Bug in bootloader
Posted: Mon Jan 10, 2005 12:00 am
I've got this code:
i'm compiling it without any errors in NASM. Rawrating on floppy, copying kernel and trying to boot in bochs. I don't know why it's don't working :/
Code: Select all
[bits 16]
[org 0]
jmp BootCode
BPB_OEM db 'ADDIX '
BPB_BytesPerSector dw 512
BPB_SectorsPerCluster db 1
BPB_ReservedSectors dw 1
BPB_FatsNum db 2
BPB_RootEntries dw 224
BPB_TotalSectors dw 2880
BPB_MediaType db 0f0h
BPB_SectorsPerFat dw 9
BPB_SectorsPerTrack dw 18
BPB_HeadsNum dw 2
BPB_HiddenSectors dd 0
BPB_TotelSectors32 dd 0
BPB_DriveNum db 0
BPB_Reserved db 0
BPB_BootSignature db 0
BPB_VolumeID dd 0bbbbddddh
BPB_VolumeLabel db 'ADDIX '
BPB_FileSystem db 'FAT 12 '
BootCode:
cli
mov ax, 7c00h
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov [BPB_DriveNum], dl
mov ax, 0000h
mov ss, ax
mov sp, 0ffffh
sti
xor cx, cx
xor dx, dx
mov ax, 32
mul word[BPB_RootEntries]
div word[BPB_BytesPerSector]
xchg ax, cx
mov al, byte[BPB_FatsNum]
mul word[BPB_SectorsPerFat]
add ax, [BPB_ReservedSectors]
mov word[DataSector], ax
add word[DataSector], cx
mov bx, 0200h
call ReadSector
mov cx, [BPB_RootEntries]
mov di, 0200h
FindLoop:
push cx
mov cx, 11
mov si, FileName
push di
rep cmpsb
pop di
je LoadFAT
pop cx
add di, 32
loop FindLoop
jmp Failure
LoadFAT:
mov dx, word[di+1ah]
mov word[Cluster], dx
xor ax, ax
mov al, byte[BPB_FatsNum]
mul word[BPB_SectorsPerFat]
mov cx, ax
mov ax, word[BPB_ReservedSectors]
mov bx, 0200h
call ReadSector
mov ax, 1000h
mov es, ax
mov bx, 0000h
push bx
LoadFile:
mov ax, word[Cluster]
pop bx
call ClusterLBA
xor cx, cx
mov cl, byte[BPB_SectorsPerCluster]
call ReadSector
push bx
mov ax, word[Cluster]
mov cx, ax
mov dx, ax
shr dx, 0x0001
add cx, dx
mov bx, 0x0200
add bx, cx
mov dx, word[bx]
test ax, 0001
jnz LoadFile2
LoadFile1:
and dx, 0000111111111111b
jmp LoadFileDone
LoadFile2:
shr dx, 4
LoadFileDone:
mov word[Cluster], dx
cmp dx, 0x0ff0
jb LoadFile
Done:
mov ax, 1000h
mov es, ax
mov ds, ax
mov ss, ax
xor ax, ax
xor bx, bx
xor cx, cx
xor dx, dx
xor si, si
xor di, di
xor sp, sp
xor bp, bp
jmp 1000h:0000h
Halt:
jmp Halt
Failure:
mov si, MSG_Failure
call PrintString
mov ax, 0
int 16h
int 19h
PrintString:
lodsb
cmp al, 0
je PrintStringEnd
mov ah, 0Eh
mov bh, 0
int 10h
jmp PrintString
PrintStringEnd:
ret
LBA_to_CHS:
xor dx, dx
div word[BPB_SectorsPerTrack]
inc dl
mov byte[AbsSector], dl
xor dx, dx
div word[BPB_HeadsNum]
mov byte[AbsHead], dl
mov byte[AbsTrack], al
ret
ClusterLBA:
sub ax, 2
xor cx, cx
mov cl, byte[BPB_SectorsPerCluster]
mul cx
add ax, word[DataSector]
ReadSector:
push ax
push bx
push cx
call LBA_to_CHS
mov ah, 02h
mov al, 01h
mov ch, byte[AbsTrack]
mov cl, byte[AbsSector]
mov dh, byte[AbsHead]
mov dl, byte[BPB_DriveNum]
int 13h
pop cx
pop bx
pop ax
add bx, word[BPB_BytesPerSector]
inc ax
loop ReadSector
ret
AbsSector db 0
AbsHead db 0
AbsTrack db 0
DataSector dw 0
Cluster dw 0
FileName db 'ADDIX SYS'
MSG_Welcome db 'AddixOS loader by Adix', 13,10,0
MSG_Loading db 'Ladowanie AddixOS...', 13,10,0
MSG_Failure db 'Blad! Nacisnij jakis klawisz...', 0
times 510-($-$$) db 0
dw 0aa55h