Help ! can anyone see the mistake ?

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Help ! can anyone see the mistake ?
by turboninja on 2013-09-11 (#117930)
Hello everybody,

I am new here, I looked into this forum and tutos regarding my problem but I could not find anything similar. So here I am.

I am developing a Tron game (the one with the motorcycles seen from above, I always dreamt on playing this game on an actual NES, don't know why) with NESASM (it does not seem to be the best assembler but it has so many tutos and sources). I am now trying to constrain the user to move along a grid (grid defined as the border of the tiles composing the screen). So what I did is quite simple : save the input in the keypad and load it into the "actual" variables (the speed of the motorbike on every axis) every 8 time the program goes through the main loop. Here is the thing I am doing.

Code:
infinite:  ; a label to start our infinite loop
    waitblank:
        bit $2002  ; these 3 lines wait for VBlank, this loop will actually miss VBlank
        bpl waitblank ; alot, in a later Day, I'll give a better way.

    jsr disp_Sprites_DMA
    jsr move_charac1   
    jsr move_charac2    ; this is optional
    jsr strobe_keypad1
    jsr strobe_keypad2 ; this is optional
    jsr update_keypad1   
   
    ldx loop_count
    inx
    stx loop_count
    txa
    cmp #8
    beq modulo
    jmp infinite

modulo:
    jsr update_speed1
    ldx #0
    stx loop_count
    lda #0;
    jmp infinite


However, with this cmp line, the motorbike has a strange diagonal direction when I press the left and right keys (that should not happen at all) but works perfectly fine with up and down keys (which confuses me a lot). And without the cmp (just jumping to "modulo") everything works perfectly fine as well.

So, here is my question, is it possible, by any chance, that I am overwriting some of my speed variables doing something that I do not suspect affects the "speed" variables ? (I am not very familiar with assembler, I don't know the kind of bugs it can produce)

If somebody wants to try the whole code, here it is, with the files needed. Any help would be more than welcome :D

Code:
    ;;--- CODE START ---;;
    .inesprg 1
    .inesmap 0
    .inesmir 1
    .ineschr 1

    .bank 1
    .org $FFFA
    .dw 0        ; no VBlank
    .dw Start    ; address to execute on reset
    .dw 0        ; no whatever
    .bank 0
    .org $0000


;; What follows will be useful to make sure the cycle follows the grid


    .org $0300 ; OAM Copy location $0300
;; THE FIRST TWO SPRITES REPRESENT THE MOTORBIKES
Sprite1_Y:     .db  0   ; sprite #1's Y value
Sprite1_T:     .db  0   ; sprite #1's Tile Number
Sprite1_S:     .db  0   ; sprite #1's special byte
Sprite1_X:     .db  0   ; sprite #1's X value
Sprite2_Y:     .db  0   ; same thing, same order for sprite #2
Sprite2_T:     .db  0   ; note that I numbered 1 2 ...
Sprite2_S:     .db  0   ; some people may actually prefer starting
Sprite2_X:     .db  0   ; the count at 0, but it doesn't really matter.
;; THESE SPRITES WILL REPRESENT THE SCORE OF EACH PLAYER
;; BETWEEN 0 AND 9
Sprite3_Y:     .db  0   ; sprite #1's Y value
Sprite3_T:     .db  0   ; sprite #1's Tile Number
Sprite3_S:     .db  0   ; sprite #1's special byte
Sprite3_X:     .db  0   ; sprite #1's X value
Sprite4_Y:     .db  0   ; same thing, same order for sprite #2
Sprite4_T:     .db  0   ; note that I numbered 1 2 ...
Sprite4_S:     .db  0   ; some people may actually prefer starting
Sprite4_X:     .db  0   ; the count at 0, but it doesn't really matter.

    .org $0500
;; This part allows variables declarations (or definition)
speed1_Up:   .db 0
speed1_Left:   .db 0
speed1_Down:   .db 0
speed1_Right:   .db 0
speed2_Up:   .db 0
speed2_Down:   .db 0
speed2_Left:   .db 0
speed2_Right:   .db 0

speed1_Up_To_Be:   .db 0
speed1_Down_To_Be:   .db 0
speed1_Left_To_Be:   .db 0
speed1_Right_To_Be:   .db 0
speed2_Up_To_Be:   .db 0
speed2_Down_To_Be:   .db 0
speed2_Left_To_Be:   .db 0
speed2_Right_To_Be:   .db 0
loop_count: .db 0


