Transcript Chapter13x - Website Staff UI

Operating Systems:
Internals and Design Principles, 6/E
William Stallings
Chapter 13
Embedded Systems
Patricia Roy
Manatee Community College, Venice,
FL
©2008, Prentice Hall
Embedded System
• Hardware and software designed to
perform a dedicated function
• Tightly coupled to their environmnet
Examples
Examples
Embedded System
Organization
Characteristics of Embedded
Operating System
• Real-time operation
• Reactive operation
– Respond to external events
• Configurability
– Large variation in systems so need flexible
configuration
Characteristics of Embedded
Operating System
• I/O device flexibility
• Streamlined protection mechanisms
• Direct use of interrupts
Adapting an Existing OS
• Add real-time capability
• Streamlining operation
• Add necessary functionality
eCos
• Embedded Configurable Operating
Systems
• Open source
• Royalty-free
• Real-time OS
• Most widely used embedded OS
eCos Configuration Tool
eCos Configuration Tool
Loading an eCos
Configuration
eCos Layered Structure
Hardware Abstraction Layer
• Presents consistent API to upper layers
• Different for each hardware platform
HAL
HAL Modules
• Architecture
– Processor family type
• Variant
– Support features of specific processor
• Platform
– Support of tightly coupled peripherals
eCos Kernel
•
•
•
•
Low interrupt latency
Low task switching latency
Small memory footprint
Deterministic behavior
Not in eCos Kernel
• Memory allocation
• Device driver
eCos I/O System
• Framework for supporting device drivers
eCos Scheduler
• Bitmap scheduler
– Efficient for small number of threads active
– Each thread has different priority
Bitmap Scheduler
eCos Scheduler
• Multilevel queue scheduler
– Appropriate when number of threads is
dynamic
– Multiple threads at each priority
– Time slicing
Multilevel Queue Scheduler
eCos Thread Synchronization
• Mutexes
• Semaphores
• Condition variables
eCos Thread Synchronization
• Event flags
• Mailboxes
• Spinlocks
– Useful in SMP (symmetric multiprocessing)
Mutexes
Mutexes and Condition
Variables
Mutexes and Condition
Variables
TinyOS
•
•
•
•
400 bytes of code
Not a real-time OS
No kernel
No memory protection
Tiny OS
•
•
•
•
Component-based OS
No processes
No memory allocation
Interrupt and exception handling
dependent on peripheral
• Nonblocking
Wireless Sensor Network
Topology
TinyOS Goals
• Allow high concurrency
• Operate with limited resources
• Adapt to hardware evolution
TinyOS Goals
• Support a wide range of applications
• Support a diverse set of platforms
• Be robust
TinyOS Components
•
•
•
•
•
Single-hop networking
Ad-hoc routing
Power management
Times
Nonvolatile storage control
TimerM Component
TimerM Configuration
TinyOS Scheduler
• Operates across all components
• Only one task executes at one time
• Simple FIFO queue
Example TinyOS Appliction
Example TinyOS Appliction
TinyOS Resource Interface
• Dedicated
• Virtualized
• Shared
Shared Resource Configuration