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| -rw-r--r-- | Discovering-GameShark-cheat-codes.md | 46 |
1 files changed, 45 insertions, 1 deletions
diff --git a/Discovering-GameShark-cheat-codes.md b/Discovering-GameShark-cheat-codes.md index a4fee22..56e2480 100644 --- a/Discovering-GameShark-cheat-codes.md +++ b/Discovering-GameShark-cheat-codes.md @@ -8,6 +8,50 @@ A GameShark cheat code looks like this: `ttvvllhh` We can reverse-engineer the meaning of particular codes, and discover our own new codes, with the [**symbol files**](https://github.com/pret/pokecrystal/tree/symbols). When we run `make` to build the ROM, along with the .gbc file it creates a .sym file. This file lists all the labels from the source code with their corresponding banks and addresses in the ROM. -For example, the code `010730D2` writes `07` to `01:D230`. We can look up this address in [pokecrystal.sym](https://raw.githubusercontent.com/pret/pokecrystal/symbols/pokecrystal.sym): it's `wBattleType`, from [wram.asm](../blob/master/wram.asm). Its appropriate values are the `BATTLETYPE_*` constants, from [constants/battle_constants.asm](../blob/master/constants/battle_constants.asm), of which #7 (remember, `const_def` counts up from 0) is `BATTLETYPE_SHINY`. So this looks like a cheat to force shiny battles like Red Gyarados. And sure enough, in this [list of Crystal codes](https://www.glitchcity.info/wiki/Pok%C3%A9mon_Crystal_GameShark_codes), that code appears as "Fight Shiny Pokémon". +For example, the code `010730D2` writes `07` to `01:D230`. We can look up this address in [pokecrystal.sym](https://raw.githubusercontent.com/pret/pokecrystal/symbols/pokecrystal.sym): it's `wBattleType`, from [wram.asm](../blob/master/wram.asm). Its appropriate values are the `BATTLETYPE_*` constants, from [constants/battle_constants.asm](../blob/master/constants/battle_constants.asm), of which #7 (remember, `const_def` counts up from 0) is `BATTLETYPE_SHINY`. So this looks like a cheat to force shiny battles like Red Gyarados. And sure enough, in [GCL's list of Crystal codes](https://www.glitchcity.info/wiki/Pok%C3%A9mon_Crystal_GameShark_codes), that code appears as "Fight Shiny Pokémon". We can design new codes this way. If your pokecrystal-based hack project ended up shifting the location of `wBattleType`, or changed the value of `BATTLETYPE_SHINY`, then the code `010730D2` would affect something else, and might do nothing, cause glitches, or crash the game. But you can just find the new address of `wBattleType` in your own .sym file and edit the code to use that. + +Note that not every address has its own label. For example, [GCL](https://www.glitchcity.info/wiki/Pok%C3%A9mon_Crystal_GameShark_codes) lists these four codes as "skill modifiers": + +``` +Skill 1 Modifier 01??E1DC +Skill 2 Modifier 01??E2DC +Skill 3 Modifier 01??E3DC +Skill 4 Modifier 01??E4DC +``` + +But this is all we have in [pokecrystal.sym](https://raw.githubusercontent.com/pret/pokecrystal/symbols/pokecrystal.sym): + +``` +01:dce1 wPartyMon1Moves +``` + +Nor is there any `wPartyMon1Moves` label in [wram.asm](../blob/master/wram.asm). However, there is this: + +``` +wPartyMon1:: party_struct wPartyMon1 +``` + +And [macros/wram.asm](../blob/master/macros/wram.asm) defines the `party_struct` macro: + +``` +party_struct: MACRO + box_struct \1 +\1Status:: db +... +\1StatsEnd:: +ENDM +``` + +``` +box_struct: MACRO +\1Species:: db +\1Item:: db +\1Moves:: ds NUM_MOVES +... +\1End:: +ENDM +``` + +That `ds NUM_MOVES` means that the label `wPartyMon1Moves` covers four bytes, not one (since `NUM_MOVES EQU 4` in [constants/battle_constants.asm](../blob/master/constants/battle_constants.asm)). Cheat codes can address any of the four move bytes, but only one label exists. |