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flat assembler > Main > bootloader doesn't work

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luish



Joined: 26 Jan 2018
Posts: 13
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?
Post 26 Jan 2018, 11:03
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ManOfSteel



Joined: 02 Feb 2005
Posts: 1146
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.
Post 26 Jan 2018, 20:55
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luish



Joined: 26 Jan 2018
Posts: 13
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?
Post 29 Jan 2018, 11:10
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luish



Joined: 26 Jan 2018
Posts: 13
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
Post 29 Jan 2018, 12:16
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luish



Joined: 26 Jan 2018
Posts: 13
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..................
Post 05 Feb 2018, 11:14
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