    .org $8000  ; code starts at $8000 or $C000
Start:
    lda #1;
    sta speed1_Up_To_Be;
    sta speed2_Up;
    sta Sprite2_T
    sta Sprite1_S;
    lda #0;
    sta Sprite2_S;
    sta Sprite1_T;
    sta speed1_Down;   
    sta speed1_Right;   
    sta speed1_Left;
    sta speed2_Down;   
    sta speed2_Right;   
    sta speed2_Left;
    ;lda #0
   
    lda #80;
    sta Sprite1_X;
    sta Sprite2_X
   
    lda #80
    sta Sprite1_Y
    lda #120
    sta Sprite2_Y

    lda #%00001000  ;
    sta $2000       ;
    lda #%00011110  ; Our typical PPU Setup code.
    sta $2001       ;

    ldx #$00    ; clear X            ;; start of palette loading code
    lda #$3F    ; have $2006 tell
    sta $2006   ; $2007 to start
    lda #$00    ; at $3F00 (palette).
    sta $2006
   
loadpal:                ; this is a freaky loop
    lda palette, x  ; that gives 32 numbers
    sta $2007       ; to $2007, ending when
    inx             ; X is 32, meaning we
    cpx #32         ; are done.
    bne loadpal     ; if X isn't =32, goto "loadpal:" line.
;; end of palette loading code
 ;;--- CODE START ---;;

   
    jsr dispBackground  ; calls the routine to display the background


;; THE MAIN LOOP

infinite:  ; a label to start our infinite loop
    waitblank:
        bit $2002  ; these 3 lines wait for VBlank, this loop will actually miss VBlank
        bpl waitblank ; alot, in a later Day, I'll give a better way.

    jsr disp_Sprites_DMA
    jsr move_charac1   
    jsr move_charac2   
    jsr strobe_keypad1
    jsr strobe_keypad2
    jsr update_keypad1   
   
    ldx loop_count
    inx
    stx loop_count
    txa
    cmp #8
    beq modulo
    jmp infinite

modulo:
    jsr update_speed1
    ldx #0
    stx loop_count
    lda #0;
    jmp infinite

 update_keypad1:
    lda $4016  ; load Abutton Status ; note that whatever we ain't interested   
    lda $4016  ; load Bbutton Status ; in we just load so it'll go to the next one.
    lda $4016  ; load Select button status
    lda $4016  ; load Start button status
    lda $4016  ; load UP button status
    and #1      ; AND status with #1
    bne UPKEYdown  ; for some reason (not gonna reveal yet), need to use NotEquals
    ;with ANDs. So it'll jump (branch) if key was down.
    lda $4016  ; load DOWN button status
    and #1     ; AND status with #1
    bne DOWNKEYdown
    lda $4016  ; load LEFT button status
    and #1     ; AND status with #1
    bne LEFTKEYdown
    lda $4016  ; load RIGHT button status
    and #1     ; AND status with #1
    bne RIGHTKEYdown
    ;ldy $0
    jmp NOTHINGdown2  ; if nothing was down, we just jump (no check for conditions)
    ; down past the rest of everything.
    UPKEYdown:
        lda speed1_Down;_To_Be
        and #1
        bne NOTHINGdown2
        lda speed1_Down_To_Be
        and #1
        bne NOTHINGdown2
        lda #1
        sta speed1_Up_To_Be
        lda #0
        sta speed1_Left_To_Be
        sta speed1_Down_To_Be
        sta speed1_Right_To_Be
        sta Sprite1_T
        jmp NOTHINGdown2  ; jump over the rest of the handling code
    DOWNKEYdown:
        lda speed1_Up;_To_Be
        and #1
        bne NOTHINGdown2
        lda speed1_Up_To_Be
        and #1
        bne NOTHINGdown2
        lda #1
        sta speed1_Down_To_Be
        lda #2
        sta Sprite1_T
        lda #0
        sta speed1_Left_To_Be
        sta speed1_Right_To_Be
        sta speed1_Up_To_Be
        jmp NOTHINGdown ; jump over the rest of handling code.
    NOTHINGdown2:
        jmp NOTHINGdown
    LEFTKEYdown:
        lda speed1_Right;_To_Be
        and #1
        bne NOTHINGdown
        lda speed1_Right_To_Be
        and #1
        bne NOTHINGdown
        lda #1
        sta speed1_Left_To_Be
        lda #0
        sta speed1_Up_To_Be
        sta speed1_Down_To_Be
        sta speed1_Right_To_Be
        lda #3
        sta Sprite1_T
        jmp NOTHINGdown
    RIGHTKEYdown:
        lda speed1_Left;_To_Be
        and #1
        bne NOTHINGdown
        lda speed1_Left_To_Be
        and #1
        bne NOTHINGdown
        lda #1
        sta speed1_Right_To_Be
        sta Sprite1_T
        lda #0
        sta speed1_Up_To_Be
        sta speed1_Down_To_Be
        sta speed1_Left_To_Be
    NOTHINGdown:
        rts

