SD Over USB - portapack-mayhem/mayhem-firmware GitHub Wiki
This application allows you to access the content of the sd card over the USB interface.
SD over USB
Just start the app and click "Run"
While the USB Mass Storage Mode is active, a little USB icon will be displayed.
Now just use the Portapack as if it was an sd card reader.
Note that "SD over USB" is very slow, around 400-500 kb/s, so in some cases it may be faster to remove the SD card and plug it into your computer. It may take up to 2 hours to copy the 2GB world_map.bin file to the SD card using "SD over USB", for example.