Real Time Operating Systems

Group A5

Amit Sharma

Ali Abbas

Dhaval Sanghvi

Strategy for today’s presentation

• Short (10 minutes)

• Outline– What is a RTOS– Types of RTOS– RTOS general structure– VxWorks in particular

Operating System Services

Operating System Hierarchy

RTOS Definition

• Must adhere to strict set of policies and rules with the most distinguishable feature that it is deterministic.

• Deterministic is a guarantee that a software system will execute within a specified time constraint.

More definitions

• Real-time computing is computing where system correctness depends not only on the correctness of the logical result of the computation but also on the result delivery time.

• A real-time system responds in a (timely) predictable way to unpredictable external stimuli arrivals.

How do GPOS and RTOS differ?

• GPOS: emphasize fairness and high resource utilization.

• RTOS: demand timeliness and predictability. – Multitasking– Inter-task Communication– Interrupt and Event Handling– Timers and Clocks

What a RTOS is not

• Real time computing is equivalent to fast computing (avg. # of transactions).

• Real time systems operate in a static environment

• Real time programming involves assembly coding, priority interrupt programming, writing device drivers

Preemptive Vs non preemptive scheduling

• Preemptive scheduling– Task execution is preempted and later resumed– Why? To execute a higher priority task

– Priorities can be fixed or dynamic

• Non preemptive scheduling– once a task is started, it completes execution– less overhead due to less context switches

Multitasking

• Multitasking is not perfect– High priority tasks hog resources and

starve low priority tasks– Low priority tasks share a resource with

high priority tasks and block high priority task

• How does a RTOS deal with some of these issues– Priority Inheritance

Types of RTOS

• Hard Real- Time – complete a critical task within a guaranteed

amount of time– catastrophe. Example?

• Soft Real-Time– Deadlines may be missed occasionally– not safety critical. Example?

Development process• Use the host to

– edit, compile, and build application programs

– configure the target

• At the target embedded system, use tools to – load, execute, debug, and monitor

(performance and timing)

Some popular RTOS

• LynxOS: LynuxWorks Inc.San Jose

• Chimera: Carnegie Mellon UniversityPittsburgh

• VxWorks: Wind River Systems Inc. Alameda, Calif.

• Maruti: University of Maryland College Park, Md.

VxWorks• A product of Wind River• Most popular RTOS for embedded systems• Current version in market is VxWorks 5.4• 1800 API’s• ‘wind’ microkernel

– advanced networking support

– powerful file system

– I/O management, and C++

microkernel• Supports

– fast multitasking

– interrupt support, and both preemptive and round-robin scheduling

– provides efficient intertask communication mechanisms

• message queues and pipes

• sockets and remote procedure calls

• signals

microkernel

• Several types of semaphores– binary, – counting– mutual exclusion with priority inheritance

• 256 priorities

• POSIX compliant

Microkernel features (cont.)• High scalability

• Incremental linking and loading of components

• Fast, efficient interrupt and exception handling

• Optimized floating-point support

• Dynamic memory management

• System clock and timing facilities

A note on POSIX

• Portable Operating System Interface• set of standards under ISO/ IEEE

charter• POSIX standard 1003.1b, (formerly

called 1003.4) for RTOS• makes it easier to move applications

from one operating system to another.

Networking facilities• first real-time operating system to integrate

industry-standard TCP/IP networking facilities

• Environments: ATM, SMDS, frame relay, ISDN, SS7, X.25, IPX/SPX, AppleTalk

Networking facilities (cont.)• VxWorks TCP/IP stack, which supports the

latest Berkeley networking features, including:

IP, IGMP, CIDR, TCP, UDP, ARP

RIP v.1/v.2

Standard Berkeley sockets and zbufs (a.k.a., zero-copy sockets)

NFS client and server, ONC RPC

Point-to-point protocol (PPP)

BOOTP, DNS, DHCP, TFTP

FTP, rlogin, telnet, rsh

Fast, flexible I/O and local file system

• POSIX asynchronous I/O and directory handling

• SCSI support

• MS-DOS compatible file system

• TrueFFS flash file system

• ISO 9660 CD-ROM file system

Supported targets• 80x86 and Pentium

• MIPS

• SPARC

• NEC V8xx

• M32 R/D

• RAD6000

• TriCore

– (and more..)

Tornado• An IDE for VxWorks• From Wind River• Latest version is Tornado 2.2• Run time component is VxWorks• integrated simulator, project facility,

compiler, debugger, system browser, and many other tools to improve software development

Applications of VxWorks

• Mars Pathfinder mission.

• Nortel: Magellan Passport Enterprise Network Switch

• Computer Industry: Networking Switches, Routers, RAID Data Storage

• Transportation Industry: ABS, Realtime Suspension, Traffic Control Systems

References

– VxWorks programmers guide– Real Time Systems. Jane W.S. Liu. Prentice

Hall – "Dynamic Scheduling of Hard Real Time

Applications in Open Systems Environment" Z. Deng, Jane W.S. Liu and J. Sun. 17th IEEE Real Time Systems Symposium.

– comp.os.vxworks Frequently Asked Questions [http://www.landfield.com]