include v86mmgr.inc VxDcall V86MMGR_SetLocalA20
Changes the default global behavior of A20 to local if the HMA is global. This service has no effect if the HMA is not global. This service is only available for Windows version 3.1 and later. Uses Flags.
When there is a global HMA user, the A20 state associated with the HMA is also global. Changing A20 in a virtual machine changes it in all virtual machines simultaneously. Some global A20 users (such as MS-DOS 5.0) desire that the A20 state be local, even though the HMA is global.
The V86MMGR device does a V86 Interrupt 2Fh device broadcast which also can set this state. This service is effectively a duplicate of the broadcast service which can be called by a virtual device. It is not an error if the state is set using both methods.
This service cannot be called after the Init_Complete system control message is processed, which occurs before the first VM is created. Essentially, this limits the use of this service to the Device_Initialization section of VxDs, and to static VxDs only (no dynamically loaded VxDs).