mos6507's Blog - Atari 2600 "DOS"

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Another thing Delicon and I were discussing was how to handle the native Chimera file format. We decided that the best approach is for a Chimera game to load in a 4K "loader" which in turn instructs the ARM where to get the rest of the data and where to put it. While this adds some extra overhead to the game, it is the most flexible approach, and closer to how a modular program for an 8-bit home computer would work. Since the ARM would have the ability to use the FAT filesystem on the flash, then the VCS simply sends a short command to the ARM requesting that a file be opened, and to seek to a position in the file, and to read out a chunk and put it anywhere in the 128K SRAM space. The ARM does all the hard work. We should be able to carry this through the wire via serial also, using the control program on the PC. Right now we're thinking the control software will probably be a java application. The upside of all this is that we abandon the notion of supercharger packets and loads and just leave it to the VCS to do general IO routines. This didn't make sense before we implemented the filesystem, but now we can do it. So the programmer can modularize his game any way he chooses. You aren't limited to 256 byte segments. Load IDs no longer mean anything. It also means that a game doesn't have to jump out into the loader ROM to fetch more data. It may still have to pause, but it could keep the kernel going and display some kind of loading indicator. So IO will be more like having a hard drive or a CD-ROM for the VCS.

 

 

 

 

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