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Real-Time Operating Systems
Published in Leanna Rierson, Developing Safety-Critical Software, 2017
Round-robin. The name of the algorithm comes from the round-robin principle, where each person has an equal share of something. I once made it to the 4-H showmanship round-robin competition. Each competitor was given an equal time to show a horse, a steer, a pig, and a lamb. You’ll be pleased to know that I earned the Reserved Grand Champion trophy. The round-robin scheduling algorithm is one of the simplest scheduling algorithms for sharing time on a processor. A minor time slice is defined by the system, and all processes are kept in a circular queue. The scheduler goes around the queue, allocating processor resources to each process for a time slice interval. As new processes arrive, they are added to the tail of the queue. The scheduler functions by selecting the first process from the queue, setting a timer to interrupt after one time slice, and then dispatching the process. If the process is not finished at the end of the time slice, it is preempted and added to the tail of the queue. If the process does finish before the end of the time slice, it releases the processor. A context switch occurs every time a process is granted access to the processor. The context switching adds overhead to the process execution time [9].
A channel-aware downlink scheduling scheme for real-time services in long-term evolution systems
Published in Artde D.K.T. Lam, Stephen D. Prior, Siu-Tsen Shen, Sheng-Joue Young, Liang-Wen Ji, Engineering Innovation and Design, 2019
Han-Sheng Chuang, Shang-Lin Hsieh, Chen-Feng Wu
Round Robin scheduling is a non-aware scheduling scheme that lets users take turns in using the shared resources (time/RBs), without taking the instantaneous channel conditions into account. Therefore, it offers great fairness among the users in radio resource assignment, but degrades the system throughput (Habaebi, et al., 2013). The algorithm selects the users without considering channel condition. If all the users have been served, the scheduler will start again with the same queue. The major advantage of this kind of algorithm is its simplicity. The major disadvantage of the RR algorithm is that this algorithm does not consider users’ CQI feedback, which leads to low and unequal throughput.
Modeling Guidelines of FreeRTOS in Event-B
Published in Ibrahiem M. M. El Emary, Anna Brzozowska, Shaping the Future of ICT, 2017
Eman H. Alkhammash, Michael J. Butler, Corina Cristea
The components of most RTOSs are [20] Scheduler—Special algorithms that are used to schedule objects. Some of the commonly used scheduling algorithms are preemptive priority-based scheduling and round-robin scheduling. In preemptive priority-based scheduling, each task must be assigned a priority. At every clock tick, the scheduler runs the highest priority task that is ready to run. In round-robin scheduling, the tasks with equal priority get an equal share of processing time.Objects—Entities that are used by the developers to create applications for real-time embedded systems. Some object constructs are tasks, which are objects created by a developer to handle a distinct topic; queues which are used for task–task communication; and semaphores and mutexes, which are used for the synchronization between the tasks and the interrupts.Services—Operations performed by the kernels, such as task management, intertask communication and synchronization, interrupt handling, and resource management. The task management includes operations such as task creation, task deletion, task suspension, and changing task priority. Intertask communication and synchronization are mechanisms that enable information to be transmitted from one task to another such as message queues, pipes, semaphores, and mutexes. Interrupt handling are software routines used to handle interrupts; an interrupt is a signal to the microprocessor indicating that an event needs immediate attention. Resource management are kernel functions used to manage system resources such as the CPU, memory, and time.
Integrated scheduling and link adaptation for heterogeneous networks: design and performance analysis
Published in International Journal of Electronics, 2020
Mehrdad Taki, Mohammad Bagher Nezafati
As a simple scheme, Round-Robin scheduling assigns time slices to each link in equal proportions. The basic scheme does not consider the different requirements of the users. To enhance the basic scheme, we consider another channel unaware scheme which allocates divisions of the time to each link with considering user requirements. We define as the division of time that is assigned to the link , irrespective of its channel state. The link adaptation is performed in the user section. This scheme is referred as the requirement-based separate scheduling and link adaptation (RSSLA). The average transmission rate of link with continuous rate adaptation and constant transmission power is computed as