Intel Extensible Firmware Interface - Manual (Page 60)

Extensible Firmware Interface Specification
2-20 12/01/02 Version 1.10
2.5.2 Driver Initialization
The file for a driver image must be loaded from some type of media. This could include ROM,
FLASH, hard drives, floppy drives, CD-ROM, or even a network connection. Once a driver image
has been found, it can be loaded into system memory with the boot service
LoadImage() .
LoadImage() loads a PE/COFF formatted image into system memory. A handle is created for
the driver, and a Loaded Image Protocol instance is placed on that handle. A handle that contains a
Loaded Image Protocol instance is called an Image Handle. At this point, the driver has not been
started. It is just sitting in memory waiting to be started. Figure 2-7 shows the state of an image
handle for a driver after
LoadImage() has been called.
Image Handle
EFI_LOADED_IMAGE_PROTOCOL
OM13148
Figure 2-7. Image Handle
After a driver has been loaded with the boot service LoadImage() , it must be started with the
boot service StartImage() . This is true of all types of EFI Applications and EFI Drivers that
can be loaded and started on an EFI-compliant system. The entry point for a driver that follows the
EFI Driver Model must follow some strict rules. First, it is not allowed to touch any hardware.
Instead, the driver is only allowed to install protocol instances onto its own Image Handle. A
driver that follows the EFI Driver Model is required to install an instance of the Driver Binding
Protocol onto its own Image Handle. It may optionally install the Driver Configuration Protocol,
the Driver Diagnostics Protocol, or the Component Name Protocol. In addition, if a driver wishes
to be unloadable it may optionally update the Loaded Image Protocol to provide its own
Unload() function. Finally, if a driver needs to perform any special operations when the boot
service ExitBootServices() is called, it may optionally create an event with a notification
function that is triggered when the boot service ExitBootServices() is called. An Image
Handle that contains a Driver Binding Protocol instance is known as a Driver Image Handle.
Figure 2-8 shows a possible configuration for the Image Handle from Figure 2-7 after the boot
service
StartImage() has been called.