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READ THIS FIRST
The Lotus/Intel/Microsoft Expanded Memory Specification changes
from time to time, so you should contact Intel occasionally to
ensure that you are using the most recent version.
You can reach us at one of our Customer Support numbers.
o If you live in the continental United States but outside
Oregon, call (800) 538-3373.
o If you live in Oregon, Hawaii, Alaska, or outside the
continental United States, call (503) 629-7354.
o If you live in Canada, call (800) 234-0444.
Customer Support representatives are ready to answer your call
Monday through Friday, from 7 a.m. to 5 p.m. Pacific time.
THE LOTUS(R)/INTEL(R)/MICROSOFT(R)
EXPANDED MEMORY SPECIFICATION
Version 3.20
Part number: 300275-003
September, 1985
Copyright (c) 1985
Lotus Development Corporation, 55 Cambridge Ave., Cambridge, MA
02142
Intel Corporation, 3065 Bowers Ave., Santa Clara, CA 95051
Microsoft Corporation, 10700 Northup Way, Bellevue, WA 98009
ii 300275-003
Note: This specification was jointly developed by Lotus
Development Corporation, Intel Corporation, and Microsoft
Corporation. Although it has been released into the public
domain and is not confidential or proprietary, the specification
is still the copyright and property of Lotus Development
Corporation, Intel Corporation, and Microsoft Corporation.
DISCLAIMER OF WARRANTY
LOTUS DEVELOPMENT CORPORATION, INTEL CORPORATION, AND MICROSOFT
CORPORATION EXCLUDE ANY AND ALL IMPLIED WARRANTIES, INCLUDING
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE. NEITHER LOTUS NOR INTEL NOR MICROSOFT MAKE ANY WARRANTY
OF REPRESENTATION, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO
THIS SPECIFICATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR
FITNESS FOR A PARTICULAR PURPOSE. NEITHER LOTUS NOR INTEL NOR
MICROSOFT SHALL HAVE ANY LIABILITY FOR SPECIAL, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES ARISING OUT OF OR RESULTING FROM THE USE OR
MODIFICATION OF THIS SPECIFICATION.
300275-003 iii
How to use this specification
If you're already familiar with the concept of expanded memory or
if you're interested in only parts of the spec reading this
preface can save you time. It gives a brief summary of each
chapter so you can decide what you need to read.
Chapter 1 -- Introduction to expanded memory
This chapter introduces the concept of expanded memory and
discusses the following topics:
o Memory addressing capabilities of the Intel 8086, 8088, and
80286 microprocessors
o Accessing expanded memory
o Frequently used terminology
You can skip this chapter if you're already familiar with the
Intel 8086, 8088, and 80286 microprocessors and you understand
expanded memory.
Chapter 2 -- Writing programs that use expanded memory
This chapter provides guidelines to help you create programs that
use expanded memory. It also describes the individual Expanded
Memory Manager (EMM) functions in detail, with assembly language
examples, parameter passing conventions, and an explanation of
the status and results returned by the function.
You should read this chapter if you want to write programs that
use expanded memory.
Chapter 3 -- Testing for the presence of the Expanded Memory
Manager
This chapter describes two methods your program can use to test
for the presence of the EMM. You should read this chapter if you
want to write programs that use expanded memory.
Chapter 4 -- Example expanded memory programs
This chapter presents examples of expanded memory programs.
iv 300275-003
Glossary
The Glossary defines some of the terms that are used frequently
in this specification. Most of the terms are defined for readers
who understand technical terminology and are familiar with IBM
PCs, XTs, and ATs, or compatibles.
300275-003 v
Contents
How to use this specification
Chapter 1 -- Introduction
The Intel 8086 and 8088 microprocessors......................1-1
The Intel 80286 microprocessor...............................1-1
How expanded memory is accessed..............................1-1
Limitations of the 8086, 8088, and 80286 microprocessors.....1-2
Terminology..................................................1-2
Chapter 2 -- Writing programs that use expanded memory
Designing your program.......................................2-1
The operating environment..................................2-1
Mechanics of the EMM.......................................2-1
Programming guidelines.....................................2-2
The EMM functions............................................2-3
Overview of the EMM functions..............................2-3
FUNCTION 1 -- Get status...................................2-5
FUNCTION 2 -- Get page frame address.......................2-6
FUNCTION 3 -- Get unallocated page count...................2-7
FUNCTION 4 -- Allocate pages...............................2-9
FUNCTION 5 -- Map handle pages.............................2-11
FUNCTION 6 -- Deallocate pages.............................2-13
FUNCTION 7 -- Get EMM version..............................2-15
FUNCTION 8 -- Save page map................................2-16
FUNCTION 9 -- Restore page map.............................2-18
FUNCTION 10 -- Reserved....................................2-20
FUNCTION 11 -- Reserved....................................2-21
FUNCTION 12 -- Get EMM handle count........................2-22
FUNCTION 13 -- Get EMM handle pages........................2-23
FUNCTION 14 -- Get all EMM handle pages....................2-25
FUNCTION 15 -- Get/set page map............................2-27
Summary of status codes......................................2-33
Chapter 3 -- Testing for presence of the manager
Which method should my program use?..........................3-1
The "open handle" technique..................................3-1
Using the "open handle" technique..........................3-1
An example of the "open handle" technique..................3-4
vi 300275-003
The "get interrupt vector" technique.........................3-6
Using the "get interrupt vector" technique.................3-6
An example of the "get interrupt vector" technique.........3-7
Chapter 4 -- Example expanded memory programs
Characteristics of the example procedures....................4-1
Transient application program................................4-1
Flow chart of a transient application program..............4-1
Explanation of the transient application program
flow chart.................................................4-2
Initialization procedures................................4-2
Processing procedures....................................4-3
Terminating procedures...................................4-3
Resident application program.................................4-3
Flow chart of a resident application program...............4-4
Explanation of the resident application program
flow chart.................................................4-5
Initializing the resident program and the EMM............4-5
Saving the current state of the CPU......................4-6
Resident processing performed before accessing
expanded memory..........................................4-6
Saving the state of the expanded memory hardware.........4-6
Accessing expanded memory................................4-6
Restoring the state of the expanded memory hardware......4-7
Terminating the resident program.........................4-7
Restoring the CPU state..................................4-7
Example EMM procedures.......................................4-8
Glossary
300275-003 vii
CHAPTER 1. INTRODUCTION TO EXPANDED MEMORY
This specification describes a way to expand the memory
addressing capabilities of the Intel 8086, 8088, and 80286
microprocessors. It introduces a "paging" mechanism to access
very large amounts of memory. This memory paging (also known as
bank switching or bank swapping) uses a type of memory called
"expanded memory."
The rest of this chapter describes the memory addressing
capabilities of the Intel 8086, 8088, and 80286 microprocessors
and how the interface described in this specification overcomes
their limitations.
The Intel 8086 and 8088 microprocessors
The Intel 8086 and 8088 microprocessors let programs or operating
systems directly access up to 1M byte of address space. DOS, the
most frequently used operating system for 8086 and 8088-based IBM
personal computers and compatibles, allows application programs
to use only up to 640K bytes of memory.
This memory space often is not enough for application programs
which require large amounts of memory to implement spreadsheets,
databases, and other memory-intensive functions.
The Intel 80286 microprocessor
Although the Intel 80286 microprocessor can address more memory
space (up to 16M bytes) than the 8086 and 8088 microprocessors,
the amount of memory DOS can access directly is still limited to
640K bytes. This limitation is imposed because the 80286
microprocessor operates under one of two modes: Real Mode or
Protected Virtual Addressing Mode (PVAM).
When operating in Real Mode, the 80286 microprocessor lets
programs or operating systems directly access only up to 1M byte
of address space. This is the mode that DOS uses, so application
programs which run on IBM's AT or AT-compatible machines are
still limited to 640K bytes of usable memory space.
When operating in PVAM, the 80286 microprocessor lets programs
that run under the XENIX operating system address up to 16M bytes
of memory. However, since most IBM AT or AT-compatible machines
operate under DOS, application programs can rarely take advantage
of this extra memory.
Introduction 300275-003 1-1
How expanded memory is accessed
Much as your computer screen acts as a small "window" into a much
larger spreadsheet, memory paging provides one or more small
"windows" of memory through which a much larger memory space can
be accessed. These windows are called physical pages.
This specification describes a method where four contiguous
physical pages of 16K bytes each (forming a block of 64K bytes)
can access up to 8M bytes of expanded memory space via the
Expanded Memory Manager (EMM).
Limitations of the 8086, 8088, and 80286 microprocessors
You can use the Expanded Memory Manager (EMM) to overcome the
memory limitations of the Intel 8086, 8088, and 80286
microprocessors. The EMM is a set of standard interface routines
which allow programs, running on IBM PCs, XTs, ATs, or
compatibles, to use up to 8M bytes of expanded memory.
Because the EMM is a standard, programs that adhere to the
Lotus/Intel/Microsoft Expanded Memory Specification can avoid
potential compatibility problems. Expanded memory application
programs that deal directly with the hardware or that don't
strictly adhere to the specification run this risk.
Chapter 3 of this specification describes the EMM in detail.
Terminology
The following terms are used frequently in this specification:
o Conventional memory
Conventional memory refers to the memory DOS recognizes. In
PCs, XTs, and ATs, this is memory between 0 and 640K bytes.
Because application programs let DOS manage their memory, they
can use only conventional memory.
o Expanded memory
Expanded memory is a special kind of memory that goes beyond
DOS's 640K-byte limit. Application programs that adhere to
the Lotus/Intel Expanded Memory Specification can use the
Expanded Memory Manager (EMM) to manage expanded memory just
as other programs use DOS to manage conventional memory.
o Extended memory
1-2 300275-003 Introduction
Extended memory is the 15M-byte address space on an IBM AT or
compatible computer outside the memory DOS can access. This
address space is of little use to those application programs
that use DOS. DOS does not recognized memory above 640K
bytes; the XENIX operating system manages extended memory.
Other terms are defined in the Glossary near the end of this
specification.
Introduction 300275-003 1-3
CHAPTER 2. WRITING PROGRAMS THAT USE
EXPANDED MEMORY
This chapter is divided into two major sections. The first
section provides guidelines to help you create programs that use
expanded memory. The second section describes the individual EMM
functions in detail, with assembly language examples, parameter
passing conventions, and an explanation of the status and results
returned by the function.
Designing your program
While designing or planning a program that uses expanded memory,
consider the following topics:
o The operating environment
o The mechanics of the Expanded Memory Manager (EMM)
o The programming guidelines presented here
This section discusses these topics and lists some guidelines to
help you to create programs that use expanded memory.
The operating environment
The guidelines in this section help ensure that your program
works in systems that use expanded memory. To be "safe," your
program should assume the system for which you're writing the
program contains:
o Multiple expanded memory boards.
o Other resident programs which also use expanded memory. An
example of a resident program is an interrupt service routine
or a device driver. It can also be a program invoked by an
interrupt service routine or just a program that preempts the
active program.
o Registers whose contents are modified by function invocations.
