Nicolas Besson - Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Device Driver Load Procedure<\/p> <\/div>

Whether you load a device driver statically or dynamically, the ActivateDeviceEx function is always involved. A dedicated driver named the Bus Enumerator (BusEnum) calls ActivateDeviceEx for every driver registered under HKEY_LOCAL_MACHINE\Drivers\BuiltIn just as you can call ActivateDeviceEx directly, passing in an alternate registry path for the driver settings in the lpszDevKey parameter.<\/p>

Device Manager uses the following procedure to load device drivers at boot time:<\/p>

1. Device Manager reads the HKEY_LOCAL_MACHINE\Drivers\RootKey entry to determine the location of the device driver entries in the registry. The default value of the RootKey entry is Drivers\BuiltIn.<\/p>

2. Device Manager reads the Dll registry value at the location specified in the RootKey location (HKEY_LOCAL_MACHINE\Drivers\BuiltIn) to determine the enumerator DLL to load. By default, this is the bus enumerator (BusEnum.dll). The bus enumerator is a stream driver that exports the Init and Deinit functions.<\/p>

3. The bus enumerator runs at startup to scan the RootKey registry location for subkeys that refer to additional buses and devices. It can be run again later with a different RootKey to load more drivers. The bus enumerator examines the Order value in each subkey to determine the load order.<\/p>

4. Starting with the lowest Order values, the bus enumerator iterates through the subkeys and calls ActivateDeviceEx passing in the current driver's registry path (that is, HKEY_LOCAL_MACHINE\Drivers\BuiltIn\< DriverName<\/em> >).<\/p>

5. ActivateDeviceEx loads the driver DLL registered in the DLL value located in the driver's subkey, and then creates a subkey for the driver under the HKEY_LOCAL_MACHINE\Drivers\Active registry key to keep track of all currently loaded drivers.<\/p>

Figure 6-4 shows a typical registration under the HKEY_LOCAL_MACHINE\Drivers\BuiltIn registry key for an audio device driver.<\/p>

Registry Settings to Load Device Drivers<\/p> <\/div>

If you use ActivateDeviceEx to load your driver dynamically, you are not required to place the driver's registry settings in a subkey under HKEY_LOCAL_MACHINE\Drivers\BuiltIn. You can use an arbitrary path, such as HKEY_LOCAL_MACHINE\SampleDriver. However, the registry values for the driver are the same in both cases. Table 6-3 lists general registry entries that you can specify for a device driver in the driver's registry subkey (see Figure 6-4 for sample values).<\/p>

Table 6-3 General registry entries for device drivers<\/strong> <\/p>