Mail Archives: djgpp/1997/01/08/02:18:53
Filip Aben wrote:
>
> hi there,
>
> I've been programmin c for some years now and i finally took the step
> towards protected mode (no big step though): DJGPP. In real mode i knew
> what i was doing as to allocating and accessing memory (segments, mem
> models and stuff), but in PM i haven't got a clue how it works...
> (selectors,gdt and stuff)
> Does anyone know or have a tutorial or some docs on this one??
Well, the simplest answer to your question is that under PM, there are
no segments. So you can just go ahead and allocate that 20 MB structure
and never again need to worry whether it is overlapping a segment or
anything! The big secret is that there is no secret. :)
The more complete answer is that protected mode still uses segments, but
in a much looser way. Your entire program, for example, has one
"segment" of memory all to itself, and can do anything it pleases within
that segment. If you want to start playing with things outside of that
segment, like DOS memory, memory-mapped devices, etc., then you need
some additional techniques. They aren't very hard to learn; just a lot
different from what you've been plodding along with in real mode.
See the DJGPP Frequently Asked Questions list (v2/faq202b.zip) for a
whole host of answers to the various questions of RM<->PM conversions.
Chapter 10 is a very good place to start.
Good luck!
--
---------------------------------------------------------------------
| John M. Aldrich, aka Fighteer I | fighteer AT cs DOT com |
| Plan: To find ANYONE willing to | http://www.cs.com/fighteer |
| play Descent 2 on DWANGO! | Tagline: <this space for rent> |
---------------------------------------------------------------------
- Raw text -