Game Killer Screenshot
|Hardware features||1 Button Freeze|
|Manual||JPG: 01 page|
|Control Registers||$DE00/$DF00 (likely all IO1/2)|
|Programming||See Tech Section|
The adverts found for this rather rare cartridge which was only available in the UK as of current knowledge contain the words:
and is somehow funny wording since the rest of the advert just mentions that the cartridge is a revolutionary survival kit, disables sprite collision and for the interesting part start your game where you want!.The company behind this advert just renamed from Robcom to ROBTEK as the advert states. Robcom was previously selling modems mainly. The change on the company name came with the introduction of the Game Killer cartridges if we can trust the adverts. Publisher Information at Amiga Hall of Light also notes ROBTEK as the company behind a few games.
On powerup a real intro pops up. It is packed with MC CRACKEN COMPRESSOR 1.3 and includes a scroller reading:
The Zzap! article and the package are explaining the only functionality of the cartridge being achieved by pressing the cartridge button alone to disable all collisions or while holding the joystick pushed up or down to disable just sprite/sprite or sprite/background collision. To enable all collisions again holding down the fire button while pressing the cartridge button is probably working fairly well. Commodore Horizons Issue 27 published some quick docs (see right) which slightly differ from the Zzap! article. They are also wrong on the last part since the cartridge button does not serve as a cheat toggle.
All Accu, X and Y reads on the sprite/sprite and sprite/background registers are properly replaced by LDA/X/Y #$00 ; NOOP where the NOOP has $1a for sprite/sprite and $7a for sprite/background. NOOP is a "stable" illegal opcode and additionally ensures that likely the correct code is replaced on restauration attempts since these code combinations are rarely used. One has to seriously admit that trying to apply these cheats very often leads to crashes and the press and people did not seem to like that either.
Game Killer _just_ made it into this wiki and the category Freezers due to it really applying the techniques required - on a very very basic level. A quick disassembly on the routine taking over the collision hunting and disabling shows a first weakness:
- Zeropage address $44 will be trashed by the cartridge - it is being modified before some work area is freed and moved to the stack (including $44 again).
- Kernal ROM routines are often hit hard and taken to a crash when trying to use Game Killer. Normal program routines are not that easily being crashed but Game Killers success rate is quite high in overall.
ROBTEK "Game Killer" - 1 8k ROM - when cartridge is active, ultimax is enabled when addr>=e000, so the rom is visible at e000, below is normal c64 ram - the code writes 0 to both de00 and df00 to disable the cartridge. we assume the cart uses the full io1 and io2 range - when the freezer button is pressed the cartridge will be enabled and an NMI will be triggered
Game_Killer_binaries_rr.c64.org_2010-04.rar contains just the C64 binaries:
- Game Killer bin and crt
- standalone prg "intro" of the cartridge with Rob Hubbard sound
- Rob Hubbard Cracker_Mix.sid tune
- all of the above
- High quality package inlay
- Manual Sheet
- As it seems the cartridge was not an overwhelming success and sales were quickly coming to an end. Advertising apparently was stopped after a very short time and likely only cartridges of a first and final production run were sold. A quick look at the market before said production run might have saved ROBTEK from doing it at all since the competition was already going strong at that time.