Fixed-priority scheduling with deferred preemption (FPDS) and fixed-priority scheduling with preemption thresholds (FPTS) have been proposed in the literature as viable alternatives to fixed-priority preemptive scheduling (FPPS), that reduce memory requirements, reduce the cost of arbitrary preemptions, and may improve the feasibility of a task set even when preemption overheads are neglected.This paper aims at advancing the relative strength of limitedpreemptive schedulers by combining FPDS and FPTS. In particular, we present a refinement of FPDS with preemption thresholds for both jobs and sub-jobs, termed FPGS. We provide an exact schedulability analysis for FPGS, and show how to maximize the feasibility of a set of sporadic tasks under FPGS for given priorities, computation times, periods, and deadlines of tasks. We evaluate the effectiveness of FPGS by comparing the feasibility of task sets under FPGS with other fixed-priority scheduling algorithms by means of a simulation. Our experiments show that FPGS allows an increase of the number of task sets that are schedulable under fixed-priority scheduling.
Controller area network (CAN) is a serial, broadcast bus, and is currently the de-facto standard for in-vehicle data transmission. CAN is the most widely used automotive communication network having the advantages of being low-cost and providing flexible and robust communication with bounded delay. CAN networks are mainly used for safety-critical real-time applications that have strict timing requirements in communication. This time-criticality makes the CAN schedulability analysis that has been studied over two decades crucial. Most of the previous studies on CAN schedulability assume an idealized communication model, with an unlimited number of transmit buffers in the communication controller. In this paper, we address the CAN schedulability analysis for the case of a single transmit buffer without buffer preemption when the buffering overhead can be ignored. We revisit the existing worst-case response-time analysis for this case that is based on the early, flawed CAN analysis, and we present a revised schedulability analysis. Moreover, we evaluate and compare the analyses by means of example message sets.
A Voronoi region can be interpreted as the shape achieved by a crystal that grows from a seed and stops growing when it reaches either the domain boundary or another crystal. This analogy is exploited here to devise a method for the generation of anisotropic boundary-conforming Voronoi regions for a set of points. This is achieved by simulating the propagation of crystals as evolving fronts modeled by a level set method. The techniques to detect the collision of fronts (crystals), formation of interfaces between seeds, and treatment of boundaries as additional (inner or outer) restricting seeds are described in detail. The generation of anisotropic Voronoi regions consistent with a user-prescribed Riemannian metric is achieved by re-interpreting the metric tensor in terms of the speed of propagation normal to the boundary of the crystal. This re-interpretation offers a better means of restricting metric fields for mesh generation.
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