add directory study

study/sabre/os/files/ProtectedMode/voodoo.asm

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+;VooDoo init!
+
+;This will setup the system into a special mode.  This code will crash if
+; EMM386, Windoze and other PMODE software is loaded.  You must also
+; enable the a20 thru XMS if himem.sys is loaded.
+
+; once complete the following will happen in real mode.
+;  - mov ax,[ebx] is legal now
+;  - code will still have a 64K limit range (IP still used not EIP)
+
+;This is presented to learn from - I really suggest not using this technique
+;as it's old and crappy.  Gamez to use this : Ultima 7. This was the day
+;I hated the PC, but things got better as DPMI and VCPI were introduced
+
+.386p
+
+vd_desc struc
+lmt   dw  0
+bsl   dw  0
+bsm   db  0
+typel db  0
+typeh db  0
+bsh   db  0
+vd_desc ENDS
+
+.code
+	cli       ;No ints
+	xor eax,eax
+	mov ax,cs
+	mov ds,ax
+	shl eax,4
+	mov ds:[oldcs.bsl],ax
+	mov ds:[oldds.bsl],ax
+	shr eax,16
+	mov ds:[oldcs.bsm],al
+	mov ds:[oldds.bsm],al
+
+	mov eax,code32
+	shl eax,4
+	add dword ptr ds:gdt32[2],eax
+	add dword ptr ds:idt32[2],eax
+
+	mov ds:[scode32.bsl],ax
+	mov ds:[sdata32.bsl],ax
+	shr eax,16
+	mov ds:[scode32.bsm],al
+	mov ds:[sdata32.bsm],al
+	mov ds:[scode32.bsh],ah
+	mov ds:[sdata32.bsh],ah   ;All mem ptr are calculated
+
+	lgdt  fword ptr ds:gdt32    ;Load the GDT
+
+	mov eax,cr0
+	or  al,1
+	mov cr0,eax       ;Hop to Prot. mode
+	db  0eah
+	dw  main32,8      ;far jmp 08:main
+
+realmode16:
+	lidt  fword ptr ds:defidt   ;load the IDT
+
+	mov eax,cr0
+	and al,0feh
+	mov cr0,eax       ;Kill the P-mode bit
+
+	db  0eah
+	dw  realmode,Code_start   ;Another far jmp
+
+
+realmode:
+	mov ebx,10000h      ;
+	mov ax,[ebx]      ;Oh my god this shit works !!
+;Jmp here to your own code !!! VERY IMPORTANT !
+	mov ax,4c00h
+	int 21h
+
+defidt    dw  3ffh,0,0    ;The normal IDT
+	ENDS
+
+code32    segment para public use32
+	assume  cs:code32,ds:code32
+
+
+main32:
+	lidt  fword ptr cs:idt32    ;The PROT MODE IDT
+	mov ax,10h
+	mov ds,ax
+	mov es,ax
+	mov fs,ax
+	mov ss,ax       ;Just loading some segs
+	mov ax,30h
+	mov gs,ax       ;This is the videoseg
+	xor esp,esp
+	mov esp,offset stackend   ;What could that be ???
+	call  enablea20
+; jmp gone        ;Testing exc6
+exit:
+	mov ax,20h
+	mov ds,ax
+	mov es,ax
+	mov fs,ax
+	mov gs,ax
+	mov ss,ax       ;Loading the segs back
+	db  0eah
+	dw  realmode16,0,18h    ;Far jmp 18:realmode16
+
+gone:
+		db  10 dup(0feh)
+
+idt32   dw  187h,idt,0
+gdt32   dw  224,dummy,0
+dummy   vd_desc  <>
+scode32   vd_desc  <0ffffh,0,0,10011010b,11001111b,0>
+sdata32   vd_desc  <0ffffh,0,0,10010010b,11001111b,0>
+oldcs   vd_desc  <0ffffh,0,0,10011010b,10000000b,0>
+oldds   vd_desc  <0ffffh,0,0,10010010b,10000000b,0>
+bios    vd_desc  <0ffffh,0,0,10010010b,11001111b,0>
+vseg    vd_desc  <0ffffh,8000h,0bh,10010010b,11001111b,0>
+
+idt   dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+		dw  inter,8,8e00h,0
+
+inter:
+	jmp exit
+
+
+enablea20:
+	call  enablea201
+	jnz short enablea20done
+	mov al,0d1h
+	out 64h,al
+	call  enablea201
+	jnz short enablea20done
+	mov al,0dfh
+	out 60h,al
+enablea201:
+	mov ecx,20000h
+enablea201l:
+	jmp short $+2
+	in  al,64h
+	test  al,2
+	loopnz  enablea201l
+enablea20done:
+	ret
+pile    db  400 dup(?)
+stackend:
+	ENDS
+	END