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Table of Contents
7. PMODE/W MSDOS Extender
7.2. PMODE/W Supported DPMI INT 31h functions
7.2.22. Function 0301 - Call Real Mode Procedure With Far Return Frame
7.2.22. Function 0301 - Call Real Mode Procedure
With Far Return Frame
This function Simulates a FAR CALL to a real mode procedure. The called
procedure must return by executing a RETF instruction.
AX = 0301h
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
2ch 2 CS
2eh 2 SP
30h 2 SS
carry flag clear
ES:EDI = selector offset of modified real mode register
carry flag set
The CS:IP in the real mode register data structure specifies the address of the
real mode procedure to call.
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 procedure is called.
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 procedure 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 a RETF and should not clear the stack of any parameters
that were passed to it on the stack.
When this function returns, the real mode register data structure will contain
the values that were returned by the real mode procedure. 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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