Nice to see Displaced Gamers getting some much deserved attention.
Some great videos of his not only show old unused code but also, in some cases, game genie codes that can be used with cartridges.
The Input Lag and Attack Animation Delay of Teenage Mutant Ninja Turtles (NES) - Behind the Code
This is the best summary I could come up with:
But a recent video from Displaced Gamers takes the idea from private theory to public execution, going into painstaking detail on how to get NES Tetris to start reading the game’s high score tables as machine code instructions.
But players can manipulate this jump thanks to a little-known vagary in how Tetris handles potential inputs when running on the Japanese version of the console, the Famicom.
As it happens, the area of RAM that Tetris uses to process this extra controller input is also used for the memory location of that jump routine we discussed earlier.
That means only a small portion of the NES’s available opcode instructions can be “coded” into the high score table using the available attack surface.
Of course, the lack of a battery-backed save system means hackers need to achieve these high scores manually (and enter these complicated names) every time they power up Tetris on a stock NES.
With that kind of full control, a top-level player could theoretically recode NES Tetris to patch out the crash bugs altogether.
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