Get and Enable Virtual Interrupt State

Enables the virtual interrupt flag and returns the previous state of the virtual interrupt flag.

Call With

AX = 0901H

Returns

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

Notes

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.