;Copyright (C) 2008 Pierre Baudemont
;
;    This file is part of bf.
;
;    bf is free software; you can redistribute it and/or modify
;    it under the terms of the GNU General Public License as published by
;    the Free Software Foundation; either version 2 of the License, or
;    (at your option) any later version.
;
;    bf is distributed in the hope that it will be useful,
;    but WITHOUT ANY WARRANTY; without even the implied warranty of
;    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;    GNU General Public License for more details.
;
;    You should have received a copy of the GNU General Public License
;    along with bf; if not, write to the Free Software
;    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA


;--screen backup--
; PARAM: none
; OUTPT: a0 
;
; The allocated memory used to save the screen content is pointed by a0
; If memory could not be allocated, a0 is null
; => TEST a0 after calling save_scr

; Used ROM CALLs :
;HeapAllocPtr equ $A2
;memcpy	equ $26A

	section ".data"
	include "OS.h"

	xdef save_scr

save_scr:
	; save of the used registries
	movem.l d3/a5,-(a7)
	
	; to use the ROM CALLs
	move.l $c8,a5
			
	; allocation sur le tas pour sauvegarder l'écran		
	move.l #3840,-(a7)	;screen: 240x128(=3840o),HeapAllocPtr 1st param
	move.l HeapAllocPtr*4(a5),a0
	jsr (a0)
	addq.l #4,a7	;clean the stack

	move.l a0,d3	;result of HeapAllocPtr in a0
	tst.l d3		;has to be tested (if null => error)
	beq nomem

	; copy the screen content in the allocated memory
	move.l #3840,-(a7)	;size (1st param)
	pea.l $4c00	;2nd param : @source (LCD mem)
	move.l d3,-(a7)	;3rd param : @dest
	move.l memcpy*4(a5),a0
	jsr (a0)
	lea 12(a7),a7	;clean the stack
	move.l d3,a0	;output in a0

nomem:
	movem.l (a7)+,d3/a5	;saved registries restoration
	
	rts