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|
; Data for the Loader.
%define LoaderAddress 0000h
%define LoaderSegment 9000h
; Return the data at the address given by the offset "x".
%define LA(x) LoaderAddress + x
; Start
[BITS 16]
[ORG 0000h]
jmp Start
StartMsg db 'Starting up...',0dh,0ah,00h
NewLine db 0dh,0ah,00h
PrintString:
pusha
PrintStringLoop:
lodsb
or al,al
je PrintStringEnd
mov ah,0eh
mov bx,0007h
int 10h
jmp PrintStringLoop
PrintStringEnd:
popa
ret
PrintChar:
push ax
PrintCharMSB:
shr al,4
cmp al,0Ah
jge PrintCharMSBAlpha
PrintCharMSBNum:
add al,30h
jmp PrintCharMSBEnd
PrintCharMSBAlpha:
add al,37h
PrintCharMSBEnd:
mov ah,0Eh
mov bx,0007h
int 10h
PrintCharLSB:
pop ax
and al,0fh
cmp al,0Ah
jge PrintCharLSBAlpha
PrintCharLSBNum:
add al,30h
jmp PrintCharLSBEnd
PrintCharLSBAlpha:
add al,37h
PrintCharLSBEnd:
mov ah,0Eh
mov bx,0007h
int 10h
ret
PrintWord:
push ax
mov al,ah
call PrintChar
pop ax
call PrintChar
ret
PrintDWord:
push eax
mov si,LA(NewLine)
call PrintString
push eax
shr eax,16
call PrintWord
pop eax
call PrintWord
pop eax
ret
; enables the a20 gate
; the usual keyboard-enable-a20-gate-stuff
enable_a20:
call _a20_loop
jnz _enable_a20_done
mov al,0xd1
out 0x64,al
call _a20_loop
jnz _enable_a20_done
mov al,0xdf
out 0x60,al
_a20_loop:
mov ecx,0x20000
_loop2:
jmp short _c
_c:
in al,0x64
test al,0x2
loopne _loop2
_enable_a20_done:
ret
Start:
; Initialize the segment register for datas.
mov ax,LoaderSegment
mov ds,ax
mov es,ax
mov ss,ax
xor ax,ax
mov sp,ax
; Display the welcome note
mov si,LA(StartMsg)
call PrintString
cli
mov ax,LoaderSegment
mov ds,ax
call enable_a20 ; enable a20 gate
lgdt [ss:gdt]
smsw ax
or al,1
lmsw ax
db 0eah ; opcode for far jump (to set CS correctly)
dw clear_pipe,08h
[BITS 32]
clear_pipe:
; mov ax,10h
; mov ds,ax
; mov ss,ax
; mov esp, 080000h
; mov byte [ds:0B8000h], 'P'
; mov byte [ds:0B8001h], 1Bh
; Infinit loop
InfLoop:
jmp InfLoop
gdt:
; the first entry serves 2 purposes: as the GDT header and as the first descriptor
; note that the first descriptor (descriptor 0) is always a NULL-descriptor
db 0xFF ; full size of GDT used
db 0xff ; which means 8192 descriptors * 8 bytes = 2^16 bytes
dw gdt ; address of GDT (dword)
dd 0
; descriptor 1 - code:
dd 0x0000ffff ; base - limit: 0 - 0xfffff * 4K
dd 0x008f9a00 ; type: 16 bit, exec-only conforming, <present>, privilege 0
; descriptor 2 - data/stack:
dd 0x0000ffff ; base - limit: 0 - 0xfffff * 4K
dd 0x008f9200 ; type: 16 bit, data read/write, <present>, privilege 0 |
Mode Protégé et Bochs 2.1.1
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