TaskPair-scheduling with optimistic case execution times-an example for an adaptive real-time system
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The paper first describes a model for an adaptive real time system, that consists of four components: the real time application, a monitor that observes the behaviour of the application, a dynamic resource manager that controls the execution of the application based on the data collected by the monitor, and finally an adaptation manager that uses the input from the monitor to implement long term adaptation strategies. In the second part of the paper, a concrete adaptation mechanism is introduced. This mechanism extends TaskPair scheduling (H. Streich, 1995), an online, fault tolerant scheduling method developed at GMD within the context of the DIRECT project (M. Gergeleit et al., 1994). TaskPair scheduling is extended with the notion of optimistic case execution time (OCET), that describes the time that a task needs in most of the cases for successful completion. As this time may depend on the system state and the environment, the system observes the actual resource consumption during execution and adapts future resource requests accordingly.Keywords:
Context switch
Resource consumption
Real-time operating system
Worst-case execution time
Purpose The purpose of this paper is to focus on the method to improve real‐time property of real‐time operating system (RTOS), one of the most essential problems in RTOS studies. Design/methodology/approach Improved task models are proposed based on the basic task and extended task models of OSEK operating system (OSEK OS). According to different task states, optimized scheduling algorithm was put forward. Some examples in a practical environment are described that illustrate the value of the method. Findings This method has been successfully implemented and evaluated in an OSEK compatible operating system, SmartOSEK OS. The time cost of context switching is decreased and the efficiency is enhanced. Research limitations/implications The improvement gained depends on the ratio of each strategy applied. In case the strategy D is applied too many times, the performance will be lead to a depressing result. For real‐time system, a long‐lived process that maybe increase the ratio of strategy D is not the optimal selection. Originality/value Dividing the ready state of task into intermediate state and initial state, can optimize the process of task context switching for OSEK OS. The method has proven to be useful in improving the real‐time property of RTOS.
Context switch
Real-time operating system
Response time
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The main difficulties in designing real-time systems are related to time constraints: if an action is performed too late, it is considered as a fault (with different levels of criticism). Designers need to use a solution that fully supports timing constraints and enables them to simulate early on the design process a real-time system. One of the main difficulties in designing HW/SW systems resides in studying the effect of serializing tasks on processors running a real-time operating system (RTOS). In this paper, we present a generic model of RTOS based on systemC. It allows assessing real-time performances and the influence of scheduling according to RTOS properties such as scheduling policy, context-switch time and scheduling latency.
Real-time operating system
Context switch
Serialization
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In a multi-tasking system, numerous tasks require CPU time, and since there is only one CPU, some form of organization and coordination is needed so each task has the CPU time it needs. In practice, each task takes a very brief amount of time, so it seems as if all the tasks are executing in parallel and simultaneously. In the case of excessive complexity applications, which usually run in hard real time constraints, the use of a real time operating system (RTOS) is strongly required. In this paper, a tiny and reliable RTOS was implemented for PIC18F family of microcontroller. This operating system, which is called SmallRTOS, is based on Round-Robin scheduler. The used system tick is based on a variable time-sliced scheduling that has a direct effect on CPU load, context switching and process waiting time.
Human multitasking
Context switch
Real-time operating system
Computer multitasking
CPU shielding
Preemption
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The software of artificial organ is more and more complex, but it lacks real-time operating system to manage and schedule its resources. In this paper, we propose a lightweight real-time operating system (RTOS) Cyborgan OS based on the SmartOSEK OS. Cyborgan OS optimizes and improves it from the code size, context switch, low power consumption, and partial dynamic update, making it suitable for the artificial organ control system. Finally, we use the heart blood pump model to analyze the task allocation and execution sequence as well as the code size of the whole program. In this application, the maximum space occupied by the code is only 15 kB, which is suitable for most microcontrollers.
