X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=blobdiff_plain;f=specs%2Ffreevga%2Ffreevga.htm;fp=specs%2Ffreevga%2Ffreevga.htm;h=7d9c1ed710cde5820ee3fa7d07a340e680896741;hp=0000000000000000000000000000000000000000;hb=8af06d1fd50343e17229618ef4d2693193b2b3d9;hpb=d0d14ca50fbac167253e1e1d8d806bfd749a5e8a diff --git a/specs/freevga/freevga.htm b/specs/freevga/freevga.htm new file mode 100644 index 0000000..7d9c1ed --- /dev/null +++ b/specs/freevga/freevga.htm @@ -0,0 +1,255 @@ + + + + + + + FreeVGA--About the FreeVGA Project + + + +
Home Intro Completeness +Contribution Membership +Questions Back  +
Hardware Level VGA and SVGA Video Programming Information +Page
+ +
About the FreeVGA Project  +
+ + +

Introduction +
        As a software programmer +for the PC architecture I have noticed that there is plenty of free information +existing on the Internet for programming PC hardware, with the notable +exception of video adapters, MPEG cards and the like. When the VGA was +the standard adapter card in PC's, programming was relatively straightforward. +However, when SVGA adapters appeared on the market, there was little standardization +between separate vendor's products. For this reason, applications and graphical +user interface systems required specialized drivers to utilize the extended +capabilities of the SVGA adapters. Either these specialized drivers were +written by the video card vendor or they had to be written by the application +vendor. Unfortunately due to the cost of specifications and complexity +of hardware, most free or shareware programs supported only the standard +VGA. The goal of this project, under my direction, is to explore the area +of low-level video programming and provide information for programmers +of free software throughout the world. +
        With the growing popularity +of the free software concept, more and more specialized applications are +written every day. Many of these applications could take advantage of the +specialized features of the video hardware but often the information required +is not available. This projects goal is to make that information available +By gaining the cooperation of both programmers and hardware manufacturers +an excellent reference can be developed. Internet technology makes it possible +to provide a free resource updated in a timely fashion as opposed to printed +matter which takes time to print and deliver. + +

Completeness +
        Why would a low-level programmer +need this reference rather than simply use datasheets and chipset specifications +from the manufacturers themselves? First, the manufacturers may no longer +provide literature on "obsolete" chipsets. Second, such datasheets are +often aimed at hardware designers rather than programmers. Programmers +are trying to implement software on existing hardware rather design hardware. +Many of the details needed to program the hardware are dependent on the +implementation of the video adapter. Datasheets typically only provide +information on one particular component of the video hardware. It is necessary +to understand how the components in the adapter are "wired" together to +be able to program the adapter. This information is rarely found in datasheets +or manufacturer's documentation. Third, as demonstrated on the VGA and +some specific SVGA hardware, there are always programmers who can find +ways to cleverly program the hardware to provide capabilities unimagined +by the manufacturer. To do this, it requires the programmer to have intimate +knowledge of the hardware, as BIOS services provide a "lowest common denominator" +of capability. + +

Contribution +
        This section is for +those interested in contributing to the FreeVGA Project. The primary objective +of this project is to gather information about video hardware, to verify +this information as best as possible, then to organize the information +in a form usable for any application, and finally to make this information +freely available to all programmers. Because of the non-profit nature of +this project, all information provided is the result of generous contribution +by myself or others. The primary resources required by this project are: +chipset datasheets/documentation, developer kits for video boards, video +adapter boards used for testing and verifying information, and finally +"postcards from the bleeding edge" i.e. information about the real world +problems and their workarounds from video programmers. If you can provide +any of these resources to the project or any other related assistance myself +and other programmers who benefit give thanks to your generosity. Your +name will be forever enshrined on the list of contributors, along with +a link to your homepage if you so desire. +
     I can be reached via the feedback +form. If you wish to donate hardware or documentation, please send +it, along with your name and the link you wish to include in the list of +contributors to: + +

Joshua Neal +
FreeVGA Project +
925 N. Coronado Dr. +
Gilbert, AZ 85234 + +

Membership +
        Because of the nature of +this project, any contributor can consider themselves a member if they +wish to do so. As the founder of this project I am willing to donate my +time and resources to ensuring the continuing organization, accuracy, and +usability of the FreeVGA Project's documentation. I will continue to do +this indefinitely, although if the task becomes overwhelming I will solicit +volunteers to assist with the project. There may at some point in the future +be special considerations for vendors that choose to support the projects +goals. + +

Open-Ended Questions +
        The problem of documenting +video card operation and behavior is difficult because of the large amount +of information available, and because video hardware is constantly evolving, +making documentation a problem of hitting a moving target. Another problem +is that because video cards are projects of human endeavor and due to their +complexity, their implementation often differs from published specifications. +Even two manufacturer's products based upon the same chipset can contain +enough variation to make them separate cases from a programmer's viewpoint. +The FreeVGA Project attempts to provide answers to the following questions: +

