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68 lines
2.0 KiB
68 lines
2.0 KiB
[BITS 16] ; We need 16-bit intructions for Real mode
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[ORG 0x7C00] ; The BIOS loads the boot sector into memory location 0x7C00
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cli ; Disable interrupts, we want to be alone
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xor ax, ax
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mov ds, ax ; Set DS-register to 0 - used by lgdt
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lgdt [gdt_desc] ; Load the GDT descriptor
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mov eax, cr0 ; Copy the contents of CR0 into EAX
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or eax, 1 ; Set bit 0
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mov cr0, eax ; Copy the contents of EAX into CR0
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jmp 08h:clear_pipe ; Jump to code segment, offset clear_pipe
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[BITS 32] ; We now need 32-bit instructions
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clear_pipe:
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mov ax, 10h ; Save data segment identifyer
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mov ds, ax ; Move a valid data segment into the data segment register
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mov ss, ax ; Move a valid data segment into the stack segment register
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mov esp, 090000h ; Move the stack pointer to 090000h
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mov byte [ds:0B8000h], 'P' ; Move the ASCII-code of 'P' into first video memory
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mov byte [ds:0B8001h], 1Bh ; Assign a color code
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hang:
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jmp hang ; Loop, self-jump
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gdt: ; Address for the GDT
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gdt_null: ; Null Segment
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dd 0
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dd 0
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gdt_code: ; Code segment, read/execute, nonconforming
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dw 0FFFFh
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dw 0
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db 0
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db 10011010b
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db 11001111b
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db 0
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gdt_data: ; Data segment, read/write, expand down
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dw 0FFFFh
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dw 0
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db 0
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db 10010010b
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db 11001111b
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db 0
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gdt_end: ; Used to calculate the size of the GDT
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gdt_desc: ; The GDT descriptor
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dw gdt_end - gdt - 1 ; Limit (size)
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dd gdt ; Address of the GDT
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times 510-($-$$) db 0 ; Fill up the file with zeros
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dw 0AA55h ; Boot sector identifyer
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