Date:	Sun, 28 Jul 1996 10:58:27 -0400 (EDT)
From:	David M Barrett <dbarrett AT engin DOT umich DOT edu>
To:	j DOT aldrich6 AT genie DOT com
cc:	djgpp AT delorie DOT com
Subject:	Re: Flat Memory Questions
In-Reply-To:	<199607271545.AA278222309@relay1.geis.com>
Message-ID:	<Pine.SOL.3.91.960728105107.6455B-100000@blazers.engin.umich.edu>
MIME-Version:	1.0

Wow, thanks a lot.  I to malloc a meg and it worked just fine.  But, when 
I tried to defind a static array (ie- char Array[1024 * 1024]) I got a 
wierd runtime error 

Exiting due to signal SIGSEGV
Stack fault at ...
eax=...
ebp=...
Call from traceback EIPs:
  0x000015b9

(the ...'s should be replaced with a ton of numbers and info).

I tried to allocate the array on the first line of the main function.  
The rest of the program is simply printf statements (except for a line 
that sets one of the array values to 5, but it never gets that far).  Is 
there something wrong with allocating a buffer this way?

Thanks a lot for all of your help!

-David :)
-----------------------------------------------------------------------------
 David M. Barrett :)         |     University of Michigan / CAEN Hotline
 dbarrett AT engin DOT umich DOT edu    | http://www-personal.engin.umich.edu/~dbarrett
-----------------------------------------------------------------------------

On Sat, 27 Jul 1996 j DOT aldrich6 AT genie DOT com wrote:

> Reply to message 2198889    from DBARRETT AT SRVR on 07/26/96  3:14PM
> 
> 
> >Ok, I admit it: I've just recently started experimented with DJGPP.  But,
> >I have searched long and hard for documentation describing how to set the
> >computer into Protected Mode with the Flat Memory option but have been
> >unsuccessful.  Could someone please point me to a tutorial or something
> >(or describe the process) to do this:
> >
> >1. Set the computer into PM with Flat addressing
> >2. Allocate a simple "char Array[1024*1024]" (for example)
> >3. Dynamically allocate memory in large chunks.
> 
> This is all done automatically for you by the DJGPP startup code.  You
> don't have to touch a thing; you can just begin programming and allocating
> however much memory you want as soon as you get DJGPP.  Since
> DJGPP _only_ runs in protected mode, I can't see any circumstance
> where you'd need to make the switch yourself.  Switching back to real
> mode to handle DOS calls and interrupts is also handled transparently
> by the DJGPP code, via __dpmi_int(), int86(), and other library functions.
> 
> The great thing to remember about protected mode is that YOU, the
> programmer, never have to worry about segments, limits on memory
> allocation, far/near pointers, interrupt handling, low-level i/o calls,
> virtual memory, memory management, or ANY of the various aspects
> of protected-mode operation unless you want or need to interface
> with these directly for the purposes of the programs you're writing.
> (wow, what a sentence!  :O)
> 
> >I've looked around a bit through the DPMI functions, but I don't
> >understand the difference between them.  Could someone please explain
> >them to me?  Thanks!
> 
> Each DPMI function is simply a wrapper for a DPMI interrupt call.  For
> an exact description of DPMI functions, download and read the DPMI
> 0.9 spec, pointers to which can be found in the FAQ (faq201b.zip).  For
> the differences between the _go32_dpmi_ * functions and the __dpmi_*
> functions, read the section of the FAQ detailing these differences.
> 
> If you _really_ want to know how to switch into and out of pmode manually,
> you can examine the stub.asm code (djgpp/src/stub/stub.asm), as well as
> the sources for cwsdpmi (csdpmi2s.zip), the free DPMI host provided with
> DJGPP.  Another possible place for information would be the library source
> code for __dpmi_int() and the other __dpmi_ functions (download djlsr200.zip).
> The DPMI spec also covers this topic, but it's far too complex an issue to
> explain in a brief post.
> 
> John
> 

- Raw text -