1. Real Time Versions of Linux Operating System Present by Tr n Duy Th nh Quách Phát Tài 1

2. Content 1. Standard Linux 2. Real-time Linux Implement core real-time Linux 3. Open-Source Distributions 4. Commercial Distributions Real-time versions 2

3. 1. Standard Linux Memory Management Memory Protection Scheduling and Task Management Hardware Interfaces File Management Communication: external, internal 3

4. 2. Real-time Linux kernel Modifications that make Linux Real Time Real-Time Patches to the Standard Kernel 4

5. 2. Real-time Linux kernel Modifications that make Linux Real TimeReal-Time Patches to the Standard Kernel Micro Kernel Nano Kernel Resource Kernel Extension POSIX Real-time Extension 5

6. 2.1 Modification that make Linux Real-time Interrupt processing in standard kernel: 2 halves The bottom-half task is the interrupt handler and reads data from the physical device into a memory buffer. The top-half task reads from the memory buffer and passes the data to a kernel accessible buffer In the standard kernel: without preemption, all interrupts are disabled when the bottom-half task is running. All variants of real-time Linux have introduced modifications at the kernel level reduce both the interrupt latency and jitter between periodic interrupts faster response to external events and higher resolution timing 6

7. 2.1 Modification that make Linux Real-time Standard kernel preemption Higher priority kernel processes can preempt lower priority Linux version 2.5.4 latency and jitter is around 1 millisecond 7

8. 2.2 Real-time Patches to the Standard Kernel adding a second, highly efficient, kernel to handle real- time tasks Micro Kernel: RTLinux, RTAI Nano Kernel Resource Kernel Extension making changes directly to the standard kernel POSIX Real-Time Extensions: implement the timers, signals, semaphores, process memory locking, shared memory,priority scheduling, synchronized and asynchronized I/O specied in IEEE 1003.1d KURT TimeSys Linux 8

9. 2.2.1 Micro Kernel Victor Yodaiken controls the execution of real-time tasks runs the standard Linux kernel as a background task RTLinux – New Mexico Tech RTAI - Politecnico di Milano 9

10. 2.2.2 Nano Kernel Adaptive Domain Environment for Operating Systems (ADEOS) similar to the micro kernel many operating systems can be run in parallel on top of the nano- kernel layer 10

11. 2.2.3 Resource Kernel Extension provides a gateway to resources such as file systems, serial and parallel ports, and network interfaces for both the normal kernel and also for user processes control the interrupt preemption issues for the standard kernel User-space can communicate directly 11

12. 2.2.4 POSIX Real-time Extensions Modify directly to the standard kernel Implement the timers, signals, semaphores, process memory locking, shared memory,priority scheduling, synchronized and asynchronized I/O specied in IEEE 1003.1d Two different approaches: KURT: The Kansas University Real-Time Linux (KURT) distribution, high resolution timers, real-time scheduling improvements TimeSys Linux making the standard kernel preemptable including a kernel scheduler that provides scheduling for the bottom- half kernel interrupt processing and for interrupts themselves 12

13. 2.3 Performance Comparison 13

14. Real-time versions of Linux Open-Source Distributions: Provide the source code and build scripts so the user can understand, modify, and build the code Documentation may be sparse and technical support nonexistent Commercial Distributions Make a profit to stay in business. Support and documentation. 14

15. 3. Open-Source Distribution ADEOS KURT RTAI RTLinux TimeSys Linux GPL 15

16. Open-Source: ADEOS Adaptive Domain Environment for Operating Systems 2002 Is a hardware abstraction layer Allow a real-time kernel and a general purpose kernel to co-exist Real-Time Mechanism nano-kernel 16

17. Open-Source: KURT Kansas University 1997 Implement the POSIX real-time extensions to Linux The patches implement the queued real-time signals and the high-resolution timers. Real-Time Mechanism: POSIX timers and scheduling. 10s of microseconds of latency and jitter 17

18. Open-Source: RTAI (Linux-RT) Politecnico di Milano, Italy. 2000 Originally based on RTLinux Evolved as a unique favor of real-time Linux. Real-Time Mechanism: micro kernel < 10 microseconds latency and jitter 18

19. Open-Source: RTLinux Victor Yodaiken, New Mexico Institute of Technology 1996 Covers the logic of running standard Linux as a background thread to the real-time tasks Real-Time Mechanism: micro kernel < 10 microseconds latency and jitter 19

20. Open-Source: TimeSys Linux GPL TimeSys 1998 Provides a preemptable kernel and an improved task scheduler Real-Time Mechanism: Preemptable Kernel < 100 microseconds of latency and jitter 20

21. 4. Commercial Distribution RedHawk Linux FSMLabs RTLinux MontaVista Linux QRTS REDICE-Linux Linux SMP TimeSys 21

22. Commercial: RedHawk Linux Concurrent Computer Corporation Packaged hardware/software solutions Targeting the real time data acquisition, video- on-demand, and simulation markets Real-Time Mechanism Kernel: preemption enhancements 22

23. Commercial: FSMLabs RTLinux Finite State Machine Labs RTLinux version 3.0 offers developers the option of using either Linux or netBSD as their general purpose OS, using the identical POSIX threads API Real-Time Mechanism: Micro kernel 23

24. Commercial: MontaVista Linux MontaVista Software Inc. Tailor to the needs of embedded software developers. Real-Time Mechanism: Kernel pre-emption enhancements 24

25. Commercial: QRTS Quality Real Time Systems Develops applications for real-time control and simulation. Real-Time Mechanism: RTLinux micro kernel 25

26. Commercial: REDICE-Linux REDSonic Inc. Integrates the dual kernel approach and the preemptable kernel to provide a hybrid solution Real-Time Mechanism: Micro kernel and Kernel Preemption. 26

27. Commercial: Linux SMP Synergy Microsystems Inc. Support RTLinux as the operating system on their PowerPC single-board computers. Real-Time Mechanism: RTLinux micro kernel 27

28. Commercial: TimeSys Linux/RealTime, TimeSys Linux/Net, TimeSys Linux/CPU TimeSys Corporation Adds three proprietary components into an open-source preemptable kernel High-resolution timers and priority inheritance. Guaranteed access to CPU resources, Guaranteed access to network resources. Real-Time Mechanism: Preemptable Kernel. 28

29. Thank you! 29