Introduction to Virtual Device Drivers



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VXDS
Sys_Critical_Exit

This is the last message sent to a virtual device. Interrupts are disabled and the Simulate_Int and Exec_Int services are not available. Virtual devices should reset their associated hardware device to ensure a trouble-free return to real mode.

Sys_Critical_Init

This is the first message a virtual device receives. Interrupts are not yet enabled, so the virtual device should carry out its tasks as quickly as possible. Most virtual devices do the following:

 Install and initialize any functions needed to support hardware interrupts from the device and software interrupts from the VMM or other virtual devices.

 Claim for exclusive use any V86-mode memory pages needed for the device. For example, the virtual display device claims the video memory.

 Initialize any data needed by the virtual device's services. This may include reading settings from the SYSTEM.INI file.



While processing this message, the Simulate_Int and Exec_Int services must not be used.

Sys_VM_Init

A virtual device receives this message after the Init_Complete message. The virtual device should initialize the state of the hardware and software in the system virtual machine. If the virtual device sets the carry flag and returns, the VMM terminates all further processing and exits Windows.


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