... for GBA emu on PSP? 
The GBA hardware is not very powerful (it has been running on PC for years and you don't even need much power to do so). There are no controller or screen issue, the PSP can handle it. I guess you just need to make it run off the memory card.
You can extend that question to other 8, 16 or 32-bit systems to be emulated on PSP.

The GBA hardware is not very powerful (it has been running on PC for years and you don't even need much power to do so). There are no controller or screen issue, the PSP can handle it. I guess you just need to make it run off the memory card.
You can extend that question to other 8, 16 or 32-bit systems to be emulated on PSP.