;; Kind of "function" in assembly style, used to relieve the main loop
move_charac1:
    lda Sprite1_Y ; load A with Y position
    sbc speed1_Up  ; subtract 1 from A. Only can do math on A register. SBC (Subtract with Borrow)
    sta Sprite1_Y; store back to memory
    lda Sprite1_Y
    adc speed1_Down  ; add 1 to A. ADC (Add with Carry)((to A register))
    sta Sprite1_Y
    lda Sprite1_X
    sbc speed1_Left
    sta Sprite1_X
    lda Sprite1_X
    adc speed1_Right
    sta Sprite1_X
    rts
   
move_charac2:
    lda Sprite2_Y ; load A with Y position
    sbc speed2_Up  ; subtract 1 from A. Only can do math on A register. SBC (Subtract with Borrow)
    sta Sprite2_Y; store back to memory
    lda Sprite2_Y
    adc speed2_Down  ; add 1 to A. ADC (Add with Carry)((to A register))
    sta Sprite2_Y
    lda Sprite2_X
    sbc speed2_Left
    sta Sprite2_X
    lda Sprite2_X
    adc speed2_Right
    sta Sprite2_X
    rts

update_speed1:
    ldx speed1_Up_To_Be
    stx speed1_Up
    ldx speed1_Down_To_Be
    stx speed1_Down
    ldx speed1_Left_To_Be
    stx speed1_Left
    ldx speed1_Right_To_Be
    stx speed1_Right
    ldx #0;
    ldy #0;
    rts

disp_Sprites_DMA:
    lda #3
    sta $4014
    lda #0;
    rts
;; ----------------------------------------------------

strobe_keypad1:
    lda #$01   ; these
    sta $4016  ; lines
    lda #$00   ; setup/strobe the
    sta $4016  ; keypad.
    lda #0;
    rts

strobe_keypad2:
    lda #$01   ; these
    sta $4017  ; lines
    lda #$00   ; setup/strobe the
    sta $4017  ; keypad.$
    lda #0;
    rts


palette:
    ; this upper line is used for the background palette
    .db $0F,$2D,$20,$20,$0F,$3D,$3D,$3D,$0F,$3D,$3D,$3D,$0F,$3D,$3D,$3D
    ; this lower line is used for the sprites palette
    .db $0F,$08,$07,$06,$0F,$01,$03,$02,$0F,$3A,$3A,$3A,$0F,$3A,$3A,$3A


;; -------------------------------------------------------------------------
;; THE FOLLOWING LOOPS ENABLE TO DISPLAY THE BACKGROUND
;; -------------------------------------------------------------------------
dispBackground:
    lda #$20
    sta $2006 ; give $2006 both parts of address $2020.
    lda #$00
    sta $2006

    ;; This displays the background using ourMap, defined ways below
        ldx #$00
    loadNames1:
        lda ourMap1, X ; load A with a byte from address (ourMap + X)
        inx
        sta $2007
        cpx #128 ; map in previous section 64 bytes long
        bne loadNames1; if not all 64 done, loop and do some more
       
        ldx #$00
    loadNames2:
        lda ourMap2, X ; load A with a byte from address (ourMap + X)
        inx
        sta $2007
        cpx #128 ; map in previous section 64 bytes long
        bne loadNames2; if not all 64 done, loop and do some more
        ldx #$00
       
    loadNames3:
        lda ourMap2, X ; load A with a byte from address (ourMap + X)
        inx
        sta $2007
        cpx #128 ; map in previous section 64 bytes long
        bne loadNames3; if not all 64 done, loop and do some more
       
        ldx #$00
    loadNames4:
        lda ourMap2, X ; load A with a byte from address (ourMap + X)
        inx
        sta $2007
        cpx #128 ; map in previous section 64 bytes long
        bne loadNames4; if not all 64 done, loop and do some more
       
        ldx #$00
    loadNames5:
        lda ourMap2, X ; load A with a byte from address (ourMap + X)
        inx
        sta $2007
        cpx #128 ; map in previous section 64 bytes long
        bne loadNames5; if not all 64 done, loop and do some more

        ldx #$00
    loadNames6:
        lda ourMap2, X ; load A with a byte from address (ourMap + X)
        inx
        sta $2007
        cpx #128 ; map in previous section 64 bytes long
        bne loadNames6; if not all 64 done, loop and do some more

        ldx #$00
    loadNames7:
        lda ourMap3, X ; load A with a byte from address (ourMap + X)
        inx
        sta $2007
        cpx #128 ; map in previous section 64 bytes long
        bne loadNames7; if not all 64 done, loop and do some more
       
    lda #%00011110 ; enable sprites, enable background
    sta $2001
       
    rts
;; -------------------------------------------------------------------------


ourMap1:
    .db 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
    .db 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
    .db 30,26,15,39,19,32,0,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,30,26,15,39,19,32,0,7,0
    .db 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
ourMap2:
    .db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
ourMap3:
    .db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,4


    .bank 2
    .org $0000
    .incbin "bkg.nes"
    .incbin "sprites.nes"
;;--- END OF CODE FILE ---;
Re: Help ! can anyone see the mistake ?
by Kasumi on 2013-09-12 (#117963)
Quote:
However, with this cmp line, the motorbike has a strange diagonal direction when I press the left and right keys (that should not happen at all) but works perfectly fine with up and down keys (which confuses me a lot). And without the cmp (just jumping to "modulo") everything works perfectly fine as well.

Sounds like you don't understand the carry flag. When you add (adc) or subtract (sbc) on the 6502, the state of the carry flag is taken into account to possibly add or subtract 1 more than the actual value given.

To get the true value that will end up in the accumulator (A) for adc, the equation is A+value+C. (where C is the value of the carry flag.)

