Chapter 13 Embedded Systems Patricia Roy Manatee Community College, Venice, FL ©2008, Prentice Hall Operating Systems: Internals and Design Principles, 6/E William Stallings

Embedded System Hardware and software designed to perform a dedicated function Tightly coupled to their environmnet

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

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

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

TinyOS Resource Interface Dedicated Virtualized Shared

Shared Resource Configuration