Operating Systems Internals and Design Principles 6E William

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

e. Cos • Embedded Configurable Operating Systems • Open source • Royalty-free • Real-time OS • Most widely used embedded OS

e. Cos Configuration Tool

e. Cos Configuration Tool

Loading an e. Cos Configuration

e. Cos 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

e. Cos Kernel • • Low interrupt latency Low task switching latency Small memory footprint Deterministic behavior

Not in e. Cos Kernel • Memory allocation • Device driver

e. Cos I/O System • Framework for supporting device drivers

e. Cos Scheduler • Bitmap scheduler – Efficient for small number of threads active – Each thread has different priority

Bitmap Scheduler

e. Cos Scheduler • Multilevel queue scheduler – Appropriate when number of threads is dynamic – Multiple threads at each priority – Time slicing

Multilevel Queue Scheduler

e. Cos Thread Synchronization • Mutexes • Semaphores • Condition variables

e. Cos Thread Synchronization • Event flags • Mailboxes • Spinlocks – Useful in SMP (symmetric multiprocessing)

Mutexes

Mutexes and Condition Variables

Mutexes and Condition Variables

Tiny. OS • • 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

Tiny. OS Goals • Allow high concurrency • Operate with limited resources • Adapt to hardware evolution

Tiny. OS Goals • Support a wide range of applications • Support a diverse set of platforms • Be robust

Tiny. OS Components • • • Single-hop networking Ad-hoc routing Power management Times Nonvolatile storage control

Timer. M Component

Timer. M Configuration

Tiny. OS Scheduler • Operates across all components • Only one task executes at one time • Simple FIFO queue

Example Tiny. OS Appliction

Example Tiny. OS Appliction

Tiny. OS Resource Interface • Dedicated • Virtualized • Shared

Shared Resource Configuration