iOS: How to talk to Apple's SD card reader?

I want to get a list of the files on the SD card that is in the Apple SD card reader. I can usually create an EASession, although that is not reliably happening, but I also have no info about the protocol, called com.apple.accessory.updater.app.20.

Can anyone here fill me in about the Apple SD card reader i.e. part #A1595? How do I talk to it?