In any case, the format is as close as possible to the existing C64 format, the only VIC20 specific things right now is the changed header (which says "VIC20 CARTRIDGE") and that i bumped the version number to 2.0. Besides that it uses the following .crt IDs right now:
0 - generic
1 - Mega-Cart
2 - Behr Bonz
3 - Vic Flash Plugin
4 - UltiMem
5 - Final Expansion
Detailed documentation will follow later when everything is implemented and working and tested (i am working on an updated crt spec with some comments etc while doing this)
Contrary to an earlier proposal, the generic type does not try to cover certain special cases, because this keeps everything much simpler and straightforward. Instead it does only handle loading into blocks 1/2/3/5 - which already covers a whole lot of cartridges anyway. All other cartridges will require a seperate ID (which can be used by all similar cartridges of course). The "tricky" type in the earlier proposal seemed a bit overengineered and too complex to justify its existance only to save a handful more seperate crt types. That means if you already have code for the C64 .crt format, it is almost trivial to also use it for this Vic20 (and soon also Plus4) variant.
Now, since i am not that much into VIC20 things, here are some questions
- for generic cartridges, when a block is used only partially (eg the upper half of a block), should we mirror the rom into the other half? My guess would be that it was common to use the cheapest way, which usually ment creating mirrors. Interesting here are the cartridges that will not work with or without a certain mirroring scheme.
- do you have more examples of edge cases (other than the ones mentioned in this thread)? for those i'll have to make extra IDs and support those in xvic
- for the above mentioned extra types i'd like to know what block they start in
shoot!
