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Real-Time Operating Systems for Embedded Computing

Real-Time Operating Systems for Embedded Computing. 李姿宜 R90921045 2003,06,10. Outline. Motivation Embedded operating systems Real-Time operating systems A case study Conclusion. Motivation. SoC  CPU + ASIC + Software Traditional application-specific systems

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Real-Time Operating Systems for Embedded Computing

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  1. Real-Time Operating Systems for Embedded Computing 李姿宜R90921045 2003,06,10

  2. Outline • Motivation • Embedded operating systems • Real-Time operating systems • A case study • Conclusion

  3. Motivation • SoC  CPU + ASIC + Software • Traditional application-specific systems • Implemented by algorithm-to-architecture methodology. • Modern Trend : Design Reuse, which • software plays an important role, and • Real-time operating systems ( RTOS ) is the critical component

  4. Role of RTOS in HW/SW Co-Design Formal Languages Partitioning SW Synthesis HW Synthesis Co-Simulation And Formal Verification RTOS Tasks Logic Synthesis Code Optimization Logic Optimization Board Level Prototyping

  5. Algorithm Development Compilation Process Management Interprocess Communication System Design RTOS Memory Management I/O Management Architecture IC Design A new system-level synthesis flow

  6. Embedded Operating System • Task Management • create, delete, suspend, resume • Time Management • system clock, generate delay • Inter Task Communication and Synchronization • Multitasking • No-OS disable interrupts / enable interrupts • With-OS enter/exit critical section

  7. Embedded Operating System (cont’) • Inter Task Communication and Synchronization • Wait for event, interrupt • Exchange data, queues, shared memory • Memory Management • temporary data buffers • allocate, free (critical in ES)

  8. Real Time Operating System • Embedded applications can and will respond to external events before deadline • Soft real-time requirements: • Breaking the time limit is unwanted, but is not immediately critical • Hard real-time requirements • Breaking the limit is always seen as a fundamental failure

  9. Real Time Operating System Characteristics • Bounded Interrupt Servicing • Priority Based Scheduling • Pre-Emptive Tasks • Scalability

  10. Previous RTOS Research(1/2) • Scheduling of the CPU : Central purpose of and RTOS • A complete process : waiting, ready, and executing • Scheduling policies • Cooperative scheduler • Static priority-driven scheduler • Dynamic priority-driven scheduler

  11. Previous RTOS Research(2/2) • Scheduling methodology examples • Rate Monotonic algorithm by Liu & Layland • static priorities based on periods • higher priorities to shorter periods • optimal among all static priority schemes • Earliest-deadline First • dynamic priority assignment • closer a task’s deadline, higher is it priority • applicable to both periodic and aperiodic tasks • need to calculate priorities when new tasks arrives • more expensive in terms of run-time overheads

  12. Commercial RTOS Offerings • Integrated Systems (pSOS system), WindRiver (VxWorks), Microtec Research (VRTX), Microware Systems (OS-9), QNX (QNX), Lynx Real-Time system (LynxOS), Microsoft (Windows-CE) • Practical application issues • Memory requriment • Context switch time • Interrupt latency

  13. An example of Commercial RTOS

  14. A Case Study • On-Chip Multimedia Real-Time OS • LSIs such as digital signal processing, image processing, and protocol processing • Two Major problems: • Overhead of Cyclic Task Execution • Memory Capacity Limiation

  15. Modeling of System LSIs HOST I/F Core CPU Memory I/O Block #C Block #A Block #B Application specific hardware unit

  16. Requirement Hardware control Scheduling Synchronization Urgent processing Memory capacity Real-Time OS function Task Management Multitasking Scheduling New cyclic task Interrupt Management Semaphore Management Very small real time OS Requirements of Embedded Software

  17. Resource for task deleted Resource for task Allocated On-Chip Multimedia Real-Time OS • Task management Cyclic task is created and start Cyclic task is deleted Cyclic task execution Dedicated interval time

  18. Resource for task Not deleted Resource for task Not allocated Resource for task deleted Resource for task Allocated On-Chip Multimedia Real-Time OS Cyclic task is created and start Cyclic task is suspended Cyclic task is deleted Cyclic task is resume

  19. On-Chip Multimedia Real-Time OS • Interrupt Management • Semaphore management

  20. Conclusion • Made a survey of real-time OS for embedded system • Factors which influence the choosing of OS? • The requirements of the applications • The special features of OS • Real- Time constrained

  21. Thank you !!!

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