I've been noticing recently quite a few people have been taking out the sound chips of the SEGA Megadrive/Genesis, and driving them directly from their PCs with arduinos and things like that. This got me thinking, do we actually understand enough about the SEGA Genesis now to, for example, connect wires to datalines on the motherboard, and inject a VGM music stream on the console while it is powered on, bypassing any need for carts or things like that? The raspberry pi for example has 8 GPIO pins, which is enough to drive a YM2612 directly but not enough for both that and the PSG. Basically this is just a "what if?" question I've had kicking around my head for a bit and would really like to hear peoples take on it.
Injecting signals onto the bus while the power is on can damage the system due to bus contention, I.e. multiple devices driving a signal high or low. That having been said, it wouldn't be too hard to e.g. make a cartridge that accepts data over a controller port (or a custom port on the cartridge) and relays it to the YM2612 or PSG.
Yes we know enough to do that, but it is not practical which is why its not being done. Bus switches and ton of wires are not worth it. Cartridge that can take data from a PC via USB or other connection is nicest method, after taking the chips out using them as is :P 8GPIO is not enough to drive a YM or PSG as is, you need some extender. You have to handle 8x Data lines, 2x Address lines and !WE lines, that's 11. !OE and !CE are important to have but you can get away with tying !OE high and !CE low. !Reset would be good to handle too.
