Possible addressing problem
Posted: Sat Mar 20, 2010 11:20 pm
Well I'm back to writing my bootloader after my kernel grew beyond the size limits I had first used when loading sectors. I think I have corrected it to load one sector at a time and increase the address until it loads the right amount of sectors. I seem to be having a number of errors with addressing specifically with; the GDT and protected mode jumps. I'm hoping you can provide some insight into why these addresses are off, or why exactly it's not jumping correctly (it may be something with my original ORG or registers too, something just doesn't add up...).
my bootsector works fine, and transfers control to this second stage, which is to load the kernel, enter protected mode and transfer control to the kernel:
Thanks for any help you can provide, I can't seem to find a solution.
my bootsector works fine, and transfers control to this second stage, which is to load the kernel, enter protected mode and transfer control to the kernel:
Code: Select all
[BITS 16]
[ORG 7E00h]
jmp 0000h:Setup
Setup:
xor AX, AX ;set segments and switch to text mode
mov DS, AX
mov ES, AX
mov SS, AX
mov SP, AX
mov AH, 00h
mov AL, 03h
int 10h
mov [BootDrive], DL
lea SI, [TITLE]
call PrintS
jmp Main
BootDrive db 0
Main:
mov CL, 05h
mov DL, [BootDrive]
.reset:
xor AX, AX
int 13h
jz .read
sub CL, 01h
jnz .reset
mov AH, 01h
jmp Error
.read:
mov AX, 1000h ; load to physical address 10000h
mov ES, AX
xor BX, BX
mov AH, 02h
mov AL, 01h
mov CH, 00h
mov CL, 06h
mov DH, 00h
.readsector:
int 13h
jc Error
cmp CL, 6Ah
je .kdone
add BX, 200h
inc CL
jmp .readsector
.kdone:
lea SI, [KLOAD]
call PrintS
.pMode:
cli
mov AX, 2401h ;enable the A20 line, fast then slow
int 15h
jc Error
jmp Final
A20_secondary:
call Empty_8042
mov AL, 0D1h
out 64h, AL
call Empty_8042
mov AL, 0DFh
out 60h, AL
call Empty_8042
Final:
lea SI, [A20SET]
call PrintS
pusha
lgdt[GDTTable] ;load GDT
popa
mov EAX, CR0 ;finally set protected mode
or EAX, 01h
mov CR0, EAX
jmp 08h:clear_pipe
[BITS 32]
clear_pipe:
mov AX, 10h
mov DS, AX
mov SS, AX
mov ES, AX
xor EAX, EAX
mov FS, AX
mov GS, AX
mov ESP, 200000h
jmp 08h:10000h
hlt
PrintS:
mov AH, 0Eh
.loop:
lodsb
test AL, AL
jz .done
int 10h
jmp .loop
.done:
ret
Empty_8042:
call Waitingloop
in AL, 64h
cmp AL, 0FFh
je .done
test AL, 01h
jz .no_output
call Waitingloop
in AL, 60h
jmp Empty_8042
.no_output:
test AL, 02h
jnz Empty_8042
.done:
ret
Waitingloop:
mov EBX,9FFFFh
.loop_start:
dec EBX
jnz .loop_start
ret
Error:
[regular error msg]
;****************
; Strings
;****************
[regulars]
GDT:
null:
dd 00h
dd 00h
code:
dw 0FFFFh
dw 00h
db 00h
db 10011010b
db 11001111b
db 00h
data:
dw 0FFFFh
dw 00h
db 00h
db 10010010b
db 11001111b
db 00h
GDTTable:
Limit dw 24
Base dd null
times 2048-($-$$) db 0
Thanks for any help you can provide, I can't seem to find a solution.
