Function 0300 - Simulate Real Mode Interrupt

Previous: Function 0205 - Set Protected Mode Interrupt Vector

Next: Function 0301 - Call Real Mode Procedure With Far Return Frame

- 7.2.21 -

PMODE/W MSDOS Extender

PMODE/W Supported DPMI INT 31h functions

Function 0300 - Simulate Real Mode Interrupt

PMODE/W API

This function Simulates an interrupt in real mode. The function transfers control to the address specified by the real mode interrupt vector. The real mode handler must return by executing an IRET.

In:
   AX     = 0300h
   BL     = interrupt number
   BH     = must be 0
   CX     = number of words to copy from the protected
            mode stack to the real mode stack
   ES:EDI = selector:offset of real mode register data
            structure in the following format:

   Offset    Length  Contents
     00h      4        EDI
     04h      4        ESI
     08h      4        EBP
     0ch      4        reserved, ignored
     10h      4        EBX
     14h      4        EDX
     18h      4        ECX
     1ch      4        EAX
     20h      2        CPU status flags
     22h      2        ES
     24h      2        DS
     26h      2        FS
     28h      2        GS
     2ah      2        IP (reserved, ignored)
     2ch      2        CS (reserved, ignored)
     2eh      2        SP
     30h      2        SS
Out:
   if successful:
     carry flag clear
     ES:EDI = selector offset of modified real mode register
              data structure
   if failed:
     carry flag set

Notes:
The CS:IP in the real mode register data structure is ignored by this function. The appropriate interrupt handler will be called based on the value passed in BL.

If the SS:SP fields in the real mode register data structure are zero, a real mode stack will be provided by the host. Otherwise the real mode SS:SP will be set to the specified values before the interrupt handler is called.

The flags specified in the real mode register data structure will be put on the real mode interrupt handler's IRET frame. The interrupt handler will be called with the interrupt and trace flags clear.

Values placed in the segment register positions of the data structure must be valid for real mode. That is, the values must be paragraph addresses, not protected mode selectors.

The target real mode handler 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.

When this function returns, the real mode register data structure will contain the values that were returned by the real mode interrupt handler. The CS:IP and SS:SP values will be unmodified in the data structure.

It is the caller's responsibility to remove any parameters that were pushed on the protected mode stack.


Function 0205 - Set Protected Mode Interrupt Vector	Table of Content	Function 0301 - Call Real Mode Procedure With Far Return Frame

- 7.2.21 -