From: Vik Heyndrickx Newsgroups: comp.os.msdos.djgpp Subject: Re: 16 o 32, no hay diferencia para mi SVGA!!! Date: Fri, 23 May 1997 11:01:16 +0200 Organization: University of Ghent, Belgium Message-ID: <33855CDC.30B3@rug.ac.be> References: <3 DOT 0 DOT 1 DOT 32 DOT 19970523011943 DOT 00687ac4 AT chasque DOT apc DOT org> NNTP-Posting-Host: eduserv1.rug.ac.be Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Lines: 78 To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Precedence: bulk baldo AT chasque DOT apc DOT org wrote: > > Hola, soy nuevo para el mailing list, y ya que respondo mensajes me > gustaria que ustedes tambien me ayuden a mi. Escribo en Español porque no > se muy bien ingles y me cuesta mucho, asi que para preguntar cosas voy a > usar el Español. Even though... you reach only a small part of the people who may know an answer to this (Spain, Latin-America, and some people in North-America). > Bueno, tengo DJGPP V2, hice pruebas para el modo de pantalla de 320x200 > con 256 colores. Usando un buffer en memoria, llenandolo este y luego > volcandolo a la pantalla, obtuve el doble de velocidad al hacerlo en 16 > bits en vez de 8 bits; pero cuando lo hice en 32 bits, yo esperaba algo > casi como el doble de velocidad, pero no obtuve algo muy significativo. > ¿Porque es esto? Tengo PCI y tarjeta de video SVGA con PCI. Realmente quede > muy desilucionado, si alguien sabe por que es esto, digamelo por favor, > porque me interesa saber al menos porque. MUCHAS GRACIAS!!! There are several factors that influence the video output speed. If you card is an ISA card, which only supports 16 bits output at a time, using 32 bit writes instead of 16 will almost not change the speed. The same when the external data bus of the cpu is 16 bits (386SX). It also depends upon the speed of the ram chips on your video card. When they are slow, say 80ns access time, using 32 bit writes will only offer a slight speed increase. When they are fast, say 50ns or less, the speed almost doubles! One interesting thing to know is that when the "video enable off" signal is on, the output is much faster on fast cards then when it is off, because the cpu has a monopoly for access at that time. And last but not least, the cpu speed also influences the output speed. A couple of weeks ago I posted a request for help from djgpp users, which let me conclude to these results. Additional reports would be highly appreciated. Here's the article. ---------------------------------------------------------------------------------- Hello djgpp user, There is a problem with some video cards for writing long words (32 bit quantities) in text modes. To elimate these problems, the video must be addressed in short word quantities. This requires the library functions to be modified. This will affect (degrade) video performance on all systems. To get a good idea how big this performance degradation will be, your help is requested. I've written a small test utility that measures the speed in both cases. It is a DOS executable. You can retrieve it at URL: http://studwww.rug.ac.be/~vheyndri/stst.exe It's about 8Kb in size and contains no viruses (so far). Purpose of the test: - check I/O speed of your video hardware - allow to see the differences between different VGA cards - establish how widely spread the video problem is Requirements to run the program: - 386 computer or higher - VGA compatible card (others may work as well, Hercules doesn't) - running some flavor of DOS Invocation is simple: stst It takes only 2 seconds! Please email the output of the program to Vik DOT Heyndrickx AT rug DOT ac DOT be I will handle all provided information as confidential and only for this purpose. When the program fails to autodetect some information items, please provide them yourself, especially the video card info. The output provides information that lets me determine whether your hardware is subject to the problem. I will personally reply to you whether this is the case or not. Thank you very much for your co-operation. -- +----------------+ | Vik Heyndrickx | +----------------+