Ch3_PerfSysProgramming.pdf

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MCTS

Exam 70-571

i

Windows Embedded CE 6.0

Preparation Kit

Self-Paced Training

Up to Date

with

R2

Content

Not for Resale.

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2

first top-level entry

Contents at a Glance

1

Customizing the Operating System Design

2

Building and Deploying the Run-Time Image

3

Performing System Programming

4

Debugging and Testing the System

5

Customizing a Board Support Package

6

Developing Device Drivers

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Chapter 3

Performing System Programming

System performance is critical for user productivity. It directly influences the user’s

perception of a device. In fact, it is not uncommon for users to judge the usefulness of

a device based on the performance of the system and the look and feel of the user

interface. By providing too complex of an interface, you can confuse users and open

your device to potential security risks or unexpected user manipulations. By using the

incorrect APIs, or incorrect applications architecture in a multithreaded environment,

you may significantly impact performance. Performance optimization and system

customization are real challenges for firmware providers. This chapter discusses the

tools and highlights best practices to achieve optimal system response times on target

devices.

Exam objectives in this chapter:

Monitoring and optimizing system performance

■

Implementing system applications

■

Programming with threads and thread synchronization objects

■

Implementing exception handling in drivers and applications

■

Supporting power management at the system level

■

Before You Begin

To complete the lessons in this chapter, you must have the following:

A thorough understanding of real-time systems design concepts, such as

scheduler functionality in an operating system, interrupts, and timers.

■

Basic knowledge of multithreaded programming, including synchronization

objects.

■

A development computer with Microsoft® Visual Studio® 2005 Service Pack 1

and Platform Builder for Microsoft Windows® Embedded CE 6.0 installed.

■

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82

Chapter 3

Performing System Programming

Lesson 1: Monitoring and Optimizing

System Performance

Performance monitoring and optimization are important tasks in the development of

small-footprint devices. The need for optimized system performance remains critical

because of an ever-growing number of increasingly complex applications and the

requirement for intuitive and therefore resource-intensive user interfaces.

Performance optimization requires firmware architects and software developers to

constrain resource consumption within their system components and applications so

that other components and applications can use the available resources. Whether

developing device drivers or user applications, optimized processing algorithms can

help to save processor cycles, and efficient data structures can preserve memory.

Tools exist at all system levels to identify performance issues within and between

drivers, applications, and other components.

After this lesson, you will be able to:

■ Identify the latency of an interrupt service routine (ISR).

■ Improve the performance of a Windows Embedded CE system.

■ Log and analyze system performance information.

Estimated lesson time: 20 minutes.

Real-Time Performance

Drivers, applications, and OEM adaptation layer (OAL) code impact system and real-

time performance. Although Windows Embedded CE may be used in real-time and

non-real-time configurations, it is important to note that using non-real-time

components and applications can decrease system performance in a real-time

operating system (OS) configuration. For example, you should keep in mind that

demand paging, device input/output (I/O), and power management are not designed

for real-time devices. Use these features carefully.

Demand Paging

Demand paging facilitates memory sharing between multiple processes on devices

with limited RAM capacity. When demand paging is enabled, Windows Embedded

CE discards and removes memory pages from active processes under low-memory

conditions. However, to keep the code of all active processes in memory, disable

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Lesson 1: Monitoring and Optimizing System Performance

demand paging for the entire operating system or for a specific module, such as a

dynamic-link library (DLL) or device driver.

You can disable demand paging by using the following methods:

■ Operating system Edit the Config.bib file and set the ROMFLAGS option in

the CONFIG section.

■ DLLs Use the LoadDriver function instead of the LoadLibrary function to load

the DLL into memory.

■ Device drivers Add the DEVFLAGS_LOADLIBRARY flag to the Flags registry

entry for the driver. This flag causes Device Manager to use the LoadLibrary

function instead of the LoadDriver function to load the driver.

Windows Embedded CE allocates and uses memory as usual, but does not discard it

automatically when you disable demand paging.

System Timer

The system timer is a hardware timer that generates system ticks at a frequency of one

tick per millisecond. The system scheduler uses this timer to determine which

threads should run at what time on the system. A thread is the smallest executable

unit within a process that is allocated processor time to execute instructions in the

operating system. You can stop a thread for an amount of time by using the Sleep

function. The minimum value that you can pass to the Sleep function is 1 ( Sleep(1) ),

which stops the thread for approximately 1 millisecond. However, the sleep time is

not exactly 1 millisecond because the sleep time includes the current system timer

tick plus the remainder of the previous tick. The sleep time is also linked to the

priority of the thread. The thread priority determines the order in which the operating

system schedules the threads to run on the processor. For those reasons, you should

not use the Sleep function if you need accurate timers for real-time applications. Use

dedicated timers with interrupts or multimedia timers for real-time purposes.

Power Management

Power management can affect system performance. When the processor enters the

Idle power state, any interrupt generated by a peripheral or the system scheduler

causes the processor to exit this state, restore the previous context, and invoke the

scheduler. Power context switching is a time-consuming process. For detailed

information about the power management features of Windows Embedded CE, see

the section “Power Management” in the Windows Embedded CE 6.0 documentation

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WindowsEmbeddedCE Fundamentals.PDF (9699 KB)
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