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Table of Contents
7. PMODE/W MSDOS Extender
7.2. PMODE/W Supported DPMI INT 31h functions
7.2.21. Function 0300 - Simulate Real Mode Interrupt
7.2.21. 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.
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