20th Century Video Alman…Century in Depth - Sports/ALMANAC_03.iso/vesa/everex/vesa05.txt

Text File | 1990-01-11 | 39KB | 1,049 lines

VESA Super VGA Standard VS891101

Video Electronics Standards Association
1330 South Bascom Avenue, Suite D
San Jose, CA 95128-4502
Phone: [phone]
Fax: [phone]





SUPER VGA BIOS EXTENSION
Standard # VS891101
November 14, 1989




OBJECTIVE

To standardize a common software interface to Super VGA video
adapters in order to provide simplified software application
access to advanced VGA products.


SUMMARY

The standard provides a set of functions which an application
program can use to a) obtain information about the
capabilities and characteristics of a specific Super VGA
implementation and b) to control the operation of such
hardware in terms of video mode initialization and video
memory access. The functions are provided as an extension to
the VGA BIOS video services, accessed through interrupt 10.




Contents


1.    Introduction

2.    Goals and Objectives
    2.1    Video environment information
    2.2    Programming support
    2.3    Compatibility
    2.4    Scope of standard

3.    Standard VGA BIOS

4.    Super VGA Mode Numbers

5.    CPU Video Memory Windows
    5.1    Hardware design considerations
        5.1.1    Limited to 64k/128k of CPU address
            space
        5.1.2    Crossing CPU video memory window
            boundaries
        5.1.3    Operating on data from different areas
        5.1.4    Combining data from two different
            windows
    5.2    Different types of hardware windows
        5.2.1    Single window systems
        5.2.2    Dual window systems

6.    Extended VGA BIOS
    6.1    Status information
    6.2    00h - Return Super VGA information
    6.3    01h - Return Super VGA mode information
    6.4    02h - Set Super VGA mode
    6.5    03h - Return Super VGA mode
    6.6    04h - Save/restore Super VGA video state
    6.7    06h - Super VGA video memory window control

7.    Application Example



1.    Introduction


This document contains a specification for a standardized
interface to extended VGA video modes and functions. The
specification consists of mechanisms for supporting standard
extended video modes and functions that have been approved by
the main VESA committee and non-standard video modes that an
individual VGA supplier may choose to add, in a uniform manner
that application software can utilize without having to
understand the intricate details of the particular VGA
hardware.

The primary topics of this specification are definitions of
extended VGA video modes and the functions necessary for
application software to understand the characteristics of the
video mode and manipulate the extended memory associated with
the video modes.

Readers of this document should already be familiar with
programming VGAs at the hardware level and Intel iAPX real
mode assembly language. Readers who are unfamiliar with
programming the VGA should first read one of the many VGA
programming tutorials before attempting to understand these
extensions to the standard VGA.


2.    Goals and Objectives


The IBM VGA(1) has become a de-facto standard in the PC graphics
world. A multitude of different VGA offerings exist in the
marketplace, each one providing BIOS or register compatibility
with the IBM VGA. More and more of these VGA compatible
products implements various supersets of the VGA standard.
These extensions range from higher resolutions and more colors
to improved performance and even some graphics processing
capabilities. Intense competition has dramatically improved
the price/performance ratio, to the benefit of the end user.

However, several serious problems face a software developer
who intends to take advantage of these "Super VGA"(2)
environments. Because there is no standard hardware
implementation, the developer is faced with widely disparate
Super VGA hardware architectures. Lacking a common software
interface, designing applications for these environments is
costly and technically difficult. Except for applications
supported by OEM-specific display drivers, very few software
packages can take advantage of the power and capabilities of
Super VGA products.

The purpose of the VESA VGA BIOS Extension is to remedy this
situation. Being a common software interface to Super VGA
graphics products, the primary objective is to enable
application and system software to adapt to and exploit the
wide range of features available in these VGA extensions.

Specifically, the VESA BIOS Extension attempts to address the
following two main issues: a) Return information about the
video environment to the application and b) Assist the
application in initializing and programming the hardware.


2.1    Video environment information

Today, an application has no standard mechanism to determine
what Super VGA hardware it is running on. Only by knowing OEM-
specific features can an application determine the presence of
a particular video board. This often involves reading and
testing registers located at I/O addresses unique to each OEM.
By not knowing what hardware an application is running on,
few, if any, of the extended features of the underlying
hardware can be used.

