What kind of directory structure does it use?

The SD card storage area for each program is fixed. The storage area for the first program starts at $00000001, the storage area for the second program starts at $00010001, ... In these storage areas, the first block contains the program header ...

Thanks for the warm welcome. :-) There is actually not (much) more to the filesystem than quoted by barrym95838: It can store up to 254 applications, and it does not allow for subdirectories. Each application has a total of $ffff blocks of 512 bytes each at its disposal. The first blocks of these ...

Spending way too much time at home during the Covid 19 pandemic, I built a little SBC based on the 65C02 CPU running at 4 MHz with 8 KB ROM and 32 KB RAM. Once I got the system running on a breadboard, I created a PCB and a case for it. (Well, the case is just two layer of acrylic sheets and four ...