but for some reason, at one punt my bootloader just freezes. And i can't find the problem.
i'm using bochs and nasm
my code
Code: Select all
org 0
mov [drive], dl
start:
cli
;setup segments
mov ax, 0x07c0
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
;setup stack
mov sp, [stack_end]
sti
; now read the lafs table
read_lafs_tbl:
mov ah, 0x02 ; we should read
mov al, 0x01 ; read one sector
mov ch, 0x00 ; read from cilinder 0x0
mov cl, 0x02 ; we want to start reading at sector 0x01
mov dh, 0x00 ; we want to read from the first head (0x0)
mov dl, [drive] ; we want to read from drive 0x0
mov bx, 0x0
mov es, bx
mov bx, 0x02000
int 0x013
;jc read_lafs_tbl
;;;;; ==>> now we need to find the stage2 name <<== ;;;;;;;;;
mov cx, WORD [LAFS_fileCount] ; load loop counter
mov di, 0x02000 ; locate first entry
.loop:
push cx
mov cx, 0x0008 ; eigth character name
mov si, stage2_name ; image name to find
push di
rep cmpsb ; test for entry match
pop di
je load_stage2
pop cx
add di, 17 ; queue next entry
loop .loop
mov si, stage2_no_find
jmp error
load_stage2:
mov si, di
;get the start sector
mov ax, [si+15]
mov [good_location] ,ax
;convert the start sector to CHS
call LBA2CHS
;now calculate the size of stage2 (it is assembled with 512 alignment)
mov di, [good_location]
mov ax, [di-2]
mov bx, 512
div bx
mov [stage2_sector_count], ax
;now print everything
;the start sector
mov si, sector_str
call print_string
xor ax, ax
mov al, [stage2_start_sector]
call print_ax_bin
;the sector count
mov si, sector_count_str
call print_string
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; It freezes here! ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov ah, 0x0
mov al, [stage2_sector_count]
call print_ax_bin
;the track number
mov si, track_str
call print_string
mov ah, 0x0
mov al, [stage2_cilinder]
call print_ax_bin
;the head number
mov si, head_str
call print_string
mov ah, 0x0
mov al, [stage2_head]
call print_ax_bin
;pause
jmp $
;;;;; =>> Functions <== ;;;;;;;
LBA2CHS:
pusha
mov ax, [good_location]
mov dl, 18
div dl
add bx, 1
mov [stage2_start_sector], bl
mov ax, [good_location]
mov bl, 18
div bl
mov [stage2_cilinder], bl
mov [stage2_head], al
popa
ret
;Sector = (LBA/SectorsPerTrack) Remainder value + 1
;Cylinder = (LBA/SectorsPerTrack)/NumHeads (Take Remainder value)
;Head = (LBA/SectorsPerTrack)/NumHeads (Take quotient value)
error:
mov si, kernel_error
call print_string
call print_ax_bin
jmp $
print_string:
pusha
lodsb
cmp al, 0
jz .done
mov ah, 0x0e
int 0x10
jmp print_string
.done:
popa
ret
print_ax_bin:
pusha
; print result value in binary:
mov cx, 16
mov bx, ax
.print:
mov ah, 0x0e ; print function.
mov al, '0'
test bx, 1000000000000000b ; test first bit.
jz .zero
mov al, '1'
.zero:
int 0x10
shl bx, 1
loop .print
; print binary suffix:
mov al, 'b'
int 0x10
popa
ret
kernel_error db 13, 10, "Read err",13, 10,0
stage2_name db "stage2 "
found_stage2 db "Found stage2", 0
stage2_no_find db 13, 10, "Couldn't find stage2",13, 10,0
loc_kern db 13, 10, "Looking for kernel",0
newline db 13, 10, 0
sector_str db 13, 10, "sector: ",0
sector_count_str db 13, 10, " ->count: ",0
head_str db 13, 10, "head: ",0
track_str db 13, 10, "track: ",0
; fill the rest with zero's
times 497 - ($-$$) db 0
; LaFS superblock
LAFS_magic db "LAFS"
LAFS_version db 0x02
LAFS_bytesPerBlock dw 512
LAFS_SizeOfTable db 0x01
LAFS_hiddenBlocks db 0x01
LAFS_fileCount dw 0x04
LAFS_volumeSize dw 2880
dw 0xaa55
section .bss
stack_begin:
resb 4096 ; Reserve 4 KiB stack space
stack_end:
drive:
resb 1
good_location:
resb 2
stage2_start_sector:
resb 1
stage2_cilinder:
resb 1
stage2_head:
resb 1
stage2_sector_count:
resb 1
