• Journal of KIISE:Computing Practices and Letters
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• v.15 no.2
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• pp.89-97
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• 2009

Embedded systems widely used in ubiquitous environments usually employ an event-driven programming model instead of thread-based programming model in order to create a more robust system that uses less memory. However, as the software for embedded systems becomes more complex, it becomes hard to program as a single event handler using the event-driven programming model. This paper discusses the implementation of non-preemptive real-time scheduling theory for the design of embedded systems. To this end, we present an efficient schedulability test method for a given non-preemptive task set using a sufficient condition. This paper also shows that the notion of sub-tasks in embedded systems can overcome the problem of low utilization that is a main drawback of non-preemptive scheduling.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.1
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• pp.22-32
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• 2003

Many of multimedia applications in distributed environments generate the packets which have the real-time characteristics for continuous audio/video data and transmit them according to the teal-time task scheduling theories. In this paper, we model the traffic for continuous media in the distributed multimedia applications based on the high-bandwidth networks and introduce the PDMA algorithm which is the hard real-time task scheduling theory for guaranteeing QoS requested by the clients. Furthermore, we propose the admission control to control the new request not to interfere the current services for maintaining the high quality of services of the applications. Since the proposed admission control is sufficient for the PDMA algorithm, the PDMA algorithm is always able to find the feasible schedule for the set of messages which satisfies it. Therefore, if the set of messages including the new request to generate the new traffic. Otherwise, it rejects the new request. In final, we present the simulation results for showing that the scheduling with the proposed admission control is of practical use.

• The KIPS Transactions:PartA
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• v.18A no.6
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• pp.255-264
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• 2011

A sensor network is a special network that makes physical data sensed by sensor nodes and manages the data. The sensor network is a technology that can apply to many parts of field. It is very important to transmit the data to a user at real-time. The core of the sensor network is a sensor node and small operating system that works in the node. TinyOS developed by UC Berkeley is a sensor network operating system that used many parts of field. It is event-driven and component-based operating system. Basically, it uses non-preemptive scheduler. If an urgent task needs to be executed right away while another task is running, the urgent one must wait until another one is finished. Because of that property, it is hard to guarantee real-time requirement in TinyOS. According to recent study, Priority Level Scheduler, which can let one task preempt another task, was proposed in order to have fast response in TinyOS. It has restrictively 5 priorities, so a higher priority task can preempt a lower priority task. Therefore, this paper suggests Preemptive EDF(Earliest Deadline First) Scheduler that guarantees a real-time requirement and reduces average respond time of user tasks in TinyOS.