AGA Fetch mode 2 on A4000 vs A1200

[ninsei]

Hi


I'm using a A4000/030 developing a game in Blitz Basic 2.1, and everything is working fine on that machine. However when testing on two different A1200 there was graphical glitches on the BOBS. Using fetch mode 1 instead of 2 fixed the problem on A1200. So what's going on here? Is it somehow more bandwidth available on the A4000?

#tilesize = 16
#bitmapwidth = 384

Buffer 0, 32768
Buffer 1, 32768

BitMap 0, #bitmapwidth, 256*2 + 5*#tilesize, 4
BitMap 1, #bitmapwidth, 256*2 + 5*#tilesize, 4
BitMap 2, 320, 768, 4                  ; playfield 2 background
BitMap 3, 320, 16, 5                   ; score panel

; Magic Eraok statement to adjust display
Statement ResizeWidth{indexnum.l, amount.l, xadjust.l}
  diwstrt.l = xadjust * 8
  diwstop.l = diwstrt + amount * 8

  dUfstrt.l = Int(diwstrt/2)
  dUfstop.l = Int(diwstop/2)

  DisplayAdjust indexnum,amount,dUfstrt,dUfstop,diwstrt,diwstop
End Statement

Statement initgamescreen{}

  flags.l = $8 +$10 +$20 +$10000 +$2000  ; fetch mode 2
  flags2.l = $5 +$00 +$10000

  SpriteMode 2

  InitCopList 0, 44, 236, flags, 8, 64, -4
  ResizeWidth{0,-4,2}

  InitCopList 1, 284, 16, flags2, 8, 32, 0

  CreateDisplay 0, 1
  DisplayPalette 0, 1
  DisplayPalette 1, 5

  DisplayControls 0, 0, $1C20, Xor($11, $22)
                                                                                                                           
  DisplayRainbow 0, 0, 2
End Statement

[jotd]

no, it's because your screen bitplanes aren't aligned on 4 bytes. FMODE=2 needs alignment on 4, if by luck it happens it works, else you get that crap.

FMODE=3 requires alignment on 8 bytes.

[ninsei]

Originally Posted by jotd

no, it's because your screen bitplanes aren't aligned on 4 bytes. FMODE=2 needs alignment on 4, if by luck it happens it works, else you get that crap.

FMODE=3 requires alignment on 8 bytes.

Thanks jotd, setting up these screens sure is tricky. For some reason it consistently works on A4000, so yeah something makes it work by luck.