This means your program can't rely on the contents of certain
registers after a function invocation. (The registers that a
particular function modifies are listed in the description of
the function; all others are unchanged)
Mechanics of the EMM
Version 3.20 of the EMM is re-entrant and its critical regions
are protected from interrupts. This means you'll never encounter
a "busy" condition.
However, the EMM requires programs to follow these rules:
2-4 300275-003 Writing programs
o The physical size of each page is fixed at 16K bytes.
o Four 16K-byte pages can be mapped into the system memory
address space simultaneously and contiguously. The 64K-byte
region which results from this mapping must begin at the
address returned by EMM FUNCTION 2 (Get page frame).
Note: Throughout the remainder of this document, the 64k-byte
region returned by FUNCTION 2 is called the "page frame."
Programming guidelines
To ensure that your program runs correctly with the EMM, it
should:
o Not locate its stack within expanded memory.
o Test for the presence of the EMM device by using one of two
methods. The first method is to use the DOS "open handle"
technique. The second method is to use the DOS "get interrupt
vector" function to obtain the contents of interrupt vector
67h. Once you get the contents of interrupt vector 67h, you
can inspect the device driver header. (Both methods are
described Chapter 3 of this specification.)
o Not use interrupt 67h. DOS normally sets aside interrupt
vector table entries 60h through 67h for non-system software
that uses software interrupts. However, the EMM uses
interrupt vector 67h. It sets the contents of interrupt
vector table entry 67h to the address of the EMM service
procedure using the DOS "Set Interrupt Vector" function.
Other software that uses this vector won't work once the EMM
installs itself because the EMM does not chain to any software
previously serviced by this interrupt vector.
Note: Resident software that uses INT 67h and installs itself
after the EMM, will disable the EMM.
o Request the page frame base address after determining that the
EMM is installed. This page frame base address is the
starting address of the 64K-byte memory segment that contains
the four 16K-byte pages. The first 16K-byte physical page
address begins at this base address. The second 16K-byte
physical page address starts at the base address offset by
4000h. The third 16K-byte physical page address starts at the
base address offset by 8000h. The fourth 16K-byte physical
page starts at the base address offset by C000h.
o Request the number of unallocated 16K-byte pages within the
expanded memory system. This determines the maximum number of
pages the program can allocate.
Writing programs 300275-003 2-5
o "Open" the EMM and allocate the number of 16K-byte pages that
it intends to use. The EMM returns a unique "EMM handle" that
the program uses to identify itself in all future transactions
with the EMM. The EMM uses this handle to identify the memory
it allocates to each program. (Your program should obtain EMM
handle(s) and allocate pages only once, at the beginning of
the program.)
The EMM attempts to assign the pages the program requests. If
the number of pages it requests is greater than the number of
free pages, the EMM returns an "error" status. The status
codes the EMM returns are listed in this chapter.
Note: A single application program can request multiple EMM
handles and as many pages per EMM handle as it desires. The
nature of the application determines the number of EMM handles
and pages required.
o Issue a map request to the EMM. (At this point the program
can map any allocated logical page into any one of the four
physical pages within the page frame.) The map operation must
be performed before any data within the physical page can be
accessed.
If the logical page has not been assigned to this particular
EMM handle, the EMM returns an error and doesn't carry out the
mapping procedure. If the physical page (at which the logical
page is mapped) isn't in the range 0 thru 3, the EMM returns
an error.
o Keep track of the contents of each page of expanded memory.
The EMM doesn't provide a facility for associating data with a
particular logical page. If a page contains data that will be
accessed within the program, the program must remember which
page contains the data.
o "Close" the Expanded Memory Manager prior to terminating.
This deallocates all pages previously allocated to the EMM
handle. The deallocated pages become available to all other
programs using expanded memory. The "close" request has no
effect on these other programs.
If the program does not perform a "close" before it exits to
DOS, the pages allocated to the EMM handle will remain
assigned. The only way to deallocate pages left in this
condition is to power off the system.
The EMM functions
This section presents a general overview of the EMM functions,
detailed descriptions of the individual functions, and a list
that summarizes the status codes the EMM functions return.
2-6 300275-003 Writing programs
Overview of the EMM functions
The EMM functions provide you with a set of standard expanded
memory functions. Because the EMM functions are standard, you
avoid potential compatibility problems with other expanded memory
programs that also adhere to the EMM specification. Programs
that deal directly with the hardware or that don't adhere to the
specification run this risk.
Functions 1 through 7 -- for general-purpose programming
Functions 1 through 7 provide the memory operators that typical
application programs require. Of these seven functions, FUNCTION
5 (Map) is the only one that a program may use a great deal while
running.
Functions 8 and 9 -- for interrupt service routines, device
drivers, and other resident software
Functions 8 and 9 aren't necessary for most application programs.
They are provided only for software that must save the current
state of the mapping hardware, switch mapping contexts,
manipulate the sections of expanded memory that they "own," and
restore the original context of the memory mapping hardware.
Examples of this type of software are interrupt service routines,
device drivers, and resident software such as print spoolers that
use expanded memory.
Functions 10 and 11 -- reserved
In previous versions of the Lotus/Intel/Microsoft Expanded Memory
Specification, Function 10 retrieved the page mapping register
I/O array and Function 11 retrieved the logical-to-physical page
translation array.
These functions are now reserved and new programs should not use
them. However, existing programs that use these functions will
still work correctly.
Functions 12, 13, and 14 -- for utility programs
Functions 12, 13, and 14 are also not necessary for most
application programs. They are provided for utility programs
that need to keep track of how expanded memory is being used.
Writing programs 300275-003 2-7
Function 15 -- for multitasking operating systems
Function 15 is for multitasking operating systems that must save
the current state of the mapping hardware within each expanded
memory board before modifying the state of the mapping hardware
on any of the boards.
2-8 300275-003 Writing programs
FUNCTION 1
Get Status
The Get Status function returns a status code that tells you
whether the EMM is present and if the hardware is working
correctly. This function doesn't require an EMM handle.
Parameter passing convention
AH The AH register contains the function number (40h).
Example invocation in assembly language
This example shows how to invoke the Get Status function in
assembly language.
MOV AH, 40h
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Get Status function modifies the contents of the AX register.
Status returned
The Get Status function returns one of the following status
codes.
AH = 0 The manager is present in the system and the hardware
is working correctly.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
Writing programs 300275-003 2-5
FUNCTION 2
Get Page Frame Address
The Get Page Frame Address function tells your program where the
page frame is located. It returns the segment portion of the
page frame address in the BX register. This function doesn't
require an EMM handle.
Parameter passing convention
AH The AH register contains the function number for the
Get Page Frame function (41h).
Example invocation in assembly language
This example shows how to invoke the Get Page Frame Address
function in assembly language.
MOV AH, 41h
INT 67h
OR AH, AH
JNZ error_handler
MOV page_segment, BX
Registers modified
The Get Page Frame Address function modifies the contents of the
AX and BX registers.
Status returned
The Get Page Frame Address function returns one of the following
status codes.
AH = 0 The manager has returned the page frame address.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
Results returned
The Get Page Frame Address function returns these results.
BX = segment The BX register contains the segment address of the
page frame. The value in BX has no meaning if AH <> 0.
2-6 300275-003 Writing programs
FUNCTION 3
Get Unallocated Page Count
The Get Unallocated Page Count function tells your program the
number of unallocated pages as well as the total number of pages
in expanded memory. This function doesn't require an EMM handle.
Parameter passing convention
AH The AH register contains the function number for the
Get Unallocated Page Count function (42h).
Example invocation in assembly language
This example shows how to invoke the Get Unallocated Pages Count
function in assembly language.
MOV AH, 42h
INT 67h
OR AH, AH
JNZ error_handler
MOV un_alloc_pages, BX
MOV total_pages, DX
Registers modified
The Get Unallocated Pages Count function modifies the contents of
the AX, BX, and DX registers.
Status returned
The Get Unallocated Pages Count function returns one of the
following status codes.
AH = 0 The manager has returned the number unallocated pages
and the number of total pages in expanded memory.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
Writing programs 300275-003 2-7
FUNCTION 3
Get Unallocated Page Count
(continued)
Results returned
The Get Unallocated Page Count function returns these results.
BX = 0 All pages in expanded memory have already been
allocated. None are currently available for expanded
memory.
BX <> 0 The number of pages that are currently available.
DX <> 0 The total number of pages in expanded memory
2-8 300275-003 Writing programs
FUNCTION 4
Allocate Pages
The Allocate Pages function allocates the number of pages your
program requests and assigns a unique EMM handle to these pages.
The EMM handle "owns" these pages until your program deallocates
them.
Parameter passing convention
AH The AH register contains the function number for the
Allocate Pages function (43h).
BX The BX register contains the number of pages your
program wishes to allocate.
Example invocation in assembly language
This example shows how to invoke the Allocate Pages function in
assembly language.
MOV AH, 43h
MOV BX, num_of_pages_to_alloc
INT 67h
OR AH, AH
JNZ error_handler
MOV emm_handle, DX
Registers modified
The Allocate Pages function modifies the contents of the AX and
DX registers.
Status returned
The Allocate Pages function returns one of the following status
codes.
AH = 0 The manager has allocated the pages to an assigned EMM
handle.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
AH = 85h All EMM handles are being used.
AH = 87h There aren't enough expanded memory pages to supply
your program's request.
Writing programs 300275-003 2-9
FUNCTION 4
Allocate Pages
(continued)
AH = 88h There aren't enough unallocated pages to supply your
program's request.
AH = 89h Can't allocate zero pages.
Results returned
The Allocate Pages function returns these results.
DX = handle The DX register contains a unique EMM handle. Your
program must use this EMM handle (as a parameter) in
any function invocations that map or deallocate
expanded memory.
2-10 300275-003 Writing programs
FUNCTION 5
Map Handle Page
The Map Handle Page function lets your program access the
information stored in logical page (i) at physical page (j)
within the page frame.
Parameter passing convention
AH The AH register contains the function number for the
Map Handle Page function (44h).
BX The BX register contains the logical page (i) that is
mapped into the physical page within the page frame.
The logical page must be in the range 0 through (number
of pages allocated to an
EMM handle - 1).
AL The AL register contains the physical page (j) into
which the logical page (i) is mapped. This physical
page must be in the range 0 thru 3.
DX The DX register contains the EMM handle your program
received from FUNCTION 4 (Allocate Pages).
Example invocation in assembly language
This example shows how to invoke the Map Handle Page function in
assembly language.
MOV DX, emm_handle
MOV BX, i
MOV AL, j
MOV AH, 44h
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Map Handle Page function modifies the contents of the AX
register.
