window ce

Windows CE

by:

K.Balamurugan

M.Tech-CSE-1st year

Introduction

Entertainment devices and CAR

What can CE do

– Industrial Automation

– Set-Top Boxes

– Medical Devices and Systems

– ATMs

– Projectors and Large Screen Displays

– VoIP Devices

– First edition released in 1996

– Windows CE .NET 4.x is widely used

Introduction to BSP

• Windows CE can run on different hardware platforms.

• How can we do that?

• The answer is BSP !• Board Support Package is the software that

implements and supports the OEM adaptation layer (OAL) and device drivers for a standard development board (SDB).

Compare with Desktop Version

– Windows XP : 1.5GB

No inherent real time support

256 levels of thread priority

Minimal : 200KB Windows XP : 1.5GB

Lager and lager… Can NOT be

customized

Quick and easy to customize OS for a particular system

More than 200 optional component

Compact Version of Win32 API, MFC..

UNICODE only

ASCII / UNICODE

Commercial software, source code is MS 1st level secret.

70% of Windows CE 5.0 source code is shared.

Memory Management

– Windows CE uses ROM (read only memory), RAM (random access memory)

• The ROM in a Windows CE system is like a small read-only hard disk

• The RAM in a Windows CE system is divided into two areas: program memory and object store

– Windows CE is a 32-bit operating system, so it supports 4GB virtual address space

Memory Management…..

– Upper 2GB is kernel space, used by the system for its own data

– Lower 2GB is user space

• 0x42000000-0x7FFFFFFF memory is used for large memory allocations, such as memory- mapped files

• 0x0-0x41FFFFFF memory is divided into 33 slots, each of which is 32MB

Memory Management…..

Processes and Threads Management

– Windows CE limits 32 processes being run at any one time

– Every process at least has a primary thread associated with it upon starting (even if it never explicitly created one)

– A process can created any number of additional threads (only limited by available memory)

– Each thread belongs to a particular process (and shares the same memory space)

– SetProcPermissions API will give the current thread access to any process

– Each thread has an ID, a private stack and a set of registers

Processes and Threads Management…..

– When a process is loaded

• Assigned to next available slot

• DLLs loaded into the slot

• Followed by the stack and default process heap

• After this, then executed

– When a process’ thread is scheduled

• Copied from its slot into slot 0

– This is mapped back to the original slot allocated to the process if the process becomes inactive


– Thread– A unit of execution – A piece of code that can be scheduled to run by the kernel– May be launch by a process or a driver

– Process– A collection of threads with a common execution environment– A process has at least on thread– Launch from an executable file– Can create threads to handle interrupts

– Driver– A DLL, (dynamically loaded library) loaded into the device

manager process– Supports the Device I/O Control Interface– Can create threads to handle interrupts


– Processes allocate stack for each thread, the default size is 64KB, depending on the link parameter when the program is compiled

• Top 2KB used to guard against stack overflow

• Remained available for use

– Variables declared inside functions are allocated in the stack

– Thread’s stack memory is reclaimed when it terminates

API Address Search

Scheduler

– Is responsible for determining which thread will run– Has a queue for threads for each priority level– Will always schedule the first thread at the highest priority level

– A thread gets to run for set length of time, called a quantum

– Typically 100 milliseconds– A quantum of 0 means the quantum never runs out

• The thread can run until blocked or interrupted

– A Thread runs until—– Its quantum runs out– It is interrupted by a higher priority thread– Its blocked by a resource contention

• Such as access to a critical section or a mutex

ISRs And ISTs

– Interrupt Service Routine (ISR)– A piece of code loaded into the kernel

– Assigned to a particular IRQ

– Called immediately to handle the hardware interrupt

– Should be written to run quickly with few outside dependencies

– Can be chained together if multiple device might use the same IRQ

– Notifies the kernel which IST should run

– Interrupt Service Thread (IST)– A thread registered to handle an interrupt

– Can be created by either a process or a driver

– Scheduled like any other thread on the system

– Should be written to do the bulk of the interrupt handling work

Priority Levels

– Windows CE 5.0 has 256 levels of priority

– Level 0 is the highest and 255 is the lowest

• The old CE model of 8 levels now map to the lowest 8 of the new model

– The default level for a thread is 252

– Levels 0 through 248 can be reserved by OEM

Interrupt Architecture

OAL Design

Scheduling algorithms in Windows CE

Conclusion

– Windows CE is real-time

– Windows CE provides all the functionality needed to qualify as a real-time operating system

– Windows CE provides tools to optimize your real-time platform

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