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Real Time Operating Systems
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  • 1. -Training Presentation by Rohit Joshi
  • 2.  Real-Time Systems.  A few Concepts.  Real-Time OS.  Case Study Nucleus – Introduction will cover in detail in next presentation.
  • 3. Decreasing order of Familiarity Applications OS Hardware System Mostly RTOS
  • 4.  A system where correctness of computation depends on logical correctness and the time upon which the results are produced.  Guaranteeing timing means predictability.  A high degree of utilization while timing constraints are met.  A bounded latency rather than high average performance.
  • 5.  Hard Real-Time Systems  If timing constraints are not met causes a catastrophic system failure.  Soft Real-Time Systems  If timing constraints are not met causes a degradation in the system performance.
  • 6.  Multiple “Task” are scheduled to run.  Each task maintains its Own state  CPU Register  Execution Stack  Not always beneficial.
  • 7.  With more than one task, some means is required to choose among them  FIFO Scheduling  Each task is run in sequence until it blocks or is finished  (cooperative multitasking)  Shortest Job First  The task requiring the least CPU time goes first  Round Robin  Scheduled tasks are periodically interrupted and another task is given the opportunity to execute  None of these algorithms are suitable for an embedded system!
  • 8.  Task may have an inherent precedence.  Precedence must be observed when allocating CPU.  Highest priority task ready to run (not pended or delayed) is allocated to the CPU  Reschedule can occur anytime, due to:  Kernel calls.  System clock tick
  • 9. t3 completes t3 preempts t2 t2 completes Task t3 t2 preempts t1 Task t2 Task t2 Task t1 Task t1 TIME
  • 10. t4 completes t4 preempts t2 Task t4 t1 t2 t3 t1 t2 t2 t3 TIME
  • 11.  Ability to provide the required level of service with a bounded response time.  Multithreaded and preemptible.  Static priorities.  Predictable thread synchronization mechanism.  Priority inheritance.
  • 12.  Documented OS behavior  Interrupt latency  Interrupt masking times  System service latency  System interrupt levels  Device IRQ levels
  • 13.  Task Switches  Number of tasks shouldn’t effect switching time.  IPC and Synchronization  Message sizes should not influence time.  Memory Allocation.  Fragmentation should be avoided.  Can’t rely on garbage collectors.
  • 14.  Multitasking real-time kernel  Priority, pre-emptive scheduler  Inter-task Communication (mailboxes,queues, pipes)  Inter-task synchronization (semaphores, signals, events)  Dynamic creation and deletion of all objects
  • 15.  Proven  Complete product line  No royalties  Source code  Vast CPU support