Get and Disable Virtual Interrupt State

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

Call With

AX = 0900H

Returns

Virtual interrupts disabled
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 0901H.
A client that does not need to know the prior interrupt state can execute the CLI instruction rather than calling this function. The instruction may be trapped by the host and should be assumed to be very slow.