Common pitfalls: Difference between revisions

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=Unwanted resets=
=Unwanted resets=
* Watchdog not written to often enough
* The [[watchdog]] isn't reset often enough, write a byte to {{Reg|REG_DIPSW}} at least each frame.
* Misaligned word or longword read/write
* An exception is occuring, set up a simple [[68k exception handling]] screen to debug your code.
* Misaligned word or longword read/write (address error)
* RTS with wrong return address in stack (or bad SP ?)
* RTS with wrong return address in stack (or bad SP ?)
* JSR to BIOSF_BOOTSCR ($C00438) instead of JMP
* JSR instead of JMP
* Jump table with bad index (address error)
* [[Timer interrupt]] too fast, causes stack to explode


=Invisible sprites=
=Invisible sprites=
* Sprites are disabled (NeoGeo CD only)
* Sprites are disabled (NeoGeo CD only, they're enabled by default)
* The [[fix layer]] is filled with non-transparent tiles and hides everything.
* The [[fix layer]] is filled with non-transparent tiles which hide everything.
* Sprite position is out of the 320x224 visible area.
* Sprite position is out of the 320*224 visible area.
* Sprite size is 0 ([[Sprites|SCB3]]).
* Sprite height is set to 0 ([[Sprites|SCB3]]).
* Sprite tiles are all transparent (bad tile numbers ?).
* Sprite tiles are all transparent (bad tile numbers ?).
* Shrinking values too low (few pixels should still be visible).
* Tile colors are the same as the backdrop color.
* Wrong palette bank.
* Shrinking values too low (at least 2 pixels should still be visible).
* Bad [[C ROM]], it happens...
* Bad [[C ROM]], it happens...
* [[Palettes|Reference color]] (0) is not black.
* [[Palettes|Reference color]] (0) is not black.


=Invisible fix layer=
=Invisible fix layer=
* Fix is disabled (NeoGeo CD only)
* Fix is disabled (NeoGeo CD only, enabled by default)
* No non-transparent tiles mapped (bad [[S ROM]] ?)
* No non-transparent tiles mapped (bad [[S ROM]] ?)
* Tile colors are the same as the backdrop color.
* Tiles are on the invisible borders.
* Tiles are on the invisible borders.
* Reference color (0) is not black.
* Reference color is not black.


=Wrong colors=
=Wrong colors=
* Reference color (0) is not black. Set $400000 to #$8000.
* The wrong palette bank is selected.
* Palettes loading routine is broken.
* Reference color is not black.
* Palettes loading routine is broken (byte load instead of word, bad offset...).
* Tiles are assigned to an uninitialized palette.
* Tiles are assigned to an uninitialized palette.


=Shrinked sprites show garbage below them=
=Erratic sprite movement or display=
* 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.
* Sprite is driven by the previous one.
* VRAM writes too fast.
* {{Reg|REG_VRAMRW}} or {{Reg|REG_VRAMMOD}} writes too fast.
* '''Never''' use CLR instructions on [[Memory mapped registers|LSPC registers]].
* The [[68k interrupts|Timer interrupt]] routine has VRAM writes which interferes with the VBlank interrupt routine. Disable the Timer interrupt when out of the display area.


=Interrupts don't work=
=Interrupts don't work=
* Some emulators ignore the [[68k interrupts|raster line interrupt]], it may work on the real hardware.
* Some emulators ignore the [[68k interrupts|timer interrupt]], it may work on the real hardware.
* Interrupt mask cause them to be ignored by the 68k. Check the SR register.
* The interrupt mask causes them to be ignored by the 68k. Check the SR register.
* Wrong configuration of the raster line interrupt, see [[Memory mapped registers|'''REG_HBLANKCNT''' ($3C0006)]].
* Wrong configuration of the timer interrupt, see {{Reg|REG_LSPCMODE}}.
* The interrupt vector points to an RTE or RTS. Beware of the different levels between cart and CD systems.
* 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)=
=Game doesn't boot (crosshatch or blue screen)=
* Check the "NEO-GEO" string at 0x100
See [[68k program header]]:
* Check the security code at (0x182).l
* Check the "NEO-GEO" string at $100
* Check the security code and pointer at $182
* NGH number at $108 must be greater than 0
 
=Game isn't recognized on Neo CD=
* Check that all files in IPL.TXT are present
* Check that IPL.TXT ends with CR+LF
* Check if the ABS, CPY and BIB files are present and that they contain the right data
 
=Neo CD resets after initial load=
* Check that a file for every type of data is listed in IPL.TXT: [[game CD structure]].
 
=Vblank routine is long=
* Stop the timer interrupt when out of the active display. The timer interrupt can be very mean.


=No sound=
* Writes to YM2610 are [[Z80/YM2610 interface|done too fast]].


[[Category:Code]]
[[Category:Code]]
[[Category:HowTo]]

Latest revision as of 19:16, 13 May 2017

Check your hardware before checking your code...

Unwanted resets

  • The watchdog isn't reset often enough, write a byte to REG_DIPSW at least each frame.
  • An exception is occuring, set up a simple 68k exception handling screen to debug your code.
  • Misaligned word or longword read/write (address error)
  • RTS with wrong return address in stack (or bad SP ?)
  • JSR instead of JMP
  • Jump table with bad index (address error)
  • Timer interrupt too fast, causes stack to explode

Invisible sprites

  • Sprites are disabled (NeoGeo CD only, they're enabled by default)
  • The fix layer is filled with non-transparent tiles which hide everything.
  • Sprite position is out of the 320*224 visible area.
  • Sprite height is set to 0 (SCB3).
  • Sprite tiles are all transparent (bad tile numbers ?).
  • Tile colors are the same as the backdrop color.
  • Wrong palette bank.
  • Shrinking values too low (at least 2 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, enabled by default)
  • No non-transparent tiles mapped (bad S ROM ?)
  • Tile colors are the same as the backdrop color.
  • 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.
  • REG_VRAMRW or REG_VRAMMOD writes too fast.
  • Never use CLR instructions on LSPC registers.
  • The Timer interrupt routine has VRAM writes which interferes with the VBlank interrupt routine. Disable the Timer interrupt when out of the display area.

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_LSPCMODE.
  • The interrupt vector points to an RTE or RTS. Beware of the different levels between cart and CD systems.

Game doesn't boot (crosshatch or blue screen)

See 68k program header:

  • Check the "NEO-GEO" string at $100
  • Check the security code and pointer at $182
  • NGH number at $108 must be greater than 0

Game isn't recognized on Neo CD

  • Check that all files in IPL.TXT are present
  • Check that IPL.TXT ends with CR+LF
  • Check if the ABS, CPY and BIB files are present and that they contain the right data

Neo CD resets after initial load

Vblank routine is long

  • Stop the timer interrupt when out of the active display. The timer interrupt can be very mean.

No sound

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