In addition to functional correctness, real-time systems offer temporal correctness which is important for safetycritical domains like avionics. Inherently, these systems deal with reoccurring functionality that can be modeled as periodic tasks. These task-sets are managed by specialized real-time operating systems (RTOS) because they feature predictability and advanced scheduling mechanisms. Within research, RTOSs are commonly used to evaluate analytical results.
When periodic task-sets are analyzed in the literature, their fixed release pattern can be exploited analytically. Furthermore, if all tasks have constrained deadlines and release their first job synchronously, the schedulability can be determined by only analyzing the first job of each task. The well-established RTOS Real-Time Executive for Multiprocessor Systems (RTEMS) provides the specification of periodic tasks without task phases. Usually, without specification of phases, periodic tasks are considered synchronous. However, in this work, we demonstrate that RTEMS invokes task phases dependent on the task execution behavior. Hence, in RTEMS tasks are not released synchronously. Furthermore, since periodic tasks do not even have a fixed release pattern, many analytical results for periodic tasks from the literature are not applicable. Our objective in this work is to shift RTEMS’ release strategy towards a fixed synchronous release of periodic task-sets with implicit deadlines. We propose two treatments that are implemented on kernel- and user-level respectively.