Boot Loader Help [Fixed]
Posted: Tue Mar 20, 2007 2:07 pm
Hey! I've been working on a simple operating system for a while, but the boot loader I've made is giving me problems (actually, I'm not sure if it's the boot loader or the kernel, but it seems to be the boot loader).
It's a simple 32-bit protected mode loader that enables A20 and reads the kernel from an unformatted floppy, then jumps to it. Virtual PC (2007) gives the an unrecoverable processor error whenever I try to boot the DD-created image. Here's the code, for anyone who has the time to check it for errors:
Thanks in advance for any help!
- Jeremiah
Edit: Updated source code.
It's a simple 32-bit protected mode loader that enables A20 and reads the kernel from an unformatted floppy, then jumps to it. Virtual PC (2007) gives the an unrecoverable processor error whenever I try to boot the DD-created image. Here's the code, for anyone who has the time to check it for errors:
Code: Select all
;;;
;; [ID]
;; Boot-Loader\Source\Boot-Loader.asm
;;
;; [Description]
;; Boot loader, or boot sector, for the Grakos kernel. The boot loader is
;; loaded at 0x7C00 by the BIOS startup routines.
;; After that, it loads the kernel at 0x1000 using the BIOS. Upon loading,
;; it disables interrupts, switches to protected mode, and starts the system.
;;
;; [Copyright]
;; Copyright (C) 2007, Griffinsoft Corporation
;;
;; [Web Site]
;; http://www.griffinsoft.net/
;;;
;; NASM is compiling 16-bit code
[BITS 16]
;; This is loaded at 0x7C00
[ORG 0x7C00]
;; Go directly to Start
jmp Start
;;;
;; [ID]
;; Start
;;
;; [Description]
;; Starts the loading process.
;;;
Start:
mov si, 0x100
mov ax, 0x1000
mov es, ax
mov ax, 0x0
mov bx, ax
mov cx, 0x0002
mov dx, ax
;;;
;; [ID]
;; ReadSector
;;
;; [Description]
;; Reads the sector.
;;;
ReadSector:
mov ax, 0x0201
int 0x13
mov ax, es
add ax, 0x20
mov es, ax
dec si
jz ReadSectorEnd
inc cl
cmp cl, 0x12
jbe ReadSector
mov cl, 1
inc dh
cmp dh, 2
jne ReadSector
mov dh, 0
inc ch
jmp ReadSector
;;;
;; [ID]
;; ReadSectorEnd
;;
;; [Description]
;; Kills the floppy drive.
;;;
ReadSectorEnd:
pusha
mov al, 0x0C
mov dx, 0x3F2
out dx, al
popa
;;;
;; [ID]
;; EnableA20
;;
;; [Description]
;; Enables the A20 gate.
;;;
EnableA20:
in al, 0x64
test al, 2
jnz EnableA20
mov al, 0xD1
out 0x64, al
;;;
;; [ID]
;; EnterProtectedMode
;;
;; [Description]
;; Enters protected mode.
;;;
EnterProtectedMode:
in al, 0x64
and ax, byte 2
jnz EnterProtectedMode
mov al, 0xDF
out 0x60, al
cli
mov eax, cr0
or eax, 1
mov cr0, eax
jmp 0x8 : ProtectedMode
[BITS 32]
;;;
;; [ID]
;; ProtectedMode
;;
;; [Description]
;; Goes to the kernel.
;;;
ProtectedMode:
jmp 0x8 : 0x10000
;; Write the boot signature
times 510-($-$$) db 0
dw 0xAA55
- Jeremiah
Edit: Updated source code.
