Hello,
When executed with bochs-2.1.1, the bochs rebooted while switching to protected mode.
What is the problem with the following code ?
;
;**********************************
;***********Boot Loader************
;**********************************
;
;
; This loader
; o will load the 2 Sector (1024 bytes) kernel in the memory
; o switches to protected mode
; o jump to the kernel
;
org 0x7c00
start:
; setting the stack for loading the program
xor ax, ax ; first we will set up the stack
cli
mov ss,ax
mov sp, 0xffff
sti
mov [bootdrv], dl ; dl contains the bootdisk name ie; dl = 0 if floppy a:\
call load ; function to load the kernel from disk into memory
mov si, msgloadsuccess
call putstr
mov ax, 0h
int 16h
; jmp init
cli ; no interrupts allowed !
; first we move the system to it's rightful place
mov ax,0x0000
cld ; 'direction'=0, movs moves forward
do_move:
mov es,ax ; destination segment
add ax,0x1000
cmp ax,0x9000
jz end_move
mov ds,ax ; source segment
sub di,di
sub si,si
mov cx,0x8000
rep
movsw
jmp do_move
; then we load the segment descriptors
end_move:
lgdt [gdtr] ; load gdt with whatever appropriate
; Load the GDTR with the base address and limit of the GDT.
lgdt [gdtr]
mov si, msgloadgdt
call putstr
mov ax, 0h
int 16h
;
; Set the PE [protected mode enable] bit in register CR0 to begin the
; switch to protected mode.
;
cli
mov eax,cr0
or al,1
mov cr0,eax
jmp 08h:init
; loader variables
bootdrv db 0
msgresetfail db 'Disk Reset Failure!', 13, 10, 0
msgresetsuccess db 'Disk reset success...', 13, 10, 0
msgkernelload db 'Loading kernel...', 13, 10, 0
msgloadsuccess db 'Kernel loaded successfully...', 13, 10, 0
msgprot db 'We are in protected mode...', 13, 10, 0
msgloadgdt db 'GDT Loaded...', 13, 10, 0
msghang db '.', 0
load:
; we have to reset the disk before it move to the loaded program
; say our real program is stored in sector 2
; let's load it
push ds ; reset disk system
mov ax, 0 ; forces controller to recalibrate drive heads (seek to track 0)
mov dl, [bootdrv]
int 13h
pop ds
jc resetfail
mov si, msgresetsuccess
call putstr
xor ax,ax ; loads sector into memory
mov es,ax
mov ah,2
mov al,2 ; 2 Sector Kernel
mov dx,0
mov cx,2 ; ch = cylinder number and cl = sector number 1-63
mov bx,7e00h ; 7e00h = 7c00h + 512 ... loading my program here makes it easy for me
int 13h
jc load ; if fail then try to load it again
mov si, msgkernelload
call putstr
retn
resetfail:
mov si, msgresetfail
call putstr
retn
putstr:
lodsb
or al,al
jz short putstrd
mov ah,0x0E
mov bx,0x0007
int 0x10
jmp putstr
putstrd:
retn
gdtr:
dw end-gdt-1
dd gdt
gdt:
dw 0,0,0,0 ; dummy
dw 0xffFF ; ffffh limit
dw 0x0000 ; base address 0
dw 0x9A00 ; Execute/Read Code Segment
dw 0x00C0
dw 0xffFF ; ffffh limit
dw 0x0000 ; Base Address 0
dw 0x9200 ; R/W Data Segment
dw 0x00C0
end:
;hangs if kernel not loaded
oops:
mov si, msghang
call putstr
jmp oops
retf
bits 32
init:
sti
jmp 0x07e00 ; Jump to the kernel @ 7e00h = 7c00h + 512
times 510-($-$$) db 90 ; Filling the remaining free space in the sector
dw 0AA55h
Thanks