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ekeeke / Genesis-Plus-GX

An enhanced port of Genesis Plus - accurate & portable Sega 8/16 bit emulator
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Sega CD bootlogo not rotating #307

Closed Pat86 closed 4 years ago

Pat86 commented 4 years ago

I'm currently trying out byuu's mega cd emulation and while doing an comparison clip i found out, that the sega cd bootlogo isn't rotating with genesis plus gx, while with byuu it does (occasionally).

byuu https://streamable.com/gunxg

genesis plus gx (latest RA core) https://streamable.com/3rcgx

ekeeke commented 4 years ago

The Model 2 BOOT ROM only starts rotating & scaling logos after a while, which only happens if there is no CD game inserted. Indeed, if a Sega CD game is detected, it will automatically be started after a few seconds before the logo effects could be started. You can see rotation/scaling effects by directly loading the Sega CD 2.00 BOOT ROM in Genesis Plus GX or loading an audio CD image file.

Seems like byuu emulator has timing issues and either is running the boot intro too fast, is starting the animation too early or is waiting too long before auto-booting loaded CD game (if it ever does). This could be related to inaccurate emulation of stopwatch register or timer interrupts on Sega CD hardware side.

NB: behavior in Fusion is similar to Genesis Plus GX, you need to use "Boot Sega CD" to see the logos animation, loading a CD game will automatically start it before animation starts.