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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 |
The GetSet_HMA_Info service returns, and sets information related to the high-memory area (HMA) region.
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.
This service is always valid (not restricted to initialization).
Action
Specifies whether to get or set information. If this parameter is zero, the service returns HMA information. Otherwise, it sets the information.
A20Enable
Specifies the A20 enable count to set for the Windows VMM loader. The service uses this parameter only if the Action parameter is nonzero.
The EAX, ECX, and EDX registers contain the following HMA information:
| 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. |
The global HMA flag and loader XMS call address cannot be set.
EAX, ECX, EDX, Flags