The VESA BIOS Extension provides several functions to return
information about the video environment. These functions
return system level information as well as video mode specific
details. Function 00h returns general system level
information, including an OEM identification string. The
function also returns a pointer to the supported video modes.
Function 01h may be used by the application to obtain
information about each supported video mode. Function 03h
returns the current video mode.


2.2    Programming support

Due to the fact that different Super VGA products have
different hardware implementations, application software has
great difficulty in adapting to each environment. However,
since each is based on the VGA hardware architecture,
differences are most common in video mode initialization and
memory mapping. The rest of the architecture is usually kept
intact, including I/O mapped registers, video buffer location
in the CPU address space, DAC location and function, etc.

The VESA BIOS Extension provides several functions to
interface to the different Super VGA hardware implementations.
The most important of these is Function 02h, Set Super VGA
video mode. This function isolates the application from the
tedious and complicated task of setting up a video mode.
Function 05h provides an interface to the underlying memory
mapping hardware. Function 04h enables an application to save
and restore a Super VGA state without knowing anything of the
specific implementation.


2.3    Compatibility

A primary design objective of the VESA BIOS Extension is to
preserve maximum compatibility to the standard VGA
environment. In no way should the BIOS extensions compromise
compatibility or performance. Another but related concern is
to minimize the changes necessary to an existing VGA BIOS.
RAM- as well as ROM-based implementations of the BIOS
extension should be possible.


2.4    Scope of standard

The purpose of the VESA BIOS Extension is to provide support
for extended VGA environments. Thus, the underlying hardware
architecture is assumed to be a VGA. Graphics software that
drives a Super VGA board, will perform its graphics output in
generally the same way it drives a standard VGA, ie. writing
directly to a VGA style frame buffer, manipulating graphics
controller registers, directly programming the palette etc. No
significant graphics processing will be done in hardware. For
this reason, the VESA BIOS Extension does not provide any
graphics output functions, such as BitBlt, line or circle
drawing, etc.

An important constraint of the functionalities that can be
placed into the VESA BIOS Extension, is that ROM-space is
severely limited in certain existing BIOS implementations.

Outside the scope of this VESA BIOS Extension is handling of
different monitors and monitor timings. Such items are dealt
with in other VESA fora. The purpose of the VESA BIOS
Extension is to provide a standardized software interface to
Super VGA graphics modes, independent of monitor and monitor
timing issues.


3.    Standard VGA BIOS


A primary design goal with the VESA BIOS Extension is to
minimize the effects on the standard VGA BIOS. Standard VGA
BIOS functions should need to be modified as little as
possible. This is important since ROM- as well as RAM-based
versions of the extension may be implemented.

However, two standard VGA BIOS functions are affected by the
VESA extension. These are Function 00h (Set video mode) and
Function 0Fh (Read current video state). VESA-aware
applications will not set the video mode using VGA BIOS
function 00h. Nor will such applications use VGA BIOS function
0Fh. VESA BIOS functions 02h (Set Super VGA mode) and 03h (Get
Super VGA mode) will be used instead.

However, VESA-unaware applications (such as old Pop-Up
programs and other TSRs, or the CLS command of MS-DOS), might
use VGA BIOS function 0Fh to get the present video mode. Later
it may call VGA BIOS function 00h to restore/reinitialize the
old video mode.

To make such applications work, VESA recommends that whatever
value returned by VGA BIOS function 0Fh (it is up to the OEM
to define this number), it can be used to reinitialize the
video mode through VGA BIOS function 00h. Thus, the BIOS
should keep track of the last Super VGA mode in effect.

It is recommended, but not mandatory, to support output
functions (such as TTY-output, scroll, set pixel, etc.) in
Super VGA modes. If the BIOS extension doesn't support such
output functions, bit D2 (Output functions supported) of the
ModeAttributes field (returned by VESA BIOS function 01h)
should be cleared.


