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OS_Project/Part1/A4/05_basic_int/boot/bootsect.asm

52 lines
1.4 KiB
NASM
Executable File

; Identical to lesson 13's boot sector, but the %included files have new paths
[org 0x7c00]
KERNEL_OFFSET equ 0x1000 ; The same one we used when linking the kernel
mov [BOOT_DRIVE], dl ; Remember that the BIOS sets us the boot drive in 'dl' on boot
mov bp, 0x9000
mov sp, bp
mov bx, MSG_REAL_MODE
call print
call print_nl
call load_kernel ; read the kernel from disk
call switch_to_pm ; disable interrupts, load GDT, etc. Finally jumps to 'BEGIN_PM'
jmp $ ; Never executed
%include "boot/print.asm"
%include "boot/print_hex.asm"
%include "boot/disk.asm"
%include "boot/gdt.asm"
%include "boot/32bit_print.asm"
%include "boot/switch_pm.asm"
[bits 16]
load_kernel:
mov bx, MSG_LOAD_KERNEL
call print
call print_nl
mov bx, KERNEL_OFFSET ; Read from disk and store in 0x1000
mov dh, 16 ; Our future kernel will be larger, make this big
mov dl, [BOOT_DRIVE]
call disk_load
ret
[bits 32]
BEGIN_PM:
mov ebx, MSG_PROT_MODE
call print_string_pm
call KERNEL_OFFSET ; Give control to the kernel
jmp $ ; Stay here when the kernel returns control to us (if ever)
BOOT_DRIVE db 0 ; It is a good idea to store it in memory because 'dl' may get overwritten
MSG_REAL_MODE db "Started in 16-bit Real Mode", 0
MSG_PROT_MODE db "Landed in 32-bit Protected Mode", 0
MSG_LOAD_KERNEL db "Loading kernel into memory", 0
; padding
times 510 - ($-$$) db 0
dw 0xaa55