Artifacts blipping around on screen, what am I doing wrong?

[h0ffman]

Hi guys

Hope you can help. Finally started reading the Amiga hardware reference manual so I can finally understand how the playfield and bitplanes work. Following the manual i've managed to be a single bitplane displayed, however, there seems to be weird artifacts blipping on the screen from time to time. I'm pretty sure it is a common problem but as I'm a total n00b i'm not sure whats going on.

I am currently writting this on an A1200.

Cooper looks like this..

_cCopper    dc.w    bplcon0,$1200    ; set as 1 bp display
        dc.w    bplcon1,$0000    ; set scroll 0
        dc.w    bpl1mod,$0000
        dc.w    bpl2mod,$0000    
        dc.w    ddfstrt,$38    ; datafetch start stop
        dc.w    ddfstop,$d0
        dc.w    diwstrt,$2c81    ; window start stop
        dc.w    diwstop,$2cc1
        dc.w    color,$000
        dc.w    color+2,$fff
_cPlanes    dc.w    bplpt,$0
        dc.w    bplpt+2,$0
        dc.w    $ffff,$fffe
        dc.w    $ffff,$fffe

This is the code which kicks off the copper / fills the bit plane pointers etc.

DemoStart    movem.l    d0-a6,-(sp)

        lea    $dff000,a4        ; hw base
        
        move.l    #_pPlane1,d0
        lea    _cPlanes,a0        
        move.w    d0,6(a0)
        swap    d0
        move.w    d0,2(a0)
        
        move.l    #_cCopper,cop1lc(a4)

        move.l    #50,d0
        lea    _pPlane1,a0
FillPlane    move.l    #$f0000000,(a0)+
        move.l    #$ff0f0f0f,(a0)+
        move.l    #$00000fff,(a0)+
        move.l    #$00000fff,(a0)+
        move.l    #$ff0f0f0f,(a0)+
        move.l    #$ff0f0f0f,(a0)+
        move.l    #$00000fff,(a0)+
        move.l    #$00000fff,(a0)+
        move.l    #$ffffffff,(a0)+
        move.l    #$ffffffff,(a0)+

        dbra    d0,FillPlane
        
.lp         btst    #6,$bfe001              ; 
            bne.s   .lp                     ;
            
            movem.l    (sp)+,d0-a6
            rts

Any help would be great.

Cheers

[StingRay]

Originally Posted by h0ffman

Following the manual i've managed to be a single bitplane displayed, however, there seems to be weird artifacts blipping on the screen from time to time.

My guess is that you didn't initialize the sprite pointers properly and thus you'll see "random" sprite data from time to time. To fix that you need to either completely disable sprite DMA or create an empty sprite in chip ram and initalize the sprite pointers, i.e. they need to point to that empty sprite.

[h0ffman]

Ahhhh, that makes sense. Cheers, I'll go read the sprite chapter now.

Sorted, cheers sting, legend!