The specifications of the weakly hard real-time systems: a review

Abstract

A real-time system is one in which the temporal aspects of its behaviour are part of their specification. The problem with traditional real-time specification is no guarantees on when and how many deadlines may be missed can be given to the tasks because their specification is focused on met all the deadlines and cannot missed it, otherwise the tasks is totally failed. Thus, the weakly hard specification solve this problem with define a gradation on how the deadlines can be missed while still guaranteeing the tasks meets their deadlines. In this paper, a review has been made on the three specifications of real-time systems which is losses or missed of the deadlines can be permitted occasionally. Three criteria used in the evaluation are the process model, temporal specifications and predictability. These three criteria were chosen because the tasks in real-time systems are usually periodic in nature, have timing constraints like deadlines and the behaviour of the systems must be predictable. The three specifications we reviewed in this paper are the skip constraints known as skip factor s, (m,k)-firm deadlines and the weakly hard constraints. The objective of review is to find which specification is better in order to predict the behaviour of a task based on those three criteria. Based on our review, it is concluded that the weakly hard constraints outperforms the two conventional specifications of weakly hard real-time systems using that three criteria based on our evaluation by using a mobile robot case study due to its capability to specify in a clear of the distribution of deadlines met and missed.