GetSet_HMA_Info

include vmm.inc

mov     ecx, Action         ; zero to get, nonzero to set
mov     dx, A20Enable       ; A20 enable count (if ecx is nonzero)
VMMCall GetSet_HMA_Info

mov     [NoGlobalHMA], eax  ; nonzero if no global HMA user
mov     [XMSCallAddr], ecx  ; loader XMS call address
mov     [A20Enable], edx    ; A20 enable count before Windows started

Gets and sets information related to the high-memory area (HMA) region. This service is always valid (not restricted to initialization). Uses EAX, ECX, EDX, Flags.

Returns the following information in the following registers:

Register	Description
EAX	Specifies whether a global HMA user is present. If this register is 0, Windows did not allocate the HMA meaning either there is a global HMA user or there is no HMA. If this register is nonzero, Windows has allocated the HMA, meaning there is no global HMA user.
ECX	Specifies the V86-mode address (segment:offset) that Windows used to call the XMS driver when loading. The segment address is in the high 16 bits of the register.
EDX	Specifies the A20 enable count before Windows started.

Action: Value specifying whether to get or set information. If zero, the service gets the HMA information; otherwise it sets the information.
A20Enable: A20 enable count to set for the Windows VMM loader. The service uses this parameter only if the Action parameter is nonzero.

This service lets the XMS driver (in the V86MMGR device) determine whether a global HMA user existed before Windows started and gives the driver access to the HMA enable count. Other devices should not call this service.

The global HMA flag and loader XMS call address cannot be set.