Mail Archives: djgpp/1998/10/13/11:11:50
On Thu, 8 Oct 1998, Jay Tseng wrote:
> I am writing C code which called DPMI service thru int386(31h,..)
> to access local memory residing in the graphics card. The code is
> compiled under gcc v2.01 without any switch except -o. General
> Protection Fault happens when accessing local (graphic) memory, even
> given the fact that I have mapped the local memory to system memory
> using int386(31h,..). I think that the mapping did not do what it is
> supposed to do since it needs DOS extender which I did not supply.
IMHO, this approach is dead wrong. Even if it will eventually work,
it is so much more complicated, and you will need to reinvent so many
things that are already done for you, that it just isn't worth it.
I suggest to toss everything and start anew. Begin by reading Chapter
18 of the DJGPP FAQ list (v2/faq211b.zip from the same place you get
DJGPP), which explains a lot of background about low-level stuff, and
includes explanation and code snippets that access memory-mapped
devices and map them into your program's address space.
If the material in the FAQ doesn't solve your problem, or is not clear
enough, please ask specific questions about what it says.
> * What's the difference between DPMI and go32-v2.exe?
> * When to use them and how? For example, how can we invoke go32-v2,
> from where to invoke it, can I link it with the c object codes,
> and how DPMI is used?
Forget about go32-v2, it has no bearing on your problem. It's just a
diagnostic program (well, not really, but that's close enough).
> * What kind of configuration settings in autoexec.bat and
> config.sys are needed?
Nothing special beyond the usual DJGPP setup. See the file README.1ST
for detailed setup instructions.
> Any other things that I should be aware of regarding the DOS
> extender?
There is no extender in DJGPP v2.
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