From: flobere AT club-internet DOT fr
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Memory in DJGPP
Date: Sun, 17 Oct 1999 14:47:12 +0200
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

> okay, i was looking in the hlp on RHIDE for the memset, and other mem
> functions.  Apparently some only allow int size moves and stuff? I thought
> you could move anything int he range of 32bits?

Take a look at the source of these functions, there are in the DJGPP
Dev Source package. You will have all the answer you need.

> Also, what does the __tb mean?  i think it stands for a transfer buffer? but
> im nto sure what that actually means, or when to use such a thing.  I
> noticed it being used in retreiving the VESA mode info.  You are supposed to
> called a interupt and the data is sent to es:di and u should set a stuct to
> this.

You are right, __tb is a transfert buffer. Actually, it is a real mode transfert
buffer.
It is very useful when a real mode interuption need a buffer (ds:si or es:di) to
work
properly.

> why do they divide by 16?

Here is how to compute a protect mode adress, from a real mode segment/offset
one :
protect adress = real mode segment * 16 + real mode offset
that is why __tb is divided by 16.
For exemple, the 03h text mode adress is, in real mode B800h, in protect mode
it is B800h * 16 = B8000h.

> I know I have sent another mesaage about this but i didnt ask this int he
> same way: whne you have the physical address of the videobuffer, what can
> you do with it?

Once you have the physical address, you have to map it in a protected memory
area, using DPMI functions. __dpmi_map_physical_adress or something.
Then, you get a protect mode pointer to the memory area where your
Vram is mapped. You can read and write in it using the _far* functions.
(_farpokel, etc). Or if you want to transfer big blocs of memory, you can
use _dosmemput or _dosmemget. You cannot directly acces the vram.
Read the Rhide Libc Docs on the _far functions, to get more informations.