Context switch
Real-time operating system
Code (set theory)
Embedded operating system
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This paper presents a novel idea of silicon RTOS (sRTOS), a real time operating system in silicon. By implementing RTOS functionality in hardware optimizes context switching, operating system overhead and interrupt latency. The sRTOS accepts priority-based interrupts from external sources and makes corresponding tasks available in ready queue waiting for their turn to take charge of CPU. A kernel implemented in hardware schedules these tasks on priority basis. Corresponding to each task register-file banks are employed for fast context switching. Resources are allocated to the tasks on priority basis. The sRTOS is integrated with AVZ2I DSP (A VAZ Inc. single MAC DSP www.avaznet.com) for applications requiring zero cycle RTOS overheads
Context switch
Real-time operating system
Interrupt handler
Embedded operating system
Kernel (algebra)
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Real-time operating system
Static timing analysis
Worst-case execution time
Kernel (algebra)
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Recently complexity of embedded software cause to be used real-time operating system (RTOS) to implement various functions in the embedded system. And also, according to requirement of complex functions in embedded systems, the number as well as complexity of tasks get increased continuously. In case that many tasks collaborated in a microprocessor, context switching time between tasks is a overhead waisting a CPU resource. Therefore the time of task context switching is an important factor that affects performance of RTOS. In this paper, we concentrate on the improvement of task context switch for reducing overhead and achieving fast response time in RTOS. To achieve these goal, we suggest multiple register files and task context switching algorithm. By reducing the context switch overhead, we try to ease scheduling and assure fast response times in multitasking environment. As a result, the context switch overhead decreased by 8~16% depend on the number of register files, and some task set which are not schedulable with single register file are schedulable due to that decrease with multiple register files.
Context switch
Human multitasking
Real-time operating system
Preemption
Task Switching
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Increasing complexity of safety-critical systems that support real-time multitasking applications requests the concurrency management offered by real-time operating systems (RTOS). Real-time systems can suffer severe consequences if the functional as well as the time specifications are not met. In addition, real-time systems are subject to transient errors originating from several sources, including the impact of high energy particles on sensitive areas of integrated circuits. Therefore, the evaluation of the sensitivity of RTOS to transient faults is a major issue. This paper explores sensitivity of RTOS kernels in safety-critical systems. We characterize and analyze the consequences of transient faults on key components of the kernel of MicroC, a popular RTOS. We specifically focus on its task scheduling and context switching modules. Classes of fault syndromes specific to safety-critical real-time systems are identified. Results reported in this paper demonstrate that 34% of faults that affect the scheduling and context switching functions led to scheduling dysfunctions. This represents an important fraction of faults that cannot be ignored during the design phase of safety-critical applications running under an RTOS
Real-time operating system
Human multitasking
Context switch
Transient (computer programming)
Life-critical system
Preemption
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This context deliberates the literature evolution of RTOS (Real Time Operating Systems) and its contributions to the embedded world. RTOS is is an operating system (OS) intended to serve real-time application process data as it comes in, typically without buffering delays. Processing time requirements (including any OS delay) are measured in tenths of seconds or shorter. An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS . It is often associated with few misconceptions & we have tried to throw some light on it. We have specified few commercial RTOS of uncommon categories of real-time applications and have discussed its real-time features. A comparison of the commercial RTOSs’ is presented. We conclude by discussing the results of the survey and comparing the RTOS based on performance parameters. This context deliberates the literature evolution of RTOS (Real Time Operating Systems) and its contributions to the embedded world. RTOS is is an operating system (OS) intended to serve real-time application process data as it comes in, typically without buffering delays. Processing time requirements (including any OS delay) are measured in tenths of seconds or shorter. An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS . It is often associated with few misconceptions & we have tried to throw some light on it. We have specified few commercial RTOS of uncommon categories of real-time applications and have discussed its real-time features. A comparison of the commercial RTOSs’ is presented. We conclude by discussing the results of the survey and comparing the RTOS based on performance parameters.
Real-time operating system
Context switch
Real-time data
Response time
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Improving real-time is one of the most essential problems in studies of real-time operating system (RTOS). The time of task context switching is an important factor that affects the real-time of RTOS. This paper concentrates on the improvement of task context switching of one kind of RTOS-OSEK operating system. According to different task states, we apply different context switching strategies to reduce the average time of context switching. This method has been successfully implemented and evaluated in our OSEK compatible operating system-SmartOSEK OS.
Context switch
Real-time operating system
Task Switching
Switching time
Embedded operating system
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