4.    Super VGA mode numbers


Standard VGA mode numbers are 7 bits wide and presently ranges
from 00h to 13h. OEMs have defined extended video modes in the
range 14h to 7Fh. Values in the range 80h to FFh cannot be
used, since VGA BIOS function 00h (Set video mode) interprets
bit 7 as a flag to clear/not clear video memory.

Due to the limitations of 7 bit mode numbers, VESA video mode
numbers are 15 bits wide. To initialize a Super VGA mode, its
number is passed in the BX register to VESA BIOS function 02h
(Set Super VGA mode).

The format of VESA mode numbers is as follows:

    D0-D8=    Mode number
        If D8 == 0, this is not a VESA defined mode
        If D8 == 1, this is a VESA defined mode
    D9-D14= Reserved by VESA for future expansion (= 0)
    D15=    Reserved (= 0)

Thus, VESA mode numbers begin at 100h. This mode numbering
scheme implements standard VGA mode numbers as well as OEM-
defined mode numbers as subsets of the VESA mode number. That
means that regular VGA modes may be initialized through VESA
BIOS function 02h (Set Super VGA mode), simply by placing the
mode number in BL and clearing the upper byte (BH). OEM-
defined video modes may be initialized in the same way.

To date, VESA has defined a 7-bit video mode number, 6Ah, for
the 800x600, 16-color, 4-plane graphics mode. The
corresponding 15-bit mode number for this mode is 102h.

The following VESA mode numbers have been defined:


15-bit    7-bit    Resolution    Colors
mode    mode
number    number
---------------------------------------

100h    -    640x400     256
101h    -    640x480     256

102h    6Ah    800x600     16
103h    -    800x600     256

104h    -    1024x768    16
105h    -    1024x768    256

106h    -    1280x1024    16
107h    -    1280x1024    256



5.    CPU Video Memory Windows


A standard VGA sub-system provides 256k bytes of memory and a
corresponding mechanism to address this memory. Super VGAs and
their extended modes require more than the standard 256k bytes
of memory but also require that the address space for this
memory be restricted to the standard address space for
compatibility reasons. CPU video memory windows provide a
means of accessing this extended VGA memory within the
standard CPU address space.

This chapter describes how several hardware implementations of
CPU video memory windows operate, their impact on application
software design, and relates them to the software model
presented by the VESA VGA BIOS extensions.

The VESA CPU video memory windows functions have been designed
to put the performance insensitive, non-standard hardware
functions into the BIOS while putting the performance
sensitive, standard hardware functions into the application.
This provides portability among VGA systems together with the
performance that comes from accessing the hardware directly.
In particular, the VESA BIOS is responsible for mapping video
memory into the CPU address space while the application is
responsible for performing the actual memory read and write
operations.

This combination software and hardware interface is
accomplished by informing the application of the parameters
that control the hardware mechanism of mapping the video
memory into the CPU address space and then letting the
application control the mapping within those parameters.


5.1    Hardware design considerations

5.1.1    Limited to 64k/128k of CPU address space

The first consideration in implementing extended video memory
is to give access to the memory to application software.

The standard VGA CPU address space for 16 color graphics modes
is typically at segment A000h for 64k. This gives access to
the 256k bytes of a standard VGA, i.e. 64k per plane. Access
to the extended video memory is accomplished by mapping
portions of the video memory into the standard VGA CPU address
space.

Every super VGA hardware implementation provides a mechanism
for software to specify the offset from the start of video
memory which is to be mapped to the start of the CPU address
space. Providing both read and write access to the mapped
memory provides a necessary level of hardware support for an
application to manipulate the extended video memory.


5.1.2    Crossing CPU video memory window boundaries

The organization of most software algorithms which perform
video operations consists of a pair of nested loops: an outer
loop over rows or scan lines and an inner loop across the row
or scan line. The latter is the proverbial inner loop, which
is the bottle neck to high performance software.

If a target rectangle is large enough, or poorly located, part
of the required memory may be within the video memory mapped
into the CPU address space and part of it may not be
addressable by the CPU without changing the mapping. It is
desirable that the test for re-mapping the video memory is
located outside of the inner loop.

