Fido Dido (Megadrive) breaks in bonus stage #2 w/fix info

[dinkc64]

Fido Dido (USA, Prototype) is a complete game, although a proto because it was never released.
When you get to the bonus round #2, it makes some unmapped reads to 0x645046 (and another address, iirc it's 0x64504e), if it returns 0x00 here, the game breaks. It might be checking for a devboard of some sort and going into some sort of debug mode.
The game works fine in kega fusion, gensplusgx, and on a real(hw) Genesis, but not PicoDrive because it's returning 0x00 for the unmapped reads.

memory.c @ m68k_unmapped_read8, m68k_unmapped_read16
possible fix:
m68k_unmapped_read8:
return (PicoIn.AHW & PAHW_MCD) ? 0x00 : 0xff;

m68k_unmapped_read16:
return (PicoIn.AHW & PAHW_MCD) ? 0x00 : 0xffff;

I made a short video on how to get to bonus room #2, where the glitch happens.
https://youtu.be/KKMS9b07Ywc

When you get to the level with the gun using PicoDrive, the game will basically be unplayable: the screen will fill with bottle sprites and cause the player sprite to flicker.
This video doesn't show the bug - it just shows how to get to the bonus room quickly for testing.

best regards,

• dink