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Fixed-priority preemption threshold scheduling (FPTS) is a limited preemptive scheduling scheme that generalizes both fixed-priority preemptive scheduling (FPPS) and fixed-priority non-preemptive scheduling (FPNS). By increasing the priority of tasks as they start executing it reduces the set of tasks that can preempt any given task. A subset of FPTS task configurations can be implemented natively on any AUTOSAR/OSEK compatible platform by utilizing the platform's native implementation of non-preemptive task groups via so called internal resources. The limiting factor for this implementation is the number of internal resources that can be associated with any individual task. OSEK and consequently AUTOSAR limit this number to one internal resource per task. In this work, we investigate the impact of this limitation on the schedulability of task sets when cache related preemption delays are taken into account. We also consider the impact of this restriction on the stack size when the tasks are executed on a shared-stack system.