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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
RTOS Tasks Logic Synthesis
Code Optimization Logic Optimization
Board Level Prototyping
Co-SimulationAnd
Formal Verification
A new system-level synthesis flow
System Design
RTOS
Process Management
Interprocess Communication
Memory Management
I/O Management
Algorithm Development
Compilation
Architecture IC Design
Embedded Operating System
Task Managementcreate, delete, suspend, resume
Time Managementsystem clock, generate delay
Inter Task Communication and SynchronizationMultitasking
No-OS disable interrupts / enable interruptsWith-OS enter/exit critical section
Embedded Operating System (cont’)
Inter Task Communication and SynchronizationWait for event, interruptExchange data, queues, shared memory
Memory Management temporary data buffersallocate, 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 criticalHard real-time requirements
Breaking the limit is always seen as a fundamental failure
Real Time Operating System Characteristics
Bounded Interrupt ServicingPriority Based SchedulingPre-Emptive TasksScalability
Previous RTOS Research(1/2)
Scheduling of the CPU : Central purpose of and RTOSA complete process : waiting, ready, and
executingScheduling policies
Cooperative schedulerStatic priority-driven schedulerDynamic 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 issuesMemory requrimentContext switch time Interrupt latency
A Case Study
On-Chip Multimedia Real-Time OS LSIs such as digital signal processing,
image processing, and protocol processingTwo Major problems:
Overhead of Cyclic Task ExecutionMemory Capacity Limiation
Modeling of System LSIs
Core CPU MemoryHOST I/F
I/O
Block #A Block #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
Conclusion
Made a survey of real-time OS for embedded system
Factors which influence the choosing of OS?The requirements of the applicationsThe special features of OSReal- Time constrained