I have my flashable GameBoy Advance ROM at home since few weeks now (it's a 256MB EFA Advance). After reading the specs and thanks to the people at gbadev.org, I could make some little ppdemo.gba that works on real hardware !
It's quite fun to write game engines at such low level, but C really piss me off for the game logic... I definitely have to port the MotionScript Virtual Machine before doing any serious work, so I can use a higher level programming language such as MTypes. But at first I need a small and fast garbage collector since I'm pretty sure the Boehm GC will either not compile/not work on ARM processor or will have too much memory overhead for such a small device.
And after all... reinventing the well is my favorite hobby !