Real-Time Operating Systems for Embedded Computing 李姿宜 R ,06,10

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

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

Role of RTOS in HW/SW Co-Design Formal Languages Partitioning HW SynthesisSW Synthesis RTOSTasksLogic Synthesis Code OptimizationLogic Optimization Board Level Prototyping Co-Simulation And Formal Verification

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

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

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)

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

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

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

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

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

An example of Commercial RTOS

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

Modeling of System LSIs Core CPUMemory HOST I/F I/O Block #ABlock #B Block #C Application specific hardware unit

Requirements of Embedded Software 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

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

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

On-Chip Multimedia Real-Time OS Interrupt Management Semaphore management

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