… is coming along nicely! I’ve disassembled about 75% of the driver now, and can talk to XD cards and receive the expected responses. The hardware interface is slightly more complex than the simple bitbanging interface I expected, and there are still a few mysterious fields of registers I must work out.
I could write a driver now which would work, but being a perfectionist (in software anyway ;), I must expose all its secrets.
I’ve actually been distracted by reading and Deathnote recently, or I’d have finished the disassembly a week or so ago.
Piccy of the XD card with debug wires attached: 
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Piccy of the XD card installed in the laptop: 
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adq 