Longmode cursor problem

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TAH

Joined: 05 Jul 2009
Posts: 8
Location: Norway

TAH 23 Feb 2011, 11:56

Hello all

I've been playing around with 64bit long mode for a while,
using PetroffHeroj's FAT12 boot sector and Tomasz Grysztar's long mode example.

For a while I've been trying to set the cursor position using the following code:

Code:

        ; BX = Offset in buffer
     mov     AL, 0Eh
     mov     AH, BH
      mov     DX, 03D4h
   out     DX, AX
      inc     AX
  mov     AH, BL
      out     DX, AX

The problem is that I can set the position to anything up to position 118 in the buffer, but as soon as i try anything above 118 the cursor disappears from the monitor.

I have tested the code using bochs 2.4.5 on two computers, same result on both.

So, my question is; is the problem in the setcursor code or is it related to the boot sector or long mode code ?

Any examples that work would be nice. Smile

References:
http://flatassembler.net/examples/phboot.zip
http://flatassembler.net/examples/longmode.zip

TAH

23 Feb 2011, 11:56

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 23 Feb 2011, 16:56

This is a nice OS (Baremetal OS) that has 64bit functions examples for cursor in it.
http://www.returninfinity.com/baremetal.html

23 Feb 2011, 16:56

edfed

Joined: 20 Feb 2006
Posts: 4352
Location: Now

edfed 23 Feb 2011, 17:10

use double buffering and update cursor position during VSYNC, before text video memory refresh.

23 Feb 2011, 17:10

TAH

Joined: 05 Jul 2009
Posts: 8
Location: Norway

TAH 23 Feb 2011, 17:16

Dex4u wrote:

This is a nice OS (Baremetal OS) that has 64bit functions examples for cursor in it.
http://www.returninfinity.com/baremetal.html

Thanks, I'll look into it. Smile

23 Feb 2011, 17:16

TAH

Joined: 05 Jul 2009
Posts: 8
Location: Norway

TAH 23 Feb 2011, 17:19

edfed wrote:

use double buffering and update cursor position during VSYNC, before text video memory refresh.

Is this really needed when using a hardware cursor?

I've done stuff like this in the good-old dos environment, vsync wasn't an issue.

23 Feb 2011, 17:19

edfed

Joined: 20 Feb 2006
Posts: 4352
Location: Now

edfed 23 Feb 2011, 17:28

test it, it is the only way to know if it solves the problem.
double buffering lets you play with video memory image, without the overhead induced by slow direct video memory accesses.

23 Feb 2011, 17:28

TAH

Joined: 05 Jul 2009
Posts: 8
Location: Norway

TAH 23 Feb 2011, 18:07

Well, seems like there is something strange going on here.

Tried the setcursor in bare-metal-os, and waiting for vsync.
None of those solved the problem.

Guess I'll have som debugging to do or start over rather Smile

23 Feb 2011, 18:07

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 23 Feb 2011, 18:20

What interface are you using to set bx is it something like this

Code:

; Set the cursor to:  DH = X   DL = Y

;--------------------------------------

setcursorxy:
             push    eax
         push    ebx
         push    edx

             movzx   bx, dl
              mov     ax, bx
              shl     ax, 4
               shl     bx, 6
               add     bx, ax
              movzx   ax, dh
              add     bx, ax

          call    setcursor

               pop     edx
         pop     ebx
         pop     eax
         ret



; Set the cursor to:  BX = Offset
;---------------------------------
setcursor:
            push    eax
         push    ebx
         push    edx

             mov     al, 0eh
             mov     ah, bh
              mov     dx, 3d4h
            out     dx, ax
              inc     ax
          mov     ah, bl
              out     dx, ax

          pop     edx
         pop     ebx
         pop     eax
         ret

And what about memory mapping for screen is that OK ?

23 Feb 2011, 18:20

TAH

Joined: 05 Jul 2009
Posts: 8
Location: Norway

TAH 23 Feb 2011, 19:04

Dex4u wrote:

What interface are you using to set bx is it something like this
Code:
; Set the cursor to:  DH = X   DL = Y
    
And what about memory mapping for screen is that OK ?

I use this for calculating the offset to move the cursor:

Code:

;       CH - Line
;       CL - Column

      mov     RAX, ScreenX
        mul     CH
  xor     CH, CH
      add     AX, CX
      mov     BX, AX

I think this is ok, it works fine for the sting output X/Y routines.
And i use the same address for screen output and clearscreen.

The only problem I have is to move the cursor to the end of the string.

23 Feb 2011, 19:04

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 23 Feb 2011, 19:52

TAH wrote:

Code:

;       CH - Line
;       CL - Column

 mov     RAX, ScreenX
        mul     CH
  xor     CH, CH
      add     AX, CX
      mov     BX, AX

Have you just hand written that, if not should it not be

Code:

;       CH - Line
;       CL - Column

        mov     RAX, [ScreenX]
      mul     CH
  xor     CH, CH
      add     AX, CX
      mov     BX, AX

23 Feb 2011, 19:52

TAH

Joined: 05 Jul 2009
Posts: 8
Location: Norway

TAH 23 Feb 2011, 20:04

ScreenX is declared as

Code:

ScreenX equ        80

As I remember I don't need the []....

And as I said, it works perfectly for the print string function.
Also, I put the value to move the cursor directly in the DX register for testing purposes.

And the code I borrowed from baremetal don't use ScreenX....

23 Feb 2011, 20:04

TAH

Joined: 05 Jul 2009
Posts: 8
Location: Norway

TAH 23 Feb 2011, 22:14

After the responses I've got here, I think the bug must be somewhere in the longmode, IDT or GDT code (which is new to me).

I'll try to redo these parts, and see if I can make it work. I'll keep you posted.

Thanks for the help guys. Smile

23 Feb 2011, 22:14

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 23 Feb 2011, 22:43

Yes i would like to know, just in case i move to 64bit and have the same problem.
Happy debugging Wink

23 Feb 2011, 22:43

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