The Xilinx® Embedded Development Kit (EDK) enables you to create powerful embedded processor systems, as well as the complex applications running on them. These applications may need to perform numerous tasks and access a wide range of peripherals, such as memory controllers, display interfaces, and network interface cards. It is difficult, expensive, and inefficient to design such large applications from scratch, especially when existing software modules are capable of meeting some or all of your system’s goals.

Integrating these modules with your application, however, can sometimes prove to be more difficult than writing equivalent modules yourself. Luckily, Xilinx Platform Studio (XPS) provides a standard interface, known as the microprocessor library definition (MLD) interface, to facilitate adding such modules to your projects. Operating systems and other software modules adhering to this interface can conveniently be configured for your application from within XPS. Micrium has adapted many of its software modules to the MLD interface, allowing you to quickly and easily add high-quality, well-documented modules to your embedded applications.

The MLD Format Each Micrium software module that can be configured using XPS has an MLD file defining that module’s configurable parameters. Generally, configurable parameters correspond to features and services that will comprise the compiled module. These parameters can also be used to identify the hardware components that the module will utilize. For example, the MLD file for a graphical user interface (GUI) module might define parameters stipulating the colors and resolutions supported by the compiled module, as well as a parameter indicating the memory-mapped location of the display controller used by the module. You would be able to configure these parameters from the Software Platform Settings dialog box in XPS, tailoring modules as needed to create a suitable software platform for nearly any application.

Once you have configured a software platform, you can build it with Library Generator (LibGen), a utility that is automatically invoked when a project is compiled in XPS. LibGen is responsible for building software modules according to the parameter values set forth in XPS, and it uses Tool Command Language (Tcl) files to meet this objective. Tcl files, which are provided with each Micrium software module that complies with the MLD interface, contain functions that are able to access the parameter values you specify. These functions are called by LibGen, and they normally generate source and header files that allow the module to be built as per the requirements of the application.

The specific role that Tcl and MLD files play in the process of configuring and building software modules can be better understood by examining one of Micrium’s software modules, ìC/OS-II, The Real-Time Kernel. ìC/OS-II is a popular realtime operating system (RTOS) that has been proven effective in hundreds of products. The module’s clean and consistent source code, which is certifiable for use in systems deemed safety-critical by the FAA and FDA, is described in “MicroC/OS-II, The Real-Time Kernel,” by Jean Labrosse. This book describes ìC/OS-II’s efficient implementation of semaphores, message timers, and other standard operating system services.

As Labrosse’s book explains, ìC/OS-II’s services are normally configured by manipulating constants in a header file, os_cfg.h. The MLD interface eliminates the need to manually edit this file, instead letting you configure the operating system from XPS’s Software Platform Settings dialog box, as shown in Figure 1. The contents of this dialog box are determined by ìC/OS-II’s MLD file, which defines configurable parameters representing the constants normally found in os_cfg.h. Because ìC/OS II’s Tcl file has access to the values specified for each of these configurable parameters, it can generate os_cfg.h whenever LibGen is run. This automatic generation of the configuration file gives you a custom version of ìC/OS-II each time you build your project, making the operating system instantly amendable to the changing needs of an application.

An Example Application
Although the benefits of the MLD interface are apparent even when considering a single module like ìC/OS-II, they are more pronounced in a large, multi-faceted application such as a Web server. A Web server has many responsibilities, and from a design perspective, it is convenient to view each of these responsibilities as a separate component, as depicted in Figure 2. Once an application has been logically divided in this manner, you can choose software modules to implement each component.

A Web server might, for example, use modules to handle the various protocols, such as HTTP and TCP, involved in serving Web pages. It might also take advantage of a module capable of interqueues, facing with a storage device, allowing Web pages to be saved as files. The Web server could rely on an RTOS to coordinate the tasks performed by each of these modules.

The use of these types of software modules as “building blocks” for constructing large applications, such as Web servers, significantly reduces the time and effort needed to develop such applications, provided that you can easily incorporate the modules in your design. Many software modules, though, are unwieldy, and they introduce unnecessary complexities into projects that use them. Our example Web server could encompass hundreds of source files, requiring the inclusion of a comparable amount of header files. Adding these files to an application in XPS would result in a cumbersome project, teeming with files that shouldn’t be of concern to application developers. To avoid such a confusing muddle of files, you could create an object code library, but this would force you to learn the compilation procedures for several software modules, and the resultant library would have to be rebuilt for different configurations and versions of the modules.

The MLD interface obscures these compilation details, resulting in organized and efficient applications running on highly configurable software platforms. A Web server designed on such a platform would be outwardly simple, with the multitude of files composing the server’s modules invisible to designers. The Web server would appear to consist only of the files directly implicated in the application’s primary task of serving Web pages, so it could be debugged quickly, even by developers unfamiliar with the project and its modules. Updating or revising the Web server would be similarly painless, because well-documented and dependable software modules, such as those provided by Micrium, could be added to the application without needing to understand the mechanics of configuring and compiling the modules.

The Micrium Software Modules
Micrium’s software modules are readily adaptable to most applications. The process of adding such high-quality software to a project is expedited in XPS, as Micrium offers an assortment of modules that comply with the MLD interface. You can add any of these modules to a project by using the Software Platform Settings dialog box, as shown in Figure 3. This dialog box gives you the ability to rapidly deploy practical software platforms to support complex applications, including Web servers. In fact, you can construct a Web server entirely of software from Micrium simply by specifying the appropriate modules in XPS.

The centerpiece of such a Web server would be ìC/TCP-IP, Micrium’s TCP/IP protocol stack. ìC/TCP-IP was meticulously developed using stringent coding standards. The module’s completely original design, which was not derived from any existing protocol stacks, supports an extensive array of network options that are presented to XPS users, along with a selection of useful add-on modules. You can use these modules in conjunction with ìC/TCP-IP to accommodate the needs of a variety of applications. At least one such module, ìC/HTTPs (which offers a consistent means of serving Web pages), would be an integral part of a Web server based on Micrium’s modules.

Another key component of a Micrium Web server would be ìC/FS, Micrium’s embedded file system. ìC/FS is a compact and versatile module, with an API similar to that available from the standard C library. The files accessed through this API can reside on storage devices implementing any of the numerous formats that ìC/FS recognizes, including CompactFlash, Secure Digital (SD), and SmartMedia. The files themselves can also be of varying formats, because ìC/FS is compatible with both the Microsoft FAT file system and a proprietary file system. Support for either of these formats is one of the many features reflected in the module’s MLD file, allowing ìC/FS, like Micrium’s other modules, to be configured in XPS and seamlessly included in a Web server or any other application.

Conclusion
By offering a convenient way of configuring useful software modules, such as ìC/FS, ìC/TCP-IP, and ìC/OS-II, the MLD interface accelerates the process of constructing complex applications from these embedded building blocks. The benefits afforded by the interface may be unintentionally relinquished, however, if poorly documented, unreliable modules are selected.

To avoid the headaches that can result from the use of such modules, you should choose dependable and easy-to-use modules. Micrium’s software modules complement the valuable tools provided with the EDK, enabling the efficient development of powerful applications.

For more information about Micrium’s modules, please visit www.micrium.com/microblaze/.

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