Status returned
The Map Handle Page function returns one of the following status
codes.
AH = 0 The manager has mapped the page. The page is now ready
to be accessed.
AH = 80h The manager detected a malfunction in the EMM software.
Writing programs 300275-003 2-11
FUNCTION 5
Map Handle Page
(continued)
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 83h The EMM couldn't find the EMM handle your program
specified.
AH = 84h The function code passed to the EMM is not defined.
AH = 8Ah The logical page is out of the range of logical pages
which are allocated to the EMM handle.
AH = 8Bh The physical page at which the logical page was
supposed to be mapped is out of the range of physical
pages.
2-12 300275-003 Writing programs
FUNCTION 6
Deallocate Pages
The Deallocate Pages function deallocates the pages currently
allocated to an EMM handle. After your program invokes this
function, other application programs can use these pages.
Caution: Your program must perform this function before it exits
to DOS. If it doesn't, no other programs can use these pages or
their handle.
Parameter passing convention
AH The AH register contains the function number for the
Deallocate Pages function (45h).
DX The DX register contains the EMM handle returned by
FUNCTION 4 (Allocate Pages).
Example invocation in assembly language
This example shows how to invoke the Deallocate Pages function in
assembly language.
MOV DX, emm_handle
MOV AH, 45h
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Deallocate Pages function modifies the contents of the AX
register.
Status returned
The Deallocate Pages function returns one of the following status
codes.
AH = 0 The manager has deallocated the pages previously
allocated to the EMM handle.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 83h The EMM couldn't find the EMM handle your program
specified.
Writing programs 300275-003 2-13
FUNCTION 6
Deallocate Pages
(continued)
AH = 84h The function code passed to the EMM is not defined.
AH = 86h The EMM detected a "save" or "restore" page mapping
context error (FUNCTION 8 or 9). There is a page
mapping register state in the "save area" for the EMM
handle specified. Save Page Map (FUNCTION 8) placed it
there and it has not been removed by a subsequent
Restore Page Map (FUNCTION 9).
You need to restore the contents of the page mapping
register before you deallocate the EMM handle's
page(s).
2-14 300275-003 Writing programs
FUNCTION 7
Get EMM Version
The Get EMM Version function returns the version number of the
Expanded Memory Manager software.
Parameter passing convention
AH The AH register contains the function number for the
Get EMM Version function (46h).
Example invocation in assembly language
This example shows how to invoke the Get EMM Version function in
assembly language.
MOV AH, 46h
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Get EMM Version function modifies the contents of the AX
register.
Status returned
The Get EMM Version function returns one of the following status
codes.
AH = 0 The manager is present in the system and the hardware
is working correctly.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
Results returned
The Get EMM Version function returns these results.
AL = version The AL register contains the Expanded Memory
Manager's version number in BCD. The upper four bits
in the AL register contain the integer digit (3.x) of
the version number. The lower four bits in the AL
register contain the fractional digit of (x.2) version
number.
Writing programs 300275-003 2-15
FUNCTION 7
Get EMM Version
The value contained in AL has no meaning if AH <> 0.
2-16 300275-003 Writing programs
FUNCTION 8
Save Page Map
(continued)
The Save Page Map function saves the contents of the page mapping
registers from all expanded memory boards. These registers
contain the memory mapping context of the EMM handle that was
active when a software or hardware interrupt occurred. (See
FUNCTION 9 -- Restore Page Map for the "restore" operation.)
If you're writing a resident program, an interrupt service
routine, or a device driver that uses expanded memory, you must
save the state of the mapping hardware. You must save this
state, because application software (using expanded memory) may
be running when your program is invoked by a hardware interrupt,
a software interrupt, or DOS. The Save Page Map function
facilitates saving the state of the mapping hardware.
The Save Page Map function requires the EMM handle that was
assigned to your resident program, interrupt service routine, or
device driver at the time it was initialized. (This is NOT the
EMM handle that the application software was using when your
software interrupted it.)
Chapter 4 of this specification discusses resident software in
general. It explains the assignment of an EMM handle and the
allocation of pages to resident programs.
Parameter passing convention
AH The AH register contains the function number for the
Save Page Map function (47h).
DX The DX register contains the EMM handle assigned to the
interrupt service routine that's servicing the software
or hardware interrupt. The interrupt service routine
needs to save the state of the page mapping hardware
before mapping any pages (FUNCTION 5).
Example invocation in assembly language
This example shows how to invoke the Save Page Map function in
assembly language.
MOV DX, emm_handle
MOV AH, 47h
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Save Page Map function modifies the contents of the AX
register.
Writing programs 300275-003 2-17
FUNCTION 8
Save Page Map
Status returned
The Save Page Map function returns one of the following status
codes.
AH = 0 The manager has saved the state of the page mapping
hardware.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 83h The EMM couldn't find the EMM handle your program
specified.
AH = 84h The function code passed to the EMM is not defined.
AH = 8Ch There is no room in the "save" area to store the state
of the page mapping registers.
AH = 8Dh The "save area" already contains the page mapping
register state for the EMM handle your program
specified..
2-18 300275-003 Writing programs
FUNCTION 9
Restore Page Map
(continued)
The Restore Page Map function restores the contents of the page
mapping registers on the expanded memory boards for a particular
EMM handle. This function lets your program restore the contents
of the mapping registers which its EMM handle saved. (See
FUNCTION 8 -- Save Page Map for the "save" operation.)
If you're writing a resident program, an interrupt service
routine, or a device driver that uses expanded memory, you must
restore the mapping hardware to the state it was in before your
program took over. You must restore this state, because
application software (using expanded memory) may be running when
your program is invoked by a hardware interrupt, a software
interrupt, or DOS. The Restore Page Map function facilitates
restoring the state of the mapping hardware.
The Restore Page Map function requires the EMM handle that was
assigned to your resident program, interrupt service routine, or
device driver at the time it was initialized. (This is NOT the
EMM handle that the application software was using when your
software interrupted it.)
Chapter 4 of this specification discusses resident software in
general. It explains the assignment of an EMM handle and the
allocation of pages to resident programs.
Parameter passing convention
AH The AH register contains the function number for the
Restore Page Map function (48h).
DX The DX register contains the EMM handle assigned to the
interrupt service routine that's servicing the software
or hardware interrupt. The interrupt service routine
needs to restore the state of the page mapping
hardware.
Example invocation in assembly language
This example shows how to invoke the Restore Page Map function in
assembly language.
MOV DX, emm_handle
MOV AH, 48h
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Restore Page Map function modifies the contents of the AX
register.
Writing programs 300275-003 2-19
FUNCTION 9
Restore Page Map
Status returned
The Restore Page Map function returns one of the following status
codes.
AH = 0 The manager has restored the state of the page mapping
registers.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 83h The EMM couldn't find the EMM handle your program
specified.
AH = 84h The function code passed to the EMM is not defined.
AH = 8Eh There is no page mapping register state in the save
area for the EMM handle your program specified. Your
program didn't save the contents of the page mapping
hardware, so Restore Page Map can't restore it.
2-20 300275-003 Writing programs
FUNCTION 10
Reserved
In previous versions of the Lotus/Intel/Microsoft Expanded Memory
Specification, Function 10 retrieved the page mapping register
I/O array. This function is now reserved and new programs should
not use it.
Note: Existing programs that use this function will still work
correctly.
Writing programs 300275-003 2-21
FUNCTION 11
Reserved
In previous versions of the Lotus/Intel/Microsoft Expanded Memory
Specification, Function 10 retrieved the logical-to-physical page
translation array. This function is now reserved and new
programs should not use it.
Note: Existing programs that use this function will still work
correctly.
2-22 300275-003 Writing programs
FUNCTION 12
Get EMM Handle Count
The Get EMM Handle Count function return the number of active EMM
handles.
Parameter passing convention
AH The AH register contains the function number for the
Get EMM Handle Count function (4Bh).
Example invocation in assembly language
This example shows how to invoke the Get EMM Handle Count
function in assembly language.
MOV AH, 4Bh
INT 67h
OR AH, AH
JNZ error_handler
MOV total_active_emm_handles, BX
Registers modified
The Get EMM Handle Count function modifies the contents of the AX
and BX registers.
Status returned
The Get EMM Handle Count function returns one of the following
status codes.
AH = 0 The manager has returned the number of active EMM
handles.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 83h The EMM couldn't find the EMM handle your program
specified.
AH = 84h The function code passed to the EMM is not defined.
Results returned
The Get EMM Handle Count function returns these results.
BX = x The BX register contains the number of active EMM
handles. This number never exceeds 255.
Writing programs 300275-003 2-23
FUNCTION 13
Get EMM Handle Pages
(continued)
The Get EMM Handle Pages function returns the number of pages
allocated to a specific EMM handle.
Parameter passing convention
AH The AH register contains the function number for the
Get EMM Handle Pages function (4Ch).
DX The DX register contains the EMM handle.
Example invocation in assembly language
This example shows how to invoke the Get EMM Handle Pages
function in assembly language.
MOV DX, emm_handle
MOV AH, 4Ch
INT 67h
OR AH, AH
JNZ error_handler
MOV num_pages_alloc_to_emm_handle, BX
Registers modified
The Get EMM Handle Pages function modifies the contents of the AX
and BX registers.
Status returned
The Get EMM Handle Pages function returns one of the following
status codes.
AH = 0 The manager has returned the number of pages allocated
to the EMM handle.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 83h THe EMM couldn't find the EMM handle your program
specified.
AH = 84h The function code passed to the EMM is not defined.
2-24 300275-003 Writing programs
FUNCTION 13
Get EMM Handle Pages
Results returned
The Get EMM Handle Pages function returns these results.
BX <> 0 The BX register contains the number of pages allocated
to the EMM handle. The number returned is never zero
because you can't allocate zero pages to an EMM handle.
This number never exceeds 512 because the EMM allows,
at most, 512 pages of expanded memory.
Writing programs 300275-003 2-25
FUNCTION 14
Get All EMM Handle Pages
(continued)
The Get All EMM Handle Pages function returns an array of the
active EMM handles and the number of pages allocated to each one.
Parameter passing convention
AH The AH register contains the function number for the
Get All EMM Handle Pages function (4Dh).
ES:DI The ES:DI address points to an array where a copy of
all active EMM handles and the number of pages
allocated to each is stored. Each entry in the array
is composed of two words. The first word contains the
active EMM handle. The second word contains the number
of pages allocated to the EMM handle.
To ensure that the array space your program must supply
is large enough, use this formula to calculate the
amount of memory required:
number of bytes = 2 * 2 * number of EMM
required in array handles returned
(Each EMM handle requires 2 bytes as does each page
number.) The array can never contain more than 1 K
bytes.
Caution: Be careful when you specify the array address in ES:DI
so as not to cause "segment wrap" when the array is transferred.
Example invocation in assembly language
This example shows how to invoke the Return Open EMM Handle Pages
function in assembly language.
