Note: This API calls are shared between DOS and Win16 personality.
DOSX is a specialized version of DPMI. Windows standard and extended mode kernel is a DPMI client app. Standard and extended mode kernel differs minimally and shares common codebase. Standard mode is just DPMI client, exnhanced mode is DPMI client running under Virtual Machime Manager. Both modes shares DPMI interface for kernel communication. The OS/2 virtual DOS Protected Mode Interface (VDPMI) device driver provides Version 0.9 DPMI support for virtual DOS machines. Win16 provides Version 1.0 DPMI support, but reported as 0.9.
Int 31H, AH=09H, AL=01H
Get and Enable Virtual Interrupt State
AX = 0901H
Virtual interrupts enabled Carry flag = clear (this function always succeeds) AL = 0 if virtual interrupts were previously disabled AL = 1 if virtual interrupts were previously enabled
Enables the virtual interrupt flag and returns the previous state of the virtual interrupt flag.
AH is not changed by this function. Therefore, the previous state can be restored by simply executing another Int 31H. See Int 31H Function 0900H.
A client that does not need to know the prior interrupt state can execute the STI instruction rather than calling this function. The instruction may be trapped by the host and should be assumed to be very slow.
Text based on http://www.delorie.com/djgpp/doc/dpmi/