Get State Save/Restore Addresses

Call With

AX = 0305H

Returns

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 save/restore state
SI:(E)DI = protected mode address of routine used to save/restore state

Notes

• 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.