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add diskbios initializer (T.Yui)

.186

CODE	SEGMENT
		ASSUME CS:CODE,DS:nothing,ES:nothing,SS:nothing
		ORG 0000H

FIXCS		equ		2eh

START:			retf						; 00
				nop
				nop
				retf						; 03
				nop
				nop
				retf						; 06
				nop
				nop
				db	055h, 0aah, 002h		; 09
				jmp		short sxsi_init		; 0c
				nop
				retf						; 0f
				nop
				nop
				retf						; 12
				nop
				nop
				jmp		short sxsi_boot		; 15
				nop
				jmp		short sxsi_bios		; 18
				nop
				retf						; 1b
				nop
				nop
				retf						; 1e
				nop
				nop
				retf						; 21
				nop
				nop
				retf						; 24
				nop
				nop
				retf						; 27
				nop
				nop
				retf						; 2a
				nop
				nop
				retf						; 2d
				nop
				nop

sxsi_init:		push	ds
				push	bx
				xor		bx, bx
				mov		ds, bx
				mov		bx, cs
				mov		ds:[04b0h], bh
				mov		ds:[04b2h], bh
				mov		ds:[04b8h], bh
				mov		ds:[04bah], bh
				mov		bl, bh
				mov		bh, 0
				and		bl, 0fh
				mov		byte ptr ds:[bx+04d0h],45h
				pop		bx
				push	ax
				mov		ax, 0300h
				int		1bh
				mov		ax, 0320h
				int		1bh
				pop		ax
				pop		ds
				retf

sxsi_bios:		cld
				mov		dx, cs
				mov		ds, dx
				mov		cx, 8
				mov		si, offset sxsibiosstr
				mov		dx, 07efh
				rep outsb
				pop		ax
				pop		bx
				pop		cx
				pop		dx
				pop		bp
				pop		es
				pop		di
				pop		si
				pop		ds
				iret

sxsi_boot:		cmp		al, 0ah
				je		short sasi_boot
				cmp		al, 0bh
				je		short sasi_boot
				cmp		al, 0ch
				je		short scsi_boot
				retf

sasi_boot:		push	ds
				pusha
				xor		bx, bx
				mov		ds, bx
				sub		al, 9
				mov		dl, 0ffh
				test	ds:[055dh], al			; sasi
				je		short boot_exit
				dec		al
				mov		ah, 06h
				jmp		short boot_main

scsi_boot:		push	ds
				pusha
				xor		bx, bx
				mov		ds, bx
				mov		ax, 4620h

boot_main:		mov		cx, 1fc0h
				mov		es, cx
				mov		bp, bx
				mov		cx, bx
				mov		dx, bx
				mov		bh, 4
				int		1bh
				jc		boot_exit
				or		al, 80h
				mov		byte ptr ds:[0584h], al
				db		9ah					; call far
				dw		0
				dw		1fc0h
boot_exit:		popa
				pop		ds
				retf

sxsibiosstr		db		"sxsibios", 0

CODE	ENDS
	END START