Function 0306 - Get Raw Mode Switch Addresses

Previous: Function 0305 - Get State Save/Restore Addresses

- 7.2.27 -

PMODE/W MSDOS Extender

PMODE/W Supported DPMI INT 31h functions

Function 0306 - Get Raw Mode Switch Addresses

PMODE/W API

This function Returns addresses that can be called for low level mode switching.

In:
   AX     = 0306h
Out:
   always successful:
     carry flag clear
     BX:CX  = segment:offset of real to protected mode
              switch procedure
     SI:EDI = selector:offset of protected to real mode
              switch procedure

Notes:
The real mode segment:offset returned by this function should be called only in real mode to switch to protected mode. The protected mode selector:offset returned by this function should be called only in protected mode to switch to real mode.

The mode switch procedures are entered by a FAR JMP to the appropriate address with the following parameters:

   AX    = new DS
   CX    = new ES
   DX    = new SS
   (E)BX = new (E)SP
   SI    = new CS
   (E)DI = new (E)IP

The processor is placed into the desired mode, and the DS, ES, SS, (E)SP, CS, and (E)IP registers are updated with the specific values. In other words, execution of the client continues in the requested mode at the address provided in registers SI:(E)DI. The values specified to be placed into the segment registers must be appropriate for the destination mode. That is, segment addresses for real mode, and selectors for protected mode.

The values in EAX, EBX, ECX, EDX, ESI, and EDI after the mode switch are undefined. EBP will be preserved across the mode switch call so it can be used as a pointer. FS and GS will contain zero after the mode switch.

If interrupts are disabled when the mode switch procedure is invoked, they will not be re-enabled by the host (even temporarily). It is up to the client to save and restore the state of the task when using this function to switch modes. This requires the state save/restore procedures whose addresses can be obtained with INT 31h function 0305h.


Function 0305 - Get State Save/Restore Addresses	Table of Content	Function 0400 - Get Version

- 7.2.27 -