49 lines
595 B
NASM
Executable File
49 lines
595 B
NASM
Executable File
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; A20 Wraparound check as gotten from osdev.org
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check_a20_wraparound:
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pushf
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push ds
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push es
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push di
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push si
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xor ax, ax ; ax = 0
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mov es, ax
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not ax ; ax = 0xFFFF
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mov ds, ax
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mov di, 0x0500
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mov si, 0x0510
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mov al, byte [es:di]
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push ax
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mov al, byte [ds:si]
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push ax
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mov byte [es:di], 0x00
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mov byte [ds:si], 0xFF
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cmp byte [es:di], 0xFF
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pop ax
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mov byte [ds:si], al
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pop ax
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mov byte [es:di], al
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mov ax, 0
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je .exit
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mov ax, 1
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.exit:
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pop si
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pop di
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pop es
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pop ds
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popf
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ret
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