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Document scripting engine fix for MBC30
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@ -14,6 +14,7 @@ These are parts of the code that do not work *incorrectly*, like [bugs and glitc
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- [The 6-bit caught level can only record up to level 63](#the-6-bit-caught-level-can-only-record-up-to-level-63)
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- [The 6-bit caught level can only record up to level 63](#the-6-bit-caught-level-can-only-record-up-to-level-63)
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- [Identical sine wave code and data is repeated five times](#identical-sine-wave-code-and-data-is-repeated-five-times)
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- [Identical sine wave code and data is repeated five times](#identical-sine-wave-code-and-data-is-repeated-five-times)
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- [`GetForestTreeFrame` works, but it's still bad](#getforesttreeframe-works-but-its-still-bad)
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- [`GetForestTreeFrame` works, but it's still bad](#getforesttreeframe-works-but-its-still-bad)
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- [The overworld scripting engine assumes no more than 127 banks](#the-overworld-scripting-engine-assumes-no-more-than-127-banks)
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## Pic banks are offset by `PICS_FIX`
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## Pic banks are offset by `PICS_FIX`
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@ -816,3 +817,36 @@ Edit `GetForestTreeFrame`:
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+ add a
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+ add a
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ret
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ret
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```
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```
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## The overworld scripting engine assumes no more than 127 banks
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The `CallCallback` and `ExitScriptSubroutine` functions in [engine/overworld/scripting.asm](https://github.com/pret/pokecrystal/blob/master/engine/overworld/scripting.asm) use the highest bit of the bank value, to store whether a certain script stack position should be treated as a return from a callback. However, it seems it was opted to explicitly use the `endcallback` command for this purpose, instead.
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As such, this bit serves no purpose but to make map scripts living in the higher banks of mappers such as Japanese Crystal's MBC30 crash for weird reasons.
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**Fix:**
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Remove the bit mask for the bank value in `ExitScriptSubroutine`:
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```diff
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ExitScriptSubroutine:
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...
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add hl, de
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ld a, [hli]
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ld b, a
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- and $7f
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ld [wScriptBank], a
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ld a, [hli]
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ld e, a
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```
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And in `CallCallback`:
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```diff
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CallCallback::
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- ld a, [wScriptBank]
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- or $80
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- ld [wScriptBank], a
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jp ScriptCall
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```
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