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[org 0x7c00] ; bootsector
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KERNEL_OFFSET equ 0x1000
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; Save the boot drive index
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mov [BOOT_DRIVE], dl
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; Move the stack pointer somewhere safe
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mov bp, 0x9000 ; move it to 0x9000
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mov sp, bp
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; Load kernel into memory
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call load_kernel
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; Switching to PM
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call pm_preinit
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jmp $ ; inf loop
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%include "bootloader/equ/ascii.asm"
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%include "bootloader/equ/bios.asm"
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; BIOS SRs
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%include "bootloader/bios/convert.asm"
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%include "bootloader/bios/print.asm"
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%include "bootloader/bios/disk.asm"
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%include "bootloader/bios/memory.asm"
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; Protected Mode SRs
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%include "bootloader/equ/vga.asm"
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%include "bootloader/pm/vga/print.asm"
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; GDT & switching to PM
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%include "bootloader/pm/gdt.asm" ; GDT defined here
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; Switching to PM
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[bits 16]
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pm_preinit:
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call mmap_e820 ; Map the physical memory
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cli ; Switch interupts
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lgdt [gdt_descriptor] ; Tell the CPU about the GDT
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mov eax, cr0 ; Set first bit of the CR0 register
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or eax, 0x1 ; to 1
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mov cr0, eax ; Update the control register
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; Initialize PM
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jmp GDT_CODE_SEG:pm_init
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[bits 32]
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; Init registers & stack when in PM
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pm_init:
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mov ax, GDT_DATA_SEG ; Point the segment registers to GDT_DATA_SEG
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; Segment registers
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mov ds, ax
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mov ss, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov ebp, 0x900000 ; Update the stack pointer
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mov esp, ebp
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call BEGIN_PM
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BEGIN_PM:
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; Call the kernel
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call KERNEL_OFFSET
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jmp $
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[bits 16]
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load_kernel:
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mov bx, KERNEL_OFFSET ; Load kernel at the kernel offset
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mov dh, 10 ; Read sectors
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mov dl, [BOOT_DRIVE] ; Drive index
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call disk_read ; Load the kernel
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ret
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BOOT_DRIVE: db 0
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; Bootsector
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times 510-($-$$) db 0
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dw 0xaa55 ; magic BIOS numbers
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