Windows ce virtual memory management

Typically, the large DLL is used by a single application. But if it is loaded early, it can impact the other application by pushing down the load address of the other applications DLLs to the point where they cannot be loaded.

This raises the issue of how to force the load order of the DLLs. One way is to sequence the startup of the different processes in the application suite but this sometimes can be problematic. The DLL loader stays running for the life of the primary application and then terminates. It can even launch the primary application by calling CreateProcess and wait until the primary application terminates by blocking on the process handle returned by CreateProcess.

All of the solutions discussed for solving the DLL load problem on the Pocket PC are hacks of one way or another. None are elegant, nor that maintainable. However, these are the solutions that developers are using to develop their products. Future releases of the Pocket PC should solve this problem, but for developers working on Pocket PC products, improvisation is the key.

By knowing how Windows CE manages memory, developers can avoid pitfalls and diagnose problems more quickly. Even when future releases of the Pocket PC appear that solve this problem, the millions of devices already in the field will need applications. Knowing where to look for the problem is the first step in finding, and then solving the problem. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account.

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Skip to content. Home About. Windows CE. Figure 1. The Windows XP virtual memory space The virtual address space of Windows CE is at first glance, organized in a similar fashion with an area reserved for the system and replicated application spaces. Figure 2. Figure 3. A Windows CE. NET application virtual memory space Any additional memory allocated by the application by either creating separate heaps or by directly calling the VirtualAlloc API is allocated from the bottom up with the system finding the first free region that is large enough to satisfy the allocation.

Figure 4. A Windows CE 3. Figure 5. Three processes loading a series of DLLs Now consider what to do if you encounter a potential problem. Figure 6. Share this: Twitter Facebook. Like this: Like Loading This entry was posted in Uncategorized. Bookmark the permalink. February 25, at pm. Leave a Reply Cancel reply Enter your comment here One way to describe Windows CE is in terms of the design goals that guided the original development team.

Windows CE contains a subset of the features you have on your desktop. But by subset I don't mean to imply incompleteness. The most useful, most used, most popular, and most powerful features have been ported from desktop versions of Windows to Windows CE. So what has been left out Redundant functions have been severely trimmed so that, for example, you only have one text drawing function instead of two.

Another category of omission is support for legacy Win16 applications on the desktop, so that there is no support for reading or writing. In general, you'll find rich support for the features your application needs. Occasionally a developer will get grumpy about something that didn't make the cut to Windows CE.

When you encounter one of these, there's often another way to do what you want. In some cases, though, you have to choose between rewriting the feature from scratch or cutting it from the Windows CE-based version of your application.

Windows CE is the first operating system from Microsoft to require Unicode characters in text strings. Unicode is a character set created by a consortium of computer companies, and blessed by international standards organizations. Unlike the single-byte character sets used for European and North American languages, or the mix of single and double-byte characters used for Far Eastern Asian languages, all Unicode characters take up two bytes.

The impact this has on your programming depends on whether your Windows CE-based program gets data from the outside world. If you use data files that were created on a PC, you might need to convert strings to Unicode. Many modems send status information and accept command strings using one-byte character strings. Other devices, like GPS devices described in Joshua Trupin's article in this issue, also use one-byte strings.

For all of these, you'll have to perform the appropriate conversion if you're writing Winbased code. There are a few odd departures from a Unicode-only approach that you should be aware of: two involve networking, and one involves Visual Basic. This is more surprising than anything else, given the Unicode-only approach everywhere else.

I suspect this has to do with the fact that technically speaking, the Windows Sockets functions are not a part of the Win32 API. After all, Winsock was created by a group of network programmers working together to create a new API. Imposing Unicode on it would no doubt break some applications.

For these functions, you'll find both ANSI and Unicode versions for each function that takes a string. Unlike the desktop version of Visual Basic, there are no built-in statements for accessing files. Instead, you need to use an ActiveX control. In my VBEdit sample application, you can see a workaround using native Win32 functions to write Unicode strings to files.

