How to move the cursor with x86 BIOS calls?-CodePudding

I'm doing some operating system tutorials from the book "Operating systems from 0 to 1". One of the exercises is to set the cursor to a position on the screen in the bootloader. However, no matter what I try, the cursor only stays in the same position, at the top left.

To make things more confusing, in the book, it mentions that the registers I need to set before raising interrupt 10h are bh for the Y coordinate and bl for the X coordinate. Wikipedia mentions bh for page number, dh and dl for the row and column. Neither of these methods have worked for me.

Here is the function I am using (using the book method):

MovCursor:
    pusha

    mov ah, 0x02

    mov bh, 0x1
    mov bl, 0x4

    int 0x10

    popa

Any help to tell me what I am doing wrong would be greatly appreciated.

CodePudding user response：

The Wikipedia register settings are correct. From your saying that "Neither of these methods have worked for me", I conclude that you have tried the Wikipedia version too. It's a pitty I can't verify your code since you didn't include it in your question.

A few points to consider regarding the cursor:

On a graphics screen the cursor is never rendered. The coordinates change but it stays invisible¹. On a text screen the cursor defaults to a blinking underline.
The coordinates (column and row) of the cursor are zero-based. The upperleft corner of the screen is at (0,0).
The cursor will disappear if you position it off screen.
You can change the shape of the cursor with BIOS.SetCursorType function 01h. You can also make it disappear this way!

Next code displays a string of colored A's in the middle of the screen:

mov  ax, 0003h    ; BIOS.SetVideoMode 80x25 16-color text
int  10h

mov  dx, 0C23h    ; DH is Row (12), DL is Column (35)
mov  bh, 0        ; DisplayPage
mov  ah, 02h      ; BIOS.SetCursorPosition
int  10h

mov  cx, 10       ; ReplicationCount
mov  bx, 002Fh    ; BH is DisplayPage (0) , BL is Attribute (BrightWhiteOnGreen)
mov  ax, 0941h    ; BIOS.WriteCharacterAndAttribute, AL is ASCII ("A")
int  10h

mov  ah, 00h      ; BIOS.WaitKeyboardKey
int  16h          ; -> AX

¹ For some light reading How can I add a blinking cursor to the graphics video modes?