This is typically accomplished by selecting the mapping offset
of the start of video memory to the start of the CPU address
space so that at least one entire row or scan line can be
processed without changing the video memory mapping.    There
are currently no super VGAs that allow this offset to be
specified on a byte boundary and there is a wide range among
super VGAs in the ability to position a desired video memory
location at the start of the CPU address space.

The number of bytes between the closest two bytes in video
memory that can be placed on any single CPU address is defined
as the granularity of the window mapping function. Some super
VGA systems allow any 4k video memory boundary to be mapped to
the start of the CPU address space, while other super VGA
systems allow any 64k video memory boundary to be mapped to
the start of the CPU address space. These two example systems
would have granularities of 4k and 64k, respectively This
concept is very similar to the bytes that can be accessed with
a 16 bit pointer in an Intel CPU before a segment register
must be changed (the granularity of the segment register or
mapping, here is 16 bytes).

Note that if the granularity is equal to the length of the CPU
address space, i.e. the least significant address bit of the
hardware mapping function is more significant than the most
significant bit of the CPU address, then the inner loop will
have to contain the test for crossing the end or beginning of
the CPU address space. This is because if the length of the
CPU address space (which is the granularity in this case) is
not evenly divisible by the length of a scan line, then the
scan line at the end of the CPU address will be in two
different video memory which cannot be mapped into the CPU
address space simultaneously.


5.1.3    Operating on data from different areas

It is sometimes required or convenient to move or combine data
from two different areas of video memory. One example of this
is storing menus in the video memory beyond the displayed
memory because there is hardware support in all VGAs for
transferring 32 bits of video data with an 8 bit CPU read and
write. Two separately mappable CPU video memory windows must
be used if the distance between the source and destination is
larger than the size of the CPU video memory window.


5.1.4    Combining data from two different windows

The above example of moving data from one CPU video memory
window to another CPU video memory only required read access
to one window and only required write access to the other
window. Sometimes it is convenient to have read access to both
windows and write access to one window. An example of this
would be a raster operation where the resulting destination is
the source data logically combined with the original
destination data.


5.2    Different types of hardware windows

Different hardware implementations of CPU video memory windows
can be supported by the VESA BIOS extension. The information
necessary for an application to understand the type of
hardware implementation is provided by the BIOS to the
application. There are three basic types of hardware windowing
implementations and they are described below.

The types of windowing schemes described below do not include
differences in granularity.

Also note that is possible for a VGA to use a CPU address
space of 128k starting at segment A000h.


5.2.1    Single window systems

Some hardware implementations only provide a single window.
This single window will be readable as well as writable.
However, this causes a significant performance degradation
when moving data in video memory a distance that is larger
than the CPU address space.


5.2.2    Dual window systems

Many super VGAs provide two windows to facilitate moving data
within video memory. There are two separate methods of
providing two windows.


5.2.2.1    Overlapping windows

Some hardware implementations distinguish window A and window
B by determining if the CPU is attempting to do a memory read
or a memory write operation. When the two windows are
distinguished by whether the CPU is trying to read or write
they can, and usually do, share the same CPU address space.
However, one window will be read only and the other will be
write only.


5.2.2.2    Non-overlapping windows

Another mechanism used by two window systems to distinguish
window A and window B is by looking at the CPU address within
the total VGA CPU address space. When the two windows are
distinguished by the CPU address within the VGA CPU address
space the windows cannot share the same address space, but
they can each be both read and written.



6.    Extended VGA BIOS


Several new BIOS calls have been defined to support Super VGA
modes. For maximum compatibility with the standard VGA BIOS,
these calls are grouped under one function number. This number
is passed in the AH register to the int 10h handler.

The designated Super VGA extended function number is 4Fh. This
function number is presently unused in most, if not all, VGA
BIOS implementations. A standard VGA BIOS performs no action
when function call 4F is made.



6.1    Status information

Every function returns status information in the AX register.
The format of the status word is as follows:

    AL ==    4Fh:    Function is supported
    AL !=    4Fh:    Function is not supported
    AH ==    00h:    Function call successful
    AH ==    01h:    Function call failed

Software should treat a non-zero value in the AH register as a
general failure condition. In later versions of the VESA BIOS
Extension new error codes might be defined.