My personal favorites are the two C runtime functions, mbstowcs and wcstombs. They take the fewest parameters, and are therefore the easiest to use. While these two functions come from the C Runtime Library, they are so useful that they have been added to the core Windows CE library coredll.

Windows CE sports great core operating system support. If you are familiar with the key features of Windows , you'll find that almost every feature from the desktop is available. Windows CE is a multithreaded operating system, and there are thread priorities that give you a high level of control over how the scheduler distributes CPU time.

All four synchronization objects from desktop versions of Windows are present in Windows CE: critical sections, mutexes, semaphores new with Windows CE 3. For more information see my article, " Windows CE 3. These will help you weave a safety net into your code to catch problems with bad pointers, overflows and underflows in math, and division-by-zero errors, to name just a few. Just like desktop versions of Windows, Windows CE is built on a foundation of dynamic link libraries.

And just like on the desktop, DLLs can hold code, data, and resources. There are a few other omissions in kernel-level support from what you find on desktop versions of Windows. In general, Windows CE was built to perform well on small devices, in a small pool of memory, on portable, battery-operated devices.

Windows CE requires a little-endian, bit processor and was built to run using paged virtual memory. This is quite a bit smaller than on desktop versions of Windows, which provide a 2GB process address space.

At first glance, this might seem to be a significant difference. But when you consider that a typical Windows CE-based device has between 16 and 32MB of physical RAM, it seems likely you'll run out of physical memory before you run out of virtual address space.

Applications that need to work with larger objects have a back door: shared memory is allocated from a gigabyte-sized part of the address space. In spite of the emphasis on a small footprint, Microsoft did not skimp on any memory-related feature. Another important difference from the desktop is that Windows CE does not support a page file. So while the pieces of executable. EXE and. Windows CE provides three basic places to store data: in the file system, in a registry much like the registry on desktop versions of Windows , and in databases.

All three live together in RAM in an area called the object store. In Windows CE 3. Many devices also have a Compact Flash CF slot into which you can plug a storage card that uses flash memory. The memory in these cards is available solely to extend the file system; it does not extend the available program execution space. Two basic types of support can be provided by a given Windows CE implementation. Devices running Windows CE 2.

The same level of support is also provided on the newer Windows CE 3. The other two are local servers and remote servers. A local server resides on the same computer as its client, except that it runs in a different address space. A remote server runs on a different computer entirely. Windows CE 3. This is a slightly different packaging than may be familiar to you from desktop versions of Windows, where DCOM typically refers just to support for remote servers and not local servers.

The difference is probably an accident of history. On the desktop, support for in-process servers and for local servers was introduced at the same time. Support for remote servers came much later. The other two types are only now being made available with Windows CE 3.

Like on the desktop, a Windows CE-based system can have a graphical output screen and provide pretty much the same set of user interface objects. A key difference is that Windows CE-based devices tend to have much smaller display screens. So while a typical desktop runs with a minimum resolution of x, the Pocket PC ships with a sideways quarter VGA x screen. Windows CE provides a handful of user interface helpers, including common dialog boxes although only four of the eight found on the desktop are present and common controls.

With the common controls, only a subset of what you have on the desktop is present. The concept of paging in Virtual Memory is used with narrower sense, only the process of mapping the virtual addresses to physical ones are taken. In the other incorrect meaning it is used synonymously for swapping. Swapping is the outsourcing of real RAM memory area to another, secondary storage, typically in a swap file on a disk by the operating system.

The idea that in typical computers the hard drive is considerably greater than the available electronic memory RAM. This memory can also be used to service memory requests of programs. Memory requests from programs that go beyond the available RAM, then served on memory from the swap space up to the maximum size of virtual memory per process. The disadvantage is that the paged memory to disk is much slower than RAM. However, still this makes the operation of the program. Low memory error message on Windows CE devices How can the device get more storage memory and less program memory?

Select the Memory tab. Adjust the slider to the left to allocate more Program memory reducing Storage memory or to the right increasing the Storage memory while reducing Program memory. Tap OK to save. Warm boot the device for the change to take effect.

The value can be modified by adding a registry key as a. Please provide additional comments. Thank you for your feedback! Don't see what you're looking for?