Real-time Linux Evaluation Kalynnda Berens, grc

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Real-time Linux Evaluation

  • Kalynnda Berens, GRC



  • Embedded System - A combination of hardware and software which together form a component of a larger machine. An embedded system is designed to run on its own without human intervention, and may be required to respond to events in real time.

  • Real-time OS - an operating system that provides a required level of service in a bounded response time

    • Hard real-time – absolute deadlines that must be met
    • Soft real-time – time tolerance within which an event can occur

What is Linux?

  • Unix “clone”, first created in 1992 by Linus Torvalds

  • Open source operating system

  • Commonly used in server environment, now used in desktops and embedded systems

  • Not useful for real-time systems because:

    • Fairness scheduling, with limited priority scheduling
    • Unpredictable, sometimes high latency
    • Non-deterministic behavior
    • Coarse timing resolution

Real-Time Linux

  • Modifications or extensions to standard Linux to allow soft or hard real-time applications to meet timing constraints.

  • One approach uses a separate real-time “kernel” that runs Linux as the lowest priority task.

  • Another approach modifies standard Linux for preemptibility, latency, timing, and/or scheduling.

  • Both open source and commercial versions are available.

Real-time Linux Projects

  • Flight Linux-a customized copy of a standard Linux distribution, adapted to the unique environment of a spacecraft embedded control computer.

  • STS-83 experiment used Debian GNU/Linux.

  • RACSI - the remote Automatic Transfer Vehicle (ATV) control at ISS.

  • GOAS - Ground Operator Assistant System for the rendezvous operations of ATV.

  • PLATINO numerical control

  • iArte - Industrial Automation Real Time Environment

  • FAA Level C certified flight simulator

  • Cascade – a RTLinux based GPS receiver

Independent Kernel Variants

Kernel Modification Variants

Real-time Linux Variants

Testing Real-Time Linux

  • Requirements derived from

    • VxWorks 5.4 Test plan, MSFC
    • VxWorks AE Test plan, GRC
    • RTOS properties
  • Specific test scenarios will be derived from the requirements, plus…

    • Variant-specific attributes
    • Known errors, defects, etc.
    • Results of static analysis (open source)

Test Plan


  • Linux Trace Toolkit

  • Dynamic Probes

  • kGDB (kernel debugger)

  • Linux Kernel Crash Dump

  • Linux Test Project

  • LMBench

  • Ballista

  • strace

  • System Call Tracker


  • Scheduling

  • Hardware Interface

  • Communication and Synchronization

  • Memory Management

  • Task Management

Error Catalog

Test Setup

Future Work

  • Static analysis of open source variants

  • Completion of variant-specific test plans

  • Test scenario creation

  • Test procedures for each scenario

  • Testing on embedded hardware

  • Test results and report

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