Code:
lda #$00
clc;Clears the carry
adc #$00
;A = #$00
A+value+C
#$00+#$00+#0 (because we cleared the carry flag) = #$00

Now see this example where we set the carry instead, but change nothing else:
Code:
lda #$00
sec;Sets the carry
adc #$00
;A = #$01
A+value+C
#$00+#$00+#1 (because we set the carry flag) = #$01


For SBC, it subtracts the OPPOSITE of the carry. So if the carry is 1 (set), sbc will subtract the value, and if it is 0 (clear) it will subtract the value and then it will subtract 1.

Additionally, the carry is set or cleared after ADC and SBC depending on the result of the instruction. (Other instructions affect it as well, like cmp.) Here's a post that explains the carry in very great detail: viewtopic.php?p=112830#p112830
Edit: Wait... that may not be the best post on the subject since it covers mainly 16 bit stuff. I swear I've written a good general one, and will look for it.

So when you have this code here:
Code:
move_charac1:
    lda Sprite1_Y ; load A with Y position


;What is the state of the carry before the following sbc?
;Because you don't set it, it's whatever the CPU last had it as. Effectively unknown!
;So you could be subtracting speed1_Up if it was last set, or speed1_Up and then another 1 if it was last clear!
;To remove this ambiguity, just use sec before an SBC when you don't know the
;state of the carry


    sbc speed1_Up  ; subtract 1 from A. Only can do math on A register. SBC (Subtract with Borrow)
    sta Sprite1_Y; store back to memory


Like so:
Code:
move_charac1:
    lda Sprite1_Y ; load A with Y position
    sec
    sbc speed1_Up  ; subtract 1 from A. Only can do math on A register. SBC (Subtract with Borrow)
    sta Sprite1_Y; store back to memory


You should read this post right here for great detail: viewtopic.php?p=112830#p112830

Edit: Wait... that may not be the best post on the subject since it covers mainly 16 bit stuff. I swear I've written a good general one, and will look for it.

But the general rule is to set the carry before subtractions and clear it before additions if you don't know the state of it.

Interesting tidbit: You say everything works fine without the cmp. Cmp affects the carry flag! So check this out:
Code:
    cmp #8
    beq modulo
    jmp infinite

In the case A = 8, we jump to modulo. This means the carry is guaranteed set when we get to modulo. (cmp would set the carry in that case)
Nothing in update_speed1 affects it, so it's still set. Nothing in the rest of modulo affects it. So we jmp to infinite with it still set.

In the case that A < 8, we jump to infinite. (if A < 8 when it hits the cmp, the carry would be cleared by cmp #8). So we jmp to infinite with it clear.

Nothing in disp_Sprites_DMA affects it...

Then we get to here:
Code:
move_charac1:
    lda Sprite1_Y ; load A with Y position
    sbc speed1_Up  ; subtract 1 from A. Only can do math on A register. SBC (Subtract with Borrow)
    sta Sprite1_Y; store back to memory


Because nothing has changed the carry between that cmp #8 and that code, when A = 8, we subtract speed1_Up, and when A < 8 (i.e. most of the time), it's subtracting speed1_Up and another one.

To fix, put a sec before that sbc.

Put a sec before all your sbcs unless you're doing 16bit math or really know what you're doing.
Put a clc before all your adcs unless you're doing 16bith math or really know what you're doing.

And I'll plug it a third time :P : viewtopic.php?p=112830#p112830
Edit: Wait... that may not be the best post on the subject since it covers mainly 16 bit stuff. I swear I've written a good general one, and will look for it.
Edit2: Yep... sadly that's all I got. It should still explain things, if not ask some questions!

Read that for full understanding.

PS: I could be totally wrong about this being the cause of the problem, but your lack of sec/clc before additions and subtractions is definitely a problem on its own. If there's still a problem after you fix that, we'll solve it then. :wink:
Re: Help ! can anyone see the mistake ?
by turboninja on 2013-09-19 (#118278)
Ok ! Thank you so much ! I had time to realize my mistake reading some code that I found here and there. Indeed, I was lacking of clc and did not realize how important it was (this game is actually my first experience with assembly).

Anyway, T H A N K Y O U !
Re: Help ! can anyone see the mistake ?
by turboninja on 2013-10-04 (#118948)
Hello everybody,

I am here because I have another problem with my code :) hope I will be able to propose a clear release someday for the people who (just as me) want to play this Tron game on their old NES.

Here is where I get stuck : switching from NES ROM to NES RAM. I definitely need to keep track of the tiles that have been visited and the other ones. So, I just tried to switch from NES ROM to NES RAM (to start with). But I am getting a lot of graphic mistakes (the graphical output has a totally unpredictable behaviour), though we can still play "decently".

