VM86 problems

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Artlav

Joined: 23 Dec 2004
Posts: 188
Location: Moscow, Russia

Artlav 24 Nov 2005, 20:54

Iam writing a BIOS module for my PM OS using VM86.
But somewhy neither interrupts nor i/o works in vmode.
On int 10h unidentified exeption is generated.

First question: What is wrong?
Second question: Is there better ways to access BIOS from PM?

Thank you in advance.

Setup:

Code:

CR4: 0x2D3

VM TSS GDT record:
00h: 0x091c00af 0xf000e920 0x00000000 0x00000000
10h: 0x00000000 0x00000000 0x00000000 0x00000000

VM TSS selector: 0xE0

VM TSS:
00h: 0x00000000 0x00000000 0x00000000 0x00000000
10h: 0x00000000 0x00000000 0x00000000 0x0042f000
20h: 0x00000000 0x000a3202 0x00000000 0x00000000
30h: 0x00000000 0x00000000 0x00000000 0x00000000
40h: 0x00000000 0x00000000 0x00001000 0x00001000
50h: 0x00001000 0x00001000 0x00000000 0x00000000
60h: 0x00000000 0x00900000 0x000001b0 0x00000000
70h: 0x00000000 0x00000000 0x00000000 0x00000000
80h: 0x00000000 0x00000000 0x00000000 0x00000000
90h: 0x00000000 0x00000000 0x00000000 0x00000000
A0h: 0x00000000 0x00000000 0x00000000 0x00000000
B0h: 0x00000000 0x00000000 0x00000000 0x00000000

VM pages:
0x00000-0x9FFFF mapped to the randomly allocated app memory.
Preserved original IVT image is copyed to 0x0.
0xA0000-0xFFFFF mapped to the same physical area.

vm code (0x1000:0x0):
use16

start:
jmp     begin

begin:
mov     sp,stacks
add     sp,199

mov     ax,0013h
int     10h

jmp     $

stacks  rb 200

24 Nov 2005, 20:54

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 24 Nov 2005, 23:08

I go back to realmode from pmode and back to pmode for my OS, for vesa mode switching etc, it works fine.
I have made a demo for doing this, let me know if you want to try it.
It needs vesa2 for the demo.

PS: You can also try these games for Dex4u (my OS) that user the switching function,
heres a self extraring image for floppy http://www.dex4u.com/Dex4uPong.zip
The image includes a old ver of Dex4u OS, along with some games.

24 Nov 2005, 23:08

Artlav

Joined: 23 Dec 2004
Posts: 188
Location: Moscow, Russia

Artlav 28 Nov 2005, 17:59

Solved the problem recently (gdt and tss is not paged in the vm86), and found, that there is no real need in the BIOS driver...
Strange thing - two years ago i didn't knew how to continue the OS without it, and when it's finally done there is already no use for it.

Dex4u: Good ones.
What about all the pmode structures - how they will be preserved in the switch? i mean paging, segments?
Or should i create a plain memory area within the first mb with the rm code?

28 Nov 2005, 17:59

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 28 Nov 2005, 18:44

Here is a simple demo of switch to & from pmode for ints, come with fasm source code http://www.dex4u.com/DemoVesa.zip
Note: the code needs vesa2 and was done when i was called ASHLEY4 Wink

.

PS: If you have any ? about the inner workings of Dex4u OS, you can ask ? here: http://dex.7.forumer.com/

28 Nov 2005, 18:44

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