Hi guys, i'm new to the forums but i saw some other articles and the advice given is pretty solid, so i thought i'd come here in my desperate hour of need.

The object is to design part of a numbers game (it's for uni, i've been working for about 2 days solid on this and i'm still not getting it)

i've got the clearing of the screen, and the basic structure along with some array usage down, but my subroutines keep pointing back to the start of my program and not to where the subroutine was called from.

The idea is to have the program in a permenant loop that does the following:
1. moves numbers down 1 row on the screen
2. decides if it needs to indroduce another number based on a randomised (with limits)countdown timer and adds it into the array accordingly (the value and column position is also random)
3. when a number reaches the bottom (row position 20) it moves it back to position 1.

Here's the code i've got so far, i swear i've redone this like 4 or 5 times (the first attempt was so dismal i decided it best to just delete it and start afresh)

All the comments that say 'should be 54' and whatnot i've reduced to 2 for the purposes of stepping through the program.

Code:
numcols .equ 54
numrows .equ 20
	clra
	clrb
	ldx enemyval
	ldab #2; should be 54
resetenemies	ldaa #0
	staa enemyrow,x
	inx
	decb 
	bne resetenemies
	ldab #2; should be 54
resetenemyval ldaa #0
	staa enemyval,x
	inx
	decb 
	bne resetenemyval
	ldaa #2
	jsr randomnumber
	ldab randno; then multiply X 2
	staa countdown
engineloop jsr clearscreen; the game engine loop
	ldaa #54
	staa updatecount; loads 54 colums for the update subroutine
	jsr updateenemies
braland	ldaa #2
	jsr checknewenemy
	bne engineloop
clearscreen ldaa #1
clrscrn	ldx	 #screen	
		stx  pcaret	;reset caret
		ldaa #$41
		staa 0,x
		staa 54,x
		staa 2,x
		staa 3,x
csnlp1	clr 0,x		;[x] = 0
		inx			;x++
		cpx	$FEE8	;screen+1000
		bne	csnlp1	;loop
		bra	braland		;return
;-------------------------
updateenemies	ldx #enemyval
	ldaa enemyval,x
	staa a
	ldx #enemyrow
	ldab enemyrow,x
	stab y
	tsta
	bgt removing
removing ldx #screen
	ldaa #$30
	staa y,x ; writes blank to position of old number
	ldaa y
	inca ; adds 1 to the current row, giving the next row
	staa y
	ldaa #a ; loads the enemyvalue
	staa y,x; writes enemyvalue onto the correct screen position
	ldaa y
	cmpa #19
	bgt movenumberup ; if y > 19, move it to the top row again ready for the next redraw
	jmp endif
movenumberup ldaa #0
	staa enemyrow,x; sets the row position that was 20 back to 0 (the top row)
endif	inx
	ldaa updatecount; loads the counter which is 54
	deca
	staa updatecount
	tsta
	bne updateenemies; loops back to the top
	rts
;;;;;;;;;;;;;;;;;;;
		
checknewenemy	ldaa countdown
	deca
	staa countdown
	tsta
	bne addnewenemy; if countdown is 0, then go to the addnewenemies function
	rts
addnewenemy jsr randomnumber
	ldaa randno; after this, divide random by 4
	staa i
	staa countdown; divide by 4 here
	ldaa i
	staa enemyval,x; stores the enemyvalue i at position i in enemyval
	staa enemyrow,x; stores the new enemy position at row 1, position i in enemyrow
	ldaa randno; then make randno between 1-54
	rts
randomnumber ldaa #7
	staa randno
Code:
a .byte 0; current value for redrawing enemyval
y .byte 0; current value for redrawing enemyrow	
i .byte 0; variable for random numbers put into enemyrow and enemyval
scrhigh .byte $FB	; high byte screen address 
scrlow 	.byte $00	; low byte screen address 
rowcount .byte 20	; number of rows to count
countdown .byte 5 ;time till next enemy
enemyval .byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ;array of enemy values
enemyrow .byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ;array holding enemy row location
randno .byte 0
count .byte 0
randcount .byte 0
updatecount .byte 0
screen	.equ $FB00
pcaret	.stw $FB00
The main problem i have is the subroutines not going to where they should be,

I'm not here for a free homework solution, i genuinely want to learn this stuff to improve my (currently underdeveloped) skills as a programmer, i've programmed before in c++ java and also zscript (pseudocode for an online mud) but assembly is totally foreign to me. Any help would be greatly appreciated, I'll be checking in over the next day or so.

This is all being done on an emulator with a fixed size of 54X20 chars. Apologies for the messiness of the code, it's still a jumble while i work out what i'm doing.

Thanks in advance for any help.

Last edited by shabbir; 19May2007 at 22:07.. Reason: Code block - http://www.go4expert.com/forums/misc.php?do=bbcode#code