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libsrc/dbg/dbgisram.s

@@ -0,0 +1,55 @@
+;
+; Ullrich von Bassewitz, 10.08.1998
+;
+; int DbgIsRAM (unsigned Addr);
+;
+
+      	.export		_DbgIsRAM
+	.import		popax, return0, return1
+	.importzp	ptr1
+
+_DbgIsRAM:
+	sta	ptr1		; Store the address
+	stx	ptr1+1
+
+	ldy	#0
+	php	       		; Save I flag
+	sei	       		; Disable interrupts
+
+	lda	(ptr1),y	; Get old value
+	pha	       		; ...and save it
+
+	ldx	#3
+L1:   	lda	TestVal,x
+   	jsr	CheckCell
+   	bne	L2
+   	dex
+   	bpl	L1
+
+; This seems to be RAM
+
+	pla
+	sta	(ptr1),y	; Restore old value
+	plp	       		; Restore old I flag
+	jmp	return1
+
+; No RAM at this address
+
+L2:	pla
+	sta	(ptr1),y	; Restore old value
+	plp	       		; Restore old I flag
+	jmp	return0
+
+; Check one memory cell
+
+CheckCell:
+	sta	(ptr1),y
+	cmp	(ptr1),y	; Could we write it?
+	rts
+
+
+.rodata
+TestVal:
+       	.byte	$55, $AA, $33, $CC
+
+