Real Time Operating System
- 2. Overview Introduction Classification System Characteristics Implementing Real-Time Operating Systems
- 3. Introduction Real-time systems are those systems in which the correctness of the system depends not only on the logical result of computation, but also on the time at which the results are produced. Supports real-time applications by providing logically correct result within the deadline required. RTOS is key to many embedded systems and provides a platform to build applications.
- 4. Classification Hard real time system • Tasks have to be performed on time • Failure to meet deadlines is fatal • Example : Flight Control System, medical systems . Soft real time system • Tasks are performed as fast as possible • Late completion of jobs is undesirable but not fatal. • Example: Online Databases, computer games.
- 5. Single purpose Small size Inexpensively mass-produced Specific timing requirements Do not require interfacing with a user System Characteristics
- 7. System-on-a-Chip Many real-time systems are designed using system-on-a-chip strategy SOC allows the CPU, memory, memory-management unit, and attached peripheral ports (i.e., USB) to be contained in a single integrated circuit
- 8. Virtual Memory in Real- Time Systems Address Translation
- 9. Implementing Real-Time Operating Systems 1. Preemptive, priority-based scheduling 2. Preemptive kernels 3. Latency must be minimized
- 10. Event latency
- 12. Dispatch Latency
- 13. Priority Inversion Problem High-level task stalled due to low-level using shared resources, then a medium-level task holding up the low- level one Solution: Priority inheritance – give low-level task high-level priority
- 14. Scheduling Algorithms in RTOS Priority Scheduling Processor never left idle when there are ready tasks Processor allocated to processes according to priorities
- 15. Priority Scheduling Earliest Deadline First (EDF) Process with earliest deadline given highest priority Least Slack Time First (LSF) slack = relative deadline – execution left Rate Monotonic Scheduling (RMS) For periodic tasks Tasks priority inversely proportional to it’s period
- 16. Examples of RTOS LynxOS OSE QNX VxWorks Windows CE RT Linux
- 17. APPLICATIONS OF RTOS Almost all the modern telecommunication systems make use of RTOS . Radar systems, network switching control systems, satellite monitoring systems, satellite launch-control and global positioning systems all have their roots in RTOS. Now a days RTOS are increasingly finding use in strategic and military operations. These are used in guided missile launching units,track-and-trace spy satellites, etc.