lec04_model - Real-Time Task Model - Chapter 3 -...

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1 Real-Time Task Model - Chapter 3 - “Monolithic approach” Good enough? •N o ! – For a complex system, it is really hard to design a single superloop – Really hard to validate cross-related temporal requirements • So, we need a more structured way to look at the problem – Reference model: abstracted view (look at only core) of • Workload •R e s o u r c e – Easy to form a structured way of design and validation – Can be generalized for many variations of problems
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2 Why Reference Model? ARM processor LeastSquare filter P control PID control Kalman filter sensor sensor actuator Specific Problem 1 Specific Problem 2 Model Problem Abstraction Customizing The Objective of A Reference Model • Directly handling wide variety of details (Kalman or Sorting, C++ or Ada, Pentium III or ARM-7, Unix or Windows)? – have to deal with irrelevant details – hard to be generalized • A Reference Model captures only relevant characteristics and categorize the problem space – workload model – resource model – algorithms • Like doctor’s reference handbook, a reference model help you – classify a given real-time problem – know if it is a solved problem or open problem – know if it is a easy problem or hard problem
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3 Overview • Workload model (characterization of applications) – Jobs and tasks – Release time (periodic/aperiodic/sporadic) – Deadline (absolute/relative, hard/soft, single stage/end to end) – Execution time (deterministic/stochastic) – Temporal distance and precedence constraints • Resource model – Processors and resources – Utilization of resource • Scheduling algorithms – Priority/preemptability/blocking – Scheduler and schedule Workload Model • Task and job • Task offset • Release time of jobs (periodic, sporadic, aperiodic) • Deadline of jobs (hard or soft) • Execution time of jobs (deterministic or stochastic) 0 (system startup time)
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4 Jobs and Tasks • A job is a unit of computation, e.g., – handling the press of a keyboard – or compute the control response in one instance of a control loop • A task is a sequence of the same type of jobs, say, a control task or the keyboard handling task. job1 Job 2 Release Time and Deadline Release time is the instant at which the job becomes ready to execute Deadline is the time by which the job should complete.
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lec04_model - Real-Time Task Model - Chapter 3 -...

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