Changing x in the line : (in the load_to_ppu routine)

Code:
   ldx #32  ; number of 256-byte chunks to load
     ldy #0


definitely modifies the behaviour of the game once compiled (for 32, we have decent sprites, for 16, something that looks like the title screen I had before trying to switch). I guess there must be some limitations I am not respecting, but I cannot figure out which one ! Some help would be more than welcome ! The whole code is below

Code:
    ;;--- CODE START ---;;
    .inesprg 1
    .inesmap 0
    .inesmir 1
    .ineschr 0

    .bank 1

    .org $FFFA
    .dw 0        ; no VBlank
    .dw Start    ; address to execute on reset
    .dw 0        ; no whatever
    .bank 0
    .org $0000
   
reset:
    sei          ; disable IRQs
    cld          ; disable decimal mode
    ldx #$40
    stx $4017    ; disable APU frame IRQ
    ldx #$FF
    txs          ; Set up stack
    inx          ; now X = 0
    stx $2000    ; disable NMI
    stx $2001    ; disable rendering
    stx $4010    ; disable DMC IRQs

nmi:
    lda        #$00
    sta        $2003        ; Set the low byte (00) of the ram address
    lda        #$02
    sta        $4014        ; Set the high byte (02) of the RAM address,
   
; actually, these variables could be stored in only one byte
; maybe a little bit less...

PPUMASK = $2001
PPUADDR = $2006
PPUDATA = $2007

speed1_Up:   .db 0
speed1_Left:   .db 0
speed1_Down:   .db 0
speed1_Right:   .db 0
speed2_Up:   .db 0
speed2_Down:   .db 0
speed2_Left:   .db 0
speed2_Right:   .db 0
; actually, these variables could be stored in only one byte
speed1_Up_To_Be:   .db 0
speed1_Down_To_Be:   .db 0
speed1_Left_To_Be:   .db 0
speed1_Right_To_Be:   .db 0
speed2_Up_To_Be:   .db 0
speed2_Down_To_Be:   .db 0
speed2_Left_To_Be:   .db 0
speed2_Right_To_Be:   .db 0

Sprite1_T_To_Be:     .db  0   ; sprite #1's Tile Number
Sprite2_T_To_Be:     .db  0   ; sprite #1's Tile Number

edge_horiz1_pos:     .db 0
edge_vert1_pos:     .db 0
edge_horiz2_pos:    .db 0
edge_vert2_pos:     .db 0

loop_count: .db 0

addrLO: .db 0  ; make "variable"s for our indirect addressing
addrHI: .db 0

vidlow: .db 0
vidhigh: .db 0

src: .db 0

    .org $0200 ; OAM Copy location $0300
;; THE FIRST TWO SPRITES REPRESENT THE MOTORBIKES
Sprite1_Y:     .db  0   ; sprite #1's Y value
Sprite1_T:     .db  0   ; sprite #1's Tile Number
Sprite1_S:     .db  0   ; sprite #1's special byte
Sprite1_X:     .db  0   ; sprite #1's X value
Sprite2_Y:     .db  0   ; same thing, same order for sprite #2
Sprite2_T:     .db  0   ; note that I numbered 1 2 ...
Sprite2_S:     .db  0   ; some people may actually prefer starting
Sprite2_X:     .db  0   ; the count at 0, but it doesn't really matter.
;; THESE SPRITES WILL REPRESENT THE SCORE OF EACH PLAYER
;; BETWEEN 0 AND 9
Sprite3_Y:     .db  0   ;
Sprite3_T:     .db  0   ; This will be the score of P1
Sprite3_S:     .db  0   ;
Sprite3_X:     .db  0   ;
Sprite4_Y:     .db  0   ;
Sprite4_T:     .db  0   ; This will be the score of P2
Sprite4_S:     .db  0   ;
Sprite4_X:     .db  0   ;

    .org $8000  ; code starts at $8000 or $C000
Start:
    cld ; supposedly useless but, let's keep it for now

    ldx #$00    ; clear X            ;; start of palette loading code
    lda #$3F    ; have $2006 tell
    sta $2006   ; $2007 to start
    lda #$00    ; at $3F00 (palette).
    sta $2006   
   
    jsr init_pal

    jsr load_to_ppu
    jsr turn_on_PPU
   
   
    jsr init_background  ; calls the routine to load the backgrounds
    jsr init_players_positions
    jsr init_scores
    jsr init_sound
    jsr title_screen ; loads the title_screen
   
   
;; THE MAIN LOOP
infinite:  ; a label to start our infinite loop

    jsr disp_Sprites_DMA
    jsr strobe_keypad1
    jsr update_keypad1   
    jsr move_charac1

    inc loop_count ; this variable will enable to distribute operations over different steps of the loop_count

    lda loop_count
    cmp #2
    beq modulo2

    lda loop_count
    cmp #4
    beq modulo4

    lda loop_count
    cmp #8
    beq modulo8
   
    jmp infinite

modulo8:
    clc ;; THIS THING IS FUCKING MANDATORY AFTER A CMP
    ;; OTHERWISE, ODD EFFECTS WILL APPEAR
    jsr update_speed1
    ldx #0
    stx loop_count
    jmp infinite
   
modulo4:
    clc
    ldy Sprite1_Y
    cpy #24
    bne south_test
    jsr player1_loose
south_test:
    clc
    cpy #224
    bne west_test
    jsr player1_loose
west_test:
    clc
    ldy Sprite1_X
    cpy #248
    bne modulo4rts
    jsr player1_loose
modulo4rts:
    clc
    jmp infinite
   
