OSDev.org

Hi everyone,
I've been trying to execute a V86 task for some
time. This is what I tried -

1. I had a piece of code under [BITS 16] block in
my protected mode code.
2. Made a code selector entry in the GDT pointing
to the 16bit code.
3. Created a TSS pointing to the 16BIT code.
The VM bit in the EFLAG slot was set.
4. Made a TSS selector entry in the GDT pointing
to the TSS.

but jumping in to the TSS selector simply reboots
my computer. Is there anything I am missing out?!!

I will greatly apprecite if someone can help.
regards,
Chatamballi

>On 2002-01-11 04:12:14, chatamballi wrote:
>Hi everyone,
>I've been trying to execute a V86 task for some
>time. This is what I tried -
>
>1. I had a piece of code under [BITS 16] block in
> my protected mode code.
>2. Made a code selector entry in the GDT pointing
> to the 16bit code.
>3. Created a TSS pointing to the 16BIT code.
> The VM bit in the EFLAG slot was set.
>4. Made a TSS selector entry in the GDT pointing
> to the TSS.
>
>but jumping in to the TSS selector simply reboots
>my computer. Is there anything I am missing out?!!

First off... I don't know much about v86 mode, so
you might want to get some confirmation on the
following

My understanding, though, was that V86 mode doesn't
necessarily equate to "emulate 16 bit programs."
In other words, I don't think it jumps to real
mode for you... you have to do that yourself.

You can use V86 mode to emulate 32-bit pmode
programs too, so I think if you're wanting to
emulate a 16-bit real mode OS, you'll have to
set up the environment first.

Jeff

ps - I say "emulate", but you know what I mean

Hi jeff,

>My understanding, though, was that V86 mode doesn't
>necessarily equate to "emulate 16 bit programs."
>In other words, I don't think it jumps to real
>mode for you... you have to do that yourself.
>
>You can use V86 mode to emulate 32-bit pmode
>programs too, so I think if you're wanting to
>emulate a 16-bit real mode OS, you'll have to
>set up the environment first.
>


From all the docs that I went through, I got the
idea that V86 stands for virtual 8086...I cannot
really understand why I would use a special mode
in protected mode to execute 32 bit code...

>From all the docs that I went through, I got the
>idea that V86 stands for virtual 8086...I cannot
>really understand why I would use a special mode
>in protected mode to execute 32 bit code...
>

Because when you're emulating a crappy OS like
Win95, you're gonna want some security! Try an
execute a cli intruction under Win95. It works.

As a general rule, if you're emulating an OS with
less security then your own, you're gonna want to
emulate it in v86 mode, in my opinion.

Jeff