171 lines
3.4 KiB
PHP
171 lines
3.4 KiB
PHP
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; copy/pasted from https://wiki.osdev.org/A20_Line
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; .... sorry I was lazy :x
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a20_get_state:
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pushf
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push si
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push di
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push ds
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push es
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cli
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xor ax, ax
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mov ds, ax
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mov si, 0x500
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not ax
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mov es, ax
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mov di, 0x0510
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mov al, [ds:si] ; save old values
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mov byte [.BufferBelowMB], al
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mov al, [es:di]
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mov byte [.BufferOverMB], al
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mov ah, 1 ; check byte [0x00100500] == byte [0x0500]
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mov byte [ds:si], 0
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mov byte [es:di], 1
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mov al, [ds:si]
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cmp al, [es:di]
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jne .exit
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dec ah
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.exit:
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mov al, [.BufferBelowMB]
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mov [ds:si], al
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mov al, [.BufferOverMB]
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mov [es:di], al
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shr ax, 8
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sti
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pop es
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pop ds
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pop di
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pop si
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popf
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ret
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.BufferBelowMB: db 0
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.BufferOverMB db 0
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a20_query_support:
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push bx
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clc
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mov ax, 0x2403
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int 0x15
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jc .error
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test ah, ah
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jnz .error
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mov ax, bx
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pop bx
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ret
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.error:
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stc
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pop bx
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ret
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a20_enable_keyboard_controller:
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cli
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call .wait_io1
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mov al, 0xad
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out 0x64, al
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call .wait_io1
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mov al, 0xd0
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out 0x64, al
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call .wait_io2
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in al, 0x60
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push eax
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call .wait_io1
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mov al, 0xd1
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out 0x64, al
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call .wait_io1
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pop eax
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or al, 2
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out 0x60, al
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call .wait_io1
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mov al, 0xae
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out 0x64, al
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call .wait_io1
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sti
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ret
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.wait_io1:
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in al, 0x64
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test al, 2
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jnz .wait_io1
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ret
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.wait_io2:
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in al, 0x64
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test al, 1
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jz .wait_io2
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ret
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; out:
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; cf - set on error
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a20_enable:
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clc ; clear cf
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pusha
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mov bh, 0 ; clear bh
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call a20_get_state
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jc .fast_gate
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test ax, ax
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jnz .done
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call a20_query_support
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mov bl, al
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test bl, 1 ; enable A20 using keyboard controller
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jnz .keybord_controller
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test bl, 2 ; enable A20 using fast A20 gate
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jnz .fast_gate
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.bios_int:
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mov ax, 0x2401
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int 0x15
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jc .fast_gate
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test ah, ah
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jnz .failed
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call a20_get_state
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test ax, ax
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jnz .done
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.fast_gate:
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in al, 0x92
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test al, 2
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jnz .done
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or al, 2
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and al, 0xfe
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out 0x92, al
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call a20_get_state
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test ax, ax
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jnz .done
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test bh, bh ; test if there was an attempt using the keyboard controller
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jnz .failed
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.keybord_controller:
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call a20_enable_keyboard_controller
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call a20_get_state
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test ax, ax
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jnz .done
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mov bh, 1 ; flag enable attempt with keyboard controller
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test bl, 2
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jnz .fast_gate
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jmp .failed
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.failed:
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stc
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.done:
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popa
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ret
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