Submission #8301: SBD's GBC The Legend of Zelda: Oracle of Ages "save glitch" in 06:09.53

Channel:

Black Winner Yoshi

Subscribers:

42

Published on June 7, 2023 3:00:20 PM ● Video Link: https://www.youtube.com/watch?v=U4bAhlPgXlE

Game:

The Legend of Zelda: Oracle of Ages (2001)

Duration: 10:00

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This is a tool-assisted speedrun. For more information, see https://tasvideos.org/8301S
TAS originally published on 2023-05-29

(note: I encoded a version of the input file ( https://tasvideos.org/UserFiles/Info/638209605267354928 ) that performs some more inputs during the credits)

! Game objectives

*Aims for fastest time
*Corrupts save data
*Executes arbitrary code
*Uses a game restart sequence
*Heavy luck manipulation
*Takes damage to save time

!Version Choice

The Japanese version is used because it allows us to write a more effective ACE payload. There are way more Japanese characters than there are alphanumeric ones and they occupy the high values ($60 - $FF), which are very useful for our purposes. It might be possible to do this run on other versions but it would be a lot more delicate and definitely slower.

In addition, the Japanese textboxes have fewer characters and the screen with the Nintendo and Capcom logos is skippable only on the Japanese version, making resets quicker (and there will be quite a few resets).

!!!The Save Glitch

This is the central glitch of this run, which allows us to skip almost all of the game. The idea behind it is pretty simple and also not terribly original: We reset the console during the saving process, thus creating a "hybrid" savefile, one part of which comes from the new file and the other part from the old file. The data that will go in the savefile is stored in addresses $C5B0 - $CAFF in WRAM (the GameBoy's working memory) and when you save, it gets copied one byte at a time to addresses $A010 - $A55F in SRAM (the save memory on the cartridge). This means that we can choose any point between $C5B0 and $CAFF to "splice" the savefile and create a file for which all the values before the splice are the same as in the new file and all the values after are the same as in the old file.

At first, this doesn't seem too promising. For example, if we put the splice in the middle of the inventory, we couldn't just get new items that way. This is because if we want the hybrid file to have a certain item, at least one of the two files (old or new) needs to already have that item. We could duplicate an item and dual-wield it but that doesn't put us any closer to beating the game.

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