modulo2:
    clc
    ldy Sprite1_X
    cpy #2
    bne modulo2rts
    jsr player1_loose
modulo2rts:
    clc
    jmp infinite
   
update_keypad1:
    lda $4016  ; load Abutton Status ; note that whatever we ain't interested   
    lda $4016  ; load Bbutton Status ; in we just load so it'll go to the next one.
    lda $4016  ; load Select button status
    lda $4016  ; load Start button status
    lda $4016  ; load UP button status
    and #1      ; AND status with #1
    bne UPKEYdown  ; for some reason (not gonna reveal yet), need to use NotEquals
    ;with ANDs. So it'll jump (branch) if key was down.
    lda $4016  ; load DOWN button status
    and #1     ; AND status with #1
    bne DOWNKEYdown
    lda $4016  ; load LEFT button status
    and #1     ; AND status with #1
    bne LEFTKEYdown
    lda $4016  ; load RIGHT button status
    and #1     ; AND status with #1
    bne RIGHTKEYdown
    ;ldy $0
    jmp NOTHINGdown2  ; if nothing was down, we just jump (no check for conditions)
    ; down past the rest of everything.
    UPKEYdown:
        lda speed1_Down;_To_Be
        and #1
        bne NOTHINGdown2
        lda speed1_Down_To_Be
        and #1
        bne NOTHINGdown2
        lda #1
        sta speed1_Up_To_Be
        lda #0
        sta speed1_Left_To_Be
        sta speed1_Down_To_Be
        sta speed1_Right_To_Be
        sta Sprite1_T_To_Be
        jmp NOTHINGdown2  ; jump over the rest of the handling code
    DOWNKEYdown:
        lda speed1_Up;_To_Be
        and #1
        bne NOTHINGdown2
        lda speed1_Up_To_Be
        and #1
        bne NOTHINGdown2
        lda #1
        sta speed1_Down_To_Be
        lda #2
        sta Sprite1_T_To_Be
        lda #0
        sta speed1_Left_To_Be
        sta speed1_Right_To_Be
        sta speed1_Up_To_Be
        jmp NOTHINGdown ; jump over the rest of handling code.
    NOTHINGdown2:
        jmp NOTHINGdown
    LEFTKEYdown:
        lda speed1_Right;_To_Be
        and #1
        bne NOTHINGdown
        lda speed1_Right_To_Be
        and #1
        bne NOTHINGdown
        lda #1
        sta speed1_Left_To_Be
        lda #0
        sta speed1_Up_To_Be
        sta speed1_Down_To_Be
        sta speed1_Right_To_Be
        lda #3
        sta Sprite1_T_To_Be
        jmp NOTHINGdown
    RIGHTKEYdown:
        lda speed1_Left;_To_Be
        and #1
        bne NOTHINGdown
        lda speed1_Left_To_Be
        and #1
        bne NOTHINGdown
        lda #1
        sta speed1_Right_To_Be
        sta Sprite1_T_To_Be
        lda #0
        sta speed1_Up_To_Be
        sta speed1_Down_To_Be
        sta speed1_Left_To_Be
    NOTHINGdown:
        rts

move_charac1:
    lda Sprite1_Y ; load A with Y position
    sbc speed1_Up  ; subtract 1 from A. Only can do math on A register. SBC (Subtract with Borrow)
    sta Sprite1_Y; store back to memory
    lda Sprite1_Y
    adc speed1_Down  ; add 1 to A. ADC (Add with Carry)((to A register))
    sta Sprite1_Y
    lda Sprite1_X
    sbc speed1_Left
    sta Sprite1_X
    lda Sprite1_X
    adc speed1_Right
    sta Sprite1_X
    rts
   
move_charac2:
    lda Sprite2_Y ; load A with Y position
    sbc speed2_Up  ; subtract 1 from A. Only can do math on A register. SBC (Subtract with Borrow)
    sta Sprite2_Y; store back to memory
    lda Sprite2_Y
    adc speed2_Down  ; add 1 to A. ADC (Add with Carry)((to A register))
    sta Sprite2_Y
    lda Sprite2_X
    sbc speed2_Left
    sta Sprite2_X
    lda Sprite2_X
    adc speed2_Right
    sta Sprite2_X
    rts

player1_loose:  ;; the following could (and will) be improved, a loop would be cleaner !
    jsr make_sound
    ldx #16
    stx Sprite1_T
    ldy #16   
loopAnim:
    jsr disp_Sprites_DMA
    inc Sprite1_T
    jsr disp_Sprites_DMA
    nop
    dey
    bne loopAnim 
    jsr init_players_positions
    inc Sprite4_T ;Recall that Sprite4_T is also the score of P2
    ldy #0
    sty loop_count
    rts
   
player2_loose:
    jsr init_players_positions
    inc Sprite3_T
    ldy #0
    sty loop_count
    rts

