Thanks for all your replies guys, I got my bootloader working, I realise why you told me that code wouldn't enable A20, it's because I put the comment in then forgot to add in the code :S *facepalm*, anyhow I figured out two reasons why it was triple faulting, and choosing to take the easy solution the resulting code is below. But first the two reasons: A: once the code was relocated, it was struggling to jump to the right piece of memory for the 32bit code (possibly a fault of my own but I got lazy so I refactored my code instead lol) B: I was trying to enable A20 before PMode (once I added the code in) which for some possibly well known reason which I am so far unaware of >.< was causing problems, I dont know if anyone else has encountered this, I didn't have to google it I went on instinct to move the call lol. So here's the new, 100% working code for your curiosities:
Code: Select all
;stage 1 boot
use16
org 0x7C00
jmp Start16
Start16:
xor ax,ax
mov ds,ax
mov es,ax
cli
xor ax,ax
mov ds,ax
mov es,ax
mov ax,0x9000
mov ss,ax
mov sp,0xFFFF
sti
mov [drive],dl ;BIOS passes drive number in DL
call LoadStage2
cmp [errorflag],0
jg hang16
jmp loadpoint16 ;jump to loaded program
hang16:
xor ah,ah
int 0x16 ; wait for a key
int 0x19 ; reboot the machine
LoadStage2:
pusha
mov [counter1],1
.tryread:
mov ax,ds ;segment
mov es,ax
mov bx,loadpoint16 ;offset
mov ah,02h ;read sectors into memory
mov al,4d ;load 4 sectors
mov ch,00h ;the track to read from
mov cl,02h ;sector id
mov dh,00h ;head
mov dl,[drive] ;drive
int 13h
jc .tryagain
jmp .fin
.tryagain:
inc [counter1]
cmp [counter1],3
jg .failed
jmp .tryread
.failed:
mov [errorflag],1
.fin:
popa
ret
drive db 0
errorflag db 0
counter1 db 0
times 510-($-$$) db 0
dw 0xAA55
;end of stage 1 boot
;=========================================
;stage 2 boot
loadpoint16:
call LoadGDT
call EnablePMode
jmp 08h:loadpoint32 ;32Bit data segment
jmp hang16
gdtr:
dw gdt_end - gdt - 1 ;limit (size of GDT)
dd gdt ;base of GDT
gdt:
dq 0 ;dummy entry (8 zero filled bytes)
;gdt code: ;code descriptor
dw 0xFFFF ;limit low
dw 0 ;base low
db 0 ;base middle
db 10011010b ;access
db 11001111b ;granularity
db 0 ;base high
;gdt data: ;data descriptor
dw 0xFFFF ;limit low
dw 0 ;base low
db 0 ;base middle
db 10010010b ;access
db 11001111b ;granularity
db 0 ;base high
gdt_end:
LoadGDT:
pusha
lgdt [gdtr]
sti
popa
ret
EnablePMode:
cli
mov eax,cr0 ;set bit 0 in CR0-go to pmode
or eax,1
mov cr0,eax
ret
;end of stage 2 boot
;=========================================
;stage 3 boot
use32
EnableA20:
mov al,0xDD ;command 0xDD enable A20
out 0x74,al ;send command to keyboard controller
ret
loadpoint32:
mov ax,0x10 ;32Bit code segment
mov ds,ax
mov ss,ax
mov es,ax
mov esp,90000h
call EnableA20
;Move 32Bit code to 0x0000:0x0000
mov esi,Start32
xor eax,eax ;eax = 0x00000000
mov edi,eax
mov cx,((End32-Start32)/4)+1 ;byte length of 32bit code
move_dword:
mov eax,[esi]
mov [edi],eax
add esi,4
add edi,4
dec cx
cmp cx,0
jg move_dword
jmp 0x00000000
Start32:
call ClearScreen32
mov ebx,HelloWorld32
call PrintText32
mov [xpos],0
mov [ypos],4
mov bh, byte [ypos]
mov bl, byte [xpos]
call SetCursorPos32
hang32:
cli
hlt
Putch32:
pusha
mov edi,0xB8000
xor eax,eax
mov ecx,160
mov al, byte [ypos]
mul ecx
push eax
mov al, byte [xpos]
mov cl,2
mul cl
pop ecx
add eax,ecx
xor ecx,ecx
add edi,eax
cmp bl,0x0A
je .row
mov dl,bl
mov dh,[char_attrib]
mov word [edi],dx
inc byte [xpos]
cmp [xpos], 80
je .row
jmp .done
.row:
mov byte [xpos], 0
inc byte [ypos]
.done:
popa
ret
PrintText32:
pusha
push ebx
pop edi
.loop:
mov bl, byte[edi]
cmp bl, 0
je .done
call Putch32
.next:
inc edi
jmp .loop
.done:
mov bh, byte [ypos]
mov bl, byte [xpos]
call SetCursorPos32
popa
ret
SetCursorPos32:
pusha
xor eax,eax
mov ecx,80
mov al,bh
mul ecx
add al,bl
mov ebx,eax
mov al,0x0F
mov dx,0x03D4
out dx,al
mov al,bl
mov dx,0x03D5
out dx,al
xor eax,eax
mov al,0x0E
mov dx,0x03D4
out dx,al
mov al,bh
mov dx,0x03D5
out dx,al
popa
ret
ClearScreen32:
pusha
cld
mov edi,0xB8000
mov cx,2000
mov ah,[char_attrib]
mov al,' '
rep stosw
popa
ret
char_attrib db 00000101b
xpos db 4
ypos db 2
HelloWorld32 db "Hello 32Bit World",0
End32:
;end of stage 3 boot
In the new code, instead of moving the 0x07C0 code to a different location, I load the second part first, the second part then sets up 32Bit PMode, then relocates the 32Bit code to 0x00000000 (finally), then jumps to it. I've checked this, by after relocating the 32Bit code, formatting the memory that it came from with 0x0s. It still ran fine after the jump to 0x00000000. If I am missing anything here please tell me but so far it works fine, my fingers are crossed lol. Oh and the 32Bit code enables A20 instead.
Do I hear a round of applause or a loud humming boo O.O?