6.2    Function 00h - Return Super VGA information

The purpose of this function is to provide information to the
calling program about the general capabilities of the Super
VGA environment. The function fills an information block
structure at the address specified by the caller. The
information block size is 256 bytes.

    Input:    AH= 4Fh Super VGA support
        AL= 00h Return Super VGA information
        ES:DI=    Pointer to buffer

    Output: AX=    Status
        All other registers are preserved


The information block has the following structure:

VgaInfoBlock struc
    VESASignature    db    'VESA'    ; 4 signature bytes
    VESAVersion    dw    ?    ; VESA version number
    OEMStringPtr    dd    ?    ; Pointer to OEM string
    Capabilities    db    4 dup (?) ; Capabilities of
                    ; the video environment
    VideoModePtr    dd    ?    ; Pointer to supported Super
                    ; VGA modes
VgaInfoBlock ends


The VESASignature field contains the characters 'VESA' if this
is a valid block.

The VESAVersion field specifies which VESA standard the Super
VGA BIOS conforms to. The higher byte would specify the major
version number. The lower byte would specify the minor version
number. The initial VESA version number is 1.0. Applications
written to use the features of a specific version of the VESA
BIOS Extension, is guaranteed to work in later versions. The
VESA BIOS Extension will be fully upwards compatible.

The OEMStringPtr is a far pointer to a null terminated OEM-
defined string. The string may used to identify the video
chip, video board, memory configuration etc., to hardware
specific display drivers. There are no restrictions on the
format of the string.

The Capabilities field describes what general features are
supported in the video environment. The bits are defined as
follows:

    D0-31= Reserved

The VideoModePtr points to a list of supported Super VGA
(VESA-defined as well as OEM-specific) mode numbers. Each mode
number occupies one word (16 bits). The list of mode numbers
is terminated by a -1 (0FFFFh). Please refer to chapter 2 for
a description of VESA mode numbers. The pointer could point
into either ROM or RAM, depending on the specific
implementation. Either the list would be a static string
stored in ROM, or the list would be generated at run-time in
the information block (see above) in RAM.



6.3    Function 01h - Return Super VGA mode information

This function returns information about a specific Super VGA
video mode. The function fills a mode information block
structure at the address specified by the caller. The mode
information block size is maximum 256 bytes.

Some information provided by this function is implicitly
defined by the VESA mode number. However, some Super VGA
implementations might support other video modes than those
defined by VESA. To provide access to these modes, this
function also returns various other information about the
mode.

    Input:    AH= 4Fh Super VGA support
        AL= 01h Return Super VGA mode information
        CX=    Super VGA video mode
        ES:DI=    Pointer to buffer

    Output: AX=    Status
        All other registers are preserved


The mode information block has the following structure:

ModeInfoBlock    struc

; mandatory information (allways provided)
ModeAttributes         dw    ?    ; mode attributes
WinAAttributes         db    ?    ; window A attributes
WinBAttributes         db    ?    ; window B attributes
WinGranularity         dw    ?    ; window granularity
WinSize            dw    ?    ; window size
WinASegment        dw    ?    ; window A start segment
WinBSegment        dw    ?    ; window B start segment
WinFuncPtr        dd    ?    ; pointer to window function
BytesPerScanLine    dw    ?    ; bytes per scan line

; optional information (provided if bit D1 of ModeAttributes is set)
XResolution        dw    ?    ; horizontal resolution
YResolution        dw    ?    ; vertical resolution
XCharSize        db    ?    ; character cell width
YCharSize        db    ?    ; character cell height
NumberOfPlanes         db    ?    ; number of memory planes
BitsPerPixel        db    ?    ; bits per pixel
NumberOfBanks        db    ?    ; number of banks
MemoryModel        db    ?    ; memory model type
BankSize        db    ?    ; bank size in kb

ModeInfoBlock    ends



The ModeAttributes field describes certain important
characteristics of the video mode. Bit D0 specifies whether
this mode can be initialized in the present video
configuration. This bit can be used to block access to a video
mode if it requires a certain monitor type, and that this
monitor is presently not connected. Bit D1 specifies whether
extended mode information is available. Video modes defined by
VESA will have certain known characteristics, like resolution,
number of planes, pixel format etc. Due to the severe space
constraint for ROM based implementations of the VESA BIOS
Extension, this information need not to be given for VESA-
defined video modes. Bit D2 indicates whether the BIOS have
support for output functions like TTY output, scroll, pixel
output etc. in this mode (it is recommended, but not
mandatory, that the BIOS have support for all output functions).

