Task attribute assignment of fixed priority scheduled tasks to reenact off-line schedules

A number of industrial applications advocate the use of time triggered approaches for reasons of predictability, distribution, and particular constraints such as jitter or end-to-end deadlines. The rigid offline scheduling schemes used for time triggered systems however, do not provide for flexibility. Fixed priority scheduling can provide more flexibility, but is limited with respect to predictability, as actual times of executions depend on run-time events. In this paper, we present a method to combine off-line schedule construction with fixed priority scheduling: by determining task attributes for the off-line scheduled tasks, such that the original schedule is reconstructed if scheduled with FPS at run-time. It analyzes all off-line schedule together with original task constraints to create sequences and windows of tasks. Priorities and offsets are set to ensure task orders in sequences and relation between windows. As FPS cannot reconstuct all schedules with periodic tasks, our algorithm can split tasks into several instances to achieve consistent task attributes. Lower priority tasks can be added for runtime use.