyere et al. in [10] for general parameterised TCTL using a translation to Presburger arithmetic and also considered by F. Wang in [13] using a parametric region construction. In contrast, we provide two efficient zone based algorithms for a useful subset of parameterised TCTL. The subset has obvious applications to worst case execution time (WCET) analysis. In [11] WCET is performed via model checking, but their approach uses a binary search strategy over several invocations of the model checker. In contrast, both our algorithms synthesise the bound directly. We provide experimental results based on a prototype implementation in Uppaal for two case studies: The first concerns response time analysis of a well known train gate scenario. The second is an execution time analysis of task graph problems where tasks have uncertain execution times.