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====== Int 31H, AH=03H, AL=05H ======

===== Version =====

0.9

===== Brief =====

Get State Save/Restore Addresses

===== Input =====

  AX = 0305H

===== Return =====

  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 =====

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 currently executing. 

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.
       
===== See also =====

   

===== Note =====

Text based on [[http://www.delorie.com/djgpp/doc/dpmi/]]

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