Real-Time Systems CSE 520 WUSTL 2016 Intro

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  1. Hard real-time system:
    requires that every task or task instance completes its execution   by its specified deadline; failure to do so even for a single task or task instance may lead to catastrophic consequences.
  2. Soft real-time system:
    allows some tasks or task instances to miss their deadlines, but a task or task instance that misses a deadline may be less useful or valuable to the system.
  3. Schedulability test:
    used to validate that a given application can satisfy its specified deadlines when scheduled according to a specific scheduling algorithm.
  4. Two types of schedulers:
    • compile-time (static)  
    • run-time (on-line or dynamic)
  5. Optimal scheduler:
    a scheduler one which may fail to meet a deadline of a task only if no other scheduler can.
  6. A task Ti is characterized by:
    following parameters:

    • S: start, release, ready, or arrival time
    • c: (maximum) computation time
    • d: relative deadline (deadline relative to the task's start time)
    • D: absolute deadline (wall clock time deadline).
  7. single-instance task:
    a type of task that executes only once.
  8. periodic task:
    type of task that

    • has many instances or iterations
    • there is a fixed period between two consecutive releases of the same task.
  9. sporadic task:
    sporadic task has zero or more instances, and there is a minimum separation (delta time) between two consecutive releases of the same task.
  10. An example of a sporadic task:
    Example: may perform emergency maneuvers of an airplane when the emergency button is pressed, but there is a minimum separation of 20 seconds between two emergency requests.
  11. aperiodic task:
    a type of task that is a sporadic task with either a soft deadline or no deadline.
  12. if the task has more than one instance (sometimes called a job), we also have the following parameter:
    p: period (for periodic tasks); minimum separation (for sporadic tasks).
  13. if the task has more than one instance (sometimes called a job), we also have the following parameter:
    p: period (for periodic tasks); minimum separation (for sporadic tasks).
  14. a task is preemptable when:
    a task is described as this when it is assumed that a task can be interrupted only at discrete time instants unless we indicate otherwise.
  15. Additional constraints that may complicate scheduling of tasks with deadlines:
    • 1.frequency of tasks requesting service periodically,
    • 2.precedence relations among tasks and subtasks,
    • 3.resources shared by tasks,
    • 4.whether task preemption is allowed or not.
  16. Dependencies of computation (or execution) times of a task:
    its source code, object code, execution architecture, memory management policies, and actual number of page faults and I/O.
  17. For determining computation time, for real-time scheduling purposes, we use:
    the worst-case execution (or computation) time (WCET) as c.
  18. MQTT (define):
    a machine-to-machine (M2M)/”Internet of Things” connectivity protocol. It was designed as an extremely lightweight publish/subscribe messaging transport.
  19. The big ticket item or top advantage of MQTT.
    It is useful for connections with remote locations where a small code footprint is required and/or network bandwidth is at a premium.

Card Set Information

Author:
geschw66
ID:
322603
Filename:
Real-Time Systems CSE 520 WUSTL 2016 Intro
Updated:
2016-10-30 17:04:44
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Real Time Systems Programming WUSTL
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Description:
First week. Important terms/concepts.
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