Enriching Enea OSE for Better Predictability Support

University essay from KTH/Skolan för informations- och kommunikationsteknik (ICT)

Author: Naveed Mustafa; [2011]

Keywords: ;

Abstract:

A real-time application is designed as a set of tasks with specific timing attributes and constraints. These tasks can be categorized as periodic, sporadic or aperiodic, based on the timing attributes that are specified for themwhich in turn de ne their runtime behaviors. To ensure correct execution and behavior of the task set at runtime, the scheduler of the underlying operating system should take into account the type of each task (i.e., periodic, sporadic, aperiodic). This is important so that the scheduler can schedule the task set in a predictable way and be able to allocate CPU time to each task appropriately in order for them to achieve their timing constraints.

ENEA OSE is a real-time operating system with fixed priority preemptive scheduling policy which is used heavily in embedded systems, such as telecommunication systems developed by Ericsson. While OSE allows for specification of priority levels for tasks and schedules them accordingly, it can not distinguish between dierent types of tasks.

This thesis work investigates mechanisms to build a scheduler on top of OSE, which can identify three types of real-time tasks and schedule them in a more predictable way. The scheduler can also monitor behavior of task set at run-time and invoke violation handlers if time constraints of a task are violated.

The scheduler is implemented on OSE5.5 soft kernel. It identifies periodic, aperiodic and sporadic tasks. Sporadic and aperiodic tasks can be interrupt driven or program driven. The scheduler implements EDF and RMS as scheduling policy of periodic tasks. Sporadic and aperiodic tasks can be scheduled using polling server or background scheme.

Schedules generated by the scheduler deviate from expected timing behavior due to scheduling overhead. Approaches to reduce deviation are suggested as future extension of thesis work. Usability of the scheduler can be increased by extending the scheduler to support other scheduling algorithm in addition to RMS and EDF.

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