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 University Pittsburgh 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