The field is defined as follows:

    D0= Mode supported in hardware
        0= Mode not supported in hardware
        1= Mode supported in hardware
    D1= Extended information available
        0= Extended mode information not available
        1= Extended mode information available
    D2= Output functions supported by BIOS
        0= Output functions not supported by BIOS
        1= Output functions supported by BIOS
    D3= Monochrome/color mode (see note below)
        0= Monochrome mode
        1= Color mode
    D4= Mode type
        0= Text mode
        1= Graphics mode
    D5-D15= Reserved

Note:    Monochrome modes have their CRTC address at 3B4h.
Color modes have their CRTC address at 3D4h. Monochrome modes
have attributes in which only bit 3 (video) and bit 4
(intensity) of the attribute controller output are
significant. Therefore, monochrome text modes have attributes
of off, video, high intensity, blink, etc. Monochrome graphics
modes are two plane graphics modes and have attributes of off,
video, high intensity, and blink. Extended two color modes
that have their CRTC address at 3D4h, are color modes with one
bit per pixel and one plane. The standard VGA modes, 06h and
11h would be classified as color modes, while the standard VGA
modes 07h and 0fh would be classified as monochrome modes.

The BytesPerScanline field specifies how many bytes each
logical scanline consists of. The logical scanline could be
equal to or larger than the displayed scanline.

The WinAAttributes and WinBAttributes describe the
characteristics of the CPU windowing scheme such as whether
the windows exist and are read/writeable, as follows:

    D0= Window supported
        0= Window is not supported
        1= Window is supported
    D1= Window readable
        0= Window is not readable
        1= Window is readable
    D2= Window writable
        0= Window is not writeable
        1= Window is writeable
    D3-D7= Reserved

WinGranularity specifies the smallest boundary, in KB, on
which the window can be placed in the video memory.

WinSize specifies the size of the window in KB.

WinASegment and WinBSegment address specify the segment
addresses where the windows are located in the CPU address
space.

WinFuncAddr specifies the address of the CPU video memory
windowing function. The windowing function can be invoked
either through VESA BIOS function 05h, or by calling the
function directly. A direct call will provide faster access to
the hardware paging registers than using Int 10h, and is
intended to be used by high performance applications.

The XResolution and YResolution specify the width and height
of the video mode. In graphics modes, this resolution is in
units of pixels. In text modes this resolution is in units of
characters. Note that text mode resolutions, in units of
pixels, can be obtained by multiplying XResolution and
YResolution by the cell width and height, if the extended
information is present.

The XCharCellSize and YCharCellSize specify the size of the
character cell in pixels.

The NumberOfPlanes field specifies the number of memory planes
available to software in that mode. For standard 16-color VGA
graphics, this would be set to 4. For standard packed pixel
modes, the field would be set to 1.

The BitsPerPixel field specifies the number of bits that
define the color of one pixel. 16-color and 256-color graphics
modes would specify 4 and 8 respectively. Non-standard memory
organizations can be specified using this field and the
NumberOfPlanes field. For example, a 16-color packed pixel
mode would be described as having 1 plane and 4 bits per
pixel.

The MemoryModel field specifies the general type of memory
organization used in this mode. The following models have been
defined:

    00h=        Text mode
    01h=        CGA graphics
    02h=        Hercules graphics
    03h=        4-plane planar
    04h=        Packed pixel
    05h=        Non-chain 4, 256 color
    06h-0fh=    Reserved, to be defined by VESA
    10h-ffh=    To be defined by OEM

NumberOfBanks. This is the number of banks in which the scan
lines are grouped. The remainder from dividing the scan line
number by the number of banks is the bank that contains the
scan line and the quotient is the scan line number within the
bank. For example, CGA graphics modes have two banks and
Hercules graphics mode has four banks. For modes that don't
have scanline banks (such as VGA modes 0Dh-13h), this field
should be set to 1.