update_speed1:
    ldx speed1_Up_To_Be
    stx speed1_Up
    ldx speed1_Down_To_Be
    stx speed1_Down
    ldx speed1_Left_To_Be
    stx speed1_Left
    ldx speed1_Right_To_Be
    stx speed1_Right
    ldx Sprite1_T_To_Be
    stx Sprite1_T
    rts
   
update_speed2:
    ldx speed2_Up_To_Be
    stx speed2_Up
    ldx speed2_Down_To_Be
    stx speed2_Down
    ldx speed2_Left_To_Be
    stx speed2_Left
    ldx speed2_Right_To_Be
    stx speed2_Right
    ldx Sprite2_T_To_Be
    stx Sprite2_T
    rts

disp_Sprites_DMA: ;; Displays all the sprites using Direct Memory Access. So cool
    waitblank:
        bit $2002  ; these 3 lines wait for VBlank, this loop will actually miss VBlank
        bpl waitblank ; alot, in a later Day, I'll give a better way.
    lda #2
    sta $4014
    lda #0;
    rts

strobe_keypad1:
    lda #$01   ; these
    sta $4016  ; lines
    lda #$00   ; setup/strobe the
    sta $4016  ; keypad.
    lda #0;
    rts

strobe_keypad2:
    lda #$01   ; these
    sta $4017  ; lines
    lda #$00   ; setup/strobe the
    sta $4017  ; keypad.$
    lda #0;
    rts

init_pal:                ; this is a freaky loop
    lda palette, x  ; that gives 32 numbers
    sta $2007       ; to $2007, ending when
    inx             ; X is 32, meaning we
    cpx #32         ; are done.
    bne init_pal     ; if X isn't =32, goto "loadpal:" line.
    rts

palette:
    ; this upper line is used for the background palette
    .db $0F,$2D,$16,$2C,$0F,$2D,$16,$2C,$0F,$2D,$16,$2C,$0F,$2D,$16,$2C
    ; this lower line is used for the sprites palette
    .db $0F,$08,$07,$06,$0F,$01,$03,$02,$0F,$3A,$3A,$3A,$0F,$3A,$3A,$3A


title_screen:
    jsr turn_off_PPU
    lda #255 ; These lines allow to scroll the background
    sta $2005 ; X POS first
    lda #0 ; Y POS
    sta $2005 ; store it at the same address
    jsr turn_on_PPU
title_screen_loop:   
    jsr strobe_keypad1
    lda $4016  ; load Abutton Status ; note that whatever we ain't interested   
    lda $4016  ; load Bbutton Status ; in we just load so it'll go to the next one.
    lda $4016  ; load Select button status
    lda $4016  ; load Start button status
    and #1      ; AND status with #1
    bne jump_to_rts_title_screen; for some reason (not gonna reveal yet), need to use NotEquals
    jmp title_screen_loop
   
jump_to_rts_title_screen:
    clc
    jsr turn_off_PPU
    lda #0
    sta $2005 ; This address regards scrolling
    lda #0
    sta $2005
    jsr turn_on_PPU
    rts
   
;; THE SOUND PART
init_sound:
    lda #$FF   ; typical
    sta $4000  ; write
    lda #%11011011  ; % means binary number, remember the '#' for immediate values.
    sta $4001  ; immediate means "not an address, just a number".
    rts
;; THIS COULD BE SOMEHOW IMPROVED, BUT IT IS NOT THE PRIORITY
make_sound:
    lda #$A5
    sta $4002
    lda #$AB
    sta $4003
    lda #%00000001
    sta $4015
    rts

   
init_players_positions:
    clc ; once again, removing it would cause nasty bugs
    lda #0
    sta loop_count
    sta Sprite2_S;
    sta Sprite1_T;
    sta Sprite1_T_To_Be
    lda #1;
    sta Sprite2_T
    sta Sprite1_S;
    lda #124;
    sta Sprite1_X;
    sta Sprite2_X
    lda #164
    sta Sprite1_Y
    lda #124
    sta Sprite2_Y
    lda #0
    sta speed1_Down;   
    sta speed1_Right;   
    sta speed1_Left;
    sta speed1_Up;
    sta speed2_Down;   
    sta speed2_Right;   
    sta speed2_Left;
    sta speed2_Up;
    sta speed1_Down_To_Be
    sta speed1_Right_To_Be
    sta speed1_Left_To_Be
    sta speed2_Up_To_Be
    sta speed2_Right_To_Be
    sta speed2_Left_To_Be
    lda #1
    sta speed1_Up_To_Be
    sta speed2_Down_To_Be
    rts
   
init_scores:
    lda #6
    sta Sprite3_T
    sta Sprite4_T
    lda #0;
    sta Sprite3_S
    sta Sprite4_S
    lda #15
    sta Sprite3_Y
    sta Sprite4_Y
    lda #72
    sta Sprite3_X
    lda #238
    sta Sprite4_X
    rts
   
init_background: ; uses indirect addressing
    ldx #0
    lda #$20  ; set the destination address in PPU memory
    sta $2006  ; should be $2000
    stx $2006
   
    lda #low(background)   ; put the high and low bytes of the address "backg"
    sta addrLO        ; into the variables so we can use indirect addressing.
    lda #high(background)
    sta addrHI
    ldx #16  ; number of 256-byte chunks to load
    ldy #0
loopIndirectAddressing:
    lda [addrLO],y
    sta $2007     ; load 256 bytes
    iny
    bne loopIndirectAddressing
;--------------------
    inc addrHI  ; increment high byte of address backg to next 256 byte chunk
    dex        ; one chunk done so X = X - 1.
    bne loopIndirectAddressing   ; if X isn't zero, do again
   
    rts

;; OKAY, this is a little bit scarying, but it is ways better than using the strange
;; programs proposed to create the .bin files..

