More VGA tests

tests/pc/vga/L29-2.ASM

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+; Program to restore a mode 10h EGA graphics screen from
+; the file SNAPSHOT.SCR.
+;
+VGA_SEGMENT	equ	0a000h
+SC_INDEX	equ	3c4h		;Sequence Controller Index register
+MAP_MASK	equ	2		;Map Mask register index in SC
+DISPLAYED_SCREEN_SIZE equ (640/8)*350	;# of displayed bytes per plane in a
+					; hi-res graphics screen
+;
+stack	segment para stack 'STACK'
+	db	512 dup (?)
+stack	ends
+;
+Data	segment word 'DATA'
+Filename	db	'SNAPSHOT.SCR',0;name of file we're restoring from
+ErrMsg1		db	"*** Couldn't open SNAPSHOT.SCR ***",0dh,0ah,'$'
+ErrMsg2		db	'*** Error reading from SNAPSHOT.SCR ***',0dh,0ah,'$'
+WaitKeyMsg	db	0dh, 0ah, 'Done. Press any key to end...',0dh,0ah,'$'
+Handle		dw	?		;handle of file we're restoring from
+Plane		db	?		;plane being written
+Data	ends
+;
+Code	segment
+	assume	cs:Code, ds:Data
+Start	proc	near
+	mov	ax,Data
+	mov	ds,ax
+;
+; Go to hi-res graphics mode.
+;
+	mov	ax,10h			;AH = 0 means mode set, AL = 10h selects
+					; hi-res graphics mode
+	int	10h			;BIOS video interrupt
+;
+; Open SNAPSHOT.SCR.
+;
+	mov	ah,3dh			;DOS open file function
+	mov	dx,offset Filename
+	sub	al,al			;open for reading
+	int	21h
+	mov	[Handle],ax		;save the handle
+	jnc	RestoreTheScreen	;we're ready to restore if no error
+	mov	ah,9			;DOS print string function
+	mov	dx,offset ErrMsg1
+	int	21h			;notify of the error
+	jmp	short Done		;and done
+;
+; Loop through the 4 planes, making each writable in turn and
+; reading it from disk. Note that all 4 planes are writable at
+; A000:0000; the Map Mask register selects which planes are readable
+; at any one time. We only make one plane readable at a time.
+;
+RestoreTheScreen:
+	mov	[Plane],0		;start with plane 0
+RestoreLoop:
+	mov	dx,SC_INDEX
+	mov	al,MAP_MASK		;set SC Index to Map Mask register
+	out	dx,al
+	inc	dx
+	mov	cl,[Plane]		;get the # of the plane we want
+					; to restore
+	mov	al,1
+	shl	al,cl			;set the bit enabling writes to
+					; only the one desired plane
+	out	dx,al			;set to read from desired plane
+	mov	ah,3fh			;DOS read from file function
+	mov	bx,[Handle]
+	mov	cx,DISPLAYED_SCREEN_SIZE;# of bytes to read
+	sub	dx,dx			;start loading bytes at A000:0000
+	push	ds
+	mov	si,VGA_SEGMENT
+	mov	ds,si
+	int	21h			;read the displayed portion of this plane
+	pop	ds
+	jc	ReadError
+	cmp	ax,DISPLAYED_SCREEN_SIZE;did all bytes get read?
+	jz	RestoreLoopBottom
+ReadError:
+	mov	ah,9			;DOS print string function
+	mov	dx,offset ErrMsg2
+	int	21h			;notify about the error
+	jmp	short DoClose		;and done
+RestoreLoopBottom:
+	mov	al,[Plane]
+	inc	ax			;point to the next plane
+	mov	[Plane],al
+	cmp	al,3			;have we done all planes?
+	jbe	RestoreLoop		;no, so do the next plane
+;
+; Close SNAPSHOT.SCR.
+;
+DoClose:
+	mov	ah,3eh			;DOS close file function
+	mov	bx,[Handle]
+	int	21h
+;
+; Wait for a keypress.
+;
+	mov	ah,8			;DOS input without echo function
+	int	21h
+;
+; Restore text mode.
+;
+	mov	ax,3
+	int	10h
+;
+; Done.
+;
+Done:
+	mov	ah,4ch			;DOS terminate function
+	int	21h
+Start	endp
+Code	ends
+	end	Start