From: "Alexei A. Frounze" <see_below AT the_message_body DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: far pointers
Date: Sat, 10 Jun 2000 13:04:45 +0400
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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

Eli Zaretskii wrote:
> 
> First, you *can* run protected-mode programs on top of plain real-mode
> DOS: that's what CWSDPMI does, for example, when it runs without EMM
> or QEMM installed; the speed of the mode switch is not really relevant
> here.  This fact alone seems to go against your text, which suggest
> that V86 allows DOS and PM programs to coexist (meaning that without
> V86, such coexistence is impossible).

I'm not sure I get your point.

> Second, even in V86 mode, a protected-mode program that calls
> real-mode DOS services needs to make an explicit PM-to-RM switch, or
> it will crash.  So there's nothing in V86 per se that allows or makes
> it simpler for PM programs to coexist with DOS.  Faster, yes, but not
> simpler.

What do you exactly mean by "simpler"? 
- Simpler for a programmer who makes a PMode program w/o regard of DPMI?
- No.
- Simpler in terms of having all the control over the situation?
- Yes.

How about IRQs? They should be handled ASAP. V86 helps here. Moreover, you
know that it's good to have 2 separate IRQ handlers: one for PMode, one for
real/v86 mode.

> In fact, I think that V86 should not be mentioned at all in the kind
> of tutorial that you are writing.  It is not really important in the
> context of DJGPP, 

WOW! Never heard DJGPP has nothing about V86... It would be impossible to
have (let's say) a disk I/O in DJGPP under DOS without V86. Sure V86 is
unnoticable for a user unless he is running into problems with VESA, IPX
stuff, etc etc and he starts to think of DPMI, PMode and V86 in order to
solve a task.

To summarise, I can tell the following... While user plays with standard
LIBC only, PMode and V86 don't bother him at all. If he's going to play with
such things as interrupts (software ones or IRQs) he must think of
particular implementation of this stuff on x86 platforms. If he doesn't know
how that works either in general or with DJGPP, he can't figure out this
himself and he comes up with a question to this NG or something. But we all
know that LIBC can't hold ready-made solutions for all the things a
programmer can imagine and try to make come true. So we have to clarify
PMode, V86 and DPMI. Otherwise he would just give up or use things he
doesn't know the meaning of.

> but it does complicate things and confuses newbies.
> I don't expect many DJGPP users to write a V86 monitor ;-)

That's right. I'm one. There is not a lot of such "users". ;))

bye.
Alexei A. Frounze
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