Common pitfalls

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Check your hardware before checking your code...

Unwanted resets

  • Watchdog not written to often enough
  • Misaligned word or longword read/write
  • RTS with wrong return address in stack (or bad SP ?)
  • JSR to BIOSF_BOOTSCR ($C00438) instead of JMP

Invisible sprites

  • Sprites are disabled (NeoGeo CD only)
  • The fix layer is filled with non-transparent tiles and hides everything.
  • Sprite position is out of the 320x224 visible area.
  • Sprite size is 0 (SCB3).
  • Sprite tiles are all transparent (bad tile numbers ?).
  • Shrinking values too low (few pixels should still be visible).
  • Bad C ROM, it happens...
  • Reference color (0) is not black.

Invisible fix layer

  • Fix is disabled (NeoGeo CD only)
  • No non-transparent tiles mapped (bad S ROM ?)
  • Tiles are on the invisible borders.
  • Reference color (0) is not black.

Wrong colors

  • Reference color (0) is not black. Set $400000 to #$8000.
  • Palettes loading routine is broken.
  • Tiles are assigned to an uninitialized palette.

Shrinked sprites show garbage below them

  • The unused part of the sprite maps isn't cleared with a transparent tile (hardware glitch ?).

Erratic sprite movement

  • Sprite is driven by the previous one.
  • VRAM writes too fast.

Interrupts don't work

  • Some emulators ignore the raster line interrupt, it may work on the real hardware.
  • Interrupt mask cause them to be ignored by the 68k. Check the SR register.
  • Wrong configuration of the raster line interrupt, see REG_HBLANKCNT ($3C0006).
  • The interrupt vector points to an RTE or RTS. Beware of the different levels between cart and CD systems.

Game don't boot (goes directly to the crosshatch)

  • Check the "NEO-GEO" string at 0x100
  • Check the security code at (0x182).l