1. A Sample RTOS Presentation 4 Group A4: Sean Hudson, Manasi Kapadia Syeda Taib

2. Overview  What is a Real-Time System?  What is a Real-Time OS (RTOS)?

3. What is a Real-Time System?  Any system in which an operation must occur within certain fixed time constraints.  In these systems, if an operation is computationally correct and arrives late, it is considered invalid.

4. Real-Time System Categories  Hard Real-Time Timing is critical. Missing a deadline causes a catastrophic failure.Timing is critical. Missing a deadline causes a catastrophic failure.  Soft Real-Time Timing is VERY important, but in spite of a failure, some progress can be made.Timing is VERY important, but in spite of a failure, some progress can be made.

5. What is an RTOS?  A specialized OS.  Designed to meet several stringent requirements.  Provides a restricted set of services to ensure these requirements.

6. RTOS Requirements  Deterministic and Responsive  User Control  Reliable  Fail-soft operation

7. OSE  Commercially available RTOS.  Developed by ENEA OSE Systems.  Kernel is fully preemptible.  Transparent IPC among multiple processors.  Supports Advanced Memory Management features.  Supports dynamic kernel reconfiguration

8. OSE Architecture  Process Handling  Inter-process Communication  Interrupt Handling

9. Process Categories  Static  Dynamic

10. Process Types  Interrupt Processes  Timer Interrupt Processes  Prioritized Processes  Background Processes  Phantom Processes

11. Process States

12. Process Scheduling   Pre-emptive   Cyclic   Priority Based   Round Robin

13. Process Priorities   Interrupt Processes   Timer Interrupt Processes   Prioritized Processes   Background Processes

14. Inter-process Communication  Signals (messages)  Fast Semaphores  Semaphores

15. Signals  Messages between processes.  Contain sender and receiver ID’s.  Identifying the target process is crucial.  Processes can selectively receive signals.  Signals change ownership when sent.

16. Signal Redirection  Mechanism to process signals with another process.  Signals can be sent to processes on another processor.  Allows a signal interface to be defined without knowledge of a particular process hierarchy.

17. Fast Semaphores  Counting Semaphore. Supports wait/signal.Supports wait/signal.  Faster than signals. Contain no data.Contain no data.  Process specific. Only the owner can wait on this semaphore.Only the owner can wait on this semaphore.  Interrupt Processes behave differently. Can not issue a wait.Can not issue a wait. Other processes can issue a signal.Other processes can issue a signal.  Used to generate software events.

18. Semaphores  Used to ensure mutual exclusion.  Any process may use these semaphores.

19. Interrupt Handling  Interrupts are special events that need to be processed ASAP.  Each interrupt is processed by an Interrupt Service Routine (ISR).  Each ISR is its own task and has a unique priority associated with it.  Methods to call an ISR: Hardware InterruptsHardware Interrupts Software Events (via Wakeup Facility)Software Events (via Wakeup Facility) Timer EventsTimer Events

20. Interrupt Handling (cont.)  Hardware Interrupts: External hardware event.External hardware event.  Software Events: Triggered by an internal system call.Triggered by an internal system call.  Timer Events: Depend on the system tick counter.Depend on the system tick counter. Handle recurring, fixed time requirements.Handle recurring, fixed time requirements.

21. Summary