Building my own SD card interface for the Apple II

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Joined: Jun 11 2013
Posts: 2

Hi there,

just out of curiosity, I am currently in the middle of building my own SD card interface for my enhanced IIe. I am not trying to build a floppy replacement, but more of a ProFile replacement with a SD card with one (later multiple) 32MB ProDos partitions.
The hardware is based around André Fachat's SPI65/B CPLD SPI controller that I have modified for my own needs. My handwired proto board is working fine and I will have a proper PCB made soon.

So far, I have written a ProDos driver (Merlin assembly) for my card, that is nearly working. Currently I install it from floppy as a software driver for the slot the card is in. In the end it should be on the card itself, of course, with auto-boot and so on.
I formatted the card in CiderPress and put a few files and folders on it.
However, when doing a CAT on ProDos I see a few files and then I get a "range error" from basic, just before the "blocks free" message would be printed. When I try to load a program it crashes or hangs.

As this is my first real Apple II project, I am absolutely sure I have multiple issues at once!
First I'd like to make sure I am installing the driver correctly. Right now, the driver is loaded from floppy disk starting at address $8000 and then registered in ProDos' driver table. I am sure there is a much better and safer place in memory, but where? I need about 750 bytes. Can the driver be stored in aux ram?
I suspect when loading a program, the driver is written over and so locking up the machine.

I appreciate your answers and I am happy to share my design and driver source with you, once it is in a working state!
Regards, Flo