Introduction
For a long time now, I've been planning on learning to play the keyboard. A couple of months ago, I decided to just do it: I bought a cheap but full-featured midi-keyboard, got myself some online piano lessons so I could set my own pace and just went for it.
For a couple of weeks, this went well, although my set-up proved to be a bit cumbersome: every time I wanted to practice, I had to lug my laptop to the keyboard, connect to it over USB and set up a software MIDI synthesizer. Apart from the software problems (I somehow got a noticable bit of latency in my setup) the effort required to set up everything stopped me from just walking to the keyboard for a bit of practice. I needed a setup that wouldn't need installing and configuring every time I wanted to use it.
Any normal person at this point would have just admitted defeat, buy a synthesizer and connect it to a pair of speakers. A more DIY-inclined person would maybe score an old wavetable card you used to plug into those ISA sound cards and connect a pair of speakers, an optocoupler and a voltage source to it. I would have done that, if I hadn't seen the awesome Chipophone first. This basically is an organ re-built to spit out MIDI messages, combined with an AVR which acts as a simple software synthesizer generating cool old-school bleeps and bloops. LFT, the maker of this contraption, has succesfully used it to play various classic video game songs live. Unfortunately, he hasn't released the sources for the microcontrollers.
So, what else could I use to make a Gameboy-esque sound? How about a standard GameBoy? Actually, this has been done before. The problem is that to run any homebrew code on a normal GameBoy, you'd need a flash card. These cards aren't really easily obtainable anymore, and programming them would be even more of a hassle under a modern OS.
How about a generation later: the GameBoy Advance? The GBA is backwards compatible with the original GB, but adds a better processor, better graphical capabilities and some extra sound capabilities. It still sports the original GB sound hardware too, so it would do just fine to make some retro music. The GBA also has something that can be quite useful: it can boot multiple GBAs over a link cable from just one cartridge, a feature called 'multibooting'. The protocol it uses for that is encrypted, but luckily has been reverse-engineerded for quite a while now. The link cable, obviously, can also be used to transmit data to and from the GBA when a program is running.
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