So, me and Blargg have been sharing ideas for a really cool new project which should be very helpful to the NES developer community and the chiptune community too. It's a new developer cartridge. The goal of our project is to produce inexpensive cartridges which can be easily reprogrammed by anyone with a USB-port equipped computer.Here's the general idea of how these cartridges work:
A NES cartridge has two primary data banks on board: the PRG or program bank, and the CHR or graphics bank. Special cartridges also have an SRAM bank for battery backup. Our development cartridge will be built from an MMC1 game which has all three.
In the PRG bank is placed a FLASH chip containing a small program known as a "bootloader." It can "bootstrap" the system, which means two things: run code already stored in the battery RAM, or load new code via the controller port-USB cable. In the CHR bank is 8kb of battery backed RAM which can be changed at will, and there is another 8kb of RAM in the SRAM spot which can also be used for code. The sizes of these banks may be changed to be larger depending on how development of the hardware goes.
You connect to the PC by using a special USB to controller port cable. A program on the PC side will accept an iNES format ROM, check to see if it is an acceptable size and mapper to work on the cartridge, and then crunch all the necessary data down into a binary file which can then be transmitted via the cable to the NES for saving and execution on the cartridge. Of course, alternate boot code could also be loaded onto the device allowing for even more funky things, like live data transmission during code execution, or running the code directly from a PC instead of from the cartridge memory banks.
For starters, these cartridges will be able to run any NROM game. With some clever bootloader coding other mappers could be supported as well. Of course, with the modifications to the cartridge it already is it's own mapper, so completely custom code could be written for it as well.
Blargg has done experiments with this kind of cartridge before, and will be writing the bootloader code. These cartridges don't require really extensive modification or really expensive parts, so they'll be pretty cheap. We're trying to shoot for the $40 price range. They do require some special tools to build though, including an EPROM programmer, which Blargg doesn't have. Since I have plenty of free time and all the necessary tools, I have offered to build cartridges to his spec. which will then be sold. In addition to building cartridges and cables for sale, I intend to make a tutorial document which will show how to make your own.
Just thought I'd spread the word and see if you guys are interested in such a thing.
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