VDH Functions

The following list summarizes most of the VDH functions:

VDH API

Description

Reserve memory for stub DOS device driver

Allocate small buffers

Allocate linear space and commit backing storage

Used to catch return from a VDHPushFarCall

Receive control when current DOS session enables simulated interrupts

Clear interrupt request flag

Used to protect global structures

Terminate communication between virtual device driver and physical device driver

Used by the EMM copy service and to copy device driver stub to VDM

Used by the EMM exchange service

Find a region of free linear space below 1MB + 64KB

Deallocate small buffers

Deallocate memory objects

Read and clear dirty-page bits (Dirty bits indicate whether a page has been written to)

Install hook for page faults

Used to hook INT 67h (EMS interrupt)

Register to get notification about VDM creation and termination

Verifies that a specified memory region is available and locks it

Used to map EMS windows to EMS objects or to unmap pages

Resets VDHPostIdle

Establish communication between virtual device driver and physical device driver

Returns an IRQ handle for use with the other VPIC services

Remove ROM return address from user's CS:IP

Put VDM into sleeping state.

Used by the EMM map and call service

Change control to the V86-interrupt handler

Used to retrieve configuration data strings

Determine amount of free virtual memory

Determine VDM conventional memory size

Change previous page allocation

Used to protect global data

Requests the operation of a VDD

Reserve region of linear space below 1MB + 64KB

Register DOS device driver

Set interrupt request flag

Unreserve region of linear space below 1MB + 64KB

Awake VDM from sleeping state

Yield the processor to any other thread of equal or higher priority

These functions are only valid when issued from within a module executing at privilege level 0; they cannot be issued by normal protected mode application processes.