126 lines
2.4 KiB
NASM
126 lines
2.4 KiB
NASM
ORG 0x7C00
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USE16
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jmp short _start
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nop
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; Boot Record
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OEM_identifier db 'STUPID '
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bytes_per_sector dw 512
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sectors_per_cluster db 1
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reserved_sectors dw 1
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FAT_count db 2
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root_dir_entries dw 224
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total_sectors dw 2880
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media_desc_type db 0xF0
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sectors_per_FAT dw 9
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sectors_per_track dw 18
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heads_per_cylinder dw 2
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hidden_sectors dd 0
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large_sector_count dd 0
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; Extended Boot Record
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drive_number db 0x0
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reserved db 0x0
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signature db 0x29 ; 0x28 or 0x29
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volume_id dd 0xB00B135 ; hope mine will grow :'(
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volume_label db 'Stupid Boot'
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system_id db 'FAT12 '
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_start:
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cli
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cld
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jmp 0x0:.canonicalize_cs
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.canonicalize_cs:
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xor ax, ax
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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 sp, 0x7c00
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; clear screen
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mov al, 0x03
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mov ah, 0
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int 0x10
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mov si, msg_hello
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call bios_print
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; reset floppy disk
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@@:
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xor ah, ah
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int 0x13
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jc @b
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mov si, msg_load_stage
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call bios_print
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; read sector into ES:BX (0100:0000)
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mov ax, 0x100 ; 100 segment
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mov es, ax ; 0100:0000 (0000:1000)
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xor bx, bx
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mov ah, 0x2 ; read
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mov al, 0x1 ; one sector
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mov ch, 0x0 ; cylinder 0
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mov cl, 0x2 ; second sector
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mov dh, 0x0 ; head 0
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int 0x13
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jc .error
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jmp 0x0:0x1000
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.error:
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mov si, msg_error_sector
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call bios_print
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hlt
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jmp $
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bios_print:
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lodsb
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or al, al
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jz @f
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mov ah, 0x0E
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int 0x10
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jmp bios_print
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@@:
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ret
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msg_hello db "StupidOS Bootloader", 0x0D, 0x0A, 0
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msg_load_stage db "Loading next stage", 0x0D, 0x0A, 0
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msg_error_sector db "ERROR: Can't read sector", 0x0D, 0x0A, 0
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rb 0x7C00+512-2-$
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db 0x55, 0xAA
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; ---------- stage 1 --------------
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ORG 0x1000
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stage2:
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push cs
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pop ds
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mov si, msg_stage2
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call bios_print
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call a20_enable
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jc .error_a20
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xchg bx, bx
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jmp .hang
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.error_a20:
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mov si, msg_error_a20
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call bios_print
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.hang:
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hlt
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jmp $
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INCLUDE 'a20.inc'
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msg_stage2 db "StupidOS Bootloader (Stage 2)", 0x0D, 0x0A, 0
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msg_error_a20 db "ERROR: can't enable a20 line", 0x0D, 0x0A, 0
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