Research On Hybrid Scheduling Algorithm In Embedded Real-time System

The applications and development of embedded system, which is widely used in many aspects of daily life, are the hot points in modern computer industry. The main indicators of embedded real-time system are real-time, high efficiency, reliability, and easiness to cut and transplant. The key to real-time is the scheduling algorithm. The way of scheduling that permit all the tasks to finish their jobs in deadlines is one key technology of real-time system. Streamlined and high-efficiency scheduling algorithm means a lot to improve the overall performance of real-time system.In this paper, the real-time kernel ofμC_OS-II are studied in details, first, without modifying the kernel, a new dynamic scheduler is added as a task, the scheduler uses the earliest deadline first scheduling algorithm, dynamic computes and changes the priority of other user tasks. Then, other user tasks are scheduled by the original priority scheduling strategy,thus hybrid scheduling strategy is achieved.Then a hybrid scheduling algorithm for hybrid real-time tasks is proposed in order to overcome the short comings of the kernel, such as low usage ratio of CPU with static strategy, unsupported to the same priority task, no division between hard and soft real-time tasks which leads to miss scheduling to the hard real-time tasks. The algorithm is combined with earliest deadline first scheduling algorithm by modify the kernel. Tasks are divide into important set and nonimportant set. The original priority of tasks is retained. Meanwhile, deadline camparetion of tasks is added to system scheduling module. Thus, hybrid scheduling algorithm for hybrid real-time tasks is achieved.And the original system scheduling policy is retained, the improved systems have both Static/Hybrid scheduling strategy.In a overloading system tasks maybe discard byμC_OS-II kernel, So the real-time scheduling performance of the improved kernel is analyzed in the overloading system. Experiments show that the scheduling algorithm can guarantee hard real-time tasks finsh before their deadlines, meanwhile, it ensure a high task completing ration of soft real-time tasks.Theoretical analysis and experiments show that, the system operating normally by using the hybrid scheduling algorithm, stability and reliability is retained, the real-time scheduling performance ofμC_OS-II is improved, so that it can be used better in more complex situations.