A82: VAT problems (help me)

To: assembly-82@lists.ticalc.org
Subject: A82: VAT problems (help me)
From: ilya winham <ilyamojo@geocities.com>
Date: Sun, 08 Mar 1998 19:06:34 -0600
Reply-To: assembly-82@lists.ticalc.org

Ok, here is the story. I have ported Joe W.'s Breakout game to the 
TI-82. It works perfectly except for the EXTERNAL LEVEL selector 
routine. You know, searches the vat for stuff and loads the level, kind 
of like penguins. Well, I can't get it to work. After I play a game, 
then quit, the next button I press crashes the calc, your typical VAT 
crash. If you can help me fix it, then porting this and Diamonds v1.5 
will be a snap. Both of those games use the same external level routine. 
And I bet more games made by Joe will, so I would love to get this 
ported!

Here is the code below, with comments:

;close to the very beginning of the game.
prmenu:	
	ld		hl,levels
	ld		(file),hl
	ld		hl,(VAT_START) ;THIS IS THE PROBLEM!!
                    ;in the 83 version this line is ld hl,(fat)
                    ;yes folks, (fat), not a typo.
                    ;I need to find the appropiate substitute for 'fat'
	ld		(curwrld),hl

.......
<snip>
;Deleted more code that IN NO WAY has any effect on the level selection.
........

;Start of level select routine, I didn't have to change anything when
;I ported it. Please take a look and see what my problem is.
;---------- Change World ----------
; the level data is set up as follows in the level sets:
; -"Breakout v1.0 by Joe W" (22 bytes)
; -number of byte to start of level
; -level name
; -$00
; -number of bytes in the level name (including the zero)
; -high score (2 bytes)
; -number of levels
; -start of levels (33 bytes each)

chgwrld:
	xor		a
	ld		(startlev),a
	ld		hl,(curwrld)    ;loads that (fat) addr here.
chgwlp:
	ld		(temp),hl	; in case a program is found
	ld		a,(hl)		; 	but no good.
	and		%00011111
	cp		0x06
	jr		z,cwchck
	cp		0x05
	jr		z,nogood2	; a program, but not protected
	cp		0x01		; (using an unprotected program
	jr		z,list		; could be dangerous)
	cp		0x0D
	jr		z,list
	jp		prmenu

cwchck:
	dec		hl		; move to ptr (skip var type)
	push		hl
	ld		b,(hl)
	dec		hl
	ld		c,(hl)
	ld		h,c
	ld		l,b
	inc		hl		; skip file length (2 bytes, but see below)
	ld		de,name-1
	ld		b,22		; "Breakout v1.0 by Joe W"
ckprog:
	inc		hl		; file length is 2 bytes so we save one byte!
	inc		de		; skip the string length (we know it already!)
	ld		c,(hl)
	ld		a,(de)
	cp		c
	jr		nz,nogood
	djnz		ckprog
	inc		hl
	ld		c,(hl)		; 24th byte of file is added to ptr to get
	ld		b,0x00		; the start of level data
	add		hl,bc
	inc		hl
	ld		(file),hl
	pop		hl
	dec		hl
	dec		hl
	ld		b,(hl)		; length of name
	inc		b		; move to next program as well in case the
skprog:
	dec		hl		; user doen't want this world
	djnz		skprog
	ld		(curwrld),hl
	jp		menu
nogood2:
	; push something so we can safely pop!
	push		hl	; anything will work but.....
nogood:
	pop		hl	; who cares (not needed)
	ld		hl,(temp)
list:
	dec		hl		; lists enter here to be skipped
	dec		hl
	dec		hl
	ld		b,(hl)
nogdlp:
	dec		hl		; not the fastest, but is the smallest!
	djnz		nogdlp
	dec		hl		; next item
	jp		chgwlp


There is all the suff. All the variables you see are stored in TEXT_MEM 
(in case your wondering) Please, Crash_Man, Dines, Thomas, Adamman, Evil 
Same, anyone who has any knowledge of the VAT please tell me why this 
doesn't work. Thanks a lot. If you need more info please email me. I 
will release Breakout, even if I can never get this level selection to 
work, all the levels then will just have to be in the game.
~Ilya