Well, I'm slowly progressing with my MMC card reading, I've gotten sector reading working okay, and from there read the boot sector with the partition information and then onto the FAT Mast Boot Record. However, I'm struggling to get from there to the root directory. The only info I have says that I use the root FAT+ReservedSectors+FatSectorSize = DirRoot, and while this works for one card, it appears to be coincedance.
Once I can get the root directory, it should be plain sailing to load a file. Each Directory entry points to a base sector (or cluster) and from there you use the FAT to cluster hop, reading in the file. I have to confess, I thought sectors were allocated rather than clusters and that sectors were resizable. But it appears that its the number of sectors in a cluster that changes. oh well, its much the same I guess.
Once I have a file loading, I'm going to build a Plus4 interface - or add it to my MemoryCard expansion, Im not sure...I guess it would be easier to build a seprate interface, although Im having a little trouble figuring out the best way of reading the card. The only way I can figure is using 2 flipflop buffers, one for in and one for out. However, the ChipSelect on the card may help with this, I havent sat down and worked it out yet.