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VIRTUAL DEVICE INITIALIZATION

The VMM initializes a virtual device by doing the following:

1. Loads the real-mode initialization segment and calls the real-mode initialization
procedure. The procedure can prevent the virtual device from being loaded, prevent
Windows from starting, specify instance data for the device, and select pages in
memory for its exclusive use.

2. Loads the rest of the virtual device segments in32-bit, flat-model protected-mode
memory and discards the real-mode initialization segment.

3. Sends a Sys_Critical_Init message to the virtual device conrtol procedure. Hardware interrupts
are enabled, so the virtual devices should spent as little time as possible
initializing itself.

4. Sends a Device_Init message to the device control procedure. Hardware interrupts
are enabled, so the virtual device must be prepared to manage interrupts from its own
device.

5. Sends a Init_Complete message to the device control procedure.

6. Discards the initialization code and data segments, freeing this memory for other uses.
The virtual device must not attempt to access the procedures and data in these
segments after it has processed the Init_Complete message.

At any time during initialization, a virtual device can set the carry flag and return to the 
VMM to prevent the virtual device from loading. Some VMM services, such as  the
Initialization Information services, are available only during initialization.

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