MOV AX, dseg
MOV ES, AX
MOV DI, OFFSET handle_pages_array
MOV AH, 4Dh
INT 67h
OR AH, AH
JNZ error_handler
MOV total_active_emm_handles, BX
Registers modified
The Get All EMM Handle Pages function modifies the contents of
the AX and BX registers.
2-26 300275-003 Writing programs
FUNCTION 14
Get All EMM Handle Pages
Status returned
The Get All EMM Handle Pages function returns one of the
following status codes.
AH = 0 The manager has returned the array.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
Results returned
The Return Open EMM Handle Pages function returns these results.
BX = x The BX register contains the number of active EMM
handles. If the number is 0 this indicates that the
manager is "idle." This number never exceeds 255.
Writing programs 300275-003 2-27
FUNCTION 15
Get/Set Page Map
(continued)
When a task switch occurs, a multitasking operating system must
save (and later restore) the mapping context of the active EMM
handle. The set of subfunctions that make up the Get/Set Page
Map function let your operating system perform these operations.
The Get/Set Page Map function is really a set of subfunctions.
These subfunctions allow a multitasking operating system to:
o "Get" the contents of the page mapping registers from the
expanded memory boards.
o "Set" the contents of the page mapping registers on the
expanded memory boards.
o "Get and Set" the contents of the page mapping registers on
the expanded memory boards. This subfunction allows the
operating system to perform both "get" and "set" in only one
EMM invocation.
o "Return Size" of the page mapping hardware state array for the
operating system.
This function is described a bit differently than the rest of the
functions in this chapter. Since it is made up of four
subfunctions, there are four subsections which contain the
parameter passing convention, example invocation, status codes,
and results returned for each service within the Get/Set Page Map
function.
Get the contents of the page mapping registers
The Get subfunction copies the contents of the mapping registers
from each expanded memory board to a destination array. The
operating system must point to the destination array.
This subfunction doesn't require an EMM handle.
Parameter passing convention
AH The AH register contains the function number for the
Get/Set Page Map function (4Eh).
AL = 0 When the AL register equals 0, the invocation requests
the Get subfunction. It copies the map registers to an
array pointed to by the ES:DI address.
ES:DI The ES:DI address points to the destination array
address in SEGMENT:OFFSET format. This address is
required only for the Get or Get and Set services.
Caution: Be careful when you specify the array address in ES:DI
so as not to cause "segment wrap" when the array is transferred.
2-28 300275-003 Writing programs
FUNCTION 15
Get/Set Page Map
Example invocation in assembly language
This example shows how to invoke the Get subfunction in assembly
language.
MOV AX, dseg
MOV ES, AX
MOV DI, OFFSET destination_page_map_array
MOV AH, 4Eh
MOV AL, 0
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Get subfunction modifies the contents of the AX register.
Status returned
The Get subfunction returns one of the following status codes.
AH = 0 The manager has returned the array.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
AH = 8Fh The subfunction parameter isn't equal to a Get request.
Results returned
The Get subfunction returns these results.
ES:DI = addr The ES:DI address points to the memory area where
the operating system has stored the state of all the
mapping registers on all boards in the system. This
memory area also contains any additional information
necessary to restore the boards to their original state
when the program invokes a Set subfunction.
Set the contents of the page mapping registers
The Set subfunction copies the contents of a source array into
the mapping registers on each expanded memory board in the
system. The operating system must point to the source array.
This subfunction doesn't require an EMM handle.
Writing programs 300275-003 2-29
FUNCTION 15
Get/Set Page Map
(continued)
Parameter passing convention
AH The AH register contains the function number for the
Get/Set Page Map function (4Eh).
AL = 1 When the AL register equals 1, the invocation requests
the Set subfunction. It copies the contents of the
array pointed to by the DS:SI address to the map
registers.
DS:SI The DS:SI address points to the source array address in
SEGMENT:OFFSET format. The operating system must point
to an array which contains the mapping register state.
This address is required only for the Set or Get and
Set services.
Caution: Be careful when you specify the array address in DS:SI
so as not to cause "segment wrap" when the array is transferred.
Example invocation in assembly language
This example shows how to invoke the Set subfunction in assembly
language.
MOV AX, dseg
MOV DS, AX
MOV SI, OFFSET source_page_map_array
MOV AH, 4Eh
MOV AL, 1
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Set subfunction modifies the contents of the AX register.
Status returned
The Set subfunction returns one of the following status codes.
AH = 0 The manager has passed the array.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
2-30 300275-003 Writing programs
FUNCTION 15
Get/Set Page Map
(continued)
AH = 8Fh The subfunction parameter isn't equal to a Set request
or the length of the array passed during the Set
request doesn't match the number of mapping registers
in the system.
Writing programs 300275-003 2-31
FUNCTION 15
Get/Set Page Map
(continued)
Results returned
The Set subfunction doesn't return any results. If the operating
system used the Get subfunction correctly, the Set service should
restore the expanded memory boards to their original state. (The
Get subfunction, described previously in this chapter, saves the
contents of the mapping register from each expanded memory
board.)
Get and set the contents of the page mapping registers
The Get and Set subfunction first copies the contents of the
mapping registers from each expanded memory board in the system
into a destination array. (The operating system must point to
the destination array.) Then, the subfunction copies the
contents of a source array into the mapping registers on each of
the expanded memory boards. (The operating system must point to
the source array.)
This subfunction doesn't require an EMM handle.
Parameter passing convention
AH The AH register contains the function number for the
Get/Set Page Map function (4Eh).
AL = 2 When the AL register equals 2, the invocation requests
the Get and Set subfunction. This subfunction first
copies the map registers to an array pointed to by the
ES:DI address. And then, it copies the contents of the
array pointed to by the DS:SI address to the map
registers.
ES:DI The ES:DI address points to the destination array
address in SEGMENT:OFFSET format. This address is
required only for the Get or Get and Set services.
DS:SI The DS:SI address points to the source array address in
SEGMENT:OFFSET format. The operating system must point
to an array which contains the mapping register state.
This address is required only for the Set or Get and
Set services.
Caution: Be careful when you specify the array address in ES:DI
and DS:SI so as not to cause "segment wrap" when the array is
transferred.
2-32 300275-003 Writing programs
FUNCTION 15
Get/Set Page Map
(continued)
Example invocation in assembly language
This example shows how to invoke the Get and Set subfunction in
assembly language.
MOV AX, dseg
MOV ES, AX
MOV DI, OFFSET destination_page_map_array
MOV DS, AX
MOV SI, OFFSET source_page_map_array
MOV AH, 4Eh
MOV AL, 2
INT 67h
OR AH, AH
JNZ error_handler
Registers modified
The Get and Set subfunction modifies the contents of the AX
register.
Status returned
The Get and Set subfunction returns one of the following status
codes.
AH = 0 The manager has returned and passed both arrays
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
AH = 8Fh The subfunction parameter isn't equal to a Get and Set
request.
Results returned
The Get and Set subfunction returns these results.
ES:DI = addr The ES:DI address points to the memory area where
the operating system stores the state of all the
mapping registers on all boards in the system. (This
happens during a Get subfunction.) This memory area
also contains any additional information necessary to
restore the boards to their original state when the
program invokes a Set subfunction.
Writing programs 300275-003 2-33
FUNCTION 15
Get/Set Page Map
(continued)
Return the size of the mapping context array for the
operating system
The Return Size subfunction determines the storage requirements
for the array passed by the other three functions prior to
invoking them.
This subfunction doesn't require an EMM handle.
2-34 300275-003 Writing programs
FUNCTION 15
Get/Set Page Map
(continued)
Parameter passing convention
AH The AH register contains the function number for the
Get/Set Page Map function (4Eh).
AL = 3 When the AL register equals 3, the invocation requests
the Return Size subfunction. This subfunction returns
the size (in bytes) of the array that the Get, Set, or
Get and Set subfunctions transfer to or from the
operating system.
Example invocation in assembly language
This example shows how to invoke the Return Size subfunction in
assembly language.
MOV AH, 4Eh
MOV AL, 3
INT 67h
OR AH, AH
JNZ error_handler
MOV size_of_array, AL
Registers modified
The Return Size subfunction modifies the contents of the AX
register.
Status returned
The Return Size subfunction returns one of the following status
codes.
AH = 0 The manager has returned the array size.
AH = 80h The manager detected a malfunction in the EMM software.
AH = 81h The manager detected a malfunction in the expanded
memory hardware.
AH = 84h The function code passed to the EMM is not defined.
AH = 8Fh The subfunction parameter isn't equal to a Return Size
request.
Results returned
The Return Size subfunction returns these results.
Writing programs 300275-003 2-35
FUNCTION 15
Get/Set Page Map
(continued)
AL = n The contents of the AL register equals the number of
bytes transferred to the memory area supplied by an
operating system whenever a program requests the Get,
Set, or Get and Set subfunction.
2-36 300275-003 Writing programs
SUMMARY OF STATUS CODES -- ALL EMM FUNCTIONS
Table 2-1 lists the possible status codes that the EMM functions
can return. This table is for quick reference; the individual
EMM functions list the status codes they return.
Table 2-1. Summary of status codes
Code Definition
AH = 0 The manager is present in the system and the
hardware is working correctly.
AH = 80h The manager detected a malfunction in the EMM
software.
AH = 81h The manager detected a malfunction in the
expanded
memory hardware.
AH = 83h The EMM couldn't find the EMM handle your
program
specified.
AH = 84h The function code passed to the EMM is not
defined.
AH = 85h All EMM handles are being used.
AH = 86h The EMM detected a "save" or "restore" page
mapping context error.
AH = 87h There aren't enough expanded memory pages to
satisfy your program's request.
Writing programs 300275-003 2-37
AH = 88h There aren't enough unallocated pages to
satisfy
your program's request.
AH = 89h Can't allocate zero (0) pages.
2-38 300275-003 Writing programs
Table 2-1. Summary of status codes (continued)
Code Definition
AH = 8Ah The logical page is out of the range of
logical
pages which are allocated to the EMM handle.
AH = 8Bh The physical page to which the logical page
is
mapped is out of the range of physical pages.
AH = 8Ch The page mapping hardware state save area is
full.
AH = 8Dh The page mapping hardware state save area
already has
a state associated with the EMM handle.
AH = 8Eh The page mapping hardware state save area
doesn't have a state associated with the EMM
handle.
AH = 8Fh The subfunction parameter passed to the
function
isn't defined.
Writing programs 300275-003 2-39
CHAPTER 3. TESTING FOR THE PRESENCE OF THE EXPANDED
MEMORY MANAGER
Before an application program can take advantage of the Expanded
Memory Manager (EMM), it must determine whether the manager has
been loaded by DOS. This chapter describes two methods your
program can use to test for the presence of the EMM and how to
choose the correct one for your situation.
