Dave of Final Burn fame has released a Genesis emu for the GBAx Coding Comp heres some of the info about this release:
Games which run well:
Sonic 1, Sonic 2, Revenge of Shinobi, Columns, TMNT,
Flicky, Mickey Mouse Castle of Illusion,
Castlevania Bloodlines, Golden Axe, Ecco the Dophin,
Spiderman, Altered Beast, After Burner
What's new
0.016 (Might be slightly faster)
0.015
Fixed Sonic 1 crash
The New Zealand Story is playable
Added SMD support
Fixed sprite priority
Download from http://pocket-emu.netfirms.com/gigadrive.shtml