With development of microelectronics technology and semiconductor processing techniques, MPU, often used in embedded operating system, is getting more powerful function and computation resource, thus getting wider use than before. Since traditional programming technology such as C and assembly language can no longer meet the requirement of embedded systems, then, in order to take full use of resources of MPU and shorten development period, embedded operating systems emerges as the times require. For all kinds of operating systems, their ultimate aims lie in providing pretty system resources management, which greatly depends on task schedule algorithms running in them, and allocating rational system resources and executing time for each task to meet demands of application systems. So in this paper, considering complexity and diversity of application of embedded systems, an open and mixed task schedule algorithm for hare real-time tasks and soft real-time tasks is proposed. Main research aspects of this paper are shown as following: 1) First give full theoretic analysis for the two-level hierarchical schedule model and structure of real-time schedule model, schedulability and stability conditions in feedback control systems. 2) Then on the basis of two-level hierarchical schedule model and real time schedule model based on feedback control, an open two-level hierarchical schedule basic model and its realizing algorithm are proposed which can farthest meet deadline requirement of soft real time tasks while fulfilling deadline requirement of hard real time tasks at the same time. Considering resources share and priority overturn in embedded systems, a rate based dynamic two-level hierarchical schedule model and its realizing algorithm is proposed, and then analysis of schedulability and deadline characteristic for periodic real time tasks and non periodic real time tasks is given under the model above. 3) Based on PID feedback control schedule algorithm, a fuzzy logic theory based feedback schedule controller is proposed. 4) Put the proposed two-level hierarchical schedule algorithm into task schedule of traffic signal controller and then show the comparative simulation results on soft real-time task schedule aspect of the two algorithms which are schedule algorithm based on PID feedback control and the schedule algorithm based on fuzzy logic feedback control. And the precondition is both of them meet deadline requirements of hard real-time tasks.
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