Common pitfalls

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