bits 16
org 0x7c00 ; Load origin for bootloader
CR: equ 0x0d
LF: equ 0x0a
BOOTLOADER_STACK_ADDRESS: equ 0xb000
%include "kernel-load-macros-inl.asm"
start:
jmp short main
nop
biosParameterBlock: times 87 db 0
main:
; Set up segments
.setup:
xor ax, ax
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov sp, BOOTLOADER_STACK_ADDRESS ; Stack
; Boot drive number
mov [bootDriveNumber], dl
; Clear screen and print welcome message
call clear_screen
mov si, welcomeMessage
call print_string
mov si, blankLine
call print_string
; Bootloader expansion
.expand_bootloader:
mov si, expandingMessage
call print_string
; Destination
mov ax, 0x07e0
mov es, ax
xor bx, bx
; Start sector and length
mov cl, 1
mov al, [bootloaderNumberOfExtraSectors]
; Read disk function
call read_disk
.after_expansion:
jmp expanded_main
; Here we would normally load the kernel from disk, but for simplicity, we'll just jump to it.
jmp 0x0000:0x8000 ; Jump to the kernel's entry point (assuming it's loaded at 0x8000)
%include "utility-inl.asm"
bootDriveNumber: db 0
welcomeMessage: db "[CrystalOS Bootloader]", CR, LF, 0
expandingMessage: db "Info: Expanding bootloader...", CR, LF, 0
diskErrorMessage: db "Error: Failed to read disk!", CR, LF, 0
rebootMessage: db "Press any key to reboot...", CR, LF, 0
end_of_first_sector:
times 504 - ($ - $$) db 0
bootloaderNumberOfExtraSectors: dw 0
kernelStartSector: dw 0
kernelNumberOfSectors: dw 0
dw 0xaa55 ; bios bootsector validy magic number
expanded_main:
mov si, expandedMessage
call print_string
call try_enable_a20 ; Try to enable A20 line for accessing memory above 1MB
call describe_gdt ; Describe the GDT so we can switch modes safely
call describe_idt ; Describe the IDT so protected mode has a valid IDT
call enable_real_mode ; Ensure we're in real mode before loading the kernel
call load_kernel ; Load the kernel from disk into memory
call enter_long_mode ; Set up paging and enter long mode to jump to the 64-bit kernel entry point
jmp $
%include "a20-utility-inl.asm"
%include "idt-utility-inl.asm"
%include "kernel-load-utility-inl.asm"
%include "long-mode-utility-inl.asm"
blankLine: db " ", CR, LF,0
enableProtectedModeMessage: db "Info: Enabling protected mode!", CR, LF, 0
enableRealModeMessage: db "Info: Enabled real mode!", CR, LF, 0
expandedMessage: db "Info: Bootloader expansion successful!", CR, LF, 0
bootloaderStackPointer: dw 0