From:	Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Generate real-mode 386 DOS executables?
Date:	Sun, 05 Jan 2003 21:59:43 CST
Organization:	Rice University, Houston TX
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> The code is run on a Pentium-based embedded system under MS-DOS v6.22.  
> I'm considering DJGPP as a replacement for the Turbo C/C++ compiler.

Other developers have followed this path - DJGPP images (and CWSDPMI)
are in the ROM of some systems.  CWSDPMI can use the real mode memory
to provide 32-bit addressing; systems with a 386+ processor with at
least 512Kb of memory should work.

> I'm willing to take the pain of the 16-bit to 32-bit conversion, but I 
> want the pain to end there.  That is, I don't want to have to install 
> himem.sys to support a protected mode application.  

HIMEM.SYS is not needed, and you can bind cwsdstub.exe into an image for
a single EXE distribution.

> The 640KB of DOS address space is enough 

You will get 32-bit addressing even if you don't need it.  Trying to use
size overrides in 16-bit mode slow down code.

> I really don't need access to extended memory, just 32-bit 
> code generation from a contemporary C compiler.

The DJGPP defaults assume lots of memory (a 512Kb stack default, for
example) but you can build images which are memory efficient and work
fine on a small memory environment.

> So... can I use DJGPP to generate a 32-bit real mode DOS application?

Not easily - but it's not clear why you would want this (unless you spend
most of the time making BIOS calls).

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