The first method uses the DOS "open handle" technique; the second
method uses the DOS "get interrupt vector" technique.
Which method should my program use?
The majority of application programs can use either the "open
file" or the "get interrupt vector" method. However, if your
program is a device driver or if it interrupts DOS during file
system operations, you must use only the "get interrupt vector"
method.
Device drivers execute from within DOS and can't access the DOS
file system; programs that interrupt DOS during file system
operations have a similar restriction. During their interrupt
processing procedures, they can't access the DOS file system
because another program may be using the system. Since the "get
interrupt vector" method doesn't require the DOS file system, you
must use it for these types of programs.
The "open handle" technique
Most application programs can use the DOS "open handle" technique
to test for the presence of the EMM. This section describes how
to use the technique and gives an example.
Caution: Don't use this technique if your program is a device
driver or if it interrupts DOS during file system operations.
Use the "get interrupt vector" technique described later in this
chapter.
Using the "open handle" technique
This section describes how to use the DOS "open handle" technique
to test for the presence of the EMM. Follow these steps in
order:
1. Issue an "open handle" command (DOS function 3Dh) in "read
only" access mode (register AL = 0). This function requires
your program to point to an ASCII string which contains the
path name of the file or device in which you're interested
(register set DS:DX contains the pointer). In this case the
file is actually the name of the EMM.
3-2 3000275-003Testing for the presence of the EMM
You should format the ASCII string as follows:
ASCII_device_name DB "EMMXXXX0", 0
where the ASCII codes for the capital letters EMMXXXX0 are
terminated by a byte containing a value of zero.
2. If DOS returns no error status code, skip Steps 3 and 4 and
go to Step 5. If DOS returns a "Too many open files" error
status code, go to Step 3. If DOS returns a "File/Path not
found" error status code, skip Step 3 and go to Step 4.
3. If DOS returns a "Too many open files" (not enough handles),
status code, your program should invoke the "open file"
command before it opens any other files. This will
guarantee that at least one file handle will be available to
perform the function without causing this error.
After the program performs the "open file" command, it
should perform the test described in Step 6 and close the
"file handle" (DOS function 3Eh). Don't keep the manager
"open" after this status test is performed since "manager"
functions are not available thru DOS. Go to Step 6.
4. If DOS returns a "File/Path not found" the EMM is not
installed. If your application requires its presence the
user will have to reboot the system with a disk containing
the EMM and the appropriate CONFIG.SYS file before
proceeding.
5. If DOS doesn't return an error status code you can assume
that either a device with the name EMMXXXX0 is resident in
the system, or a file with this name is on disk in the
current disk drive. Go to Step 6.
6. Issue an "I/O Control for Devices" command (DOS function
44h) with a "get device information" command (register AL =
0h). DOS function 44h determines whether EMMXXXX0 is a
device or a file. It also requires a pointer to a buffer
(register set DS:DX). The EMM does not use the buffer for
anything and will not pass information in it.
You can set the number of bytes this function requires to
perform read/write operations to zero (register CX) since no
data is passed back in the buffer. You must use the file
handle (register BX) which you obtained in Step 1 to access
the "EMM" device.
This function returns the "device information" in a word
(register DX). Go to step 7.
Testing for the presence of the EMM300275-003 3-3
7. If DOS returns any error status code, you should assume that
the EMM device driver is not installed. If your application
requires its presence the user will have to reboot the
system with a disk containing the EMM and the appropriate
CONFIG.SYS file before proceeding.
8. If DOS didn't return an error status, test the contents of
bit 7 (counting from 0) of the "device information" word
(register DX) the function returned. Go to Step 9.
9. If bit 7 of the "device information" word contains a zero,
then EMMXXXX0 is a file and the EMM device driver is not
present. If your application requires its presence, the
user will have to reboot the system with a disk containing
the EMM and the appropriate CONFIG.SYS file before
proceeding.
If bit 7 contains a one, then EMMXXXX0 is a device. Go to
Step 10.
10. Issue an "I/O Control for Devices" command (DOS function
44h) with a "get output status" command (register AL = 7h).
This function requires a pointer to a buffer (register set
DS:DX). The EMM does not use the buffer for anything and
will not pass information in it.
You can set the number of bytes (register CX) this function
requires to perform read/write operations to zero since no
data is passed back in the buffer. You must use the file
handle you obtained in Step 1 to access the "EMM" device
(register BX). Go to Step 11.
11. If the expanded memory device driver is "ready," the EMM
passes a status value of "0FFh" in register AL. The status
value is "00h" if the device driver is "not ready."
If the the EMM device driver is "not ready" and your
application requires its presence, the user will have to
reboot the system with a disk containing the EMM and the
appropriate CONFIG.SYS file before proceeding.
If the EMM device driver is "ready", go to Step 12.
12. Issue a "Close File Handle" command (DOS function 3Eh) to
close the expanded memory device driver. You must use the
file handle you obtained in Step 1 to close the "EMM" device
(register BX).
3-4 3000275-003Testing for the presence of the EMM
An example of the "open handle" technique
The following procedure is an example of the "open handle"
technique outlined in the previous section.
;;
;______________________________________________________________
______________________________________________________________;
;_____The following procedure tests for the presence of the EMM
______________________________________________________________;
;___in the system. It returns the CARRY FLAG SET if the EMM is
______________________________________________________________;
;___present. If the EMM is not present, this procedure returns
______________________________________________________________;
;_________________________________________the CARRY FLAG CLEAR.
______________________________________________________________;
;;
first_test_for_EMM PROC NEAR
___________________________________________________________PUSH D
S______________________________________________________________
___________________________________________________________PUSH C
S
____________________________________________________________POP D
S
____________________________________________________________MOV A
H, 3Dh__________________________________________; issue "device
____________________________________________________________LEA D
X, ASCII_device_name___________________________; open" in "read
____________________________________________________________MOV A
L, 0_______________________________________________; only" mode
____________________________________________________________INT 2
1h
_____________________________________________________________JC f
irst_test_for_EMM_error_exit___________________; test for error
_______________________________________________________________
; during "device
_______________________________________________________________
; open"
____________________________________________________________MOV B
X, AX___________________________________________; get the "file
_______________________________________________________________
; handle" returned
_______________________________________________________________
; by DOS
____________________________________________________________MOV A
X, 44h__________________________________________; issue "IOCTL"
____________________________________________________________MOV A
L, 00h______________________________________; "get device info"
____________________________________________________________INT 2
1h
Testing for the presence of the EMM300275-003 3-5
_____________________________________________________________JC f
irst_test_for_EMM_err_exit_____________________; test for error
_______________________________________________________________
; during "get device
_______________________________________________________________
; info"
___________________________________________________________TEST D
X, 0080h_________________________________; test to determine if
_____________________________________________________________JZ f
irst_test_for_EMM_err_exit__________________; ASCII_device_name
_______________________________________________________________
; is a device or a
_______________________________________________________________
; file
____________________________________________________________MOV A
H, 44h__________________________________________; issue "IOCTL"
____________________________________________________________LEA D
X, dummy_buffer___________________________________; "get output
____________________________________________________________MOV C
X, 0__________________________________________________; status"
____________________________________________________________MOV A
L, 07h
____________________________________________________________INT 2
1h
_____________________________________________________________JC f
irst_test_for_EMM_error_exit___________________; test for error
_______________________________________________________________
; during "IOCTL"
___________________________________________________________PUSH A
X________________________________________________; save "IOCTL"
_______________________________________________________________
; status
3-6 3000275-003Testing for the presence of the EMM
____________________________________________________________MOV A
H, 3Eh___________________________________________; issue "close
____________________________________________________________INT 2
1h_______________________________________________; file handle"
______________________________________________________________
____________________________________________________________POP A
X_____________________________________________; restore "IOCTL"
_______________________________________________________________
; status
____________________________________________________________CMP A
L, 0FFh______________________________________; test for "device
____________________________________________________________JNE f
irst_test_for_EMM_error_exit____________________; ready" status
_______________________________________________________________
; returned by the
_______________________________________________________________
; driver
first_test_for_EMM_exit:
____________________________________________________________POP D
S______________________________________________; EMM is present
____________________________________________________________STC
; in the system
____________________________________________________________RET
first_test_for_EMM_error_exit:
____________________________________________________________POP D
S__________________________________________; EMM is NOT present
____________________________________________________________CLC
; in the system
____________________________________________________________RET
ASCII_device_name: DB "EMMXXXX0", 0
dummy_buffer DB 0
first_test_for_EMM ENDP
Testing for the presence of the EMM300275-003 3-7
The "get interrupt vector" technique
Any type of program can use the DOS "get interrupt vector"
technique to test for the presence of the EMM. This section
describes how to use the technique and gives an example.
Caution: Be sure to use this technique (and not the "open handle
technique) if your program is a device driver or if it interrupts
DOS during file system operations.
Using the "get interrupt vector" technique
This section describes how to use the DOS "get interrupt vector"
technique to test for the presence of the EMM. Follow these
steps in order:
1. Issue a "get vector" command (DOS function 35h) to obtain
the contents of interrupt vector array entry number 67h
(addresses 0000:019C thru 0000:019F).
The EMM uses this interrupt vector to perform all manager
functions. The OFFSET portion of this interrupt service
routine address is stored in the word located at address
0000:019Ch; the SEGMENT portion is stored in the word
located at address 0000:019Eh.
2. Compare the "device name field" with the contents of the
ASCII string which starts at the address specified by the
segment portion of the contents of interrupt vector address
67h and a fixed offset of 000Ah. If DOS loaded the Expanded
Memory Manager at boot time this name field will have the
name of the device in it.
Since the Expanded Memory Manager is implemented as a
character device driver, its program origin is 0000h.
Device drivers are required to have a "device header"
located at the program origin. Within the "device header"
is an 8 byte "device name field." For a character mode
device driver this name field is always located at offset
000Ah within the device header. The device name field
contains the name of the device which DOS uses when the
device is referenced by DOS.
If the result of the "string compare" in this technique is
positive you can be certain that the EMM driver is present.
3-8 3000275-003Testing for the presence of the EMM
An example of the "get interrupt vector" technique
The following procedure is an example of the "get interrupt
vector" technique outlined in the previous section.
