Embedded Pentium® Processor-Based POS Terminal Sample Design

Whether or not a given type of device driver is built-in or installable is pre-determined by the MDD/OS interface defined by Microsoft for that type of device. For built-in drivers, Microsoft has defined a set of custom MDD/OS interfaces. For installable drivers, Microsoft has defined a set of common MDD/OS interfaces.

Note: Windows CE device drivers implementation is not required as MDD and PDD components. They may be implemented as a single, monolithic entity providing that the MDD/OS interface, as defined by Microsoft for a given device, is used. See Figure 2.

Figure 7. Device Driver Architecture

9.3Interaction with Application Software

Installable device drivers are viewed as a special file in the file system by the application software. The interface exposed to the application corresponds to the standard Win32 file I/O functions such as OpenFile, ReadFile, DeviceIOControl, and others. The file system recognizes filenames as being special devices when they consist of exactly three uppercase letters, a single digit, and a colon ( : ). An example of this would be “COM1:”, which references the first serial port available on the platform.

Built-in device drivers are accessed by application software using API calls that Microsoft has implemented in the Windows CE operating system for each device.

9.4Incorporating Device Drivers

To include drivers in the Windows CE image, first take the compiled driver or file and place it in the following directory:

%_WINCEROOT%\public\maxall\files