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Certication-Cognizant Mixed-Criticality Scheduling in Time-Triggered Systems


Category: PhD thesis
Author(s)Jens Theis
Source.
Date Mar 2015

Abstract

In embedded systems, there is a trend of integrating several dierent functionalities on a common platform. This has been enabled by increasing processing power and the arise of integrated system-on-chips. The composition of safety-critical and nonsafety-critical applications results in mixed-criticality systems. Certication Authorities (CAs) demand the certication of safety-critical applications with strong condence in the execution time bounds. As a consequence, CAs use conservative assumptions in the worst-case execution time (WCET) analysis which result in more pessimistic WCETs than the ones used by designers. The existence of certied safety-critical and non-safetycritical applications can be represented by dual-criticality systems, i.e., systems with two criticality levels. In this thesis, we focus on the scheduling of mixed-criticality systems which are subject to certication. Scheduling policies cognizant of the mixed-criticality nature of the systems and the certication requirements are needed for ecient and effective scheduling. Furthermore, we aim at reducing the certication costs to allow faster modication and upgrading, and less error-prone certication. Besides certication aspects, requirements of different operational modes result in challenging problems for the scheduling process. Despite the mentioned problems, schedulers require a low runtime overhead for an ecient execution at runtime. The presented solutions are centered around time-triggered systems which feature a low runtime overhead. We present a transformation to include event-triggered activities, represented by sporadic tasks, already into the oine scheduling process. Further, this transformation can also be applied on periodic tasks to shorten the length of schedule tables which reduces certication costs. These results can be used in our method to construct schedule tables which creates two schedule tables to fulll the requirements of dual-criticality systems using mode changes at runtime. Finally, we present a scheduler based on the slot-shifting algorithm for mixed-criticality systems. In a rst version, the method schedules dual-criticality jobs without the need for mode changes. An already certied schedule table can be used and at runtime, the scheduler reacts to the actual behavior of the jobs and thus, makes effective use of the available resources. Next, we extend this method to schedule mixed-criticality job sets with different operational modes. As a result, we can schedule jobs with varying parameters in different modes.

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