I've actually done some work on the GBA driver lately (not just making it run under current MESS). Fixed some issues with interrupts but raster interrupts still aren't right. For some reason the games I'm using to test only enable them during vblank, which is obviously wrong Also a recently released prototype ROM (Turok) is showing an ARM7 core bug I'm trying to track down.
Thank you so much Arbee, for your c l e a r description how to add gba driver source to compile it. It works.