Hauptmenu

486er-mainboard

SUPER VGA BIOS EXTENSION Standard # VS891001

Video Electronics Standards Association

1330 South Bascom Avenue, Suite D Phone: (408) 971-7525
San Jose, CA 95128-4502 Fax: (408) 286-8988

SUPER VGA BIOS EXTENSION Standard # VS891001 October 1, 1989

PROPOSAL

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.

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 andfunctions that have
been approved by the main VESA co mmittee 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 VGA1 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 impl ements 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
competitionhas 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 architectu res. 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 fewsoftware 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 theVGA hardware architecture,
differences are most comm on 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
andfunction, 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 functionisolates the application
from the tedious and compli cated 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 VGAboard, 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 proce

sing will be done in hardware. For this reason, the V
ESA 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 astandardized 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 BIOSfunction 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 throughVGA 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 VGABIOS 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 VGAmode).

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 function02h (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 800×600, 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 – 640×400 256
101h – 640×480 256

102h 6Ah 800×600 16
103h – 800×600 256

104h – 1024×768 16
105h – 1024×768 256

106h – 1280×1024 16
107h – 1280×1024 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 por tability 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
addressspace 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 extendedvideo memory is accomplished by
mapping portions ofthe 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. Thelatter 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 CPUwithout 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 currentl y 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 CPUaddress 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 allowany 4k video memory boundary to
be mapped to the sta rt 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 c ontain 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 3 2 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 isconvenient to have read
access to both windows andwrite 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 theCPU 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 strin
Capabilities db 4 dup (?) ; capabilities of the
video environmentVideoModePtr dd ? ;
pointer to supported Super VGA modesVgaInfoBlock 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 descripti on 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 generatedat
run-time in the information block (see above) inRAM.

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 ismaximum 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 provideaccess 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
ModeAttributes1 dw ? ; mode attributes
WinAAttributes1 db ? ; window A attributes
WinBAttributes1 db ? ; window B attributes
WinGranularity1 dw ? ; window granularity
WinSize1 dw ? ; window size
WinASegment1 dw ? ; window A start segment
WinBSegment1 dw ? ; window B start segment
WinFuncPtr1 dd ? ; pointer to window function
BytesPerScanLine1 dw ? ; bytes per scan line
; extended information
; optional information
XResolution2 dw ? ; horizontal resolution
YResolution2 dw ? ; vertical resolution
XCharSize2 db ? ; character cell width
YCharSize2 db ? ; character cell height
NumberOfPlanes2 db ? ; number of memory planes
BitsPerPixel2 db ? ; bits per pixel
NumberOfBanks2 db ? ; number of banks
MemoryModel2 db ? ; memory model type
BankSize2 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 toblock access to a video
mode if it requires a certai n 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. D
ue 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, mono chrome 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 3D4 h, 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 directcall 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 beobtained 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 fieldwould 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. Forexample, 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 fieldshould 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 afailure 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 specificbuffer 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 modeinformation) 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 ofthis 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 applicationis not limited to supporting just
VESA-defined videomodes. 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 determinethat 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 ‘V ESA’ 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 OEMStringPtrto 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 wouldcall 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 videomode.

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 vid eo 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 byteis
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 bycalling VESA BIOS function 02h (Set Super VGA
mode). The application would then exit.

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 information2 Information provided only if bit D1 of Mode Attributes
is set
ied.


No comments yet.

Powered by WordPress. Designed by Woo Themes