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Real-Time Operating System Design

Real-Time Operating System Design. Alvin AuYoung ee290O 4/19/01. Real-Time OS Design - 1. Overview. Introduction - Motivation - Goals Design Issues Methodologies - Priority-based Kernel - RT extensions of timesharing systems - Research operating systems Case study: Java-OS

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Real-Time Operating System Design

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  1. Real-Time Operating System Design Alvin AuYoung ee290O 4/19/01 Real-Time OS Design - 1

  2. Overview Introduction - Motivation - Goals Design Issues Methodologies - Priority-based Kernel - RT extensions of timesharing systems - Research operating systems Case study: Java-OS Conclusions Real-Time OS Design - 2

  3. Motivation Most current operating systems are not suitable for developing or deploying applications with real-time constraints i.e. scheduling policies, process synchronization, system architecture Real-Time OS Design - 3

  4. Goals Create an environment suitable for developing applications with hard real-time constraints on task execution in a reactive environment. Two key ideas: Predictability: Predict direct consequences of any scheduling decision. Schedulability Guarantees: Verify the schedulability of a given set of tasks. Real-Time OS Design - 4

  5. Design Issues How can I guarantee predictability and schedulability with the different components of my system? Architecture, Memory Management, Task structure, Kernel, etc... Real-Time OS Design - 5

  6. Methodologies Priority-based Kernels VxWorks, OS9, pSOS RT extensions of timesharing systems RT-Mach, RT-Unix Research operating systems Spring, HARTIK Real-Time OS Design - 6

  7. Priority-based kernels Objective: - High performance for average response time to external events. Characteristics: - fast context switching - small footprint - efficient interrupt handling - preemptable primitives - fast communication mechanisms Real-Time OS Design - 7

  8. Priority-based kernels Driven by a real-time clock Task Scheduling with fixed priorities Synchronization tools, limitations Communication protocols Problem? Real-Time OS Design - 8

  9. Real-Time extensions of timesharing OS • Objective: • Extend current (commerical) time-sharing systems to satisfy real-time constraints. • Characteristics: • - Reuse standard peripherals and interfaces • - Speedier development Real-Time OS Design - 9

  10. Real-Time extensions of timesharing OS - Reused Kernel - Task Scheduling with fixed priorities Tasks vs Threads? (N. Wirth) - Re-implemented User-Level Threads - Nonpreemptable syscalls, interrupts problems? Real-Time OS Design - 10

  11. Research Operating Systems Objective: The ability to treat tasks with explicit timing constraints, such as periods and deadlines Characteristics: - Scheduling guarantee mechanisms - Characterize tasks with additional parameters - Avoidance of nondeterministic blocking time Real-Time OS Design - 11

  12. Research Operating Systems Case Study: Spring Kernel Real-Time OS Design - 12

  13. A Java Solution: JMD A Java Kernel for Embedded Systems in Distributed Process Control Java Microcontrolled Device (JMD) - JMD applications (high level) - JMD-OS API - JMD Kernel - MicroKernel (low level) Real-Time OS Design - 13

  14. A Java Solution: Task Model Task Methods and Behaviors: parameterized by: - period of execution - deadline - WCET - Priority Class (1 - 10) Variable Scheduling Algorithm Real-Time OS Design - 14

  15. A Java Solution: Conclusions Not yet RTSJ compliant Flexible Kernel provides abstraction and possibility for future development. Maybe in the future? Real-Time OS Design - 15

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