The Modeling Optimization And The Algorithm Of IO Jitter And Latency In The Hard Real-time Task Scheduling

Embedded real-time system is more and more being used in the industrial control field and real-time scheduling has always been the core theory issue. But the jitter and latency of hard real-time task caused by scheduling directly influences the stability and reliability of systems, even leads to the collapse of systems. Therefore, how to control the jitter and latency of hard real-time task has become the hot issue in the current real-time scheduling theory research.In view of the task jitter and latency question, this thesis provide a preemptable threshold scheduling model which divides the task. This model can reduce the task jitter and latency caused by task scheduling when it does not affect the system scheduling. Using this model to analyze IO jitter of the task, the results showed that the IO jitter of the task reduced along with decrease of the preemptable threshold. By the way of minimizing threshold of the preemptable threshold scheduling model, it can reduce the jitter and latency of hard real-time task and control the negative influence of the system stability caused by the control scheduling. According as the necessary and sufficient Conditions of RM Scheduling Algorithm, this paper presents an optimal threshold value allocation algorithm by the complexity of O(|Tn/T1|·n2) and according as sufficient Conditions of EDF Scheduling Algorithm presents a better threshold value allocation algorithm with complexity of O(n). To test the performance of the model in different scheduling circumstances, this paper structured a simulation testing environment on the TORSCHE toolbox of Matlab and carried on the simulation to the preemptable threshold scheduling algorithm. From the simulation results, it can be easily seen that the preemptable threshold scheduling model based on the division of tasks can effectively reduce the jitter and latency of tasks caused by scheduler in the typical scheduling algorithm. In order to measure the difference between the model theory and the model after the realization, this paper carried on a hardware simulation to the scheduling algorithm in Atmel megal28 hardware platforms, through modifications to the existing WORIX OS kernel. By comparing the hardware test results with the simulation results, the author found that the model simulation results accord with the actual situation, that is, the model can effectively reduce the jitter and latency of tasks in the practical application.