|
Rate-monotonic Scheduling
In computer science, rate-monotonic scheduling (RMS) is a priority assignment algorithm used in real-time operating systems (RTOS) with a static-priority scheduling class. The static priorities are assigned according to the cycle duration of the job, so a shorter cycle duration results in a higher job priority. These operating systems are generally preemptive and have deterministic guarantees with regard to response times. Rate monotonic analysis is used in conjunction with those systems to provide scheduling guarantees for a particular application. Introduction A simple version of rate-monotonic analysis assumes that threads have the following properties: *No resource sharing (processes do not share resources, ''e.g.'' a hardware resource, a queue, or any kind of semaphore blocking or non-blocking ( busy-waits)) *Deterministic deadlines are exactly equal to periods *Static priorities (the task with the highest static priority that is runnable immediately preempts all other ta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Science
Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, applied disciplines (including the design and implementation of Computer architecture, hardware and Software engineering, software). Algorithms and data structures are central to computer science. The theory of computation concerns abstract models of computation and general classes of computational problem, problems that can be solved using them. The fields of cryptography and computer security involve studying the means for secure communication and preventing security vulnerabilities. Computer graphics (computer science), Computer graphics and computational geometry address the generation of images. Programming language theory considers different ways to describe computational processes, and database theory concerns the management of re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MicroC/OS-II
Micro-Controller Operating Systems (MicroC/OS, stylized as μC/OS, or Micrium OS) is a real-time operating system (RTOS) designed by Jean J. Labrosse in 1991. It is a priority-based preemptive real-time kernel for microprocessors, written mostly in the programming language C. It is intended for use in embedded systems. MicroC/OS allows defining several functions in C, each of which can execute as an independent thread or task. Each task runs at a different priority, and runs as if it owns the central processing unit (CPU). Lower priority tasks can be preempted by higher priority tasks at any time. Higher priority tasks use operating system (OS) services (such as a delay or event) to allow lower priority tasks to execute. OS services are provided for managing tasks and memory, communicating between tasks, and timing. History The MicroC/OS kernel was published originally in a three-part article in Embedded Systems Programming magazine and the book ''μC/OS The Real-Time Kernel'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kingman's Formula
In queueing theory, a discipline within the mathematical theory of probability, Kingman's formula, also known as the VUT equation, is an approximation for the mean waiting time in a G/G/1 queue. The formula is the product of three terms which depend on utilization (U), variability (V) and service time (T). It was first published by John Kingman in his 1961 paper ''The single server queue in heavy traffic''. It is known to be generally very accurate, especially for a system operating close to saturation. Statement of formula Kingman's approximation states: :\mathbb E(W_q) \approx \left( \frac \right) \left( \frac\right) \tau where \mathbb E(W_q) is the mean waiting time, ''τ'' is the mean service time (i.e. ''μ'' = 1/''τ'' is the service rate), ''λ'' is the mean arrival rate, ''ρ'' = ''λ''/''μ'' is the utilization, ''ca'' is the coefficient of variation In probability theory and statistics, the coefficient of variation (CV), also known as normalized r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Queueing Theory
Queueing theory is the mathematical study of waiting lines, or queues. A queueing model is constructed so that queue lengths and waiting time can be predicted. Queueing theory is generally considered a branch of operations research because the results are often used when making business decisions about the resources needed to provide a service. Queueing theory has its origins in research by Agner Krarup Erlang, who created models to describe the system of incoming calls at the Copenhagen Telephone Exchange Company. These ideas were seminal to the field of teletraffic engineering and have since seen applications in telecommunications, traffic engineering, computing, project management, and particularly industrial engineering, where they are applied in the design of factories, shops, offices, and hospitals. Spelling The spelling "queueing" over "queuing" is typically encountered in the academic research field. In fact, one of the flagship journals of the field is '' Queue ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scheduling (computing)
In computing, scheduling is the action of assigning resources to perform tasks. The resources may be processors, network links or expansion cards. The tasks may be threads, processes or data flows. The scheduling activity is carried out by a mechanism called a scheduler. Schedulers are often designed so as to keep all computer resources busy (as in load balancing), allow multiple users to share system resources effectively, or to achieve a target quality-of-service. Scheduling is fundamental to computation itself, and an intrinsic part of the execution model of a computer system; the concept of scheduling makes it possible to have computer multitasking with a single central processing unit (CPU). Goals A scheduler may aim at one or more goals, for example: * maximizing '' throughput'' (the total amount of work completed per time unit); * minimizing '' wait time'' (time from work becoming ready until the first point it begins execution); * minimizing '' latency'' o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RTEMS
Real-Time Executive for Multiprocessor Systems (RTEMS), formerly Real-Time Executive for Missile Systems, and then Real-Time Executive for Military Systems, is a real-time operating system (RTOS) designed for embedded systems. It is free and open-source software. Development began in the late 1980s with early versions available via File Transfer Protocol (ftp) as early as 1993. OAR Corporation managed the RTEMS project in cooperation with a steering committee until the early 2000's when project management evolved into a subset of the core developers managing the project. In 2014, hosting was moved from OAR Corporation to the Oregon State UniversitOpen Source Lab hosting Design RTEMS is designed for real-time embedded systems and to support various open application programming interface (API) standards including Portable Operating System Interface (POSIX) and μITRON (dropped in RTEMS 4.10). The API now known as the Classic RTEMS API was originally based on the Real-Time Executiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earliest Deadline First Scheduling
Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) the queue will be searched for the process closest to its deadline. This process is the next to be scheduled for execution. EDF is an ''optimal'' scheduling algorithm on preemptive uniprocessors, in the following sense: if a collection of independent ''jobs,'' each characterized by an arrival time, an execution requirement and a deadline, can be scheduled (by any algorithm) in a way that ensures all the jobs complete by their deadline, the EDF will schedule this collection of jobs so they all complete by their deadline. With scheduling periodic processes that have deadlines equal to their periods, EDF has a utilization bound of 100%. Thus, the schedulability test for EDF is: :U = \sum_^ \frac \leq 1, where the \left\ are the worst-case com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Priority Scheduling
Dynamic priority scheduling is a type of scheduling algorithm in which the priorities are calculated during the execution of the system. The goal of dynamic priority scheduling is to adapt to dynamically changing progress and to form an optimal configuration in a self-sustained manner. It can be very hard to produce well-defined policies to achieve the goal depending on the difficulty of a given problem. Earliest deadline first scheduling and Least slack time scheduling are examples of Dynamic priority scheduling algorithms. Optimal schedulable utilization The idea of real-time scheduling is to confine processor utilization under schedulable utilization of a certain scheduling algorithm, which is scaled from 0 to 1. Higher schedulable utilization means higher utilization of resource and the better the algorithm. In preemptible scheduling, dynamic priority scheduling such as earliest deadline first (EDF) provides the optimal schedulable utilization of 1 in contrast to less than 0 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deos
DDC-I, Inc. is a privately held company providing software development of real-time operating systems, software development tools, and software services for Life-critical system, safety-critical embedded applications, headquartered in Phoenix, Arizona. It was first created in 1985 as the Danish firm DDC International A/S (also known as DDC-I A/S), a commercial outgrowth of Dansk Datamatik Center, a Danish software research and development organization of the 1980s. The American subsidiary was created in 1986. For many years, the firm specialized in language compilers for the programming language Ada (programming language), Ada. In 2003, the Danish office was closed and all operations moved to the Phoenix location. Origins The origins of DDC International A/S lay in Dansk Datamatik Center, a Danish software research and development organization that was formed in 1979 to demonstrate the value of using modern techniques, especially those involving formal methods, in software desi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deadline-monotonic Scheduling
Deadline-monotonic priority assignment is a priority assignment policy used with fixed-priority pre-emptive scheduling. With deadline-monotonic priority assignment, tasks are assigned priorities according to their deadlines. The task with the shortest deadline is assigned the highest priority. This priority assignment policy is optimal for a set of periodic or sporadic tasks which comply with the following system model: # All tasks have deadlines less than or equal to their minimum inter-arrival times (or periods). # All tasks have worst-case execution times (WCET) that are less than or equal to their deadlines. # All tasks are independent, and so do not block each other's execution (e.g., by accessing mutually exclusive shared resources). # No task voluntarily suspends itself. # There is some point in time, referred to as a critical instant, where all of the tasks become ready to execute simultaneously. # Scheduling overheads (switching from one task to another) are zero. # Al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interrupt Service Routine
In computer systems programming, an interrupt handler, also known as an interrupt service routine (ISR), is a special block of code associated with a specific interrupt condition. Interrupt handlers are initiated by hardware interrupts, software interrupt instructions, or software exceptions, and are used for implementing device drivers or transitions between protected modes of operation, such as system calls. The traditional form of interrupt handler is the hardware interrupt handler. Hardware interrupts arise from electrical conditions or low-level protocols implemented in digital logic, are usually dispatched via a hard-coded table of interrupt vectors, asynchronously to the normal execution stream (as interrupt masking levels permit), often using a separate stack, and automatically entering into a different execution context (privilege level) for the duration of the interrupt handler's execution. In general, hardware interrupts and their handlers are used to handle high-prio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mars Pathfinder
''Mars Pathfinder'' was an American robotic spacecraft that landed a base station with a rover (space exploration), roving probe on Mars in 1997. It consisted of a Lander (spacecraft), lander, renamed the Carl Sagan Memorial Station, and a lightweight, wheeled robotic Mars rover named ''Sojourner (rover), Sojourner'', the first rover to operate outside the Earth–Moon system. The mission terminated in 1998. Launched on December 4, 1996, by NASA aboard a Delta II booster a month after the ''Mars Global Surveyor'', it landed on July 4, 1997, on Mars's Ares Vallis, in a region called Chryse Planitia in the Oxia Palus quadrangle. The lander (spacecraft), lander then opened, exposing the rover which conducted many experiments on the Martian surface. The mission carried a series of scientific instruments to analyze the Martian Celestial body atmosphere, atmosphere, climate, and geology and the composition of its rock (geology), rocks and soil. It was the second project from NASA's D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
