Use a destructor instead of atexit

git-svn-id: svn://svn.cc65.org/cc65/trunk@515 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/cbm610/break.s

@@ -8,7 +8,7 @@
        	.export	      	_set_brk, _reset_brk
        	.export	       	_brk_a, _brk_x, _brk_y, _brk_sr, _brk_pc
 	.import	      	_atexit
-		      
+
 	.include	"zeropage.inc"
 	.include   	"page3.inc"
 
@@ -45,10 +45,6 @@ uservec:    	jmp	$FFFF		; Patched at runtime
  	lda 	BRKVec+1
  	sta	oldvec+1	; Save the old vector
 
-	lda	#<_reset_brk
-	ldx	#>_reset_brk
-	jsr	_atexit		; Install an exit handler
-
 L1:	lda	#<brk_handler	; Set the break vector to our routine
 	sta	BRKVec
 	lda	#>brk_handler
@@ -61,11 +57,13 @@ L1:	lda	#<brk_handler	; Set the break vector to our routine
 ; Reset the break vector
 .proc	_reset_brk
 
-	lda	oldvec
-	sta	BRKVec
-	lda	oldvec+1
-	sta	BRKVec+1
-	rts
+	lda  	oldvec
+	bne  	@L1
+	ldx  	oldvec
+	beq  	@L9		; Jump if vector not installed
+@L1:	sta    	BRKVec
+	stx  	BRKVec+1
+@L9:	rts
 
 .endproc