Int 31H Function 0305H
Get State Save/Restore Addresses
Returns the addresses of two procedures used to save and restore the
state of the current task's registers in the mode which is not
AX = 0305H
Carry flag = clear (this function always succeeds)
AX = size of buffer in bytes required to save state
BX:CX = real mode address of routine used to
SI:(E)DI = protected mode address of routine used to
- The real mode address returned by this function in BX:CX
is called only in real mode to save/restore the state of
the protected mode registers. The protected mode address
returned by this function in SI:(E)DI is called only in
protected mode to save/restore the state of the real mode
registers; 16-bit programs should call the address in
SI:DI, 32-bit programs should call the address in SI:EDI.
Registers for the current mode can be saved by simply
pushing them on the stack.
- Both of the state-save procedures are entered by a FAR
CALL with the following parameters:
AL = 0 to save state, or 1 to restore state
ES:(E)DI = (selector or segment):offset of state-save buffer
The state-save buffer must be at least as large as the value returned
in AX by Int 31H Function 0305H. The state save/restore
procedures do not modify any registers. For a further
discussion of use of the state save/restore procedures,
see that page.
- Some DPMI hosts will not require the state to be saved,
indicating this by returning a buffer size of zero in AX.
In such cases, the addresses returned by this function
can still be called, although they will simply return
without performing any useful function.
- Clients do not need to call the state save/restore procedures
before using Int 31H Functions 0300H, 0301H, or 0302H. The
state save/restore procedures are provided specifically for clients
that use the raw mode switch services.
- A client can use the function to save its state in the destination
mode before switching modes using the raw mode switch or issuing
real-mode calls from a protected mode hardware interrupt
handler. Refer to that page for the
detailed information on stacks and mode switching.