Common pitfalls
Check your hardware before checking your code...
Unwanted resets
- Watchdog not written to often enough
- Misaligned word or longword read/write (generates an Address error)
- 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 height is set to 0 (SCB3).
- Sprite tiles are all transparent (bad tile numbers ?).
- Shrinking values too low (at least one pixel 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 is not black.
Wrong colors
- The wrong palette bank is selected.
- Reference color is not black.
- Palettes loading routine is broken (byte load instead of word, bad offset...).
- Tiles are assigned to an uninitialized palette.
Erratic sprite movement or display
- Sprite is driven by the previous one.
- VRAM writes too fast.
- Never use CLR instructions on LSPC registers.
Interrupts don't work
- Some emulators ignore the timer interrupt, it may work on the real hardware.
- The interrupt mask causes them to be ignored by the 68k. Check the SR register.
- Wrong configuration of the timer 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