1 Real-time Linux Evaluation Kalynnda Berens, GRC

2 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

3 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

4 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.

5 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

6 Independent Kernel Variants Hardware Standard Linux Kernel Kernel Space User Space Linux Process Real-Time Micro Kernel Real-Time Task

7 Kernel Modification Variants Hardware Modified Linux Kernel Preemptible, Micro Timing, and/or Low Latency Modified Linux Kernel Preemptible, Micro Timing, and/or Low Latency Loadable Module Kernel Space User Space Linux Process Real-time Process

8 Real-time Linux Variants RTAI (Real-time Application Interface) Kernel, User space hard real-time (LXRT) Open source RT-LinuxKernelCommercial, open source OnCore OSSeparate RTOSCommercial KURT (Kansas University Real- time) ModifiedOpen source HardHatModifiedCommercial

9 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)

10 Test Plan Linux RTOS Test Plan Specific Linux RTOS Test Plans VxWorks 5.4 VxWorks AE RTOS Testing Variant Specific Errors Static Analysis

11 Tools Linux Trace Toolkit Dynamic Probes kGDB (kernel debugger) Linux Kernel Crash Dump Linux Test Project LMBench Ballista strace System Call Tracker

12 Requirements Scheduling Hardware Interface Communication and Synchronization Memory Management Task Management Timing Configuration External Communications Error Reporting Embedded Features File system Reliability

13 Error Catalog

14 Test Setup Development System (Mandrake 8.1 Linux) Embedded Pentium PC/104 Embedded PowerPC Ethernet Connection

15 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