The BankSize field specifies the size of a bank (group of scan
lines) in units of 1 KB. For CGA and Hercules graphics modes
this is 8, as each bank is 8192 bytes in length. For modes
that don't have scanline banks (such as VGA modes 0Dh-13h),
this field should be set to 0.

MapFuncAddr specifies the address of the Mapping function. The
mapping function can be invoked either through VESA BIOS
Function 06h, or by calling the function directly. A direct
call will provide a faster memory mapping than using Int 10h,
and is intended to be used by high performance applications.


6.4    Function 02h - Set Super VGA video mode

This function initializes a Super VGA video mode. The BX
register contains the Super VGA mode to set. The format of
VESA mode numbers is described in chapter 2. If the mode
cannot be set, the BIOS should leave the video environment
unchanged and return a failure error code.

    Input:    AH= 4Fh Super VGA support
        AL= 02h Set Super VGA video mode
        BX=    Video mode
            D0-D14= Video mode
            D15= Clear memory flag
                0= Clear video memory
                1= Don't clear video memory

    Output: AX=    Status
        All other registers are preserved




6.5    Function 03h - Return current video mode

This function returns the current video mode in BX. The format
of VESA video mode numbers is described in chapter 2 of this
document.

    Input:    AH= 4Fh Super VGA support
        AL= 03h Return current video mode

    Output: AX=    Status
        BX=    Current video mode
        All other registers are preserved

Notes:

In a standard VGA BIOS, function 0Fh (Read current video
state) returns the current video mode in the AL register. In
D7 of AL, it also returns the status of the memory clear bit
(D7 of 40:87). This bit is set if the mode was set without
clearing memory. In this Super VGA function, the memory clear
bit will not be returned in BX since the purpose of the
function is to return the video mode only. If an application
wants to obtain the memory clear bit, it should call VGA BIOS
function Fh.




6.6    Function 04h - Save/Restore Super VGA video state
These functions provide a mechanism to save and restore the
Super VGA video state. The functions are a superset of the
three subfunctions under standard VGA BIOS function 1Ch
(Save/restore video state). The complete Super VGA video state
(except video memory) should be saveable/restorable by setting
the requested states mask (in the CX register) to 000Fh.

    Input:    AH= 4Fh Super VGA support
        AL= 04h Save/Restore Super VGA video state
        DL= 00h Return save/restore state buffer size
        CX=    Requested states
                D0= Save/restore video hardware state
                D1= Save/restore video BIOS data state
                D2= Save/restore video DAC state
                D3= Save/restore Super VGA state

    Output: AX=    Status
        BX=    Number of 64-byte blocks to hold the state buffer
        All other registers are preserved


    Input:    AX= 4Fh Super VGA support
        AL= 04h Save/Restore Super VGA video state
        DL= 01h Save Super VGA video state
        CX=    Requested states (see above)
        ES:BX=    Pointer to buffer

    Output: AX=    Status
        All other registers are preserved


    Input:    AH= 4Fh Super VGA support
        AL= 04h Save/Restore Super VGA video state
        DL= 02h Restore Super VGA video state
        CX=    Requested states (see above)
        ES:BX=    Pointer to buffer

    Output: AX=    Status
        All other registers are preserved


Notes:

Due to the goal of complete compatibility with the VGA
environment, the standard VGA BIOS function 1Ch (Save/Restore
VGA state) has not been extended to save the Super VGA video
state. VGA BIOS compatibility requires that function 1Ch
returns a specific buffer size with specific contents, in
which there is no room for the Super VGA state.




6.7    Function 05h - CPU Video Memory Window Control

This function sets or gets the position of the specified
window in the video memory. The function allows direct access
to the hardware paging registers. To use this function
properly, the software should use VESA BIOS Function 01h
(Return Super VGA mode information) to determine the size,
location and granularity of the windows.

