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|
bits 16
org 0x7c00
global _start
_start:
; Clear screen
mov ax, 0x003
int 0x10
; Welcome user!
mov si, hello_msg
call print
; Check LBA support
mov ah, 0x41
mov bx, 0x55AA
int 0x13
jc lba_error
cmp bx, 0xAA55
jnz lba_error
; Check disk and move dl
and dl, 0x80 ; Use disk 0
jz disk_error
mov [drive], dl
; Load stage two
mov bx, stage_two
mov [dest], bx
call disk_read
; JUMP
jmp stage_two
print:
mov ah, 0x0E
xor bh, bh
print_ch:
lodsb
test al, al
jz print_end
int 0x10
jmp print_ch
print_end:
ret
disk_read:
mov si, packet ; Address of dap
mov ah, 0x42 ; Extended read
mov dl, [drive] ; Drive number
int 0x13
jc disk_error
ret
; Errors
disk_error:
mov si, disk_error_msg
call print
jmp $
lba_error:
mov si, lba_error_msg
call print
jmp $
; Variables
hello_msg db "Welcome! Loading Melvix...", 0x0A, 0x0D, 0x00
disk_error_msg db "Disk error!", 0x0a, 0x0d, 0x00
lba_error_msg db "LBA error!", 0x0a, 0x0d, 0x00
stage_two_msg db "Stage2 loaded", 0x0a, 0x0d, 0x00
disk_success_msg db "Disk is valid", 0x0a, 0x0d, 0x00
inode_table_msg db "Found inode table", 0x0a, 0x0d, 0x00
drive db 0
; Data
packet:
db 0x10 ; Packet size
db 0 ; Always 0
count:
dw 4 ; Number of sectors to transfer
dest:
dw 0 ; Destination offset
dw 0 ; Destination segment
lba:
dd 1 ; LBA number
dd 0 ; More storage bytes
; End of boot sector
times 510 - ($ - $$) db 0
dw 0xAA55
stage_two:
mov si, stage_two_msg
call print ; yay!
; Verify signature
mov ax, [superblock +56]
cmp ax, 0xEF53
jne disk_error
mov si, disk_success_msg
call print
; load inode table
mov ax, [superblock + 1024 + 8] ; Inode table
mov cx, 2
mul cx ; ax = cx * ax
mov [lba], ax ; Sector
mov ax, 2
mov [count], ax ; Read 1024 bytes
mov bx, 0x1000 ; Copy data to 0x1000
mov [dest], bx
call disk_read
mov si, inode_table_msg
call print
; Load root dir
xor bx, bx
mov ax, bx
mov bx, 0x1080 ; First block ((2 - 1) * 128 + dest)
mov ax, word [bx + 0] ; Filetype
and ax, 0x4000 ; Check if dir
cmp ax, 0x4000
jne disk_error
mov cx, [bx + 28] ; Number of sectors for inode
lea di, [bx + 40] ; Address of first block pointer
mov bx, 0x5000
mov [dest + 2], bx
mov bx, 0 ; Inode location = 0xF0000
mov [dest], bx
call stage_three_load
jmp protected_mode_enter
stage_three_load:
xor ax, ax ; Clear ax
mov dx, ax ; Clear dx
mov ax, [di] ; Set ax = block pointer
mov dx, 2 ; Mul 2 for sectors
mul dx ; ax = dx * ax
mov [lba], ax
mov [dest], bx
call disk_read
add bx, 0x400 ; 1kb increase
add di, 0x4 ; Move to next block pointer
sub cx, 0x2 ; Read 2 blocks
jnz stage_three_load
ret
nop
hlt
protected_mode_enter:
cli ; Turn off interrupts
; TODO: Check A20 support?
in al, 0x92 ; Enable A20
or al, 2
out 0x92, al
; Clear registers
xor ax, ax
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
lgdt [gdt_desc] ; Load GDT
mov eax, cr0
or eax, 1 ; Set bit 0
mov cr0, eax
jmp 08h:protected_mode ; JUMP!
bits 32 ; Woah!
protected_mode:
xor eax, eax
mov ax, 10h ; Set data segement indentifier
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax ; Stack segment
mov esp, 0x00900000 ; Move stack pointer
mov edx, 0x00050000
lea eax, [edx]
call eax
; GDT
align 32
gdt:
gdt_null:
dd 0
dd 0
gdt_code:
dw 0xFFFF
dw 0
db 0
db 0x9A
db 0xCF
db 0
gdt_data:
dw 0xFFFF
dw 0
db 0
db 0x92
db 0xcF
db 0
gdt_end:
gdt_desc:
dw gdt_end - gdt - 1
dd gdt
times 1024 - ($ - $$) db 0
superblock:
|
