Real-time Linux Evaluation Kalynnda Berens, grc

Real-time Linux Evaluation

• Kalynnda Berens, GRC

• [e-mail]

Definitions

• 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

Tools

• Linux Trace Toolkit

• Dynamic Probes

• kGDB (kernel debugger)

• Linux Kernel Crash Dump

• Linux Test Project

• LMBench

• Ballista

• strace

• System Call Tracker

Requirements

• 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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