;;
;______________________________________________________________
______________________________________________________________;
;_________The following procedure tests for the presence of the E
MM_____________________________________________________________ ;
;___in the system. It returns the CARRY FLAG SET if the EMM is
______________________________________________________________;
;___present. It returns the CARRY FLAG CLEAR if the EMM is not
______________________________________________________________;
;______________________________________________________present.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
second_test_for_EMM PROC NEAR
___________________________________________________________PUSH D
S
___________________________________________________________PUSH C
S
____________________________________________________________POP D
S
____________________________________________________________MOV A
H, 35h___________________________________; issue "get interrupt
____________________________________________________________MOV A
L, 67h________________________________________________; vector"
____________________________________________________________INT 2
1h
____________________________________________________________MOV D
I, 000Ah___________________________________; use the SEGMENT in
_______________________________________________________________
; ES returned by DOS,
_______________________________________________________________
; place the "device
_______________________________________________________________
; name field"OFFSET in DI
____________________________________________________________LEA S
I, ASCII_device_name______________________; place the OFFSET of
_______________________________________________________________
; the EMMXXXX0 name
_______________________________________________________________
; string in SI, the
_______________________________________________________________
; SEGMENT is already in DS
Testing for the presence of the EMM300275-003 3-9
____________________________________________________________MOV C
X, 8_________________________________; compare the name strings
____________________________________________________________CLD
__________________________________________________________REPE C
MPSB
___________________________________________________________JNE s
econd_test_for_EMM_error_exit
second_test_for_EMM_exit:
____________________________________________________________POP D
S___________________________________________; EMM is present in
____________________________________________________________STC
; the system
____________________________________________________________RET
second_test_for_EMM_error_exit:
____________________________________________________________POP D
S__________________________________________; EMM is NOT present
____________________________________________________________CLC
; in the system
____________________________________________________________RET
ASCII_device_name: DB "EMMXXXX0"
second_test_for_EMM ENDP
3-10 3000275-003Testing for the presence of the EMM
CHAPTER 4. EXAMPLE EXPANDED MEMORY PROGRAMS
This chapter presents example procedures that use expanded
memory. The first part of this chapter lists the basic
characteristics of the example procedures. Later sections
present annotated outlines (or flow charts) for writing transient
and resident application programs that use expanded memory.
The actual example code (with comments) is listed at the end of
the chapter.
Characteristics of the example procedures
The example procedures in this chapter illustrate the EMM
operations that a typical transient or resident program carries
out when using expanded memory. When reading the examples, keep
in mind that they:
1. Are implemented in assembly language.
2. Assume that all variables reside in the same segment and
that DS is already set up for access to all the variables.
3. Assume that the application program will determine what to
do with EMM error conditions when they are returned from the
example procedures. The example procedures do not provide
any error processing when an EMM error is detected. You
could include a simple EMM error handling procedure that
displays the function which was invoked and the status which
was returned.
Transient application program
A transient program is loaded by DOS, executes, and doesn't
remain resident in the system after it returns control to DOS.
After a transient program returns control to DOS, the memory it
used is available for other programs.
This section presents an outline (or flow chart) which
illustrates the structure of an example transient application
program. It also includes a detailed explanation of the outline.
Flow chart of a transient application program
The following flow chart shows the structure of an example
transient application program that uses expanded memory. The
next section contains detailed explanations of the individual
processes.
Example expanded memory programs300275-003 4-11
Explanation of the transient application program flow chart
This example transient application program is invoked from the
DOS command line and loaded by DOS. It first executes some
initialization procedures, then some processing procedures that
use expanded memory, and finally, some terminating procedures.
After the program terminates, it returns control to DOS.
The following subsections describe the individual procedures
within the flow chart. These subsections refer you to the actual
code for each procedure.
4-12 300275-003Example expanded memory programs
Initialization procedures
The block labeled "transient application initialization"
represents any preliminary processing and interaction with the
user that the program may need to perform. After the transient
program performs these operations, it should initialize the EMM.
The block labeled "EMM transient initialization" represents code
that prepares the EMM so it can run with the application program.
An example of this type of procedure (called EMM_transient_init)
is shown on page 4-10.
This procedure uses the "open handle" technique to determine
whether the EMM is present in the system. (The "open handle"
technique is described in Chapter 3 of this specification.) The
procedure also ensures that the version of the EMM loaded in the
system is compatible with the version required by the application
program, and it obtains the number of expanded memory pages your
application code requests.
Processing procedures
The block labeled "transient application processing (not
requiring expanded memory)" represents processing the program
performs which does not require access to expanded memory.
The block labeled "EMM access" represents the code that the
application must execute before it can access expanded memory.
(The expanded memory was allocated to it by the "EMM transient
initialization" procedure.) An example of this type of procedure
(called EMM_access) is shown on page 4-16. The example procedure
maps the logical page allocated to the EMM handle into the
physical page the application program specified. (The
"EMM_transient_init" procedure assigned the EMM handle.)
The block labeled "transient application processing (requiring
expanded memory)" represents the processing within the program
that uses the expanded memory area. The application can use the
expanded memory area for data or code. An application program
can locate code in the page frame and execute it, or it can just
store data and access it. Your program can use the page frame to
store anything except its stack; there is no code restriction.
The loop to the block labeled "EMM access" represents a possible
iterative process. The application may have a requirement to
access many pages within expanded memory. The process of calling
the "EMM_access" procedure and accessing the data in the mapped
page is iterative.
Terminating procedure
Once the application completes its task, it must return the
expanded memory that the EMM allocated to it.
Example expanded memory programs300275-003 4-13
The block labeled "EMM termination" represents this phase of the
application program's execution. An example of this type of
procedure (called EMM_termination) is shown on page 4-17. This
example procedure returns both the EMM handle and the logical
pages to the EMM. (The EMM handle was issued and the logical
pages were allocated by "EMM_transient_init" procedure.)
The block labeled "transient application termination" represents
the code the application needs to execute by before it terminates
and returns control to DOS.
Resident application program
A resident application program is loaded by DOS, executes, and
remains resident in the system after it returns control to DOS.
This type of program is usually invoked by the operating system,
a hardware interrupt, or a software interrupt.
This section presents an outline (or flow chart) which
illustrates the structure of an example resident application
program. It also includes a detailed explanation of the flow
chart.
Flow Chart of a resident application program
The following flow chart shows the structure of an example
resident application program that uses expanded memory. The next
section contains detailed explanations of the individual
processes.
4-14 300275-003Example expanded memory programs
Explanation of the resident application program flow chart
Resident application programs are loaded from the CONFIG.SYS file
as drivers or they are loaded by DOS and use the DOS "terminate
and stay resident" function.
Resident programs have special characteristics which must be
taken into consideration when using expanded memory. They must
initialize their own data structures as well as initializing the
EMM (getting the page frame address, getting a handle assigned
and allocating pages). Resident programs also consume a portion
of conventional memory, making it unavailable for use by
transient programs.
Since they may interrupt transient programs which use expanded
memory, resident programs must save and restore the state of the
page mapping registers when using expanded memory. Functions 8
and 9 (described in Chapter 2) are provided for just this
purpose.
This example resident application program illustrated by the
previous flow chart performs the following operations:
o initializes its internal data structures as well as
initializing the EMM
o saves the CPU state
o performs any processing it requires before accessing expanded
memory
o saves the state of the expanded memory hardware
o accesses expanded memory
o restores the state of the expanded memory hardware
o terminates
o restores the CPU state
The remainder of this section describes these operations in
detail.
Initializing the resident program and the EMM
The block labeled "resident application initialization "
represents any preliminary processing the resident program may
need to perform.
The block labeled "EMM resident initialization" represents the
code that prepares the EMM so it can run with the resident
application program. A example of this type of procedure (called
EMM_resident_init) is shown on page 4-13.
Example expanded memory programs300275-003 4-15
This procedure uses the "get interrupt vector" test described in
Chapter 3 to determine whether the EMM is present in the system.
The procedure also ensures that the version of the EMM loaded in
the system is compatible with the version required by the
application program. In addition this procedure obtains an EMM
handle and allocates the required number of pages for the
resident program. Typically, the resident program will keep the
handle assigned to it as well as the pages allocated to it until
the system is rebooted.
The first two blocks in the flow chart aren't directly connected
to the blocks that follow. This flow chart depicts a common
situation encountered in resident programs. Resident programs
can be divided into a section of code which executes and then
isn't needed afterwards. The programs usually return the memory
consumed by the initialization section of the resident program to
DOS for re-use by other programs.
The "resident" section of the resident program remains in the
memory until the system is rebooted. Typically, this code is
executed whenever a particular hardware or software interrupt
occurs, or when it is "called" by DOS.
The first two blocks represent initialization code, which after
it executes, never needed again. So, the code returns the memory
which it used to DOS. The succeeding blocks in the flow chart
represent the resident section of the code which is executed only
when some event, such as a hardware or software interrupt,
occurs. For this reason, the first two blocks in the flow chart
are not connected to the succeeding blocks.
Saving the current state of the CPU
The block labeled "suspend transient program's execution"
represents the code responsible for saving the current state of
the CPU when the resident code begins executing. A hardware or
software interrupt usually causes the resident code to begin
executing.
Saving the CPU's state is essential. At some point, the resident
program must return control to the previously-executing program.
Before the original program can continue to function correctly,
the CPU must be returned to the exact state it was in before the
resident program began executing.
Resident processing performed before accessing expanded memory
The block labeled "resident processing (not requiring expanded
memory)" represents processing which must be performed by the
resident application before it needs to access expanded memory.
4-16 300275-003Example expanded memory programs
Saving the state of the expanded memory hardware
The block labeled "save EMM map state" represents the code that
must be executed before the resident program attempts to access
expanded memory. This code must save the state of the expanded
memory hardware before the resident program can map any of its
pages into the page frame.
Saving the state of the expanded memory hardware is essential,
because another program may have been using it when the resident
program took over. Saving the mapping state of the expanded
memory hardware ensures that both the resident program and any
transient program that may have been executing when the resident
program started are not corrupted. An example of such a
procedure (called EMM_save_map_state) is shown on page 4-18.
Accessing expanded memory
The block labeled "EMM access" represents the code that the
resident program must execute before it can access expanded
memory. (The expanded memory was allocated to it by "EMM
resident initialization" procedure described earlier.) An
example of this type of procedure (called EMM_access) is shown on
page 4-16.
The example procedure simply maps one of the logical pages
allocated to the EMM handle assigned by the "EMM_resident_init"
procedure into the physical page the resident program specified.
The block labeled "resident application processing (requiring
expanded memory)" represents the processing within the resident
program which uses expanded memory. The resident program can use
expanded memory for data or code. A resident program can locate
code in the page frame and execute it or it can just store data
and access it. Your program can use the page frame to store
anything except its stack; there is no code restriction.
The loop to the block labeled "EMM access" represents a possible
iterative process. The resident program may have a requirement
to access many pages within expanded memory. The process of
calling the "EMM_access" procedure and accessing the data in the
mapped page is iterative.
Restoring the state of the expanded memory hardware
The block labeled "restore EMM map state" represents the code in
a resident program that restores the state of the expanded memory
hardware. This code restores the expanded memory hardware to the
state it was in before the resident program mapped its pages into
the page frame. An example procedure (called
EMM_restore_map_state) is shown on page 4-19.
Example expanded memory programs300275-003 4-17
Terminating the resident program
The block labeled "resident processing termination" represents
any processing that the resident program must do before it
terminates. After the resident program terminates, it returns
control to the transient program that was executing before it
took control.
