a) The CS:IP in the real
mode register data structure specifies the address of the real mode procedure
to call.
b) If the SS:SP fields
in the real mode register data structure are zero, a real mode stack will
be provided by the DPMI host. Otherwise, the real mode SS:SP will be set
to the specified values before the interrupt handler is called.
c) The flags specified
in the real mode register data structure will be pushed on the real mode
stack's IRET frame. The procedure will be called with the interrupt and
trace flags clear.
d) Values placed in the
segment register positions of the data structure must be valid for real
mode; ie the values must be paragraph addresses and not selectors.
e) All general register
fields in the data structure are DWORDs so that 32-bit registers can be
passed to real mode.
f) The target real mode
handler or procedure must return with the stack in the same state as when
it was called. This means that the real mode code may switch stacks while
it is running, but must return on the same stack that it was called on
and must return with an IRET or discard the flags from the stack with a
RETF(2) .
g) When this function
returns, the real mode register data structure will contain the values
that were returned by the real mode procedure. The CS:IP and SS:SP values
will be unmodified in the register data structure.
h) It is the caller's
responsibility to remove any parameters that were pushed on the protected
mode stack.