+        Because video hardware was developed +by many independent vendors along separate evolutionary paths, there is +very little knowledge about how to identify the particular model of video +card present in a machine. Because identifying the particular model is +crucial to utilizing the advanced features of a specific model, this is +an important task that nearly all software written for the SVGA needs to +perform. In many cases, such as when writing programs under an operating +system other than MS-DOS/Windows, it may not be possible nor is it good +practice to access BIOS for determining the specific model. Furthermore, +the more recent PCI bus design is being incorporated into many systems +with non-80x86 chips, such as the PowerPC, Alpha, and even high end workstations. +However, the manufacturers of the hardware may only support Mac and PC +versions of their cards, considering other platforms too much of a niche +market to support. Since their inception in the PC market, most video cards +have had the capability to work with another card (albeit different) in +the same machine. Some newer PCI cards allow multiple cards to be used +in one machine. Until recently this capability has been unsupported by +operating systems and programs. For debugging video routines there is no +equal to having a second monitor attached--one monitor can display the +program's output while the other provides the debugging interface. Note +that the need for a second monitor could be reduced somewhat if better +virtualization of the display hardware was implemented. This project aims +to give programmers the skills and knowledge to better utilize the video +hardware. + +        BIOS was designed to support +MS-DOS programs on the 8086. Computers have progressed far beyond that +point but BIOS has remained basically the same (with the exception of VESA +BIOS.) Even then, most facilities provided by the video BIOS are not particularly +useful. An example is the BIOS Read and Write Pixel commands. These are +the only BIOS provided method of accessing video memory other than text +functions. Anyone like myself who started learning 8086 assembler to speed +up their graphics discovered this function, and said "Cool. This is going +to be easy." I then ran my first program and discovered that I had just +lost a few orders of magnitude of performance. Thus I started to learn +to interact with the video card hardware directly. VESA BIOS is better, +although I have seen very few on-board implementations that work properly +(if present), usually resulting in the user having to run a TSR program +that provides VESA services in RAM. While VESA BIOS does provide some facilities +for non-real mode problems it still does place a function call penalty +on video code. My biggest complaint is that with VESA BIOS you are restricted +to programming to the lowest common denominator of all video hardware, +and thus to utilize any special features of a chipset, you still have to +learn to program the card directly. Many video cards are now considered +"obsolete" by their manufacturer (or the manufacturer has joined the great +corporation in the sky...) and developer support is no longer available. +The unfortunate problem is that these "obsolete" cards are the same cards +being used by non-profit organizations and schools who could otherwise +reap the benefits of a wide variety of free software. + +       This is probably the area where +the documentation is most important. These features are programmed differently +on each vendor's video hardware, but can improve the performance of a particular +application by several orders of magnitude. Programmers such as video game +programmers and assembly demo programmers have demonstrated that by pushing +hardware to its limits, previously inconceivable animation and special +effects are possible. Recent advances in 3D acceleration have made virtual +reality on the desktop a possibility. It is crucial to developers that +they be able to thoroughly understand the hardware's operation to maximize +its performance. + +      Even programmers programming for +the relatively standard VGA hardware can run into problems in this area. +This is the reason so many packages state support for IBM VGA or 100% compatible. +Frequently programmers encounter slight differences in hardware that, under +specific circumstances can cause their programs to fail to operate properly. +If programmers had detailed documentation of the hardware differences of +specific implementations, programmers could, and are generally willing +to, write workarounds in their code in order to provide support for this +hardware. Occasionally subtle hardware problems arise in a particular version +of a board and is corrected in a later revision (possibly by simply revising +the BIOS.) It is important to recognize the earlier version and be able +to write software that can deal with its particular problem. In addition, +many chipsets are designed in such a way that they can work with a variety +of support devices such as clock generators and Video DACs. It is important +to know how to detect and control these support devices, which may (and +usually is) be different in every implementation. Some of these devices +could be interchanged with pin-compatible devices which could provide additional +functionality. However, this would require special programming to utilize +the device's features. + +      While testing and verifying the operation +of various video boards. I discovered some cards that did not respond properly +to my programming. My initial thought was that I was doing something wrong +and tried to figure out what was wrong. However, further testing on another +identical card demonstrated that the first board had simply failed. There +is little diagnostic software for the VGA and SVGA adapters particularly +when dealing with some of the more esoteric features. This is primarily +because little has been identified about the correct behavior of video +cards. Many manufacturers fail to include a thorough diagnostics utility +with their hardware, and the diagnostics that are provided are usually +specific to one operating system. + +        This is a particular +are of interest to myself and others. This knowledge can be used to create +a virtual machine capable of multitasking legacy applications. Particular +features that could be provided are the ability to execute a full-screen +program in the background, execute a full-screen program in a virtual window +on a desktop, emulate a particular video adapter and translate its output +to a form compatible with the hardware on the machine, provide the ability +to remotely view an applications screen across a network, provide the ability +to debug a full-screen application without having to use a dual monitor +system or attached text terminal. Huge benefits can be reaped, but all +of the details of a particular hardware configuration must be known for +proper emulation/virtualization. For example, programs that attempt to +autodetect the hardware often rely on undocumented behaviors of video adapters. +These undocumented behaviors must be emulated properly for the application +to work properly. + +

Notice: All trademarks used or referred to on this page are the property +of their respective owners. +
All pages are Copyright © 1997, 1998, J. D. Neal, except where +noted. Permission for utilization and distribution is subject to the terms +of the FreeVGA Project Copyright License.  + +