Interrupt 2Fh Function 4310h Get HIMEM.SYS Entry-Point Address

mov ax, 4310h ;Get HIMEM.SYS Entry-Point Address

int 2Fh ;Multiplex Interrupt

mov word ptr [XMMAddr], bx

mov word ptr [XMMAddr+2], es ;es:bx contains entry-point address

Get HIMEM.SYS Entry-Point Address (Interrupt 2Fh Function 4310h) returns the 32-bit address (segment:offset) of the entry point for the extended-memory-management functions for HIMEM.SYS.

Parameters

This function has no parameters.

Return Value

The ES:BX registers contain the 32-bit address (segment:offset) of the entry point.

Comments

Before retrieving and calling this entry point, programs must use Get HIMEM.SYS Installed State (Interrupt 2Fh Function 4300h) to ensure that HIMEM.SYS has been loaded.

The extended-memory-management functions enable programs to manage extended memory, the high memory area (HMA), and upper memory blocks (UMBs). Programs also use the functions to enable and disable the A20 address line. A program calls a function by placing the function number in the AH register, filling other registers as needed, and calling the entry point. Following is a list of the extended-memory-management functions:

Number

Name

00h	Get XMS Version
01h	Allocate HMA
02h	Free HMA
03h	Global Enable A20 Line
04h	Global Disable A20 Line
05h	Local Enable A20 Line
06h	Local Disable A20 Line
07h	Query A20 Line Status
08h	Query Free Extended Memory
09h	Allocate EMB
0Ah	Free EMB
0Bh	Move EMB
0Ch	Lock EMB
0Dh	Unlock EMB
0Eh	Get Handle Information
0Fh	Resize EMB
10h	Allocate UMB
11h	Free UMB

A full description of these functions is beyond the scope of this book. For more information about them, see the Lotus/Intel/Microsoft/AST eXtended Memory Specification (XMS) version 2.0.

Programs must not use extended-memory-management functions to manage the HMA or UMBs if MS-DOS already manages these areas.

This function returns the entry-point address of any extended-memory manager as long as the manager conforms to the eXtended Memory Specification.