load_to_ppu:
    ldy #0       ;; starting index into the first page
    sty PPUMASK  ;; turn off rendering just in case
    sty PPUADDR  ;; load the destination address into the PPU
    sty PPUADDR

   lda #0  ; set the destination address in PPU memory
     sta $2006  ; should be $0000
     sta $2006
     lda #low(ppumem)   ; put the high and low bytes of the address ppumem
     sta vidlow        ; into the variables so we can use indirect addressing.
     lda #high(ppumem)
     sta vidhigh

   ldx #32  ; number of 256-byte chunks to load
     ldy #0
ppuloop:
     lda [vidlow],y
     sta $2007     ; load 256 bytes
     iny
     bne ppuloop
     inc vidhigh  ; increment high byte of address vidhigh to next 256 byte chunk
     dex        ; one chunk done so X = X - 1.
     bne ppuloop   ; if X isn't zero, do again
   rts

turn_on_PPU:
    lda #%00001000  ;
    sta $2000       ;
    lda #%00011110  ; Our typical PPU Setup code.
    sta $2001       ;
    rts

turn_off_PPU:
    lda #%00000000  ;
    sta $2000       ;
    lda #%00000000  ; Our typical PPU Setup code.
    sta $2001       ;
    rts

title:
    .db 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
    .db 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
    .db 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
    .db 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
    .db 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
    .db 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
    .db 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
    .db 0,0,0,0,0,0,0,0,0,0,0,42,43,44,47,48,55,56,57,64,65,66,0,0,0,0,0,0,0,0,0,0
    .db 0,0,0,0,0,0,0,0,0,0,0,0,45,0,49,50,63,0,62,67,68,69,0,0,0,0,0,0,0,0,0,0
    .db 0,0,0,0,0,0,0,0,0,0,0,0,45,0,51,54,58,0,62,70,71,72,0,0,0,0,0,0,0,0,0,0
    .db 0,0,0,0,0,0,0,0,0,0,0,0,46,0,52,53,59,60,61,73,74,75,0,0,0,0,0,0,0,0,0,0
    .db 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
    .db 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
    .db 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
    .db 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
    .db 0,0,0,0,0,0,76,77,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,83,84,0,0,0,0,0
    .db 0,0,0,0,0,0,78,79,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,85,86,0,0,0,0,0
    .db 0,0,0,0,0,0,80,81,82,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,87,88,89,0,0,0,0,0
    .db 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
    .db 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
    .db 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
    .db 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
    .db 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
    .db 0,0,0,0,0,0,0,0,0,30,32,19,33,33,0,33,34,15,32,34,0,0,0,0,0,0,0,0,0,0,0,0
    .db 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
    .db 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
    .db 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
    .db 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
   
background:   
    .db 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
    .db 0,16,39,0,24,35,26,23,19,28,0,32,19,36,19,26,26,19,0,0,0,0,0,0,0,7,5,6,8,0,0,0,0
    .db 0,0,0,0,0,0,0,00,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
    .db 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
    .db 30,26,15,39,19,32,0,6,0,0,0,0,0,0,0,0,0,0,0,0,0,30,26,15,39,19,32,0,7,0,0,0
    .db 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
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2   
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2   
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2
    .db 0,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,4
    .db 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
    .db 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

ppumem: .incbin "bkg.nes"
my_sprites: .incbin "sprites.nes"


Re: Help ! can anyone see the mistake ?
by lidnariq on 2013-10-04 (#118950)
Here's some things that I immediately see:

1- Don't leave the old stubs (from "reset" through "nmi") in your code). They're misleading (and currently horrifically wrong)
2- You need to wait two vblanks before you start writing to any PPU register: see http://wiki.nesdev.com/w/index.php/PPU_power_up_state
Re: Help ! can anyone see the mistake ?
by turboninja on 2013-10-04 (#118953)
Thanks for the quick answer ! I just tried and unfortunately this does not solve the problem :(
Re: Help ! can anyone see the mistake ?
by turboninja on 2013-10-06 (#119027)
Well, my bad. It actually works. I had forgotten to turn off the rendering everywhere when I first did it. However, my sprites are not displayed any more now... Instead, I just have big squares. Help please :)
Re: Help ! can anyone see the mistake ?
by lidnariq on 2013-10-06 (#119029)
Try running it inside an emulator with a debugger, such as FCEUX (windows build only), NO$NES, or Nintendulator. They should all let you look at the CHR-RAM and sprite memory and trace back why you're seeing squares.