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Re: Writing a boot menu
Posted: Fri Feb 27, 2009 5:21 am
by mangaluve
Thanks for the explanation!
Just a short one.. I dont want to move the stuff I load to "buffer", but instead to the memory location 08h:01000h. I replace "offset buffer" with 01000h but it doesnt seem to work. Am I doing something wrong? It seems like I never get pass this code
still_going:
in al,dx
test al,8
jz still_going
Re: Writing a boot menu
Posted: Fri Feb 27, 2009 11:05 am
by Dex
Try this (untested)
Code: Select all
;************************************
; By Dex
; Assemble with fasm
; c:\fasm Hdd.asm Hdd.bin
;
;************************************
org 0x7C00
use16
;****************************
; Realmode startup code.
;****************************
start:
xor ax,ax
mov ds,ax
mov es,ax
mov ss,ax
mov sp,0x7C00
;*****************************
; Setting up, to enter pmode.
;*****************************
cli
lgdt [gdtr]
mov eax, cr0
or al,0x1
mov cr0,eax
jmp 0x10: protected
;*****************************
; Pmode. ;-)
;*****************************
use32
protected:
mov ax,0x8
mov ds,ax
mov es,ax
mov ss,ax
mov esp,0x7C00
;*****************************
; Turn floppy off (if space).
;*****************************
mov dx,3F2h
mov al,0
out dx,al
;*********************************
; Print T in the right hand corner
;*********************************
mov byte [es:0xB809E], "1"
mov dx,1f6h ;Drive and head port
mov al,0a0h ;Drive 0, head 0
out dx,al
mov dx,1f2h ;Sector count port
mov al,1 ;Read one sector
out dx,al
mov dx,1f3h ;Sector number port
mov al,1 ;Read sector one
out dx,al
mov dx,1f4h ;Cylinder low port
mov al,0 ;Cylinder 0
out dx,al
mov dx,1f5h ;Cylinder high port
mov al,0 ;The rest of the cylinder 0
out dx,al
mov dx,1f7h ;Command port
mov al,20h ;Read with retry.
out dx,al
mov byte [es:0xB809E], "2"
still_going:
in al,dx
test al,8 ;This means the sector buffer requires
;servicing.
jz still_going ;Don't continue until the sector buffer
;is ready.
mov byte [es:0xB809E], "3"
mov ecx,512/2 ;One sector /2
mov edi,0x1000
mov dx,1f0h ;Data port - data comes in and out of here.
rep insw
mov byte [es:0xB809E], "4"
mov esi,0x1000 ; dump it to screen
mov edi,0xB8000
mov ecx,512
mov ah,' '
ScreenDump:
lodsb
stosw
loop ScreenDump
mov byte [es:0xB809E], "5"
jmp $ ; Just loop for now
;*************************************
; GDT.
;*************************************
gdt: dw 0x0000, 0x0000, 0x0000, 0x0000
sys_data: dw 0xFFFF, 0x0000, 0x9200, 0x00CF
sys_code: dw 0xFFFF, 0x0000, 0x9800, 0x00CF
gdt_end:
gdtr: dw gdt_end - gdt - 1
dd gdt
;*************************************
; Make program 510 byte's + 0xaa55
;*************************************
times 510- ($-start) db 0
dw 0xaa55
The above code will dump mostlly unreadable words, but there should be some ASCII in there you can read.
Note: also the above code gesses your hdd address, is your's the first drive ?
Also is your base zero based (GDT) and are you tranlating the 0x1000 from realmode ?, as if so it will be 0x10000 for pmode.
Re: Writing a boot menu
Posted: Fri Feb 27, 2009 1:30 pm
by mangaluve
Thanks man! I'm still stuck after 2 has been printed, by I think that maybe I've configured Bochs wrong (only been using it for floppys before). I'ma give your code a real try
Exactly how do I tell Bochs that my first harddrive should be a certain file, like
floppya: 1_44=booting.bin, status=inserted
but for a hard drive
edit: never mind, it works now.. I think the problem was the following lines:
mov ecx,512/2 ;One sector /2
mov edi, 01000h
I used cx and di instead of ecx and edi before...
Re: Writing a boot menu
Posted: Wed Mar 04, 2009 2:27 pm
by Sly
uh... Dex, a little off-topic, but I didn't see anything for enabling the A20 gate.
Re: Writing a boot menu
Posted: Wed Mar 04, 2009 8:36 pm
by Dex
Sly wrote:uh... Dex, a little off-topic, but I didn't see anything for enabling the A20 gate.
Why would we need to do that for this little demo ?, we are not going over 1MB, Unless your coding a full OS, you only put what is need for the demo, you need to keep things simple, to help beginners understand whats going on.
Re: Writing a boot menu
Posted: Mon Mar 09, 2009 3:33 am
by ScorchOS
That's a good way of doing it, but there is an easier way if you don't want to create your own bootloader from scratch. If you're using grub, you just need to edit the boot/grub/menu.lst file.