    Input:    AH= 4Fh Super VGA support
        AL= 05h Super VGA video memory window control
        BH= 00h Select super VGA video memory window
        BL=    Window number
                0= Window A
                1= Window B
        DX=    Window position in video memory
                (in window granularity units)

    Output: AX=    Status
        See notes below


    Input:    AH= 4Fh Super VGA support
        AL= 05h Super VGA video memory window control
        BH= 01h Return super VGA video memory window
        BL=    Window number
                0= Window A
                1= Window B

    Output: AX=    Status
        DX=    Window position in video memory
                (in window granularity units)
        See notes below


Notes:

This function is also directly accessible through a far call
from the application. The address of the BIOS function may be
obtained by using VESA BIOS Function 01h, return Super VGA
mode information. A field in the ModeInfoBlock contains the
address of this function. Note that this function may be
different among video modes in a particular BIOS
implementation so the function pointer should be obtained
after each set mode.

In the far call version, no status information is returned to
the application. Also, in the far call version, the AX and DX
registers will be destroyed. Therefore if AX and/or DX must be
preserved, the application must do so prior to making the far
call.

The application must load the input arguments in BH, BL, and
DX (for set window) but does not need to load either AH or AL
in order to use the far call version of this function.





7.    Application example


The following sequence illustrates how an application would
interface to the VESA BIOS Extension. The hypothetical
application is VESA-aware and calls the VESA BIOS functions.
However, the application is not limited to supporting just
VESA-defined video modes. Thus, it will inquire what video
modes are available, before setting up the video mode.

1)    The application would first allocate a 256 byte
buffer. This buffer will be used by the VESA BIOS to return
information about the video environment. Some applications
will statically allocate this buffer, others will use system
calls to temporarily obtain buffer space.

2)    The application would then call VESA BIOS function 00h
(Return Super VGA information). If the AX register does not
contain 004Fh on return from the function call, the
application can determine that the VESA BIOS Extension is not
present and handle such situation.

    If no error code is passed in AX, the function call
was successful. The buffer has been filled by the VESA BIOS
Extension with various information. The application can verify
that indeed this is a valid VESA block by identifying the
characters 'VESA' in the beginning of the block. The
application can inspect the VESAVersion field to determine
whether the VESA BIOS Extension has sufficient functionality.
The application may use the OEMStringPtr to locate OEM-
specific information.

    Finally, the application can obtain a list of the
supported Super VGA modes, by using the VideoModePtr. This
field points to a list of the video modes supported by the
video environment.

3)    The application would then create a new buffer and
call the VESA BIOS function 01h (Return Super VGA mode
information), to obtain information about the supported video
modes. Using the VideoModePtr, obtained in step 2 above, the
application would call this function with a new mode number
until a suitable video mode is found. If no appropriate video
mode is found, its up to the application to handle this
situation.

    The Return Super VGA mode information function fills a
buffer specified by the application with information
describing the features of the video mode. The data block
contains all the information an application needs to take
advantage of the video mode.

    The application would examine the ModeAttributes
field. To verify that the mode indeed is supported, the
application would inspect bits D0. If D0 is cleared, then the
mode is not supported by the hardware. This might happen if a
specific mode requires a certain type of monitor, but that
monitor is not present.

4)    After the application has selected a video mode, the
next step is to initialize the mode. However, the application
might first want to save the present video mode. When the
application exits, this mode would be restored. To obtain the
present video mode, the VESA BIOS function 03h (Get Super VGA
mode), would be used. If a non-VESA (standard VGA or OEM-
specific) mode is in effect, only the lower byte in the mode
number is filled. The upper byte is cleared.

5)    To initialize the video mode, the application would
use VESA BIOS function 02h (Set Super VGA mode). The
application has from this point on full access to the VGA
hardware and video memory.

6)    When the application is about to terminate, it would
restore the prior video mode. The prior video, obtained in
step 4) above could be either a standard VGA mode, OEM-
specific mode, or VESA-supported mode. It would reinitialize
the video mode by calling VESA BIOS function 02h (Set Super
VGA mode). The application would then exit.



Footnotes:

1 IBM and VGA are trademarks of International Business
Machines Corporation.
2 The term "Super VGA" is used in this document as a term for
video graphics products implementing a superset of the
standard IBM VGA display adapter.
1 Mandatory information
2 Information provided only if bit D1 of Mode Attributes is
set