Mail Archives: djgpp/1997/05/23/11:33:38
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 |
+----------------+
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