Restoring the CPU state
The block labeled "restore CPU state" represents the code
responsible for restoring the CPU to the state it was before the
resident program took control.
4-18 300275-003Example expanded memory programs
Example EMM procedures
This section lists the code for all the EMM procedures referenced
in the previous examples.
;;
;______________________________________________________________
______________________________________________________________;
;___________FUNCTIONAL "EQUATES" USED THROUGHOUT THESE EXAMPLES
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
EMM_interrupt EQU 67h
get_page_frame_address EQU 41h
get_unalloc_page_count EQU 42h
allocate_pages EQU 43h
map_handle_page EQU 44h
deallocate_pages EQU 45h
get_emm_version EQU 46h
save_page_map EQU 47h
restore_page_map EQU 48h
;;
;______________________________________________________________
______________________________________________________________;
;_______________STATUS "EQUATES" USED THROUGHOUT THESE EXAMPLES
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
function_passed EQU 00h ; status which
indicates
; that the function
; invocation
completed
; successfully
EMM_not_resident EQU 01h ; status which
indicates
; the the EMM is not
; loaded in the
system
EMM_version_mismatch EQU 02h ; status which
indicates
; that the version
of EMM
; is not compatible
with
; the version
required by
Example expanded memory programs300275-003 4-19
; the application
program
insuff_total_pages EQU 87h ; status which EMM
; returns if an
attempt
; was made to
allocate
; more pages than
exist
; in expanded memory
insuff_unalloc_pages EQU 88h ; status which EMM
; returns if an
attempt
; was made to
allocate
; more pages than
are
; currently un-
allocated
4-20 300275-003Example expanded memory programs
;;
;______________________________________________________________
______________________________________________________________;
;______________________VARIABLES USED THROUGHOUT THESE EXAMPLES
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
application_EMM_version DB 30h ; the lowest version
; number of the EMM
which
; the application is
; compatible with
application_pages_req DW 0 ; number of pages
the
; application
requires
EMM_handle DW 0 ; storage for the
handle
; which the EMM
assigns
; to the application
EMM_status DB 0 ; storage for the
status
; which the EMM
returns
; to the application
logical_page DW 0 ; specifies the
logical
; page which the
; application needs
to
; access
physical_page DB 0 ; specifies where
within
; the page frame the
; application needs
to
; access the logical
page
page_frame_segment DW 0 ; specifies the page
; frame base segment
; address at which
the
; EMM has located
the
; physical pages
Example expanded memory programs300275-003 4-21
;;
;______________________________________________________________
______________________________________________________________;
;___________EXAMPLE PROCEDURE #1 EMM TRANSIENT INITIALIZATION
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;_______This example PROCEDURE determines whether or not EMM is
______________________________________________________________;
;_present in your your system. Next, it determines whether the
______________________________________________________________;
;____application can run with the version of EMM present in the
______________________________________________________________;
;___system and whether the application will "fit" in the number
______________________________________________________________;
;_____of unallocated pages the EMM has available for use. The,
______________________________________________________________;
;__procedure then locates the page frame segment, and allocates
______________________________________________________________;
;__________________________________________the pages requested.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;___If the application does not "fit" in the available expanded
______________________________________________________________;
;__memory, or if some other EMM error is encountered, then this
______________________________________________________________;
;____________________________________________________procedure:
______________________________________________________________;
;__________________1. Returns the status returned by the EMM in E
MM_status._____________________________________________________ ;
;________________________________2. Returns to the application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;____If the application "fits" in the available expanded memory
______________________________________________________________;
;_______________________________________________then it should:
______________________________________________________________;
;__________1. Get the version number and determines whether the
______________________________________________________________;
;________ application is compatible with this version of EMM.
______________________________________________________________;
;________2. Get the page frame segment address from the EMM and
______________________________________________________________;
;_____________________________ save it in page_frame_segment.
______________________________________________________________;
;___________________3. Get a handle from the EMM and save it in
______________________________________________________________;
;________________________________________________ EMM_handle.
______________________________________________________________;
;____________________________4. Allocate the pages specified in
______________________________________________________________;
;_____________________________________ application_pages_req.
______________________________________________________________;
4-22 300275-003Example expanded memory programs
;_________________5. Return an EMM passed status in emm_status.
______________________________________________________________;
;_________________________________6. Return to the application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
EMM_transient_init PROC NEAR
;;
; DETERMINE WHETHER OR NOT EMM IS RESIDENT IN THE SYSTEM ___
_______________________________________________________________ ;
;;
_______________________________________________________________
____________________________________________________________MOV B
YTE PTR EMM_status, EMM_not_resident___________________________
_______________________________________________________________
; assume that the test
___________________________________________________________CALL f
irst_test_for_EMM_________________________; for the presence of
____________________________________________________________JNC E
MM_transient_init_exit__________________________; EMM will fail
;;
; DETERMINE WHETHER RESIDENT VERSION OF EMM IS_______________
______________________________________________________________;
; COMPATIBLE WITH APPLICATION________________________________
______________________________________________________________;
;;
____________________________________________________________MOV A
H, get_emm_version________________________; get the EMM version
____________________________________________________________INT 6
7h
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
Example expanded memory programs300275-003 4-23
____________________________________________________________ORA A
H, AH_________________________________________; if the function
____________________________________________________________JNZ E
MM_transient_init_exit___________________; failed return to the
_______________________________________________________________
; application
____________________________________________________________MOV B
YTE PTR emm_status,emm_version mismatch
____________________________________________________________CMP A
L, application_emm_version__; assume that the installed version
_____________________________________________________________JB e
mm_transient_init_exit_______________; is incompatible with the
_______________________________________________________________
; application version
;;
; GET THE PAGE FRAME SEGMENT ADDRESS_________________________
______________________________________________________________;
;;
____________________________________________________________MOV A
H, get_page_frame_address__________________; get the page frame
____________________________________________________________INT E
MM_interrupt__________________________________; segment address
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
____________________________________________________________ORA A
H, AH_________________________________________; if the function
____________________________________________________________JNZ E
MM_transient_init_exit___________________; failed return to the
_______________________________________________________________
; application
____________________________________________________________MOV p
age_frame_segment, BX_____________________; save the page frame
_______________________________________________________________
; segment address
;;
; GET THE NUMBER OF TOTAL AND UNALLOCATED PAGES PRESENT______
______________________________________________________________;
;;
____________________________________________________________MOV A
H, get_unalloc_page_count___________________; get the total and
____________________________________________________________INT E
MM_interrupt_______________________________; un-allocated pages
_______________________________________________________________
; in the system
4-24 300275-003Example expanded memory programs
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
____________________________________________________________ORA A
H, AH_________________________________________; if the function
____________________________________________________________JNZ E
MM_transient_init_exit___________________; failed return to the
_______________________________________________________________
; application
;;
; DETERMINE WHETHER APPLICATION CAN RUN WITH THIS NUMBER_____
______________________________________________________________;
; OF TOTAL AND UNALLOCATED______________________________PAGES
______________________________________________________________;
;;
____________________________________________________________MOV B
YTE PTR EMM_status, insuff_total_pages_________________________
_______________________________________________________________
; check total pages
____________________________________________________________CMP a
pplication_pages_req, DX_________________________; not required
_____________________________________________________________JA E
MM_transient_init_exit
____________________________________________________________MOV B
YTE PTR EMM_status, insuff_unalloc_pages
____________________________________________________________CMP a
pplication_pages_req, BX______________; check unallocated pages
_____________________________________________________________JA E
MM_transient_init_exit
Example expanded memory programs300275-003 4-25
;;
; GET AN EMM HANDLE AND SAVE IT______________________________
______________________________________________________________;
; ALLOCATE THE NUMBER OF PAGES THE APPLICATION REQUIRES______
______________________________________________________________;
;;
____________________________________________________________MOV A
H, allocate_pages____________________________; get a handle and
____________________________________________________________MOV B
X, application_pages_req_______________________; allocate pages
____________________________________________________________INT E
MM_interrupt___________________________________; to that handle
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
EMM_transient_init_exit:
;;
; RETURN TO THE APPLICATION__________________________________
______________________________________________________________;
;;
____________________________________________________________RET
; return to the
_______________________________________________________________
; application
EMM_transient_init ENDP
4-26 300275-003Example expanded memory programs
;;
;______________________________________________________________
______________________________________________________________;
;____________EXAMPLE PROCEDURE #2 EMM RESIDENT INITIALIZATION
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;_______This example PROCEDURE determines whether or not EMM is
______________________________________________________________;
;_present in your your system. Next, it determines whether the
______________________________________________________________;
;____application can run with the version of EMM present in the
______________________________________________________________;
;___system and whether the application will "fit" in the number
______________________________________________________________;
;_____of unallocated pages the EMM has available for use. The,
______________________________________________________________;
;__procedure then locates the page frame segment, and allocates
______________________________________________________________;
;__________________________________________the pages requested.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;___If the application does not "fit" in the available expanded
______________________________________________________________;
;__memory, or if some other EMM error is encountered, then this
______________________________________________________________;
;____________________________________________________procedure:
______________________________________________________________;
;__________________1. Returns the status returned by the EMM in E
MM_status._____________________________________________________ ;
;________________________________2. Returns to the application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;____If the application "fits" in the available expanded memory
______________________________________________________________;
;_______________________________________________then it should:
______________________________________________________________;
;__________1. Get the version number and determines whether the
______________________________________________________________;
;________ application is compatible with this version of EMM.
______________________________________________________________;
;________2. Get the page frame segment address from the EMM and
______________________________________________________________;
;_____________________________ save it in page_frame_segment.
______________________________________________________________;
;___________________3. Get a handle from the EMM and save it in
______________________________________________________________;
;________________________________________________ EMM_handle.
______________________________________________________________;
;____________________________4. Allocate the pages specified in
______________________________________________________________;
;_____________________________________ application_pages_req.
______________________________________________________________;
Example expanded memory programs300275-003 4-27
;______________________5. Return a passed status in EMM_status.
