Chapter 19 Real - time systems

19.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005Overview of Real-Time Systems specified deadline period.. 19.8 Silberschatz, Galvin and Gag

Chapter 19: Real-Time Systems

19.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

Chapter 19: Real-Time Systems

19.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

Objectives

19.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

Overview of Real-Time Systems

specified deadline period

system (I.e automobile, airliner.)

results in case of failure

completed within their required deadlines

non real-time tasks

19.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

19.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

System-on-a-Chip

(SOC) strategy

attached peripheral ports (I.e USB) to be contained in a single integrated circuit

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Bus-Oriented System

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Features of Real-Time Kernels

standard desktop system

hardware that what is typically available in a real-time system

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Virtual Memory in Real-Time Systems

addresses

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Address Translation

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Implementing Real-Time

Operating Systems

(1) Preemptive, priority-based scheduling

(2) Preemptive kernels

(3) Latency must be minimized

19.12 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

Minimizing Latency

when it is serviced

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Interrupt Latency

at the CPU to when it is serviced

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Dispatch Latency

to stop one process and start another

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Real-Time CPU Scheduling

■ p is the duration of the period

■ d is the deadline by when the process must be serviced

■ t is the processing time

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19.17 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

Rate Montonic Scheduling

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Missed Deadlines with Rate Monotonic Scheduling

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Earliest Deadline First Scheduling

the earlier the deadline, the higher the priority;

the later the deadline, the lower the priority

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Proportional Share Scheduling

■ T shares are allocated among all processes in the system.

processor time

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Pthread Scheduling

(1) SCHED_FIFO - threads are scheduled using a FCFS strategy with a FIFO queue There is no time-slicing for threads of equal priority

(2) SCHED_RR - similar to SCHED_FIFO except time-slicing occurs for threads of equal priority

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VxWorks 5.0

19.23 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 1, 2005

Wind Microkernel

(1) Processes and threads;

(2) preemptive and non-preemptive round-robin scheduling;

(3) manages interrupts (with bounded interrupt and dispatch latency times);

(4) shared memory and message passing interprocess communication facilities

End of Chapter 19