bootloader doesn't work

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luish

Joined: 26 Jan 2018
Posts: 13

luish 26 Jan 2018, 11:03

i am writing a bootloader that read the MBR of the OS at sector 7 and jmp to original MBR but instead of do it, my PC freeze.

Code:

start:
MOV AX,201H
MOV BX,0E00H
MOV CX,1
MOV DX,80H
INT 13H
MOV CX,7
MOV AX,301H
INT 13H
MOV CX,1BDH
MOV SI,example
MOV DI,0E00H
REP MOVSB
MOV AX,301H
MOV BX,0E00H
MOV AX,301H
MOV CX,1
INT 13H
RET

example:
MOV AX,201H
PUSH ES
MOV BX,0
MOV ES,BX
MOV BX,7C00H
MOV CX,7
INT 13H
POP ES
cs
jmp bx

codesize:

why my PC freeze when run my code?

26 Jan 2018, 11:03

ManOfSteel

Joined: 02 Feb 2005
Posts: 1154

ManOfSteel 26 Jan 2018, 20:55

Since that's your first post, welcome to the forums.

Using visual indicators (through int 0x10 or directly writing to video memory) for debugging is usually a good idea. Printing, say, a dot every now and then will tell you exactly where your code is freezing.

It also never hurts to stick to the convention of including the 0x55AA boot signature at the end of the sector.

26 Jan 2018, 20:55

luish

Joined: 26 Jan 2018
Posts: 13

luish 29 Jan 2018, 11:10

INT 10h or write at video memory don't help me nothing for me. the problem is that PC is halted when cs change to 0 == 0:7C00h then PC halted. no one video indicators apppears on my display. why PC halt when CS == 0?

29 Jan 2018, 11:10

luish

Joined: 26 Jan 2018
Posts: 13

luish 29 Jan 2018, 12:16

Code:

...
example:
MOV AX,201H
PUSH ES
MOV BX,0
MOV ES,BX
MOV BX,7C00H
MOV CX,7
INT 13H
POP ES
cs
jmp bx                    ;when jmp to 0:7c00h windows MBR is started...

codesize:
windows MBR:
XOR     AX,AX
MOV     SS,AX
MOV     SP,7C00
MOV     ES,AX
MOV     DS,AX
MOV     SI,7C00
MOV     DI,0600
MOV     CX,0200
CLD
REPZ                            ;HERE IS WHEN THE PC IS HALTED. WHY IS HALTED HERE ???
MOVSB

29 Jan 2018, 12:16

luish

Joined: 26 Jan 2018
Posts: 13

luish 05 Feb 2018, 11:14

i alredy soved my prblem mysef!!! thanks for none help me at these foruns!!! now i only want to modify the IVT with my bootloader!!! if someone want to hel me..................

05 Feb 2018, 11:14

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