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High Confidence Computing with the New Windows

Embedded Compact 7

Windows Embedded Technical Article

October 2010

Applies to: Windows Embedded Compact 7

Introduction

Building a reliable computer system is always important, but for embedded systems it is essential. Windows®

Embedded Compact 7 provides a highly reliable foundation for today’s modern embedded systems. Compact

7 is the latest version of Windows® Embedded CE, complete with an updated kernel, a new network stack,

updated tools, and a variety of other new features.

Compact 7 builds on years of involvement in the embedded marketplace for Microsoft. Its purpose-built

embedded operating system is designed for high reliability, high confidence computing. Along with the

updated operating system, the Platform Builder for Windows Embedded Compact 7 tool set has also been

To demonstrate the new multi-core abilities of the operating system, a CPU load application was developed

that is similar to what is available on the desktop versions of Windows®. The following figure shows the

System Monitor usage of the application on a computer running Compact 7 while Windows® Internet

Explorer® Embedded loads a web page. Notice how the kernel takes advantage of each core on this multi-

core system.

High Confidence Computing with the New Windows Embedded Compact 7

© 2011 Microsoft Corporation. All Right Reserved

one running at normal application priority, it would noticeably affect the user interface (UI) and the

performance of many other background threads.

In an SMP system, the runaway thread would consume the capacity of one of the cores, but the other cores in

the CPU would remain available to the operating system for other applications. The following code sample

provides a trivial example of such a nightmare scenario for an embedded system, in which an application runs

a thread at a very high priority, but does not block the system.

High Confidence Computing with the New Windows Embedded Compact 7

© 2011 Microsoft Corporation. All Right Reserved

the CPU System Monitor application displays the CPU usage of the Lockup application in this scenario. Notice

From a programming perspective, the addition of multi-core support does not affect single threaded

applications. If interested, an application can query how many cores are available on a system using the

function CeGetTotalProcessors.

While there is no need to worry about single threaded applications, multi-core systems can introduce

consequences to multithreaded applications. Multithreaded applications not tested on multi-core systems may

experience timing issues when their threads are truly executing simultaneously on separate cores instead of

sharing a single core. To avoid these issues, if an application is compiled as an earlier version of the operating

system, all the threads of the application will be assigned to the same core.

function CeSetProcessAffinity.

CeGetProcessAffinity. In addition, a new idle time function GetIdleTimeEx has been added that allows

applications to query the idle time on a per-core basis.

In addition to managing processes and threads, the embedded engineer can manage the cores on the CPU. All

but the primary core of the CPU can be powered down and then powered up as needed. The appropriately

named APIs to manage the cores are CePowerOffProcessor and CePowerOnProcessor.

High Confidence Computing with the New Windows Embedded Compact 7

© 2011 Microsoft Corporation. All Right Reserved

a few extra CPU cores available to handle heavy load situations, as well as errant threads to calm the worried

Memory Manager Updates

SMP is not the only area of improvement in the kernel. RAM capacity is improved as well. The previous

generations of Windows Embedded CE had a hard, architectural limit of 512 MB of physical RAM that the

system could manage. Some systems used more, but the operating system had no knowledge of the additional

limit by providing up to 2 GB of virtual space per application, the capabilities and footprint of some embedded

applications increased to the point that some high end systems needed more than 512 MB of RAM.

Windows Embedded Compact 7 raises the supported RAM limit to 3 GB of physical RAM. Now, Compact 7

supports enough RAM to run hundreds of applications using as much RAM as they might need. The following

figure shows a screen capture of the System Control Panel applet displaying a Compact 7 operating system

running in a Windows Virtual PC with 2 GB of available RAM.

High Confidence Computing with the New Windows Embedded Compact 7

© 2011 Microsoft Corporation. All Right Reserved

Figure 3

For systems that need the additional RAM, the BSP needs to be configured to pass a special flag in the

OEMAddressTable, and to provide two additional configuration tables: the OEMRAMTable to point to the

additional RAM, and the OEMDeviceTable to map in any uncached hardware registers. In addition, using

VirtualCopy to dynamically map in hardware still works in Windows Embedded Compact 7. The mappings can

be designed to reduce or eliminate changes to the mapped virtual addresses of the hardware.