The original Gameboy had a 16-bit Checksum that went through the boot code and the Nintendo logo. This security was circumvented by Codemasters by using their own logo. The trick was to have some graphic smoke around their logo that made the checksum work. Codemasters went head to head with Nintendo and won a huge sum in damages. The Gameboy colour used a more complex check so it was not so easy to get around. I know this isn't much of a thread, but I remember hearing it from a former Codemasters coder. Apparently the damages were SO big that the day that they won, both brothers went out and returned driving matching Farraris. Anyone else with cunning tricks to bypass console protection? :nod:
Actually, it literally does compare the logo tiles. However, the way nintendo did it, was a big mistake. What Nintendo did, was read the logo tiles from the cart, scroll down the logo that it read from the cart. Once it had made the sound, rather than compare the logo it had read from the cart the first time around, it rereads the cart and compares to that copy instead. Because of this, if you can set something up right, you can supply your own custom logo for the logo to display, then supply the correct logo on the second readout of that logo.
I was interested that the GBC set up the registers to initial values to provide facts (like it WAS a GBC and what revision number).
More inforamtion and a disassembly of the original GB Bootstrap can be found here: http://gameboygenius.8bitcollective.com/gbdev-wiki/articles/Gameboy_Bootstrap_ROM /frax