______________________________________________________________;
;_________________________________6. Return to the application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
EMM_resident_init PROC NEAR
;;
; DETERMINE WHETHER EMM IS RESIDENT IN THE SYSTEM ___________
_______________________________________________________________ ;
;;
_______________________________________________________________
____________________________________________________________MOV B
YTE PTR EMM_status, EMM_not_resident___________________________
_______________________________________________________________
; assume that the test
___________________________________________________________CALL s
econd_first_test_for_EMM__________________; for the presence of
____________________________________________________________JNC E
MM_resident_init_exit___________________________; EMM will fail
;;
; DETERMINE WHETHER RESIDENT VERSION OF EMM IS_______________
______________________________________________________________;
; COMPATIBLE WITH APPLICATION________________________________
______________________________________________________________;
;;
____________________________________________________________MOV A
H, get_EMM_version________________________; get the EMM version
____________________________________________________________INT 6
7h
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
4-28 300275-003Example expanded memory programs
____________________________________________________________ORA A
H, AH_________________________________________; if the function
____________________________________________________________JNZ E
MM_resident_init_exit____________________; failed return to the
_______________________________________________________________
; application
____________________________________________________________MOV B
YTE PTR EMM_status, EMM_version_mismatch_______________________
_______________________________________________________________
;assume that the installed
____________________________________________________________CMP A
L, application_EMM_version______;version of EMM is incompatible
_____________________________________________________________JB E
MM_resident_init_exit_______; incompatible with the application
_______________________________________________________________
; version
;;
; GET THE PAGE FRAME SEGMENT ADDRESS_________________________
______________________________________________________________;
;;
____________________________________________________________MOV A
H, get_page_frame_address__________________; get the page frame
____________________________________________________________INT E
MM_interrupt__________________________________; segment address
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
____________________________________________________________ORA A
H, AH_________________________________________; if the function
____________________________________________________________JNZ E
MM_resident_init_exit____________________; failed return to the
_______________________________________________________________
; application
____________________________________________________________MOV p
age_frame_segment, BX_____________________; save the page frame
_______________________________________________________________
; segment address
;;
; GET THE NUMBER OF TOTAL AND UNALLOCATED PAGES PRESENT______
______________________________________________________________;
;;
____________________________________________________________MOV A
H, get_unalloc_page_count___________________; get the total and
____________________________________________________________INT E
MM_interrupt________________________________; un-allocated page
_______________________________________________________________
; in the system
Example expanded memory programs300275-003 4-29
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
____________________________________________________________ORA A
H, AH_________________________________________; if the function
____________________________________________________________JNZ E
MM_resident_init_exit____________________; failed return to the
_______________________________________________________________
; application
;;
; DETERMINE WHETHER APPLICATION CAN RUN WITH THIS NUMBER_____
______________________________________________________________;
; OF TOTAL AND UNALLOCATED______________________________PAGES
______________________________________________________________;
;;
____________________________________________________________MOV B
YTE PTR EMM_status, insuff_total_pages_________________________
_______________________________________________________________
;check total pages
____________________________________________________________CMP a
pplication_pages_req, DX
_____________________________________________________________JA E
MM_resident_init_exit
____________________________________________________________MOV B
YTE PTR EMM_status, insuff_unalloc_pages
____________________________________________________________CMP a
pplication_pages_req, BX_______________;check unallocated pages
_____________________________________________________________JA E
MM_resident_init_exit
;;
; GET AN EMM HANDLE AND SAVE IT______________________________
______________________________________________________________;
; ALLOCATE THE NUMBER OF PAGES THE APPLICATION REQUIRES______
______________________________________________________________;
;;
____________________________________________________________MOV A
H, allocate_pages____________________________; get a handle and
____________________________________________________________MOV B
X, application_pages_req_______________________; allocate pages
____________________________________________________________INT E
MM_interrupt___________________________________; to that handle
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
EMM_resident_init_exit:
4-30 300275-003Example expanded memory programs
;;
; RETURN TO THE APPLICATION__________________________________
______________________________________________________________;
;;
____________________________________________________________RET
; return to the
_______________________________________________________________
; application
EMM_resident_init ENDP
Example expanded memory programs300275-003 4-31
;;
;______________________________________________________________
______________________________________________________________;
;_____________________________EXAMPLE PROCEDURE #3 EMM ACCESS
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;_____This example PROCEDURE performs the following processing:
______________________________________________________________;
;_________1. Maps the logical page specified by logical_page at
______________________________________________________________;
;___________ the physical page specified by physical_page. It
______________________________________________________________;
;_______________________ uses the handle saved in EMM_handle.
______________________________________________________________;
;_________2. Save the status returned by the EMM in EMM_status.
______________________________________________________________;
;_________________________________3. Return to the application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
EMM_access PROC NEAR
_______________________________________________________________
;;
; MAP THE LOGICAL PAGE SPECIFIED BY logical_page AT THE______
______________________________________________________________;
; PHYSICAL PAGE SPECIFIED BY physical_page___________________
______________________________________________________________;
;;
____________________________________________________________MOV A
H, map_handle_page_______________________________; map the page
____________________________________________________________MOV D
X, EMM_handle
____________________________________________________________MOV B
X, logical_page
____________________________________________________________MOV A
L, physical_page
____________________________________________________________INT E
MM_interrupt
;;
; RETURN THE STATUS_______________________________________
______________________________________________________________;
;;
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
;;
4-32 300275-003Example expanded memory programs
; RETURN TO THE APPLICATION_______________________________
______________________________________________________________;
;;
____________________________________________________________RET
; return to the
_______________________________________________________________
; application
EMM_access ENDP
Example expanded memory programs300275-003 4-33
;;
;______________________________________________________________
______________________________________________________________;
;________________________EXAMPLE PROCEDURE #4 EMM TERMINATION
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;_____This example PROCEDURE performs the following processing:
______________________________________________________________;
;____________1. "Close" the EMM handle assigned to your program
______________________________________________________________;
;____________ and deallocates the pages EMM allocated to your
______________________________________________________________;
;___________ program. It uses the handle saved in EMM_handle.
______________________________________________________________;
;_________2. Save the status returned by the EMM in EMM_status.
______________________________________________________________;
;_________________________________3. Return to the application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
EMM_terminate PROC NEAR
;;
; CLOSE THE EMM HANDLE_______________________________________
______________________________________________________________;
; DEALLOCATE ALL PAGES ALLOCATED TO IT_______________________
______________________________________________________________;
;;
____________________________________________________________MOV A
H, deallocate_pages______________________; close the handle and
____________________________________________________________MOV D
X, EMM_handle____________________________; deallocate all pages
____________________________________________________________INT E
MM_interrupt__________________________________; allocated to it
;;
; RETURN THE STATUS__________________________________________
______________________________________________________________;
;;
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
;;
; RETURN TO THE APPLICATION__________________________________
______________________________________________________________;
;;
4-34 300275-003Example expanded memory programs
____________________________________________________________RET
; return to the
_______________________________________________________________
; application
EMM_terminate ENDP
Example expanded memory programs300275-003 4-35
;;
;______________________________________________________________
______________________________________________________________;
;_____________________EXAMPLE PROCEDURE #5 EMM SAVE MAP STATE
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;_____This example PROCEDURE performs the following processing:
______________________________________________________________;
;_____________________1. Saves the page mapping register state.
______________________________________________________________;
;_________________________2. Save the EMM status in EMM_status.
______________________________________________________________;
;________________________3. Return to the resident application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
EMM_save_map_state PROC NEAR
____________________________________________________________MOV A
H, save_page_map_________________________; save the contents of
____________________________________________________________MOV D
X, EMM_handle________________________________; the page mapping
____________________________________________________________INT E
MM_interrupt________________________________________; registers
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
____________________________________________________________RET
; return to the
_______________________________________________________________
; application
EMM_save_map_state ENDP
4-36 300275-003Example expanded memory programs
;;
;______________________________________________________________
______________________________________________________________;
;__________________EXAMPLE PROCEDURE #6 EMM RESTORE MAP STATE
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;_____This example PROCEDURE performs the following processing:
______________________________________________________________;
;________________1. Restore the page mapping register state, if p
ossible._______________________________________________________ ;
;_________________________2. Save the EMM status in EMM_status.
______________________________________________________________;
;________________________3. Return to the resident application.
______________________________________________________________;
;______________________________________________________________
______________________________________________________________;
;;
EMM_restore_map_state PROC NEAR
____________________________________________________________MOV A
H, restore_page_map______________________; restore the contents
____________________________________________________________MOV D
X, EMM_handle_____________________________; of the page mapping
____________________________________________________________INT E
MM_interrupt________________________________________; registers
____________________________________________________________MOV E
MM_status, AH_________________________________; save the status
____________________________________________________________RET
; return to the
_______________________________________________________________
; application
EMM_restore_map_state ENDP
Example expanded memory programs300275-003 4-37
GLOSSARY
This glossary defines some of the terms that are used frequently
in this specification. The terms are listed in alphabetical
order.
Most of these terms are defined for readers who understand
technical terminology and are familiar with IBM PCs, XTs, and ATs
or compatibles.
Application program
An application program is the program you write and your customer
uses. Some categories of application software are word
processors, database managers, spreadsheet managers, and project
managers.
Conventional memory
Conventional memory refers to the memory DOS recognizes. In PCs,
XTs, and ATs, this is memory between 0 and 640K bytes. Because
application programs let DOS manage their memory, they can use
only conventional memory.
EMM
See Expanded Memory Manager.
EMM functions
The EMM functions are a set of standard interfaces to expanded
memory. They provide application programs with the operators
required to use expanded memory.
EMM handle
An EMM handle is a value that the EMM assigns to a file or a
device. Previous versions of this specification referred to an
EMM handle as a Process ID.
EMM Status code
A code that an EMM function returns which indicates something
about the result of running the function. Some status codes may
indicate whether the function worked correctly and others may
tell you something about the expanded memory hardware or
software.
Glossary-38 300275-003
Expanded memory
Expanded memory is a special kind of memory that goes beyond
DOS's 640K-byte limit. Application programs that adhere to the
Lotus/Intel Expanded Memory Specification can use the Expanded
Memory Manager (EMM) to manage expanded memory just as other
programs use DOS to manage conventional memory.
Expanded Memory Manager
The Expanded Memory Manager (EMM) is a standard device driver
that manages expanded memory in much the same way DOS manages
conventional memory.
Extended memory
Extended memory is the 15M-byte address space outside the memory
DOS can access. This address space is of little use to those
application programs that use DOS. DOS does not recognized
memory above 640K bytes; the XENIX operating system uses extended
memory.
Logical page
The EMM allocates expanded memory in 16K-byte units called
logical pages.
Mapping
Mapping is the process of making a logical page of memory
available for the processor to use. Mapping is done within one
of the four physical pages defined by this specification.
Page frame
A page frame is the collection of four 16k-byte contiguous,
physical pages from which an application program accesses
expanded memory.
Page frame base address
A page frame base address is the location (in segment format) of
the first byte of the page frame.
300275-003 Glossary-39
Physical page
A physical page is the range of memory addresses occupied by a
single 16k-byte page. The 16k-byte page is one of the four pages
defined as a page frame.
Process ID
See EMM handle.
Resident application program
A resident application program is loaded by DOS, executes, and
remains resident in the system after it returns control to DOS.
This type of program occupies memory and is usually invoked by
the operating system, an application program, or the hardware.
Some examples of resident application programs are RAM disk
drivers, print spoolers, and "pop-up" desktop programs.
Transient application program
A transient application program is loaded by DOS, executes, and
doesn't remain in the system after it returns control to DOS.
After a transient application program returns control to DOS, the
memory it used is available for other programs.
Glossary-40 300275-003
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