I've now managed to load a file from the MMC64 given a full path+filename! Very cool indeed. It's a shame that you can't page in a ROM that has this functionality built into it. My plan of doing a Plus/4 MMC card was to have a built in ROM with lots of extra features built in like the Kernal, that way adding loading to a game would ultimately be very cheap and you wouldn't need to add all this code.
Still... thats a future thing, for now I need to test this code and load up lots of other files and make sure it all works. Im pretty sure it won't be terribly fast either as its pretty noddy code, however keep it simple and get it working - THEN speed it up and make it impossible to read.
The code is sitting at 1,860 bytes long (1,236 code and 624 data) so it would be nice to shrink this too. If the code can fit inside 1k that would be perfect I think. RAW loading is pretty simple, but including path searching and other features will push up the code space a little.
Anyway... all this aside, it's now working and is pretty cool. As a side note it should now be possible to load large files for my SCPU work; very neat.